arXiv subjects

Varsha P. Kulkarni

Publications and source records attributed to Varsha P. Kulkarni.

At least 55 records · Page 3Linked to original sources

arXiv2013

Element Abundances at High-redshift: Magellan MIKE Observations of sub-Damped Lyman-alpha Absorbers at 1.7 < z <2.4

We present chemical abundance measurements from high-resolution observations of 5 sub-damped Lyman-alpha absorbers at 1.7 < z < 2.4 observed with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5-m Magellan II Clay telescope. Lines of Zn II, Mg I, Mg II, Al II, Al III, S II, Si II, Si IV, C II, C II*, C IV, Ni II, Mn II and Fe II were detected and column densities were determined. The metallicity of the absorbing gas, inferred from the nearly undepleted element Zn, is in the range of < -0.95 to +0.25 dex for the five absorbers in our sample, with three of the systems being near-solar or super-solar. We also investigate the effect of ionisation on the observed abundances using photoionisation modelling. Combining our data with other sub-DLA and DLA data from the literature, we report the most complete existing determination of the metallicity vs. redshift relation for sub-DLAs and DLAs. We confirm the suggestion from previous investigations that sub-DLAs are, on average, more metal-rich than DLAs and evolve faster. We also discuss relative abundances and abundance ratios in these absorbers. The more metal-rich systems show significant dust depletion levels, as suggested by the ratios [Zn/Cr] and [Zn/Fe]. For the majority of the systems in our sample, the [Mn/Fe] vs. [Zn/H] trend is consistent with that seen previously for lower-redshift sub-DLAs. We also measure the velocity width values for the sub-DLAs in our sample from unsaturated absorption lines of Fe II 2344, 2374, 2600 A, and examine where these systems lie in a plot of metallicity vs. velocity dispersion. Finally, we examine cooling rate vs. H I column density in these sub-DLAs, and compare this with the data from DLAs and the Milky Way ISM. We find that most of the systems in our sample show higher cooling rate values compared to those seen in the DLAs.

astro-ph.CO↗

arXiv2012

Galaxies with Background QSOs, I: A Search for Strong Galactic H-alpha Lines

A search for emission lines in foreground galaxies in quasar spectra (z(gal) < z(QSO)) of the Sloan Digital Sky Survey (SDSS) data release 5 (DR5) reveals 23 examples of quasars shining through low redshift, foreground galaxies at small impact parameters (< 10 kpc). About 74,000 quasar spectra were examined by searching for narrow Hα emission lines at z < 0.38, at a flux level greater than 5 \times 10^-17 ergs cm^-2 s^-1, then confirming that other expected emission lines of the H II regions in the galaxy are detected. The galaxies were deblended from the quasar images to get colors and morphologies. For cases that allow the galaxy and the quasar to be deblended, the galaxies are blue (0.95 <(u-r)< 1.95). Extinction and reddening through the galaxies is determined from the (g-i) color excesses of the quasars. These reddening values are compared with the flux ratio of Hα to Hβ, which reflect the extinction for an undetermined fraction of the sightline through each galaxy. No trends were found relating E(B-V)_(g-i), impact parameter (b), and (u-r) for the galaxies or between E(B-V) derived from (g-i) and that derived from Hα/Hβ. Comparison with previous studies of quasar absorption systems indicate our sample is more reddened, suggesting disk-dominated absorber galaxies. Measurement or limits on galactic, interstellar Ca II and Na I absorption lines are given from the quasar spectrum. No trends were found relating Ca II equivalent width (W (Ca II)) or Na I equivalent width (W (Na I)) to b, but a correlation of r_s = -0.77 (α = 0.05) was found relating W (Ca II) and E(B-V)(g-i) .

astro-ph.GA↗

arXiv2012

A Super-Damped Lyman-alpha QSO Absorber at z=2.2

We report the discovery of a "super-damped" Lyman-alpha absorber at $z_{abs}=2.2068$ toward QSO Q1135-0010 in the Sloan Digital Sky Survey, and follow-up VLT UVES spectroscopy. Voigt profile fit to the DLA line indicates log $N_{\rm H I} = 22.05 \pm 0.1$. This is the second QSO DLA discovered to date with such high $N_{\rm H I}$. We derive element abundances [Si/H] = $-1.10 \pm 0.10$, [Zn/H] = $-1.06 \pm 0.10$, [Cr/H] = $-1.55 \pm 0.10$, [Ni/H] = $-1.60 \pm 0.10$, [Fe/H] = $-1.76 \pm 0.10$, [Ti/H] = $-1.69 \pm 0.11$, [P/H] = $-0.93 \pm 0.23$, and [Cu/H] = $-0.75 \pm 0.14$. Our data indicate detection of Ly-$α$ emission in the DLA trough, implying a star formation rate of $\sim$10 $M_{\odot}$ yr$^{-1}$ in the absence of dust attenuation. C II$^{*} \, λ1336$ absorption is also detected, suggesting SFR surface density $-2 < {\rm log} \, \dot{ψ_{*}} < 0$ $M_{\odot}$ yr$^{-1}$ kpc$^{-2}$. We estimate electron density in the range $3.5 \times 10^{-4}$ to 24.7 cm$^{-3}$ from C II$^{*}$/C II, and $\sim$0.5-0.9 cm$^{-3}$ from Si II$^{*}$/Si II. Overall, this is a robustly star-forming, moderately enriched absorber, but with relatively low dust depletion. Fitting of the SDSS spectrum yields low reddening for Milky Way, LMC, or SMC extinction curves. No CO absorption is detected, and C I absorption is weak. The low dust and molecular content, reminiscent of some SMC sight-lines, may result from the lower metallicity, and a stronger radiation field (due to higher SFR). Finally, we compare this absorber with other QSO and GRB DLAs.

astro-ph.CO↗

arXiv2012

Interstellar Silicate Dust in the z=0.89 Absorber Towards PKS 1830-211: Crystalline Silicates at High Redshift?

We present evidence of a >10-sigma detection of the 10 micron silicate dust absorption feature in the spectrum of the gravitationally lensed quasar PKS 1830-211, produced by a foreground absorption system at redshift 0.886. We have examined more than 100 optical depth templates, derived from both observations of Galactic and extragalactic sources and laboratory measurements, in order to constrain the chemical structure of the silicate dust. We find that the best fit to the observed absorption profile is produced by laboratory crystalline olivine, with a corresponding peak optical depth of tau_10=0.27+/-0.05. The fit is slightly improved upon by including small contributions from additional materials such as silica, enstatite, or serpentine, which suggests that the dust composition may consist of a blend of crystalline silicates. Combining templates for amorphous and crystalline silicates, we find that the fraction of crystalline silicates needs to be at least 95%. Given the rarity of extragalactic sources with such a high degree of silicate crystallinity, we also explore the possibility that the observed spectral features are produced by amorphous silicates in combination with other molecular or atomic transitions, or by foreground source contamination. While we cannot rule out these latter possibilities, they lead to much poorer profile fits than for the crystalline olivine templates. If the presence of crystalline interstellar silicates in this distant galaxy is real, it would be highly unusual, given that the Milky Way interstellar matter contains essentially only amorphous silicates. It is possible that the z=0.886 absorber towards PKS 1830-211, well known for its high molecular content, has a unique star-forming environment that enables crystalline silicates to form and prevail.

astro-ph.GA↗

arXiv2011

A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - III. Three Additional Detections

We report three additional SINFONI detections of H-alpha emission line from quasar absorbers, two of which are new identifications. These were targeted among a sample of systems with log N(HI)>19.0 and metallicities measured from high-resolution spectroscopy. The detected galaxies are at impact parameters ranging from 6 to 12 kpc from the quasar's line-of-sight. We derive star formation rates (SFR) of a few solar masses per year for the two absorbers at z_abs~1 and SFR=17 solar masses per year for the DLA at z_abs~2. These three detections are found among a sample of 16 DLAs and sub-DLAs (5 at z_abs~1 and 7 at z_abs~2). For the remaining undetected galaxies, we derive flux limits corresponding to SFR<0.1--11.0 solar masses per year depending on redshift of the absorber and depth of the data. When combined with previous results from our survey for galaxy counterparts to HI-selected absorbers, we find a higher probability of detecting systems with higher metallicity as traced by dust-free [Zn/H] metallicity. We also report a higher detection rate with SINFONI for host galaxies at z_abs~1 than for systems at z_abs~2. Using the NII/H-alpha ratio, we can thus compare absorption and emission metallicities in the same high-redshift objects, more than doubling the number of systems for which such measures are possible.

astro-ph.CO↗

arXiv2011

Exploring the dust content of SDSS DR7 damped Lyman alpha systems at 2.15$\le z_{ab}< $5.2

We have studied a sample of 1084 intervening absorption systems with 2.15$\le z_{ab}\le$5.2, having log(N$_{\rm HI}$) $>$ 20.0 in the spectra of QSOs in Sloan Digital Sky Survey (SDSS) data release 7 (DR7), with the aim of understanding the nature and abundance of the dust and the chemical abundances in the DLA absorbers. Composite spectra were constructed for the full sample and several subsamples, chosen on the basis of absorber and QSO properties. Average extinction curves were obtained for the samples by comparing their geometric mean composite spectra with those of two samples of QSOs, matching in z$_{em}$ and i magnitude with the DLA sample, one sample without any absorbers along their lines of sight and the other without any DLAs along their lines of sight irrespective of the presence of other absorption systems. While the average reddening in the DLA sample is small, we find definite evidence for the presence of dust in subsamples based on absorber properties, in particular the strength of metal absorption lines. DLAs along lines of sight to QSOs which are not colour selected are found to be more dusty compared to those along the lines of sight to the more numerous colour selected QSOs. From these studies and from the strengths of absorption lines in the composite spectra, we conclude that $\le$ 10% of the DLAs in SDSS DR7 cause significant reddening, have stronger absorption lines and have higher abundances as compared to the rest of the sample. The rest of the sample shows little reddening. Due to the dominant color selection method used to target QSOs in the SDSS DR7, this fraction of 10% likely represents a lower limit for the global fraction of dusty DLAs at high-z.

astro-ph.CO↗

arXiv2010

SOAR Imaging of sub-Damped Lyman-Alpha Systems at z<1

We present deep ground based imaging of the environments of five QSOs that contain sub-Damped Lyman-alpha systems at z<1 with the SOAR telescope and SOI camera. We detect a clear surplus of galaxies in these small fields, supporting the assumption that we are detecting the galaxies responsible for the absorption systems. Assuming these galaxies are at the redshift of the absorption line systems, we detect luminous L>L* galaxies for four of the five fields within 10" of the QSO. In contrast to previous imaging surveys of DLA systems at these redshifts, which indicate a range of morphological types and luminosities for the host galaxies of the systems, the galaxies we detect in these sub-DLA fields appear to be luminous (L>L*). In the case of the absorber towards Q1009-0026 at z=0.8866 we have spectroscopic confirmation that the candidate galaxy is at the redshift of the absorber, at an impact parameter of ~35 kpc with a luminosity of 3 < L/L* < 8 depending on the magnitude of the K-correction. These observations are in concordance with the view that sub-DLAs may be more representative of massive galaxies than DLA systems. The environments of the absorbers span a range of types, from the inner disk of a galaxy, the periphery of a luminous galaxy, and the outskirts of interacting galaxies. The large impact parameters to some of the candidate galaxies suggest that galactic outflows or tidal tails are likely responsible for the material seen in absorption. We find a weak correlation between N(HI) and the impact parameter at the 2 sigma level, which may be expected from the heterogeneous population of galaxies hosting the absorption line systems and random orientation angles. In addition, we detect a possible gravitationally lensed image of the BL-Lac object Q0826-2230.

astro-ph.CO↗

arXiv2010

A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - II. Dynamical Properties of the Galaxies towards Q0302-223 and Q1009-0026

Details of processes through which galaxies convert their gas into stars need to be studied in order to obtain a complete picture of galaxy formation. One way to tackle these phenomena is to relate the HI gas and the stars in galaxies. Here, we present dynamical properties of Damped and sub-Damped Lyman-alpha Systems identified in H-alpha emission with VLT/SINFONI at near infra-red wavelengths. While the DLA towards Q0302-223 is found to be dispersion-dominated, the sub-DLA towards Q1009-0026 shows clear signatures of rotation. We use a proxy to circular velocity to estimate the mass of the halo in which the sub-DLA resides and find M_halo=10^12.6 M_sun. We also derive dynamical masses of these objects, and find M_dyn=10^10.3 M_sun and 10^10.9 M_sun. For one of the two systems (towards Q0302-223), we are able to derive a stellar mass of M_*=10^9.5 M_sun from Spectral Energy Distribution fit. The gas fraction in this object is 1/3rd, comparable to similar objects at these redshifts. Our work illustrates that detailed studies of quasar absorbers can offer entirely new insights into our knowledge of the interaction between stars and the interstellar gas in galaxies.

astro-ph.CO↗

arXiv2010

A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - I. New Detections and Limits for Intervening and Associated Absorbers

Detailed studies of Damped and sub-Damped Lyman-alpha systems (DLA), the galaxies probed by the absorption they produce in the spectra of background quasars, rely on identifying the galaxy responsible for the absorber with more traditional methods. Integral field spectroscopy provides an efficient way of detecting faint galaxies near bright quasars, further providing immediate redshift confirmation. Here, we report the detection of H-alpha emission from a DLA and a sub-DLA galaxy among a sample of 6 intervening quasar absorbers targeted. We derive F(H-alpha)=7.7+/-2.7*10^-17 erg/s/cm^2 (SFR=1.8+/-0.6 M_sun/yr) at impact parameter b=25 kpc towards quasar Q0302-223 for the DLA at z_abs=1.009 and F(H-alpha)=17.1+/-6.0*10^-17 erg/s/cm^2 (SFR=2.9+/-1.0 M_sun/yr) at b=39 kpc towards Q1009-0026 for the sub-DLA at z_abs=0.887. These results are in line with low star formation rates previously reported in the literature for quasar absorbers. We use the NII 6585/H-alpha ratio to derive the HII emission metallicities and compare them with the neutral gas H I absorption metallicities derived from high-resolution spectra. In one case, the absorption metallicity is actually found to be higher than the emission line metallicity. For the remaining objects, we achieve 3-sigma limiting fluxes of the order F(H-alpha)~10^-17 erg/s/cm^2 (corresponding to SFR~ 0.1 M_sun/yr at z~1 and ~1 M_sun/yr at z~2), i.e. among the lowest that have been possible with ground-based observations. We also present two other galaxies associated with C IV systems and serendipitously discovered in our data.

astro-ph.CO↗

arXiv2010

Do Damped and Sub-damped Lyman-alpha Absorbers Arise in Galaxies of Different Masses?

We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra differ intrinsically in metallicity, and whether they could arise in galaxies of different masses. Using the recent measurements of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm that sub-DLAs have higher mean metallicities than DLAs, especially at $z \lesssim 2$. We find that the intercept of the metallicity-redshift relation derived from Zn and S is higher than that derived from Fe by 0.5-0.6 dex. We also show that, while there is a correlation between the metallicity and the rest equivalent width of Mg II $λ2796$ or Fe II $λ2599$ for DLAs, no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II selection criteria employed in the discovery of both types of systems at lower redshifts, the difference between metallicities of DLAs and sub-DLAs appears to be real and not an artefact of selection. This conclusion is supported by our simulations of Mg II $λ2796$ and Fe II $λ2599$ lines for a wide range of physical conditions. On examining the velocity spreads of the absorbers, we find that sub-DLAs show somewhat higher mean and median velocity spreads ($Δv$), and an excess of systems with $Δv > 150$ km s$^{-1}$, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and thick disk stars, possibly suggesting different stellar populations. The absorber data appear to be consistent with galaxy down-sizing. The data are also consistent with the relative number densities of low-mass and high-mass galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on average than DLAs.

astro-ph.GA↗

arXiv2009

Adaptive Optics Imaging of a Massive Galaxy Associated with a Metal-rich Absorber

The damped and sub-damped Lyman-alpha absorption line systems in quasar spectra are believed to be produced by intervening galaxies. However, the connection of quasar absorbers to galaxies is not well-understood, since attempts to image the absorbing galaxies have often failed. While most DLAs appear to be metal-poor, a population of metal-rich absorbers, mostly sub-DLAs, has been discovered in recent studies. Here we report high-resolution K-band imaging with the Keck Laser Guide Star Adaptive Optics (LGSAO) system of the field of quasar SDSSJ1323-0021 in search of the galaxy producing the z = 0.72 sub-DLA absorber. With a metallicity of 2-4 times the solar level, this absorber is of the most metal-rich systems found to date. Our data show a large bright galaxy with an angular separation of only 1.25" from the quasar, well-resolved from the quasar at the high resolution of our data. The galaxy has a magnitude of K = 17.6-17.9, which corresponds to a luminosity of ~ 3-6 L*. Morphologically, the galaxy is fit with a model with an effective radius, enclosing half the total light, of R_e = 4 kpc and a bulge-to-total ratio of 0.4-1.0, indicating a substantial bulge stellar population. Based on the mass-metallicity relation of nearby galaxies, the absorber galaxy appears to have a stellar mass > 10^{11} M_sun. Given the small impact parameter, this massive galaxy appears to be responsible for the metal-rich sub-DLA. The absorber galaxy is consistent with the metallicity-luminosity relation observed for nearby galaxies, but is near the upper end of metallicity. Our study marks the first application of LGSAO for study of structure of galaxies producing distant quasar absorbers. Finally, this study offers the first example of a massive galaxy with a substantial bulge producing a metal-rich absorber.

astro-ph.CO↗

arXiv2009

A MIKE + UVES survey of Sub-Damped Lyman-Alpha Systems at z<1.5

We have combined the results from our recent observations of Damped and sub-Damped Lyman-alpha systems with the MIKE and UVES spectrographs on the Magellan Clay and VLT Kueyen telescopes with ones from the literature to determine the N(HI)-weighted mean metallicity of these systems based both on Fe, a depleted element in QSO absorbers and the local ISM, and Zn a relatively undepleted element. In each case, the N(HI)-weighted mean metallicity is higher and shows faster evolution in sub-DLAs than the classical DLA systems. Large grids of photoionisation models over the sub-DLA \nhI range with CLOUDY show that the ionisation corrections to the abundances are in general small, however the fraction of ionized H can be up to ~90 per cent. The individual spectra have been shifted to the rest frame of the absorber and averaged together to determine the average properties of these systems at z<1.5. We find that the average abundance pattern of the Sub-DLA systems is similar to the gas in the halo of the Milky Way, with an offset of ~0.3 dex in the overall metallicity. Both DLAs and Sub-DLAs show similar characteristics in their relative abundances patterns, although the DLAs have smaller <[Mn/Zn]> as well as higher <[Ti/Zn]> and <[Cr/Zn]>. We calculate the contribution of sub-DLAs to the metal budget of the Universe, and find that the sub-DLA systems at z<1.5 contain a comoving density of metals Omega_met (3.5-15.8)x10^{5} M_sun Mpc^{-3}, at least twice the comoving density of metals in the DLA systems. The sub-DLAs do however track global chemical evolution models much more closely than do the DLAs, perhaps indicating that they are a less dust biased metallicity indicator of galaxies at high redshifts than the DLA systems.

astro-ph.CO↗

arXiv2009

New Magellan Inamori Kyocera Echelle Observations of z<1.5 sub-damped Lyman-alpha systems

The Damped and sub-Damped Lyman-alpha (DLA and sub-DLA) systems seen in the spectra of QSOs offer a unique way to study the interstellar medium of high redshift galaxies. In this paper we report on new abundance determinations in a sample of 10 new systems, nine of the lesser studied sub-DLAs and one DLA, along the line of sight to seven QSOs from spectra taken with the MIKE spectrograph. Lines of Mg I, Mg II, Al II, Al III, Ca II, Mn II, Fe II, and Zn II were detected. Here, we give the column densities and equivalent widths of the observed absorption lines, as well as the abundances determined for these systems. Zn, a relatively undepleted element in the local interstellar medium (ISM) is detected in one system with a high metallicity of [Zn/H]=+0.27\pm0.18. In one other system, a high abundance based on the more depleted element Fe is seen with [Fe/H]=-0.37\pm0.13, although Zn is not detected. The N(HI)-weighted mean metallicity of these sub-DLA systems based on Fe is <[Fe/H]>=-0.76\pm0.11, nearly ~0.7 dex higher (a factor of 5) than what is seen in DLAs in this redshift range. The relative abundance of [Mn/Fe] is also investigated. A clear trend is visible for these systems as well as systems from the literature, with [Mn/Fe] increasing with increasing metallicity in good agreement with with Milky Way stellar abundances.

astro-ph.CO↗

arXiv2007

The chemical compositions of 10 new sub-DLAs and strong Lyman-limit systems at z < 1.5

We present chemical abundance measurements from medium resolution observations of 8 sub-damped Lyman-alpha absorber and 2 strong Lyman-limit systems at z < 1.5 observed with the MIKE spectrograph on the 6.5m Magellan II Clay telescope. These observations were taken as part of an ongoing project to determine abundances in z < 1.5 quasar absorption line systems (QSOALS) focusing on sub-DLA systems. These observations increase the sample of Zn measurements in z < 1.5 sub-DLAs by ~50%. Lines of Mg I, Mg II, Al II, Al III, Ca II, Mn II, Fe II, and Zn II were detected and column densities were determined. Zn II, a relatively undepleted element and tracer of the gas phase metallicity is detected in two of these systems, with [Zn/H]=-0.05\pm0.12 and [Zn/H]>+0.86. The latter system is however a weak system with N(H I)<18.8, and therefore may need significant ionisation corrections to the abundances. Fe II lines were detected in all systems, with an average Fe abundance of <[Fe/H]>=-0.68, higher than typical Fe abundances for DLA systems at these redshifts. This high mean [Fe/H] could be due to less depletion of Fe onto dust grains, or to higher abundances in these systems. We also discuss the relative abundances in these absorbers. The systems with high metallicity show high ratios of [Mn/Fe] and [Zn/Fe], as seen previously in another sub-DLA. These higher values of [Mn/Fe] could be a result of heavy depletion of Fe onto grains, unmixed gas, or an intrinsically non-solar abundance pattern. Based on Cloudy modeling, we do not expect ionisation effects to cause this phenomenon.

astro-ph↗

arXiv2007

9.7 micrometer Silicate Absorption in a Damped Lyman-alpha Absorber at z=0.52

We report a detection of the 9.7 micrometer silicate absorption feature in a damped Lyman-alpha (DLA) system at z_{abs} = 0.524 toward AO0235+164, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The feature shows a broad shallow profile over about 8-12 micrometers in the absorber rest frame and appears to be > 15 sigma significant in equivalent width. The feature is fit reasonably well by the silicate absorption profiles for laboratory amorphous olivine or diffuse Galactic interstellar clouds. To our knowledge, this is the first indication of 9.7 micrometer silicate absorption in a DLA. We discuss potential implications of this finding for the nature of the dust in quasar absorbers. Although the feature is relatively shallow (tau_{9.7} = 0.08-0.09), it is about 2 times deeper than expected from extrapolation of the tau_{9.7} vs. E(B-V) relation known for diffuse Galactic interstellar clouds. Further studies of the 9.7 micrometer silicate feature in quasar absorbers will open a new window on the dust in distant galaxies.

astro-ph↗

arXiv2007

New abundance determinations in z < 1.5 QSO absorbers: seven sub-DLAs and one DLA

We present chemical abundance measurements from high resolution observations of 7 sub-damped Lyman-alpha absorbers and 1 damped Lyman-alpha system at z<1.5. Three of these objects have high metallicity, with near or super-solar Zn abundance. Grids of Cloudy models for each system were constructed to look for possible ionization effects in these systems. For the systems in which we could constrain the ionization parameter, we find that the ionization corrections as predicted by the Cloudy models are generally small and within the typical error bars (~0.15 dex), in general agreement with previous studies. The Al III to Al II ratio for these and other absorbers from the literature are compared, and we find that while the sub-DLAs have a larger scatter in the Al III to Al II ratios than the DLAs, there appears to be little correlation between the ratio and N(H I). The relationship between the metallicity and the velocity width of the profile for these systems is investigated. We show that the sub-DLAs that have been observed to date follow a similar trend as DLA absorbers, with the more metal rich systems exhibiting large velocity widths. We also find that the systems at the upper edge of this relationship with high metallicities and large velocity widths are more likely to be sub-DLAs than DLA absorbers, perhaps implying that the sub-DLA absorbers are more representative of massive galaxies.

astro-ph↗

arXiv2007

The nature of damped Lyman alpha and sub-damped Lyman alpha absorbers

We present arguments based on the measured abundances in individual damped Lyman alpha systems (DLAs) and sub-damped Lyman alpha systems (sub-DLAs), and also the average abundances inferred in large samples of QSO absorption line systems, to suggest that the amount of dust in intervening QSO absorbers is small and is not responsible for missing many QSOs in magnitude limited QSO surveys. While we can not totally rule out a bimodal dust distribution with a population of very dusty, metal rich, absorbers which push the background QSOs below the observational threshold of current optical spectroscopic studies, based upon the current samples it appears that the metallicity in QSO absorbers decreases with increase in H I column densities beyond 10^{19} cm^{-2}. Thus the sub-DLA population is more metal rich than the DLAs, a trend which may possibly extend to the non-damped Lyman limit systems (NDLLS). Based on the recently discovered mass-metallicity relation for galaxies, we suggest that most sub-DLAs and possibly NDLLS, are associated with massive spiral/elliptical galaxies while most DLAs are associated with low mass galaxies. The sub-DLA galaxies will then contribute a larger fraction of total mass (stellar and ISM) and therefore metals, to the cosmic budget, specially at low redshifts, as compared to the DLAs.

astro-ph↗

arXiv2006

Emission Line Spectroscopy of a Damped Lyman-alpha Absorbing Galaxy at z = 0.437

We present Keck/LRIS spectra of a candidate damped Lyman-alpha (DLA) galaxy toward the QSO 3C196 (z_em = 0.871). The DLA absorption system has a redshift of z_DLA = 0.437, and a galaxy at 1.5" from the QSO has been identified in high resolution imaging with WFPC2/HST. We have detected emission lines of [O II] 3727A, Hbeta, [O III] 5007A, Halpha and [N II] 6584A at the absorption redshift. Based on the emission lines, we have found the redshift of the galaxy to be z_em = 0.4376 +/- 0.0006. The emission lines also enabled us to calculate the extinction-corrected luminosities and metallicity indicators using established indices based on line strengths of different emission lines. These indicators suggest that the ISM of the DLA galaxy has a high metallicity comparable to or perhaps twice as much as solar (e.g. 12+log (O/H) = 8.98 +/- 0.07). Based on the strengths of Halpha and on the reddening derived from the relative strengths of Halpha and Hbeta, the star formation rate is 4.7 +/- 0.8 M_solar/yr. This places the galaxy in the range of gas-rich spiral galaxies.

astro-ph↗