2009 (IPP)
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Item Uncovering strong MgII absorbing galaxies: Imaging below the Lyman limit(2009-08-01) Christensen, L.; Petitjean, Patrick; Ledoux, C.Context. The nature of the galaxies that give rise to absorption lines, such as damped Lyman-α systems (DLAs) or strong Mg ii lines, in quasar spectra is difficult to investigate in emission. These galaxies can be very faint and located close to the lines of sight of the much brighter background quasars. Aims. 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 Mg ii absorbers have equivalent width large enough to be potential DLA systems. Methods. 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 Mg ii absorption lines at z = 1.87 (Wr(Mg ii) = 2.46 Å) and z = 1.98 (Wr(Mg ii) = 1.89 Å), 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. Results. No galaxies are found close to the sight line of the QSO to a point source limit of UAB ∼ 28.0. In both fields, the closest objects lie at an impact parameter of ∼5′′ 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 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⊙ yr −1 , while the SFRs are half these values if the U band flux is due to Lyα emission alone. Conclusions. The non-detection of galaxies near to the line of sight is most likely explained by low metallicities and luminosities of the Mg ii galaxies. Alternatively, the Mg ii clouds are part of extended halos or in outflows from low-metallicity galaxies.Item Optical identification of XMM sources in the CFHTLS(2009-05-01) Stalin, C. S.; Petitjean, Patrick; Srianand, R.; et al.We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5 1.5 10 5 at the 3 level over a redshift range of approximately 0:5 2:5 for the fine-structure constant, , the proton-to-electron mass ratio, and a combination of the proton gyromagnetic factor and the two previous constants, gp( 2= ) , for only one claimed variation of . It is therefore very important to perform new measurements to improve the sensitivity of the numerous methods to at least <0.1 10 5 which should be possible in the next few years. Future instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders in the radio will undoutedly boost this field by allowing to reach much better signal-to-noise ratios at higher spectral resolution and to perform measurements on molecules in the ISM of high redshift galaxiItem Damped and sub-damped Lyman-alpha absorbers in z > 4 QSOs(2009-10-01) Guimaraes, R.; Petitjean, PatrickWe present the results of a survey for damped (DLA, log N(H i) > 20.3) and sub-damped Lyman-α systems (19.5 < log N(H i) < 20.3) at z > 2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4 < zem < 6.3. Intermediate resolution (R ∼ 4300) spectra have been obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with log N(H i) > 19.5 are detected of which 40 systems are damped Lyman-α systems for an absorption length of ∆X = 378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs.We study the evolution with redshift of the cosmological density of the neutral gas and find, consistently with previous studies at similar resolution, that ΩDLA,HI decreases at z > 3.5. The overall cosmological evolution of ΩHI shows a peak around this redshift. The H i column density distribution for log N(H i) ≥ 20.3 is fitted, consistently with previous surveys, with a single power-law of index α ∼ -1.8±0.25. This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower H i column densities with an index of α ∼ −1.4 for the column density range log N(H i) = 19.5−21. The fraction of H i mass in sub-DLAs is of the order of 30%. The H i column density distribution does not evolve strongly from z ∼ 2.5 to z ∼ 4.5.Item Constraining fundamental constants of physics with quasar absorption line systems(2009-08-01) Petitjean, Patrick; Vivek, M.; Mohan, V.; et al.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 fromthe Sloan Digital Sky Survey (SDSS), obtained 4 years prior to our observations. Comparing the redshifts of [Oiii]λλ4960,5008 we put a 3σ 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]λ5008 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]λ5008 line at zem = 0.7128 and the QSO trace when the slit is aligned at a position angle of 299◦ . 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 scenariosItem Complete sample of 21-cm absorbers at z ~ 1.3: Giant Metrewave Radio Telescope Survey Using Mg II Systems(2009-04-01) Gupta, N.; Srianand, R.; Petitjean, Patrick; et al.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 Mg ii systems in the redshift range: zabs∼1.10−1.45, 33 of which have Wr ≥1˚ A. The survey using ∼400 hrs of telescope time has resulted in 9 new 21-cm detections and stringent 21-cm optical depth upper limits (median 3σ optical depth per 10 kms−1 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 ≤ z ≤ 1.5. We discuss the relation between the detectability of 21-cm absorption and various properties of UV absorption lines. We show that if Mg ii systems are selected with the following criteria, Mg ii doublet ratio ≤1.3 and Wr(Mg i)/Wr(Mg ii) ≥ 0.3, then a detection rate of 21-cm absorption up to 90% can be achieved. We estimate n21, the number per unit redshift of 21-cm absorbers with Wr(Mg ii) > Wo and integrated optical depth T21 > To and show that n21 decreases with increasing redshift. In particular, for Wo = 1.0 ˚ A and To > 0.3 km s−1, n21 falls by a factor 4 from < z > = 0.5 to < z > = 1.3. The evolution seems to be stronger for stronger Mg ii 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 Mg ii systems. We find no correlation between the velocity spread of the 21-cm absorption feature and Wr(Mg ii) at z ∼ 1.3Item 21-cm absorbers at intermediate redshifts(2009-02-01) Gupta, N.; Srianand, R.; Petitjean, Patrick; et al.Damped Lyman-α 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 H2 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 Mg ii 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 (TS) 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).