J/A+A/629/A131ivo://CDS.VizieR/J/A+A/629/A131doi:10.26093/cds/vizier.36290131CDSHeintz K.E.Bolmer J.Ledoux C.Noterdaeme P.Krogager J.-K.,Fynbo J.P.U.Jakobsson P.Covino S.D'Elia V.De Pasquale M.,Hartmann D.H.Izzo L.Japelj J.Kann D.A.Kaper L.Petitjean P.,Rossi A.Salvaterra R.Schady P.Selsing J.Starling R.Tanvir N.R.,Thoene C.C.de Ugarte Postigo A.Vergani S.D.Watson D.Wiersema K.,Zafar T.2019-09-16T08:40:40Z2019-09-16T08:10:39ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgamma-ray-astronomyspectroscopyultraviolet-astronomyvisible-astronomyinfrared-astronomyWe report the detections of molecular hydrogen (H_2_), vibrationally-excited H_2_ (H_2_*), and neutral atomic carbon (CI), an efficient tracer of molecular gas, 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 logN(HI,H_2_)=22.20+/-0.05, 20.40+/-0.04 (GRB 181020A) and logN(HI, H_2_)=22.15+/-0.05, 19.44+/-0.04 (GRB 190114A). The DLA metallicites, depletion levels, and dust extinctions are within the typical regimes probed by GRBs with [Zn/H]=-1.57+/-0.06, [Zn/Fe]=0.67+/-0.03, and AV=0.27+/-0.02mag (GRB 181020A) and [Zn/H]=-1.23+/-0.07, [Zn/Fe]=1.06+/-0.08, and AV=0.36+/-0.02mag (GRB 190114A). In addition, we examine the molecular gas content of all known H2-bearing GRB-DLAs and explore the physical conditions and characteristics required to simultaneously probe CI and H_2_*. We confirm that H2 is detected in all CI- and H2*-bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H2 absorbers. We find that a large molecular fraction of f_H2_>~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 also find that the observed line profiles of the molecular-gas tracers are kinematically "cold", with small velocity offsets of {delta}v<20km/s from the bulk of the neutral absorbing gas. We then derive the H_2_ excitation temperatures of the molecular gas and find that they are relatively low with Tex~=100-300K, however, there could be evidence of warmer components populating the high-J H_2_ levels in GRBs 181020A and 190114A. Finally, we demonstrate that even though the X-shooter GRB afterglow campaign has been successful in recovering several H2-bearing GRB-host absorbers, this sample is still hampered by a significant dust bias excluding the most dust-obscured H_2_ absorbers from identification. CI and H_2_* could open a potential route to identify molecular gas even in low-metallicity or highly dust-obscured bursts, though they are only efficient tracers for the most H2-rich GRB-host absorption systems.2019A&A...629A.131Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/629/A131CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/629/A131https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/629/A131http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/629/A131https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/629/A131https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/629/A131http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/629/A131GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/629/A131/list (List of fits spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/629/A131/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/629/A131/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/629/A131/list?GETtext/xml+votable180.050000true65.54391672.19141670.0055555555555555566/23306https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/629/A131?format=asciiGamma-rayUVOpticalInfrareddefaultJ/A+A/629/A131/listList of fits spectrarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintObs.dateObservation datestime.epoch;obsnullablesizeSize of FITS fileKibytephys.size;meta.fitsintspShow the spectrummeta.ref.urlcharFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitschar