Requirements for Investigating the Connection Between Lyman Alpha Absorption Clouds and the Large-Scale Distribution of Galaxies

We model the requirements on observational data that would allow an accurate determination of the degree of association between Lyman alpha absorbers and peaks in the redshift distribution of galaxies (large-scale structures like clusters of galaxies). We compare simulated distributions of low-redshift Lyman alpha absorption systems, constrained to be consistent with the distribution observed with HST, with the large-scale distribution of galaxies determined from pencil-beam redshift surveys. We estimate the amount of observational data required from catalogues of Lyman alpha absorbers and galaxies to allow a statistically significant test of the association of absorbers with large-scale structures of galaxies. We find that for each line-of-sight observed for Lyman alpha absorption lines (assuming that the entire redshift range out to z=0.4 is observable), redshifts must be obtained for at least 18 galaxies brighter than Mb=-18 and having redshifts between 0.2 and 0.4. Based on the redshift surveys used in this study, a search radius of 10' from the quasar line-of-sight is required. This will ensure that all peaks in the galaxy redshift distribution are represented by at least one galaxy in the observed sample. If Lyman alpha absorbers are intrinsically uncorrelated with galaxies, we find that 8 lines-of-sight must be observed to show that the distributions are different at the 95% confidence level. However, if a fraction of the Lyman alpha absorbers are distributed with the peaks in the galaxy distribution, 38 lines-of-sight must be mapped for the distribution of both Lyman alpha absorbers and galaxies in order to determine the fraction of absorbers distributed with the peaks of the galaxy distribution to an accuracy of 10%.Comment: 17 pages LaTeX file, plus 6 uuencoded compressed .eps figures to be printed seperately, to appear in Feb. 1, 1996 Ap

The Hidden Nuclear Spectrum of the Luminous IRAS Source FSC10214++4724

Optical spectropolarimetry of the luminous IRAS source FSC10214$+$4724 (z$=2.286$) reveals that the strong (\twid17\%) linear polarization detected by Lawrence \etal\/ is shared by both the narrow UV emission lines and the underlying continuum. This observation and the brightness of the source rule out synchrotron emission and dichroic extinction by dust as the polarizing mechanism, leaving scattering as the only plausible cause of the polarized emission. The narrowness of the lines requires that the scatterers be dust grains or cool ($<1.6\times$10$^4$~K) electrons. We can recover the spectrum that is incident on the scattering medium provided we make some reasonable assumptions regarding the source geometry. The scattered UV spectrum has a power law index $\alpha$~ of $-1.2 \pm 0.6$ ($F_\nu\propto\nu^\alpha$), steeper than what would be expected from a young burst of star formation, but similar to many AGN.Comment: 10 pages, with figure, uuencoded postscript Institute for Advanced Study number AST 94/1

The Faint End of the Quasar Luminosity Function at z ~ 4: Implications for Ionization of the Intergalactic Medium and Cosmic Downsizing

We present an updated determination of the z ~ 4 QSO luminosity function (QLF), improving the quality of the determination of the faint end of the QLF presented by Glikman et al. (2010). We have observed an additional 43 candidates from our survey sample, yielding one additional QSO at z = 4.23 and increasing the completeness of our spectroscopic follow-up to 48% for candidates brighter than R = 24 over our survey area of 3.76 deg^2. We study the effect of using K-corrections to compute the rest-frame absolute magnitude at 1450 Å compared with measuring M_(1450) directly from the object spectra. We find a luminosity-dependent bias: template-based K-corrections overestimate the luminosity of low-luminosity QSOs, likely due to their reliance on templates derived from higher luminosity QSOs. Combining our sample with bright quasars from the Sloan Digital Sky Survey and using spectrum-based M 1450 for all the quasars, we fit a double power law to the binned QLF. Our best fit has a bright-end slope, α = 3.3 ± 0.2, and faint-end slope, β = 1.6^(+0.8)_(–0.6). Our new data revise the faint-end slope of the QLF down to flatter values similar to those measured at z ~ 3. The break luminosity, though poorly constrained, is at M* = –24.1^(+0.7)_(–1.9), approximately 1-1.5 mag fainter than at z ~ 3. This QLF implies that QSOs account for about half the radiation needed to ionize the intergalactic medium at these redshifts