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Acknowledgements. Dee McDougall acknowledges financial assistance from the Carnegie Trust for the Universities of Scotland and a travel grant from the International Astronomical Union. |
# Source: arxiv 0808.0151 # Title: A photometric redshift of $z=1.8^{+0.4}_{-0.3}$ for the \agile GRB 080514B # Sections: all # Downloaded: 2026-03-02T07:59:00.382667+00:00 |
A photometric redshift of [MATH] for the AGILE GRB 080514B Abstract Aims. The AGILE gamma-ray burst GRB 080514B is the first burst with detected emission above 30 MeV and an optical afterglow. However, no spectroscopic redshift for this burst is known. |
Methods. We compiled ground-based photometric optical/NIR and millimeter data from several observatories, including the multi-channel imager GROND, as well as ultraviolet Swift UVOT and X-ray XRT observations. The spectral energy distribution of the optical/NIR afterglow shows a sharp drop in the Swift UVOT UV filters ... |
Results. Fitting the SED from the Swift UVOT [MATH] band to the [MATH] band, we estimate a photometric redshift of [MATH] consistent with the pseudo redshift reported by Pelangeon & Atteia (2008) based on the gamma-ray data. |
Conclusions. The afterglow properties of GRB 080514B do not differ from those exhibited by the global sample of long bursts, supporting the view that afterglow properties are basically independent of prompt emission properties. |
Key Words.: Gamma rays: bursts: individual: GRB 080514B Introduction Gamma-Ray Bursts (GRBs) are the most luminous explosions in the Universe, with the bulk of the released energy emerging in the 0.1 to 1 MeV range (e.g., Kaneko et al. 2006; Preece et al. 2000). Indeed, most bursts have not been observed at energies mu... |
To date no burst detected above 30 MeV has an observed afterglow. The discovery of GRB 080514B by the Italian AGILE gamma-ray satellite (Tavani et al. Tavani ( 2008 ) on May 14, 2008 at 09:55:56 UT (Rapisarda et al. 2008) was therefore of particular interest. AGILE carries three instruments covering the energy range fr... |
The burst was also observed by Mars Odyssey, operating as part of the Interplanetary Network (IPN) (Hurley et al. 2006), making it possible to constrain the error box of the burst to about 100 arcmin (Rapisarda et al. 2008). This localization led to the discovery of its X-ray afterglow by the Swift satellite at coordin... |
; fig. ). Here we report our optical/near-infrared follow-up observations of the afterglow of GRB 080514B starting 0.43 days after the trigger, extending to late times of 24 days. |
Observations and data reduction Swift UVOT began observing the afterglow 0.43 days after the SuperAGILE/IPN detection (Holland holland ( 2008 ), in the broad-band [MATH] [MATH] [MATH] [MATH] |
[MATH] and [MATH] lenticular filters, covering the wavelength range between 1600 Å and 6000 Å (Poole et al. 2008). A second set of observations were obtained in the [MATH] band [MATH] days after the trigger, covering the wavelength range from 1600 Å to 8000 Å. Photometry was performed on the UVOT data using the standar... |
Ground-based follow-up observations were performed by our group using the [MATH] Watcher telescope in South Africa, the IAC80 telescope at Observatorio del Teide, the MPG/ESO 2.2m telescope on La Silla equipped with GROND (Greiner et al. 2007, 2008), the Nordic Optical Telescope on La Palma, the Kitt Peak 4m telescope,... |
Our dataset is completed by an observation at 86 GHz with the Plateau de Bure interferometer (Guilloteau et al. 1992) using the 5-antenna compact D configuration and performed 3.92 days after the burst. We did not detect any source at the afterglow position within a 3-sigma detection limit of 0.57 mJy. |
Afterglow coordinates were derived from the GROND first epoch stacked [MATH] -band image, which has an absolute astrometric precision of about [MATH] corresponding to the RMS accuracy of the USNO-B1 catalogue (Monet et al. 2003). The coordinates of the optical afterglow are R.A., Dec. (J2000) = |
[MATH] [MATH] (Galactic coordinates [MATH] [MATH] [MATH] ). The Schlegel, Finkbeiner, & Davis (1998) extinction maps give [MATH] mag along this line of sight through the Galaxy. Assuming a ratio of visual-to-selective extinction of 3.1, this implies [MATH] 0.19 mag. |
Swift performed a Target of Opportunity (ToO) observation of the AGILE /IPN error box 0.43 days after the trigger and found two new X-ray sources. The brightest of these was found to fade, identifying it as the X-ray afterglow. X-ray data were obtained from the Swift data archive and the light curve from the Swift ligh... |
Results 3.1 The X-ray afterglow Fitting the spectrum of the first observing block ( [MATH] days; total exposure time 5916 s) with an absorbed power-law |
results in a spectral slope of [MATH] and an effective hydrogen column density of [MATH] [MATH] ), in agreement with values reported by Page et al. (2008; Fig. [MATH] uncertainties). We were unable to constrain the possibility of spectral evolution. The derived hydrogen column density is higher than the Galactic value ... |
The canonical X-ray afterglow light curve derived by Nousek et al. (2006) shows a transition from a plateau to the normal decay phase between [MATH] and [MATH] days post-burst and a jet break thereafter. Unfortunately, for GRB 080514B at early times (0.463 to 0.694 days) the X-ray light curve exhibits substantial scatt... |
3.2 The optical afterglow While the optical afterglow is detected over a broad range of filters, from the Swift UVOT [MATH] band to the [MATH] band (160-1700 nm), the data set is sparse, with some scatter (Fig. ). To determine the slope of the light curve decay as well as the spectral energy distribution (SED) of the a... |
3.3 SED and photometric redshift The simultaneous fitting procedure described in § 3.2 yields magnitudes normalized to one day after the GRB for each band, which define the spectral energy distribution (SED) of the afterglow. We find no evidence for strong chromatic evolution but caution again that the data are sparse ... |
[MATH] ) from the [MATH] band to the [MATH] band (Fig. ). The UVOT [MATH] band is an outlier of the fit but it does not significantly disturb the result. We do not find evidence for dust in the host galaxy, which would create spectral curvature. The three UVOT UV filters, on the other hand, show a much steeper slope. S... |
uncertainties, see Avni Avni ( 1976 ), in agreement with the constraint of [MATH] based on Gemini-North observations (Perley et al. 2008) and the pseudo redshift of [MATH] based on the burst spectrum (Pelangeon & Atteia 2008). On the other hand, it is intermediate between the two redshift estimations presented by Gendr... |
Fixing [MATH] , we re-fit the SED (now excluding the UVOT UV filters) with dust models for the Milky Way, Large and Small Magellanic Clouds (see Kann et al. 2006 for the procedure). In all cases, adding [MATH] as an additional parameter does not improve the fits significantly, and the derived extinction is zero within ... |
[MATH] for MW, [MATH] for LMC and [MATH] for SMC dust). No evidence for a 2175 Å feature (which would lie close to the [MATH] and [MATH] bands) is apparent, and no discrimination is possible between dust models. |
The assumption of zero extinction is consistent with several studies (Starling et al. 2007; Schady et al. 2007) on the dust-to-gas ratios in host galaxies of GRBs where it is shown that the observed GRBs occur in low-metallicity environments. |
For an assumed redshift of [MATH] , and fixing the Galactic hydrogen column density to the value given by Kalberla et al. (2005), this implies a host-intrinsic column density of [MATH] and an unabsorbed spectral index of [MATH] |
[MATH] ). The deduced value for the spectral slope is consistent with the mean value found for Swift X-ray afterglows (O’Brien et al. 2006). |
Using the derived spectral slope and redshift, the absolute magnitude of the afterglow is [MATH] and [MATH] , at one and four days after the GRB, respectively (for the method see Kann et al. 2006, 2008; no extinction is assumed). A comparison with the sample presented in Kann et al. (2008) shows that these are typical ... |
3.4 The host galaxy A galaxy underlying the position of the optical transient is detected in all GROND optical bands at 8.9 days, as well as in the deep Keck [MATH] and [MATH] -band images obtained 24.13 days post-burst. Using the stacked GROND [MATH] |
images, the coordinates of this galaxy are R.A., Dec. (J2000) = [MATH] [MATH] , which is [MATH] off from the position of the optical afterglow. Assuming a cosmological model with [MATH] km s -1 Mpc [MATH] (Spergel et al. Spergel2003 ( 2003 ), for a redshift of 1.8 the offset of the optical transient from the center of ... |
Assuming a power-law spectrum for the putative host galaxy of the form [MATH] , its absolute [MATH] -band magnitude is [MATH] , where [MATH] mag is the distance modulus and [MATH] is the cosmological [MATH] -correction, [MATH] ). Hence, |
[MATH] , which for [MATH] =0.45, as it follows from the third epoch GROND [MATH] data, makes this galaxy approximately 0.5 mag more luminous than the characteristic magnitude of the Schechter function describing the [MATH] -band luminosity function of galaxies in the Las Campanas redshift survey (Lin et al. 1996). Its ... |
As mentioned in § 3.1 and 3.2 , based on the light curve alone we cannot unambiguously decide whether the data belong to the pre-jet break phase or to the post-jet break phase. However, using the standard |
[MATH] relations (e.g., Sari et al. 1999), the data favors an isotropic model and a wind environment with, at [MATH] =1 day, the position of the cooling frequency in between the optical/NIR and the X-ray band (Tab. ). The difference of the spectral slopes between both bands is |
[MATH] , which has to be compared to the theoretical value of [MATH] Unfortunately, the non-detection of the afterglow at 86 GHz does not constrain the shape of the SED further. |
Summary and conclusions To our knowledge, GRB 080514B is the first gamma-ray burst detected above 30 MeV for which an afterglow has been found in the X-ray band and in the optical/NIR bands. Based on our ground-based follow-up observing campaign, in combination with Swift UVOT and Swift XRT data starting 0.4 days after... |
We conclude that according to our data set the afterglow properties as well as the properties of the host galaxy match into what is known about the corresponding properties of the long burst sample. The only property that make this burst remarkable is its detection above 30 MeV. |
Acknowledgements. A.R., P.F., D.A.K. and S.K. acknowledge support by DFG Kl 766/11-3 and 13-1. R.F. and S.S. were supported by the Thüringer Landessternwarte Tautenburg. T.K acknowledges support by the DFG cluster of excellence ’Origin and Structure of the Universe’. J.P.U.F. acknowledges support by the DNRF and J. Gor... |
# Source: arxiv 0808.0161 # Title: Gamma Rays from Ultra-High Energy Cosmic Rays in Cygnus A # Sections: all # Downloaded: 2026-03-02T07:59:01.651210+00:00 |
Gamma Rays from Ultra-High Energy Cosmic Rays in Cygnus A Abstract Ultra-high energy cosmic rays (UHECRs) accelerated in the jets of active galactic nuclei can accumulate in high magnetic field, [MATH] kpc-scale regions surrounding powerful radio galaxies. Photohadronic processes involving UHECRs and photons of the ext... |
[MATH] -ray telescopes if radio galaxies are the sources of UHECRs. Galaxies: individual (Cygnus A) — cosmic rays: theory — galaxies: active — galaxies: jets — radiation processes: nonthermal |
Introduction Active galactic nuclei (AGN) and gamma-ray bursts are considered as two of the most plausible classes of astrophysical accelerators of extragalactic ultra-high energy cosmic rays (UHECRs; see, e.g., Halzen & Hooper, 2002 The recent report of the Pierre Auger Collaboration ( 2007 about clustering of the arr... |
of the directions to AGN at distances [MATH] strongly suggests that effective production of cosmic rays with energies [MATH] takes place in at least one of these source classes. Because of photohadronic GZK interactions of protons or ions with the CMB radiation, the study of super-GZK UHECRs from sources at [MATH] beco... |
Relativistic beams of energy from the central nuclei of AGN are thought to power the multi-kpc scale radio lobes of powerful galaxies and form an extended cavity (Scheuer, 1974 Acceleration of UHECRs in the compact inner jets of the radio galaxy on the sub-parsec scale, followed by production of collimated beams of ult... |
[MATH] are produced. Such secondaries can initiate pair-photon cascades to form large multi-Mpc scale halos of GeV/TeV radiation due to Compton and synchrotron processes (Aharonian et al., 1994 ; Aharonian, 2002 ; Inoue et al., 2005 |
In this Letter, we predict that synchrotron GeV fluxes from UHECR AGN sources are detectable with the Fermi Gamma ray Space Telescope (FGST; formerly the Gamma ray Large Area Space Telescope, GLAST) if UHECRs are captured in the vicinity of radio galaxies for sufficiently long times. Magnetic fields at the |
[MATH] G level in the kpc – Mpc vicinity from the AGN core are required to isotropize UHECRs accelerated by jets of radio galaxies. Indeed, for protons with energy [MATH] , the mean magnetic field [MATH] required to provide gyroradii smaller than size [MATH] is |
[MATH] , where [MATH] is the spatial scale where the isotropization occurs. Here we consider the specific case of the powerful radio galaxy Cygnus A, where the mean magnetic field in the surrounding cavity could reach 10 – 100 [MATH] at 100 kpc scales. Its properties are considered in Section 2, and calculations are pr... |
Model Parameters Magnetic fields [MATH] could be present at [MATH] Mpc scales in clusters of galaxies (Kim et al., 1990 ; Feretti et al., 1995 ; Ferrari et al., 2008 . Even higher magnetic fields, [MATH] G, could be present in the [MATH] kpc vicinity of cD galaxies near the center of galaxy clusters like the powerful r... |
produced in photomeson interactions is in the TeV domain. Furthermore, synchrotron radiation of lower energy electrons produced in |
[MATH] interactions by UHECRs extends to the GeV domain and could become detectable with the Fermi Telescope. Here we consider the detectability of these fluxes from the powerful and well-studied radio galaxy Cyg A. |
2.1 Power of the Cosmic Ray Accelerator Observations of Cygnus A ( [MATH] , luminosity distance [MATH] by the Chandra X-ray Observatory show that the central |
[MATH] kpc size luminous prolate spheroidal region of Cygnus A, called a “cavity,” can be understood as a shock expanding into the accretion cooling-flow gas (Wilson et al., 2006 The kinetic power of expansion of this X-ray cavity deduced by Wilson et al. ( 2006 is |
[MATH] erg s -1 . This is much larger than the total radio luminosity [MATH] erg s -1 of the two bright radio lobes of Cygnus A (Perley et al., 1984 The value of [MATH] should be considered as a lower |
limit to the overall power [MATH] of cosmic rays injected into the cavity, if the cosmic-ray power is assumed to drive the expansion of the cavity. A few times larger power, [MATH] ergs s -1 |
therefore seems a reasonable assumption. This value is in a good agreement with the “neutral beam” model (Atoyan & Dermer, 2001 2003 which explains the collimated relativistic X-ray jets that remain straight up to |
[MATH] Mpc distances in sources such as Pictor A (Wilson, Young, and Shopbell, 2001 as the result of energy transport by beams of UHE neutrons and gamma-rays. These linear X-ray features, surrounded by a broader and less collimated radio structure in Pictor A, and coincident with narrow radio structures exhibiting bend... |
(Carilli et al., 1996 ; Steenbrugge & Blundell, 2008 terminate in X-ray hot spots. Because of the large inclination angle, the X-ray jets in Cyg A cannot be detected. However detection of bright X-ray hot spots located at [MATH] distances on opposite sides of the nucleus (Wilson et al., 2006 strongly implies production... |
Detailed calculations in the framework of this model show that neutral beams of ultrarelativistic neutrons and [MATH] rays, produced by the compact relativistic jets in the central sub-parsec scale environment of FRII galaxies, can take a few percent of the total power of this inner jet. That energy is then deposited, ... |
[MATH] , on distance scales [MATH] , and also via photopair production of UHE gamma-rays through the process [MATH] These secondary charged relativistic particles initially form a beam in the same direction as the jet, and can effectively interact with and transfer momentum and energy to the ambient magnetized medium, ... |
detected from the lobes of Cyg A (Carilli & Barthel, 1996 ; Wilson et al., 2006 imposes the minimum power requirement for the beam. Given the [MATH] efficiency of neutral beam production, the acceleration power of the CRs in the relativistic inner jet must be |
[MATH] This power is then released in CRs when the inner jet decelerates to subrelativistic speeds in the dense medium at kpc scales. This scenario is in agreement with the assumption that the expansion of the cavity against the cooling flow observed (Smith et al., 2002 |
at distances [MATH] – 100 kpc is powered by cosmic-ray pressure. Protons are accelerated in the inner jet of Cyg A to a maximum energy [MATH] eV, consistent with size scales and magnetic fields inferred from a synchrotron model of blazars corresponding to Cyg A if observed along its jet. This value of [MATH] is in acco... |
[MATH] eV. In our model, we assume that acceleration of UHECRs to [MATH] eV occurs. 2.2 Magnetic Field Strength The lower limit to the equipartition magnetic field in the radio lobes of Cyg A inferred from radio observations is [MATH] |
(Carilli et al., 1991 The equipartition magnetic field in the cavity derived from X-ray observations is [MATH] (Wilson et al., 2006 Moreover, the field outside the cavity could also be very high given the large thermal electron energy density inferred from the X-ray emission at [MATH] or in the |
[MATH] kpc environment around Cyg A. The pressure of hot thermal gas decreases from [MATH] erg cm -3 in the regions near the cavity to [MATH] erg cm -3 at distances [MATH] |
kpc from the center of Cyg A (Smith et al., 2002 The corresponding equipartition magnetic fields would then vary from [MATH] to [MATH] at the periphery of this region. |
2.3 Injection Age The duration of injection of UHECRs, i.e., the jet injection age, represents one of the important parameters of the model. |
Wilson et al. ( 2006 find that the expansion age of the cavity, determined from the speed of the shock deduced from the analysis of X-ray data, is [MATH] yr. The injection age can be larger than this dynamical age because the derived value neglects the magnetic-field pressure of the intracluster medium (ICM) upstream o... |
[MATH] distances (Smith et al., 2002 , the virial speed [MATH] where [MATH] cm is, formally, the Schwarzschild radius for the total mass [MATH] The value of [MATH] gives a measure of the accretion/cooling flow velocities at radius [MATH] , and is comparable to the average [MATH] speed of the shock derived by Wilson et ... |
in the rest frame of the fluid upstream of the shock. These factors can significantly decrease the speed of expansion of the cavity in the stationary frame, so that the real injection age of the cavity can be significantly larger than the age inferred by Wilson et al. ( 2006 |
We now estimate the age of activity of the black-hole jet from energetics arguments. The inferred jet power, [MATH] corresponds to [MATH] of the Eddington luminosity for a black-hole mass [MATH] in Cygnus A |
(Tadhunter et al., 2003 To produce such power, the black hole should accrete mass at the rate [MATH] with an efficiency [MATH] with [MATH] The age of the central black hole is estimated by its growth time |
[MATH] giving an upper estimate for the jet’s age as the jet might be active for only a fraction of the BH growth phase. These estimates are in accord with the characteristic jet age [MATH] yr inferred from a model for “cocoon” (or cavity) dynamics by Begelman & Cioffi ( 1989 |
2.4 Cosmic Ray Diffusive Confinement Time The maximum confinement timescale [MATH] of UHECRs in a source of size [MATH] is given in the Bohm diffusion approximation by |
[MATH] , where the Bohm diffusion coefficient [MATH] and [MATH] is the Larmor radius of a particle with charge [MATH] From this expression we obtain the UHECR proton confinement time |
[EQUATION] For [MATH] kpc and [MATH] G, [MATH] Myr for [MATH] eV protons. Fig. compares timescales [MATH] for energy losses due to photomeson and photopair production with values of [MATH] for characteristic parameters [MATH] kpc and [MATH] G in the region surrounding Cyg A. Also shown is the value of [MATH] yrs for th... |
[MATH] eV can be extracted through photohadronic processes. Because of the increased confinement time and the much lower production threshold for photopair than photomeson processes, the photopair process can make a comparable or dominant contribution to the electromagnetic channel compared to photomeson processes. |
Results Fig. shows [MATH] -ray fluxes calculated for the electromagnetic cascade initiated by the injection of [MATH] -1 of UHECR protons into the cavity, and further cosmic ray interactions with the EBL in the [MATH] region surrounding Cyg A. Even though the EBL is dominated by the CMBR, interactions with the diffuse ... |
eV. We assume a mean magnetic field [MATH] Escape of particles is given by the Bohm diffusion approximation in a single zone model. The method of calculation follows the approach described by Atoyan & Dermer ( 2003 |
The solid, dashed, and dot-dashed curves in Fig. show the contributions to the fluxes from the photohadronic secondary electrons and the first two generations of cascade electrons for injection ages [MATH] The secondary electrons also include the electrons from [MATH] -decay [MATH] rays that convert promptly into elect... |
The open dots, full dots and stars in Fig. show the received [MATH] spectral energy fluxes for injection ages [MATH] Myr, 100 Myr and 300 Myr, respectively. The lower and higher energy peaks in the spectral energy distributions primarily result from photopair and photomeson processes, respectively. The sensitivities fo... |
Discussion and Conclusions If the radio lobes of Cyg A are powered by UHECR production from the inner pc-scale jets, then trapping of these particles in the surrounding strong magnetic-field region leads to the production of secondary [MATH] rays that should be significantly detected with the FGST in one year of observ... |
Detection of GeV [MATH] rays from Cyg A with the FGST might also be expected to arise from other processes. The [MATH] – 100 GeV radio-emitting electrons from the lobes of radio galaxies will Compton-scatter CMB photons to MeV – GeV energies (e.g., Cheung, 2007 . For the strong magnetic field, [MATH] G, in the lobes of... |
[MATH] . Thus the total energy flux of Compton-scattered CMBR from Cyg A is [MATH] erg s [MATH] ergs cm -2 -1 , with the [MATH] flux a factor of [MATH] – 10 lower. As can be seen from Fig. this process is almost two orders of magnitude below the UHECR-induced synchrotron flux, and well below the FGST sensitivity. |
Inoue et al. ( 2005 considered fluxes expected from the [MATH] halos of clusters of galaxies with weaker magnetic fields, [MATH] [MATH] G in a model where acceleration of UHECRs occurs in accretion shocks in the cluster. Because of lower maximum energies of accelerated protons, [MATH] , and lower magnetic fields, this ... |
Gabici & Aharonian ( 2005 predicted that synchrotron radiation from [MATH] electrons is produced by secondaries of UHECRs that leave the acceleration region and travel nearly rectilinearly through weak intergalactic magnetic fields at the level [MATH] [MATH] G. These sources would appear as point-like quiescent GeV – T... |
[MATH] spectra in the 100 GeV – TeV domain. In contrast to both these models, we predict soft 0.1 – 1 GeV spectra with [MATH] and hard, [MATH] |
spectra at TeV energies due to the much higher magnetic field in the confinement region. These models can be clearly distinguished if Cygnus A is resolved by the Fermi Gamma ray Space Telescope or the ground-based |
[MATH] -ray telescopes, as the emission region in our model subtends an angle [MATH] Because Cygnus A lies outside the GZK horizon, only UHECRs with energy below the GZK energy could be correlated with this source. Other closer FRII radio galaxies that are correlated with the arrival directions of UHECRs are, however, ... |
Mpc, recently discovered with INTEGRAL (Molina et al., 2007 , is 2.1 degrees away from a HiRes Stereo event with [MATH] EeV (C. C. Cheung, private communication, 2008). PKS 2158-380 at |
[MATH] Mpc is also within 3.2 degrees of an Auger UHECR with [MATH] EeV (Moskalenko et al., 2008 . By comparison with Cyg A, these are low luminosity FRIIs, and their predicted flux level will require detailed modeling for each source, as done here for Cyg A. Variability of [MATH] -ray emission would rule out our model... |
We thank Vladimir Vassiliev for discussion and providing the VERITAS sensitivities, Teddy Cheung and Felix Aharonian for important comments, and the referee for a detailed report. The work of AA and visits to NRL were supported by the GLAST Interdisciplinary Science Investigation Grant DPR-S-1563-Y. The work of CDD is ... |
# Source: arxiv 0808.0165 # Title: The Combined NVSS-FIRST Galaxies (CoNFIG) Sample - I. Sample Definition, Classification and Evolution # Sections: all # Downloaded: 2026-03-02T07:59:04.253657+00:00 |
The Combined NVSS-FIRST Galaxies (CoNFIG) Sample - I. Sample Definition, Classification and Evolution (Accepted . Received ; in original form ) |
Abstract The CoNFIG (Combined NVSS-FIRST Galaxies) sample is a new sample of 274 bright radio sources at 1.4 GHz. It was defined by selecting all sources with [MATH] [MATH] 1.3 Jy from the NRAO-VLA Sky Survey (NVSS) in the North field of the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey. New radio observati... |
keywords: Surveys - Radio Continuum: Galaxies - Galaxies: Active - Galaxies: Statistics - Galaxies: Luminosity Function Introduction |
Longair ( 1966 determined that powerful radio sources undergo strong differential evolution, the first indication of cosmic downsizing. Since then our understanding of the space density of AGN as a function of cosmic epoch has steadily continued to advance. |
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