C<scp>ii</scp>* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Wolfe, Arthur M.; Prochaska, J. Xavier; Gawiser, Eric

doi:10.1086/376520

Cited by 160 publications

(292 citation statements)

References 68 publications

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“…5.4), the cooling rate scales with the dust-togas ratio (D/G), the photoelectric efficiency, and the FUV field. Since the latter is a good gauge of the star-formation rate (SFR) per unit physical area, the similar cooling rate between I Zw 18 and DLAs could in principle imply a similar surface SFR density (Wolfe et al 2003b). Following Bowen et al (2005), we can estimate the SFR from C * by using the Milky Way (MW) as a reference times lower than the MW value; Rémy et al, in prep.).…”

Section: Cooling Rate and Sfrmentioning

confidence: 99%

Chemical enrichment and physical conditions in I Zw 18

Lebouteiller

Heap

Hubený

et al. 2013

A&A

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Context. Low-metallicity star-forming dwarf galaxies are prime targets to understand the chemical enrichment of the interstellar medium. The H  region contains the bulk of the mass in blue compact dwarfs, and it provides important constraints on the dispersal and mixing of heavy elements released by successive star-formation episodes. The metallicity of the H  region is also a critical parameter to investigate the future star-formation history, as metals provide most of the gas cooling that will facilitate and sustain star formation. Aims. Our primary objective is to study the enrichment of the H  region and the interplay between star-formation history and metallicity evolution. Our secondary objective is to constrain the spatial-and time-scales over which the H  and H  regions are enriched, and the mass range of stars responsible for the heavy element production. Finally, we aim to examine the gas heating and cooling mechanisms in the H  region. Methods. We observed the most metal-poor star-forming galaxy in the Local Universe, I Zw 18, with the Cosmic Origin Spectrograph onboard Hubble. The abundances in the neutral gas are derived from far-ultraviolet absorption-lines (H , C , C *, N , O , ...) and are compared to the abundances in the H  region. Models are constructed to calculate the ionization structure and the thermal processes. We investigate the gas cooling in the H  region through physical diagnostics drawn from the fine-structure level of C + . Results. We find that H  region abundances are lower by a factor of ∼2 as compared to the H  region. There is no differential depletion on dust between the H  and H  region. Using sulfur as a metallicity tracer, we calculate a metallicity of 1/46 Z (vs. 1/31 Z in the H  region). From the study of the C/O, [O/Fe], and N/O abundance ratios, we propose that C, N, O, and Fe are mainly produced in massive stars. We argue that the H  envelope may contain pockets of pristine gas with a metallicity essentially null. Finally, we derive the physical conditions in the H  region by investigating the C * absorption line. The cooling rate derived from C * is consistent with collisions with H 0 atoms in the diffuse neutral gas. We calculate the star-formation rate from the C * cooling rate assuming that photoelectric effect on dust is the dominant gas heating mechanism. Our determination is in good agreement with the values in the literature if we assume a low dust-to-gas ratio (∼2000 times lower than the Milky Way value).

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Section: Cooling Rate and Sfrmentioning

confidence: 99%

Chemical enrichment and physical conditions in I Zw 18

Lebouteiller

Heap

Hubený

et al. 2013

A&A

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“…Rafelski et al 2012). The excitation of different atomic and/or molecular species provides indirect constraints on instantaneous surface star-formation rates (SFRs Wolfe et al 2003;Srianand et al 2005;Noterdaeme et al 2007a,b). Prochaska & Wolfe (1997) tested a variety of models and concluded that the DLA kinematics, as traced by the profiles of low-ionisation metal absorption lines, could be characteristic of rapidly rotating discs.…”

Section: Introductionmentioning

confidence: 99%

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

Noterdaeme

Petitjean

Pâris

et al. 2014

A&A

107

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We present a study of ∼100 high redshift (z ∼ 2−4) extremely strong damped Lyman-α systems (ESDLA, with N(H i) ≥ 0.5 × 10 22 cm −2 ) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(H i) frequency distribution has a relatively shallow slope with power-law index −3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ∼1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly α emission with L ESDLA (Ly α) (0.6 ± 0.2) × 10 42 erg s −1 in the core of ESDLAs (corresponding to about 0.1 L at z ∼ 2−3), obtained through stacking the fibre spectra (of radius 1 corresponding to ∼8 kpc at z ∼ 2.5). Statistical errors on the Ly α luminosity are of the order of 0.1 × 10 42 erg s −1 but we caution that the measured Ly α luminosity may be overestimated by ∼35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2 × 10 42 erg s −1 . The properties of the Ly α line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-α emitting galaxies (LAEs) with L LAE (Ly α) ≥ 10 41 erg s −1 detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r gas = 2.5 kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly α luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M yr −1 ) ≈ 0.6/ f esc , where f esc < 1 is the Ly α escape fraction. Assuming the typical escape fraction of LAEs, f esc ∼ 0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r gal ≈ 2.5 kpc. Finally, we note that possible overestimation of the Ly α emission would result in both smaller r gas and r gal . Our results support a close association between LAEs and stro...

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“…Fynbo et al 2008). Nevertheless, DLA galaxies can provide substantial contributions to the global star formation rate (SFR) density at high redshifts (Wolfe et al 2003;Srianand et al 2005;Rauch et al 2008;Rahmani et al 2010). In addition, it has long been debated whether the kinematics of the absorbing gas, studied in terms of the velocity profiles of metal absorption lines, is more representative of that of large rotating galactic discs (Prochaska & Wolfe 1997) or small low-mass galactic clumps ) that build up hierarchically to form the galaxies known today (e.g.…”

Section: Introductionmentioning

confidence: 99%

Discovery of a compact gas-rich damped Lyman-αgalaxy atz = 2.2: evidence of a starburst-driven outflow

Noterdaeme

Laursen

Petitjean

et al. 2012

A&A

125

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We present the detection of Ly α, [O iii], and H α emission associated with an extremely strong damped Lyman-α (DLA) system (N(H i) = 10 22.10 cm −2 ) at z = 2.207 towards the quasar SDSS J113520.39−001053.56. This is the largest H i column density ever measured along a quasi-stellar object (QSO) line of sight, though typical of those often found in DLAs associated to gamma-ray bursts (GRBs). This absorption system can also be classified as an ultra-strong Mg ii system with W λ2796 , and is unresolved. From the H α line, we measure a significant star formation rate (SFR) ≈ 25 M yr −1 (uncorrected for dust). The shape of the Ly α line is double-peaked, which is the signature of a resonant scattering of Ly α photons, and the Ly α emission is spatially extended. More strikingly, the blue and red Ly α peaks arise from distinct regions extended over a few kpc on either side of the star-forming region. We propose that this is the consequence of a Ly α transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the high SFR together with the small size and low mass of the galaxy (M vir ∼ 10 10 M ). By placing constraints on the stellar UV continuum luminosity of the galaxy, we estimate an age of at most a few 10 7 yr, again consistent with a recent starburst scenario. We interpret these data as the observation of a young, gas-rich, compact starburst galaxy, from which material is expelled through collimated winds powered by the vigorous star formation activity. We substantiate this picture by modelling the radiative transfer of Ly α photons in the galactic counterpart. Though our model (a spherical galaxy with bipolar outflowing jets) is a simplistic representation of the true gas distribution and velocity field, the agreement between the observed and simulated properties is particularly good (spectral shape and width of the Lyman-α emission, spatial configuration, escape fraction as well as absorption kinematics, H i column density, and dust reddening). Finally, we propose that selecting DLAs with very high H i column densities may be an efficient way of detecting star-forming galaxies at small impact parameters from the background QSO lines of sight.

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Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Cited by 160 publications

References 68 publications

Chemical enrichment and physical conditions in I Zw 18

Chemical enrichment and physical conditions in I Zw 18

A connection between extremely strong damped Lyman-αsystems and Lyman-αemitting galaxies at small impact parameters

Discovery of a compact gas-rich damped Lyman-αgalaxy atz = 2.2: evidence of a starburst-driven outflow

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