Query : 2007A&A...469..425N

2007A&A...469..425N - Astronomy and Astrophysics, volume 469, 425-436 (2007/7-2)

Physical conditions in the neutral interstellar medium at z=2.43 toward Q 2348-011.


Abstract (from CDS):

We aim at deriving the physical conditions in the neutral gas associated with damped Lyman-α systems using observation and analysis of H2 and CI absorptions. We obtained a high-resolution VLT-UVES spectrum of the quasar Q2348-011 over a wavelength range that covers most of the prominent metal and molecular absorption lines from the logN(HI)=20.50±0.10 damped Lyman-α system at zabs=2.4263. We detected H2 in this system and measured column densities of H2, CI, CI*, CI**, SiII, PII, SII, FeII, and NiII. From the column density ratios and, in particular, the relative populations of H2 rotational and Ci fine-structure levels, we derived the physical conditions in the gas (relative abundances, dust-depletion, particle density, kinetic temperature, and ionising flux) and discuss physical conditions in the neutral phase. Molecular hydrogen was detected in seven components in the first four rotational levels (J=0-3) of the vibrational ground state. Absorption lines of H2 J=4 (resp. J=5) rotational levels are detected in six (resp. two) of these components. This leads to a total molecular fraction of logf≃-1.69+0.37–0.58. Fourteen components are needed to reproduce the metal-line profiles. The overall metallicity is found to be -0.80, -0.62, -1.17±0.10 for, respectively, [Si/H], [S/H] and [Fe/H]. We confirm the earlier findings that there is a correlation between logN(FeII)/N(SII) and logN(SiII)/N(SII) from different components indicative of a dust-depletion pattern. Surprisingly, however, the depletion of metals onto dust in the H2 components is not large in this system: [Fe/S]=-0.8 to -0.1. The gas in H2-bearing components is found to be cold but still hotter than similar gas in our Galaxy (T>130K, instead of typically 80K) and dense (n∼100-200cm–3). There is an anti-correlation (R=-0.97) between the logarithm of the photo-absorption rate, logβ0, and logN(H2)/N(CI) derived for each H2 component. We show that this is mostly due to shielding effects and imply that the photo-absorption rate β0 is a good indicator of the physical conditions in the gas. We find that the gas is immersed in an intense UV field, about one order of magnitude higher than in the solar vicinity. These results suggest that the gas in H2-bearing DLAs is clumpy, and star-formation occurs in the associated object.

Abstract Copyright:

Journal keyword(s): galaxies: ISM - quasars: absorption lines - quasars: individual: Q2348-011

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 LBQS 0013-0029 QSO 00 16 02.4050159808 -00 12 25.077257064   18.67 18.36     ~ 191 0
2 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6630 1
3 HE 0515-4414 QSO 05 17 07.6238702856 -44 10 55.579731312 14.74 15.49 15.16     ~ 114 0
4 QSO B0528-2505 QSO 05 30 07.9627395840 -25 03 29.900044512   18.17 17.34 17.7   ~ 413 0
5 QSO B0551-36 QSO 05 52 46.1824785360 -36 37 27.608212524   17.72 17.57     ~ 94 0
6 QSO B1331+170 Bla 13 33 35.7827544072 +16 49 04.013500728   16.84 16.71 16.41   ~ 436 0
7 QSO J1443+2724 QSO 14 43 31.1697928632 +27 24 36.768781008     19.3     ~ 87 0
8 QSO B2348-0108 QSO 23 50 57.8771296800 -00 52 09.886281492   19.23 18.77 18.7   ~ 146 0

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