abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
context. the inter-line comparison between high- and low-ionization emission lines has yielded a wealth of information on the structure and dynamics of the quasar broad line region (blr), including perhaps the earliest unambiguous evidence in favor of a disk + wind structure in radio-quiet quasars.aims: we carried out an analysis of the c ivλ1549 and hβ line profiles of 28 hamburg-eso high-luminosity quasars and of 48 low-z, low-luminosity sources in order to test whether the width of the high-ionization line c ivλ1549 could be correlated with hβ and be used as a virial broadening estimator.methods: we analyze intermediate- to high-s/n, moderate-resolution optical and near-infrared (nir) spectra covering the redshifted c ivλ1549 and hβ over a broad range of luminosity log l ∼ 44 - 48.5 [erg s-1] and redshift (0 - 3), following an approach based on the quasar main sequence.results: the present analysis indicates that the line width of c ivλ1549 is not immediately offering a virial broadening estimator equivalent to hβ. at the same time a virialized part of the blr appears to be preserved even at the highest luminosities. we suggest a correction to fwhm(c ivλ1549) for eddington ratio (using the c ivλ1549 blueshift as a proxy) and luminosity effects that can be applied over more than four dex in luminosity.conclusions: great care should be used in estimating high-l black hole masses mbh from c ivλ1549 line width. however, once a corrected fwhm c ivλ1549 is used, a c ivλ1549-based scaling law can yield unbiased mbh values with respect to the ones based on hβ with sample standard deviation ≈0.3 dex. | black hole mass estimates in quasars. a comparative analysis of high- and low-ionization lines |
we present the x-ray point-source catalogs in two of the xmm-spitzer extragalactic representative volume survey (xmm-servs) fields, w-cdf-s (4.6 deg2) and elais-s1 (3.2 deg2), aiming to fill the gap between deep pencil-beam x-ray surveys and shallow x-ray surveys over large areas. the w-cdf-s and elais-s1 regions were targeted with 2.3 and 1.0 ms of xmm-newton observations, respectively; 1.8 and 0.9 ms exposures remain after flare filtering. the survey in w-cdf-s has a flux limit of 1.0 × 10-14 erg cm-2 s-1 over 90% of its area in the 0.5-10 kev band; 4053 sources are detected in total. the survey in elais-s1 has a flux limit of 1.3 × 10-14 erg cm-2 s-1 over 90% of its area in the 0.5-10 kev band; 2630 sources are detected in total. reliable optical-to-ir multiwavelength counterpart candidates are identified for ≈89% of the sources in w-cdf-s and ≈87% of the sources in elais-s1. a total of 3129 sources in w-cdf-s and 1957 sources in elais-s1 are classified as active galactic nuclei (agns). we also provide photometric redshifts for x-ray sources; ≈84% of the 3319/2001 sources in w-cdf-s/elais-s1 with optical-to-near-ir forced photometry available have either spectroscopic redshifts or high-quality photometric redshifts. the completion of the xmm-newton observations in the w-cdf-s and elais-s1 fields marks the end of the xmm-servs survey data gathering. the ≈12,000 pointlike x-ray sources detected in the whole ≈13 deg2 xmm-servs survey will benefit future large-sample agn studies. | the xmm-servs survey: xmm-newton point-source catalogs for the w-cdf-s and elais-s1 fields |
we report on the jvla observations of three high-redshift active galactic nuclei (agns) that have black hole masses estimated to be among the largest known. two of them, sdss j0100+2802 and sdss j0306+1853 at redshift 6.326 and 5.363, respectively, are radio-quiet agns according to the classic definition, while the third (b2 1023+25 at z = 5.284) is a powerful blazar. the jvla data clearly show a radio structure in the first source and a radio emission with a relatively steep radio spectrum in the second one, indicating the presence of a radio jet and a diffuse component. therefore, being radio-quiet does not exclude the presence of a powerful relativistic jet, which has important consequences on population studies and on the ratio between jetted and non-jetted agns. we can estimate the viewing angle of these jets, and this allows us to find, albeit with some uncertainty, the density of black holes with a mass in excess of 1010 m⊙ at high redshifts. we found that their density in jetted agns is very large in the redshift bin 5-6 and comparable with the overall agn population of the same optical luminosity. jets might thus play a crucial role in the fast formation and evolution of the most massive black holes in the early universe. they are more common than what is expected from wide radio surveys with millijansky flux sensitivity. deeper jvla or very-long-baseline interferometry observations are key to discovering a possible relativistic jet population hiding in plain sight at very high redshift. the discovery of powerful relativistic jets associated with the most massive black holes in the early universe revives the question: is the jet instrumental for a rapid growth of the black hole or, instead, is the black hole mass the main driver for the jet formation? | jetted radio-quiet quasars at z > 5 |
for the first time, we present the simultaneous detection and characterization of three distinct phases at >105 k in z = 0 absorption using deep chandra observations toward mrk 421. the extraordinarily high signal-to-noise ratio (≥60) of the spectra has allowed us to detect a hot phase of the milky way circumgalactic medium (cgm) at ${3.2}_{-0.5}^{+1.5}\times $ 107 k coexisting with a warm-hot phase at 1.5 ± 0.1 × 106 k and a warm phase at 3.0 ± 0.4 × 105 k. the warm-hot phase is at the virial temperature of the galaxy, and the warm phase may have cooled from the warm-hot phase, but the supervirial hot phase remains a mystery. we find that [c/o] in the warm and warm-hot phases, [mg/o] in the warm-hot phase, and [ne/o] in the hot phase are supersolar, and the hot and the warm-hot phases are α-enhanced. nonthermal line broadening is evident in the warm-hot and the hot phases, and it dominates the total line broadening. our results indicate that the >105 k cgm is a complex ecosystem. it provides insights on the thermal and chemical history of the milky way cgm and theories of galaxy evolution. | the hot circumgalactic medium of the milky way: evidence for supervirial, virial, and subvirial temperatures; nonsolar chemical composition; and nonthermal line broadening |
among known strongly lensed quasar systems, ~25% have gravitational potentials sufficiently flat (and sources sufficiently well aligned) to produce four images rather than two. the projected flattening of the lensing galaxy and tides from neighboring galaxies both contribute to the potential's quadrupole. witt's hyperbola and wynne's ellipse permit determination of the overall quadrupole from the positions of the quasar images. the position of the lensing galaxy resolves the distinct contributions of intrinsic ellipticity and tidal shear to that quadrupole. among 31 quadruply lensed quasars systems with statistically significant decompositions, 15 are either reliably (2σ) or provisionally (1σ) shear-dominated and 11 are either reliably or provisionally ellipticity-dominated. for the remaining eight, the two effects make roughly equal contributions to the combined cross section (newly derived here) for quadruple lensing. this observational result is strongly at variance with the ellipticity-dominated forecast of oguri & marshall. | what makes quadruply lensed quasars quadruple? |
this paper provides a catalogue of stars, quasars, and galaxies for the southern photometric local universe survey data release 2 (s-plus dr2) in the stripe 82 region. we show that a 12-band filter system (5 sloan-like and 7 narrow bands) allows better performance for object classification than the usual analysis based solely on broad bands (regardless of infrared information). moreover, we show that our classification is robust against missing values. using spectroscopically confirmed sources retrieved from the sloan digital sky survey dr16 and dr14q, we train a random forest classifier with the 12 s-plus magnitudes + 4 morphological features. a second random forest classifier is trained with the addition of the w1 (3.4 $\mu\mathrm{m} $) and w2 (4.6 $\mu\mathrm{m} $) magnitudes from the wide-field infrared survey explorer (wise). forty-four per cent of our catalogue have wise counterparts and are provided with classification from both models. we achieve 95.76 per cent (52.47 per cent) of quasar purity, 95.88 per cent (92.24 per cent) of quasar completeness, 99.44 per cent (98.17 per cent) of star purity, 98.22 per cent (78.56 per cent) of star completeness, 98.04 per cent (81.39 per cent) of galaxy purity, and 98.8 per cent (85.37 per cent) of galaxy completeness for the first (second) classifier, for which the metrics were calculated on objects with (without) wise counterpart. a total of 2926 787 objects that are not in our spectroscopic sample were labelled, obtaining 335 956 quasars, 1347 340 stars, and 1243 391 galaxies. from those, 7.4 per cent, 76.0 per cent, and 58.4 per cent were classified with probabilities above 80 per cent. the catalogue with classification and probabilities for stripe 82 s-plus dr2 is available for download. | on the discovery of stars, quasars, and galaxies in the southern hemisphere with s-plus dr2 |
we report the results of a visual inspection of images of the rapid askap continuum survey (racs) in search of extended radio galaxies (erg) that reach or exceed linear sizes on the order of one megaparsec. we searched a contiguous area of 1059 deg2 from raj = 20h20m to 06h20m, and ‑50∘<decj<‑40∘, which is covered by deep multi-band optical images of the dark energy survey (des) and in which previously only three ergs larger than 1 mpc had been reported. for over 1800 radio galaxy candidates inspected, our search in optical and infrared images resulted in hosts for 1440 erg, for which spectroscopic and photometric redshifts from various references were used to convert their largest angular size (las) to projected linear size (lls). this resulted in 178 newly discovered giant radio sources (grs) with lls >1 mpc, of which 18 exceed 2 mpc and the largest one is 3.4 mpc. their redshifts range from 0.02 to ∼2.0, but only 10 of the 178 new grs have spectroscopic redshifts. for the 146 host galaxies, the median r-band magnitude and redshift are 20.9 and 0.64, while for the 32 quasars or candidates these are 19.7 and 0.75. merging the six most recent large compilations of grs results in 458 grs larger than 1 mpc, so we were able to increase this number by ∼39% to 636. | discovery of 178 giant radio galaxies in 1059 deg2 of the rapid askap continuum survey at 888 mhz |
mrk 231 is the closest radio-quiet quasar known and one of the most luminous infrared galaxies in the local universe. it is characterized by the co-existence of a radio jet and powerful multiphase multiscale outflows, making it an ideal laboratory to study active galactic nucleus (agn) feedback. we analyse the multi-epoch very long baseline interferometry data of mrk 231 and estimate the jet head advance speed to be ≲0.013 c, suggesting a sub-relativistic jet flow. the jet position angle changes from -113○ in the inner parsec to -172○ at a projected distance of 25 pc. the jet structure change might result from either a jet bending following the rotation of the circum-nuclear disc or the projection of a helical jet on the plane of the sky. in the large opening angle (~60○) cone, the curved jet interacts with the interstellar medium and creates wide-aperture-angle shocks that subsequently dissipate a large portion of the jet power through radiation and contribute to powering the large-scale outflows. the low power and bent structure of the mrk 231 jet, as well as extensive radiation dissipation, are consistent with the obstruction of the short-length jet by the host galaxy's environment. | the obstructed jet in mrk 231 |
we report the discovery of a new "changing-look" active galactic nucleus (clagn) event, in the quasar sdss j162829.17+432948.5 at z = 0.2603, identified through repeat spectroscopy from the fifth sloan digital sky survey (sdss-v). optical photometry taken during 2020-2021 shows a dramatic dimming of δg ≈ 1 mag, followed by a rapid recovery on a timescale of several months, with the ≲2 month period of rebrightening captured in new sdss-v and las cumbres observatory spectroscopy. this is one of the fastest clagn transitions observed to date. archival observations suggest that the object experienced a much more gradual dimming over the period of 2011-2013. our spectroscopy shows that the photometric changes were accompanied by dramatic variations in the quasar-like continuum and broad-line emission. the excellent agreement between the pre- and postdip photometric and spectroscopic appearances of the source, as well as the fact that the dimmest spectra can be reproduced by applying a single extinction law to the brighter spectral states, favor a variable line-of-sight obscuration as the driver of the observed transitions. such an interpretation faces several theoretical challenges, and thus an alternative accretion-driven scenario cannot be excluded. the recent events observed in this quasar highlight the importance of spectroscopic monitoring of large active galactic nucleus samples on weeks-to-months timescales, which the sdss-v is designed to achieve. | a transient "changing-look" active galactic nucleus resolved on month timescales from first-year sloan digital sky survey v data |
the distribution of gas and metals in the circumgalactic medium (cgm) plays a critical role in how galaxies evolve. the muse-alma haloes survey combines muse, alma, and hst observations to constrain the properties of the multiphase gas in the cgm and the galaxies associated with the gas probed in absorption. in this paper, we analyse the properties of galaxies associated with 32 strong ${\rm h\, {\small i}}$ ly-α absorbers at redshift 0.2 ≲ z ≲ 1.4. we detect 79 galaxies within ±500 kms-1 of the absorbers in our 19 muse fields. these associated galaxies are found at physical distances from 5.7 kpc and reach star formation rates as low as 0.1 m⊙ yr-1. the significant number of associated galaxies allows us to map their physical distribution on the δv and b plane. building on previous studies, we examine the physical and nebular properties of these associated galaxies and find the following: (i) 27/32 absorbers have galaxy counterparts and more than 50 per cent of the absorbers have two or more associated galaxies, (ii) the ${\rm h\, {\small i}}$ column density of absorbers is anticorrelated with the impact parameter (scaled by virial radius) of the nearest galaxy as expected from simulations, (iii) the metallicity of associated galaxies is typically larger than the absorber metallicity, which decreases at larger impact parameters. it becomes clear that while strong ${\rm h\, {\small i}}$ absorbers are typically associated with more than a single galaxy, we can use them to statistically map the gas and metal distribution in the cgm. | muse-alma haloes - viii. statistical study of circumgalactic medium gas |
reverberation mapping measurements have been used to constrain the relationship between the size of the broad-line region and luminosity of active galactic nuclei (agn). this r-l relation is used to estimate single-epoch virial black hole masses, and has been proposed to use to standardize agn to determine cosmological distances. we present reverberation measurements made with hβ from the 6-yr australian dark energy survey (ozdes) reverberation mapping program. we successfully recover reverberation lags for eight agn at 0.12 < z < 0.71, probing higher redshifts than the bulk of hβ measurements made to date. our fit to the r-l relation has a slope of α = 0.41 ± 0.03 and an intrinsic scatter of σ = 0.23 ± 0.02 dex. the results from our multi-object spectroscopic survey are consistent with previous measurements made by dedicated source-by-source campaigns, and with the observed dependence on accretion rate. future surveys, including lsst, tides, and sdss-v, which will be revisiting some of our observed fields, will be able to build on the results of our first-generation multi-object reverberation mapping survey. | ozdes reverberation mapping program: hβ lags from the 6-yr survey |
the gas cycling in the circumgalactic regions of galaxies is known to be multi-phase. the muse-alma haloes survey gathers a large multi-wavelength observational sample of absorption and emission data with the goal to significantly advance our understanding of the physical properties of such cgm gas. a key component of the muse-alma haloes survey is the multi-facility observational campaign conducted with vlt/muse, alma, and hst. muse-alma haloes targets comprise 19 vlt/muse ifs quasar fields, including 32 zabs <0.85 strong absorbers with measured n(h i) ≥1018 cm-2 from uv-spectroscopy. we additionally use a new complementary hst medium program to characterize the stellar content of the galaxies through a 40-orbit three-band uvis and ir wfc3 imaging. beyond the absorber-selected targets, we detect 3658 sources all fields combined, including 703 objects with spectroscopic redshifts. this galaxy-selected sample constitutes the main focus of the current paper. we have secured millimeter alma observations of some of the fields to probe the molecular gas properties of these objects. here, we present the overall survey science goals, target selection, observational strategy, data processing and source identification of the full sample. furthermore, we provide catalogues of magnitude measurements for all objects detected in vlt/muse, alma, and hst broad-band images and associated spectroscopic redshifts derived from vlt/muse observations. together, this data set provides robust characterization of the neutral atomic gas, molecular gas and stars in the same objects resulting in the baryon census of condensed matter in complex galaxy structures. | muse-alma haloes vii: survey science goals & design, data processing and final catalogues |
a sample of 102 local (0.02 ≤ z ≤ 0.1) seyfert galaxies with black hole masses mbh > 107m⊙ was selected from the sloan digital sky survey (sdss) and observed using the keck 10 m telescope to study the scaling relations between mbh and host galaxy properties. we study profile changes of the broad hβ emission line within the three to nine year time frame between the two sets of spectra. the variability of the broad hβ emission line is of particular interest, not only because it is used to estimate mbh, but also because its strength and width are used to classify seyfert galaxies into different types. at least some form of broad-line variability (in either width or flux) is observed in the majority (∼66%) of the objects, resulting in a seyfert-type change for ∼38% of the objects, likely driven by variable accretion and/or obscuration. the broad hβ line virtually disappears in 3/102 (∼3%) extreme cases. we discuss potential causes for these changing look active galactic nuclei. while similar dramatic transitions have previously been reported in the literature, either on a case-by-case basis or in larger samples focusing on quasars at higher redshifts, our study provides statistical information on the frequency of hβ line variability in a sample of low-redshift seyfert galaxies. | broad hβ emission-line variability in a sample of 102 local active galaxies |
the distribution of diffuse gas in the intergalactic medium (igm) imprints a series of hydrogen absorption lines on the spectra of distant background quasars known as the lyman-α forest. cosmological hydrodynamical simulations predict that igm density fluctuations are suppressed below a characteristic scale where thermal pressure balances gravity. we measured this pressure-smoothing scale by quantifying absorption correlations in a sample of close quasar pairs. we compared our measurements to hydrodynamical simulations, where pressure smoothing is determined by the integrated thermal history of the igm. our findings are consistent with standard models for photoionization heating by the ultraviolet radiation backgrounds that reionized the universe. | measurement of the small-scale structure of the intergalactic medium using close quasar pairs |
we present multisightline absorption spectroscopy of cool gas around three lensing galaxies at z = 0.4-0.7. these lenses have half-light radii re = 2.6-8 kpc and stellar masses of log m*/m⊙ = 10.9-11.4, and therefore resemble nearby passive elliptical galaxies. the lensed qso sightlines presented here occur at projected distances of d = 3-15 kpc (or d ≈ 1-2 re) from the lensing galaxies, providing for the first time an opportunity to probe both interstellar gas at r ∼ re and circumgalactic gas at larger radii r ≫ re of these distant quiescent galaxies. we observe distinct gas absorption properties among different lenses and among sightlines of individual lenses. specifically, while the quadruple lens for he 0435-1223 shows no absorption features to very sensitive limits along all four sightlines, strong mg ii, fe ii, mg i, and ca ii absorption transitions are detected along both sightlines near the double lens for he 0047-1756, and in one of the two sightlines near the double lens for he 1104-1805. the absorbers are resolved into 8-15 individual components with a line-of-sight velocity spread of δ v ≈ 300-600 km s-1. the large ionic column densities, log n ≳ 14, observed in two components suggest that these may be lyman limit or damped ly α absorbers with a significant neutral hydrogen fraction. the majority of the absorbing components exhibit a uniform supersolar fe/mg ratio with a scatter of <0.1 dex across the full δ v range. given a predominantly old stellar population in these lensing galaxies, we argue that the observed large velocity width and fe-rich abundance pattern can be explained by sne ia enriched gas at radius r ∼ re. we show that additional spatial constraints in line-of-sight velocity and relative abundance ratios afforded by a multisightline approach provide a powerful tool to resolve the origin of chemically enriched cool gas in massive haloes. | probing the cool interstellar and circumgalactic gas of three massive lensing galaxies at z = 0.4-0.7 |
galaxies often contain large reservoirs of molecular gas that shape their evolution. this can be through cooling of the gas - which leads to star formation, or accretion on to the central supermassive black hole - which fuels active galactic nucleus (agn) activity and produces powerful feedback. molecular gas has been detected in early-type galaxies on scales of just a few tens to hundreds of solar masses by searching for absorption against their compact radio cores. using this technique, alma has found absorption in several brightest cluster galaxies, some of which show molecular gas moving towards their galaxy's core at hundreds of km s-1. in this paper, we constrain the location of this absorbing gas by comparing each galaxy's molecular emission and absorption. in four galaxies, the absorption properties are consistent with chance alignments between the continuum and a fraction of the molecular clouds visible in emission. in four others, the properties of the absorption are inconsistent with this scenario. in these systems, the absorption is likely produced by a separate population of molecular clouds in close proximity to the galaxy core and with high inward velocities and velocity dispersions. we thus deduce the existence of two types of absorber, caused by chance alignments between the radio core and: (i) a fraction of the molecular clouds visible in emission, and (ii) molecular clouds close to the agn, in the process of accretion. we also present the first alma observations of molecular emission in s555, abell 2390, rxc j1350.3+0940, and rxc j1603.6+1553 - with the latter three having $m_{\rm {mol}} \gt 10^{10}\, \rm {m}_{\odot }$. | does absorption against agn reveal supermassive black hole accretion? |
optical identifications of a few thousands of iras sources showed that iras point source and iras faint source catalogues (psc and fsc, respectively) contain many quasars and active galactic nuclei, late-type stars, planetary nebulae, variables, etc. to increase the efficiency of using iras psc and fsc, which contain a lot of common sources, one needs a joint catalogue of all iras point sources with improved data based on both catalogues. however, cross-correlation of the catalogues is not so easy, as the association of many sources is relative, and not always it is obvious, whose source from one catalogue corresponds to the other one in the second catalogue. this problem exists in case of using standard cross-correlation tools like vizier. therefore, we have created a tool for cross-matching astronomical catalogues and we have applied it to iras psc and fsc. using this tool we have carried out identifications with a search radius corresponding to 3 σ of errors for each source individually rather than a standard radius for all sources. as a result, we obtained 73,770 associations. we showed that in case of cross-correlation of these catalogues by vizier, we had to take 161.95 arcseconds radius not to lose any association; however, in this case a lot of false associations appear for many sources. in addition, we have made cross-correlations with akari-irc, akari-fis and wise catalogues. as a result we created a catalogue with high positional accuracy and with 17 photometric measurements from 1.25 to 160 μm range, providing a detailed catalogue for iras point sources. | the iras psc/fsc combined catalogue |
recently, carnall et al. discovered two bright high-redshift quasars using the combination of the very large telescope (vlt) survey telescope (vst) atlas and wide-field infrared survey explorer (wise) surveys. the technique involved using the 3d colour plane i-z : z-w1 : w1-w2 with the wise w1 (3.4 micron) and w2 (4.5 micron) bands taking the place of the usual nir j band to help decrease stellar dwarf contamination. here, we report on our continued search for 5.7 < z < 6.4 quasars over an ≈2 × larger area of ≈3577 deg2 of the southern hemisphere. we have found two further z > 6 quasars, vst-atlas j158.6938-14.4211 at z = 6.07 and j332.8017-32.1036 at z = 6.32 with magnitudes of zab = 19.4 and 19.7 mag, respectively. j158.6938-14.4211 was confirmed by keck lris observations and j332.8017-32.1036 was confirmed by eso ntt efosc-2 observations. here, we present vlt x-shooter visible and nir spectra for the four atlas quasars. we have further independently rediscovered two z > 5.7 quasars previously found by the viking/kids and panstarrs surveys. this means that in atlas we have now discovered a total of six quasars in our target 5.7 < z < 6.4 redshift range. making approximate corrections for incompleteness, we find that our quasar space density agrees with the sloan digital sky survey results of jiang et al. at m1450 å ≈ -27. preliminary virial mass estimates based on the c iv and mg ii emission lines give black hole masses in the range mbh ≈ 1-6 × 109 m⊙ for the four atlas quasars. | two more, bright, z > 6 quasars from vst atlas and wise |
“direct collapse black holes” (dcbhs) provide possible seeds for supermassive black holes that exist at z∼ 7. we study lyα radiative transfer through simplified representations of the dcbh scenario. we find that gravitational heating of the collapsing cloud gives rise to a lyα cooling luminosity of up to ∼ {10}38{({m}{{gas}}/{10}6{m}⊙ )}2 erg s-1. photoionization by a central source boosts the lyα luminosity to {l}α ∼ {10}43({m}{{bh}}/{10}6 {m}⊙ ) erg s-1, where {m}{{bh}} denotes the mass of the black hole powering this source. we predict that the width and velocity offsets of the lyα spectral line range from a few tens to few thousands km s-1, depending sensitively on the evolutionary state of the cloud. we apply our predictions to observations of cr7, a luminous lyα emitter at z∼ 7, which may be associated with a dcbh. if cr7 is powered by a black hole, then its lyα flux requires that {m}{{bh}}\gt {10}7 {m}⊙ , which exceeds the mass of dcbhs when they first form. the observed width of the lyα spectrum favors the presence of only a low column density of hydrogen, {log}[{n}{hi}/{{{cm}}}-2]∼ 19{--}20. the shape of the lyα spectrum indicates that this gas is outflowing. these requirements imply that if cr7 harbors a dcbh, then the physical conditions that enabled its formation have been mostly erased, which is in agreement with theoretical expectations. these constraints weaken if the observed lyα emission represents the central peak of a more extended halo. | lyα signatures from direct collapse black holes |
we present a new accurate catalog of narrow-line seyfert 1 galaxies (nls1s) in the southern hemisphere from the six-degree field galaxy survey (6dfgs) final data release, which is currently the most extensive spectroscopic survey available in the southern sky whose database has not yet been systematically explored. we classified 167 sources as nls1s based on their optical spectral properties. we derived flux-calibrated spectra for the first time that the 6dfgs does not provide. by analyzing these spectra, we obtained strong correlations between the monochromatic luminosity at 5100 å and the luminosities of hβ and [o iii]λ5007 lines. the central black hole mass and the eddington ratio have average values of 8.6 × 106m⊙ and 0.96 ledd respectively, which are typical values for nls1s. in the sample, 23 (13.8%) nls1s were detected at radio frequencies, and 12 (7.0%) of them are radio-loud. our results confirmed that radio-loud sources tend to have higher redshift, a more massive black hole, and higher radio and optical luminosities than radio-quiet sources. tables 1, 2, 4, and 5 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/615/a167 | probing narrow-line seyfert 1 galaxies in the southern hemisphere |
we analyse the circular polarization data accumulated in the first 7 years of the polarimetric monitoring of active galactic nuclei at millimetre wavelengths (polami) project introduced in an accompanying paper. in the 3-mm wavelength band, we acquired more than 2600 observations, and all but one of our 37 sample sources were detected, most of them several times. for most sources, the observed distribution of the degree of circular polarization is broader than that of unpolarized calibrators, indicating that weak (≲0.5 per cent) circular polarization is present most of the time. our detection rate and the maximum degree of polarization found, 2.0 per cent, are comparable to previous surveys, all made at much longer wavelengths. we argue that the process generating circular polarization must not be strongly wavelength dependent, and we propose that the widespread presence of circular polarization in our short wavelength sample dominated by blazars is mostly due to faraday conversion of the linearly polarized synchrotron radiation in the helical magnetic field of the jet. circular polarization is variable, most notably on time-scales comparable to or shorter than our median sampling interval of ≲1 month. longer time-scales of about 1 yr are occasionally detected, but severely limited by the weakness of the signal. at variance with some longer wavelength investigations we find that the sign of circular polarization changes in most sources, while only seven sources, including three already known, have a strong preference for one sign. the degrees of circular and linear polarization do not show any systematic correlation. we do find however one particular event where the two polarization degrees vary in synchronism during a time span of 0.9 yr. this paper also describes a novel method for calibrating the sign of circular polarization observations. | polami: polarimetric monitoring of active galactic nuclei at millimetre wavelengths - ii. widespread circular polarization |
we present {hcn} j=4\to 3 and {hco}}+ j=4\to 3 maps of six nearby star-forming galaxies, ngc 253, ngc 1068, ic 342, m82, m83, and ngc 6946, obtained with the james clerk maxwell telescope as part of the malatang survey. all galaxies were mapped in the central 2‧ × 2‧ region at 14″ (fwhm) resolution (corresponding to linear scales of ∼0.2-1.0 kpc). the l ir-l‧dense relation, where the dense gas is traced by the {hcn} j=4\to 3 and the {hco}}+ j=4\to 3 emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. we find that the luminosity ratio, l ir/l‧dense, shows systematic variations with l ir within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. a rising trend is also found between l ir/l‧dense ratio and the warm-dust temperature gauged by the 70 μm/100 μm flux ratio. we find that the luminosity ratios of ir/hcn (4-3) and ir/hco+ (4-3), which can be taken as a proxy for the star formation efficiency (sfe) in the dense molecular gas (sfedense), appear to be nearly independent of the dense gas fraction (f dense) for our sample of galaxies. the sfe of the total molecular gas (sfemol) is found to increase substantially with f dense when combining our data with those on local (ultra)luminous infrared galaxies and high-z quasars. the mean l{{\prime} }hcn(4{--}3)}/l{{\prime} }hco}+(4{--}3)} line ratio measured for the six targeted galaxies is 0.9 ± 0.6. no significant correlation is found for the l{{\prime} }hcn(4{--}3)}/l{{\prime} }hco}+(4{--}3)} ratio with the star formation rate as traced by l ir, nor with the warm-dust temperature, for the different populations of galaxies. | the malatang survey: the l gas-l ir correlation on sub-kiloparsec scale in six nearby star-forming galaxies as traced by hcn j = 4 → 3 and hco+ j = 4 → 3 |
we show that a subdominant component of dissipative dark matter resembling the standard model can form many intermediate-mass black hole seeds during the first structure formation epoch. we also observe that, in the presence of this matter sector, the black holes will grow at a much faster rate with respect to the ordinary case. these facts can explain the observed abundance of supermassive black holes feeding high-redshift quasars. the scenario will have interesting observational consequences for dark substructures and gravitational wave production. | massive black holes from dissipative dark matter |
any successful alternative gravity theory that obviates the need for dark matter must fit our cosmological observations. measurements of microwave background polarization trace the large-scale baryon velocity field at recombination and show very strong o (1 ) baryon acoustic oscillations. measurements of the large-scale structure of galaxies at low redshift show much weaker features in the spectrum. if the alternative gravity theory's dynamical equations for the growth rate of structure are linear, then the density field growth can be described by a green's function: δ (x → ,t )=δ (x → ,t')g (x ,t ,t') . we show that the green's function g (x ,t ,t') must have dramatic features that erase the initial baryon oscillations. this implies an acceleration law that changes sign on the ∼150 mpc scale. on the other hand, if the alternative gravity theory has a large nonlinear term that couples modes on different scales, then the theory would predict large-scale non-gaussian features in large-scale structure. these are not seen in the distribution of galaxies nor in the distribution of quasars. no proposed alternative gravity theory for dark matter seems to satisfy these constraints. | what is the price of abandoning dark matter? cosmological constraints on alternative gravity theories |
understanding the growth of high-redshift massive black holes (mbhs) is a problem of great astrophysical interest. the most luminous quasars at z > 6 are frequently observed but they represent only the tip of the iceberg as the majority of the low-luminosity active galactic nuclei (agn) population remains undetected. in this study, we perform a radiation hydrodynamics cosmological simulation to study the growth of `normal' black holes in the high-redshift universe. in our simulation, we model the formation of pop iii and pop ii stars along with their chemical, mechanical, and radiative feedback. we consider both uv and x-ray emission from an accreting bh to simulate its radiative feedback. the selected halo has a mass of 3 × 10^{10} m_{⊙} at z = 7.5 and we turn on radiative feedback from a mbh seed of 10^5 m_{⊙} along with in situ star formation at z = 12 when the halo mass reaches well above the atomic cooling limit. we find that the mbh accretes only about 2200 m_{⊙} during 320 myr and the average mass accretion on to the mbh is a few times 10^{-6} m_{⊙} yr^{-1}. our results suggest that the stunted growth of mbh is a consequence of supernovae in tandem with mbh feedback which drive large outflows and evacuate the gas from mbh vicinity. this may explain why a population of low-luminosity agn has not been detected so-far at z > 6; the large contrast between the star formation rate and the mbh accretion rate may make then hard to detect even in upcoming deep surveys. | early growth of typical high-redshift black holes seeded by direct collapse |
we present a catalog of quasars selected from broad-band photometric ugri data of the kilo-degree survey data release 3 (kids dr3). the qsos are identified by the random forest (rf) supervised machine learning model, trained on sloan digital sky survey (sdss) dr14 spectroscopic data. we first cleaned the input kids data of entries with excessively noisy, missing or otherwise problematic measurements. applying a feature importance analysis, we then tune the algorithm and identify in the kids multiband catalog the 17 most useful features for the classification, namely magnitudes, colors, magnitude ratios, and the stellarity index. we used the t-sne algorithm to map the multidimensional photometric data onto 2d planes and compare the coverage of the training and inference sets. we limited the inference set to r < 22 to avoid extrapolation beyond the feature space covered by training, as the sdss spectroscopic sample is considerably shallower than kids. this gives 3.4 million objects in the final inference sample, from which the random forest identified 190 000 quasar candidates. accuracy of 97% (percentage of correctly classified objects), purity of 91% (percentage of true quasars within the objects classified as such), and completeness of 87% (detection ratio of all true quasars), as derived from a test set extracted from sdss and not used in the training, are confirmed by comparison with external spectroscopic and photometric qso catalogs overlapping with the kids footprint. the robustness of our results is strengthened by number counts of the quasar candidates in the r band, as well as by their mid-infrared colors available from the wide-field infrared survey explorer (wise). an analysis of parallaxes and proper motions of our qso candidates found also in gaia dr2 suggests that a probability cut of pqso > 0.8 is optimal for purity, whereas pqso > 0.7 is preferable for better completeness. our study presents the first comprehensive quasar selection from deep high-quality kids data and will serve as the basis for versatile studies of the qso population detected by this survey. a copy of the catalog is available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/624/a13we publicly release the resulting catalog at http://kids.strw.leidenuniv.nl/dr3/quasarcatalog.php, and the code at https://github.com/snakoneczny/kids-quasars. | catalog of quasars from the kilo-degree survey data release 3 |
we explore the connection between the atomic gas fraction, fatm, and `global disc stability' parameter, q, of galaxies within a fully cosmological context by examining galaxies in the dark sage semi-analytic model. the q parameter is determined by the ratio of disc specific angular momentum to mass, i.e. q ∝ jdisc/mdisc. dark sage is well suited to our study, as it includes the numerical evolution of one-dimensional disc structure, making both jdisc and q predicted quantities. we show that dark sage produces a clear correlation between gas fraction and jdisc at fixed disc mass, in line with recent results from observations and hydrodynamic simulations. this translates to a tight q-fatm sequence for star-forming central galaxies, which closely tracks the analytic prediction of obreschkow et al. the scatter in this sequence is driven by the probability distribution function of mass as a function of j (pdf of j) within discs, specifically where it peaks. we find that halo mass is primarily responsible for the peak location of the pdf of j, at least for low values of q. two main mechanisms of equal significance are then identified for disconnecting fatm from q. mergers in the model can trigger quasar winds, with the potential to blow out most of the gas disc, while leaving the stellar disc relatively unharmed. ram-pressure stripping of satellite galaxies has a similar effect, where fatm can drop drastically with only a minimal effect to q. we highlight challenges associated with following these predictions up with observations. | connecting and dissecting galaxies' angular momenta and neutral gas in a hierarchical universe: cue dark sage |
warm absorbers are present in many active galactic nuclei (agn), seen as mildly ionized gas outflowing with velocities of a few hundred to a few thousand kilometres per second. these slow velocities imply a large launch radius, pointing to the broad-line region and/or torus as the origin of this material. thermal driving was originally suggested as a plausible mechanism for launching this material but recent work has focused instead on magnetic winds, unifying these slow, mildly ionized winds with the more highly ionized ultrafast outflows. here we use the recently developed quantitative models for thermal winds in black hole binary systems to predict the column density, velocity, and ionization state from agn. thermal winds are sensitive to the spectral energy distribution (sed), so we use realistic models for seds which change as a function of mass and mass accretion rate, becoming x-ray weaker (and hence more disc dominated) at higher eddington ratio. these models allow us to predict the launch radius, velocity, column density, and ionization state of thermal winds as well as the mass-loss rate and energetics. while these match well to some of the observed properties of warm absorbers, the data point to the presence of additional wind material, most likely from dust driving. | thermally driven wind as the origin of warm absorbers in agn |
galaxy clustering data from current and upcoming large-scale structure surveys can provide strong constraints on primordial non-gaussianity through the scale-dependent halo bias. to fully exploit the information from galaxy surveys, optimal analysis methods need to be developed and applied to the data. since the halo bias is sensitive to local non-gaussianity predominately at large scales, the volume of a given survey is crucial. consequently, for such analyses we do not want to split into redshift bins, which would lead to information loss due to edge effects, but instead analyse the full sample. we present an optimal technique to directly constrain local non-gaussianity parametrized by f_nl^loc, from galaxy clustering by applying redshift weights to the galaxies. we derive a set of weights to optimally measure the amplitude of local non-gaussianity, f_nl^loc, discuss the redshift weighted power spectrum estimators, outline the implementation procedure and test our weighting scheme against lognormal catalogues for two different surveys: the quasar sample of the extended baryon oscillation spectroscopic survey (eboss) and the emission line galaxy sample of the dark energy spectroscopic instrument (desi) survey. we find an improvement of 30 per cent for eboss and 6 per cent for desi compared to the standard feldman, kaiser, and peacock weights, although these predictions are sensitive to the bias model assumed. | optimizing primordial non-gaussianity measurements from galaxy surveys |
we introduce a new time-dependent lepto-hadronic model for blazar emission that takes into account the radiation emitted by secondary particles, such as pions and muons, from photo hadronic interactions. starting from a baseline parameter set guided by a fit to the spectral energy distribution of the blazar 3c 279, we perform a parameter study to investigate the effects of perturbations of the input parameters to mimic different flaring events to study the resulting light curves in the optical, x-ray, high-energy (he: e\gt 100 mev), and very-high-energy (e\gt 100 gev) γ-rays as well as the neutrino emission associated with charged-pion and muon decay. we find that flaring events from an increase in the efficiency of fermi ii acceleration will produce a positive correlation between all bandpasses and a marked plateau in the he γ-ray lightcurve. we also predict a distinctive dip in the he lightcurve for perturbations caused by a change in the proton injection spectral index. these plateaus/dips could be a tell tale signature of hadronic models for perturbations that lead to more efficient acceleration of high-energy protons in parameter regimes where pion and muon synchrotron emission is non-negligible. | time dependent hadronic modeling of flat spectrum radio quasars |
the ∼10 per cent of tidal disruption events (tdes) due to stars more massive than m* ≳ m⊙ should show abundance anomalies due to stellar evolution in helium, carbon and nitrogen, but not oxygen. helium is always enhanced, but only by up to ∼25 per cent on average because it becomes inaccessible once it is sequestered in the high-density core as the star leaves the main sequence. however, portions of the debris associated with the disrupted core of a main-sequence star can be enhanced in helium by factors of 2-3 for debris at a common orbital period. these helium abundance variations may be a contributor to the observed diversity of hydrogen and helium line strengths in tdes. a still more striking anomaly is the rapid enhancement of nitrogen and the depletion of carbon due to the cno cycle - stars with m* ≳ m⊙ quickly show an increase in their average n/c ratio by factors of 3-10. because low-mass stars evolve slowly and high-mass stars are rare, tdes showing high n/c will almost all be due to ∼1-2 m⊙ stars disrupted on the main sequence. like helium, portions of the debris will show still larger changes in c and n, and the anomalies decline as the star leaves the main sequence. the enhanced [n/c] abundance ratio of these tdes provides the first natural explanation for the rare, nitrogen-rich quasars and may also explain the strong nitrogen emission seen in ultraviolet spectra of asassn-14li. | abundance anomalies in tidal disruption events |
supermassive stars forming at z ~ 15-20 are one of the leading contenders for the origin of the first quasars, over 200 of which have now been discovered at z > 6. these stars likely form in pristine, atomically cooled haloes immersed in strong lyman-werner ultraviolet backgrounds or in highly supersonic baryon streaming flows. atomic cooling triggers catastrophic baryon collapse capable of building up stars at rates of up to ~1 m⊙ yr-1. here, we examine the evolution of supermassive stars with a much larger and finer grid of accretion rates than in previous studies with the mesa stellar evolution code. we find that their final masses range from 3.5 × 103 to 3.7 × 105 m⊙ at accretion rates of 0.001-1 m⊙ yr-1, respectively. we also find that supermassive star evolution diverges at accretion rates of 0.01-0.02 m⊙ yr-1, above which they evolve as cool red hypergiants along the hayashi track and collapse via the general relativistic instability during central hydrogen burning, and below which they evolve as hot blue supergiants and collapse at the end of their nuclear burning lifetimes after exiting the main sequence. | modelling supermassive primordial stars with mesa |
we present herschel (pacs and spire) far-infrared (fir) photometry of a complete sample of z> 1 3cr sources, from the herschel guaranteed time project the herschel legacy of distant radio-loud agn. combining these with existing spitzer photometric data, we perform an infrared (ir) spectral energy distribution (sed) analysis of these landmark objects in extragalactic research to study the star formation in the hosts of some of the brightest active galactic nuclei (agn) known at any epoch. accounting for the contribution from an agn-powered warm dust component to the ir sed, about 40% of our objects undergo episodes of prodigious, ulirg-strength star formation, with rates of hundreds of solar masses per year, coeval with the growth of the central supermassive black hole. median seds imply that the quasar and radio galaxy hosts have similar fir properties, in agreement with the orientation-based unification for radio-loud agn. the star-forming properties of the agn hosts are similar to those of the general population of equally massive non-agn galaxies at comparable redshifts, thus there is no strong evidence of universal quenching of star formation (negative feedback) within this sample. massive galaxies at high redshift may be forming stars prodigiously, regardless of whether their supermassive black holes are accreting or not. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa.tables 1, 2, 4 and appendices are available in electronic form at http://www.aanda.org | star formation in z > 1 3cr host galaxies as seen by herschel |
we present a detailed analysis of three extremely strong, intervening damped lyman-α systems (esdlas, with log n(h i) ≥ 21.7) observed towards quasars with the ultraviolet and visual echelle spectrograph on the very large telescope. we measure overall metallicities of [zn/h] ~ -1.2, -1.3, and -0.7 at, respectively, zabs = 2.34 towards sdss j214043.02-032139.2 (log n(h i) = 22.4 ± 0.1), zabs = 3.35 towards sdss j145646.48+160939.3 (log n(h i) = 21.7 ± 0.1), and zabs = 2.25 towards sdss j015445.22+193515.8 (log n(h i) = 21.75 ± 0.15). iron depletion of about a factor 15 compared to volatile elements is seen in the dla towards j2140-0321, while the other two show deletion that is typical of known dlas. we detect h2 towards j2140-0321 (log n(h2) = 20.13 ± 0.07) and j1456+1609 (log n(h2) = 17.10 ± 0.09) and argue for a tentative detection towards j0154+1935. absorption from the excited fine-structure levels of o i, c i, and si ii are detected in the system towards j2140-0321, which has the largest h i column density detected so far in an intervening dla. this is the first detection of o i fine-structure lines in a qso-dla, which also provides us with a rare possibility to study the chemical abundances of less abundant atoms like co and ge. simple single-phase photo-ionisation models fail to reproduce all the observed quantities. instead, we suggest that the cloud has a stratified structure: h2 and c i most likely stem from a dense (log nh ~ 2.5-3) and cold (80 k) phase and from a warm (250 k) phase. they contain a fraction of the total h i, while a warmer (t> 1000 k) phase probably contributes significantly to the high excitation of o i fine-structure levels. the observed c i/h2 column density ratio is surprisingly low compared to model predictions, and we do not detect co molecules: this suggests a possible underabundance of c by 0.7 dex compared to other alpha elements. the absorber could be a photo-dissociation region close to a bright star (or a star cluster) where higher temperature occurs in the illuminated region. direct detection of on-going star formation through e.g. near-infrared emission lines in the surroundings of the gas would enable a detailed physical modelling of the system. based on observations collected with the ultraviolet and visual echelle spectrograph on the very large telescope at the european organisation for astronomical research in the southern hemisphere, chile, under programme id 091.a-0370(a). | vlt/uves observations of extremely strong intervening damped lyman-α systems. molecular hydrogen and excited carbon, oxygen, and silicon at log n(h i) = 22.4 |
the detection of high-redshift (z > 3) blazars enables the study of the evolution of the most luminous relativistic jets over cosmic time. more importantly, high-redshift blazars tend to host massive black holes and can be used to constrain the space density of heavy black holes in the early universe. here, we report the first detection with the fermi-large area telescope of five γ-ray-emitting blazars beyond z = 3.1, more distant than any blazars previously detected in γ-rays. among these five objects, nvss j151002+570243 is now the most distant known γ-ray-emitting blazar at z = 4.31. these objects have steeply falling γ-ray spectral energy distributions (seds), and those that have been observed in x-rays have a very hard x-ray spectrum, both typical of powerful blazars. their compton dominance (ratio of the inverse compton to synchrotron peak luminosities) is also very large (> 20). all of these properties place these objects among the most extreme members of the blazar population. their optical spectra and the modeling of their optical-uv seds confirm that these objects harbor massive black holes ({m}{bh}∼ {10}8-10 {m}⊙ ). we find that, at z≈ 4, the space density of > {10}9 {m}⊙black holes hosted in radio-loud and radio-quiet active galactic nuclei are similar, implying that radio-loudness may play a key role in rapid black hole growth in the early universe. | gamma-ray blazars within the first 2 billion years |
the latest measurements of cosmic microwave background electron-scattering optical depth reported by planck significantly reduces the allowed space of {{h}} {{i}} reionization models, pointing toward a later ending and/or less extended phase transition than previously believed. reionization impulsively heats the intergalactic medium (igm) to ∼ {10}4 {{k}}, and owing to long cooling and dynamical times in the diffuse gas that are comparable to the hubble time, memory of reionization heating is retained. therefore, a late-ending reionization has significant implications for the structure of the z∼ 5{--}6 lyα forest. using state-of-the-art hydrodynamical simulations that allow us to vary the timing of reionization and its associated heat injection, we argue that extant thermal signatures from reionization can be detected via the lyα forest power spectrum at 5< z< 6. this arises because the small-scale cutoff in the power depends not only the the igm temperature at these epochs, but is also particularly sensitive to the pressure-smoothing scale set by the igm full thermal history. comparing our different reionization models with existing measurements of the lyα forest flux power spectrum at z=5.0{--}5.4, we find that models satisfying planck’s {τ }e constraint favor a moderate amount of heat injection consistent with galaxies driving reionization, but disfavoring quasar-driven scenarios. we study the feasibility of measuring the flux power spectrum at z≃ 6 using mock quasar spectra and conclude that a sample of ∼10 high-resolution spectra with an attainable signal-to-noise ratio will allow distinguishing between different reionization scenarios. | constraining reionization with the z ∼ 5-6 lyα forest power spectrum: the outlook after planck |
using observations from the first 2 yr of the mosfire deep evolution field (mosdef) survey, we study 13 active galactic nucleus (agn) driven outflows detected from a sample of 67 x-ray, ir, and/or optically selected agns at z∼ 2. the agns have bolometric luminosities of ∼ {10}44{--}{10}46 {erg} {{{s}}}-1, including both quasars and moderate-luminosity agns. we detect blueshifted, ionized gas outflows in the hβ, [o iii], hα, and/or [n ii] emission lines of 19% of the agns, while only 1.8% of the mosdef galaxies have similarly detected outflows. the outflow velocities span ∼300 to 1000 km s-1. eight of the 13 outflows are spatially extended on similar scales to the host galaxies, with spatial extents of 2.5-11.0 kpc. outflows are detected uniformly across the star-forming main sequence, showing little trend with the host galaxy star formation rate. line ratio diagnostics indicate that the outflowing gas is photoionized by the agns. we do not find evidence for positive agn feedback, in either our small mosdef sample or a much larger sloan digital sky survey sample, using the bpt diagram. given that a galaxy with an agn is 10 times more likely to have a detected outflow, the outflowing gas is photoionized by the agns, and estimates of the mass and energy outflow rates indicate that stellar feedback is insufficient to drive at least some of these outflows; they are very likely to be agn driven. the outflows have mass-loading factors of the order of unity, suggesting that they help regulate star formation in their host galaxies, though they may be insufficient to fully quench it. | the mosdef survey: the prevalence and properties of galaxy-wide agn-driven outflows at z ∼ 2 |
observing the interstellar medium (ism) in the z ≳ 6 quasar host galaxies is essential for understanding the coevolution between supermassive black holes and their hosts. to probe the gas physical conditions and search for imprints of active galactic nuclei (agns) on the ism, we report alma observations of the [n ii]122 μm and [o i]146 μm lines and the underlying continuum from the z = 6.003 quasar sdss j231038.88+185519.7. together with previous [c ii]158 μm and [o iii]88 μm observations, we use the ratios of these fine-structure lines to probe the ism properties. similar to other high-z systems, this object exhibits a [c ii]158 μm/[o i]146 μm ratio comparable to the lowest values found in local (ultra)luminous infrared galaxies, suggesting a "warmer" and "denser" gas component compared to typical local systems. the [o iii]88 μm/[o i]146 μm ratio is lower than that of other local and high-z systems, indicating a smaller ionized gas fraction in this quasar. the [o iii]88 μm/[n ii]122 μm ratio is comparable to that of local systems and suggests a metallicity of z/z⊙ = 1.5-2.1. based on the [n ii]122 μm detection, we estimate that 17% of the [c ii]158 μm emission is associated with ionized gas. the [n ii]122 μm line shows a "flux deficit" comparable to local systems. the [o i]146 μm line, with an [o i]146 μm/fir ratio >2× than expected from the local relation, indicates no [o i]146 μm deficit. the low [c ii]158 μm/[o i]146 μm ratio, together with the high [o i]146 μm/fir ratio in j2310+1855, reveals that the warm and dense gas is likely a result of agn heating of the ism. | ionized and atomic interstellar medium in the z = 6.003 quasar sdss j2310+1855 |
we study constraints on the population of neutrino emitting blazars imposed by the absence of doublets in astrophysical muon neutrino signal and z 0.3 redshift of nearest identified neutrino-emitting blazar (an order of magnitude further away than the nearest γ-ray emitting blazar). we show that in spite of the absence of correlation of neutrino arrival directions with positions of gamma-ray emitting blazars, cumulative blazar flux could explain most of astrophysical neutrino flux measured in muon neutrino channel. this is possible if the population of neutrino emitting blazars has experienced rapid positive evolution at least as (1 + z)5 at z 1. such a model avoids previously derived constraint on the low level of blazar contribution to extragalactic neutrino flux because gamma-ray and neutrino fluxes are dominated by different sets of blazars. rapid evolution of neutrino emitting blazars could be explained by the fact that only rapidly evolving sub-population of blazars, which can include parts of flat spectrum radio quasar and bright bl lac populations, are efficient neutrino sources, although their neutrino luminosity has to be systematically lower than the γ-ray luminosity. | self-consistent model of extragalactic neutrino flux from evolving blazar population |
to understand the evolution of extinction curve, we calculate the dust evolution in a galaxy using smoothed particle hydrodynamic simulations incorporating stellar dust production, dust destruction in supernova shocks, grain growth by accretion and coagulation, and grain disruption by shattering. the dust species are separated into carbonaceous dust and silicate. the evolution of grain size distribution is considered by dividing grain population into large and small grains, which allows us to estimate extinction curves. we examine the dependence of extinction curves on the position, gas density and metallicity in the galaxy, and find that extinction curves are flat at t ≲ 0.3 gyr because stellar dust production dominates the total dust abundance. the 2175 å bump and far-ultraviolet (fuv) rise become prominent after dust growth by accretion. at t ≳ 3 gyr, shattering works efficiently in the outer disc and low-density regions, so extinction curves show a very strong 2175 å bump and steep fuv rise. the extinction curves at t ≳ 3 gyr are consistent with the milky way extinction curve, which implies that we successfully included the necessary dust processes in the model. the outer disc component caused by stellar feedback has an extinction curve with a weaker 2175 å bump and flatter fuv slope. the strong contribution of carbonaceous dust tends to underproduce the fuv rise in the small magellanic cloud extinction curve, which supports selective loss of small carbonaceous dust in the galaxy. the snapshot at young ages also explains the extinction curves in high-redshift quasars. | evolution of dust extinction curves in galaxy simulation |
several recent studies have reported different intrinsic correlations between the active galactic nucleus (agn) mid-ir luminosity ({l}mir}) and the rest-frame 2-10 kev luminosity (l x) for luminous quasars. to understand the origin of the difference in the observed {l}{{x}}{--}{l}mir} relations, we study a sample of 3247 spectroscopically confirmed type 1 agns collected from boötes, xmm-cosmos, xmm-xxl-north, and the sloan digital sky survey quasars in the swift/xrt footprint spanning over four orders of magnitude in luminosity. we carefully examine how different observational constraints impact the observed {l}{{x}}{--}{l}mir} relations, including the inclusion of x-ray-nondetected objects, possible x-ray absorption in type 1 agns, x-ray flux limits, and star formation contamination. we find that the primary factor driving the different {l}{{x}}{--}{l}mir} relations reported in the literature is the x-ray flux limits for different studies. when taking these effects into account, we find that the x-ray luminosity and mid-ir luminosity (measured at rest-frame 6 μ {{m}}, or {l}6μ {{m}}) of our sample of type 1 agns follow a bilinear relation in the log-log plane: {log}{l}{{x}}=(0.84+/- 0.03)× {log}{l}6μ {{m}}/{10}45 erg s-1 + (44.60 ± 0.01) for {l}6μ {{m}}< {10}44.79 erg s-1, and {log}{l}{{x}}=(0.40+/- 0.03)× {log}{l}6μ {{m}}/{10}45 erg s-1 + (44.51 ± 0.01) for {l}6μ {{m}} ≥slant {10}44.79 erg s-1. this suggests that the luminous type 1 quasars have a shallower {l}{{x}}{--}{l}6μ {{m}} correlation than the approximately linear relations found in local seyfert galaxies. this result is consistent with previous studies reporting a luminosity-dependent {l}{{x}}{--}{l}mir} relation and implies that assuming a linear {l}{{x}}{--}{l}6μ {{m}} relation to infer the neutral gas column density for x-ray absorption might overestimate the column densities in luminous quasars. | the x-ray and mid-infrared luminosities in luminous type 1 quasars |
the relationship between galaxies and the state/chemical enrichment of the warm-hot intergalactic medium (whim) expected to dominate the baryon budget at low-z provides sensitive constraints on structure formation and galaxy evolution models. we present a deep redshift survey in the field of 1es1553+113, a blazar with a unique combination of ultraviolet (uv)+x-ray spectra for surveys of the circumgalactic/intergalactic medium (cgm/igm). nicastro et al. reported the detection of two o vii whim absorbers at z = 0.4339 and 0.3551 in its spectrum, suggesting that the whim is metal rich and sufficient to close the missing baryons problem. our survey indicates that the blazar is a member of a z = 0.433 group and that the higher-z o vii candidate arises from its intragroup medium. the resulting bias precludes its use in baryon censuses. the z = 0.3551 candidate occurs in an isolated environment 630 kpc from the nearest galaxy (with stellar mass {log}{m}* /{m}⊙ ≈ 9.7), which we show is unexpected for the whim. finally, we characterize the galactic environments of broad h i lyα absorbers (doppler widths of b = 40-80 km s-1 t ≲ 4 × 105 k) that provide metallicity-independent whim probes. on average, broad lyα absorbers are ≈2× closer to the nearest luminous (l > 0.25l *) galaxy (700 kpc) than narrow (b < 30 km s-1 t ≲ 4 × 105 k) ones (1300 kpc) but ≈2× further than o vi absorbers (350 kpc). these observations suggest that gravitational collapse heats portions of the igm to form the whim, but with feedback that does not enrich the igm far beyond galaxy/group halos to levels currently observable in uv/x-ray metal lines. | the physical origins of the identified and still missing components of the warm-hot intergalactic medium: insights from deep surveys in the field of blazar 1es1553+113 |
we present the analysis of a new near-infrared (nir) spectrum of a recently discovered z = 6.621 quasar pso j006 + 39 in an attempt to explore the early growth of supermassive black holes (smbhs). this nir (rest-frame ultraviolet, uv) spectrum shows blue continuum slope and rich metal emission lines in addition to lyα line. we utilize the {mg ii} line width and the rest-frame luminosity l_{3000 \mathringa} to find the mass of smbh (mbh) to be {∼ } 10^8 m_\odot, making this one of the lowest mass quasars at high redshift. the power-law slope index (αλ) of the continuum emission is -2.94 ± 0.03, significantly bluer than the slope of αλ = -7/3 predicted from standard thin disc models. we fit the spectral energy distribution (sed) using a model which can fit local smbhs, which includes warm and hot comptonization powered by the accretion flow as well as an outer standard disc. the result shows that the very blue slope is probably produced by a small radial (∼230 gravitational radius, rg) extent of the standard accretion disc. all plausible sed models require that the source is super-eddington (lbol/ledd ≳ 9), so the apparently small disc may simply be the inner funnel of a puffed up flow, and clearly the smbh in this quasar is in a rapid growth phase. we also utilize the rest-frame uv emission lines to probe the chemical abundance in the broad-line region (blr) of this quasar. we find that this quasar has super solar metallicity through photoionization model calculations. | rapid black hole growth at the dawn of the universe: a super-eddington quasar at z = 6.6 |
supermassive stars with masses of m* ≃ 104-105 m⊙ are invoked as possible seeds of high-redshift supermassive black holes, but it remains under debate whether their protostar indeed acquires sufficient mass via gas accretion overcoming radiative feedback. we investigate protostellar growth in dynamically heated atomic cooling haloes (achs) found in recent cosmological simulations, performing three-dimensional radiation hydrodynamical simulations that consider stellar evolution under variable mass accretion. we find that one of the achs feeds the central protostar at rates exceeding a critical value, above which the star evolves in a cool bloating phase and hardly produces ionizing photons. consequently, the stellar mass reaches m* ≳ 104 m⊙ unimpeded by radiative feedback. in the other ach, where the mass supply rate is lower, the star evolves almost as a hot main-sequence star, emitting intense ionizing radiation. then, the stellar mass growth is terminated around 500 m⊙ by photoevaporation of the circumstellar disc. our simulations provide a formula of the final stellar mass determined either by stellar feedback or their lifetime as a function of the mass supply rate from the parent cloud. combining the results with the statistical properties of star-forming clouds in high-redshift quasar progenitor haloes, we construct a top-heavy mass distribution of primordial stars over m* ≃ 100-105 m⊙, approximately following a power-law spectrum of ${\propto} m_\ast ^{-1.3}$. their black hole remnants would be further fed via the dense debris disc, powering 'milliquasars' with a bolometric luminosity of lbol ≳ 1043 erg s-1. | radiative feedback on supermassive star formation: the massive end of the population iii initial mass function |
we present sheep, a new machine learning approach to the classic problem of astronomical source classification, which combines the outputs from the xgboost, lightgbm, and catboost learning algorithms to create stronger classifiers. a novel step in our pipeline is that prior to performing the classification, sheep first estimates photometric redshifts, which are then placed into the data set as an additional feature for classification model training; this results in significant improvements in the subsequent classification performance. sheep contains two distinct classification methodologies: (i) multi-class and (ii) one versus all with correction by a meta-learner. we demonstrate the performance of sheep for the classification of stars, galaxies, and quasars using a data set composed of sdss and wise photometry of 3.5 million astronomical sources. the resulting f1 -scores are as follows: 0.992 for galaxies; 0.967 for quasars; and 0.985 for stars. in terms of the f1-scores for the three classes, sheep is found to outperform a recent randomforest-based classification approach using an essentially identical data set. our methodology also facilitates model and data set explainability via feature importances; it also allows the selection of sources whose uncertain classifications may make them interesting sources for follow-up observations. | photometric redshift-aided classification using ensemble learning |
it is well known that time delays due to strong lensing offer the opportunity of a one-step measurement of the hubble constant h 0 that is independent of the cosmic distance ladder. in this paper, we go further and propose a cosmological model-independent approach to simultaneously determine the hubble constant and cosmic curvature with measurements of the time delay due to strong lensing, without any prior assumptions regarding the content of the universe. the data we use comprise the recent compilation of six well studied strongly lensed quasars, while the cosmic chronometer data are utilized to reconstruct distances via cosmographic parameters. in the framework of third-order taylor expansion and (2, 1) order padé approximation for cosmographic analysis, our results provide model-independent estimations of the hubble constant ${h}_{0}={72.24}_{-2.52}^{+2.73}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ and ${h}_{0}={72.45}_{-2.02}^{+1.95}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ , which are well consistent with that derived from the local distance ladder by the sh0es collaboration. the measured cosmic curvature ${{\rm{\omega }}}_{k}={0.062}_{-0.078}^{+0.117}$ and ${{\rm{\omega }}}_{k}={0.069}_{-0.103}^{+0.116}$ shows that zero spatial curvature is supported by the current observations of time delays due to strong lensing and cosmic chronometers. imposing the prior of spatial flatness leads to more precise (at 1.6% level) determinations of the hubble constant ${h}_{0}={70.47}_{-1.15}^{+1.14}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ and ${h}_{0}={71.66}_{-1.57}^{+1.15}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{mpc}}^{-1}$ , values located between the results from planck and the sh0es collaboration. if a prior of local (sh0es) h 0 measurement is adopted, the constraint on curvature parameter can be further improved to ${{\rm{\omega }}}_{k}={0.123}_{-0.046}^{+0.060}$ and ${{\rm{\omega }}}_{k}={0.101}_{-0.072}^{+0.090}$ , supporting no significant deviation from a flat universe. finally, we also discuss the effectiveness of the padé approximation in reconstructing the cosmic expansion history for redshifts up to z ~ 2.3, considering its better performance in the bayes information criterion. | revisiting the hubble constant, spatial curvature, and cosmography with strongly lensed quasar and hubble parameter observations |
observations of the most luminous quasars at high redshifts (z > 6) have revealed that the largest supermassive black holes (smbhs) at those epochs tend to be substantially overmassive relative to their host galaxies compared to the local relations, suggesting they experienced rapid early growth phases. we propose an assembly model for the smbhs that end up in rare massive ~1012 m ⊙ host halos at z ~ 6-7, applying a kinetic feedback prescription for bhs accreting above the eddington rate, provided by radiation hydrodynamic simulations for the long-term evolution of the accretion-flow structure. the large inflow rates into these halos during their assembly enable the formation of >109 m ⊙ smbhs by z ~ 6, even starting from stellar-mass seeds at z ~ 30, and even in the presence of outflows that reduce the bh feeding rate, especially at early times. this mechanism also naturally yields a high bh-to-galaxy mass ratio of >0.01 before the smbh mass reaches m bh > 109 m ⊙ by z ~ 6. these fast-growing smbh progenitors are bright enough to be detected by upcoming observations with the james webb space telescope over a wide range of redshift (7 < z < 15), regardless of how they were seeded. | supercritical growth pathway to overmassive black holes at cosmic dawn: coevolution with massive quasar hosts |
quasars powered by supermassive black holes (>108 m⊙) at z ~ 6 are predicted to reside in cosmic overdense regions. however, observations so far could not confirm this expectation due to limited statistics. the picture is further complicated by the possible effects of quasar outflows (i.e. feedback) that could either suppress or stimulate the star formation rate (sfr) of companion galaxies, thus modifying the expected bias. here, we quantify feedback effects on the properties and detectability of companions by comparing cosmological zoom-in simulations of a quasar in which feedback is either included or turned-off. with respect to the no-feedback case, companions (a) directly impacted by the outflow have their sfr increased by a factor of 2-3, and (b) tend to be more massive. both effects shift the [c ii] 158 μm and uv luminosity functions towards brighter magnitudes. this leads us to conclude that quasar feedback slightly increases the effective quasar bias, boosting the number density of observable quasar companions, in agreement with what has been found around the brightest quasars of recent atacama large millimeter array (alma) [c ii] surveys. deeper observations performed with james webb space telescope and/or alma will improve the statistical significance of this result by detecting a larger number of fainter quasar companions. | enhanced star formation in z 6 quasar companions |
we report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the north american nanohertz observatory for gravitational waves. the correlations follow the hellings-downs pattern expected for a stochastic gravitational-wave background. the presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a bayes factor in excess of 1014, and this same model is favored over an uncorrelated common power-law spectrum model with bayes factors of 200-1000, depending on spectral modeling choices. we have built a statistical background distribution for the latter bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10-3 (≈3σ) for the observed bayes factors in the null no-correlation scenario. a frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10-5 to 1.9 × 10-4 (≈3.5σ-4σ). assuming a fiducial f -2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is ${2.4}_{-0.6}^{+0.7}\times {10}^{-15}$ (median + 90% credible interval) at a reference frequency of 1 yr-1. the inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. the observation of hellings-downs correlations points to the gravitational-wave origin of this signal. | the nanograv 15 yr data set: evidence for a gravitational-wave background |
we present observations and timing analyses of 68 millisecond pulsars (msps) comprising the 15 yr data set of the north american nanohertz observatory for gravitational waves (nanograv). nanograv is a pulsar timing array (pta) experiment that is sensitive to low-frequency gravitational waves (gws). this is nanograv's fifth public data release, including both "narrowband" and "wideband" time-of-arrival (toa) measurements and corresponding pulsar timing models. we have added 21 msps and extended our timing baselines by 3 yr, now spanning nearly 16 yr for some of our sources. the data were collected using the arecibo observatory, the green bank telescope, and the very large array between frequencies of 327 mhz and 3 ghz, with most sources observed approximately monthly. a number of notable methodological and procedural changes were made compared to our previous data sets. these improve the overall quality of the toa data set and are part of the transition to new pulsar timing and pta analysis software packages. for the first time, our data products are accompanied by a full suite of software to reproduce data reduction, analysis, and results. our timing models include a variety of newly detected astrometric and binary pulsar parameters, including several significant improvements to pulsar mass constraints. we find that the time series of 23 pulsars contain detectable levels of red noise, 10 of which are new measurements. in this data set, we find evidence for a stochastic gw background. | the nanograv 15 yr data set: observations and timing of 68 millisecond pulsars |
several pulsar timing arrays including nanograv, epta, ppta, and cpta have recently reported the observation of a stochastic background of gravitational wave spectrum in the nanohertz frequencies. an inflationary interpretation of this observation is challenging from various aspects. we report that such a signal can arise from the chern-simons coupling in axion inflation, where a pseudoscalar inflaton couples to a (massive) u (1 ) gauge field, leading to efficient production of a transverse gauge mode. such tachyonic particle production during inflation exponentially enhances the primordial perturbations and leads to a unique parity-violating gravitational wave spectrum, that remains flat near the cmb scales but becomes blue-tilted at smaller scales. we identify the parameter space consistent with various cosmological constraints and show that the resultant gravitational wave signals can provide extra contribution on top of the standard astrophysical contribution from inspiraling supermassive black hole binaries towards explaining the observed excess at nanograv. the parity-violating nature of the signal can be probed in future interferometers, distinguishing it from most other new physics signals attempting to explain the nanograv result. | nanograv signal from axion inflation |
the australian, chinese, european, indian, and north american pulsar timing array (pta) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational wave background (gwb). given that each pta made different choices in modeling their data, we perform a comparison of the gwb and individual pulsar noise parameters across the results reported from the ptas that constitute the international pulsar timing array (ipta). we show that despite making different modeling choices, there is no significant difference in the gwb parameters that are measured by the different ptas, agreeing within $1\sigma$. the pulsar noise parameters are also consistent between different ptas for the majority of the pulsars included in these analyses. we bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and ptas, finding that under this model there is a reduction in the tension in the pulsar noise parameters. as part of this reanalysis, we "extended" each pta's data set by adding extra pulsars that were not timed by that pta. under these extensions, we find better constraints on the gwb amplitude and a higher signal-to-noise ratio for the hellings and downs correlations. these extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the ipta, i.e., the ipta's data release 3, which will involve not just adding in additional pulsars, but also including data from all three ptas where any given pulsar is timed by more than as single pta. | comparing recent pta results on the nanohertz stochastic gravitational wave background |
in this paper, we analyse sound waves arising from a cosmic phase transition where the full velocity profile is taken into account as an explanation for the gravitational wave spectrum observed by multiple pulsar timing array groups. unlike the broken power law used in the literature, in this scenario the power law after the peak depends on the macroscopic properties of the phase transition, allowing for a better fit with pulsar timing array (pta) data. we compare the best fit with that obtained using the usual broken power law and, unsurprisingly, find a better fit with the gravitational wave (gw) spectrum that utilizes the full velocity profile. we then discuss models that can produce the best-fit point and complementary probes using cmb experiments and searches for light particles in dune, icecube-gen2, neutrinoless double beta decay, and forward physics facilities at the lhc like faser nu, etc. | did we hear the sound of the universe boiling? analysis using the full fluid velocity profiles and nanograv 15-year data |
recently, the hellings downs correlation has been observed by different pulsar timing array (pta) collaborations, such as nanograv, european pta, parkes pta, and chinese pta. these pta measurements of the most precise pulsars within the milky way show the first robust evidence for the stochastic gravitational wave background of our universe. we study the ultralight axion interpretation of the new discovery by investigating the gravitational wave from the energy-level transition of the gravitational atoms, which is composed of cosmic populated kerr black holes and their surrounding axion clouds from the superradiance process. we demonstrate that this new observation admits an axion interpretation for the ultralight axion mass around $10^{-20}$ ev. meanwhile, we obtain strong constraints on the fuzzy dark matter for the axion mass range $10^{-22}\sim 10^{-21}$ ev. | implication of nano-hertz stochastic gravitational wave background on ultralight axion particles |
we searched for an isotropic stochastic gravitational wave background in the second data release of the international pulsar timing array, a global collaboration synthesizing decadal-length pulsar-timing campaigns in north america, europe, and australia. in our reference search for a power-law strain spectrum of the form $h_c = a(f/1\, \mathrm{yr}^{-1})^{\alpha }$, we found strong evidence for a spectrally similar low-frequency stochastic process of amplitude $a = 3.8^{+6.3}_{-2.5}\times 10^{-15}$ and spectral index α = -0.5 ± 0.5, where the uncertainties represent 95 per cent credible regions, using information from the auto- and cross-correlation terms between the pulsars in the array. for a spectral index of α = -2/3, as expected from a population of inspiralling supermassive black hole binaries, the recovered amplitude is $a = 2.8^{+1.2}_{-0.8}\times 10^{-15}$. none the less, no significant evidence of the hellings-downs correlations that would indicate a gravitational-wave origin was found. we also analysed the constituent data from the individual pulsar timing arrays in a consistent way, and clearly demonstrate that the combined international data set is more sensitive. furthermore, we demonstrate that this combined data set produces comparable constraints to recent single-array data sets which have more data than the constituent parts of the combination. future international data releases will deliver increased sensitivity to gravitational wave radiation, and significantly increase the detection probability. | the international pulsar timing array second data release: search for an isotropic gravitational wave background |
in this work, we construct promising model-building routes towards so(10) grand unified theory inflation and examine their ability to explain the recent pulsar timing arrays (ptas) results hinting at a stochastic gravitational wave (gw) background at nanohertz frequencies. we consider a supersymmetric framework within which the so-called doublet-triplet splitting problem is solved without introducing fine-tuning. additionally, realistic fermion masses and mixings, gauge coupling unification, and cosmic inflation are incorporated by utilizing superfields with representations no higher than the adjoint representation. among the three possible scenarios, two of these cases require a single adjoint higgs field, and do not lead to cosmic strings. in contrast, the third scenario featuring two adjoints, can lead to a network of metastable cosmic strings that generates a gw background contribution compatible with the recent pta findings and testable by various ongoing and upcoming gw observatories. | singling out so(10) gut models using recent pta results |
we investigate the potential of the warped extradimension framework as an explanation for the recently observed stochastic gravitational background at nhz frequencies in pulsar timing arrays (pta). our analysis reveals that the pta data can be effectively accommodated by a first-order phase transition triggered by a radion at the mev-gev scale feebly coupled to the standard model. remarkably, this outcome remains robust irrespective of the specific details of the warped extradimension embedding, providing a foundation for future investigations aiming to develop concrete extradimension descriptions of nature. we also demonstrate that many existing embeddings are not viable, as their radion and graviton phenomenology clash with a mev-gev scale radion. as a possible way out, we sketch a promising solution involving multiple branes, wherein the light radion, graviton, and ensuing light resonances remain consistent with collider bounds and gravity tests. | pulsar timing array stochastic background from light kaluza-klein resonances |
inspired by the recent evidences of nano-hertz stochastic gravitational waves observed by the pulsar timing array collaborations, we explore their implied supercooled electroweak phase transition in the singlet extension of the standard model. our findings reveal that by adjusting the model parameter at per milli level, the corresponding percolation temperature can be continuously lowered to 1 gev. with such a low percolation temperature, the singlet dark matter may freeze out before the electroweak phase transition, and, consequently, the entropy generated during the transition can significantly affect the dark matter relic density. it alleviates the tension between the requirement of a strong electroweak phase transition and the constraints imposed by dark matter direct detection, and can be tested in future experiments. | implications of nano-hertz gravitational waves on electroweak phase transition in the singlet dark matter model |
this paper presents rigorous tests of pulsar timing array methods and software, examining their consistency across a wide range of injected parameters and signal strength. we discuss updates to the 15-year isotropic gravitational-wave background analyses and their corresponding code representations. descriptions of the internal structure of the flagship algorithms \texttt{enterprise} and \texttt{ptmcmcsampler} are given to facilitate understanding of the pta likelihood structure, how models are built, and what methods are currently used in sampling the high-dimensional pta parameter space. we introduce a novel version of the pta likelihood that uses a two-step marginalization procedure that performs much faster when the white noise parameters remain fixed. we perform stringent tests of consistency and correctness of the bayesian and frequentist analysis software. for the bayesian analysis, we test prior recovery, injection recovery, and bayes factors. for the frequentist analysis, we test that the cross-correlation-based optimal statistic, when modified to account for a non-negligible gravitational-wave background, accurately recovers the amplitude of the background. we also summarize recent advances and tests performed on the optimal statistic in the literature from both gwb detection and parameter estimation perspectives. the tests presented here validate current and future analyses of pta data. | the nanograv 15-year gravitational-wave background analysis pipeline |
for the first time, the expected stochastic gravitational wave background is probably discovered after observing the hellings downs correlation curve by several pulsar timing array (pta) collaborations around the globe including nanograv, european pta, parkes pta, and chinese pta. these new observations can help to explore or constrain the dark matter formation mechanisms in the early universe. we study the implication of those results on the dynamical dark matter formation mechanisms through a first-order phase transition in the early universe. both the q-ball dark matter and super-cool dark matter are investigated in the strong super-cooling phase transition scenario which may give an interpretation of the observed stochastic gravitational wave background. | implication of nano-hertz stochastic gravitational wave on dynamical dark matter through a first-order phase transition |
accreting millisecond x-ray pulsars (amxps) are astrophysical laboratories without parallel in the study of extreme physics. in this chapter we review the past fifteen years of discoveries in the field. we summarize the observations of the fifteen known amxps, with a particular emphasis on the multi-wavelength observations that have been carried out since the discovery of the first amxp in 1998. we review accretion torque theory, the pulse formation process, and how amxp observations have changed our view on the interaction of plasma and magnetic fields in strong gravity. we also explain how the amxps have deepened our understanding of the thermonuclear burst process, in particular the phenomenon of burst oscillations. we conclude with a discussion of the open problems that remain to be addressed in the future. | accreting millisecond x-ray pulsars |
the power-law parametrization for the energy density spectrum of gravitational wave (gw) background is a useful tool to study its physics and origin. while scalar induced secondary gravitational waves (sigws) from some particular models fit the signal detected by nanograv, parkers pulsar timing array, european pulsar timing array, and chinese pulsar timing array collaborations better than gws from supermassive black hole binaries (smbhbs), we test the consistency of the data with the infrared part of sigws which is somewhat independent of models. through bayesian analysis, we show that the infrared parts of sigws fit the data better than gw background from smbhbs. the results give tentative evidence for sigws. | scalar induced gravitational waves in light of pulsar timing array data |
we demonstrate that the asymptotic oscillatory tails of massive gravitons, present in both massive theories of gravity and effectively in extra-dimensional scenarios, could potentially contribute to gravitational waves with very long wavelengths. however, their impact on recent pulsar timing array observations is expected to be relatively small, predominantly consisting of radiation emitted by black holes in our region of the milky way. | asymptotic tails of massive gravitons in light of pulsar timing array observations |
there are several common conventions in use by the gravitational-wave community to describe the amplitude of sources and the sensitivity of detectors. these are frequently confused. we outline the merits of and differences between the various quantities used for parameterizing noise curves and characterizing gravitational-wave amplitudes. we conclude by producing plots that consistently compare different detectors. similar figures can be generated on-line for general use at http://rhcole.com/apps/gwplotter. | gravitational-wave sensitivity curves |
we propose a new dark matter contender within the context of the so-called ``dark dimension'', an innovative 5-dimensional construct that has a compact space with characteristic length-scale in the micron range. the new dark matter candidate is the radion, a bulk scalar field whose quintessence-like potential drives an inflationary phase described by a 5-dimensional de sitter (or approximate) solution of einstein equations. we show that the radion could be ultralight and thereby serve as a fuzzy dark matter candidate. we advocate a simple cosmological production mechanism bringing into play unstable kaluza-klein graviton towers which are fueled by the decay of the inflaton. we demonstrate that the fuzzy radion can accommodate the signal recently observed in pulsar timing arrays. | fuzzy dark matter, the dark dimension, and the pulsar timing array signal |
releasing the 12.5-year pulsar timing array data, the north american nanohertz observatory for gravitational waves (nanograv) has recently reported the evidence for a stochastic common-spectrum which would herald the detection of a stochastic gravitational wave background (sgwb) for the first time. we investigate if the signal could be generated from the end of a ∼10 mev but still phenomenologically viable double-field inflation when the field configuration settles to its true vacuum. during the double-field inflation at such scales, bubbles of true vacuum that can collapse to ligo mass, and heavier primordial black holes form. we show that only when this process happens with a first-order phase transition, the produced gravitational wave spectrum can match with the nanograv acclaimed sgwb signal. we show that the produced gravitational wave spectrum matches the nanograv sgwb signal only when this process happens through a first-order phase transition. using latticeeasy, we also examine the previous observation in the literature that by lowering the scale of preheating, despite the shift of the peak frequency of the gravitational wave profile to smaller values, the amplitude of the sgwb could be kept almost constant. we notice that this observation breaks down at the preheating scale, m ≲10-14mpl. | nanograv signal from the end of inflation and the ligo mass and heavier primordial black holes |
the north american nanohertz observatory for gravitational waves (nanograv) has reported evidence for the presence of an isotropic nanohertz gravitational-wave background (gwb) in its 15 yr data set. however, if the gwb is produced by a population of inspiraling supermassive black hole binary (smbhb) systems, then the background is predicted to be anisotropic, depending on the distribution of these systems in the local universe and the statistical properties of the smbhb population. in this work, we search for anisotropy in the gwb using multiple methods and bases to describe the distribution of the gwb power on the sky. we do not find significant evidence of anisotropy. by modeling the angular power distribution as a sum over spherical harmonics (where the coefficients are not bound to always generate positive power everywhere), we find that the bayesian 95% upper limit on the level of dipole anisotropy is (cl=1/cl=0) < 27%. this is similar to the upper limit derived under the constraint of positive power everywhere, indicating that the dipole may be close to the data-informed regime. by contrast, the constraints on anisotropy at higher spherical-harmonic multipoles are strongly prior dominated. we also derive conservative estimates on the anisotropy expected from a random distribution of smbhb systems using astrophysical simulations conditioned on the isotropic gwb inferred in the 15 yr data set and show that this data set has sufficient sensitivity to probe a large fraction of the predicted level of anisotropy. we end by highlighting the opportunities and challenges in searching for anisotropy in pulsar timing array data. | the nanograv 15 yr data set: search for anisotropy in the gravitational-wave background |
the unexpectedly high flux of cosmic-ray positrons detected at earth may originate from nearby astrophysical sources, dark matter, or unknown processes of cosmic-ray secondary production. we report the detection, using the high-altitude water cherenkov observatory (hawc), of extended tera-electron volt gamma-ray emission coincident with the locations of two nearby middle-aged pulsars (geminga and psr b0656+14). the hawc observations demonstrate that these pulsars are indeed local sources of accelerated leptons, but the measured tera-electron volt emission profile constrains the diffusion of particles away from these sources to be much slower than previously assumed. we demonstrate that the leptons emitted by these objects are therefore unlikely to be the origin of the excess positrons, which may have a more exotic origin. | extended gamma-ray sources around pulsars constrain the origin of the positron flux at earth |
we review detection methods that are currently in use or have been proposed to search for a stochastic background of gravitational radiation. we consider both bayesian and frequentist searches using ground-based and space-based laser interferometers, spacecraft doppler tracking, and pulsar timing arrays; and we allow for anisotropy, non-gaussianity, and non-standard polarization states. our focus is on relevant data analysis issues, and not on the particular astrophysical or early universe sources that might give rise to such backgrounds. we provide a unified treatment of these searches at the level of detector response functions, detection sensitivity curves, and, more generally, at the level of the likelihood function, since the choice of signal and noise models and prior probability distributions are actually what define the search. pedagogical examples are given whenever possible to compare and contrast different approaches. we have tried to make the article as self-contained and comprehensive as possible, targeting graduate students and new researchers looking to enter this field. | detection methods for stochastic gravitational-wave backgrounds: a unified treatment |
the crab nebula is a bright source of gamma rays powered by the crab pulsar's rotational energy through the formation and termination of a relativistic electron-positron wind. we report the detection of gamma rays from this source with energies from 5 × 10^{-4} to 1.1 peta-electron volts with a spectrum showing gradual steepening over three energy decades. the ultrahigh-energy photons imply the presence of a peta-electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. we constrain the pevatron' size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. the production rate of peta-electron volt electrons, 2.5 × 10^{36} ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta-electron volt protons to the production of the highest-energy gamma rays. | peta-electron volt gamma-ray emission from the crab nebula |
we present time-of-arrival (toa) measurements and timing models of 47 millisecond pulsars observed from 2004 to 2017 at the arecibo observatory and the green bank telescope by the north american nanohertz observatory for gravitational waves (nanograv). the observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. these data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. we detail our observational methods and present a set of toa measurements, based on "narrowband" analysis, in which many toas are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. a separate set of "wideband" toas will be presented in a companion paper. we detail a number of methodological changes, compared to our previous work, which yield a cleaner and more uniformly processed data set. our timing models include several new astrometric and binary pulsar measurements, including previously unpublished values for the parallaxes of psrs j1832-0836 and j2322+2057, the secular derivatives of the projected semimajor orbital axes of psrs j0613-0200 and j2229+2643, and the first detection of the shapiro delay in psr j2145-0750. we report detectable levels of red noise in the time series for 14 pulsars. as a check on timing model reliability, we investigate the stability of astrometric parameters across data sets of different lengths. we also report flux density measurements for all pulsars observed. searches for stochastic and continuous gravitational waves using these data will be subjects of forthcoming publications. | the nanograv 12.5 yr data set: observations and narrowband timing of 47 millisecond pulsars |
we study sample efficient reinforcement learning (rl) under the general framework of interactive decision making, which includes markov decision process (mdp), partially observable markov decision process (pomdp), and predictive state representation (psr) as special cases. toward finding the minimum assumption that empowers sample efficient learning, we propose a novel complexity measure, generalized eluder coefficient (gec), which characterizes the fundamental tradeoff between exploration and exploitation in online interactive decision making. in specific, gec captures the hardness of exploration by comparing the error of predicting the performance of the updated policy with the in-sample training error evaluated on the historical data. we show that rl problems with low gec form a remarkably rich class, which subsumes low bellman eluder dimension problems, bilinear class, low witness rank problems, po-bilinear class, and generalized regular psr, where generalized regular psr, a new tractable psr class identified by us, includes nearly all known tractable pomdps and psrs. furthermore, in terms of algorithm design, we propose a generic posterior sampling algorithm, which can be implemented in both model-free and model-based fashion, under both fully observable and partially observable settings. the proposed algorithm modifies the standard posterior sampling algorithm in two aspects: (i) we use an optimistic prior distribution that biases towards hypotheses with higher values and (ii) a loglikelihood function is set to be the empirical loss evaluated on the historical data, where the choice of loss function supports both model-free and model-based learning. we prove that the proposed algorithm is sample efficient by establishing a sublinear regret upper bound in terms of gec. in summary, we provide a new and unified understanding of both fully observable and partially observable rl. | gec: a unified framework for interactive decision making in mdp, pomdp, and beyond |
anisotropies in the nanohertz gravitational-wave background are a compelling next target for pulsar timing arrays (ptas). measurements or informative upper limits to the anisotropies are expected in the near future and can offer important clues about the origin of the background and the properties of the sources. given that each source is expected (in the simplest scenario of circular inspirals) to emit at a fixed frequency, the anisotropy will most generally vary from one frequency to another. the main result presented in this work is an analytical model for the anisotropies produced by a population of inspiralling supermassive black-hole binaries (smbhbs). this model can be immediately connected with parametrizations of the smbhb mass function and can be easily expanded to account for new physical processes taking place within the pta frequency band. we show that a variety of smbhb models predict significant levels of anistropy at the highest frequencies accessible to pta observations and that measurements of anisotropies can offer new information regarding this population beyond the isotropic component. we also model the impact of additional dynamical effects driving the binary towards merger and show that, if these processes are relevant within the pta band, the detectability of anisotropies relative to the isotropic background will be enhanced. finally, we use the formalism presented in this work to predict the level anisotropy of the circular and linear polarizations of the sgwb due to the distribution of binary orientation angles with respect to the line of sight. | exploring the spectrum of stochastic gravitational-wave anisotropies with pulsar timing arrays |
we present a new catalog of tev gamma-ray sources using 1523 days of data from the high-altitude water cherenkov (hawc) observatory. the catalog represents the most sensitive survey of the northern gamma-ray sky at energies above several tev, with three times the exposure compared to the previous hawc catalog, 2hwc. we report 65 sources detected at ≥5σ significance, along with the positions and spectral fits for each source. the catalog contains eight sources that have no counterpart in the 2hwc catalog, but are within 1° of previously detected tev emitters, and 20 sources that are more than 1° away from any previously detected tev source. of these 20 new sources, 14 have a potential counterpart in the fourth fermi large area telescope catalog of gamma-ray sources. we also explore potential associations of 3hwc sources with pulsars in the australia telescope national facility (atnf) pulsar catalog and supernova remnants in the galactic supernova remnant catalog. | 3hwc: the third hawc catalog of very-high-energy gamma-ray sources |
we point out that so(2n) pure yang-mills theory provides a candidate for dark matter (dm) without the explicit need to impose any additional symmetry. the dm candidate is a particular type of glueball, which we refer to as a baryonic glueball, that is naturally stable and produced by a novel production mechanism for a moderately large n. in this case, the intercommutation probability of cosmic strings (or macroscopic color flux tubes) is quite low, which offers characteristic gravitational wave signals to test our model. in particular, our model can simultaneously account for both abundance of dm and the recently reported gravitational wave signals detected in pulsar timing array experiments, including nanograv. | dark baryon from pure yang-mills theory and its gw signature from cosmic strings |
the international pulsar timing array 2nd data release is the combination of data sets from worldwide collaborations. in this study, we search for continuous waves: gravitational wave signals produced by individual supermassive black hole binaries in the local universe. we consider binaries on circular orbits and neglect the evolution of orbital frequency over the observational span. we find no evidence for such signals and set sky averaged 95 per cent upper limits on their amplitude h95. the most sensitive frequency is 10 nhz with h95 = 9.1 × 10-15. we achieved the best upper limit to date at low and high frequencies of the pta band thanks to improved effective cadence of observations. in our analysis, we have taken into account the recently discovered common red noise process, which has an impact at low frequencies. we also find that the peculiar noise features present in some pulsars data must be taken into account to reduce the false alarm. we show that using custom noise models is essential in searching for continuous gravitational wave signals and setting the upper limit. | searching for continuous gravitational waves in the second data release of the international pulsar timing array |
strong evidence of the existence of the stochastic gravitational-wave background (sgwb) has been reported by the nanograv, ppta, epta and cpta collaborations. the bayesian posteriors of the gravitational-wave background (gwb) amplitude and spectrum are compatible with current astrophysical predictions for the gwb from the population of supermassive black hole binaries (smbhbs). in this paper, we discuss the corrections arising from the extra scalar or vector radiation to the characteristic dimensionless strain in pta experiments and explore the possibility to detect charges surrounding massive black holes, which could give rise to sgwb with vector or scalar polarizations. the parametrized frequency-dependent characteristic dimensionless strain is used to take a bayesian analysis and the bayes factor is also computed for charged and neutral smbhbs. the bayesian posterior of gwb tensor amplitude is $\log_{10} a_t=-14.85^{+0.26}_{-0.38}$ and spectral exponent $\alpha=-0.60^{+0.32}_{-0.36}$. the bayesian posterior for vector or scalar amplitude $a_{v, s}$ is nearly flat and there is nearly no constraint from the current observation data. the bayesian factor is $0.71$ far less than 100, so the current observation can not support the existence of the charged smbhb. | detecting new fundamental fields with pulsar timing arrays |
we describe 14 yr of public data from the parkes pulsar timing array (ppta), an ongoing project that is producing precise measurements of pulse times of arrival from 26 millisecond pulsars using the 64-m parkes radio telescope with a cadence of approximately 3 weeks in three observing bands. a comprehensive description of the pulsar observing systems employed at the telescope since 2004 is provided, including the calibration methodology and an analysis of the stability of system components. we attempt to provide full accounting of the reduction from the raw measured stokes parameters to pulse times of arrival to aid third parties in reproducing our results. this conversion is encapsulated in a processing pipeline designed to track provenance. our data products include pulse times of arrival for each of the pulsars along with an initial set of pulsar parameters and noise models. the calibrated pulse profiles and timing template profiles are also available. these data represent almost 21 000 h of recorded data spanning over 14 yr. after accounting for processes that induce time-correlated noise, 22 of the pulsars have weighted root-mean-square timing residuals of $<\!\!1 μs$ in at least one radio band. the data should allow end users to quickly undertake their own gravitational wave analyses, for example, without having to understand the intricacies of pulsar polarisation calibration or attain a mastery of radio frequency interference mitigation as is required when analysing raw data files. | the parkes pulsar timing array project: second data release |
this paper describes the design and implementation of stingray, a library in python built to perform time series analysis and related tasks on astronomical light curves. its core functionality comprises a range of fourier analysis techniques commonly used in spectral-timing analysis, as well as extensions for analyzing pulsar data, simulating data sets, and statistical modeling. its modular build allows for easy extensions and incorporation of its methods into data analysis workflows and pipelines. we aim for the library to be a platform for the implementation of future spectral-timing techniques. we describe the overall vision and framework, core functionality, extensions, and connections to high-level command-line and graphical interfaces. the code is well tested, with a test coverage of currently 95%, and is accompanied by extensive application program interface (api) documentation and a set of step-by-step tutorials. | stingray: a modern python library for spectral timing |
the pattern of neutrino flavor oscillations could be altered by the influence of noisy perturbations such as those arising from a gravitational wave background (gwb). a stochastic process that is consistent with a gwb has been recently reported by the independent analyses of pulsar timing array (pta) datasets collected over a decadal timescale by the north american nanohertz observatory for gravitational waves, the european pta jointly with the indian pulsar timing array, the parkes pta, and the chinese pta collaborations. we investigate the modifications in the neutrino flavor oscillations under the influence of the gwb reported by the pta collaborations and we discuss how such effects could be potentially revealed in near-future neutrino detectors, possibly helping the discrimination of different models for the gwb below the nhz frequency range. | astrophysical neutrino oscillations after pulsar timing array analyses |
the evidence of the stochastic gravitational-wave background around the nanohertz frequency range was recently found by worldwide pulsar timing array (pta) collaborations. one of the cosmological explanations is the gravitational waves induced by enhanced curvature perturbations, but the issue of primordial black hole (pbh) overproduction in this scenario was pointed out in the literature. motivated by this issue and the ωgw∼f2 scaling suggested by the data, we study the gravitational waves induced in a cosmological epoch dominated by a stiff fluid (w =1 ) and find that they can safely explain the pta data well without pbh overproduction. | induced gravitational waves with kination era for recent pulsar timing array signals |
the nanograv collaboration reported strong bayesian evidence for a common-spectrum stochastic process in its 12.5 yr pulsar timing array data set, with median characteristic strain amplitude at periods of a year of ${a}_{\mathrm{yr}}={1.92}_{-0.55}^{+0.75}\times {10}^{-15}$ . however, evidence for the quadrupolar hellings & downs interpulsar correlations, which are characteristic of gravitational-wave signals, was not yet significant. we emulate and extend the nanograv data set, injecting a wide range of stochastic gravitational-wave background (gwb) signals that encompass a variety of amplitudes and spectral shapes, and quantify three key milestones. (i) given the amplitude measured in the 12.5 yr analysis and assuming this signal is a gwb, we expect to accumulate robust evidence of an interpulsar-correlated gwb signal with 15-17 yr of data, i.e., an additional 2-5 yr from the 12.5 yr data set. (ii) at the initial detection, we expect a fractional uncertainty of 40% on the power-law strain spectrum slope, which is sufficient to distinguish a gwb of supermassive black hole binary origin from some models predicting more exotic origins. (iii) similarly, the measured gwb amplitude will have an uncertainty of 44% upon initial detection, allowing us to arbitrate between some population models of supermassive black hole binaries. in addition, power-law models are distinguishable from those having low-frequency spectral turnovers once 20 yr of data are reached. even though our study is based on the nanograv data, we also derive relations that allow for a generalization to other pulsar timing array data sets. most notably, by combining the data of individual arrays into the international pulsar timing array, all of these milestones can be reached significantly earlier. | astrophysics milestones for pulsar timing array gravitational-wave detection |
many symmetry breaking patterns in grand unified theories (guts) give rise to cosmic strings that eventually decay when pairs of gut monopoles spontaneously nucleate along the string cores. these strings are known as metastable cosmic strings and have intriguing implications for particle physics and cosmology. in this article, we discuss the current status of metastable cosmic strings, with a focus on possible gut embeddings and connections to inflation, neutrinos, and gravitational waves (gws). the gw signal emitted by a network of metastable cosmic strings in the early universe differs, in particular, from the signal emitted by topologically stable strings by a suppression at low frequencies. therefore, if the underlying symmetry breaking scale is close to the gut scale, the resulting gw spectrum can be accessible at current ground-based interferometers as well as at future space-based interferometers, such as lisa, and at the same time account for the signal in the most recent pulsar timing data sets. metastable cosmic strings thus nourish the hope that future gw observations might shed light on fundamental physics close to the gut scale. | metastable cosmic strings |
we present a model-independent search for a gravitational wave background from cosmic domain walls (dws) in the nanograv 12.5 years dataset and international pta data release 2. dws that annihilate at temperatures ~ 20-50 mev with tensions ~ (40-100 tev)3 provide as good a fit to both datasets as the astrophysical background from supermassive black hole mergers. dws may decay into the standard model (sm) or a dark sector. in the latter case we predict an abundance δ n eff of dark radiation well within the reach of upcoming cmb surveys. complementary signatures at colliders and laboratories can arise if couplings to the sm are present. as an example, we discuss heavy axion scenarios, where dw annihilation may interestingly be induced by qcd confinement. | gravitational waves from domain walls in pulsar timing array datasets |
primordial black holes (pbhs) are one of the candidates to explain the gravitational wave (gw) signals observed by the ligo detectors. among several phenomena in the early universe, cosmic inflation is a major example to generate pbhs from large primordial density perturbations. in this paper, we discuss the possibility to interpret the observed gw events as mergers of pbhs that are produced by cosmic inflation. the primordial curvature perturbation should be large enough to produce a sizable amount of pbhs, and thus we have several other probes to test this scenario. we point out that the current pulsar timing array (pta) experiments already put severe constraints on gws generated via the second-order effects, and that the observation of the cosmic microwave background puts severe restriction on its μ distortion. in particular, it is found that the scalar power spectrum should have a very sharp peak at k ∼1 06 mpc-1 to fulfill the required abundance of pbhs while evading constraints from the pta experiments together with the μ distortion. we propose a mechanism that can realize such a sharp peak. in the future, simple inflation models that generate pbhs via almost gaussian fluctuations could be probed/excluded. | inflationary primordial black holes for the ligo gravitational wave events and pulsar timing array experiments |
the five-hundred-meter aperture spherical radio telescope (fast) was completed with its main structure installed on september 25, 2016, after which it entered the commissioning phase. this paper aims to introduce the commissioning progress of the fast over the past two years. to improve its operational reliability and ensure effective observation time, fast has been equipped with a real-time information system for the active reflector system and hierarchical commissioning scheme for the feed support system, which ultimately achieves safe operation of the two systems. for meeting the high-performance indices, a high-precision measurement system was set up based on the effective control methods that were implemented for the active reflector system and feed support system. since the commissioning of the fast, a low-frequency ultra-wideband receiver and 19-beam 1.05-1.45 ghz receiver have been mainly used. telescope efficiency, pointing accuracy, and system noise temperature were completely tested and ultimately achieved the acceptance indices of the telescope. the fast has been in the process of national acceptance preparations and has begun to search for pulsars. in the future, it will still strive to improve its capabilities and expand its application prospects. | commissioning progress of the fast |
in seesaw mechanism, if right handed (rh) neutrino masses are generated dynamically by a gauged u(1) symmetry breaking, a stochastic gravitational wave background (sgwb) sourced by a cosmic string network could be a potential probe of leptogenesis. we show that the leptogenesis mechanism that facilitates the dominant production of lepton asymmetry via the quantum effects of right-handed neutrinos in gravitational background, can be probed by gw detectors as well as next-generation neutrinoless double beta decay (0νββ) experiments in a complementary way. we infer that for a successful leptogenesis, an exclusion limit on f − ωgwh2 plane would correspond to an exclusion on the |mββ| − m1 plane as well. we consider a normal light neutrino mass ordering and discuss how recent nanograv pulsar timing data (if interpreted as gw signal) e.g., at 95% cl, would correlate with the potential discovery or null signal in 0νββ decay experiments. | gravitational wave complementarity and impact of nanograv data on gravitational leptogenesis |
the megajansky radio burst, frb 20200428, and other bright radio bursts detected from the galactic source sgr j1935+2154 suggest that magnetars can make fast radio bursts (frbs), but the emission site and mechanism of frb-like bursts are still unidentified. here, we report the emergence of a radio pulsar phase of the magnetar 5 months after frb 20200428. pulses were detected in 16.5 hours over 13 days using the five-hundred-meter aperture spherical radio telescope, with luminosities of about eight decades fainter than frb 20200428. the pulses were emitted in a narrow phase window anti-aligned with the x-ray pulsation profile observed using the x-ray telescopes. the bursts, conversely, appear in random phases. this dichotomy suggests that radio pulses originate from a fixed region within the magnetosphere, but bursts occur in random locations and are possibly associated with explosive events in a dynamically evolving magnetosphere. this picture reconciles the lack of periodicity in cosmological repeating frbs within the magnetar engine model. a pulsar phase from a galactic-frb magnetar shows that its frb bursts and pulsar emission originate differently. | a radio pulsar phase from sgr j1935+2154 provides clues to the magnetar frb mechanism |
having achieved "first light" immediately prior to the ceremony introducing it on 25 september 2016, china's 500-m aperture spherical radio telescope (fast) is now being kept busy with commissions. its innovative design requires 1,000 points to be measured and driven instead of just the two axes of motion, e.g., azimuth and elevation for most conventional antennas, to realize pointing and tracking. we have devised a survey plan to exploit the full sensitivity of fast, while minimizing the complexities involved during system operation. the 19-beam l-band focal plan array will be rotated to specific angles and receive continuous data streams, while the surface shape and the focal cabin stay fixed. such a survey will cover the northern sky in about 220 full days. our aim is to obtain data simultaneously for pulsar search, detection of neutral hydrogen (hi) galaxies, hi imaging, and radio transients through multiple back ends. these data sets could represent a significant contribution to all related fields in radio astronomy and remain relevant for decades. | fast in space: considerations for a multibeam, multipurpose survey using china's 500-m aperture spherical radio telescope (fast) |
we investigate a new mechanism to create large curvature perturbations on small scales due to parameter resonance in a single-field inflationary model with a small periodic structure upon the potential. after reentering the horizon, the amplified curvature perturbations can lead to observable primordial black holes as well as stochastic gravitational waves. the mass of primordial black holes and frequency of the induced gravitational waves depend on the model parameters. the resulted primordial black hole could constitute all dark matter or a fraction of dark matter in the universe, and corresponding stochastic gravitational waves fall in the frequency band measurable for the pulsar timing array and the space-based gravitational wave detectors. | primordial black holes and gravitational waves from parametric amplification of curvature perturbations |
in this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early universe, which could lead to a detectable gravitational wave signal. we summarize the basic conditions for a strong first order phase transition for su (n ) dark sectors with nf flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at elisa or in pulsar timing array experiments. the gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. the discussion includes the twin higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios. | gravitational waves from a dark phase transition |
it has recently been pointed out that gaia is capable of detecting a stochastic gravitational wave background in the sensitivity band between the frequency of pulsar timing arrays and lisa. we argue that gaia and theia have great potential for early universe cosmology, since such a frequency range is ideal for probing phase transitions in asymmetric dark matter, simp and the cosmological qcd transition. furthermore, there is the potential for detecting primordial black holes in the solar mass range produced during such an early universe transition and distinguish them from those expected from the qcd epoch. finally, we discuss the potential for gaia and theia to probe topological defects and the ability of gaia to potentially shed light on the recent nanograv results. | exploring the early universe with gaia and theia |
in recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts. these signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations. every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy; we measure the galaxy’s redshift to be z = 0.492 ± 0.008. the dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of ωigm = 4.9 ± 1.3 per cent, in agreement with the expectation from the wilkinson microwave anisotropy probe, and including all of the so-called ‘missing baryons’. the ~6-day radio transient is largely consistent with the radio afterglow of a short γ-ray burst, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. this contrasts with the interpretation of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts. | the host galaxy of a fast radio burst |
we compare primordial black hole (pbh) constraints on the power spectrum and mass distributions using the traditional press schechter formalism, peaks theory, and a recently developed version of peaks theory relevant to pbhs. we show that, provided the pbh formation criteria and the power spectrum smoothing are treated consistently, the constraints only vary by ~ 10% between methods (a difference that will become increasingly important with better data). our robust constraints from pbhs take into account the effects of critical collapse, the non-linear relation between ζ and δ, and the shift from the pbh mass to the power spectrum peak scale. we show that these constraints are remarkably similar to the pulsar timing array (pta) constraints impacting the black hole masses detected by ligo and virgo, but that the μ-distortion constraints rule out supermassive black hole (smbh) formation and potentially even the much lighter mass range of ~(1-100) m⊙ that ligo/virgo probes. | the power spectrum on small scales: robust constraints and comparing pbh methodologies |
ultralight boson fields, with a mass around 10-23 ev, are promising candidates for the elusive cosmological dark matter. these fields induce a periodic oscillation of the spacetime metric in the nanohertz frequency band, which is detectable by pulsar timing arrays. in this paper, we investigate the gravitational effect of ultralight tensor dark matter on the arrival time of radio pulses from pulsars. we find that the pulsar timing signal caused by tensor dark matter exhibits a different angular dependence than that by scalar and vector dark matter, making it possible to distinguish the ultralight dark matter signal with different spins. combining the gravitational effect and the coupling effect of ultralight tensor dark matter with standard model matter provides a complementary way to constrain the coupling parameter α. we estimate α ≲ 10-6 ~ 10-5 in the mass range m < 5 × 10-23 ev with current pulsar timing array. | pulsar timing residual induced by ultralight tensor dark matter |
the recent astronomical milestone by the pulsar timing arrays (pta) has revealed galactic-size gravitational waves (gw) in the form of a stochastic gravitational wave background (sgwb), correlating the radio pulses emitted by millisecond pulsars. this draws the outstanding questions toward the origin and the nature of the sgwb; the latter is synonymous to testing how quadrupolar the inter-pulsar spatial correlation is. in this paper, we tackle the nature of the sgwb by considering correlations beyond the hellings-downs (hd) curve of einstein's general relativity. we put the hd and non-einsteinian gw correlations under scrutiny with the nanograv and the cpta data, and find that both data sets allow a graviton mass $m_{\rm g} \lesssim 1.04 \times 10^{-22} \ {\rm ev}/c^2$ and subluminal traveling waves. we discuss gravitational physics scenarios beyond general relativity that could host non-einsteinian gw correlations in the sgwb and highlight the importance of the cosmic variance inherited from the stochasticity in interpreting pta observation. | beyond the hellings-downs curve: non-einsteinian gravitational waves in pulsar timing array correlations |
the conventional wisdom, dating back to 2012, is that the mass distribution of galactic double neutron stars (dnss) is well-fit by a gaussian distribution with a mean of 1.33 m ⊙ and a width of 0.09 m ⊙. with the recent discovery of new galactic dnss and gw170817, the first neutron star merger event to be observed with gravitational waves, it is timely to revisit this model. in order to constrain the mass distribution of dnss, we perform bayesian inference using a sample of 17 galactic dnss, effectively doubling the sample used in previous studies. we expand the space of models so that the recycled neutron star need not be drawn from the same distribution as the nonrecycled companion. moreover, we consider different functional forms including uniform, single-gaussian, and two-gaussian distributions. while there is insufficient data to draw firm conclusions, we find positive support (a bayes factor (bf) of 9) for the hypothesis that recycled and nonrecycled neutron stars have distinct mass distributions. the most probable model—preferred with a bf of 29 over the conventional model—is one in which the recycled neutron star mass is distributed according to a two-gaussian distribution, and the nonrecycled neutron star mass is distributed uniformly. we show that precise component mass measurements of ≈20 dnss are required in order to determine with high confidence (a bf of 150) whether recycled and nonrecycled neutron stars come from a common distribution. approximately 60 dnss are needed in order to establish the detailed shape of the distributions. | the mass distribution of galactic double neutron stars |
the neutron star interior composition explorer (nicer) recently measured the mass and equatorial radius of the isolated neutron star psr j0030+0451. we use these measurements to infer the moment of inertia, the quadrupole moment, and the surface eccentricity of an isolated neutron star for the first time, using relations between these quantities that are insensitive to the unknown equation of state of supranuclear matter. we also use these results to forecast the moment of inertia of neutron star a in the double pulsar binary j0737-3039, a quantity anticipated to be directly measured in the coming decade with radio observations. combining this information with the measurement of the tidal love number with ligo/virgo observations, we propose and implement the first theory-agnostic and equation-of-state-insensitive test of general relativity. specializing these constraints to a particular modified theory, we find that consistency with general relativity places the most stringent constraint on gravitational parity violation to date, surpassing all other previously reported bounds by 7 orders of magnitude and opens the path for a future test of general relativity with multimessenger neutron star observations. | astrophysical and theoretical physics implications from multimessenger neutron star observations |
magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. the energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. we carry out two- and three-dimensional (3d) kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. the simulations focus on electron-positron plasmas starting with a magnetically dominated, force-free current sheet (σ \equiv {b}2/(4π {n}e{m}e{c}2)\gg 1). for this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order fermi process accomplished by the curvature drift of particles along the electric field induced by the relativistic flows. this mechanism gives rise to the formation of hard power-law spectra f\propto {(γ -1)}-p and approaches p = 1 for sufficiently large σ and system size. eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. an analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. the development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to nonrelativistic regimes. in the 3d simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. this study suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications for a variety of high-energy astrophysical problems. | particle acceleration and plasma dynamics during magnetic reconnection in the magnetically dominated regime |
the high-frequency radio sky is bursting with synchrotron transients from massive stellar explosions and accretion events, but the low-frequency radio sky has, so far, been quiet beyond the galactic pulsar population and the long-term scintillation of active galactic nuclei. the low-frequency band, however, is sensitive to exotic coherent and polarized radio-emission processes, such as electron-cyclotron maser emission from flaring m dwarfs1, stellar magnetospheric plasma interactions with exoplanets2 and a population of steep-spectrum pulsars3, making galactic-plane searches a prospect for blind-transient discovery. here we report an analysis of archival low-frequency radio data that reveals a periodic, low-frequency radio transient. we find that the source pulses every 18.18 min, an unusual periodicity that has, to our knowledge, not been observed previously. the emission is highly linearly polarized, bright, persists for 30-60 s on each occurrence and is visible across a broad frequency range. at times, the pulses comprise short-duration (<0.5 s) bursts; at others, a smoother profile is observed. these profiles evolve on timescales of hours. by measuring the dispersion of the radio pulses with respect to frequency, we have localized the source to within our own galaxy and suggest that it could be an ultra-long-period magnetar. | a radio transient with unusually slow periodic emission |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.