A HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1:
Molecular fraction and excitation temperature
S. Muzahid, R. Srianand, and J. Charlton. (2014)cite arxiv:1410.3828Comment: 14 pages, 9 figures, 4 tables (+additional 21 pages of appendices), Submitted to the MNRAS, comments welcome!.
Abstract
We present the results of a systematic search for molecular hydrogen (H2) in
low redshift (0.05 < z < 0.7) damped and sub-damped Lya absorption systems
(DLAs/sub-DLAs) with N(HI) > 10^19.0 cm^-2, in the archival Hubble Space
Telescope (HST)/Cosmic Origins Spectrograph (COS) spectra. Our core sample is
comprised of 27 systems with a median log N(HI) = 19.6. This is a factor of ~
10 lower than that of the high-z (z > 2) sample of Noterdaeme et al. H2
absorption is detected in 10 cases (3/5 in DLAs and 7/22 in sub-DLAs). On the
average, our survey is sensitive down to log N(H2) = 14.4 corresponding to a
molecular mass fraction of log f_H2 = -4.9 at the median N(HI). The H2
incidence rate of 50^+25_-12 percent, is a factor of > 2 higher than that
of the high-z sample, for systems with N(H2) > 10^14.4 cm^-2. The enhanced
incidence rate could result from the increase of the cosmic mean metallicities
of DLAs and sub-DLAs with cosmic time. In spite of having systematically lower
N(HI) values, low-z H2 systems show molecular mass fractions (log f_H2 = -1.93
$\pm$ 0.63) that are comparable to the high-z measurements. The rotational
excitation temperatures (T_01 = 133 $\pm$ 55 K), as measured in our low-z
sample, are typically consistent with high-z measurements. Simple
photoionization models demonstrate that the radiation field prevailing in the
low-z H2 systems cannot have an appreciable stellar contribution for densities
of 10-100 cm^-3. The impact parameters of the nearest possible host-galaxy
candidates are typically large (e.g. 10 < $\rho$ (kpc) < 80). We, therefore,
conjecture that the low-z H2 bearing gas is not related to star-forming disks
but stems from self-shielded, tidally stripped or ejected disk-material in the
extended halo.
Description
[1410.3828] A HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1: Molecular fraction and excitation temperature
%0 Generic
%1 muzahid2014hstcos
%A Muzahid, Sowgat
%A Srianand, Raghunathan
%A Charlton, Jane
%D 2014
%K dla gas low-z molecular
%T A HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1:
Molecular fraction and excitation temperature
%U http://arxiv.org/abs/1410.3828
%X We present the results of a systematic search for molecular hydrogen (H2) in
low redshift (0.05 < z < 0.7) damped and sub-damped Lya absorption systems
(DLAs/sub-DLAs) with N(HI) > 10^19.0 cm^-2, in the archival Hubble Space
Telescope (HST)/Cosmic Origins Spectrograph (COS) spectra. Our core sample is
comprised of 27 systems with a median log N(HI) = 19.6. This is a factor of ~
10 lower than that of the high-z (z > 2) sample of Noterdaeme et al. H2
absorption is detected in 10 cases (3/5 in DLAs and 7/22 in sub-DLAs). On the
average, our survey is sensitive down to log N(H2) = 14.4 corresponding to a
molecular mass fraction of log f_H2 = -4.9 at the median N(HI). The H2
incidence rate of 50^+25_-12 percent, is a factor of > 2 higher than that
of the high-z sample, for systems with N(H2) > 10^14.4 cm^-2. The enhanced
incidence rate could result from the increase of the cosmic mean metallicities
of DLAs and sub-DLAs with cosmic time. In spite of having systematically lower
N(HI) values, low-z H2 systems show molecular mass fractions (log f_H2 = -1.93
$\pm$ 0.63) that are comparable to the high-z measurements. The rotational
excitation temperatures (T_01 = 133 $\pm$ 55 K), as measured in our low-z
sample, are typically consistent with high-z measurements. Simple
photoionization models demonstrate that the radiation field prevailing in the
low-z H2 systems cannot have an appreciable stellar contribution for densities
of 10-100 cm^-3. The impact parameters of the nearest possible host-galaxy
candidates are typically large (e.g. 10 < $\rho$ (kpc) < 80). We, therefore,
conjecture that the low-z H2 bearing gas is not related to star-forming disks
but stems from self-shielded, tidally stripped or ejected disk-material in the
extended halo.
@misc{muzahid2014hstcos,
abstract = {We present the results of a systematic search for molecular hydrogen (H2) in
low redshift (0.05 < z < 0.7) damped and sub-damped Lya absorption systems
(DLAs/sub-DLAs) with N(HI) > 10^19.0 cm^{-2}, in the archival Hubble Space
Telescope (HST)/Cosmic Origins Spectrograph (COS) spectra. Our core sample is
comprised of 27 systems with a median log N(HI) = 19.6. This is a factor of ~
10 lower than that of the high-z (z > 2) sample of Noterdaeme et al. H2
absorption is detected in 10 cases (3/5 in DLAs and 7/22 in sub-DLAs). On the
average, our survey is sensitive down to log N(H2) = 14.4 corresponding to a
molecular mass fraction of log f_H2 = -4.9 at the median N(HI). The H2
incidence rate of 50^{+25}_{-12} percent, is a factor of > 2 higher than that
of the high-z sample, for systems with N(H2) > 10^14.4 cm^{-2}. The enhanced
incidence rate could result from the increase of the cosmic mean metallicities
of DLAs and sub-DLAs with cosmic time. In spite of having systematically lower
N(HI) values, low-z H2 systems show molecular mass fractions (log f_H2 = -1.93
$\pm$ 0.63) that are comparable to the high-z measurements. The rotational
excitation temperatures (T_01 = 133 $\pm$ 55 K), as measured in our low-z
sample, are typically consistent with high-z measurements. Simple
photoionization models demonstrate that the radiation field prevailing in the
low-z H2 systems cannot have an appreciable stellar contribution for densities
of 10-100 cm^{-3}. The impact parameters of the nearest possible host-galaxy
candidates are typically large (e.g. 10 < $\rho$ (kpc) < 80). We, therefore,
conjecture that the low-z H2 bearing gas is not related to star-forming disks
but stems from self-shielded, tidally stripped or ejected disk-material in the
extended halo.},
added-at = {2014-10-16T10:06:24.000+0200},
author = {Muzahid, Sowgat and Srianand, Raghunathan and Charlton, Jane},
biburl = {https://www.bibsonomy.org/bibtex/2aa76bffd526ea9a9ac1bb15e8d46ccf2/miki},
description = {[1410.3828] A HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1: Molecular fraction and excitation temperature},
interhash = {82088bf87c9af1b1e97547acf6da6b03},
intrahash = {aa76bffd526ea9a9ac1bb15e8d46ccf2},
keywords = {dla gas low-z molecular},
note = {cite arxiv:1410.3828Comment: 14 pages, 9 figures, 4 tables (+additional 21 pages of appendices), Submitted to the MNRAS, comments welcome!},
timestamp = {2014-10-16T10:06:24.000+0200},
title = {A HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1:
Molecular fraction and excitation temperature},
url = {http://arxiv.org/abs/1410.3828},
year = 2014
}