Query : 2015A&A...577A..24N

2015A&A...577A..24N - Astronomy and Astrophysics, volume 577A, 24-24 (2015/5-1)

VLT/UVES observations of extremely strong intervening damped Lyman-α systems. Molecular hydrogen and excited carbon, oxygen, and silicon at log N(HI) = 22.4.


Abstract (from CDS):

We present a detailed analysis of three extremely strong, intervening damped Lyman-α systems (ESDLAs, with logN(HI)≥21.7) observed towards quasars with the Ultraviolet and Visual Echelle Spectrograph on the Very Large Telescope. We measure overall metallicities of [Zn/H]~-1.2, -1.3, and -0.7 at, respectively, zabs=2.34 towards SDSSJ214043.02-032139.2 (logN(HI)=22.4±0.1), zabs=3.35 towards SDSSJ145646.48+160939.3 (logN(HI)=21.7±0.1), and zabs=2.25 towards SDSSJ015445.22+193515.8 (logN(HI)=21.75±0.15). Iron depletion of about a factor 15 compared to volatile elements is seen in the DLA towards J2140-0321, while the other two show deletion that is typical of known DLAs. We detect H2 towards J2140-0321 (logN(H2)=20.13±0.07) and J1456+1609 (logN(H2)=17.10±0.09) and argue for a tentative detection towards J0154+1935. Absorption from the excited fine-structure levels of OI, CI, and SiII are detected in the system towards J2140-0321, which has the largest HI column density detected so far in an intervening DLA. This is the first detection of OI fine-structure lines in a QSO-DLA, which also provides us with a rare possibility to study the chemical abundances of less abundant atoms like Co and Ge. Simple single-phase photo-ionisation models fail to reproduce all the observed quantities. Instead, we suggest that the cloud has a stratified structure: H2 and CI most likely stem from a dense (lognH∼2.5-3) and cold (80K) phase and from a warm (250K) phase. They contain a fraction of the total HI, while a warmer (T>1000K) phase probably contributes significantly to the high excitation of OI fine-structure levels. The observed CI/H2 column density ratio is surprisingly low compared to model predictions, and we do not detect CO molecules: this suggests a possible underabundance of C by 0.7dex compared to other alpha elements. The absorber could be a photo-dissociation region close to a bright star (or a star cluster) where higher temperature occurs in the illuminated region. Direct detection of on-going star formation through e.g. near-infrared emission lines in the surroundings of the gas would enable a detailed physical modelling of the system.

Abstract Copyright:

Journal keyword(s): quasars: absorption lines

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10598 1
2 SDSS J015445.22+193515.8 QSO 01 54 45.2204008776 +19 35 15.885751992           ~ 12 0
3 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6625 1
4 QSO B0945+4337 QSO 09 48 35.9613489240 +43 23 02.600924892   18.54 18.37     ~ 55 0
5 SDSS J113520.39-001053.5 QSO 11 35 20.3944527984 -00 10 53.572769436   19.36       ~ 49 0
6 SDSS J123714.60+064759.5 QSO 12 37 14.6105371632 +06 47 59.612187624   19.66 19.15     ~ 59 0
7 SDSS J145646.48+160939.3 QSO 14 56 46.4832762504 +16 09 39.365377812   20.89 20.04     ~ 20 0
8 SDSS J214043.02-032139.2 QSO 21 40 43.0124617776 -03 21 39.253768020           ~ 22 0

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