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New constraints on the physical conditions in H$_2$-bearing GRB-host damped Lyman-$alpha$ absorbers | K. E. Heintz
; J. Bolmer
; C. Ledoux
; P. Noterdaeme
; J.-K. Krogager
; J. P. U. Fynbo
; P. Jakobsson
; S. Covino
; V. D'Elia
; M. De Pasquale
; D. H. Hartmann
; L. Izzo
; J. Japelj
; D. A. Kann
; L. Kaper
; P. Petitjean
; A. Rossi
; R. Salvaterra
; P. Schady
; J. Selsing
; R. Starling
; N. R. Tanvir
; C. C. Thöne
; A. de Ugarte Postigo
; S. D. Vergani
; D. Watson
; K. Wiersema
; T. Zafar
; | Date: |
6 Aug 2019 | Abstract: | We report the detections of molecular hydrogen (H$_2$), vibrationally-excited
H$_2$ (H$^*_2$), and neutral atomic carbon (CI), in two new afterglow spectra
of GRBs,181020A ($z=2.938$) and 190114A ($z=3.376$), observed with X-shooter
at the Very Large Telescope (VLT). Both host-galaxy absorption systems are
characterized by strong damped Lyman-$alpha$ absorbers (DLAs) and substantial
amounts of molecular hydrogen with $log N$(HI, H$_2$) = $22.20pm
0.05,~20.40pm 0.04$ (GRB,181020A) and $log N$(HI, H$_2$) = $22.15pm
0.05,~19.44pm 0.04$ (GRB,190114A). The DLA metallicites, depletion levels and
dust extinctions are [Zn/H] = $-1.57pm 0.06$, [Zn/Fe] = $0.67pm 0.03$, and
$A_V = 0.27pm 0.02$,mag (GRB,181020A) and [Zn/H] = $-1.23pm 0.07$, [Zn/Fe]
= $1.06pm 0.08$, and $A_V = 0.36pm 0.02$,mag (GRB,190114A). We then examine
the molecular gas content of all known H$_2$-bearing GRB-DLAs and explore the
physical conditions and characteristics of these systems. We confirm that H$_2$
is detected in all CI- and H$^*_2$-bearing GRB absorption systems, but that
these rarer features are not necessarily detected in all GRB H$_2$ absorbers.
We find that a large molecular fraction of $f_{
m H_2} gtrsim 10^{-3}$ is
required for CI to be detected. The defining characteristic for H$^*_2$ to be
present is less clear, though a large H$_2$ column density is an essential
factor. We then derive the H$_2$ excitation temperatures of the molecular gas
and find that they are relatively low with $T_{
m ex} approx 100 - 300$,K,
however, there could be evidence of warmer components populating the high-$J$
H$_2$ levels in GRBs,181020A and 190114A. Finally, we demonstrate that the
otherwise successful X-shooter GRB afterglow campaign is hampered by a
significant dust bias excluding the most dust-obscured H$_2$ absorbers from
identification [Abridged]. | Source: | arXiv, 1908.2309 | Services: | Forum | Review | PDF | Favorites |
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