2003A&A...402..487V


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.01CET09:18:29

2003A&A...402..487V - Astronomy and Astrophysics, volume 402, 487-497 (2003/5-1)

Ar I as a tracer of ionization evolution.

VLADILO G., CENTURION M., D'ODORICO V. and PEROUX C.

Abstract (from CDS):

We present a study of Ar abundances in 15 damped Ly α systems (DLAs) in the redshift interval 2.3≤z≤3.4. The sample includes 4 UVES/VLT measurements of ArI column densities presented here for the first time, together with 6 measurements and 5 upper/lower limits collected from the literature (UVES/VLT and HIRES/Keck observations). The majority of DLAs show significant underabundances of Ar relative to other α-capture elements with common nucleosynthetic origin. We show that neither dust depletion nor intervening HII regions inside DLAs offer a viable justification to these underabundances. A natural explanation is found in the framework of photoionization models of HI regions embedded in an ionizing continuum with varying spectral distribution. At z∼2.5 the observed Ar deficiencies are large, [Ar/α]≃-0.6/-0.8dex, suggestive of a hard, QSO-dominated spectrum. At z>3 the deficiencies are instead small, suggestive of a soft, stellar-type spectrum, though more data are needed to generalize this high-z result. Should the change of Ar abundances with redshift be governed by the evolution of the UV stellar emission internal to DLAs, a synchronization of the star formation in DLAs would be required, with a strong stellar emission at z>3, but weak at z<3. This variation seems inconsistent with the weak signal of evolution indicated by abundance studies of DLAs. More likely, the change of Ar abundances is induced by the evolution of the UV metagalactic continuum, in which case the UV emission internal to DLAs must be small (i.e. DLAs should have modest star formation rates) and the external background must become softer at z>3. The former requirement is consistent with the modest evolution of DLAs abundances and the lack of Lyα and Hα emissions associated with DLAs. The latter requirement is consistent with the observed evolution of SiIV/CIV ratios in the IGM, the claims of high escape fraction of UV photons from Ly-break galaxies at z>3, and the recent finding that the HeII re-ionization seems to occur between z∼3.4 and z∼3. Comparison with results from local interstellar studies indicates that Ar abundances can be used to trace the evolution of the ionization history of the universe down to z=0, where [Ar/α]~-0.2dex. We predict a rise of Ar abundances in the redshift range from z≃2.3 to z=0, at the epoch at which the metagalactic field of galaxies overcomes that of quasars.

Abstract Copyright:

Journal keyword(s): intergalactic medium - ultraviolet: galaxies - cosmology: observations - quasars: absorption lines

CDS comments: QXO 0001 not identified.

Simbad objects: 12

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Number of rows : 12

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 7C 020156.39+363507.00 QSO 02 04 55.5955913869 +36 49 17.985305866     18.1     ~ 115 1
2 QSO B0336-017 QSO 03 39 00.9861802 -01 33 17.607418   20.1 19.1 18.8   ~ 104 2
3 QSO B0347-383 QSO 03 49 43.6605705480 -38 10 30.834942758     17.3     ~ 185 0
4 QSO B0528-2505 QSO 05 30 07.96279681 -25 03 29.8994010   18.17 17.34 17.7   ~ 406 0
5 QSO J0745+4734 QSO 07 45 21.7881463456 +47 34 36.191344902   16.76 16.44     ~ 88 0
6 QSO B0841+129 BLL 08 44 24.2446850407 +12 45 46.527740081   18.28 18.5     ~ 109 0
7 9C J0933+2845 QSO 09 33 37.2816369450 +28 45 32.316257697   19.63 17.94 17.50   ~ 62 0
8 QSO B1425+606 QSO 14 26 56.1848058014 +60 25 50.814100630   16.82 16.54     ~ 126 0
9 QSO B1759+7539 BLL 17 57 46.3591958319 +75 39 16.182864362     16.50     ~ 82 0
10 QSO J2246-6015 QSO 22 47 08.9261267635 -60 15 45.301367673           ~ 61 0
11 QSO B2343+125 QSO 23 46 28.200 +12 49 00.00     17.5     ~ 130 2
12 QSO B2344+125 QSO 23 46 32.80 +12 45 40.0     17.0     ~ 82 1

    Equat.    Gal    SGal    Ecl

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