Metal-line Absorption Systems Research Articles

Three Emission‐Line Galaxies atz ∼ 2.4

We present Keck near-infrared and WIYN (Wisconsin-Indiana-Yale NOAO) optical photometry of a sample of galaxies detected by near-infrared narrowband imaging in the fields of quasar metal absorption line systems at z ~ 2.4. Wide separations (0.6-1.6 h-1 Mpc) from the quasars indicate that they are not directly responsible for the absorption systems. From the color excess of the galaxies we derived line fluxes, star formation rates, and equivalent widths. The data are consistent with one source having an active nucleus and two sources containing regions of star formation. The blue (R-K) colors for the sources suggest relatively lower dust content. We discuss possible projects using current wide-field infrared instruments, which can cover an order of magnitude greater area with modest allocations of telescope time.

Dusty haloes of galaxies at intermediate redshifts

The presence and amount of dust in the halo matter producing narrow metal line absorption systems is still uncertain. We consider the parameter Σ a = Σ(1 + z a ), summed over the detected aborption line system redshifts z a , and ask whether radio-loud quasars at z < 2 and with a large value of the parameter Σ a are redder in the B - V colour than those with a smaller Σ a . This is anticipated if the absorption lines originate in sites which contain normal dust causing selective extinction. The answer is positive, and a mean intrinsic reddening e 0 per halo is consistent with 0.05, or about 0.2 B-mag extinction, roughly as expected.

C [CSC]iv[/CSC] and other Metal Absorption Line Systems in 18 [CLC][ITAL]z[/ITAL][/CLC] = 4 Quasars

We present a modest survey of quasar metal line absorption systems at redshifts 2.3–4.5. Relatively high signal-to-noise ratio (~25 pixel^(-1)) spectra of 18 quasars at 2 A FWHM resolution show many absorption systems with strong metal lines in the region redward of the Lyα emission lines. We conducted a systematic search and found 55 C IV doublets, 19 Si IV doublets, three Mg II doublets, and seven N V doublets. The present data alone hint that the number of C IV absorption doublets per unit redshift, N(z), decreases with increasing redshift for 2.3 0.3 A are approximately 55% of all C IV systems with W > 0.15 A, but by z ≃ 4 that percentage is less than 37%. Similar conclusions were reached by Sargent, Boksenberg, & Steidel and by Steidel, primarily at lower redshifts. However, we measure approximately twice the density of C IV systems at 2.3 0.15 A that was reported by Steidel. The probability that our sample and previous samples come from the same distribution is only ~2%. But this could be a statistical accident because it is an a posteriori comparison. We believe that the systems that we report are real, and we have no other explanation for this difference. For Si IV absorption lines, there is a 1 σ hint of evolution with the same sense. In contrast, Lyα and Mg II systems are known to show evolution of the opposite sense with more absorbers at larger redshifts. The physical cause of this difference may be a mixture of ionization and chemical evolution effects.

A new 21-cm absorber identified with an $L \sim L^\star$ galaxy

We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted 21-cm absorption from the $z=0.437$ metal line absorption system towards PKS 1243-072. HI absorption is clearly detected; the absorption profile has a velocity spread of $\sim 20$ km/s. Detection of 21-cm absorption indicates that the absorber has an HI column density large enough to be classified as a damped Lyman-$\alpha$ system. Follow up ground based optical imaging and spectroscopy allow us to identify the absorber with an $L \sim L^\star$ galaxy at an impact parameter of $\sim 9.8$ kpc from the line of sight to the QSO. The absorbing galaxy is unusual in that it has bright emission lines. On the basis of the optical spectrum we are unable to uniquely classify the galaxy since its emission line ratios lie in the transition region between starburst and Seyfert II type spectra.

The Gravitational Lens Candidate FBQ 1633+3134

We present our ground-based optical imaging, spectral analysis, and high-resolution radio mapping of the gravitational lens candidate FBQ 1633+3134. This z = 1.52, B = 17.7 quasar appears double on CCD images with an image separation of 066 and a relatively constant flux ratio of ∼3 : 1 across B, V, R, and I filters. A single 0.27 mJy radio source is detected at 8.46 GHz, coincident within an arcsecond of both optical components, but no companion at radio wavelengths is detected for the system down to a flux level of 0.1 mJy (3 σ). Spectral observations reveal a rich metal-line absorption system consisting of a strong Mg II doublet and associated Fe I and Fe II absorption features, all at an intervening redshift of z = 0.684, suggestive of a lensing galaxy. Point-spread function subtraction of ground-based images however shows no obvious signs of a third object between the two quasar images and places a detection limit of I ≳ 23.0 if such an object exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot be ruled out, the evidence presented here is consistent with FBQ 1633+3134 being a single quasar lensed by a faint, metal-rich galaxy.

Red companions to a z=2.15 radio-loud quasar

We have conducted observations of the environment around the z=2.15 radio loud quasar 1550-269 in search of distant galaxies associated either with it or the z=2.09 CIV absorber along its line of sight. Such objects will be distinguished by their red colours, R-K > 4.5. We find five such objects in a 1.5 arcmin^2 field around the quasar, with typical K' magnitudes of ~20.4 and no detected R band emission. We also find a sixth object with K=19.6 +/- 0.3, and undetected at R, just two arcseconds from the quasar. The nature of all these objects is currently unclear, and will remain so until we have determined their redshifts. We suggest that it is likely that they are associated with either the quasar or the CIV absorber, in which case their properties might be similar to those of the z=2.38 red Ly-alpha emitting galaxies discovered by Francis et al. (1997). The small separation between the quasar and the brightest of our objects suggests that it may be the galaxy responsible for the CIV metal line absorption system. The closeness to the quasar and the red colour might have precluded similar objects from being uncovered in previous searches for emission from CIV and eg. damped absorbers.

Highly Ionized High‐Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?

In the course of our studies of the gaseous halo surrounding the Milky Way, we have recently identified several high-velocity clouds (HVCs; VLSR<-100 km s-1) in the directions of Mrk 509 and PKS 2155-304 that have unusual ionization properties. The clouds exhibit strong C IV absorption with little or no detectable low ion (C II, Si II) absorption or H I 21 cm emission down to very sensitive levels. As the closest known analog to the outer diffuse halos of damped Lyα absorbers and the low H I column density metal-line absorption systems seen in the spectra of high-redshift quasars, these "C IV HVCs" present unique opportunities for relating the conditions within the Milky Way halo and nearby intergalactic gas to the properties of galactic halos at higher redshift. In this paper we present new Goddard High Resolution Spectrograph (GHRS) intermediate-resolution measurements of the absorption lines within these C IV HVCs and study the ionization properties of the gas in detail. The present data represent the most complete set of measurements available for studying the ionization conditions within HVCs. The C IV HVCs have ionization properties consistent with photoionization by extragalactic background radiation, although some contribution by collisional ionization within a hot plasma cannot be ruled out. The clouds are probably low density (nH~10−4 cm-3), large (greater than several kiloparsecs), and mostly ionized (nHI/nH~10−3) regions located well beyond the neutral gas layer of the Galaxy. The presence of weak H I HVCs detected through their 21 cm emission near both sight lines indicates that the C IV HVCs trace the extended, ionized, low-density regions of the H I HVCs. Several lines of evidence, including very low thermal pressures (P/k ~2 cm-3 K), favor a location for the C IV HVCs in the Local Group or very distant Galactic halo. If the clouds are intergalactic in nature, their metallicities could be [Z/H]~-1 or lower, but higher metallicities [Z/H]>-1 are favored if the clouds are located in the distant Galactic halo since the cloud sizes scale inversely with metallicity. We provide a summary of the HVCs detected in absorption at intermediate resolution with the GHRS and the IUE satellite and find that C IV HVCs are detected along three of 10 extragalactic sight lines down to a level of logN(C IV)≈13.3 (3σ).

Q1208+1011: Search for the Lensing Galaxy

We present a high-resolution spectrum of the high-redshift, lensed quasar Q1208+1101, obtained with the echellette spectrograph on the Multiple Mirror Telescope. We examine the new and published spectra and provide an updated list of high-confidence metal-line absorption systems at z = 1.1349, 2.8626, 2.9118, 2.9136, and 2.9149. Combining this with a simple model of the gravitational lens system allows us to constrain the possible lens redshifts. The high-redshift (z > 2.5) and low-redshift (z < 0.4) candidates can be ruled out with high confidence. The current spectra effectively probe about 40% of the redshift range in which the lens is expected. In that range, there is only one known metal-line absorption system, an Mg II absorber at z = 1.1349. We consider the possibility that this system is the lensing galaxy and discuss the implied parameters of the galaxy.

Serendipitous Discovery of a Broad Absorption Line QSO at [CLC][ITAL]z[/ITAL][/CLC] = 2.169

We report the serendipitous discovery of a broad absorption line (BAL) QSO at z = 2.169, located 41'' southwest of 3C 48. We present Keck Low Resolution Imaging Spectrometer spectroscopy covering rest-frame wavelengths 1500–2300 A. The C IV BAL has three components, and it extends to outflow velocities of at least 12,000 km s-1. The BAL QSO has an intervening low-ionization metal-line absorption system at z = 1.667, which is likely to be a damped Lyα absorber. Hubble Space Telescope images show extended luminous material around the QSO, which could be either the host galaxy or the intervening system.

A Large Structure of Galaxies at Redshiftz∼ 3 and Its Cosmological Implications

We report the discovery of a highly significant concentration of galaxies at a redshift of =3.090. The structure is evident in a redshift histogram of photometrically selected ``Lyman break'' objects in a 9' by 18' field in which we have obtained 78 spectroscopic redshifts in the range 2.0 ~6 for \Omega_M=1. In a Cold Dark Matter scenario the large bias values suggest that individual Lyman-break galaxies are associated with dark halos of mass M~10^{12} M_{\sun}, reinforcing the interpretation of these objects as the progenitors of massive galaxies at the present epoch. Preliminary results of spectroscopy in additional fields suggest that such large structures are common at z~3, with about one similar structure per survey field. The implied space density is consistent with the possibility that we are observing moderately rich clusters of galaxies in their early non-linear evolution. Finally, the spectrum of one of the QSOs discovered in our survey (z_{em} = 3.356) exhibits metal line absorption systems within the 3 redshift bins having the largest number of galaxies in field, z = 2.93, 3.09, and 3.28. These results are the first from an ongoing ``targeted'' redshift survey designed to explore the nature and distribution of star-forming galaxies in the redshift range 2.7 <~ z <~ 3.4.

Quasar Absorbing Galaxies atz≲ 1: Deep Imaging and Spectroscopy in the Field of 3C 336

We present very deep WFPC2 images and FOS spectroscopy from the Hubble Space Telescope (HST) together with numerous supporting ground-based observations of the field of the quasar 3C 336 ($z_{em}=0.927$). The observations are designed to investigate the nature of galaxies producing metal line absorption systems in the spectrum of the QSO. Along a single line of sight, we find at least 6 metal line absorption systems (of which 3 are newly discovered) ranging in redshift from 0.317 to 0.892. Through an extensive program of optical and IR imaging, QSO spectroscopy, and faint galaxy spectroscopy, we have identified 5 of the 6 metal line absorption systems with luminous (L_K > 0.1 L*_K) galaxies. These have morphologies ranging from very late-type spiral to S0, and exhibit a wide range of inclination and position angles with respect to the QSO sightline. The only unidentified absorber, despite our intensive search, is a damped Lyman $\alpha$ system at $z_{abs}=0.656$. Analysis of the absorption spectrum suggests that the metal abundances ([Fe/H]$=-1.2$) in this system are similar to those in damped systems at $z \sim 2$, and to the two other damped systems for which abundances have been determined at $z <1$. We have found no examples of intrinsically faint galaxies ($L < 0.1 L^{\ast}$) at small impact parameters that might have been missed as absorber candidates in our previous ground-based imaging and spectroscopic programs on MgII absorbing galaxies. There are no bright galaxies (L > 0.1 L_K) within 50h^{-1} kpc which do not produce detectable metal lines (of Mg II 2796, 2803 and/or C IV 1548, 1550) in the QSO spectrum. All of these results generally support the inferences which we have previously reached from a larger survey for absorption-selected galaxies at $z\simlt 1$.

Radiative Transfer in a Clumpy Universe. II. The Ultraviolet Extragalactic Background

view Abstract Citations (1427) References (99) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiative Transfer in a Clumpy Universe. II. The Ultraviolet Extragalactic Background Haardt, Francesco ; Madau, Piero Abstract The integrated ultraviolet flux arising from QSOs and/or hot, massive stars in metal-producing young galaxies is likely responsible for maintaining the intergalactic diffuse gas and the Lyα forest clouds in a highly ionized state. The spectrum and intensity of such UV background have generally been obtained by modeling the reprocessing due to intervening material as a pure photoelectric absorption process. However, owing to the emission from radiative recombinations within the absorbing clouds, a photoionized clumpy medium could contribute substantially to the metagalactic flux. In other words, QSO absorption- line systems are sources, not just sinks of ionizing photons. We present a detailed calculation of the propagation of AGN-like ionizing radiation through the intergalactic space. We model the ionization state of absorbing clouds, and show that the universe will be more opaque above 4 Ry than previously estimated. Singly ionized helium in Lyα forest clouds and Lyman-limit systems is found to be very efficient in reprocessing soft X-ray, helium-ionizing photons into ultraviolet, hydrogen-ionizing ones. We demonstrate that a significant fraction of the absorbed primary photons (emitted, e.g., by quasar sources) will be reradiated by the photoionized gas through Lyα line emission, two-photon continuum, and recombination continuum radiation. In the light of new data and recent studies, we also reassess the contribution of the QSOs observed in optical surveys to the UV extragalactic background, and find that the stochastic reprocessing of quasar Lyman continuum radiation by hydrogen and helium along the line of sight will significantly affect the amplitude, spectral shape, and fluctuation properties of the metagalactic flux. In a scenario in which QSOs are the primary source of ionizing photons in the universe, the integrated H I Lyα emission at z = 0 from photoionized Lyα clouds and Lyman limit systems is found to be at a level of less than 5% of current observational limits on the far-UV extragalactic radiation flux. We show that J_912_ increases from ~10^-23^ ergs cm^-2^ s^-1^ Hz^- 1^ sr^-1^ at the present epoch to ~5 x 10^-22^ ergs cm^-2^ s^-1^ Hz^-1^ sr^-1^ at z = 2.5. The attenuated direct quasar emission plus recombination radiation from intergalactic gas appear to provide enough hydrogen-ionizing photons to satisfy the proximity effect at large redshift. The He II/H I ratio in the diffuse intergalactic medium and the Lyα clouds increases from ~25 at z = 0 to ~45 at z = 2.5, to decrease again below 30 for z >~ 4.5. The spectrum of the ionizing background at high redshift is shown to have a hump at energies below 40.8 eV due to redshift-smeared He Il Lyα line and two-photon continuum emission. We propose that observations of low-ionization species such as O II in metal-line absorption systems may be able to test the presence of such a prominent feature in the UV background spectrum. We also note that, if the metagalactic flux is dominated by QSOs, the suggested steep decline of their ionizing emissivity beyond z ~ 4 should produce an increase in the observed rate of incidence of Lyα forest clouds at these redshifts relative to an extrapolation from the intermediate-z regime, as observed by Williger et al. (1994). Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177035 arXiv: arXiv:astro-ph/9509093 Bibcode: 1996ApJ...461...20H Keywords: COSMOLOGY: THEORY; COSMOLOGY: DIFFUSE RADIATION; GALAXIES: INTERGALACTIC MEDIUM; GALAXIES: QUASARS: ABSORPTION LINES; RADIATIVE TRANSFER; Astrophysics E-Print: revised version submitted to ApJ 20 sept 95, full text sources arXiv | ADS | data products SIMBAD (4) Related Materials (3) Part 1: 1995ApJ...441...18M Part 3: 1999ApJ...514..648M Part 4: 2012ApJ...746..125H

A Gravitational Lens Candidate Behind The Fornax Dwarf Spheroidal Galaxy

CCD astrometry makes possible milli-arcsecond precision relative astrometry at faint magnitudes (Tinney 1994a). The measurement of proper motions for the nearest galaxies is therefore a project requiring only years – not decades. A prerequisite for such measurements, however, is a set of unresolved, extragalactic reference objects – ie. QSOs. While searching for such objects behind the Fornax dSph galaxy, Tinney (1995b) discovered the QJ0240-343AB system as a pair of bright, UV-excess objects (U-B = −1.0, B = 19.0 &amp; 19.8) with a separation of 6.1″. Spectra obtained with the 3.9 m Anglo-Australian telescope and the RGO+FORS spectrographs (Fig. 1) have shown both components of the pair to be at a redshift of z = 1.4, with a rest velocity difference consistent with zero at a 1-σ limit of 180 km/s. The spectra also show a definite metal-line absorption system at z = 0.543 and a possible system at z = 0.337. No bright lens is seen, but the strong similarities in the spectra suggest a gravitational lens nature.

Lyman Imaging of High-Redshift Galaxies.III.New Observations of Four QSO Fields

view Abstract Citations (247) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lyman Imaging of High-Redshift Galaxies.III.New Observations of Four QSO Fields Steidel, Charles C. ; Pettini, Max ; Hamilton, Donald Abstract We present the results of deep Lyman limit imaging in four new fields as part of a continuing search for galaxies at 3.0 < z< 3.5. The technique uses a custom broadband filter set (U_n_GR) designed to isolate objects having Lyman continuum breaks superposed on otherwise flat-spectrum ultraviolet continua. The observations are specifically aimed at detecting known galaxies producing optically thick QSO metal line absorption systems, but are equally sensitive to more generally distributed objects at the redshifts of interest. We have identified a plausible candidate for the QSO absorber in one out of the four new fields surveyed; in the other three the absorbing galaxy must be either fainter than R = 25.5 or closer than ~1 arcsec to the QSO sight line (or both). Together with previously published results of the survey, we have now detected in two out of six cases objects with the expected properties of star-forming galaxies at z ~> 3 within 3 arcsec of the QSO sight lines; the two candidate absorbers have similar luminosities, M_B_ ~ 22 (q_0_ = 0.5, H_0_ = 50 km s^-1^ Mpc^-1^), and impact parameters, R ~ 10h^-1^ kpc. We find the average surface density of robust Lyman break objects to be ~0.5 galaxies per square arcminute to a magnitude limit R = 25.0. A simple, "no evolution" model based on the properties of normal galaxies at z <~ 1 predicts a density of Lyman break objects only a few times larger than observed. We conclude that there is a substantial population of star-forming galaxies, of relatively normal luminosity, already in place at z = 3-3.5. If normal galaxies experienced a period of very high star formation early on in their history, it must have occurred prior to z = 3.5. It is possible that the observed surface density of z > 3 objects is biased by the presence of a luminous QSO in the redshift range of interest; the surveyed fields are too small to examine the possibility of a spatial association of the z > 3 candidates with the QSOs. We suggest a number of future observations that would resolve this question and clarify the nature of the putative "normal" galaxy population beyond z ~ 3. Publication: The Astronomical Journal Pub Date: December 1995 DOI: 10.1086/117709 arXiv: arXiv:astro-ph/9509089 Bibcode: 1995AJ....110.2519S Keywords: COSMOLOGY: THEORY; COSMOLOGY: OBSERVATIONS; GALAXIES: EVOLUTION; Astrophysics E-Print: 35 pages, uuencoded, compressed postscript. 15 Figures available on ftp://astro.caltech.edu/users/ccs/llg_figures.tar.Z, or request preprints from ccs@astro.caltech.edu. To appear in The Astronomical Journal, 1995 December full text sources arXiv | ADS | data products NED (344) SIMBAD (5)

An Emission-Line Protogalaxy Candidate at [ITAL]z[/ITAL] = 2.5

Narrow-band infrared imaging has revealed a faint red galaxy with a strong (equivalent width = 2%) emission line at 2.30 μm. The field was observed because of its proximity to the quasar SBS 0953+549, which has a metal-line absorption system at zabs = 2.50. The emission-line galaxy is only separated from the quasar line of sight by a projected distance of 240 kpc, and we identify the emission line as Hα/[N II] in a galaxy which is in the same group as the z = 2.50 absorber. Since all the galaxy properties are also consistent with a young age and a redshift of 2.5, it is a prime candidate for a protogalaxy.

Probing the interstellar medium along the lines of sight to supernovae SN 1994D and SN1994I

view Abstract Citations (37) References (73) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Probing the Interstellar Medium along the Lines of Sight to SN 1994D and SN 1994I Ho, Luis C. ; Filippenko, Alexei V. Abstract We present high-resolution (~8 km s^-1^) echelle observations of SN 1994D and 1994I covering the optical Na D interstellar absorption lines and the region around Hα. The high-quality spectra reveal a complex pattern of Na D absorption systems along the path to both supernovae. The velocity systems can be identified with contributions from the Galactic disk, the host galaxy of each supernova, and absorbing material having "anomalous" velocities inconsistent with simple rotation within our Galaxy or the respective host galaxies. The anomalous velocity gas along the line of sight to SN 1994D may be intergalactic in origin and is infalling toward NGC 4526, the Virgo cluster host galaxy of SN 1994D. We consider several hypotheses for the anomalous velocity systems seen toward SN 1994I. The most likely explanation is that they are optical counterparts of "high-velocity clouds," normally studied in 21 cm emission, associated with either the Galactic halo or the halo of the host galaxy NGC 5194 (M51). These metal-bearing, low-column density clouds may be much more common than previously thought. At least some metal-line QSO absorption systems may be associated with high-velocity clouds in the halos of intervening galaxies. We use the derived Na column densities to estimate the extinction of the two supernovae. For SN 1994D, we obtain A_V_ = 0.08^-0.04_^+0.08 mag, consistent with independent estimates based on considerations of the supernova colors near maximum brightness. Several complications conspire to make the extinction estimate for SN 1994I very uncertain. Our best estimate yields A_V_ = 3.1_-1.5_^+3.1^ mag, although there are reasons to believe that the true extinction is <~ 1.4 mag. Finally, we note that no narrow Hα emission or absorption is detected to 2 σ equivalent width limits of 3 mA in the spectrum of SN 1994D, a Type Ia supernova. Unfortunately, this observation does not provide very significant constraints on models of the progenitor; SN 1994D was observed ~3 weeks after maximum brightness, by which time little if any Hα would be expected even if circumstellar hydrogen were present. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175591 Bibcode: 1995ApJ...444..165H Keywords: Absorption Spectra; Astronomical Spectroscopy; Interstellar Matter; Light (Visible Radiation); Line Of Sight; Supernovae; Cosmic Gases; Galactic Halos; H Alpha Line; Intergalactic Media; Interstellar Extinction; Quasars; Spectrum Analysis; Virgo Galactic Cluster; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 5194; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4526; ISM: ABUNDANCES; STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1994D; STARS: SUPERNOVAE: INDIVIDUAL ALPHANUMERIC: SN 1994I full text sources ADS | data products SIMBAD (28) NED (19) Related Materials (1) Erratum: 1996ApJ...463..818H

The Z = 0.8596 damped Ly-alpha absorbing galaxy toward PKS 0454+039

We present Hubble Space Telescope (HST) and ground-based data on the Z(sub abs) = 0.8596 metal-line absorption system along the line of sight to PKS 0454+0356. The system is a moderate-redshift damped Ly-alpha system, with N(H I) = (5.7 +/- 0.3) x 10(exp 20)/sq cm as measured from the Faint Object Spectrograph (FOS) spectrum. We also present ground-based images which we use to identify the galaxy which most probably gives rise to the damped system; the most likely candidate is relatively underluminous by QSO absorber standards M(sub B) approximately -19.0 for A(sub 0) = 0.5 and H(sub 0) = 50 km/s/Mpc) and lies approximately 8.5/h kpc in projection from the QSO sight line. Ground-based measurements of Zn II, Cr II, and Fe II absorption lines from this system allow us to infer abundances of (Zn/H) = -1.1, (Cr/H) = -1.2, and (Fe/H) = -1.2 indicating overall metallicity similar to damped systems at z is greater than 2, and that the depletion of Cr and Fe onto dust grains may be even less important than in many of the high-redshift systems of comparable metallicity. Limits previously placed on the 21 cm optical depth in the z = 0.8596 system, together with our new N(H I) measurement, suggest a very high spin temperature for the H I, T(sub s) is greater than 580 K.

The Hubble Space Telescope quasar absorption line key project. 6: Properties of the metal-rich systems

view Abstract Citations (85) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Hubble Space Telescope Quasar Absorption Line Key Project. VI. Properties of the Metal-rich Systems Bergeron, Jacqueline ; Petitjean, Patrick ; Sargent, W. L. W. ; Bahcall, John N. ; Boksenberg, Alec ; Hartig, George F. ; Jannuzi, Buell T. ; Kirhakos, Sofia ; Savage, Blair D. ; Schneider, Donald P. ; Turnshek, David A. ; Weymann, Ray J. ; Wolfe, Arthur M. Abstract We present an analysis of the properties of a sample of 18 metal-rich, low-redshift z_abs_ < z_em_ absorbers seen in low- and medium-resolution spectra obtained for the Quasar Absorption Line Key Project with the Hubble Space Telescope Faint Object Spectrograph. For most of the C IV and Lyman-limit systems, observations in the optical wavelength range of the expected associated Mg II absorption are available. As at high redshift (z ~ 2), there are two subclasses of absorbers which are characterized by the presence or absence of Mg II absorption. However, some low-redshift Mg II and Fe II absorptions originate from regions optically thin to UV ionizing photons and thus, at low redshift, the low- ionization systems do not always trace high opacities, as is the case at high redshift. This implies that the mean ionization state of metal-rich, optically thin absorbing clouds falls with decreasing redshift, which is consistent with the hypothesis that the gas is photoionized by the metagalactic UV background radiation field. Two main constraints are derived from the analysis of the Lyman-limit sample, assuming photoionization models are valid. First, a low opacity to ionizing photons (τ_LL_ <~ 1), as observed for several Mg II-Fe II systems at z ~ 0.5, sets limits on the ionization level of hydrogen, thus on the total hydrogen column density and the heavy element abundances, [Z/H] ~ -0.5 to -0.3. Second, the dimensions of individual Mg II clouds are smaller than at high redshift by a factor 3-10. At z >~ 0.6, the O VI absorption doublet is detected in four of the five z_abs_ < z_em_ systems for which the O VI wavelength range has been observed, whereas the associated N V doublet is detected in only two cases. This suggests that the presence of a high-ionization O VI phase is a general property of z ~ 0.6-1 absorption systems, as is also probably the case at high redshift. These O VI absorbers can be ionized by the UV metagalactic field if their density is low, n_H_ <~ 3 x 10^-4^ cm^-3^. The O VI phase would then be a homogeneous region of large extent, r ~> 50 kpc. A detailed photoionization model of the z_abs_ = 0.791 absorber toward PKS 2145 + 06 confirms the properties derived from the Mg II, C IV, O VI, and Lyman-limit samples. The galaxy causing this extensive metal-line absorption system has been identified, and its possible contribution to the UV ionizing flux does not substantially modify the value of the derived parameters. The heavy element abundances are about half the solar values. The O VI region has a density about 20 times lower than the Mg II clouds and a size of ~70 kpc. Alternatively, the high-ionization phase could be collisionally ionized and trace gas associated with a possible group of galaxies at the absorber redshift. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/174878 Bibcode: 1994ApJ...436...33B Keywords: Absorption Spectra; Cosmology; Galactic Evolution; Metallicity; Quasars; Red Shift; Ultraviolet Spectra; Astronomical Models; Astronomical Photometry; Flux Density; Galactic Structure; Hubble Space Telescope; Photoionization; Astronomy; COSMOLOGY: OBSERVATIONS; GALAXIES: EVOLUTION; GALAXIES: QUASARS: ABSORPTION LINES full text sources ADS | data products NED (39) SIMBAD (12) MAST (1) ESA (1) Related Materials (14) Part 1: 1993ApJS...87....1B Part 2: 1993ApJS...87...45S Part 3: 1993ApJ...413..116S Part 4: 1994ApJ...428...93T Part 5: 1995ApJ...444...64S Part 7: 1996ApJ...457...19B Part 8: 1994PASP..106..646K Part 10: 1994PASP..106.1020K Part 11: 1994ApJ...434..484E Part 12: 1995ApJS...97....1L Part 13: 1996ApJ...470L..11J Part 14: 1998ApJS..118....1J Part 15: 1998ApJ...506....1W Part 16: 2000ApJS..129..563S

Halo model for intermediate-redshift quasar absorption systems

view Abstract Citations (18) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Halo Model for Intermediate-Redshift Quasar Absorption Systems Srianand, R. ; Khare, Pushpa Abstract We have constructed a simple model for the halo regions of galaxies responsible for producing sharp metal line absorption systems in the spectra of quasars at z ~ 1.5. The model assumes spherical halo. The cloud number density as well as the metal abundance decrease with distance from the galactic center. We have constructed photoionization models for individual clouds to obtain the column densities of various ions in them clouds, for a range of values for ionization parameter, metallicity, and size of the clouds. The equivalent widths of a number of lines produced by individual clouds have been calculated and used to obtain the total equivalent width of these lines along a given line of sight through the halo. The predicted equivalent width distribution for Mg II is compared with observations in order to restrict the possible range of values for cloud parameters. For the range of parameters considered, the models can produce Lyman limit systems (LLSs) with and without lines of singly ionized species, LLSs without accompanying metal lines, highly ionized systems with τ_LLS_ < 1, as well as damped Lyman alpha systems. Equivalent width distribution for C IV lines associated with Mg II lines as well as for C IV lines not associated with Mg II lines have been obtained from observations by performing maximum likelihood analysis and are shown to be consistent with the model results. The models reproduce the doublet ratios of Mg II and associated C IV lines as a function of their equivalent widths. The doublet ratios of C IV lines not associated with Mg II can not be reproduced satisfactorily by our model. The range of observed equivalent width ratios of several lines and the probability of these ratios exceeding 1 are consistent with the model results, except for the observed high values of Si IV/C IV, which cannot be reproduced by the models. Observed equivalent widths of different lines in a number of absorption systems are compared individually with model predictions. Barring a few exceptions, the observations are well reproduced by our models. The impact parameters are in the range 10-40 kpc, which is similar to the observed range. All these comparisons with observations show that a range in column densities, abundance, and ionization parameter is needed in order to explain the observations. The values of the ionization parameter close to 10^-2^ are more likely than 10^-3^. Neutral hydrogen column density distribution obtained, based on our models, seems to be consistent with the observed distribution for column densities between (5 x 10^16^)-(2 x 10^21^) cm^-2^. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/174222 Bibcode: 1994ApJ...428...82S Keywords: Absorption Spectra; Astronomical Models; Galactic Halos; Optical Density; Quasars; Red Shift; Abundance; Density Distribution; Ion Distribution; Line Spectra; Metallicity; Astrophysics; GALAXIES: STRUCTURE; GALAXIES: QUASARS: ABSORPTION LINES full text sources ADS | data products NED (30) SIMBAD (15)

Hydrogen and metal absorption lines in PKS 0405-123 from the halos of low redshift galaxies

HST ultraviolet spectra and ground-based optical spectra of the bright quasar PKS 0405-123 are used to identify two absorption-line systems probably produced by the halos of foreground galaxies. The quasar lies in a rich galaxy field. Loose groups of galaxies are present in the field at mean z1 = 0.1669 and mean z2 = 0.3519. Ly-alpha, C IV 1549 A, and probably Mg II 2798 A resonance lines are detected in an absorption system at z = 0.1670. An absorption system consisting of only Ly-alpha is observed at z = 0.3516. We cannot be completely certain which foreground galaxy is responsible for the metal line absorption system at z1. A likely candidate is a large, luminous, early-type spiral 40 arcsec to the east of the quasar. However, the origin of the z1 system could possibly be a small undetected galaxy more precisely aligned along our line of sight to PKS 0405-123, or a very faint galaxy whose redshift has not yet been measured.