Evidence for diffuse molecular gas and dust in the hearts of gamma-ray burst host galaxies
J. Bolmer, C. Ledoux, P. Wiseman, A. De Cia, J. Selsing, P. Schady, J. Greiner, S. Savaglio, J. M. Burgess, V. D'Elia, J. P. U. Fynbo, P. Goldoni, D. Hartmann, … 展开作者
J. Bolmer, C. Ledoux, P. Wiseman, A. De Cia, J. Selsing, P. Schady, J. Greiner, S. Savaglio, J. M. Burgess, V. D'Elia, J. P. U. Fynbo, P. Goldoni, D. Hartmann, K. E. Heintz, P. Jakobsson, J. Japelj, L. Kaper, N. R. Tanvir, P. M. Vreeswijk, T. Zafar
Here we built up a sample of 22 GRBs at redshifts $z > 2$ observed with X-shooter to determine the abundances of hydrogen, metals, dust, and molecular species. This allows us to study the metallicity and dust depletion effects in the neutral ISM at high redshift and to answer the question whether (and why) there might be a lack of H$_2$ in GRB-DLAs. We fit absorption lines and measure the column densities of different metal species as well as atomic and molecular hydrogen. The derived relative abundances are used to fit dust depletion sequences and determine the dust-to-metals ratio and the host-galaxy intrinsic visual extinction. There is no lack of H$_2$-bearing GRB-DLAs. We detect absorption lines from H$_2$ in 6 out of 22 GRB afterglow spectra, with molecular fractions ranging between $f\simeq 5\cdot10^{-5}$ and $f\simeq 0.04$, and claim tentative detections in three other cases. The GRB-DLAs in the present sample have on average low metallicities ($\mathrm{[X/H]}\approx -1.3$), comparable to the rare population of QSO-ESDLAs (log N(HI) $> 21.5$). H$_2$-bearing GRB-DLAs are found to be associated with significant dust extinction, $A_V > 0.1$ mag, and have dust-to-metals ratios DTM$ > 0.4$. All of these systems exhibit column densities of log N(HI) $> 21.7$. The overall fraction of H$_2$ detections is $\ge 27$% (41% including tentative detections), which is three times larger than in the general population of QSO-DLAs. For $2<z<4$, and for log N(HI) $> 21.7$, the H$_2$ detection fraction is 60-80% in GRB-DLAs as well as in extremely strong QSO-DLAs. This is likely a consequence of the fact that both GRB- and QSO-DLAs with high N(HI) probe sight-lines with small impact parameters that indicate that the absorbing gas is associated with the inner regions of the absorbing galaxy, where the gas pressure is higher and the conversion of HI to H$_2$ takes place.
The Star Formation History and Evolution of the Ultra-Diffuse M81 Satellite F8D1
Space Telescope Science Institute（太空望远镜科学研究所）；Tufts University（塔夫茨大学）；University of Michigan（密歇根大学）；University of Washington（华盛顿大学）；Dartmouth College（达特茅斯学院）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；University of Alabama（阿拉巴马大学）；The Chinese University of Hong Kong（香港中文大学）；Flatiron Institute（平顿研究所）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）
