J/A+A/566/A24 Extremely strong damped Lyman-α systems (Noterdaeme+, 2014)
A connection between extremely strong damped Lyman-α systems and
Lyman-α emitting galaxies at small impact parameters.
Noterdaeme P., Petitjean P., Paris I., Cai Z., Finley H., Ge J.,
Pieri M.M., York D.G.
<Astron. Astrophys., 566, A24-24 (2014)>
=2014A&A...566A..24N 2014A&A...566A..24N
ADC_Keywords: QSOs ; Redshifts
Keywords: quasars: absorption lines - galaxies: high-redshift - galaxies: ISM -
galaxies: star formation
Abstract:
We present a study of ∼100 high redshift (z ∼2-4) extremely strong
damped Lyman-α systems (ESDLA, with N(HI)≥0.5x1022cm-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(HI) 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 Lyα emission with
<LESDLA(Lyα)≥~(0.6±0.2)x1042erg/s in the core of ESDLAs
(corresponding to about 0.1L* at z∼2-3), obtained through stacking
the fibre spectra (of radius 1" corresponding to ∼8kpc at z∼2.5).
Statistical errors on the Lyα luminosity are of the order of
0.1x1042erg/s but we caution that the measured Lyα 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 0.2x1042erg/s. The properties of the Lyα 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
LLAE(Lyα)≥1041erg/s 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 rgas=2.5kpc, i.e., significantly smaller than the
radius corresponding to the BOSS fibre aperture, making fibre losses
likely negligible. Finally, the average measured Lyα luminosity
indicates a star-formation rate consistent with the Schmidt-Kennicutt
law, SFR (M☉/yr)≃0.6/fesc, where fesc<1 is the Lyα
escape fraction. Assuming the typical escape fraction of LAEs,
fesc∼0.3, the Schmidt-Kennicutt law implies a galaxy radius of about
rgal≃2.5kpc. Finally, we note that possible overestimation of the
Lyα emission would result in both smaller rgas and rgal. Our
results support a close association between LAEs and strong DLA host
galaxies.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 66 104 Intervening extremely strong damped
Lymna-α systems (ESDLA) sample
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See also:
J/A+A/547/L1 : SDSS-III DR9 DLA catalogue (Noterdaeme+, 2012)
http://www.sdss.org : SDSS Home Page
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- QSO QSO name (JHHMMSS.ss+DDMMSS.ss)
22- 36 A15 --- MPF SDSS MJD-plate-fiber
38- 42 F5.3 --- zQSO QSO redshift
44- 47 F4.1 --- C/N Continuum-to-noise ratio
49- 53 F5.3 --- zabs Absoption redshift
55- 59 F5.2 [cm-2] logN(HI) HI column density
61- 64 F4.2 10+36W/nm sig.dark 1σ noise level in the DLA trough
(luminosity at DLA rest-frame σdark
in 1042erg/s/Å)
66 A1 --- Stack? [y/n] Used in stack?
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 29-Jul-2014