arXiv subjects

P. Noterdaeme

Publications and source records attributed to P. Noterdaeme.

At least 109 records · Page 6Linked to original sources

arXiv2011

Search for cold gas in z>2 damped Lyman-alpha systems: 21-cm and H_2 absorption

(Abridged) We present the results of a systematic GBT and GMRT survey for 21-cm absorption in a sample of 10 DLAs at 2 2 is predominantly constituted by WNM. The detection rate of 21-cm absorption seems to be higher for systems with higher N(HI) or metallicity. However, no clear correlation is found between the integrated 21-cm optical depth (or spin temperature) and either N(HI), metallicity or velocity spread of the low ionization species. There are 13 DLAs in our sample for which high resolution optical spectra covering the expected wavelength range of H_2 absorption are available. We report the detection of H_2 molecules in the z_abs = 3.3871 21-cm absorber towards J0203+1134 (PKS 0201+113). In 8 cases, neither H_2 nor 21-cm absorption are detected. The lack of 21-cm and H_2 absorption in these systems can be explained if most of the HI in these DLAs originate from low density high temperature gas. In one case we have a DLA with 21-cm absorption not showing H_2 absorption. In two cases, both species are detected but do not originate from the same velocity component. In the remaining 2 cases 21-cm absorption is not detected despite the presence of H_2 with evidence for the presence of cold gas. All this is consistent with the idea that the H_2 components seen in DLAs are compact (with sizes of < 15 pc) and contain only a small fraction (i.e typically <10%) of the total N(HI) measured in the DLAs.

astro-ph.CO↗

arXiv2011

Partial coverage of the Broad Line Region of Q1232+082 by an intervening H2-bearing cloud

We present a detailed analysis of the partial coverage of the Q1232+082 (z_em =2.57) broad line region by an intervening H_2-bearing cloud at z_abs=2.3377. Using curve of growth analysis and line profile fitting, we demonstrate that the H_2-bearing component of the cloud covers the QSO intrinsic continuum source completely but only part of the Broad Line Region (BLR). We find that only 48\pm6 % of the C IV BLR emission is covered by the C I absorbing gas. We observe residual light (~6 %) as well in the bottom of the O I λ1302 absorption from the cloud, redshifted on top of the QSO Lyman-α emission line. Therefore the extent of the neutral phase of the absorbing cloud is not large enough to cover all of the background source. The most likely explanation for this partial coverage is the small size of the intervening cloud, which is comparable to the BLR size. We estimate the number densities in the cloud: n_H2~110 cm^{-3} for the H_2-bearing core and n_H ~30 cm^{-3} for the neutral envelope. Given the column densities, N(H2)=(3.71\pm0.97)\times10^19 cm^{-2} and N(H I)=(7.94\pm1.6)\times10^20 cm^{-2}, we derive the linear size of the H_2-bearing core and the neutral envelope along the line of sight to be l_H2~0.15^{+0.05}_{-0.05} pc and l_HI~8.2^{+6.5}_{-4.1} pc, respectively. We estimate the size of the C IV BLR by two ways (i) extrapolating size-luminosity relations derived from reverberation observations and (ii) assuming that the H_2-bearing core and the BLR are spherical in shape and the results are ~0.26 and ~0.18 pc, respectively. The large size we derive for the extent of the neutral phase of the absorbing cloud together with a covering factor of ~0.94 of the Lyman-α emission means that the Lyman-α BLR is probably fully covered but that the Lyman-α emission extends well beyond the limits of the BLR.

astro-ph.CO↗

arXiv2011

Galaxy counterparts of metal-rich damped Lyman-alpha absorbers - II. A solar-metallicity and dusty DLA at z_abs=2.58

[Abridged]. Here, we report on the discovery of the galaxy counterpart of the z_abs=2.58 DLA on the line-of-sight to the z=3.07 quasar SDSS J091826.16+163609.0. The galaxy counterpart of the DLA is detected in the OIII 5007 and OII 3726,3729 emission lines redshifted into the NIR at an impact parameter of 16 kpc. Ly-alpha emission is not detected. The upper limit implies that Ly-alpha emission from this galaxy is suppressed by more than an order of magnitude. The DLA is amongst the most metal-rich DLAs studied so far at comparable redshifts. We find evidence for substantial depletion of refractory elements onto dust grains. Fitting the main metal line component of the DLA, which is located at z_abs=2.5832 and accounts for at least 85% of the total column density of low-ionisation species, we measure metal abundances from ZnII, SII, SiII, CrII, MnII, FeII and NiII of -0.12, -0.26, -0.46, -0.88, -0.92, -1.03 and -0.78, respectively. In addition, we detect absorption in the Lyman and Werner bands of hydrogen, which represents the first detection of H_2 molecules with X-shooter. The background quasar Q0918+1636 is amongst the reddest QSOs at redshifts 3.02<z<3.12 from the SDSS catalogue. Its UV to NIR spectrum is well fitted by a composite QSO spectrum reddened by SMC/LMC-like extinction curves at z_abs=2.58 with a significant amount of extinction given by A_V = 0.2 mag. This supports previous claims that there may be more metal-rich DLAs missing from current samples due to dust reddening of the background QSOs. The fact that there is evidence for dust both in the central emitting regions of the galaxy (as evidenced by the lack of Ly-alpha emission) and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust is widespread in this system.

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arXiv2010

The evolution of the Cosmic Microwave Background Temperature: Measurements of TCMB at high redshift from carbon monoxide excitation

A milestone of modern cosmology was the prediction and serendipitous discovery of the Cosmic Microwave Background (CMB), the radiation left over after decoupling from matter in the early evolutionary stages of the Universe. A prediction of the standard hot Big-Bang model is the linear increase with redshift of the black-body temperature of the CMB (TCMB). This radiation excites the rotational levels of some interstellar molecules, including carbon monoxide (CO), which can serve as cosmic thermometers. Using three new and two previously reported CO absorption-line systems detected in quasar spectra during a systematic survey carried out using VLT/UVES, we constrain the evolution of TCMB to z~3. Combining our precise measurements with previous constraints, we obtain TCMB(z)=(2.725+/-0.002)x(1+z)^(1-beta) K with beta=-0.007+/-0.027, a more than two-fold improvement in precision. The measurements are consistent with the standard (i.e. adiabatic, beta=0) Big-Bang model and provide a strong constraint on the effective equation of state of decaying dark energy (i.e. w_eff=-0.996+/-0.025).

astro-ph.CO↗

arXiv2010

The Lyman-alpha emission of high-z damped Lyman-alpha systems

Using a spectral stacking technique we searched for the average \lya emission from high-z Damped \lya (DLA) galaxies detected in the Sloan Digital Sky Survey QSO spectra. We used a sample of 341 DLAs of mean redshift = 2.86 and log N(HI) > 20.62 to place a 3$σ$ upper limit of 3.0 \times 10^{-18} erg s^{-1} cm^{-2} on the \lya flux emitted within $\sim$1.5 arcsec (or 12 kpc) from the QSO line of sight. This corresponds to an average \lya luminosity of < 2 \times 10^{41} erg s^{-1} or 0.03 $L_\star$(\lya). This limit is deeper than the limit of most surveys for faint \lya emitters. The lack of \lya emission in DLAs is consistent with the in situ star formation, for a given N(HI), being less efficient than what is seen in local galaxies. Thus, the overall DLA population seems to originate from the low luminosity end of the high redshift \lya emitting galaxies and/or to be located far away from the star forming regions. The latter may well be true since we detect strong OVI absorption in the stacked spectrum, indicating that DLAs are associated with a highly ionized phase possibly the relics of galactic winds and/or originating from cold accretion flows. We find the contribution of DLA galaxies to the global star formation rate density to be comparatively lower than that of Lyman Break Galaxies.

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arXiv2010

A translucent interstellar cloud at z=2.69: CO, H2 and HD in the line-of-sight to SDSS J123714.60+064759.5

We present the analysis of a sub-DLA system (log N(H^0)=20.0+/-0.15, z_abs=2.69) toward SDSS J123714+064759 (z_em=2.78). Using the VLT/UVES and X-shooter spectrographs, we detect H2, HD and CO molecules in absorption with log N(H2,HD,CO)=(19.21,14.48,14.17). The overall metallicity of the system is super-solar ([Zn/H]=+0.34) and iron is highly depleted ([Fe/Zn]=-1.39), revealing metal-rich and dusty gas. The strongest H2 component does not coincide with the centre of the HI absorption. This implies that the molecular fraction in this component, f=2N(H2)/(2N(H2)+N(H^0)), is larger than the mean molecular fraction =1/4 in the system. This is supported by the detection of Cl^0 associated with this H2-component having N(Cl^0)/N(Cl^+)>0.4. Since Cl^0 is tied up to H2 by charge exchange reactions, this means that the molecular fraction in this component is not far from unity. The size of the molecular cloud is probably smaller than 1pc. Both the CO/H2=10^-5 and CO/C^0~1 ratios for f>0.24 indicate that the cloud classifies as translucent, i.e., a regime where carbon is found both in atomic and molecular form. The corresponding extinction, Av=0.14, albeit lower than the definition of a translucent sightline (based on extinction properties), is high for the observed H^0 column density. This means that intervening clouds with similar local properties but with larger column densities could be missed by current magnitude-limited QSO surveys. The excitation of CO is dominated by radiative interaction with the Cosmic Microwave Background Radiation (CMBR) and we derive Tex(CO)=10.5+0.8-0.6 K when TCMBR(z=2.69)=10.05 K is expected. The astration factor of deuterium -with respect to the primordial D/H ratio- is only about 3. This can be the consequence of accretion of unprocessed gas from the intergalactic medium onto the associated galaxy. [abridged]

astro-ph.CO↗

arXiv2010

Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946

We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyman-alpha absorbers (DLAs). The spectral coverage of X-shooter allows us to search for not only Lyman-alpha emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII], Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946. This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and -0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII] lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8 arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to the recently determined Halpha luminosity function for z=2.2 galaxies the DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA is consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.

astro-ph.CO↗

arXiv2010

Detection of 21-cm, H2 and Deuterium absorption at z>3 along the line-of-sight to J1337+3152

We report the detection of 21-cm and H2 absorption lines in the same DLA system (log N(HI)=21.36+-0.10) at zabs=3.17447 towards SDSSJ133724+315254 (z=3.174). We estimate the spin temperature of the gas to be, Ts~600 K, intermediate between the expected values for cold and warm neutral media. This suggests that the HI absorption originates from a mixture of different phases. The total molecular fraction is low, f=10^-7, and H2 rotational level populations are not in equilibrium. The average abundance of the alpha-elements is, [S/H]=-1.45. N and Fe are found underabundant with respect to alpha-elements by ~1.0 dex and ~0.5 dex respectively. Using photoionization models we conclude that the gas is located more than 270 kpc away from the QSO. While the position of 21-cm absorption line coincides with the H2 velocity profile, their centroid are shifted by 2.7+-1.0 km/s from each other. However, the position of the strongest metal absorption component matches the position of the 21-cm absorption line within 0.5 km/s. From this, we constrain the variation of the combination of fundamental constants x=alpha^2 Gp/mu, Delta x/x=-(1.7+-1.7)x10^-6. This system is unique as we can at the same time have an independent constrain on mu using H2 lines. However only Werner band absorption lines are seen and the range of sensitivity coefficients is too narrow to provide a stringent constraint: Delta mu/mu <= 4.0x10^-4. The VLT/UVES spectrum reveals another DLA at zabs=3.16768 with log N(HI)=20.41+-0.15 and low metallicity, [Si/H]=-2.68+-0.11. We derive log N(DI)/N(HI)=-(4.93+-0.15) in this system. This is a factor of two smaller than the value expected from the best fitted value of Omega_b from the WMAP 5 yr data. This confirms the presence of astration of deuterium even at very low metallicity. [abridged]

astro-ph.CO↗

arXiv2010

HD molecules at high redshift: The absorption system at z=2.3377 towards Q 1232+082

We present a detailed analysis of the H_2 and HD absorption lines detected in the Damped Lyman-alpha (DLA) system at z_abs=2.3377 towards the quasar Q1232+082. We show that this intervening cloud has a covering factor smaller than unity and covers only part of the QSO broad emission line region. The zero flux level has to be corrected at the position of the saturated H_2 and optically thin HD lines by about 10%. We accurately determine the Doppler parameter for HD and CI lines (b = 1.86+/-0.20 km/s). We find a ratio N(HD)/N(H_2)=(7.1 +3.7 -2.2)x10^-5 that is significantly higher than what is observed in molecular clouds of the Galaxy. Chemical models suggest that in the physical conditions prevailing in the central part of molecular clouds, deuterium and hydrogen are mostly in their molecular forms. Assuming this is true, we derive D/H = (3.6 +1.9 -1.1)x10^-5. This implies that the corresponding baryon density of the Universe is Ω_b h^2 = (0.0182 +0.0047 -0.0042). This value coincides within 1σwith that derived from observations of the CMBR as well as from observations of the D/H atomic ratio in low-metallicity QSO absorption line systems. The observation of HD at high redshift is therefore a promising independent method to constrain Ω_b. This observation indicates as well a low astration factor of deuterium. This can be interpreted as the consequence of an intense infall of primordial gas onto the associated galaxy.

astro-ph.CO↗

arXiv2009

Quasars probing intermediate redshift star-forming galaxies

We present a sample of 46 [OIII]-emitting galaxies at z<0.8 detected in the fibre spectra of quasars from the SDSS-DR7 through an automatic search procedure. We also detect [OII] and Hb emission lines from most of these galaxies in the SDSS spectra. We study both the emission and absorption properties of a sub-sample of 17 galaxies in the redshift range z=0.4-0.7, where MgII lines are covered by the SDSS spectra. The measured lower-limits on the star-formation rates of these galaxies are in the range 0.2-20 M_sun/yr. The emission line luminosities and (O/H) metallicities from R23 measured in this sample are similar to what is found in normal galaxies at these redshifts. Thus, this constitutes a unique sample of intermediate redshift star-forming galaxies where we can study the QSO absorber - galaxy connection. Strong MgII (W>1A) as well as MgI absorption lines are detected in the QSO spectra at the redshift of most of these galaxies. Strong FeII (W>1A) absorption lines are also generally detected whenever the appropriate wavelength ranges are covered. This suggests that most of these systems could be bona-fide Damped Lyman-alpha systems. We investigate various possible relations between the MgII rest equivalent widths and the emission line properties. We find a possible (2 sigma) correlation between the emission-line metallicity of the galaxies and the MgII rest equivalent width of the absorbers [truncated].

astro-ph.CO↗

arXiv2009

SDSS J092712.64+294344.0: recoiling black hole or merging galaxies?

We report long-slit spectroscopic observations of SDSS J092712+294344 carried-out at the recently commissioned 2m telescope in IUCAA Girawali Observatory, India. This AGN-like source is known to feature three sets of emission lines at zem = 0.6972, 0.7020 and 0.7128. Different scenarios such as a recoiling black hole after asymmetric emission of gravitational waves, binary black holes and possible merging systems are proposed for this object. We test these scenarios by comparing our spectra with that from the Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [OIII]4960,5008 we put a 3 sigma limit on the relative acceleration to be less than 32 km s^-1 yr^-1 between different emitting regions. Using the 2D spectra obtained at different position angles we show that the [OIII]5008 line from the zem = 0.7128 component is extended beyond the spectral point spread function. We infer the linear extent of this line emitting region is ~8 kpc. We also find a tentative evidence for an offset between the centroid of the [OIII]5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299 degrees. This corresponds to the zem = 0.7128 system being at an impact parameter of ~1 kpc with respect to the zem = 0.6972 in the north west direction. Based on our observations we conclude that the binary black hole model is most unlikely. The spatial extent and the sizes are consistent with both black hole recoil and merging scenarios.

astro-ph.CO↗

arXiv2009

Uncovering strong MgII absorbing galaxies: Imaging below the Lyman limit

The nature of the galaxies that give rise to absorption lines, such as damped Lyman-alpha systems (DLAs) or strong MgII lines, in quasar spectra is difficult to investigate in emission. Taking advantage of the total absorption of the QSO light bluewards of the Lyman limit of two DLAs at z>3.4, we look for the continuum emission from intervening galaxies at z~2 that are identified via strong metal absorption lines. The MgII absorbers have equivalent width large enough to be potential DLA systems. Deep images are obtained with the FOcal Reducer and Spectrograph (FORS1) on the Very Large Telescope for the fields towards SDSS J110855+120953 and SDSS J140850+020522. These quasars have MgII absorption lines at z=1.87 (W_r(MgII)=2.46 A) and z=1.98 (W_r(MgII)=1.89 A), respectively, and each QSO has two intervening higher redshift DLAs at z>3. The U and R bands of FORS1 lie blue and redwards of the Lyman limit of the background DLAs, allowing us to search for emission from the foreground galaxies directly along the lines of sight to the QSOs. No galaxies are found close to the sight line of the QSO to a point source limit of U_AB=28.0. In both fields, the closest objects lie at an impact parameter of 5 arcsec corresponding to 40 kpc in projection at z=2, and have typical colours of star forming galaxies at that redshift. However, the currently available data do not allow us to confirm if the galaxies lie at the same redshifts as the absorption systems. A more extended structure is visible in the SDSS J14085+020522 field at an impact parameter of 0.8 arcsec or 7 kpc. If these objects are at z~2 their luminosities are 0.03-0.04 L* in both fields. The star formation rates estimated from the UV flux are 0.5-0.6 M_sun yr^-1. (Abbreviated).

astro-ph.CO↗

arXiv2009

Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7

We present the results of a search for damped Lyman-alpha (DLA) systems in the Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fully automatic procedure to identify DLAs and derive their column densities. The procedure is checked against the results of previous searches for DLAs in SDSS. We discuss the agreements and differences and show the robustness of our procedure. For each system, we obtain an accurate measurement of the absorber's redshift, the HI column density and the equivalent width of associated metal absorption lines, without any human intervention. We find 1426 absorbers with 2.15 < z < 5.2 with log N(HI)>=20, out of which 937 systems have log N(HI)>= 20.3. This is the largest DLA sample ever built, made available to the scientific community through the electronic version of this paper. In the course of the survey, we discovered the intervening DLA with highest HI column density known to date with log N(HI)=22.0+/-0.1. This single system provides a strong constraint on the high-end of the N(HI) frequency distribution now measured with high accuracy. We show that the presence of a DLA at the blue end of a QSO spectrum can lead to important systematic errors and propose a method to avoid them. This has important consequences for the measurement of the cosmological mass density of neutral gas at z~2.2 and therefore on our understanding of galaxy evolution over the past 10 billion years. [truncated]

astro-ph.CO↗

arXiv2009

Diffuse molecular gas at high redshift: Detection of CO molecules and the 2175 Å dust feature at z=1.64

We present the detection of carbon monoxide molecules (CO) at z=1.6408 towards the quasar SDSSJ160457.50+220300.5 using the VLT Ultraviolet and Visual Echelle Spectrograph. CO absorption is detected in at least two components in the first six A-X bands and one d-X(5-0) inter-band system. This is the second detection of this kind along a quasar line of sight. The CO absorption profiles are well modelled assuming a rotational excitation of CO in the range 6<Tex<16 K, which is consistent with or higher than the temperature of the CMB radiation at this redshift. We derive a total CO column density of N(CO)=4e14 cm^-2. The measured column densities of SI, MgI, ZnII, FeII and SiII indicate a dust depletion pattern typical of cold gas in the Galactic disc. The background quasar spectrum is significantly reddened (u-K~4.5 mag) and presents a pronounced 2175 A dust absorption feature at the redshift of the CO absorber. Using a control sample of ~500 quasars we find the chance probability for this feature to be spurious is ~0.3%. We show that the SED of the quasar is well fitted with a QSO composite spectrum reddened with a LMC supershell extinction law at the redshift of the absorber. It is noticeable that this quasar is absent from the colour-selected SDSS quasar sample. This demonstrates our current view of the Universe may be biased against dusty sightlines. These direct observations of carbonaceous molecules and dust open up the possibility of studying physical conditions and chemistry of diffuse molecular gas in high redshift galaxies.

astro-ph.CO↗

arXiv2009

A complete sample of 21-cm absorbers at z~1.3: Giant Metrewave Radio Telescope Survey Using MgII Systems

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 was known in the above redshift range and only one system was known in the redshift range 0.7 0.3, then a detection rate of 21-cm absorption up to 90% can be achieved. We estimate n_{21}, the number per unit redshift of 21-cm absorbers with W_r(Mg(II)>W_o and integrated optical depth Tau_{21}>Tau_o and show that n_{21} decreases with increasing redshift. In particular, for W_o=1.0 Åand Tau_o>0.3 km\s, n_{21} falls by a factor 4 from =0.5 to =1.3. The evolution seems to be stronger for stronger MgII systems. Using a subsample of systems for which high frequency VLBA images are available, we show that the effect is not related to the structure of the background radio sources and is most probably due to the evolution of the cold neutral medium filling factor in MgII systems. We find no correlation between the velocity spread of the 21-cm absorption feature and W_r(MgII) at z~1.3.

astro-ph.CO↗

arXiv2009

21-cm absorbers at intermediate redshifts

Damped Lyman-alpha systems (DLAs) seen in the spectra of high-z QSOs allow us to probe the physical conditions in protogalaxies. Our understanding of physical conditions in DLAs at high-z is primarily based on the absorption lines of H_2 molecules and fine-structure transitions. Another important way of probing the thermal state of interstellar medium in these systems is by studying the 21-cm absorption in the spectra of background quasars. Here we report the main results of our GMRT survey to search for 21-cm absorption in a representative and unbiased sample of 35 DLA candidates at 1.10<z<1.45. Our sample of DLA candidates is drawn from the strong MgII systems in SDSS DR5 and has resulted in discovery of 9 new 21-cm absorbers. Prior to our survey only one 21-cm absorber was known in the redshift range: 0.7<z<2. This survey has allowed us to investigate the dependence of detectability of 21-cm absorption on the properties of UV absorption lines detected in SDSS spectra and estimate the number per unit redshift of 21-cm absorbers. Our GMRT survey provides a representative sample of systems that can be used in combination with various follow-up observations: (1) for investigating the physical conditions in the absorbing gas using spin temperature measurements, (2) for investigating the effect of metallicity and dust content on the detectability of 21-cm absorption, (3) for studying the morphology of the absorbing gas and (4) for probing the time evolution of various fundamental constants. Results from the first phase of our survey are presented in Gupta et al. (2007). Detailed description of the entire sample and results from the survey are presented in Gupta et al. (2009).

astro-ph.CO↗

arXiv2008

HD molecules at high redshift: A low astration factor of deuterium in a solar-metallicity DLA system at z=2.418

We present the detection of deuterated molecular hydrogen (HD) in the remote Universe in a damped Lyman-alpha cloud at zabs=2.418 toward the quasar SDSS J143912.04+111740.5. This is a unique system in which H2 and CO molecules are also detected. The chemical enrichment of this gas derived from ZnII and SII is as high as in the Sun. We measure N(HD)/2 N(H2)=1.5+0.6-0.4 x 10^-5, which is significantly higher than the same ratio measured in the Galaxy and close to the primordial D/H ratio estimated from the WMAP constraint on the baryonic matter density Omega_b. This indicates a low astration factor of deuterium that contrasts with the unusually high chemical enrichment of the gas. This can be interpreted as the consequence of an intense infall of primordial gas onto the associated galaxy. Detection of HD molecules at high-z also opens the possibility to obtain an independent constraint on the cosmological-time variability of mu, the proton-to-electron mass ratio.

astro-ph↗

arXiv2008

Detection of the 2175Å~ extinction feature and 21-cm absorption in two MgII systems at z~1.3

We have discovered two dusty intervening MgII absorption systems at z~1.3 in the Sloan Digital Sky Survey (SDSS) database. The overall spectra of both QSOs are red (u-K>4.5 mag) and are well modelled by the composite QSO spectrum reddened by the extinction curve from the Large Magellanic Cloud (LMC2) Supershell redshifted to the rest-frame of the MgII systems. In particular, we detect clearly the presence of the UV extinction bump at $λ_{\rm rest}\sim 2175$~Å. Absorption lines of weak transitions like SiII$λ$1808, CrII$λ$2056, CrII+ZnII$λ$2062, MnII$λ$2594, CaII$λ$3934 and TiII$λ$1910 from these systems are detected even in the low signal-to-noise ratio and low resolution SDSS spectra, suggesting high column densities of these species. The depletion pattern inferred from these absorption lines is consistent with that seen in the cold neutral medium of the LMC. Using the LMC A_V vs. N(HI) relationship we derive N(HI)~$6\times 10^{21}$ cm$^{-2}$ in both systems. Metallicities are close to solar. Giant Metrewave Radio Telescope (GMRT) observations of these two relatively weak radio loud QSOs (f$_ν$~50mJy) resulted in the detection of 21-cm absorption in both cases. We show that the spin temperature of the gas is of the order of or smaller than 500K. These systems provide a unique opportunity to search for molecules and diffuse interstellar bands at z>1.

astro-ph↗