Search

We apply halo abundance matching to obtain galaxy virial masses, M_h, and radii, Rvir, for the 183 isolated galaxies in the "MgII Absorber-Galaxy Catalog" (MAGIICAT, Nielsen et al.). All galaxies have spectroscopic redshifts (0.1 < z < 1.1) and their circumgalactic medium (CGM) is probed in MgII absorption within projected galactocentric distances D < 200 kpc. We examine the behavior of equivalent width, W(2796), and covering fraction, f_c, as a function of D, D/Rvir, and M_h. We find: [1] systematic segregation of M_h on the W(2796)-D plane (4.0 sigma); high-mass halos are found at higher D with larger W(2796) compared to lower mass halos. On the W(2796)-D/Rvir plane, mass segregation vanishes and we find W(2796) ~ (D/Rvir)^-2 (8.9 sigma); [2] higher mass halos have larger f_c at a given D, whereas f_c is independent of M_h at all D/Rvir; [3] f_c is constant with M_h over the range 10.7 < log(M_h/Msun) < 13.8 within a given D or D/Rvir. The combined results suggest that the MgII absorbing CGM is self-similar with halo mass, even above log(M_h/Msun)~12, where cold mode accretion is theoretically predicted to be quenched. If theory is correct, either outflows or sub-halos must contribute to absorption in high-mass halos such that low- and high-mass halos are observationally indistinguishable using MgII absorption strength once impact parameter is scaled by halo mass. Alternatively, the data may indicate that predictions of a universal shut down of cold-mode accretion in high-mass halos may require revision., Comment: revised version includes additional galaxies and is the published version in Astrophysical Letters

We present detailed photo+collisional ionization models and kinematic models of the multi-phase absorbing gas, detected within the HST/COS, HST/STIS, and Keck/HIRES spectra of the background quasar TON 153, at 104 kpc along the projected minor axis of a star-forming spiral galaxy (z=0.6610). Complementary g'r'i'Ks photometry and stellar population models indicate that the host galaxy is dominated by a 4 Gyr stellar population with slightly greater than solar metallicity and has an estimated log(M*)=11 and a log(Mvir)=13. Photoionization models of the low ionization absorption, (MgI, SiII, MgII and CIII) which trace the bulk of the hydrogen, constrain the multi-component gas to be cold (logT=3.8-5.2) and metal poor (-1.68<[X/H]<-1.64). A lagging halo model reproduces the low ionization absorption kinematics, suggesting gas coupled to the disk angular momentum, consistent with cold accretion mode material in simulations. The CIV and OVI absorption is best modeled in a separate collisionally ionized metal-poor (-2.50<[X/H]<-1.93) warm phase with logT=5.3. Although their kinematics are consistent with a wind model, given the 2-2.5dex difference between the galaxy stellar metallicity and the absorption metallicity indicates the gas cannot arise from galactic winds. We discuss and conclude that although the quasar sight-line passes along the galaxy minor axis at projected distance of 0.3 virial radii, well inside its virial shock radius, the combination of the relative kinematics, temperatures, and relative metallicities indicated that the multi-phase absorbing gas arises from cold accretion around this massive galaxy. Our results appear to contradict recent interpretations that absorption probing the projected minor axis of a galaxy is sampling winds., Comment: 16 pages, 11 figures, accepted for publication in MNRAS

Using HST/COS/STIS and HIRES/Keck high-resolution spectra, we have studied a remarkable HI absorbing complex at z=0.672 toward the quasar Q1317+277. The HI absorption has a velocity spread of 1600 km/s, comprises 21 Voigt profile components, and resides at an impact parameter of D=58 kpc from a bright, high mass [log(M_vir/M_sun) ~ 13.7] elliptical galaxy that is deduced to have a 6 Gyr old, solar metallicity stellar population. Ionization models suggest the majority of the structure is cold gas surrounding a shock heated cloud that is kinematically adjacent to a multi-phase group of clouds with detected CIII, CIV and OVI absorption, suggestive of a conductive interface near the shock. The deduced metallicities are consistent with the moderate in situ enrichment relative to the levels observed in the z ~ 3 Ly-alpha forest. We interpret the HI complex as a metal-poor filamentary structure being shock heated as it accretes into the halo of the galaxy. The data support the scenario of an early formation period (z > 4) in which the galaxy was presumably fed by cold-mode gas accretion that was later quenched via virial shocking by the hot halo such that, by intermediate redshift, the cold filamentary accreting gas is continuing to be disrupted by shock heating. Thus, continued filamentary accretion is being mixed into the hot halo, indicating that the star formation of the galaxy will likely remain quenched. To date, the galaxy and the HI absorption complex provide some of the most compelling observational data supporting the theoretical picture in which accretion is virial shocked in the hot coronal halos of high mass galaxies., Comment: 20 pages, 9 figures, submitted to ApJ

We present equivalent width measurements and limits of six diffuse interstellar bands (DIBs) in seven damped Ly-alpha absorbers (DLAs) over the redshift range 0.091

(Abridged) We compared the quantified morphological properties of 37 intermediate redshift MgII absorption selected galaxies to the properties of the absorbing halo gas, observed in the spectra of background quasars. The galaxy morphologies were measured using GIM2D modeling of Hubble Space Telescope WFPC-2 images and the absorbing gas properties were obtained from HIRES/Keck and UVES/VLT quasar spectra. We found a 3.1 sigma correlation between galaxy morphological asymmetries normalized by the quasar-galaxy projected separations, A/D, and the MgII rest-frame equivalent widths. Saturation effects cause increased scatter in the relationship with increasing W_r(2796). We defined a subsample for which the fraction of saturated pixels in the absorption profiles is f_sat<0.5. The correlation strengthened to 3.3 sigma. We also find a paucity of small morphological asymmetries for galaxies selected by MgII absorption as compared to those of the general population of field galaxies, as measured in the Medium Deep Survey. The K-S probability that the two samples are drawn from the same galaxy population is ruled out at a 99.8% confidence level. The A/D-W_r(2796) correlation suggests a connection between the processes that perturb galaxies and the quantity of gas in their halos, normalized by the impact parameter. Since the perturbations are minor, it is clear that dramatic processes or events are not required for a galaxy to have an extended halo; the galaxies appear "normal". We suggest that common, more mild processes that populate halos with gas, such as satellite galaxy merging, accretion of the local cosmic web, and longer-range galaxy-galaxy interactions, consequently also induce the observed minor perturbations in the galaxies., Comment: Accepted for publication in the Astrophysical Journal

We examine the properties of two galaxy "halos" at z ~ 0.7 in the TON 153 (z_em = 1.01) quasar field. The first absorber-galaxy pair (G1) is a z = 0.672, L_B = 4.3 L*_B, E/S0 galaxy probed at D = 58 kpc. G1 is associated with a remarkable five-component Ly-alpha complex having tau_LL < 0.4, W_r(Lya) = 2.8 A, and a velocity spread of v = 1420 km/s. We find no MgII, CIV, NV, nor OVI absorption in these clouds and infer metallicity upper limits of -3 < log(Z/Z_sun) < -1, depending upon assumptions of photoionized or collisionally ionized gas. The second absorber-galaxy pair (G2) is a z = 0.661, L_B = 1.8 L*_B, Sab galaxy probed at D = 103 kpc. G2 is associated with metal--enriched (log Z/Z_sun ~ -0.4) photoionized gas having N(HI) ~ 18.3 and a velocity spread of v = 200 km/s. The very different G1 and G2 systems both have gas-galaxy properties inconsistent with the standard luminosity dependent galaxy "halo" model commonly invoked for quasar absorption line surveys. We emphasize that mounting evidence is revealing that extended galactic gaseous envelopes in the regime of D < 100 kpc do not exhibit a level of homogeneity supporting a standardized halo model. Selection effects may have played a central role in the development of a simple model. We discuss the G1 and G2 systems in the context of Lambda-CDM models of galaxy formation and suggest that the heterogeneous properties of absorber-galaxy pairs is likely related to the range of overdensities from which galaxies and gas structures arise., Comment: 5 pages, 2 figures, Accepted to ApJ

We report the first detection of the 5705 and 5780 A Diffuse Interstellar Bands (DIBs) in a moderate redshift Damped Lyman alpha (DLA) system. We measure a rest frame equivalent width of 63.2 +- 8.7 mA for the 5705 and 216+-9 mA for the 5780 A feature in the z_abs 0.524 DLA towards AO 0235+164 and derive limits for the equivalent widths of the bands at 5797, 6284, and 6613 A. The equivalent width of the 5780 band is lower than would be expected based on the Galactic correlation of DIB strength with N(HI), but is in good agreement with the correlation with E(B-V). The relative strengths of the 5780 and 6284 A DIBs are inconsistent with all Galactic and extragalactic sightlines, except one Small Magellanic Cloud wing sightline towards Sk 143. However, the relative strengths of the 5705 and 5780 A DIBs are consistent with the Galactic relation, indicating that the relative strengths of these bands may be less sensitive to environment or that they may be associated with a similar carrier. The detection of DIBs at z~0.5 demonstrates that the organic compounds usually assumed to be the band carriers were already present in the universe some five gigayears ago., Comment: Accepted for publication in ApJ Letters

A Near-infrared (1.18-1.35 micron) high-resolution spectrum of the gravitationally-lensed QSO APM 08279+5255 was obtained with the IRCS mounted on the Subaru Telescope using the AO system. We detected strong NaI D 5891,5897 doublet absorption in high-redshift DLAs at z=1.062 and 1.181, confirming the presence of NaI, which was first reported for the rest-frame UV NaI 3303.3,3303.9 doublet by Petitjean et al. This is the first detection of NaI D absorption in a high-redshift (z>1) DLA. In addition, we detected a new NaI component in the z=1.062 DLA and four new components in the z=1.181 DLA. Using an empirical relationship between NaI and HI column density, we found that all "components" have large HI column density, so that each component is classified as DLA absorption. We also detected strong NaI D absorption associated with a MgII system at z=1.173. Because no other metal absorption lines were detected in this system at the velocity of the NaI absorption in previously reported optical spectra (observed 3.6 years ago), we interpret this NaI absorption cloud probably appeared in the line of sight toward the QSO after the optical observation. This newly found cloud is likely to be a DLA based upon its large estimated HI column density. We found that the N(NaI)/N(CaII) ratios in these DLAs are systematically smaller than those observed in the Galaxy; they are more consistent with the ratios seen in the Large Magellanic Cloud. This is consistent with dust depletion generally being smaller in lower metallicity environments. However, all five clouds of the z=1.181 system have a high N(NaI)/N(CaII) ratio, which is characteristic of cold dense gas. We tentatively suggest that the host galaxy of this system may be the most significant contributor to the gravitational-lens toward APM 08279+5255., Comment: 22 pages, 6 Postscript figures, 3 tables, ApJ in press (Vol.643, 2 June 2006)

There has been a renewed interest in searching for diffuse interstellar bands (DIBs) due to their probable connection to organic molecules and, thus, their possible link to life in the Universe. Our group is undertaking an extensive search for DIBs in DLAs via QSO absorption-line systems. Six of our DLA targets are presented here. Our equivalent width (EW) limits for the 5780 DIB line strongly suggests that DIB abundance is below the Milky Way expected value or that metallicity plays a large role in DIB strengths., Comment: 3 pages; 2 figures; presented at IAU 199; Probing Galaxies through Quasar Absorption Lines

We studied a sample of 38 intermediate redshift MgII absorption-selected galaxies using (1) Keck/HIRES and VLT/UVES quasar spectra to measure the halo gas kinematics from MgII absorption profiles and (2) HST/WFPC-2 images to study the absorbing galaxy morphologies. We have searched for correlations between quantified gas absorption properties, and host galaxy impact parameters, inclinations, position angles, and quantified morphological parameters. We report a 3.2-sigma correlation between asymmetric perturbations in the host galaxy morphology and the MgII absorption equivalent width. We suggest that this correlation may indicate a connection between past merging and/or interaction events in MgII absorption-selected galaxies and the velocity dispersion and quantity of gas surrounding these galaxies., Comment: 6 pages; 3 figures; contributed talk for IAU 199: Probing Galaxies through Quasar Absorption Lines

The current status and remaining questions of MgII absorbers are reviewed with an eye toward new results incorporating high quality Hubble Space Telescope images of the absorbing galaxies. In the end, we find that our current picture of extended gaseous regions around galaxies at earlier epochs is in need of some revision; MgII absorbing "halos" appear to be patchier and their geometry less regular than previously inferred. We also find that the so-called "weak" MgII absorbers are associated with normal galaxies over a wide range of impact parameters, suggesting that this class of absorber does not strictly select low surface brightness, dwarf galaxies, or IGM material. We emphasize the need for a complete survey of the galaxies in quasar fields, and the importance of obtaining rotation curves of confirmed absorbing galaxies., Comment: 18 pages; 8 figures; review talk for IAU 199: Probing Galaxies through Quasar Absorption Lines

We present the following results of photoionization modeling of six MgII-selected absorption systems, at redshift 0.5 < z 0.9, along lines of sight toward three quasars: PG 1241+176, PG 1248+401, and PG 1317+274. These are part of a larger sample of ~20 MgII absorbers at intermediate redshift, that facilitates a survey of the properties of, and processes active in, the multiple phases of gas, both in and outside of galaxies. We present new high resolution ultraviolet spectra from HST/STIS as well as high resolution optical spectra obtained with HIRES/Keck. Together, these spectra allow simultaneous study of a variety of ionization states of different chemical elements, with resolution of the kinematics providing strong constraints on multiphase properties. The six systems presented here include several that are likely to arise from lines of sight through disk and halo structures of spiral galaxies. For these we find that the high ionization gas, traced by CIV is consistent with coronal structures that resemble that of the Milky Way, along with high velocity clouds at 100-200 km/s. Another system has relatively weak CIV, relative to the low ionization absorption, which leads to a discussion of the circumstances in which a corona might be weak or absent in a galaxy, i.e. an early-type morphology or low star formation rate. Finally, we present systems that are examples of single-cloud and multiple-cloud weak MgII absorbers, which are as a class not likely to be within ~50 kpc of luminous galaxies. Based the physical conditions inferred from models, we discuss the nature of these types of systems, which may trace outer regions of galaxies, dwarf galaxy satellites, or metal-rich regions of the intergalactic medium., Comment: 31 pages, 6 figures, 9 tables, accepted to Astrophysical Journal

We analyze high resolution spectra of a multi--cloud weak [defined as W_r(MgII) < 0.3 A] absorbing system along the line of sight to PG 1634+706. This system gives rise to a partial Lyman limit break and absorption in MgII, SiII, CII, SiIII, SiIV, CIV, and OVI. The lower ionization transitions arise in two kinematic subsystems with a separation of ~150 km/s. Each subsystem is resolved into several narrow components, having Doppler widths of 3-10 kms. For both subsystems, the OVI absorption arises in a separate higher ionization phase, in regions dominated by bulk motions in the range of 30-40 km/s. The two OVI absorption profiles are kinematically offset by ~50 km/s with respect to each of the two lower ionization subsystem. In the stronger subsystem, the SiIII absorption is strong with a distinctive, smooth profile shape and may partially arise in shock heated gas. Moreover, the kinematic substructure of SiIV traces that of the lower ionization MgII, but may be offset by ~3 km/s. Based upon photoionization models, constrained by the partial Lyman limit break, we infer a low metallicity of ~0.03 solar for the low ionization gas in both subsystems. The broader OVI phases have a somewhat higher metallicity, and they are consistent with photoionization; the profiles are not broad enough to imply production of OVI through collisional ionization. Various models, including outer disks, dwarf galaxies, and superwinds, are discussed to account for the phase structure, metallicity, and kinematics of this absorption system. We favor an interpretation in which the two subsystems are produced by condensed clouds far out in the opposite extremes of a multi-layer dwarf galaxy superwind.

A new and mysterious class of object has been revealed by the detection of numerous weak MgII doublets in quasar absorption line spectra. The properties of these objects will be reviewed. They are not in close proximity to luminous galaxies, yet they have metallicities close to the solar value; they are likely to be self-enriched. A significant fraction of the weak MgII absorbers are constrained to be less than 10 parsecs in size, yet they present a large cross-section for absorption, indicating that there are more than a million times more of them than there are luminous galaxies. They could be remnants of Population III star clusters or tracers of supernova remnants in a population of "failed dwarf galaxies" expected in cold dark matter structure formation scenarios., Comment: 10 pages, 6 figures, To appear in "Extragalactic Gas at Low Redshift", ASP Proceedings, TBD, ed. J. Mulchaey

We present an investigation of MgII absorbers characterized as single-cloud weak systems at z~1. We measured column densities and Doppler parameters for MgII and FeII in 15 systems found in HIRES/Keck spectra at 6.6 km/s. Using these quantities and CIV, Lyman alpha and Lyman limit absorption observed with FOS/HST (resolution ~230 km/s) we applied photoionization models to each system to constrain metallicities, densities, ionization conditions, and sizes. We find that: (1) Single-cloud weak systems are optically thin in neutral hydrogen and may have their origins in a population of objects distinct from the optically thick strong MgII absorbers, which are associated with bright galaxies. (2) Weak systems account for somewhere between 25% to 100% of the z < 1 Lyman alpha forest clouds in the range 15.8

Despite previous intensive ground-based imaging and spectroscopic campaigns and wide-band HST imaging of the z=0.927 QSO 3C336 field, the galaxy that hosts the damped Ly-alpha system along this line-of-sight has eluded detection. We present a deep narrow-band H-alpha image of the field of this z=0.656 damped Ly-alpha absorber, obtained through the F108N filter of NICMOS 1 onboard the Hubble Space Telescope. The goal of this project was to detect any H-alpha emission 10 times closer than previous studies to unveil the damped absorber. We do not detect H-alpha emission between 0.05'' and 6'' (0.24 and 30 $h^{-1}$ kpc) from the QSO, with a 3-sigma flux limit of $3.70 \times 10^{-17} h^{-2}$ erg/s/cm^2 for an unresolved source, corresponding to a star formation rate (SFR) of $0.3 h^{-2}$ M_sun/yr. This leads to a 3-sigma upper limit of 0.15 M_sun/yr/kpc^2 on the SFR density, or a maximum SFR of 1.87 M_sun/yr assuming a disk of 4 kpc in diameter. This result adds to the number of low redshift damped Ly-alpha absorbers that are not associated with the central regions of Milky-Way-like disks. Damped Ly-alpha absorption can arise from high density concentrations in a variety of galactic environments including some that, despite their high local HI densities, are not conducive to widespread star formation., Comment: 18 pages, 3 figures. Replaced to match published version in ApJ, 550, 585 (Apr 1 2001)

We present a statistical analysis of the associated, high ionization narrow absorption line (NAL) systems in a sample of 59 QSOs defined from the HST QSO Absorption Line Key Project. We have compiled the QSO luminosities at 2500 A, 5 GHz, and 2 keV, spectral indices at 2500 A and 5 GHz, the H-beta emission line FWHM, the CIV emission line FWHM, and the radio core fraction. We find 17 associated NALs toward 15 QSOs, of which ~10 are statistically expected to be intrinsic. From a multivariate clustering analysis, the QSOs seem to group together based primarily on radio luminosity, followed by radio spectral index, CIV emission line FWHM, and soft X-ray luminosity. Radio-loud QSOs which have compact radio morphologies, flat radio spectra, and mediocre CIV FWHM (<6000 km/s) do not have detectable associated NALs, down to REW(CIV)=0.35 A. We find that BALQSOs have an enhanced probability of hosting detectable NAL gas and that the velocities of associated NALs are peaked around the emission redshifts, rather than the systemic redshifts of the QSOs. There is only one strong NAL [REW(CIV)>1.5 A] in our low redshift sample which implies evolution in the number of strong NALs with redshift. We interpret these results in the context of an accretion-disk model. In this framework, we suggest that the observational clues result from differences in orientation and wind properties, the latter presumably associated with the QSO radio properties. (abridged), Comment: Accepted for publication in ApJ, 20 pages text, 13 figures, 6 tables, 43 pages total, uses AASTeX 5.0, also available at http://www.astro.psu.edu/users/ganguly/ under Related Publications

We briefly review, at a level appropriate for graduate students and non-specialists, the field of quasar absorption lines (QALs). Emphasis is on the intervening absorbers. We present the anatomy of a quasar spectrum due to various classes of intervening absorption systems, and a brief historical review of each absorber class (Lyman-alpha forest and Lyman limit systems, and metal-line and damped Lyman-alpha absorbers). We also provide several heuristic examples on how the physical properties of both the intergalactic medium and the gaseous environments associated with earlier epoch galaxies can be inferred from QALs. The evolution of these environments from z=4 are discussed., Comment: 15 pages, 9 figures; Written for the Encyclopedia of Astronomy and Astrophysics (to be published in 2000 by Mac Millan and the Institute of Physics Publishing)

[Abridged] We examine a sample of 45 Mg II absorption-selected systems over the redshift range 0.4 to 1.4. Mg II and Fe II absorption profiles were observed at a resolution of ~6 km/s with HIRES/Keck. Lyman-alpha and C IV data were measured in archival FOS/HST spectra (~230 km/s). We perform a multivariate analysis of W(MgII), W(FeII), W(CIV) and W(Lya) (rest-frame) equivalent widths and the Mg II kinematic spread. We find five categories of Mg II absorbers: "Classic", "C IV-deficient", "Single/Weak", "Double", and "DLA/HI-Rich". There is a strong connection between low-ionization kinematics and the location of an absorber on the W(CIV)-W(MgII) plane. In most absorbers a significant fraction of the C IV arises in a phase separate from Mg II. Many of the C IV profiles are resolved in the FOS spectra due to velocity structure.. For 16 galaxies, we compare the available absorption-line properties (taken from Churchill et al. 2000, Paper I) to the galaxy properties but find no significant (greater than 3-sigma) correlations, although several suggestive trends are apparent. We compare the locations of our intermediate redshift absorbers on the W(CIV)-W(MgII) plane with those of lower and higher redshift data taken from the literature and find evidence for evolution that is connected with the Mg II kinematics. We discuss the potential of using the above categorizations of absorbers to understand the evolution in the underlying physical processes giving rise to the gas and governing its ionization phases and kinematics., Comment: Accepted: The Astrophysical Journal; Work based upon data presented in Paper I [astro-ph/0005585]

We present extensive metal-line absorption properties for 45 absorption systems that were selected by their Mg II absorption at redshifts between 0.4 and 1.4. For each system the properties of several chemical species are determined, including a wide range of ionization conditions. In the optical, the absorption systems have been observed at ~6 km/s resolution with HIRES/Keck, which covered Mg II, several Fe II transitions, Mg I, and in some cases (depending upon redshift), Ca II, Ti II, Mn II, and Al III. Ultraviolet, lower resolution (~230 km/s) Faint Object Spectrograph data (1600 - 3275 Ang) were obtained from the Hubble Space Telescope archive. These spectra covered Al II, Al III, Si II, Si III, Si IV, C II, C III, C IV, N V, O VI, and several Lyman series transitions, with coverage dependent upon the absorption system redshift. From these data, we infer that Mg II absorbing galaxies at intermediate redshifts have multiphase gaseous structures., Comment: Accepted: The Astrophysical Journal

We show that the number statistics of moderate redshift MgII and Lyman limit absorbers may rule out the hypothesis that high velocity clouds are infalling intragroup material., Comment: 4 pages, no figures; submitted to Astrophysical Journal Letters; revised version, more general and includes more about Braun and Burton CHVCs

The z=4.591 quasar PC 1415+3408 exhibits very strong associated metal-line absorption from the N V (1238,1242), Si IV (1393,1402), and C IV (1548,1550) doublets spanning the velocity interval -1700 < v < 0 km/s. Also present, are detached absorption troughs in N V and C IV spanning -5000 < v < -3000 km/s; this is characteristic of broad absorption line (BAL) quasars, but the small overall velocity spread suggests that PC 1415+3408 be classified as a Mini-BAL quasar. The N V doublet is consistent with black saturation over the velocity interval -1200 to -500 km/s; black N V absorption is extraordinary in all classes of quasars at all redshifts. Over this velocity interval, the C IV doublet is severely blended, but also consistent with black saturation. The material over this range of velocity appears to fully occult the continuum source, the broad emission line region, and any material that could give rise to scattered light. In view of a unified scenario for BAL and Mini-BAL absorption, these facts imply that the quasar is being viewed along a preferred direction. On the other hand, the black Mini-BALs in PC 1415+3408 could be explained if the BAL flow has an unusual geometry compared to the population of BAL quasars, and/or the spatial extent of a scattering region is small at the lower velocities (-1700 < v < 0 km/s)., Comment: 12 pages; 7 included figures, emulateapj.sty; accepted to The Astronomical Journal

In the course of a large intervening MgII survey of 25 quasars, the CIV emission lines of six (three radio-loud and three radio-quiet) were observed serendipitously. In four of these six quasars, we detected associated narrow absorption lines. Three of these four quasars are radio-quiet while the other is radio-loud. As a result of the original target selection, the small sample of six quasars is unbiased towards finding associated CIV absorption lines. In three of these four cases, the absorption line optical-depth ratios deviate from the prediction based on atomic physics, suggesting that the background photon source(s) are only partially covered by the absorbing medium and, by extension, that the absorption lines are intrinsic to the quasar. We have used the method of Barlow & Sargent to determine the effective coverage fraction of background source(s) and we have extended it to constrain the coverage fraction of the continuum and broad-emission line sources separately. We have also applied this refined method to the narrow intrinsic absorption lines in three additional quasars for which the necessary data were available from the literature. We find that in two objects from our sample, the continuum source must be partially covered regardless of the covering factor of the emission-line source. We discuss these results in the context of the properties of absorption lines observed in different types of active galaxies and related outflow phenomena. We cannot distinguish between possible mechanisms for the origin of the partial coverage signature although we do consider possible observational tests. Finally, we speculate on how the gas responsible for the narrow lines may be related to the accretion disk wind that may be responsible for the broad absorption lines observed in some quasars., Comment: 34 pages including figures, accepted by AJ

We used HIRES/Keck profiles (R=6 km/s) of MgII and FeII in combination with FOS/HST spectra (R=230 km/s) to place constraints on the physical conditions (metallicities, ionization conditions, and multi-phase distribution) of absorbing gas in three galaxies at z=0.9254, 0.9276, and 0.9343 along the line of sight to PG 1206+459. The chemical and ionization species covered in the FOS/HST spectra are HI, SiII, CII, NII, FeIII, SiIII, SiIV, NIII, CIII, CIV, SVI, NV, and OVI, with ionization potentials ranging from 13.6 to 138 eV. The multiple MgII clouds exhibit complex kinematics and the CIV, NV and OVI are exceptionally strong in absorption. We assumed that the MgII clouds are photoionized by the extra-galactic background and determined the allowed ranges of their physical properties as constrained by the absorption strengths in the FOS spectra. A main result of this paper is that the low resolution spectra can provide meaningful constraints on the physical conditions of the MgII clouds, including allowed ranges of cloud to cloud variations within a system. We find that the MgII clouds, which have a typical size of ~100 pc, give rise to the SiIV, the majority of which arises in a single, very large (~5 kpc), higher ionization cloud. However, the MgII clouds cannot account for the strong CIV, NV, and OVI absorption. We conclude that the MgII clouds are embedded in extended (10-20 kpc), highly ionized gas that gives rise to CIV, NV, OVI; these are multi-phase absorption systems. The high ionization phases have near-solar metallicity and are consistent with Galactic-like coronae surrounding the individual galaxies, as opposed to a very extended common "halo" encompassing all three galaxies., Comment: Accepted for publication in the Astronomical Journal

We present a search for "weak" MgII absorbers [those with W_r(2796) < 0.3 A in the HIRES/Keck spectra of 26 QSOs. We found 30, of which 23 are newly discovered. The spectra are 80% complete to W_r(2796) = 0.02 A and have a cumulative redshift path of ~17.2 for the redshift range 0.4 < z < 1.4. The number of absorbers per unit redshift, dN/dz, is seen to increase as the equivalent width threshold is decreased; we obtained dN/dz = 1.74+/-0.10 for our 0.02 <= W_r(2796) < 0.3 A sample. The equivalent width distribution follows a power law with slope -1.0; there is no turnover down to W_r(2796) = 0.02 A at = 0.9. Weak absorbers comprise at least 65% of the total MgII absorption population, which outnumbers Lyman limit systems (LLS) by a factor of 3.8+/-1.1; the majority of weak MgII absorbers must arise in sub-LLS environments. Tentatively, we predict that ~5% of the Lyman-alpha forest clouds with W_r(1215) > 0.1 A will have detectable MgII absorption to W_r,min(2796) = 0.02 A and that this is primarily a high-metallicity selection effect (Z/Z_sun] > -1). This implies that MgII absorbing structures figure prominently as tracers of sub-LLS environments where gas has been processed by stars. We compare the number density of W_r(2796) > 0.02 A absorbers with that of both high and low surface brightness galaxies and find a fiducial absorber size of 35h^-1 to 63h^-1 kpc, depending upon the assumed galaxy population and their absorption properties. The individual absorbing "clouds" have W_r(2796) <= 0.15 A and their narrow (often unresolved) line widths imply temperatures of ~25,000 K. We measured W_r(1548) from CIV in FOS/HST archival spectra and, based upon comparisons with FeII, found a range of ionization conditions (low, high, and multi-phase) in absorbers selected by weak MgII., Comment: Accepted Version: 43 pages, PostScript figures embedded; accepted to ApJ; updated version includes analysis of CIV absorption

A method offering an order of magnitude sensitivity gain is described for using quasar spectra to investigate possible time or space variation in the fine structure constant, alpha. Applying the technique to a sample of 30 absorption systems, spanning redshifts 0.5 < z< 1.6, obtained with the Keck I telescope, we derive limits on variations in alpha over a wide range of epochs. For the whole sample Delta(alpha)/alpha = -1.1 +/- 0.4 x 10^{-5}. This deviation is dominated by measurements at z > 1, where Delta(alpha)/alpha = -1.9 +/- 0.5 x 10^{-5}. For z < 1, Delta(alpha)/alpha = -0.2 +/- 0.4 x 10^{-5}, consistent with other known constraints. Whilst these results are consistent with a time-varying alpha, further work is required to explore possible systematic errors in the data, although careful searches have so far not revealed any., Comment: 4 pages, 1 figure, accepted for publication in Physical Review Letters

In the z=1.94 CIV absorption line system in the spectrum of quasar Q1222+228 (z_em=2.04), we find two clouds which have contrasting physical conditions, although they are only at a 17 km/s velocity separation. In the first cloud SiII, SiIV, and CII are detected, and AlII and AlIII column density limits in conjunction with photoionization models allow us to infer that this cloud has a large Si abundance and a small Al abundance relative to a solar abundance pattern. This pattern resembles that of Galactic metal-poor halo stars, which must have formed from such high redshift gas. The second cloud, in contrast, has detected AlII and AlIII (also SiIV and CII), but no detected SiII. We demonstrate, using photoionization models, that Al/Si must be greater than (Al/Si)_Sun in this unusual cloud. Such a ratio is not found in absorption profiles looking through Milky Way gas. It cannot be explained by dust depletion since Al depletes more severely than Si. Comparing to other Al-rich environments, we speculate about the processes and conditions that could give rise to this abundance pattern., Comment: 10 pages, 2 figures, AASTEX (aaspp4), to be published in ApJL

Echelle spectra have been obtained of the Ca II H and K lines for a sample of metal-poor subdwarf stars as well as for a number of nearby Population I dwarfs selected from among those included in the Mount Wilson HK survey. The main conclusion of this paper is that Ca II H- and K-line emission does occur among subdwarfs. It is particularly notable among those subdwarfs with colours of B-V > 0.75; all such stars observed exhibit chromospheric emission, although emission is observed among some subdwarfs bluer than this colour. The Ca II K emission profile in most subdwarfs exhibits an asymmetry of V/R > 1, similar to that seen in the integrated light of the solar disk. Two quantitative indicators of the contrast between the peaks in the emission profile and the neighbouring photospheric line profile are introduced. Measurements of these indicators show that the level of Ca II emission among the subdwarfs is similar to that among low-activity Population I dwarfs., Comment: Accepted to MNRAS

We report the discovery of two iron-group enhanced high-metallicity Mg II absorbers in a search through 28 Lyman Alpha forest clouds along the PKS 0454+039 sight line. Based upon our survey and the measured redshift number densities of W_r(MgII) <= 0.3 A absorbers and Lyman Alpha absorbers at z ~ 1, we suggest that roughly 5% of Lyman Alpha absorbers at z < 1 will exhibit "weak" Mg II absorption to a 5-sigma W_r(2796) detection limit of 0.02 A. The two discovered absorbers, at redshifts z = 0.6248 and z = 0.9315, have W_r(Lya) = 0.33 and 0.15 A, respectively. Based upon photoionization modeling, the H I column densities are inferred to be in the range 15.8 <= log N(HI) <= 16.8 cm^-2. For the z = 0.6428 absorber, if the abundance pattern is solar, then the cloud has [Fe/H] > -1; if its gas-phase abundance follows that of depleted clouds in our Galaxy, then [Fe/H] > 0 is inferred. For the z = 0.9315 absorber, the metallicity is [Fe/H] > 0, whether the abundance pattern is solar or suffers depletion. Imaging and spectroscopic studies of the PKS 0454+039 field reveal no candidate luminous objects at these redshifts. We discuss the possibility that these Mg II absorbers may arise in the class of "giant" low surface brightness galaxies, which have [Fe/H] >= -1, and even [Fe/H] >= 0, in their extended disks. We tentatively suggest that a substantial fraction of these "weak" Mg II absorbers may select low surface brightness galaxies out to z ~ 1., Comment: Accepted The Astrophysical Journal; 25 pages; 6 encapsulated figures

The study of galaxy evolution using quasar absorption lines requires an understanding of what components of galaxies and their surroundings are contributing to the absorption in various transitions. This paper considers the kinematic composition of the class of 0.4 < z < 1.0 MgII absorbers, particularly addressing the question of what fraction of this absorption is produced in halos and what fraction arises from galaxy disks. We design models with various fractional contributions from radial infall of halo material and from a rotating thick disk component. We generate synthetic spectra from lines of sight through model galaxies and compare the resulting ensembles of MgII profiles with the 0.4 < z < 1.0 sample observed with HIRES/Keck. We apply a battery of statistical tests and find that pure disk and pure halo models can be ruled out, but that various models with rotating disk and infall/halo contributions can produce an ensemble that is nearly consistent with the data. A discrepancy in all models that we considered requires the existence of a kinematic component intermediate between halo and thick disk. The variety of MgII profiles can be explained by the gas in disks and halos of galaxies not very much different than galaxies in the local Universe. In any one case there is considerable ambiguity in diagnosing the kinematic composition of an absorber from the low ionization high resolution spectra alone. Future data will allow galaxy morphologies, impact parameters, and orientations, FeII/MgII of clouds, and the distribution of high ionization gas to be incorporated into the kinematic analysis. Combining all these data will permit a more accurate diagnosis of the physical conditions along the line of sight through the absorbing galaxy., Comment: 34 pages including 14 postscript figures; Accepted by the Astrophysical Journal; URL http://www.astro.psu.edu/users/cwc/pubs.html

Based upon QSO absorption line studies, galaxies at 0.3 < z < 1.0 are seen to have extended gaseous "halos". When the absorption lines are observed at high resolution, the velocity distribution of the absorbing gas gives clues as to where this gas actually arises in and around the galaxies. Cloud to cloud abundance ratios provide further clues, given that the ionization conditions and chemical evolution histories of outer halos clouds, spiral disk clouds, and clouds in elliptical galaxies are different. The key to interpreting the high redshift data is the Milky Way galaxy, the absorption line "Rosetta stone.", Comment: 3 pages; Latex; paspconf.sty; figures included; To appear in the Proceedings of the UC Santa Cruz Workshop on Galactic Halos (ed. D. Zaritsky)

A consensus is developing on the nature of various populations of absorbers at different redshift regimes and in particular on their relationships to galaxies at those epochs. As one example we discuss the population of z < 1 MgII absorbers. Kinematic models are presented that show this population to be consistent with some combination of halo and disk kinematics and not with a pure disk or halo model. In contrast, the 2 < z < 3 CIV absorbers are likely to represent a mix of already formed halos and protogalactic clumps in the process of assembly. Clues could be provided by the level at which SiIV traces the same kinematic components as CIV (relative to how it traces lower ionization gas) and this is illustrated by a simple application of principal components analysis. It remains uncertain how much unambiguous information it will be possible to extract about the detailed properties of the gas along the line of sight through an individual absorption profile. However, ratios of various low and high ionization transitions along the line of sight can be combined with insights gained from kinematic models and from observations of galaxy properties. There is reason for optimism that we will progress toward a point when we will someday study the interstellar medium and gaseous halos and environments of absorbing galaxies at close to the same level as we study these components in the Milky Way., Comment: 6 pages, 4 EPS figures, conf_iap.sty. To appear in 13th IAP Workshop (1-5 July 1997) "Evolution of the Intergalactic Medium From QSO Absorption Line Systems"

We report the detection of Mg II absorption in two Lyman alpha forest clouds along the line of sight to PKS 0454+039. These clouds, at redshifts z=0.6248 and z=0.9315, respectively, also have strong Fe II absorption. We present results on the z=0.9315 cloud. The upper limit on log N(HI) is 16.5 cm^-2. Based upon UV background photoionization models, we infer that the cloud has super-solar metallicity. Photoionization by a late-type stellar population is ruled out., Comment: 2 pages, 1 EPS figures, conf_iap.sty To appear in 13th IAP Workshop (1-5 July 1997) "Evolution of the Intergalactic Medium from QSO Absorption Line Systems" eds. P. Petitjean & S. Charlot

First results from a study of high ionization absorption properties in roughly 30 Mg II absorption selected galaxies are presented. We have tested for correlations of Mg II, C IV, Si IV, N V, and O VI equivalent widths with the galaxy properties and Mg II gas kinematics. The results are suggestive of multi-phase halos with little to no global ionization gradient with impact parameter. C IV may arise in both the Mg II - Lyman alpha clouds and a high ionization "halo" traced by O VI. We also report on an unbiased survey for weak Mg II systems using HIRES/Keck spectra. At = 0.9, we find dN/dz = 1.6 +/- 0.1 for 0.02 < W(2796) < 0.3 [A] and that weak systems comprise roughly 65% of all Mg II absorbers. In all but one case, the weak Mg II systems exhibit Fe II absorption with = -0.3 +/- 0.4 measured for the sample. We suggest that weak Mg II absorbers comprise a substantial yet-to-be explored population. If weak systems select the LSB and/or dwarf galaxy population, then the weakest Mg II absorbers may provide one of the most sensitive tracers of chemical enrichment and evolution of the UV background from z = 2 to z = 0., Comment: (minor changes to conform with submitted version; To appear in 13th IAP Workshop (1-5 July 1997) "Evolution of the Intergalactic Medium from QSO Absorption Line Systems" eds. P. Petitjean and S. Charlot

By charting the kinematic, chemical, and ionization conditions of galactic and intergalactic gas over the redshift range 0 - 4 with QSO absorption lines, the evolution of chemical abundances, the UV meta-galactic background, and the clustering dynamics of galactic gas can be studied. HIRES/Keck Mg II 2796 profiles arising in = 1 galaxies are presented and the Mg II kinematic clustering function is given. The intriguing z = 0.93 systems toward Q1206+459 are shown and compared to z = 2 HIRES/Keck C IV profiles to illustrate how STIS/HST can be exploited for studies of the high ionization conditions in z < 1 Mg II selected systems. The scientific motives and plans for a large Mg II survey for 2 < z < 4 in the Near IR using the new 10-meter Hobby-Eberly Telescope are presented., Comment: 5 pages, 4 EPS figures, REVTeX 3.0 aipproc.sty for LaTex2e; Contributed Talk at "The UV Universe at Low and High Redshift" meeting, May 1 1997. To appear in proceedings edited by W. Waller

(Abridged) We present HIRES/Keck spectra having resolution 6 km/s of Mg II 2796 absorption profiles which arise in the gas associated with 15 identified galaxies over the redshift range 0.5 < z < 0.9. Using non-parametric rank correlation tests, we searched for correlations of the absorption strengths, saturation, and line-of-sight kinematics with the galaxy redshifts, rest frame B and K luminosities, rest colors, and impact parameters D. We found no correlations at the 2.5-sigma level between these properties. Of primary significance is the fact that the QSO-galaxy impact parameter apparently does not provide the primary distinguishing factor by which absorption properties can be characterized. The galaxy absorption properties exhibit a large scatter, which, we argue, is suggestive of a picture in which the gas arises from a variety of on-going dynamical events. Inferences from our study include: (1) The spatial distribution of absorbing gas in galaxies does not appear to follow a simple galactocentric functional dependence. (2) A single systematic kinematic model apparently cannot describe the observed velocity spreads in the absorbing gas. It is more that a heterogeneous population of sub-galaxy scale structures are giving rise to the observed cloud velocities. (3) The absorbing gas spatial distribution and kinematics may depend upon gas producing events and mechanisms that are recent to the epoch at which the absorption is observed. These distributions likely change over a few Gyr timescale. Based upon these inferences, we note that any evolution in the absorption gas properties over a larger redshift range should be directly quantifiable from a larger dataset of high-resolution absorption profiles., Comment: uuencoded: 22 pages, AASTeX file, 5 encapsulated PostScript figures; Accepted for publication in The Astrophysical Journal; Also available for pick-up at http://www.ucolick.org/~cwc/qso/abstract.html

To understand which parts of galaxies give rise to the variety of observed MgII absorption profiles seen in QSO spectra, we have embarked upon a program to generate simulated absorption profiles as they would arise from the many typical galactic structures we see today. Here, we present preliminary results for a clumpy, rotating disk which has been sampled by a variety of QSO lines of sight. The resulting ensemble of simulated profiles is qualitatively similar to those observed in HIRES spectra of 0.4 < z < 1.0 MgII systems (Churchill, this volume). Additionally, we discuss the statistical contribution from satellite galaxies, which would be expected to contribute additional absorption subcomponents and are likely to have been more numerous at intermediate redshifts. Our preliminary finding is that the common disk and satellite components of galaxies may, to a large degree, be the structures giving rise to a variety of the observed MgII absorption profiles., Comment: 4 pages, Latex file, and 1 PostScript figure; To appear in IAGUSP Workshop on Young Galaxies and QSO Absorbers, eds. S. M. Viegas, R. Gruenwald, and R. de Carvalho, (PASP Conference Series); Available as a single PostScript file at http://www.ucolick.org/~cwc/qso/abstract.html

HIRES/Keck spectra of Mg II (2796) absorption arising in the "halos" of 15 identified 0.4 < z < 0.9 galaxies are presented. Comparison of the galaxy and absorbing gas properties reveal that the spatial distribution of galactic/halo gas does not follow a smooth galactocentric dependence. The kinematics of absorbing gas in z < 1 galaxies are not suggestive of a single systematic velocity field (i.e. rotation or radial flow) and show little dependence on the QSO-galaxy impact parameter. From the full HIRES dataset of 41 systems (0.4 < z < 1.7), strong redshift evolution in the cloud-cloud velocity dispersion is measured. Direct evidence for turbulent or bulk motion in "high velocity" clouds is found by comparing Fe II and Mg II Doppler parameters., Comment: uuencoded: 4 pages, AASTeX file, 2 encapsulated PostScript figures; To appear in IAGUSP Workshop on Young Galaxies and QSO Absorbers, eds. S.M. Viegas, R.Gruenwald, & R. de Carvalho, (PASP Conference Series) Available as a single compressed PostScript file at http://www.ucolick.org/~cwc/qso/abstract.html

Quasar absorption lines provide detailed information on the chemical, kinematic, and ionization conditions in galaxies and their environments, and provide a means for studying the evolution of these conditions back to the epoch of the first quasars. Among the collection of absorbing structures along the lines of sight to quasars there is an evolutionary sequence of galaxies that represent predecessors of the Milky Way and provide a direct view of its history. Absorption spectra of lines of sight through the Milky Way and through nearby galaxies reveal a variety of chemical species, ionization conditions, and kinematic substructures. These absorption profiles are produced by low density gas distributed in rotating disks, high velocity halo clouds, satellite galaxies and their debris, superbubbles, and other sub-galactic gaseous fragments. Guided by knowledge gained by studying nearby galaxies, we are developing interpretations of the variety of observed absorption signatures. Images of .4 < z < 1 galaxies responsible for MgII absorption also allow us to explore the statistical connections between the galaxy properties and their gaseous content. Quasar absorption lines are fast becoming a powerful evolutionary probe of gaseous conditions in the Milky Way., Comment: 10 pages, Latex file, and 3 PostScript figures; To appear in Galactic Chemodynamics 4: The History of the Milky Way and its Satellite System, eds. A. Burkert, D. Hartmann, and S. Majewski (PASP Conference Series); Available as a single PostScript file at http://www.ucolick.org/~cwc/qso/abstract.html

Studies of high resolution quasar absorption lines (QALs), arising from gas in local and z < 1.5 galaxies, provide direct probes of the kinematic, chemical, and ionization conditions and evolution of Milky Way-like galaxies. Inferences drawn from these studies provide a powerful analog for those based upon direct studies of the Halo. The observed gas kinematics and velocity evolution reveal that galactic halos are complex dynamical components, consistent with Searle--Zinn formation scenarios., Comment: 4 pages, Latex file, and 2 PostScript figures; To appear in Formation of the Galactic Halo... Inside and Out, eds. H. Morrison & A. Sarajedini (PASP Conference Series); Available as a single compressed PostScript file at http://www.ucolick.org/~cwc/qso/abstract.html

We challenge the conventional view that the majority of MgII/Lyman limit absorbers are extended halos of galaxies comprised of ``clouds'' with near-unity covering factor. The gaseous disks of spiral galaxies are known to extend to large radii and likely contribute a significant cross-section for absorption. We perform a Monte-Carlo survey of QSO fields in which the model galaxies have MgII absorbing ``clouds'' in a spherical halo or in a randomly oriented disk. For both geometries, models that recover the observed properties of MgII absorbers have only a 70-80% covering factor. Therefore, regardless of absorber geometry, a survey of randomly selected QSO fields should yield a non-negligible number of non-absorbing galaxies at small impact parameters. Very few have been observed (Steidel (1995)). However, selection effects are important, and once the observational procedures are applied to our model fields we find that this result is expected. Since both spherical halo and disk models can be made consistent with survey results, we present tests for discerning the geometric distribution of absorbing gas from Hubble Space Telescope images and high resolution spectra., Comment: 22 pages, Latex file, and 7 PostScript figures; Accepted to the Astrophysical Journal; Available as a single compressed PostScript file at http://www.ucolick.org/~cwc/qso/abstract.html

Study of Lyman-alpha absorption lines in the spectra of double line of sight (DLOS) quasars holds the promise of diagnosing the nature of the structures that give rise to Lyman-alpha absorption. Based on simulations of DLOS with various separations through a single population of absorbers, four tests have been designed to diagnose absorber mass distributions (smoothly varying with radius or irregular), geometries (spherical or disk/slab--like), and kinematics (isotropic or systematic velocities). Applying the tests to existing data at redshifts around two we find that: (1) The observed neutral hydrogen column density (N(HI)) distributions of Lyman-alpha lines coincident to both LOS are consistent with a smooth mass distribution. (2) Observed large anticoincident N(HI) are not consistent with a single population of smooth spherical absorbers, which should exhibit sharp cut--offs at small N(HI) in the N(HI) distribution. (3) There is marginal evidence that the observed RMS value of velocity differences between coincident lines increases with DLOS separation as is expected for disk/slab--like absorbers that have systematic velocity fields. (4) The observed velocity dispersion along a single LOS is small compared to the RMS difference between widely separated LOS, which is not consistent with models of cloudlets moving isotropically within a spherical structure. Overall, only a smooth disk/slab--like model with systematic velocities remains consistent with the inferred properties of a single population of Lyman-alpha absorbers., Comment: 7 pages with figures included, gzipped postscript; also available at http://ucowww.ucsc.edu/~cwc/qso/abstract.html ; Astrophysical Journal Letters (in press)