arXiv subjects

C. Peroux

Publications and source records attributed to C. Peroux.

32 records · Page 2Linked to original sources

arXiv2010

VLT LBG Redshift Survey II: Interactions between galaxies and the IGM at z ~3

We have measured redshifts for 243 z ~3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Lya forest and 1020 Lyman-break galaxies at z ~3. We find an increase in neutral hydrogen absorption within 5 h^-1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Lya-LBG cross-correlation can be described by a power-law on scales larger than 3 h^-1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (<2 h^-1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We find that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Lya absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 CIV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h^-1 Mpc consistent with the relation measured at ~Mpc scales.

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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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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 missing metals problem: I. How many metals are in submm galaxies?

We use a sample of submillimetre-selected galaxies (SMGs) with molecular gas and dynamical mass measurements from the literature to put constraints on the contribution of such galaxies to the total metal budget. Compared to Lyman break galaxies (LBGs), for example, SMGs are rarer (by a factor of 10 or more), but contain much more gas and are more metal rich. We estimate that SMGs brighter than 3 mJy contain only less than 9% of the metals when we combine the observed dynamical masses (few$\times 10^{11}$ \msun), number density ($n\simeq 10^{-4}$ Mpc$^{-3}$), observed gas metallicity (1--2 x solar), and observed gas fractions (~40%) assuming a molecular to neutral hydrogen ratio of 1. Including SMGs fainter than 3 mJy, we estimate that SMGs contain at the most 15% of the metals, where our incompleteness correction is estimated from the dust mass function. Our results are strong upper limits given that high gas fractions and high overall metallicity are mutually exclusive. In summary, SMGs make a significant contribution to the metal budget (< 15%) but not sufficient to solve the `missing metals problem.' A consequence of our results is that SMGs can only add $\approx 3.5$% to $Ω_{\rm DLA}$, and can not be the source of a significant population of dusty DLAs.

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arXiv2006

The missing metals problem: II. How many metals are in z ~ 2.2 galaxies?

In the context of the ``missing metals problem'', the contributions of the UV-selected z=2.2 ``BX'' galaxies and z=2.5 ``distant red galaxies'' (DRGs) have not been discussed previously. Here we show that: (i) DRGs only make a marginal contribution to the metal budget (~ 5%); (ii) BX galaxies contribute as much as 18% to the metal budget; and (iii) the K-bright subsample ($K<20$) of the BX sample (roughly equivalent to the `BzK' selected samples) contributes roughly half of this 18%, owing both to their larger stellar masses and higher metallicities, implying that the rare K-bright galaxies at z>2 are a major source of metals in the budget. We showed in the first paper of this series that submm galaxies (SMGs) brighter than 3 mJy contribute ~5% (<9% as an upper limit) to the metal budget. Adding the contribution of SMGs and damped Ly-alpha absorbers, to the contribution of UV selected galaxies, implies that at least 30% of the metals (in galaxies) have been accounted for at z=2. The cosmic metal density thus accounted for is ~ 1.3\times 10^6 \rhosun. This is a lower limit given that galaxies on the faint-end of the luminosity function are not included. An estimate of the distribution of metals in local galaxies as a function luminosity suggests that galaxies with luminosity less than L^{\star}$ contribute about half of the total mass of metals. If the metals in galaxies at z ~ 2 are similarly distributed then faint galaxies alone cannot solve the `missing metals problem.' Galaxy populations at z ~ 2 only account for about 50% of the total metals predicted.

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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

Measuring the halo mass of MgII absorbers from their cross-correlation with Luminous Red Galaxies

We study the cross-correlation between 716 MgII quasar absorption systems and about 100,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 3 in the redshift range 0.4<z<0.8. The MgII systems were selected to have 2796 & 2803 rest-frame equivalent widths greater than 1.0 Åand identifications confirmed by the FeII 2600 or MgI 2852 lines. Over co-moving scales 0.2--13/h Mpc, the MgII--LRG cross-correlation has an amplitude 0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have halo-masses of 10^{13} \msun, this strong cross-correlation implies that the absorber host-galaxies have halo-masses 1--2 times 10^{12} \msun.

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arXiv2004

The clustering of Luminous Red Galaxies around MgII absorbers

We study the cross-correlation between 212 MgII quasar absorption systems and \~20,000 Luminous Red Galaxies (LRGs) selected from the Sloan Digital Sky Survey Data Release 1 in the redshift range 0.4 =1.0 Angstrom and identifications confirmed by the FeII 2600 or MgI 2852 lines. Over comoving scales 0.05--13 h^-1 Mpc, the MgII--LRG cross-correlation has an amplitude 0.69+/-0.09 times that of the LRG--LRG auto-correlation. Since LRGs have halo-masses greater than 3.5 x 10^12 solar masses for M_R<-21, this relative amplitude implies that the absorber host-galaxies have halo-masses greater than 2--8 x 10^11 Msun. For 10^13 Msun LRGs, the absorber host-galaxies have halo-masses 0.5--2.5 x 10^12 Msun. Our results appear consistent with those of Steidel et al. (1994) who found that MgII absorbers with W_r>=0.3 Angstrom are associated with ~0.7 L^*_B galaxies.

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arXiv2003

Nitrogen Abundances in High-z DLAs

Determination of chemical abundances for elements produced mainly by Type I SNae and intermediate mass stars in high redshift DLAs probes the early chemical build-up on time-scales comparable with their production. Nitrogen shows a peculiar behaviour never detected before in any other class of objects. For [N/H] < -3 there is a plateau with [N/Si]= -1.45(\pm 0.05). We interpret this as empirical evidence for primary N production by massive stars in young systems where AGB stars have not yet had time to make their contribution. The plateau provides the observational integrated yields for N production by massive stars which are theoretically rather uncertain. High N/Si and solar [alpha/iron-peak] ratios are observed at high redshift and place at an earlier epoch the onset of star formation. On the other hand, low N/Si, i.e. young objects, are observed also at relatively low redshifts. These evidences suggest that DLAs started to be formed at a very early epoch but their formation has been extended up to later times.

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arXiv2003

A Homogeneous Sample of Sub-DLAs I: Construction of the Sample and Chemical Abundance Measurements

In this first paper of a series, we report on the use of quasar spectra obtained with the UVES high resolution spectrograph and available through the ESO VLT archive to build the first sample of sub-DLA systems, absorbers with HI column densities > 10^{19} cm^{-2} but lower than the classical definition of damped Ly-alpha systems (DLAs) 2x10^{20} cm^{-2}. A systematic investigation of the properties of these systems and a comparison with those of the DLAs (Paper II of this series; Peroux et al. 2003b) is expected to provide new clues on the association of high column density absorbers with galaxies and on the overall evolution of the neutral hydrogen gas mass and metal content in the Universe. In the spectra of 22 quasars which were found suitable for a sub-DLA search, we identified 12 sub-DLAs and 1 borderline case between the DLA and sub-DLA systems in the redshift interval z = 1.8-4.3. We measured the column densities of HI and up to 16 ions of low-, intermediate- and high-ionization. We further investigated the significance of the ionization corrections in the determination of the chemical abundances from the low-ionization ions in the sub-DLA HI column density range. Using the predictions of different ion ratios as a function of the ionization parameter computed with the CLOUDY software package, we have estimated that with the exception of one case, the ionization corrections to the abundances of 9 systems for which we were able to constrain the ionization parameter, are lower than 0.2 dex for all of the elements except AlII and ZnII down to HI column densities of log N(HI) = 19.3 cm^{-2}. We finally present the first sub-DLA chemical abundance database which contains the abundance measurements of 11 different elements (O, C, Si, N, S, Mg, Al, Fe, Ni, Zn, and Cr).

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arXiv2003

Early stages of Nitrogen enrichment in galaxies: Clues from measurements in damped Lyman alpha systems

We present 4 new measurements of nitrogen abundances and one upper limit in damped Lyman alpha absorbers (DLAs) obtained by means of high resolution (FWHM \~ 7 km/s) UVES/VLT spectra. In addition to these measurements we have compiled data from all DLAs with measurements of nitrogen and alpha-capture elements (O, S or Si) available in the literature, including all HIRES/Keck and UVES/VLT data for a total of 33 systems, i.e. the largest sample investigated so far. We find that [N/alpha] ratios are distributed in two groups: 75% of the DLAs show a mean value of [N/alpha] = -0.87 with a scatter of 0.16 dex, while the remaining 25% shows ratios clustered at [N/alpha] = -1.45 with an even lower dispersion of 0.05 dex. The high [N/alpha] plateau is consistent with the one observed in metal-poor HII regions of blue compact dwarf (BCD) galaxies ([N/alpha] = -0.73 +/- 0.13), while the [N/alpha] ~ -1.5 values are the lowest ever observed in any astrophysical site. These low [N/alpha] ratios are real and not due to ionization effects. They provide a crucial evidence against the primary production of N by massive stars as responsible for the plateau at -0.9/-0.7 dex observed in DLAs and BCD galaxies. The transition between the low-N ([N/alpha] ~ -1.5) and high-N ([N/alpha] ~ -0.9) DLAs occurs at a nitrogen abundance of [N/H] ~ -2.8, suggesting that the separation may result from some peculiarity of the nitrogen enrichment history. The [N/alpha] ~ -1.5 values and their low dispersion are consistent with a modest production of primary N in massive stars; however, due to the limited sample, specially for the low-N DLAs, we cannot exclude a primary origin in intermediate mass stars as responsible for the low N abundances observed.

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arXiv2001

UVES observations of a damped Ly-alpha system at z_abs = 4.466 towards the quasar APM BR J0307-4945

We present the first high-resolution (6.2 to 7.7 km/s FWHM) spectra of the APM BR J0307-4945 quasar at z_em = 4.73 obtained with UVES on the 8.2m VLT Kueyen telescope. We focus our analysis on a damped Ly-alpha (DLA) system at z_abs = 4.466 with a neutral hydrogen column density N(HI) = (4.68 +/- 0.97) 10^{20} cm^{-2}. It is the most distant DLA system known to the present date, observed when the age of the universe was only 1.3 Gyr. It shows complex low- and high-ionization line profiles spanning ~240 and 300 km/s in velocity space respectively. We derive accurate abundances for N, O, Al, Si and Fe, and place a lower limit on C and an upper limit on Ni: [N/H] = -3.07 +/- 0.15, [O/H] = -1.63 +/- 0.19, [Al/H] = -1.79 +/- 0.11, [Si/H] = -1.54 +/- 0.11, [Fe/H] = -1.97 +/- 0.19, [C/H] > -1.63 and [Ni/H] < -2.35. The derived high metallicity, 1/90 solar, shows that this very young absorber (< 1.3 Gyr) has already experienced a significant metal enrichment. The [O/Si] ratio is nearly solar suggesting a limited amount of dust, the relative [Si,O/Fe] abundance ratios show a similar enhancement as observed in the Milky Way stars with comparable metallicities, and the [N/O] ratio is very low. All these results point to an enrichment pattern dominated by Type II supernovae which suggests a Milky Way type evolutionary model.

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