1998A&A...333..841B


Query : 1998A&A...333..841B

1998A&A...333..841B - Astronomy and Astrophysics, volume 333, 841-863 (1998/5-3)

A HST spectroscopic study of QSOs with intermediate redshift damped Lyα systems.

BOISSE P., LE BRUN V., BERGERON J. and DEHARVENG J.-M.

Abstract (from CDS):

We present HST spectra for a sample of six QSOs with intermediate redshift (za≤1.) damped Lyα systems. These observations aim at measuring the HI column density and detect metal lines in order to investigate the metal enrichment of the gas, as well as the presence of neutral species, molecules and dust. All systems selected on the basis of 21cm absorption and/or strong FeII lines relative to MgII ones turn out to have N(HI) larger than 1020cm–2. From our detection of weak lines from minor metals and already published optical data, we determine relative abundances of Si, Mn, Fe, Ni, Zn. In PKS 1229-021, we measure [Zn/H]=-0.5 at za=0.3950 while in two other cases with intervening spiral galaxies and for which only [Fe/H] and [Mn/H] could be estimated, the metallicity could be close to solar. Thus, it appears that although the scatter of metallicities is as large at za≤1. as at high redshift, an increasing proportion of systems with metallicities ≃30% solar are found when going to lower redshifts. CI lines are tentatively detected in two systems. Given the low metallicity, the observed CI/HI ratio suggests that physical conditions in the absorbers are comparable to those in our Galaxy. In PKS 1229-021, the 21 cm absorption data combined with the new Lyα observations, imply a low temperature, Ts≤200K, for the za=0.3950 absorbing gas. For the three systems in which they could be searched for, H2 molecules are not detected with an upper limit of about 10x18cm–2 on N(H2). No evidence is found for Galactic-type dust, except possibly in the 3C 286 za=0.6922 system. Our results suggest that available observations may be biased against dust-rich absorbers. Further, when all available measurements of N(HI) and [Zn/H] are considered, a clear deficiency of systems with large N(HI) and high metallicity is apparent. We conclude that dust extinction causes a preferential selection of QSOs with intervening gas relatively poor in metals, dust and molecules. As a consequence, the high end of the HI column density distribution (and hence {OMEGA}g, the contribution of neutral gas to the cosmological mass density) is probably more heavily underestimated than previously thought, especially at low redshift. Such a bias could also explain the high incidence of non-spiral morphologies in our sample. We stress that observation of a larger sample of low z damped Lyα systems as well as surveys of damped Lyα systems in fainter QSOs would give a more representative view of the true diversity of absorber properties and should help to probe the denser phases of the interstellar medium in distant galaxies. Our program also provides a few new results on other (likely non-damped) metal systems. In PKS 0454+039, we detect for the first time MgII absorption from a dwarf galaxy halo at za=0.072. Strong MgII and FeII absorption is also found in EX 0302-223 from a spiral galaxy at z=0.118.

Abstract Copyright:

Journal keyword(s): quasars: absorption lines - galaxies: ISM - galaxies: halos

CDS comments: Table 1 : QSO 1209-107 misprint for 1209+107

Simbad objects: 13

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Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 LBQS 0013-0029 QSO 00 16 02.4050159808 -00 12 25.077257064   18.67 18.36     ~ 186 0
2 PHL 957 QSO 01 03 11.2741573824 +13 16 17.809871484   16.97 16.57     ~ 334 0
3 QSO J0304-2211 QSO 03 04 49.8652311288 -22 11 51.882127548   16.43 16.40     ~ 107 0
4 QSO B0454+0356 QSO 04 56 47.1747907776 +04 00 52.946102484   16.76 16.53 16.26   ~ 234 1
5 HE 0515-4414 QSO 05 17 07.6238702856 -44 10 55.579731312 14.74 15.49 15.16     ~ 107 0
6 QSO B0528-2505 QSO 05 30 07.9627395840 -25 03 29.900044512   18.17 17.34 17.7   ~ 409 0
7 3C 196 Sy1 08 13 36.0561170112 +48 13 02.644966020   18.36 17.79     ~ 512 2
8 QSO B1122-168 QSO 11 24 42.8658917592 -17 05 17.389038732   16.5 16.5 16.1   ~ 124 1
9 LBQS 1209+1046 QSO 12 11 40.6043132184 +10 30 02.074373208   18.52 18.37     ~ 111 0
10 4C -02.55 QSO 12 32 00.0159535440 -02 24 04.793069304   17.41 17.06 16.4   ~ 401 1
11 3C 286 Sy1 13 31 08.2883506368 +30 30 32.960091564   17.51 17.25     ~ 4065 2
12 QSO B1331+170 QSO 13 33 35.7827544072 +16 49 04.013500728   16.84 16.71 16.41   ~ 426 0
13 4C 23.43 Sy1 16 24 39.0838297968 +23 45 12.223370412   17.91 17.47     ~ 326 1

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2022.05.26-04:18:16

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