Damped Lyα Research Articles

The ESO UVES advanced data products quasar sample

We present here a dataset of quasars observed with the Ultraviolet Visual Echelle Spectrograph (UVES) on the VLT and available in the ESO UVES Advanced Data Products archive. The sample is made up of a total of 250 high resolution quasar spectra with emission redshifts ranging from 0.191 < z_em <6.311. The total UVES exposure time of this dataset is 1560 hours. Thanks to the high resolution of UVES spectra, it is possible to unambiguously measure the column density of absorbers with damping wings, down to N_HI > 10^{19} cm^{-2}, which constitutes the sub-damped Lya absorber (sub-DLA) threshold. Within the wavelength coverage of our UVES data, we find 150 damped Lya systems (DLAs)/sub-DLAs in the range 1.5 < z_abs < 4.7. Of these 150, 93 are DLAs and 57 are sub-DLAs. An extensive search in the literature indicates that 6 of these DLAs and 13 of these sub-DLAs have their N_HI measured for the first time. Among them, 10 are new identifications as DLAs/sub-DLAs. For each of these systems, we obtain an accurate measurement of the HI column density and the absorber's redshift in the range 1.7 < z_abs < 4.2 by implementing a Voigt profile-fitting algorithm. These absorbers are further confirmed thanks to the detection of associated metal lines and/or lines from members of the Lyman series. In our data, a few quasars' lines-of-sight are rich. An interesting example is towards QSO J0133+0400 (z_em = 4.154) with six DLAs and sub-DLAs reported.

Comprehensive study of a z = 2.35 DLA Galaxy: mass, metallicity, age, morphology and SFR from HST and VLT★

We present a detailed study of the emission from a z = 2.35 galaxy that causes damped Lyman α absorption in the spectrum of the background quasar (QSO), SDSS J2222−0946. We present the results of extensive analyses of the stellar continuum covering the rest frame optical–UV regime based on broad-band Hubble Space Telescope (HST) imaging, and of spectroscopy from VLT/X-Shooter of the strong emission lines: Lyα, [O ii], [O iii], [N ii], Hα and Hβ. We compare the metallicity from the absorption lines in the QSO spectrum with the oxygen abundance inferred from the strong-line methods (R23 and N2). The two emission-line methods yield consistent results: [O/H] = −0.30 ± 0.13. Based on the absorption lines in the QSO spectrum a metallicity of −0.49 ± 0.05 is inferred at an impact parameter of 6.3 kpc from the centre of the galaxy with a column density of hydrogen of log (NHI/cm−2 = 20.65 ± 0.05. The star formation rates (SFRs) of the galaxy from the UV continuum and Hα line can be reconciled assuming an amount of reddening of E(B − V) = 0.06 ± 0.01, giving an inferred SFR of 13 ± 1 M⊙ yr−1 (Chabrier initial mass function). From the HST imaging, the galaxy associated with the absorption is found to be a compact (re = 1.12 kpc) object with a disc-like, elongated (axis ratio 0.17) structure indicating that the galaxy is seen close to edge-on. Moreover, the absorbing gas is located almost perpendicularly above the disc of the galaxy suggesting that the gas causing the absorption is not corotating with the disc. We investigate the stellar and dynamical masses from spectral energy distribution-fitting and emission-line widths, respectively, and find consistent results of 2 × 109 M⊙. We suggest that the galaxy is a young proto-disc with evidence for a galactic outflow of enriched gas. This galaxy hints at how star-forming galaxies may be linked to the elusive population of damped Lyα absorbers.

The explosion energy of early stellar populations: the Fe-peak element ratios in low-metallicity damped Lyα systems★

The relative abundances of the Fe-peak elements (Ti-Zn) at the lowest metallicities are intimately linked to the physics of core-collapse supernova explosions. With a sample of 25 very metal-poor damped Lyman-alpha systems, we investigate the trends of the Fe-peak element ratios with metallicity. For nine of the 25 DLAs, a direct measurement (or useful upper limit) of one or more of the Ti,Cr,Co,Ni,Zn/Fe abundance ratios could be determined from detected absorption lines. For the remaining systems (without detections), we devised a new form of spectral stacking to estimate the typical Fe-peak element ratios of the DLA population in this metallicity regime. We compare these data to analogous measurements in metal-poor stars of the Galactic halo and to detailed calculations of explosive nucleosynthesis in metal-free stars. We conclude that most of the DLAs in our sample were enriched by stars that released an energy of < 1.2 x 10^51 erg when they exploded as core-collapse supernovae. Finally, we discuss the exciting prospect of measuring Fe-peak element ratios in damped Lyman-alpha systems with Fe/H < 1/1000 of solar when 30-m class telescopes become available. Only then will we be able to pin down the energy that was released by the supernovae of the first stars.

THE BOSS Lyα FOREST SAMPLE FROM SDSS DATA RELEASE 9

We present the BOSS Lyman-alpha (Lya) Forest Sample from SDSS Data Release 9, comprising 54,468 quasar spectra with zqso > 2.15 suitable for Lya forest analysis. This data set probes the intergalactic medium with absorption redshifts 2.0 < z_alpha < 5.7 over an area of 3275 square degrees, and encompasses an approximate comoving volume of 20 h^-3 Gpc^3. With each spectrum, we have included several products designed to aid in Lya forest analysis: improved sky masks that flag pixels where data may be unreliable, corrections for known biases in the pipeline estimated noise, masks for the cores of damped Lya systems and corrections for their wings, and estimates of the unabsorbed continua so that the observed flux can be converted to a fractional transmission. The continua are derived using a principal component fit to the quasar spectrum redwards of restframe Lya (lambda > 1216 Ang), extrapolated into the forest region and normalized by a linear function to fit the expected evolution of the Lya forest mean-flux. The estimated continuum errors are ~5% rms. We also discuss possible systematics arising from uncertain spectrophotometry and artifacts in the flux calibration; global corrections for the latter are provided. Our sample provides a convenient starting point for users to analyze clustering in BOSS Lya forest data, and it provides a fiducial data set that can be used to compare results from different analyses of baryon acoustic oscillations in the Lya forest. The full data set is available from the SDSS-III DR9 web site.

A new candidate for probing Population III nucleosynthesis with carbon-enhanced damped Lyα systems

We report the identification of a very metal poor damped Lyα system (DLA) at zabs = 3.067 295 that is modestly carbon enhanced, with an iron abundance of ∼1/700 solar ([Fe/H] =−2.84) and [C,O/Fe] ≃ +0.6. Such an abundance pattern is likely to be the result of nucleosynthesis by massive stars. On the basis of 17 metal absorption lines, we derive a 2σ upper limit on the DLA's kinetic temperature of TDLA ≤ 4700 K, which is broadly consistent with the range of spin temperature estimates for DLAs at this redshift and metallicity. While the best-fitting abundance pattern shows the expected hallmarks of Population III nucleosynthesis, models of high-mass Population II stars can match the abundance pattern almost as well. We discuss current limitations in distinguishing between these two scenarios and the marked improvement in identifying the remnants of Population III stars expected from the forthcoming generation of 30-m class telescopes.

H i content, metallicities and spin temperatures of damped and sub-damped Lyα systems in the redshift desert (0.6 &lt; zabs &lt; 1.7)★

The HI 21cm absorption optical depth and the N(HI) derived from Lya absorption can be combined to yield the spin temperature (Ts) of DLAs. Although Ts measurements exist for samples of DLAs with z <0.6 and z >1.7, the intermediate redshift regime currently contains only 2 HI 21cm detections, leading to a `redshift desert' that spans 4 Gyrs of cosmic time. To connect the low and high z regimes, we present observations of the Lya line of six 0.6<z<1.7 HI 21cm absorbers. The dataset is complemented by both VLBA observations (to derive the absorber covering factor, f), and optical echelle spectra from which metal abundances are determined. Our dataset therefore not only offers the largest statistical study of HI 21cm absorbers to date, and bridges the redshift desert, but is also the first to use a fully f-corrected dataset to look for metallicity-based trends. In agreement with trends found in Galactic sightlines, we find that the lowest N(HI) absorbers tend to be dominated by warm gas. In the DLA regime, spin temperatures show a wider range of values than Galactic data, as may be expected in a heterogenous galactic population. However, we find that low metallicity DLAs are dominated by small cold gas fractions and only absorbers with relatively high metallicities exhibit significant fractions of cold gas. Using a compilation of HI 21cm absorbers which are selected to have f-corrected spin temperatures, we confirm an anti-correlation between metallicity and Ts at 3.4 sigma significance. Finally, one of the DLAs in our sample is a newly-discovered HI 21cm absorber (at z=0.602 towards J1431+3952), which we find to have the lowest f-corrected spin temperature yet reported in the literature: Ts=90+-23 K. The observed distribution of Ts and metallicities in DLAs and the implications for understanding the characteristics of the interstellar medium in high redshift galaxies are discussed.

A SUPER-DAMPED Lyα QUASI-STELLAR OBJECT ABSORBER ATz= 2.2

We report the discovery of a super-damped Lyα absorber at z abs = 2.2068 toward quasi-stellar object (QSO) Q1135-0010 in the Sloan Digital Sky Survey (SDSS) and follow-up Very Large Telescope (VLT) UVES spectroscopy. A Voigt profile fit to the damped Lyα (DLA) line indicates log . This is the second QSO DLA discovered to date with such high . We derive element abundances [Si/H] = –1.10 ± 0.10, [Zn/H] = –1.06 ± 0.10, [Cr/H] = –1.55 ± 0.10, [Ni/H] = –1.60 ± 0.10, [Fe/H] = –1.76 ± 0.10, [Ti/H] = –1.69 ± 0.11, [P/H] = –0.93 ± 0.23, and [Cu/H] = –0.75 ± 0.14. Our data indicate detection of Lyα emission in the DLA trough, implying a star formation rate (SFR) of ~10 M ☉ yr–1 in the absence of dust attenuation. C II* λ1336 absorption is also detected, suggesting SFR surface density M ☉ yr–1 kpc–2. We estimate electron density in the range 3.5 × 10–4 to 24.7 cm–3 from C II*/C II and ~0.5-0.9 cm–3 from Si II*/Si II. Overall, this is a robustly star-forming, moderately enriched absorber, but with relatively low dust depletion. Fitting of the SDSS spectrum yields low reddening for Milky Way, Large Magellanic Cloud, or Small Magellanic Cloud (SMC) extinction curves. No CO absorption is detected, and C I absorption is weak. The low dust and molecular content, reminiscent of some SMC sight lines, may result from the lower metallicity and a stronger radiation field (due to higher SFR). Finally, we compare this absorber with other QSO and gamma-ray burst DLAs.

First stars in damped Lyα systems

ABSTRACT In order to characterize damped Lyα absorption systems (DLAs) potentially hosting first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf galaxies. The merger tree method previously developed is extended to include inhomogeneous reionization and metal mixing, and it is validated by matching both the metallicity distribution function of Galactic halo stars and the Fe–luminosity relation of dwarf spheroidal galaxies. The model explains the observed –Fe relation of DLAs along with the chemical abundances of [Fe/H] &amp;lt; −2 systems. In this picture, the recently discovered zabs≈ 2.34 C-enhanced DLA pertains to a new class of absorbers hosting first stars along with second-generation long-living low-mass stars. These ‘Population III DLAs’ are the descendants of H2-cooling minihaloes with , which virialize at z &amp;gt; 8 in neutral, primordial regions of the MW environment and passively evolve after a short initial period of star formation. The gas in these systems is warm K, and strongly C-enriched by long-living, extremely metal-poor stars of total mass M*≈ 102–104 M⊙.

Filamentary infall of cold gas and escape of Lyα and hydrogen ionizing radiation from an interacting high-redshift galaxy★

We present observations of a peculiar Lyα-emitting galaxy at redshift z = 3.344, discovered in a deep, blind spectroscopic survey for faint Lyα emitters with the Magellan II telescope in the Hubble Ultra Deep Field. The galaxy exhibits complex Lyα emission, including an extended, asymmetric component that is partially suppressed by damped Lyα absorption, and two spatially elongated, narrow emission features. Archival Hubble Space Telescope Advanced Camera for Surveys imaging shows evidence for tidal disruption of the stellar component. This V = 27 galaxy appears to give us unprecedented insight into two fundamental stages in the formation of structure at high redshift: the inflow of gas into ordinary galaxies, and the escape of ionizing radiation into the intergalactic medium. Neutral hydrogen, falling in partly in the form of a narrow filament, appears to emit fluorescent Lyα photons induced by the stellar ionizing flux escaping from the disturbed galaxy. The in-falling material may represent primary cold accretion or an interaction-triggered inflow. The rate of ionizing photons required by the observed Lyα emission is consistent with the rate of photons produced by the observed stellar population, with roughly 50 per cent of ionizing photons escaping from the immediate galaxy and encountering the in-falling gas. We briefly discuss cooling radiation and large-scale shocks as additional sources for Lyα and ionizing radiation in high-redshift galaxies, but find that stellar radiation is likely to be the dominant source of ionizing photons for most faint galaxies. The observational properties of the galaxy lend support to a picture where galaxy interactions facilitate the escape of both Lyα and ionizing radiation. We argue that galaxies like the present object may be common at high redshift. This galaxy may therefore be a late example of an interacting population of dwarf galaxies that contribute significantly to the reionization of the universe.

How neutral is the intergalactic medium surrounding the redshift z = 7.085 quasar ULAS J1120+0641?

Abstract The quasar ULAS J1120+0641 at redshift z = 7.085 has a highly ionized near zone which is smaller than those around quasars of similar luminosity at z ≃ 6. The spectrum also exhibits evidence for a damping wing extending redward of the systemic Lyα redshift. We use radiative transfer simulations in a cosmological context to investigate the implications for the ionization state of the inhomogeneous intergalactic medium (IGM) surrounding this quasar. Our simulations show that the transmission profile is consistent with an IGM in the vicinity of the quasar with a volume averaged H i fraction of and that ULAS J1120+0641 has been bright for 106–107 yr. The observed spectrum is also consistent with smaller IGM neutral fractions, , if a damped Lyα system in an otherwise highly ionized IGM lies within 5 proper Mpc of the quasar. This is, however, predicted to occur in only ∼5 per cent of our simulated sightlines for a bright phase of 106–107 yr. Unless ULAS J1120+0641 grows during a previous optically obscured phase, the low age inferred for the quasar adds to the theoretical challenge of forming a 2 × 109 M⊙ black hole at this high redshift.

The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime★

We present a high spectral resolution survey of the most metal-poor damped Lyman-alpha absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these are reported here for the first time. Together with recent measures of the abundances of C and O in Galactic metal-poor stars, we reinvestigate the trend of C/O in the very metal-poor regime and we compare, for the first time, the O/Fe ratios in the most metal-poor DLAs and in halo stars. We confirm the near-solar values of C/O in DLAs at the lowest metallicities probed, and find that their distribution is in agreement with that seen in Galactic halo stars. We find that the O/Fe ratio in very metal-poor (VMP) DLAs is essentially constant, and shows very little dispersion, with a mean [<O/Fe>] = +0.39 +/- 0.12, in good agreement with the values measured in Galactic halo stars when the oxygen abundance is measured from the [O I] 6300 line. We speculate that such good agreement in the observed abundance trends points to a universal origin for these metals. In view of this agreement, we construct the abundance pattern for a typical very metal-poor DLA and compare it to model calculations of Population II and Population III nucleosynthesis to determine the origin of the metals in VMP DLAs. Our results suggest that the most metal-poor DLAs may have been enriched by a generation of metal-free stars; however, given that abundance measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars.

Galactic winds and extended Lyα emission from the host galaxies of high column density quasi-stellar object absorption systems

We present 3D resonant radiative transfer simulations of the spatial and spectral diffusion of the Lya radiation from a central source in the host galaxies of high column density absorption systems at z ~ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations that reproduce a wide range of observed properties of damped Lya absorption systems. The Lya emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lya emission is broadened to several hundred (in some case more than thousand) km/s. The distribution and the dynamical state of the gas in the simulated galaxies is complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lya radiation extends to gas with column densities of N_HI ~ 10^{18} cm^{-2} and its spectral shape varies strongly with viewing angle. The strong dependence on the central \hi column density and the HI velocity field suggests that the Lya emission will also vary strongly with time on timescales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lya emission and - somewhat counterintuitively - a narrower spectral distribution.

THROUGH THICK AND THIN—H I ABSORPTION IN COSMOLOGICAL SIMULATIONS

We investigate the column density distribution function of neutral hydrogen at redshift z = 3 using a cosmological simulation of galaxy formation from the OverWhelmingly Large Simulations (OWLS) project. The base simulation includes gravity, hydrodynamics, star formation, supernovae feedback, stellar winds, chemodynamics, and element-by-element cooling in the presence of a uniform UV background. Self-shielding and formation of molecular hydrogen are treated in post-processing, without introducing any free parameters, using an accurate reverse ray-tracing algorithm and an empirical relation between gas pressure and molecular mass fraction. The simulation reproduces the observed z = 3 abundance of Ly-A forest, Lyman Limit and Damped Ly-A HI absorption systems probed by quasar sight lines over ten orders of magnitude in column density. Self-shielding flattens the column density distribution for NHI > 10^18 cm-2, while the conversion to fully neutral gas and conversion of HI to H2 steepen it around column densities of NHI = 10^20.3 cm-2 and NHI = 10^21.5 cm-2, respectively.

STAR FORMATION FROM DLA GAS IN THE OUTSKIRTS OF LYMAN BREAK GALAXIES ATz∼ 3

We present evidence for spatially extended low surface brightness emission around Lyman break galaxies (LBGs) in the V-band image of the Hubble Ultra Deep Field, corresponding to the z ∼ 3 rest-frame far-UV (FUV) light, which is a sensitive measure of star formation rates (SFRs). We find that the covering fraction of molecular gas at z ∼ 3 is not adequate to explain the emission in the outskirts of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas at high redshift is sufficient. We develop a theoretical framework to connect this emission around LBGs to the expected emission from neutral H i gas, i.e., damped Lyα systems (DLAs), using the Kennicutt–Schmidt (KS) relation. Working under the hypothesis that the observed FUV emission in the outskirts of LBGs is from in situ star formation in atomic-dominated hydrogen gas, the results suggest that the SFR efficiency in such gas at z ∼ 3 is between factors of 10 and 50 lower than predictions based on the local KS relation. The total SFR density in atomic-dominated gas at z ∼ 3 is constrained to be ∼10% of that observed from the inner regions of LBGs. In addition, the metals produced by in situ star formation in the outskirts of LBGs yield metallicities comparable to those of DLAs, which is a possible solution to the "Missing Metals" problem for DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both high and low redshifts has similar reduced SFR efficiencies and is consistent with the same power law.

NEAR-INFRARED IMAGING OF SIX METAL-RICH QUASAR ABSORBER GALAXY FIELDS

Absorption lines in quasar spectra allow us to locate and study intervening galaxies. In order to obtain a clearer picture of these absorber galaxies, we have used the Near-Infrared Camera Fabry-Perot System at Apache Point Observatory to obtain near-infrared broadband images in one or more filters (J and Ks ) of six quasar fields containing metal-rich low-z damped or sub-damped Lyα systems. These data allow us to search for the galaxies and constrain their luminosities. Candidate absorber galaxies are detected at 201-738 separation from the quasar in three out of six fields in the J and Ks bands at >3σ level with luminosities ranging from log(L/L ☉) = 10.44-10.36 in the J band (for E-Sc type galaxies) and log(L/L ☉) = 11.59-10.03 in the Ks band for our detections. We place limits on the remaining fields with no detections of log(L/L ☉) <10.83-9.75 for the J band and log(L/L ☉) <10.43-10.05 for the Ks band. We are also able to utilize Sloan Digital Sky Survey spectra for each field to calculate optical fluxes and limits as well as limits on star formation rate via [O II]λ3727 emission in spectra. Our data, combined with other recent imaging results for metal-rich absorbers, suggest a possible positive correlation between absorber metallicity and galaxy luminosity, although the samples are still small.

The small covering factor of cold accretion streams

Abstract Theoretical models of galaxy formation predict that galaxies acquire most of their baryons via cold mode accretion. Observations of high-redshift galaxies, while showing ubiquitous outflows, have so far not revealed convincing traces of the predicted cold streams, which has been interpreted as a challenge for the current models. Using high-resolution, zoom-in smooth particle hydrodynamics simulations of Lyman break galaxy (LBG) haloes combined with ionizing radiative transfer, we quantify the covering factor of the cold streams at z= 2–4. We focus specifically on Lyman limit systems (LLSs) and damped Lyα absorbers (DLAs), which can be probed by absorption spectroscopy using a background galaxy or quasar sightline, and which are closely related to low-ionization metal absorbers. We show that the covering factor of these systems is relatively small and decreases with time. At z= 2, the covering factor of DLAs within the virial radius of the simulated galaxies is ∼3 per cent (∼1 per cent within twice this projected distance), and arises principally from the galaxy itself. The corresponding values for LLSs are ∼10 and 4 per cent. Because of their small covering factor compared to the order unity covering fraction expected for galactic winds, the cold streams are naturally dominated by outflows in stacked spectra. We conclude that the existing observations are consistent with the predictions of cold mode accretion, and outline promising kinematic and chemical diagnostics to separate out the signatures of galactic accretion and feedback.

Faint resonantly scattered Lyα emission from the absorption troughs of damped Lyα systems at z∼ 3

We demonstrate that the Lyman alpha emission in the absorption troughs of a large sample of stacked damped Lyman alpha absorption systems (DLAS) presented by Rahmani et al (2010) is consistent with the spectral profiles and luminosities of a recently detected population of faint Lyman alpha emitters at z ~ 3. This result supports the suggestion that the faint emitters are to be identified with the host galaxies of DLAS at these redshifts.

The Minimum Mass for a Dwarf Galaxy

A widely held view is that a “mini halo” with much less than 10 8 M ⊙ in dark matter is unlikely to retain any baryons because even a single SN event is expected to sweep out all of the gas. But we show that a clumpy medium is much less susceptible to SN sweeping (particularly if it is off-centred) because the coupling efficiency of the explosive energy is much lower than for a diffuse interstellar medium. With the aid of the sophisticated 3D hydro code Fyris, we show that baryons are retained and stars are formed in dark matter haloes down to 3 × 10 6 M ⊙ . The gas survives the SN explosion and is enriched with specific abundance yields of the discrete events. The smallest galaxies may not contribute a large fraction of baryons and dark matter to the formation of galaxies. But they are likely to carry important chemical signatures that were laid down in the earliest epochs of star formation, as we show. We discuss the results in light of the newly discovered, very metal poor, damped Lyα systems and ultra-faint dwarf galaxies.

A carbon-enhanced metal-poor damped Lyα system: probing gas from Population III nucleosynthesis?★

We present high resolution observations of an extremely metal-poor damped Lyman-alpha system, at z_abs = 2.3400972 in the spectrum of the QSO J0035-0918, exhibiting an abundance pattern consistent with model predictions for the supernova yields of Population III stars. Specifically, this DLA has [Fe/H] = -3.04, shows a clear `odd-even' effect, and is C-rich with [C/Fe] = +1.53, a factor of about 20 greater than reported in any other damped Lyman-alpha system. In analogy to the carbon-enhanced metal-poor stars in the Galactic halo (with [C/Fe] > +1.0), this is the first reported case of a carbon-enhanced damped Lyman-alpha system. We determine an upper limit to the mass of 12C, M(12C) < 200 solar masses, which depends on the unknown gas density n(H); if n(H) > 1 atom per cubic cm (which is quite likely for this DLA given its low velocity dispersion), then M(12C) < 2 solar masses, consistent with pollution by only a few prior supernovae. We speculate that DLAs such as the one reported here may represent the `missing link' between the yields of Pop III stars and their later incorporation in the class of carbon-enhanced metal-poor stars which show no enhancement of neutron-capture elements (CEMP-no stars).

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

Abstract Using a spectral stacking technique we searched for the average Lyman α (Lyα) emission from high-z damped Lyα (DLA) galaxies detected in the Sloan Digital Sky Survey quasi-stellar object (QSO) spectra. We used a sample of 341 DLA galaxies of mean redshift 〈z〉= 2.86 and log N(H i) ≥ 20.62 to place a 3σ upper limit of 3.0 × 10−18 erg s−1 cm−2 on the Lyα flux emitted within ∼1.5 arcsec (or 12 kpc) from the QSO line of sight. This corresponds to an average Lyα luminosity of ≤2 × 1041 erg s−1 or 0.03L★(Lyα). This limit is deeper than the limit of most surveys for faint Lyα emitters. The lack of Lyα emission in DLA galaxies is consistent with the in situ star formation, for a given N(H i), 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 Lyα-emitting galaxies and/or to be located far away from the star-forming regions. The latter may well be true since we detect strong O vi absorption in the stacked spectrum, indicating that DLA galaxies 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.