arXiv subjects

V. P. Kulkarni

Publications and source records attributed to V. P. Kulkarni.

15 recordsLinked to original sources

arXiv2021

PKS1830-211: OH and HI at z=0.89 and the first MeerKAT UHF spectrum

The Large Survey Project (LSP) "MeerKAT Absorption Line Survey" (MALS) is a blind HI 21-cm and OH 18-cm absorption line survey in the L- and UHF-bands, with the primary goal to better determine the occurrence of atomic and molecular gas in the circum-galactic and inter-galactic medium, and its redshift evolution. Here we present the first results using the UHF-band, obtained towards the strongly lensed radio source PKS1830, detecting absorption in the lens galaxy. With merely 90min of data acquired on-source for science verification and processed using the Automated Radio Telescope Imaging Pipeline (ARTIP), we detect in absorption the known HI 21-cm and OH 18-cm main lines at z=0.89 at an unprecedented signal-to-noise ratio (4000 in the continuum, with 6km/s channels). For the first time we report the detection at z=0.89 of OH satellite lines, so far not detected at z $>$ 0.25. We decompose the OH lines into a thermal and a stimulated contribution, where the 1612 and 1720MHz lines are conjugate. The total OH 1720MHz emission line luminosity is 6100Lsun. This is the most luminous known 1720MHz maser line. The absorption components of the different images of the background source sample different light paths in the lensing galaxy, and their weights in the total absorption spectrum are expected to vary in time, on daily and monthly time scales. We compare our normalized spectra with those obtained more than 20 yrs ago, and find no variation. We interpret the absorption spectra with the help of a lens galaxy model, derived from an N-body hydro-dynamical simulation, with a morphology similar to its optical HST image. It is possible to reproduce the observations without invoking any central gas outflows. There are, however, distinct and faint high-velocity features, most likely high-velocity clouds. These clouds may contribute to broaden the HI and OH spectra.

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arXiv2020

Blind HI and OH absorption line search: first results with MALS and uGMRT processed using ARTIP

We present details of the Automated Radio Telescope Imaging Pipeline (ARTIP) and results of a sensitive blind search for HI and OH absorbers at $z<0.4$ and $z<0.7$, respectively. ARTIP is written in Python 3.6, extensively uses the Common Astronomy Software Application (CASA) tools and tasks, and is designed to enable the geographically-distributed MeerKAT Absorption Line Survey (MALS) team to collaboratively process large volumes of radio interferometric data. We apply it to the first MALS dataset obtained using the 64-dish MeerKAT radio telescope and 32K channel mode of the correlator. With merely 40 minutes on target, we present the most sensitive spectrum of PKS1830-211 ever obtained and characterize the known HI ($z=0.19$) and OH ($z=0.89$) absorbers. We further demonstrate ARTIP's capabilities to handle realistic observing scenarios by applying it to a sample of 72 bright radio sources observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) to blindly search for HI and OH absorbers. We estimate the numbers of HI and OH absorbers per unit redshift to be $n_{21}(z\sim0.18)<$0.14 and $n_{\rm OH}(z\sim0.40)<$0.12, respectively, and constrain the cold gas covering factor of galaxies at large impact parameters (50 kpc $<ρ<$ 150 kpc) to be less than 0.022. Due to the small redshift path, $Δz\sim$13 for HI with column density$>5.4\times10^{19}$ cm$^{-2}$, the survey has probed only the outskirts of star-forming galaxies at $ρ>30$ kpc. MALS with the expected $Δz\sim10^{3-4}$ will overcome this limitation and provide stringent constraints on the cold gas fraction of galaxies in diverse environments over $0<z<1.5$.

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arXiv2016

The ESO UVES Advanced Data Products Quasar Sample - VI. Sub-Damped Lyman-$α$ Metallicity Measurements and the Circum-Galactic Medium

The Circum-Galactic Medium (CGM) can be probed through the analysis of absorbing systems in the line-of-sight to bright background quasars. We present measurements of the metallicity of a new sample of 15 sub-damped Lyman-$α$ absorbers (sub-DLAs, defined as absorbers with 19.0 < log N(H I) < 20.3) with redshift 0.584 < $\rm z_{abs}$ < 3.104 from the ESO Ultra-Violet Echelle Spectrograph (UVES) Advanced Data Products Quasar Sample (EUADP). We combine these results with other measurements from the literature to produce a compilation of metallicity measurements for 92 sub-DLAs as well as a sample of 362 DLAs. We apply a multi-element analysis to quantify the amount of dust in these two classes of systems. We find that either the element depletion patterns in these systems differ from the Galactic depletion patterns or they have a different nucleosynthetic history than our own Galaxy. We propose a new method to derive the velocity width of absorption profiles, using the modeled Voigt profile features. The correlation between the velocity width delta_V90 of the absorption profile and the metallicity is found to be tighter for DLAs than for sub-DLAs. We report hints of a bimodal distribution in the [Fe/H] metallicity of low redshift (z < 1.25) sub-DLAs, which is unseen at higher redshifts. This feature can be interpreted as a signature from the metal-poor, accreting gas and the metal-rich, outflowing gas, both being traced by sub-DLAs at low redshifts.

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arXiv2014

Interstellar Silicate Dust in the z=0.685 Absorber Toward TXS 0218+357

We report the detection of interstellar silicate dust in the z_abs=0.685 absorber along the sightline toward the gravitationally lensed blazar TXS 0218+357. Using Spitzer Space Telescope Infrared Spectrograph data we detect the 10 micron silicate absorption feature with a detection significance of 10.7-sigma. We fit laboratory-derived silicate dust profile templates obtained from literature to the observed 10 micron absorption feature, and find that the best single-mineral fit is obtained using an amorphous olivine template with a measured peak optical depth of tau_10=0.49+/-0.02, which rises to tau_10~0.67+/-0.04 if the covering factor is taken into account. We also detected the 18 micron silicate absorption feature in our data with a >3-sigma significance. Due to the proximity of the 18 micron absorption feature to the edge of our covered spectral range, and associated uncertainty about the shape of the quasar continuum normalization near 18 micron, we do not independently fit this feature. We find, however, that the shape and depth of the 18 micron silicate absorption are well-matched to the amorphous olivine template prediction, given the optical depth inferred for the 10 micron feature. The measured 10 micron peak optical depth in this absorber is significantly higher than those found in previously studied quasar absorption systems. The reddening, 21-cm absorption, and velocity spread of Mg II are not outliers relative to other studied absorption systems, however. This high optical depth may be evidence for variations in dust grain properties in the ISM between this and the previously studied high redshift galaxies.

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arXiv2013

A Mini X-Ray Survey of Sub-DLAs; Searching for AGNs Formed in Protogalaxies

A significant fraction of the sub-damped Lyman-alpha (sub-DLA) absorption systems in quasar spectra appear to be metal-rich, many with even super-solar element abundances. This raises the question whether some sub-DLAs may harbor active galactic nuclei (AGN) since supersolar metallicities are observed in AGN. Here we investigate this question based on a mini-survey of 21 quasars known to contain sub-DLAs in their spectra. The X-ray observations were performed with the Chandra X-ray Observatory. In cases of no detection we estimated upper limits of the X-ray luminosities of possible AGNs at the redshifts of the sub-DLAs. In six cases we find possible X-ray emission within ~ 1 arcsec of the background quasar consistent with the presence of a nearby X-ray source. If these nearby X-ray sources are at the redshifts of the sub-DLAs, their estimated 0.2-10 keV luminosities range between 0.8 x 10^{44}h^{-2} and 4.2 x 10^{44}h^{-2} erg s^{-1}, thus ruling out a normal late-type galaxy origin, and suggesting that the emission originates in a galactic nucleus near the center of a protogalaxy. The projected distances of these possible nearby X-ray sources from the background quasars lie in the range of 3-7 h^{-1} kpc, consistent with our hypothesis that they represent AGNs centered on the sub-DLAs. Deeper follow-up X-ray and optical observations are required to confirm the marginal detections of X-rays from these sub-DLA galaxies.

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arXiv2010

A Dusty Mg~II absorber Associated with the Quasar SDSS J003545.13+011441.2

We report on a dusty Mg~II absorber associated with the quasar SDSSJ003545.13+011441.2 (hereafter J0035+0114) at $z$=1.5501, which is the strongest one among the three Mg~II absorbers along the sight line of quasar. The two low redshift intervening absorbers are at $z$=0.7436, 0.5436, respectively. Based on the photometric and spectroscopic data of Sloan Digital Sky Survey (hereafter SDSS), we infer the rest frame color excess E(\bv) due to the associated dust is more than 0.07 by assuming a Small Magellanic Cloud (hereafter SMC) type extinction curve. Our follow-up moderate resolution spectroscopic observation at the 10-m Keck telescope with the ESI spectrometer enable us to reliably identify most of the important metal elements, such as Zn, Fe, Mn, Mg, Al, Si, Cr, and Ni in the associated system. We measure the column density of each species and detect significant dust depletion. In addition, we develop a simulation technique to gauge the significance of 2175-Å dust absorption bump on the SDSS quasar spectra. By using it, we analyze the SDSS spectrum of J0035+0114 for the presence of a associated 2175-Å extinction feature and report a tentative detection at $\sim$2$σ$ significant level.

astro-ph.CO↗

arXiv2008

Metal abundances at z<1.5: new measurements in sub-Damped Lyman-alpha Absorbers

Damped Lyman-alpha systems (DLAs) and sub-DLAs seen toward background quasars provide the most detailed probes of elemental abundances. Somewhat paradoxically these measurements are more difficult at lower redshifts due to the atmospheric cut-off, and so a few years ago our group began a programme to study abundances at z < 1.5 in quasar absorbers. In this paper, we present new UVES observations of six additional quasar absorption line systems at z < 1.5, five of which are sub-DLAs. We find solar or above solar metallicity, as measured by the abundance of zinc, assumed not to be affected by dust, in two sub-DLAs: one, towards Q0138-0005 with [Zn/H]=+0.28 +/- 0.16; the other towards Q2335+1501 with [Zn/H]=+0.07 +/- 0.34. Relatively high metallicity was observed in another system: Q0123-0058 with [Zn/H]=-0.45 +/- 0.20. Only for the one DLA in our sample, in Q0449-1645, do we find a low metallicity, [Zn/H]=-0.96 +/- 0.08. We also note that in some of these systems large relative abundance variations from component to component are observed in Si, Mn, Cr and Zn.

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arXiv2008

Average Properties of a Large Sample of z_abs ~ z_em associated Mg II Absorption Line Systems

We have studied a sample of 415 associated (z_ab z_em; relative velocity with respect to QSO <3000km/s) Mg II absorption systems with 1.0<=z_ab<=1.86, in the spectra of SDSS DR3 QSOs, to determine the dust content and ionization state in the absorbers. We studied the dependence of these properties on the properties of the QSOs and also, compared the properties with those of a similarly selected sample of 809 intervening systems (apparent relative velocity with respect to the QSO of >3000km/s), so as to understand their origin. From the analysis of the composite spectra, as well as from the comparison of measured equivalent widths in individual spectra, we conclude that the associated Mg II absorbers have higher apparent ionization, measured by the strength of the C IV absorption lines compared to the Mg II absorption lines, than the intervening absorbers. The ionization so measured appears to be related to apparent ejection velocity, being lower as the apparent ejection velocity is more and more positive. There is clear evidence, from the composite spectra, for SMC like dust attenuation in these systems; the 2175AA absorption feature is not present. The extinction is almost twice that observed in the similarly selected sample of intervening systems. We reconfirm that QSOs with non-zero FIRST radio flux are intrinsically redder than the QSOs with no detection in the FIRST survey. The incidence of associated Mg II systems in QSOs with non-zero FIRST radio flux is 1.7 times that in the QSOs with no detection in the FIRST survey. The associated absorbers in radio-detected QSOs which comprise about 12% of our sample, cause 3 times more reddening than the associated absorbers in radio-undetected QSOs. This excess reddening possibly suggests an intrinsic nature for the associated absorbers in radio-detected QSOs.

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arXiv2007

The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals

Observations of low mean metallicity of damped Lyman-alpha (DLA) quasar absorbers at all redshifts studied appear to contradict the predictions for the global mean interstellar metallicity in galaxies from cosmic chemical evolution models. On the other hand, a number of metal-rich sub-DLA systems have been identified recently, and the fraction of metal-rich sub-DLAs appears to be considerably larger than that of metal-rich DLAs, especially at z < 1.5. In view of this, here we investigate the evolution of metallicity in sub-DLAs. We find that the mean Zn metallicity of the observed sub-DLAs may be higher than that of the observed DLAs, especially at low redshifts, reaching a near-solar level at z <~ 1. This trend does not appear to be an artifact of sample selection, the use of Zn, the use of N_{HI}-weighting, or observational sensitivity. While a bias against very low metallicity could be present in the sub-DLA sample in some situations, this cannot explain the difference between the DLA and sub-DLA metallicities at low z. The primary reason for the difference between the DLAs and sub-DLAs appears to be the dearth of metal-rich DLAs. We estimate the sub-DLA contribution to the total metal budget using measures of their metallicity and comoving gas density. These calculations suggest that at z <~ 1, the contribution of sub-DLAs to the total metal budget may be several times that of DLAs. At higher redshifts also, there are indications that the sub-DLAs may contribute significantly to the cosmic metal budget.

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arXiv2006

Metal-rich Damped/sub-Damped Lyman-alpha Quasar Absorbers at z<1

Damped Lyman-alpha absorbers (DLAs), seen in absorption against a background quasar, provide the most detailed probes available of element abundances in the Universe over > 90 % of its age. DLAs can be used to observationally measure the global mean metallicity in the Universe and its evolution with time. Paradoxically, these observations are more difficult at lower redshifts, where the absorber rest-frame UV spectra are cut-off due to the atmospheric absorption. We present here high-resolution VLT/UVES observations of several elements contained in three DLAs and one sub-DLA with 0.6<z_abs<0.9. We detect Mg I, Mg II, Fe II, Zn II, Cr II, Mn II, Ti II and Ca II. Our observations more than double the high-resolution sample of [Zn/H] at z<1. We also report the discovery of three metal-rich systems, whereas most previous measurements show low N(HI)-weighted mean metallicity projecting to about 1/6th solar level at z=0. We derive [Zn/H]=-0.11+/-0.04 at z_abs=0.725, [Zn/H]=-0.54+/-0.20 at z_abs=0.740 and [Zn/H]=-0.49+/-0.22 at z_abs=0.652, plus one additional upper limit ([Zn/H]<-0.36 at z_abs=0.842). These measurements confirm the existence of quasar absorbers with relatively high metallicities based on abundance estimates free from the effect of dust depletion. Possible implications of these results for the metallicity of neutral gas phase in the past ~ 8 Gyr are presented and compared with models.

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arXiv2006

Extinction and metal column density of HI regions up to redshift z~2

We used the photometric database of the Sloan Digital Sky Survey (SDSS) to estimate the reddening of 13 SDSS quasars selected on the basis of the presence of zinc absorption lines in an intervening Damped Ly alpha (DLA) system. In 5 of these quasars the reddening is detected at ~2 sigma confidence level in two independent color indices of the SDSS ugriz photometric system. A detailed analysis of the data supports an origin of the reddening in the intervening absorbers. We used these rare measurements of extinction in DLA systems to probe the relation between extinction and metal column density in the interval of absorption redshift 0.7 </~ z </~ 2.0. We find that the mean extinction in the V band per atom of iron in the dust is remarkably similar to that found in interstellar clouds of the Milky Way. This result lends support to previous estimates of the dust obscuration effect in DLA systems based on a Milky Way extinction/metal column density relation. We propose a simple mechanism, based on dust grain destruction/accretion properties, which may explain the approximate constancy of the extinction per atom of iron in the dust.

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arXiv2006

The Most Metal-Rich Intervening Quasar Absorber Known

The metallicity in portions of high-redshift galaxies has been successfully measured thanks to the gas observed in absorption in the spectra of quasars, in the Damped Lyman-alpha systems (DLAs). Surprisingly, the global mean metallicity derived from DLAs is about 1/10th solar at 0<z<4 leading to the so-called ``missing-metals problem''. In this paper, we present high-resolution observations of a sub-DLA system at z_abs=0.716 with super-solar metallicity toward SDSS J1323-0021. This is the highest metallicity intervening quasar absorber currently known, and is only the second super-solar absorber known to date. We provide a detailed study of this unique object from VLT/UVES spectroscopy. We derive [Zn/H]=+0.61, [Fe/H]=-0.51, [Cr/H]=<-0.53, [Mn/H] = -0.37, and [Ti/H] = -0.61. Observations and photoionisation models using the CLOUDY software confirm that the gas in this sub-DLA is predominantly neutral and that the abundance pattern is probably significantly different from a Solar pattern. Fe/Zn and Ti/Zn vary among the main velocity components by factors of \~ 3 and ~ 35, respectively, indicating non-uniform dust depletion. Mn/Fe is super-solar in almost all components, and varies by a factor of ~ 3 among the dominant components. It would be interesting to observe more sub-DLA systems and determine whether they might contribute significantly toward the cosmic budget of metals.

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arXiv2005

A Fabry-Perot Imaging Search for Lyman-alpha Emission in Quasar Absorbers at z ~ 2.4

We have carried out a deep narrow-band imaging survey of six fields with heavy-element quasar absorption lines, using the Goddard Fabry-Perot (FP) system at the Apache Point Observatory (APO) 3.5-meter telescope. The aim of these observations was to search for redshifted Ly-$α$ emission from the galaxies underlying the absorbers at $z = 2.3-2.5$ and their companion galaxies. The 3 $σ$ sensitivity levels ranged between $1.9 \times 10^{-17}$ and $5.4 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ in observed-frame Ly-$α$ flux. No significant Ly-$α$ emitters were detected at $> 3 σ$ level. The absence of significant Ly-$α$ emission implies limits on the star formation rate (SFR) of 0.9-2.7 $M_{\odot}$ yr$^{-1}$ per 2-pixel x 2-pixel region, if no dust attenuation is assumed. We compare our results with those from other emission-line studies of absorber fields and with predictions for global average SFR based on the models of cosmic chemical evolution. Our limits are among the tightest existing constraints on Ly-$α$ emission from galaxies in absorber fields, but are consistent with many other studies. In the absence of dust attenuation, these studies suggest that SFRs in a large fraction of objects in the absorber fields may lie below the global mean SFR. However, it is possible that dust attenuation is responsible for the low emission line fluxes in some objects. It is also possible that the star-forming regions are compact and at smaller angular separations from the quasar than the width of our point spread function and, get lost in the quasar emission. We outline future observations that could help to distinguish between the various possibilities.

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arXiv2005

Evidence for the presence of dust in intervening QSO absorbers from the Sloan Digital Sky Survey

We find evidence for dust in the intervening QSO absorbers from the spectra of QSOs in the Sloan Digital Sky Survey Data Release 1. No evidence is found for the 2175 A feature which is present in the Milky Way dust extinction curve. The extinction curve resembles the SMC extinction curve. The observed Delta(g-i) excess for QSOs with strong absorption systems appears to be a result of the reddening due to dust in the intervening absorbers.

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arXiv1997

Abundance Patterns of Heavy Elements in Damped Lyman-Alpha Galaxies

We present a quantitative analysis of the abundances of heavy elements in damped Ly-alpha galaxies in the sample of Lu et al. (1996). In particular, we compare the observed gas-phase abundances with those expected when the intrinsic (i.e., nucleosynthetic) pattern is the same as that in either the Sun or in Galactic halo stars and when the depletion pattern is the same as that in the warm Galactic interstellar medium, but with various values of the dust-to-metals ratio. We find that the observations are equally consistent with the solar and halo-star intrinsic patterns and that they favor some depletion, the typical dust-to-metals ratio being 40%-90% of that in the Milky Way today. However, neither intrinsic pattern matches the observations perfectly. For the solar pattern, the discrepancy is mainly with [Mn/Fe], while for the halo-star pattern, the discrepancy is with [Zn/Fe], [Ni/Fe], and possibly [Al/Fe]. Our analysis does not support the claim by Lu et al. that the damped Ly-alpha galaxies have halo-star abundance patterns and no dust depletion.

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