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NASA NTRS1992

PKS 0483-436 - A high-redshift quasar with strong X-ray absorption

The first X-ray spectrum of a high-redshift (z = 2.85) quasar is reported. The Rosat PSPC spectrum of PKS 0438-436, covering 0.3-9 keV in the quasar's rest frame, reveals unexpected absorption of about 1 x 10 exp 22/sq cm, assuming it occurs at the source. Only one other high-luminosity quasar (of greater than about 50 observed by Einstein) shows significant absorption in its X-ray spectrum. Of the common line-of-sight absorbers, only highly ionized Ly-alpha forest clouds may be able to explain this amount of absorption. Candidates for an intrinsic absorber are discussed. Absorption at about 1 keV (rest frame) is due primarily to heavy elements. (O, Ne, Mg, Si, S) raising the possibility of measuring early universe abundances via X-ray absorption in this and like quasars. PKS 0438-436 may be a high-redshift member of a population of quasars which can contribute to the X-ray background above 2 keV, without being detectable by previous imaging missions.

Wilkes, Belinda J.↗
NASA NTRS1992

Deep imaging of high redshift QSO fields below the Lyman limit. I - The field of Q0000-263 and galaxies at Z = 3.4

Results are presented for the first field completed in a new survey involving very deep imaging of the fields of high redshift QSOs which exhibit thick Lyman limit absorption systems that completely remove the QSO from the observed broadband UV bandpass. The broadband colors of galaxies near the QSO sightline are examined with knowledge of the redshifts of heavy element absorption systems already discovered in the QSO spectrum. It is suggested that the colors and magnitudes are more consistent with a moderately underluminous galaxy at z = 0.438. A galaxy is identified which is 2.3 mag fainter and is only 2.8 arcsec from the QSO sightline, which is undetected in the present UV bandpass, and could plausibly be associated with the object responsible for the 3.390-z damped Ly-alpha absorption system in the spectrum of Q0000-263.

Steidel, Charles C.↗
NASA NTRS1993

Omega from the anisotropy of the redshift correlation function

Peculiar velocities distort the correlation function of galaxies observed in redshift space. In the large scale, linear regime, the distortion takes a characteristic quadrupole plus hexadecapole form, with the amplitude of the distortion depending on the cosmological density parameter omega. Preliminary measurements are reported here of the harmonics of the correlation function in the CfA, SSRS, and IRAS 2 Jansky redshift surveys. The observed behavior of the harmonics agrees qualitatively with the predictions of linear theory on large scales in every survey. However, real anisotropy in the galaxy distribution induces large fluctuations in samples which do not yet probe a sufficiently fair volume of the Universe. In the CfA 14.5 sample in particular, the Great Wall induces a large negative quadrupole, which taken at face value implies an unrealistically large omega 20. The IRAS 2 Jy survey, which covers a substantially larger volume than the optical surveys and is less affected by fingers-of-god, yields a more reliable and believable value, omega = 0.5 sup +.5 sub -.25.

Hamilton, A. J. S.↗
NASA NTRS1993

Extremely red objects in the fields of high redshift radio galaxies

We are engaged in a program of infrared imaging photometry of high redshift radio galaxies. The observations are being done using NICMOS2 and NICMOS3 arrays on the DuPont 100-inch telescope at Las Campanas Observatory. In addition, Persson and Matthews are measuring the spectral energy distributions of normal cluster galaxies in the redshift range 0 to 1. These measurements are being done with a 58 x 62 InSb array on the Palomar 5-m telescope. During the course of these observations we have imaged roughly 20 square arcminutes of sky to limiting magnitudes greater than 20 in the J, H, and K passbands (3 sigma in 3 square arcseconds). We have detected several relatively bright, extremely red, extended objects during the course of this work. Because the radio galaxy program requires Thuan-Gunn gri photometry, we are able to construct rough photometric energy distributions for many of the objects. A sample of the galaxy magnitudes within 4 arcseconds diameter is given. All the detections are real; either the objects show up at several wavelengths, or in subsets of the data. The reddest object in the table, 9ab'B' was found in a field of galaxies in a rich cluster at z = 0.4; 9ab'A' lies 8 arcseconds from it.

Persson, S. E.↗
NASA NTRS1993

Can quasars photoionize the intergalactic medium at high redshift?

The reionization of the intergalactic medium (IGM) by quasar sources at high redshift are discussed. The integrated UV background from observed QSO's, taking into account the hydrogen opacity associated with intervening Ly-alpha clouds and Lyman limit systems are computed. It is noted that the published data appear to indicate a significant underdensity of absorption systems in the Ly-alpha forest with column densities N(sub HI) greater than 10(exp 15) cm(sup -2). This deficit results in a reduction of the opacity of the universe by a factor of 1.5-3 at z = 3-5 relative to previous estimates. The QSO contribution to the metagalactic flux at the Lyman edge may be as large as J(sub 912)(z) is approximately 6((1 + z)/4.5)(sup 0.5) x 10(exp -22) erg cm(sup -2) s(sup -1) Hz(sup -1) sr(sup -1) for q(sup o) = O, and slightly lower for q(sub o) = 1/2. For a density of the diffuse component of the IGM of omega(sub D)(h(sub 50)(sup 2)) less than 0.025, QSO's could photoionize a smooth IGM sufficiently to satisfy the constraints imposed by the Gunn-Peterson effect. The epoch of reionization could be as recent as z is approximately greater than 5. As a result, neutral patches of IGM would be detectable in the spectra of high redshift quasars. The patches would appear as absorption line systems with typical column densities of 10(exp 19) - 10(exp 20) cm(sup -2), and velocity widths of 100 - 1000 km s(sup -1).

Meiksin, Avery↗
NASA NTRS1993

HST/FOS spectra of PG 1351+64: An intrinsic absorber at low redshift

A 1 A resolution spectra of the nearby (z = 0.08797) Seyfert galaxy PG 1351+64 taken with the Faint Object Spectrograph (FOS) onboard the Hubble Space Telescope is presented. Spectral coverage runs from 1200-3200 A in the observed frame and includes emission and absorption features due to Ly-alpha, N 5, Si 4, C 4, and Mg 2. Three distinct intrinsic absorption systems in Ly-alpha, N 5, Si 4, and C 4, and tentatively in Mg 2, at velocities of 900 km/s, 1630 km/s, and 2900 km/s (plus or minus 100 km/s) relative to the emission-line redshift of the QSO were detected. The maximum relative velocity of these absorbers is less than 5000 km/s and therefore does not meet Weymann, Carswell, & Smith's criteria for Broad-Absorption-Line (BAL) QSO's at high-z. However, the absorptions are almost certainly intrinsic to the QSO given the low redshift of this object. In addition, PG 1351+64 is marginally radio-quiet, as are all BALQSO's, based on recent estimates of the radio-loud/radio-quiet dividing line. The narrow velocity width, less than 500 km/s, and low outflow velocities of the absorption systems are more similar to so called 'associated absorbers' seen at high-z in radio-loud quasars, but whose absorptions are thought to arise in clouds much farther from the nucleus (greater than 1 kpc) than are BAL clouds (1-10 pc). Despite the qualitative resemblance to the associated absorbers, the absorption systems in PG 1351+64 appear to be the low-luminosity analogs of BALQSO absorption troughs. The lower observed outflow velocities in PG 1351+64 are due to the much lower luminosity of the nuclear source in comparison to the high-z, high-luminosity BALQSO's. In addition, 'satellite' emission lines displaced 4000-5000 km/s blueward and redward of the Mg 2 emission were discovered.

Granados, Arno↗
NASA NTRS1992

N-point correlation functions in the CfA and SSRS redshift distribution of galaxies

Using counts in cells, we estimate the volume-average N-point galaxy correlation functions for N = 2, 3, and 4, in redshift samples of the CfA and SSRS catalogs. Volume-limited samples of different sizes are used to study the uncertainties at different scales, the shot noise, and the problem with the boundaries. The hierarchical constants S3 and S4 agree well in all samples in CfA and SSRS, with average S3 = 194 +/- 0.07 and S4 = 4.56 +/- 0.53. We compare these results with estimates obtained from angular catalogs and recent analysis over IRAS samples. The amplitudes SJ seem larger in real space than in redshift space, although the values from the angular analysis correspond to smaller scales, where we might expect larger nonperturbative effects. It is also found that S3 and S4 are smaller for IRAS than for optical galaxies. This, together with the fact that IRAS galaxies have smaller amplitude for the above correlation functions, indicates that the density fluctuations of IRAS galaxies cannot be simply proportional to the density fluctuations of optical galaxies, i.e., biasing has to be nonlinear between them.

Gaztanaga, Enrique↗
NASA NTRS1992

Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

Maloney, Philip↗
NASA NTRS1993

Omega from the anisotropy of the redshift correlation function in the IRAS 2 Jansky survey

Peculiar velocities distort the correlation function of galaxies in redshift space. In the linear regime, the distortion has a characteristic quadrupole plus hexadecapole form, with amplitude depending on the cosmological density parameter Omega. I report here measurements of the anisotropy of the correlation function in the IRAS 2 Jy redshift survey. The inferred value of Omega is Omega = 0.5 + 0.5 or - 0.25.

Hamilton, A. J. S.↗
NASA NTRS1993

The Galileo solar redshift experiment

From the October 1989 launch to the first December 1990 earth gravity assist, we regularly obtained frequency measurements of the spacecraft clock - an ultrastable crystal oscillator (USO) supplied by Frequency Electronics, Inc. The solar gravitational redshift in frequency was readily detectable, and because of the unique variations in heliocentric distance we could separate the general relativistic effects from the USO's intrinsic frequency variations. We have verified the total frequency shift predicted by general relativity to 0.5 percent accuracy, and the solar gravitational redshift to 1 percent accuracy.

Krisher, Timothy P.↗
NASA NTRS1993

Redshift space clustering of galaxies and cold dark matter model

The distorting effect of peculiar velocities on the power speturm and correlation function of IRAS and optical galaxies is studied. The observed redshift space power spectra and correlation functions of IRAS and optical the galaxies over the entire range of scales are directly compared with the corresponding redshift space distributions using large-scale computer simulations of cold dark matter (CDM) models in order to study the distortion effect of peculiar velocities on the power spectrum and correlation function of the galaxies. It is found that the observed power spectrum of IRAS and optical galaxies is consistent with the spectrum of an Omega = 1 CDM model. The problems that such a model currently faces may be related more to the high value of Omega in the model than to the shape of the spectrum. A low-density CDM model is also investigated and found to be consistent with the data.

Bahcall, Neta A.↗
NASA NTRS1993

Tests of smoothing methods for topological study of galaxy redshift surveys

Studying the topology of large-scale structure as a way to better understand initial conditions has become more widespread in recent years. Studying topology of simulations (which have periodic boundary conditions) in redshift space produces results compatible with the real topological characteristics of the simulation. Thus we expect we can extract useful information from redshift surveys. However, with nonperiodic boundary conditions, the use of smoothing must result in the loss of information at survey boundaries. In this paper, we test different methods of smoothing samples with nonperiodic boundary conditions to see which most efficiently preserves the topological features of the real distribution. We find that a smoothing method which (unlike most previous published analysis) sums only over cells inside the survey volume produces the best results among the schemes tested.

Melott, Adrian L.↗
NASA NTRS1993

Properties of high-redshift Lyman-alpha clouds. I - Statistical analysis of the Schneider-Schmidt-Gunn quasars

Techniques for statistical analysis of the Lyman-alpha forest in high-redshift quasars are developed, and applied to the low-resolution (25 A) spectra of 29 of the 33 quasars in the Schneider-Schmidt-Gunn sample. We extrapolate each quasar's continuum shortward of Lyman-alpha emission, then consider each spectral bin of each quasar to be an (approximately) independent measurement of the absorption due to the Lyman-alpha clouds. With several thousand such measurements thus available, we can obtain good determinations of some interesting properties of clouds in the redshift range 2.5-4.3 without actually resolving any single cloud. We find that the mean absorption increases with z approximately as a power law (1 + z) exp (gamma + 1) with gamma = 2.46 +/- 0.37. The mean ratio of Lyman-alpha to Lyman-beta absorption in the clouds is 0.476 +/- 0.054. We also detect, and obtain ratios, for Lyma-gamma, delta, and possibly epsilon.

Press, William H.↗
NASA NTRS1993

Ultraviolet spectropolarimetry of high redshift quasars with the Hubble Space Telescope

Ultraviolet spectropolarimetry of three bright high-redshift low polarization quasars (LPQ's) was obtained with the Faint Object Spectrograph of the Hubble Space Telescope. Two of the quasars, PG 1634+706 and PG 2302+029, had polarizations of rho is approximately equal to 0.5-1.0 percent throughout the ultraviolet, and showed no significant variation of polarization amplitude or position angle with wavelength. PG 2302+029 was also marginally (2.4 sigma) circularly polarized in the optical continuum. For the highest redshift quasar, PG 1222+228 (Ton 1530), the polarization was measured down to rest wavelengths below 800 A. Although the continuum of PG 1222+228 was weakened by Lyman limit absorption from an intergalactic gas cloud, the polarization increased sharply from 1 percent to about 4.5 percent, a change of 4 sigma significance. This abrupt rise in polarization does not appear attributable to any known instrumental artifact. These UV polarizations were only slightly less than those previously observed for these same objects in the optical. The polarization spectra were flat with a typical slope of the polarized flux pF(sub upsilon) varies as upsilon(exp -0.8 plus or minus 0.5). Unlike the polarization spectra of several high luminosity Seyfert 1 nuclei studied previously, such a flat wavelength dependence of polarization cannot be explained by scattering from dust grains. The hypotheses that the polarization in these quasars is produced by transmission through aligned interstellar grains (in the Milky Way or the host galaxy), or by a synchrotron power law component, also appear to be ruled out. These observed spectra are consistent with a wavelength-independent polarization proportional to the total nonstellar light or, possibly, to the contribution of the blue thermal component.

Impey, Chris D.↗
NASA NTRS1993

Properties of low-redshift QSO absorption systems - QSO-galaxy pairs

The chance proximity of QSOs and galaxies provides unique opportunities to probe the extent and content of gas in the foreground galaxies through evaluation of the incidence and strength of absorption lines in the spectra of the background QSOs. Recent results on the observed properties of these low-redshift, heavy-element absorption systems are summarized. These results are discussed in the context of the galaxy morphologies and environments and are briefly compared with Galactic absorption and with the inferred properties of higher-redshift QSO absorption systems.

Womble, Donna S.↗
NASA NTRS1994

Power spectrum, correlation function, and tests for luminosity bias in the CfA redshift survey

We describe and apply a method for directly computing the power spectrum for the galaxy distribution in the extension of the Center for Astrophysics Redshift Survey. Tests show that our technique accurately reproduces the true power spectrum for k greater than 0.03 h Mpc(exp -1). The dense sampling and large spatial coverage of this survey allow accurate measurement of the redshift-space power spectrum on scales from 5 to approximately 200 h(exp -1) Mpc. The power spectrum has slope n approximately equal -2.1 on small scales (lambda less than or equal 25 h(exp -1) Mpc) and n approximately -1.1 on scales 30 less than lambda less than 120 h(exp -1) Mpc. On larger scales the power spectrum flattens somewhat, but we do not detect a turnover. Comparison with N-body simulations of cosmological models shows that an unbiased, open universe CDM model (OMEGA h = 0.2) and a nonzero cosmological constant (CDM) model (OMEGA h = 0.24, lambda(sub zero) = 0.6, b = 1.3) match the CfA power spectrum over the wavelength range we explore. The standard biased CDM model (OMEGA h = 0.5, b = 1.5) fails (99% significance level) because it has insufficient power on scales lambda greater than 30 h(exp -1) Mpc. Biased CDM with a normalization that matches the Cosmic Microwave Background (CMB) anisotropy (OMEGA h = 0.5, b = 1.4, sigma(sub 8) (mass) = 1) has too much power on small scales to match the observed galaxy power spectrum. This model with b = 1 matches both Cosmic Background Explorer Satellite (COBE) and the small-scale power spect rum but has insufficient power on scales lambda approximately 100 h(exp -1) Mpc. We derive a formula for the effect of small-scale peculiar velocities on the power spectrum and combine this formula with the linear-regime amplification described by Kaiser to compute an estimate of the real-space power spectrum. Two tests reveal luminosity bias in the galaxy distribution: First, the amplitude of the pwer spectrum is approximately 40% larger for the brightest 50% of galaxies in volume-limited samples that have M(sub lim) greater than M*. This bias in the power spectrum is independent of scale, consistent with the peaks-bias paradigm for galaxy formation. Second, the distribution of local density around galaxies shows that regions of moderate and high density contain both very bright (M less than M* = -19.2 + 5 log h) and fainter galaxies, but that voids preferentially harbor fainter galaxies (approximately 2 sigma significance level).

Park, Changbom↗
NASA NTRS1994

Galaxy formation in Lambda greater than 0 Friedmann models: Consequences for the number counts versus redshift test

We study the effect of the cosmological constant Lambda on galaxy formation using a simple spherical top-hat overdensity model. We consider models with Omega(sub 0) = 0.2, lambda(sub 0) = 0, and Omega(sub 0) = 0.2, lambda(sub 0) = 0.8 (where Omega(sub 0) is the density parameter, and lambda(sub 0) identically equal Lambda/3 H(sub 0 exp 2) where H(sub 0) is the Hubble constant). We adjust the initial power spectrum amplitude so that both models reproduce the same large-scale structures. The galaxy formation era in the lambda(sub 0) = 0 model occurs early (z approximately 6) and is very short, whereas in the lambda(sub 0) = 0.8 model the galaxy formation era starts later (z approximately 4), and last much longer, possibly all the way to the present. Consequently, galaxies at low redshift (z less than 1) are significantly more evolved in the lambda(sub 0) = 0 model than in the lambda(sub 0) = 0.8 model. This result implies that previous attempts to determine Lambda using the number counts versus redshift test are probably unreliable.

Martel, Hugo↗
NASA NTRS1995

Morphology of galaxy mergers at intermediate redshift

Using a combination of numerical simulation and synthesized Hubble Space Telescope Wide Field Camera 2 (HST WFC2) images, we follow the detectability of morphological signatures of disk galaxy mergers at intermediate redshifts z = 0.4 and z = 1.0. Rapid evolution in the surface brightness of tidal tails makes their use as an interaction signature limited; long tidal tails will only be detectable relatively early in the encounter, before the galaxies actually merge. Violent relaxation rapidly smooths isophotal irregularities after the galaxies merge, leaving the very low surface brightness tidal debris surrounding the remnant as the only sign of peculiarity after a few hundred Myr. This debris becomes indistinguishable from the main body of the remnant after less than or approximately equal to 0.2 (z = 1.0) to 1 (z = 0.4) Gyr, leaving a morphologically normal elliptical galaxy behind. Using WFC1, all signatures become undetectable almost immediately once the galaxies merge, due to the aberrated Point Speed Function (PSF). We interpret these results in light of recent HST programs investigating the nature of starburst and E + A galaxies in moderate redshift clusters.

Mihos, J. Christopher↗