We report the detection of a strong HI 21-cm absorption system at z=0.5344, as well as a candidate system at z=0.3389, in the sight-line towards the z=2.64 quasar MG J0414+0534. This, in addition to the absorption at the host redshift and the other two intervening absorbers, takes the total to four (possibly five). The previous maximum number of 21-cm absorbers detected along a single sight-line is two and so we suspect that this number of gas-rich absorbers is in some way related to the very red colour of the background source. Despite this, no molecular gas (through OH absorption) has yet been detected at any of the 21-cm redshifts, although, from the population of 21-cm absorbers as a whole, there is evidence for a weak correlation between the atomic line strength and the optical--near-infrared colour. In either case, the fact that so many gas-rich galaxies (likely to be damped Lyman-alpha absorption systems) have been found along a single sight-line towards a highly obscured source may have far reaching implications for the population of faint galaxies not detected in optical surveys, a possibility which could be addressed through future wide-field absorption line surveys with the Square Kilometre Array.
We investigate the dependence of residual rotation measure (RRM) on intervening absorption systems at cosmic distances by using a large sample of 539 SDSS quasars in conjunction with the available rotation measure catalog at around 21cm wavelength. We found an excess extragalactic contribution in standard deviation of observed RRM of about 8.11+/-4.83 Rad/m^2 in our sample with intervening MgII absorber as compare to the sample without MgII absorber. Our results suggest that intervening absorbers could contribute to the enhancement of RRM at around 21cm wavelength, as was found earlier for RM …
(Abridged) We present a systematic study of weak intervening CaII absorbers at low redshift (z<0.5), based on the analysis of archival high resolution (R>45,000) optical spectra of 304 quasars and active galactic nuclei observed with VLT/UVES. Along a total redshift path of Dz~100 we detected 23 intervening CaII absorbers in both the CaII H & K lines, with rest frame equivalent widths W_r,3934=15-799 mA and column densities log N(CaII)=11.25-13.04. We obtain a bias corrected number density of weak intervening CaII absorbers of dN/dz=0.117+-0.044 at z=0.35 for absorbers with log N(CaII)>11.65. …
Context: A significantly higher incidence of strong (rest equivalent width W_r > 1 Å) intervening Mg II absorption is observed along gamma-ray burst (GRB) sight-lines relative to those of quasar sight-lines. A geometrical explanation for this discrepancy has been suggested: the ratio of the beam size of the source to the characteristic size of a Mg II absorption system can influence the observed Mg II equivalent width, if these two sizes are comparable. Aims: We investigate whether the differing beam sizes of the continuum source and broad-line region of Sloan Digital Sky Survey (SDSS) quasars…
We have identified 469 MgII doublet systems having W_r >= 0.02 Å in 252 Keck/HIRES and UVES/VLT quasar spectra over the redshift range 0.1 < z < 2.6. Using the largest sample yet of 188 weak MgII systems (0.02 Å <= W_r < 0.3 Å), we calculate their absorber redshift path density, dN/dz. We find clear evidence of evolution, with dN/dz peaking at z ~ 1.2, and that the product of the absorber number density and cross section decreases linearly with increasing redshift; weak MgII absorbers seem to vanish above z ~ 2.7. If the absorbers are ionized by the UV background, we estimate number densities …
We present the first search for galaxy counterparts of intervening high-z (2<z< 3.6) sub-DLAs and DLAs towards GRBs. Our final sample comprises of five intervening sub-DLAs and DLAs in four GRB fields. To identify candidate galaxy counterparts of the absorbers we use deep optical and near-infrared imaging, and low-, mid- and high-resolution spectroscopy acquired with 6 to 10-m class telescopes, the Hubble and the Spitzer space telescopes. Furthermore, we use the spectroscopic information and spectral-energy-distribution fitting techniques to study them in detail. Our main result is the detecti…
Damped Lyman-$α$ Absorber (DLA), or HI 21cm Absorber (H21A), is an important probe to model-independently measure the acceleration of spectroscopic velocity ($v_\mathrm{S}$) via the Sandage-Loeb (SL) effect. Confined by the shortage of DLAs and Background Radio Sources (BRSs) with adequate information, the detectable amount of DLAs is ambiguous in the bulk of previous work. After differing the acceleration of scale factor ($\ddot{a}$) from the first order time derivative of spectroscopic velocity ($\dot{v}_\mathrm{S}$), we make a statistical investigation of the amount of potential DLAs in the…
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.…
We report on the detection of Ne VIII in an intervening multiphase absorption line system at z=0.32566 in the FUSE spectrum of the quasar 3C 263. The Ne VIII 770 A line detection has a 3.9 sigma significance. At the same velocity we also find absorption lines from C IV, O III, O IV and N IV. The line parameter measurements yield log [N(Ne VIII), cm^-2] =13.98 (+0.10,-0.13) and b = 49.8 +/- 5.5 km/s. We find that the ionization mechanism in the gas phase giving rise to the Ne VIII absorption is inconsistent with photoionization. The absorber has a multi-phase structure, with the intermediate io…
We performed multi-band deep imaging of the field around GRB 050730 to identify the host galaxies of intervening absorbers, which consist of a damped Lyα absorption (DLA) system at zabs=3.564, a sub-DLA system at zabs=3.022, and strong MgII absorption systems at zabs=1.773 and 2.253. Our observations were performed after the gamma-ray burst afterglow had disappeared. Thus, our imaging survey has a higher sensitivity to the host galaxies of the intervening absorbers than the normal imaging surveys in the direction of QSOs, for which the QSO glare tends to hide the foreground galaxies. In this d…
We study the Gamma Ray Burst (GRB) environment and intervening absorbers by analyzing the optical absorption features produced by gas surrounding the GRB or along its line of sight. We analyzed high resolution spectroscopic observations (R=40000, S/N=3 - 6) of the optical afterglow of GRB080330, taken with UVES at the VLT ~ 1.5 hours after the GRB trigger. The spectrum illustrates the complexity of the ISM of the GRB host galaxy at z = 1.51 which has at least four components in the main absorption system. We detect strong FeII, SiII, and NiII excited absorption lines associated with the bluemo…
We wish to study the extent and subparsec scale spatial structure of intervening quasar absorbers, mainly those involving neutral and molecular gas. We have selected quasar absorption systems with high spectral resolution and good S/N data, with some of their lines falling on quasar emission features. By investigating the consistency of absorption profiles seen for lines formed either against the quasar continuum source or on the much more extended emission line region (ELR), we can probe the extent and structure of the foreground absorber over the extent of the ELR (0.3-1 pc). The spatial cov…
The aim of this paper is to investigate the properties of the intervening absorbers lying along the line of sight of Gamma-Ray Burst (GRB) 080319B through the analysis of its optical absorption features. To this purpose, we analyze a multi-epoch, high resolution spectroscopic observations (R=40000, corresponding to 7.5 km/s) of the optical afterglow of GRB080319B (z=0.937), taken with UVES at the VLT. Thanks to the rapid response mode (RRM), we observed the afterglow just 8m:30s after the GRB onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise, high resoluti…
We present the Voigt profile analysis of 132 intervening CIV+CIII components associated with optically-thin HI absorbers at 2.1 < z < 3.4 in the 19 high-quality UVES/VLT and HIRES/Keck QSO spectra. For log N(CIV) = [11.7, 14.1], N(CIII) is proportional to N(CIV) with an exponent (1.42 +- 0.11) and < N(CIII)/N(CIV) > = 1.0 +- 0.3 with a negligible redshift evolution. For 54 CIV components tied (aligned) with HI at log N(HI) = [12.2, 16.0] and log N(CIV) = [11.8, 13.8], the gas temperature T_b estimated from absorption line widths is well-approximated to a Gaussian peaking at log T_b ~ 4.4 +- 0.…
We report a detection of an absorption line at ~44.8 Å in a > 500 ks Chandra HRC-S/LETG X-ray grating spectrum of the blazar H 2356-309. This line can be identified as intervening CV-Kα absorption, at z\approx0.112, produced by a warm (log T = 5.1 K) intergalactic absorber. The feature is significant at a 2.9σ level (accounting for the number of independent redshift trials). We estimate an equivalent hydrogen column density of log N_H=19.05 (Z/Zsun)^-1 cm^-2. Unlike other previously reported FUV/X-ray metal detections of warm-hot intergalactic medium (WHIM), this CV absorber lies in a region w…
We present HST/COS high S/N observations of the z = 0.32566 multi-phase absorber towards 3C263. The COS data shows absorption from H I, O VI, C III, N III, Si III and C II. The Ne VIII in this absorber is detected in the FUSE spectrum. The low and intermediate ions are kinematically aligned with each other and H I and display narrow line widths of 6 km/s. The O VI lines are kinematically offset by 12 km/s from the low ions and are a factor of four broader. All metal ions except O VI and Ne VIII are consistent with an origin in gas photoionized by the extragalactic background radiation. The bul…
Doubly ionized silicon (SiIII) is a powerful tracer of diffuse ionized gas inside and outside of galaxies. It can be observed in the local Universe in ultraviolet (UV) absorption against bright extragalactic background sources. We here present an extensive study of intervening SiIII-selected absorbers and their relation to the circumgalactic medium (CGM) of galaxies at low redshift (z<=0.1), based on the analysis of UV absorption spectra along 303 extragalactic lines of sight obtained with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). Along a total redshift p…
We are just starting to understand the physical processes driving the dramatic change in cosmic star-formation rate between $z\sim 2$ and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing t…
We investigate the origin and physical properties of OVI absorbers at low redshift (z = 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening OVI absorbers are believed to trace shock-heated gas in the Warm-Hot Intergalactic Medium (WHIM) and may thus play a key role in the search for the missing baryons in the present-day Universe. When compared to observations, the predicted distributions of the different OVI line parameters (column density, Doppler parameter, rest equivalent width) from our simulations exhibit …
We argue that most strong intervening metal absorption line systems, where the rest equivalent width of the MgII 2796A line is >0.5A, are interstellar material in, and outflowing from, star-forming disks. We show that a version of the Kennicutt-Schmidt law is readily obtained if the MgII equivalent widths are interpreted as kinematic broadening from absorbing gas in outflowing winds originating from star-forming galaxies. Taking a phenomenological approach and using a set of observational constraints available for star-forming galaxies, we are able to account for the density distribution of st…
We report 4 new detections of 21-cm absorption from a systematic search of 21-cm absorption in a sample of 17 strong (Wr(MgII 2796)>1A) intervening MgII absorbers at 0.5<z<1.5. We also present 20-cm milliarcsecond scale maps of 40 quasars having 42 intervening strong MgII absorbers for which we have searched for 21-cm absorption. Combining 21-cm absorption measurements for 50 strong MgII systems from our surveys with the measurements from literature, we obtain a sample of 85 strong MgII absorbers at 0.5<z<1 and 1.1<z<1.5. We present detailed analysis of this sample, taking into account the eff…
We present here results from a survey of intervening C IV absorbers at $z < 0.16$ conducted using 223 sightlines from the Hubble Spectroscopic Legacy Archive. Most systems (83%) out of the total sample of 69 have simple kinematics with 1 or 2 C IV components. In the 22 C IV systems with well constrained H I column densities, the temperatures from the $b$-values imply predominantly photoionized plasma ($T\leq 10^5$ K) and non-thermal dynamics. These systems also have solar or higher metallicities. We obtain a C IV line density of $d\mathcal{N}/dX = 5.1\pm 1.0$ for $\log [N(C~IV)~(cm^{-2})]\geq1…
We present a re-analysis, with newly acquired atomic data, of the two detections of two highly ionized intervening OVII absorbers reported by Nicastro and collaborators (2018). We confirm both intervening Warm-Hot Intergalactic Medium OVII detections, and revise statistical significance and physical parameters of the absorber at $z=0.4339$ in light of its partial contamination by Galactic interstellar medium NII K$α$ absorption.
Composite spectra of 85 proximate absorbers (log N(HI)>20 and velocity difference between the absorption and emission redshift, dv<10,000 km/s) in the SDSS are used to investigate the trends of metal line strengths with velocity separation from the QSO. We construct composites in 3 velocity bins: dv<3000 km/s, 3000<dv<6000 km/s and dv>6000 km/s, with further sub-samples to investigate the metal line dependence on N(HI) and QSO luminosity. Low (e.g. SiII and FeII) and high ionization (e.g. SiIV and CIV) species alike have equivalent widths (EWs) that are larger by factors of 1.5 -- 3 in the dv<…
We searched for evidence of reddening of background SDSS QSO spectra due to dust in intervening DLA systems. We utilise the Data Releases 5 and 7 to arrive at sample sizes of 475 (DR5) and 676 (DR7) absorbers, based on two different published lists of SDSS DLAs. Both samples span roughly the redshift range of 2.2 < z_abs < 5.2, with a mean of z~3.0, and the majority of the DLAs (75%) below z=3.3. We construct geometric mean spectra in the absorber restframes ranging from 1240 to ~2800 A, and composite spectra of samples matching the 'DLA' QSOs in i band magnitude and emission redshift z_em, bu…
We analyze the cross-correlation of 2,705 unambiguously intervening Mg II (2796,2803A) quasar absorption line systems with 1,495,604 luminous red galaxies (LRGs) from the Fifth Data Release of the Sloan Digital Sky Survey within the redshift range 0.36<=z<=0.8. We confirm with high precision a previously reported weak anti-correlation of equivalent width and dark matter halo mass, measuring the average masses to be log M_h(M_[solar]h^-1)=11.29 [+0.36,-0.62] and log M_h(M_[solar]h^-1)=12.70 [+0.53,-1.16] for systems with W[2796A]>=1.4A and 0.8A<=W[2796A]<1.4A, respectively. Additionally, we inv…
To explore the ionization conditions in highly-ionized absorbers at high redshift we have studied in detail two intervening OVI absorbers at z=2 towards the quasar PKS1448-232, based on high (R=75,000) and intermediate (R=45,000) resolution optical VLT/UVES spectra. We find that both absorption systems are composed of several narrow subcomponents with CIV/OVI Doppler-parameters b<10 km/s, typically. This implies that the gas temperatures are T<10^5 K and that the absorbers are photoionized by the UV background. The system at z=2.1098 represents a simple, isolated OVI absorber that has only two…
We present a catalogue of MgII absorption systems obtained from high resolution UVES/VLT data of 77 QSOs in the redshift range 0.6 < z < 2.0, and down to an equivalent width W_0 > 0.1 Å. The statistical properties of our sample are found to be in agreement with those from previous work in the literature. However, we point out that the previously observed increase with redshift of dN/dz for weak absorbers, pertains exclusively to very weak absorbers with W_0 < 0.1 Å. Instead, dN/dz for absorbers with W_0 in the range 0.1-0.3 Åactually decreases with redshift, similarly to the case of strong abs…
Unlike the neutral gas density, which remains largely constant over redshifts of 0 < z < 5, the star formation density exhibits a strong redshift dependence, increasing from the present day before peaking at a redshift of z ~ 2.5. Thus, there is a stark contrast between the star formation rate and the abundance of raw material available to fuel it. However, using the ratio of the strength of the HI 21-cm absorption to the total neutral gas column density to quantify the spin temperature of the gas, it has recently been shown that its reciprocal may trace the star formation density. This would …
We report the detection of a third HI 21-cm absorber in the sight-line towards the z=2.64 quasar MG J0414+0534 (4C +05.19). In addition to the absorption at the host redshift and in the z=0.96 gravitational lens, we find, through a decimetre-wave spectral scan towards this source, strong absorption at z=0.38. We believe this may be associated with "Object X", an additional feature apparent in the field of the lensing galaxy and lensed images, on the basis of its close proximity to the quasar images and the possible detection of the [OIII] doublet in a published optical spectrum. If real, the s…
Strong foreground absorption features from singly-ionized Magnesium (Mg II) are commonly observed in the spectra of quasars and are presumed to probe a wide range of galactic environments. To date, measurements of the average dark matter halo masses of intervening Mg II absorbers by way of large-scale cross-correlations with luminous galaxies have been limited to z<0.7. In this work we cross-correlate 21 strong (Wλ2796>0.6 °A) Mg II absorption systems detected in quasar spectra from the Sloan Digital Sky Survey Data Release 7 with ~32,000 spectroscopically confirmed galaxies at 0.7<z<1.45 from…
GRB afterglows offer a probe of the intergalactic medium out to high redshift which complements observations along more abundant quasar lines-of-sight. Although both quasars and GRB afterglows should provide a-priori random sight-lines through the intervening IGM, it has been observed that strong Mg-II absorbers are twice as likely to be found along sight-lines toward GRBs. Several proposals to reconcile this discrepancy have been put forward, but none has been found sufficient to explain the magnitude of the effect. In this paper we estimate the effect of gravitational lensing by galaxies and…
The Complete Optical and Radio Absorption Line System (CORALS) survey has previously been used to demonstrate that the number density, gas and metals content of z>1.6 damped Lyman alpha systems is not significantly under-estimated in magnitude limited surveys. In this paper, a sample of strong MgII absorbers selected from the optically complete 0.7 < z < 1.6 CORALS sample of Ellison et al. is used to assess the potential of dust bias at intermediate redshifts. From echelle spectra of all CORALS absorbers with MgII lambda 2796 and FeII lambda 2600 rest equivalent widths > 0.5 A in the redshift …
We report the first comparative study of strong MgII absorbers seen towards radio-loud quasars of core-dominated (CDQs) and lobe-dominated (LDQs) types and normal QSOs. The MgII associated absorption systems having a velocity offset v < 5000km/s from the systemic velocity of the background quasar were also excluded. Existing spectroscopic data for redshift-matched sightlines of 3975 CDQs and 1583 LDQs, covering a emission redshift range 0.39-4.87, were analysed and 864 strong MgII absorbers were found, covering the redshift range 0.45-2.17. The conclusions reached using this well-defined large…
There is nearly a factor of four difference in the number density of intervening MgII absorbers as determined from gamma-ray burst (GRB) and quasar lines of sight. We use a Monte-Carlo simulation to test if a dust extinction bias can account for this discrepancy. We apply an empirically determined relationship between dust column density and MgII rest equivalent width to simulated quasar sight-lines and model the underlying number of quasars that must be present to explain the published magnitude distribution of SDSS quasars. We find that an input MgII number density dn/dz of 0.273 +- 0.002 ov…
We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-Å dust extinction feature. Column densities are measured from low-ionization absorption lines using Apparent Optical Depth Method on the Keck/ESI spectra. We find the dust depletion patterns resemble to that of cold diffuse clouds in the Milky Way (MW). The values, [Fe/Zn]$\approx -1.5$ and [Si/Zn]$<-0.67$, are among the highest dust depletion measured for quasar absorption line systems. In another 2175-Å absorber at $z$=1.64 toward the quasar SDS…
We present the results of a systematic Giant Metrewave Radio Telescope (GMRT) survey of 21-cm absorption in a representative and unbiased sample of 35 strong MgII systems in the redshift range: zabs~1.10-1.45, 33 of which have W_r>1 Å. The survey using ~400hrs of telescope time has resulted in 9 new 21-cm detections and stringent 21-cm optical depth upper limits (median 3-sigma optical depth per 10 km/s of 0.017) for the remaining 26 systems. This is by far the largest number of 21-cm detections from any single survey of intervening absorbers. Prior to our survey no intervening 21-cm system wa…
In 2006, Prochter et al. reported a statistically significant enhancement of very strong Mg II absorption systems intervening the sightlines to gamma-ray bursts (GRBs) relative to the in- cidence of such absorption along quasar sightlines. This counterintuitive result, has inspired a diverse set of astrophysical explanations (e.g. dust, gravitational lensing) but none of these has obviously resolved the puzzle. Using the largest set of GRB afterglow spectra available, we reexamine the purported enhancement. In an independent sample of GRB spectra with a survey path 3 times larger than Prochter…
We present the results of a recent (March 2011) 160 ks Chandra-LETGS observation of the Seyfert galaxy NGC 4593, and the analysis of archival X-ray and UV spectra taken with XMM-Newton and HST/STIS in 2002. We find evidence of a multi-component warm absorber (WA) in the X-rays with four distinct ionisation degrees (log xi = 1.0, log xi = 1.7, log xi = 2.4, and log xi = 3.0) outflowing at several hundreds of km/s. In the UV we detect 15 kinematic components in the absorbers, blueshifted with respect to the systemic velocity of the source, ranging from -60 km/s to -1520 km/s. Although the predic…
[Abridged] We present a detailed study of the largest sample of intervening O VI systems in the redshift range 1.9 < z < 3.1 detected in high resolution (R ~ 45,000) spectra of 18 bright QSOs observed with VLT/UVES. Based on Voigt profile and apparent optical depth analysis we find that (i) the Doppler parameters of the O VI absorption are usually broader than those of C IV (ii) the column density distribution of O VI is steeper than that of C IV (iii) line spread (δv) of the O VI and C IV are strongly correlated (at 5.3σlevel) with δv(O VI) being systematically larger than δv(C IV) and (iv) δ…
We present a catalog of intervening MgII quasar absorption-line systems in the redshift interval 0.36 <= z <= 2.28. The catalog was built from Sloan Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the catalog contains > 17,000 measured MgII doublets. We also present data on the ~44,600 quasar spectra which were searched to construct the catalog, including redshift and magnitude information, continuum-normalized spectra, and corresponding arrays of redshift-dependent minimum rest equivalent widths detectable at our confidence threshold. The catalog is available on the…
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, ma…
We present new far-ultraviolet spectra from the Cosmic Origins Spectrograph (HST/COS) of the BL Lac object 1ES1553+113 covering the wavelength range 1135-1795 A. The data show a smooth continuum with a wealth of narrow absorption features arising in the ISM and IGM. These features include 41 Lya absorbers at 0<z<0.43, fourteen of which are detected in multiple Lyman lines and six in one or more metal lines. We analyze a metal-rich triplet of Lya absorbers at z=0.188 in which OVI, NV, and CIII absorption is detected. Silicon ions (SiIII/IV) are not detected to fairly strong upper limits, and we…
We report on the observed properties of the plasma revealed through high signal-to-noise (S/N) observations of 54 intervening O VI absorption systems containing 85 O VI and 133 H I components in a blind survey of 14 QSOs observed at ~18 km s-1 resolution with the Cosmic Origins Spectrograph (COS) over a redshift path of 3.52 at z < 0.5. Simple systems with one or two H I components and one O VI component comprise 50% of the systems. For a sample of 45 well-aligned absorption components where the temperature can be estimated, we find evidence for cool photoionized gas in 31 (69%) and warm gas (…
(Abridged). We present a sample of 77 optical afterglows (OAs) of Swift detected GRBs for which spectroscopic follow-up observations have been secured. We provide linelists and equivalent widths for all detected lines redward of Ly-alpha. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray selected sample of Swift bursts with optimal conditions for ground-based follow up from the period March 2005 to September 2008; 146 bursts fulfill our sample criteria. We derive the redshift d…
We present an empirical connection between cold gas in galactic halos and star formation. Using a sample of more than 8,500 MgII absorbers from SDSS quasar spectra, we report the detection of a 15 sigma correlation between the rest equivalent width W0 of MgII absorbers and the associated OII luminosity, an estimator of star formation rate. This correlation has interesting implications: using only observable quantities we show that MgII absorbers trace a substantial fraction of the global OII luminosity density and recover the overall star formation history of the Universe derived from classica…
We present the catalogue of the Mg II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the twelfth data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars were searched for the presence of absorption systems in their spectra. The continuum modelling for the quasar spectra was performed using a mean filter. A pseudo-continuum derived using a median filter was used to trace the emission lines. The absorption system catalogue contains 39,694 Mg II systems detected at a 6.0, 3.0$σ$ level respecti…
We present a detailed analysis of the galaxy and group distributions around three reported X-ray absorption line systems in the spectrum of the quasar H2356-309. Previous studies associated these absorbers with known large-scale galaxy structures (i.e., walls and filaments) along the line of sight. Such absorption lines typically trace 10^{5-7} K gas, and may be evidence of the elusive warm-hot intergalactic medium (WHIM) thought to harbor the bulk of the low-redshift "missing baryons;" alternatively, they may be linked to individual galaxies or groups in the filaments. Here we combine existin…
