2008 (IPP)
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Item Molecular hydrogen in high-redshift damped lyman-alpha systems: the VLT/UVES database(2008-02) Noterdaeme, P.; Srianand, R.Aims. We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 < zabs ≤ 4.2) Damped Lyman-α systems (DLAs) capitalising on observations performed with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). Methods. We identify 77 DLAs/strong sub-DLAs, with log N(Hi) ≥ 20 and zabs > 1.8, which have data that include redshifted H2 Lyman and/or Werner-band absorption lines. This sample of Hi, H2 and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) considering every system in which searches for H2 could be completed so far, including all non-detections. Results. H2 is detected in thirteen of the systems, which have molecular fractions of values between f ≃ 5 × 10−7 and f ≃ 0.1, where f = N(H2)/(2N(H2) + N(Hi)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N(H2) ∼ 14.3, corresponding to log f < −5. We find that about 35% of the DLAs with metallicities relative to solar [X/H] ≥ −1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f > −4.5, while H2 is detected – regardless of the molecular fraction – in ∼ 50% of them. In contrast, only about 4% of the [X/H] < −1.3 DLAs have log f > −4.5. We show that the presence of H2 does not strongly depend on the total neutral hydrogen column density, although the probability of finding log f > −4.5 is higher for log N(Hi) ≥ 20.8 than below this limit (19% and 7% respectively). The overall H2 detection rate in log N(Hi) ≥ 20 DLAs is found to be about 16% (10% considering only log f > −4.5 detections) after correction for a slight bias towards large N(Hi). There is a strong preference for H2-bearing DLAs to have significant depletion factors, [X/Fe] > 0.4. In addition, all H2-bearing DLAs have column densities of iron into dust grains larger than log N(Fe)dust ∼ 14.7, and about 40% of the DLAs above this limit have detected H2 lines with log f > −4.5. This demonstrates the importance of dust in governing the detectability of H2 in DLAs. Our extended sample supports neither the redshift evolution of the detection fraction of H2-bearing DLAs nor that of the molecular fraction in systems with H2 detections over the redshift range 1.8 < zabs ≤ 3.Item HD molecules at high redshift: A low astration factor of deuterium in a solar-metallicity DLA system at z=2.418(2008-08) Noterdaeme, P.; Srianand, R.We present the detection of deuterated molecular hydrogen (HD) in the remote Universe in a damped Lyman-α 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 Zn ii and S ii is as high as in the Sun. We measure N(HD)/2N(H2) = 1.5+0.6 −0.4 × 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 (Ωb). 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 , the proton-to-electron mass ratio.Item First detection of CO in a high-redshift damped Lyman - Alpha system(2008-04) Srianand, R.We present the first detection of carbon monoxide (CO) in a damped Lyman-α system (DLA) at zabs =2.41837 toward SDSS J143912.04+111740.5. We also detected H2 and HD molecules. The measured total column densities (in log units) of H i, H2, and CO are 20.10±0.10, 19.38±0.10, and 13.89±0.02, respectively. The molecular fraction, f = 2N(H2)/(N(H i)+2N(H2)) = 0.27+0.10 −0.08, is the highest among all known DLAs. The abundances relative to solar of S, Zn, Si, and Fe are −0.03±0.12, +0.16±0.11, −0.86±0.11, and −1.32±0.11, respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the cold ISM of our Galaxy. The measured N(CO)/N(H2) = 3×10−6 is much less than the conventional CO/H2 ratio used to convert the CO emission into gaseous mass but is consistent with what is measured along translucent sightlines in the Galaxy. The CO rotational excitation temperatures are higher than those measured in our Galactic ISM for similar kinetic temperature and density. Using the C i fine structure absorption lines, we show that this is a consequence of the excitation being dominated by radiative pumping by the cosmic microwave background radiation (CMBR). From the CO excitation temperatures, we derive TCMBR = 9.15±0.72 K, while 9.315±0.007 K is expected from the hot big-bang theory. This is the most precise high-redshift measurement of TCMBR and the first confirmation of the theory using molecular transitions at high redshift.Item Detection of the 2175\AA~ extinction feature and 21-cm absorption in two MgII systems at z~1.3(2008-09) Srianand, R.We have discovered two dusty intervening Mg ii 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 Mg ii systems. In particular, we detect clearly the presence of the UV extinction bump at λrest ∼ 2175 ˚ A. Absorption lines of weak transitions like Si iiλ1808, Cr iiλ2056, Cr ii+Zn iiλ2062, Mn iiλ2594, Ca iiλ3934 and Ti iiλ1910 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 AV vs. N(H i) relationship we derive N(H i)∼ 6×1021 cm−2 in both systems. Metallicities are close to solar. Giant Metrewave Radio Telescope (GMRT) observations of these two relatively weak radio loud QSOs (fν ∼ 50 mJy) 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 500 K. These systems provide a unique opportunity to search for molecules and diffuse interstellar bands at z > 1.Item Constrained semi-analytical models of Galactic outflows(2008-01) Samui, Saumyadip; Subramanian, Kandaswamy; Srianand, R.We present semi-analytic models of galactic outflows that are constrained by available ob- servations on high redshift star formation and reionization. Galactic outflows are modeled in a manner akin to models of stellar wind blown bubbles. Large scale outflows can generically escape from low mass halos (M . 109 M ) for a wide range of model parameters while this is not the case in high mass halos (M & 1011 M ). The flow generically accelerates within the halo virial radius, then starts to decelerate, and traverses well into the intergalactic medium (IGM), before freezing to the Hubble flow. The acceleration phase can result in shell fragmentation due to the Rayleigh-Taylor instability, although the final outflow radius is not significantly altered. The gas phase metallicity of the outflow and within the galaxy are computed assuming uniform instantaneous mixing. Ionization states of different metal species are calculated and used to examine the detectability of metal lines from the outflows. The global influence of galactic outflows is also investigated using porosity weighted averages and probability density functions of various physical quantities. Models with only atomic cooled halos significantly fill the IGM at z 3 with metals (with 2:5 & [Z=Z ] & 3:7), the actual extent depending on the efficiency of winds, the initial mass function (IMF) and the fractional mass that goes through star formation. The reionization history has a significant effect on the volume filling factor, due to radiative feedback. In these models, a large fraction of outflows at z 3 are supersonic, hot (T 105K) and have low density, making metal lines difficult to detect. They may also result in significant perturbations in the IGM gas on scales probed by the Lyman- forest. On the contrary, models including molecular cooled halos with a normal mode of star formation can potentially volume fill the universe at z 8 without drastic dynamic effects on the IGM, thereby setting up a possible metallicity floor ( 4:0 [Z=Z ] 3:6). The order unity fluctuations at z 8 that becomes the mildly non-linear fluctuations traced by Lyman- forest at z < 4 will then have this metallicity. Interestingly, molecular cooled halos with a “top-heavy” mode of star formation are not very successful in establishing the metallicity floor because of the additional radiative feedback, that they induce.