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We investigate the implications of the intergalactic opacity for the evolution of the cosmic ultraviolet luminosity density and its sources. Our main constraint follows from our measurement of the Lyman-α forest opacity at redshifts EQUATION from a sample of 86 high-resolution quasar spectra. In addition, we impose the... |
Finally, we use estimates of the spectrum of the softness of the UV background from measurements of the HI to HeII column density ratio obtained by combining HI and HeII forest spectra. |
Although the thermal history of the IGM may only have a modest effect on the gas density PDF, the parameters EQUATION and β must be known in order to unambiguously solve for the evolution of the background hydrogen photoionization rate, Γ. In this paper, we do not attempt to infer EQUATION and β directly from the data;... |
Note that the systematic uncertainties in the temperature of the IGM at the mean density EQUATION and on the slope of the temperature-density relation β, especially if they conspire to affect the inferred Γ in the same direction, could go some way in resulting in a declining photoionization rate toward high redshifts E... |
We finally note that even for identical choices of (EQUATION, β, γ), our estimate of the mean free path would exceed that of ARTICLE by about 30% owing to their assumption of an Einstein-de Sitter cosmology, in contrast to the WMAP cosmology we adopt. |
Although equation 28 appears to assume isotropic quasar emissivity, it is more generally valid. For instance, if quasars emit with constant intensity in some directions and are completely obscured toward the others, then the overestimate of the total photon output of a quasar based on its observed magnitude and the ass... |
To compare the photoionization rate measured from the forest to what can be accounted for by the observed quasars and estimated star formation history, we proceed as follows. We begin by fixing the quasar contribution, with the working assumption that it is better constrained than that of stars. For each star formation... |
Many early calculations of the evolution of the global ionized fraction during reionization assumed clumping factors derived from averaging over the entire gas content of high-resolution simulations, which were as large as EQUATION at the redshifts EQUATION relevant for hydrogen reionization. Such clumping factors are ... |
The conclusions of the present section are in general agreement with the similar analysis of ARTICLE, who found that the ionizing comoving emissivity cannot decline from EQUATION up to EQUATION by more than a factor 1.5 if reionization is to be complete at EQUATION. Our results also support the picture of a ``photon-st... |
Second, the vast majority of the absorbers for which the column density ratio η has been measured are optically thin to both HI and HeII ionizing photons, whereas the systems that are optically thick to HeII ionizing photons are likely to contribute significantly to limiting their mean free path. As the expected column... |
The arguments of this section have thus far fundamentally relied on the shape of the redshift evolution of the quasar emissivity and of the total photoionization rate. This is the reason we used analytic fits (which can be straightforwardly extrapolated to higher redshifts) to the star formation history, a quantity whi... |
In Figure 53, we show both the SFR density derived from galaxy UV luminosity functions and from the UV emissivity derived from our forest opacity measurement, assuming the best-fit escape fraction of 40. We find no compelling evidence for a decline in the comoving SFR density over the redshift range probed by our measu... |
Inspection of Figure 53 suggests that the present data are instead roughly consistent with a constant EQUATION at EQUATION. Since our analysis assumes a dust correction consistent with these authors at high redshifts, but is based on more recent data, it thus seems that (in combination with the arguments given in 18 an... |
An intriguing possibility is that the very high redshift Universe harbors a large number of extremely faint galaxies that are missed by even the deepest surveys to date ARTICLE. As we have integrated the measured luminosity functions down to zero luminosity, this would require a significant steepening of the faint-end ... |
1. The intergalactic hydrogen photoionization rate is remarkably constant over the redshift range EQUATION, with a value EQUATION sEQUATION, subject to remaining systematic uncertainties in normalization. 2. Because the quasar luminosity function is strongly peaked near EQUATION, the lack of redshift evolution implies ... |
Although the present uncertainties in the redshift evolution of UV dust corrections, the escape fraction of ionizing photons from galaxies, and possible evolution of the stellar initial mass function however prohibit definitive conclusions about the cosmic SFR to be reached at this time, we have illustrated how the IGM... |
Better constraints on the thermal history of the IGM and on the abundance of the Lyman-limit systems which determine the mean free path of ionizing photons will be key in reducing the systematic uncertainties in the arguments presented here. In addition, improved determinations of the spectral indices of quasars and st... |
In Figure 5 we plot the mean values of a and e over the span of the simulations for the different cases, with and without the gas disk. While the inner planets show no clear separation in distribution, there is a consistent difference in eccentricity for the outer planets. The arrows connect the properties of the outer... |
We have used widely spaced in time Hubble Space Telescope images to determine tangential velocities of features associated with outflows from young stars. These observations were supplemented by groundbased telescope spectroscopy and from the resultant radial velocities, space velocities were determined for many outflo... |
The long operational life of the Hubble Space Telescope (HST) has presented the opportunity to obtain and compare emission-line images of the central (Huygens) region of the Orion Nebula over a sufficiently long time-base to determine highly accurate motions in the plane of the sky. These motions enable us to study the... |
In this paper we present the results of the determination of new tangential and radial velocities and their interpretation. We will show that a number of new stellar outflows (Herbig Haro objects, HH) have been found, that some previously designated HH objects are not what was originally argued, and that these motions ... |
Our observational material consists of both new spectroscopic and imaging data. The spectroscopic observations were made at Observatorio Astron\'omico Nacional en San Pedro M\'artir operated by the Universidad Nacional Aut\'onoma de M\'exico using the MEZCAL echelle spectrograph ARTICLE. The new imaging observations we... |
The Huygens region of the Orion Nebula has been the subject of many spectroscopic studies. Most of these did not have velocity resolutions to determine with sufficient accuracy the radial velocities of features moving about the speed of sound (about 10 ) and the studies with this necessary spectral resolution usually t... |
These new observations were made over the period 11–14 January 2007. The instrument configuration and performance was the same as in our earlier study of the Ring Nebula ARTICLE. The spectrograph was employed in a single spectral order mode by isolating the order containing the 6563 and [N II] 6548 and 6583 lines with ... |
Our imaging program was planned to allow a homogenous set of data to be obtained, which was intended to allow the best possible comparison of earlier and later images. In planning the observations it was recognized that the high spatial resolution of the ACS-WFC (0.05 / pixel in the drizzled images) was better than tha... |
In this paper we report on the analysis of new images in four areas of the Orion Nebula, supplemented by similar investigation of pairs of earlier observations. The four areas were selected to coincide as much as possible with earlier images of what were thought to be the most interesting and relevant objects. The char... |
We drew on a large body of earlier observations made with the WFPC2 and the ACS-WFC. Their characteristics are presented in Table 4. This listing includes not only the images matched with the new observations, but also images that were reprocessed and analyzed as part of this program. In addition to these long time-bas... |
The first step in comparison of the first and second epoch images was to align the two. In each case we took the first epoch images as the standard and shifted the second epoch images. Since the individual CCD detectors of both cameras can change with respect to their neighbors, alignment and comparison was only made u... |
After alignment the signal of the two images was normalized and a search was made for moving objects by taking a ratio of the first and second epoch images. In the case of identical images, the ratio image would be a smooth value of unity and in the case where objects are moving there would be a pattern with a dark lea... |
Figure 3 and Figure 4 show ratio images for our Visit 1 and Visit 2 images for the WFPC2 F656N and F658N filters, supplemented by images near HH 203 and HH 204 from a comparison of archived GO 5193 and GO 8121 images which have been smoothed by median filtering. The difference in time between the first and second epoch... |
The detailed coding of the superimposed data for Figure 3, Figure 4, and Figure 5 are described here, rather than in the figure captions. The markings on the outer borders show the Declination south of EQUATION and the Right Ascension east of 5EQUATION 35EQUATION. Filled circles indicate the positions of stars mentione... |
Figure 6 shows the Visit 5 region of overlap with the GO 9460 field near HH 502. In this case the time interval was 4.29 years and the velocity scale 24.3 per ACS-WFC pixel. It has had the faint fine features enhanced by division by a third order polynomial fit to the background. The nomenclature is that of ARTICLE. |
This rich body of new data allows us to draw conclusions about many aspects of gas-flow and star formation in the Orion Nebula Cluster (ONC) and its secondary star formation regions in the BN-KL and Orion-S regions. In this discussion we will first consider outflows associated with the Orion-S region (both as individua... |
There is by now a rich literature about large-scale (greater than 0.1 pc) outflows probably originating from the Orion-S region, the idea going back to the symmetric forms of HH 202 and HH 203+HH 204 being pointed in opposite directions across Orion-S, then developing as more outflows (HH 269, HH 529, HH 528, HH 625) w... |
Once again we find the well known result that all of the large-scale outflows are blue-shifted with respect to the OMC. When their current motions are projected backwards, these projected lines cross in the Orion-S regions, suggesting that they have a common origin in one or more objects located there. The results for ... |
HH 202. HH 202 is at the apex of a large parabolic high ionization feature, as shown in Figure 5. The variety of ionization stages indicates that although it forms as a collimated high velocity outflow it also contains neutral material. This can be due to the flow impacting neutral material or that the flow has compre... |
HH 203. HH 203 is a well defined bow shock with low ionization features at its tip. It is apparently driven by a high velocity, high ionization jet that emerges into the zone ionized by or the nearer (in the plane of the sky) (which dominates the ionization of some of the proplyds in this area) about half the distance... |
HH 204. HH 204 is nearly at the same PA as HH 203, but shows marked differences. Its apex is a flocculent structure that includes low ionization features even though the body of the enclosed parabolic form has extended [O III] emission, indicating that it is forming in ionized gas. No driving jet is seen. It should be... |
HH 269. HH 269 is composed of a series of well defined, wide-ionization range, shocks oriented almost due west ARTICLE. In this study, only features near 116-345 were measured (the so-called HH 269-East shock) but both in tangential and radial velocity. A 5 narrow but wiggly low ionization feature was also measured at... |
HH 528. HH 528 shows a broad band of irregular, low ionization, structures headed southeast from the Orion-S region. It is composed of two regions, the base or ``jet'' (as designated in HO07) and the southeast-most bow shock (again as designated in HO07). The term ``jet'' only loosely applies as this feature is much b... |
There is a peculiar complex of features around 5:35:17.6 EQUATION:24:54 (all coordinates in this paper will be in epoch 2000). Parts of this complex seem related to the HH 528 flow, such as the 177-454 shock, which is measured in [S II] to be moving at 37 towards PA=199. However, there are other features that seem to b... |
HH 529. HH 529 is composed of a series of shocks oriented towards the east and moving in that direction. Here we break it down into designated shocks HH 529-III, HH 529-II, and HH 529-I proceeding from east to west (as shown in Figure 2–Figure 5). There is a series of small, rapidly moving features which may represent... |
The brightest infrared and radio sources lie to the southwest of the putative source or sources producing the multiple large-scale HH objects associated with Orion-S. Recent radio observations reveal two well defined molecular outflows in this southwest part of Orion-S. CO observations ARTICLE detail a bipolar outflow ... |
The SiO blueshifted component coming from 136-355 intersects with the HH 269 series of shocks, which have an orientation of 273 ARTICLE, an orientation strengthened by the presence of long filaments ARTICLE. The feature for which we have measured the tangential velocity lies upon a projection of the SiO blueshifted out... |
There is a well defined series of optical and infrared features associated with the CO blueshifted component. One sees features extending towards 136-400 and there are a series of knots ARTICLE extending out to 204 (0.44 pc). There is a peculiar, low ionization, optical feature that has been designated as HH 625 and we... |
In Figure 7 we show the central portion of the Huygens region that includes Orion-S. This incorporates all of the area where the axes of symmetry of the flows (ordered counter-clockwise) of HH 202, HH 529, HH 203, HH 204, HH 528, HH 269, and HH 625 intersect, this general area having been previously identified as the m... |
Although we have derived higher accuracy tangential velocities, these have not narrowed down the identification of the sources of the large outflows except that various outflows seem to originate in the eastern part of this small field. If the features we call in this paper the HH 269-Ram and HH 529-Ram are from the sa... |
A recent infrared polarization study ARTICLE may provide additional useful information. ARTICLE argue that imbedded stars with bipolar outflows create dumbbell shaped cavities along the inner parts of the outflow and that starlight scattered from the surface of these cavities would have a characteristic polarization pa... |
In the southwest portion of Figure 7 one finds the sources of the molecular outflows, 136-400 producing the bipolar CO flow, whose northwest blueshifted portion creates the optical object HH 625 plus the series of H₂ knots ahead of it, and 136-355, producing the SiO outflow, portions of which may be in the features we ... |
Study of the BN-KL region is primarily the subject of infrared and radio investigations since most of outflowing material and all of the luminous central sources are invisible at optical wavelength. However, optical studies have aided in narrowing down the origin [7, 46]. Study of the motion of the three most massive s... |
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