J/A+A/618/A184ivo://CDS.VizieR/J/A+A/618/A184doi:10.26093/cds/vizier.36180184CDSRanjan A.Noterdaeme P.Krogager J.-K.Petitjean P.Balashev S.,Bialy S.Srianand R.Gupta N.Fynbo J.P.U.Ledoux C.Laursen P.2018-11-26T08:36:42Z2018-11-02T10:26:47ZCDS support team

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

cds-question@unistra.frquasarsvisible-astronomyspectroscopyultraviolet-astronomyWe present the detection and detailed analysis of a diffuse molecular cloud at z_abs_=2.4636 towards the quasar SDSS J151349.52+035211.28 (hereafter J1513+0352) (zem~=2.68) observed with the X-shooter spectrograph at the Very Large Telescope. We measure very high column densities of atomic and molecular hydrogen, with logN(HI,H_2_)~=21.8,21.3. This is the highest H_2_ column density ever measured in an intervening damped Lyman-{alpha}system but we do not detect CO, implying log N(CO)/N(H_2_)<-7.8, which could be due to a low metallicity of the cloud. From the metal absorption lines, we derive the metallicity to be Z~=0.15Z_{sun}_ and determine the amount of dust by measuring the induced extinction of the background quasar light, AV~=0.4. We simultaneously detect Ly{alpha} emission at the same redshift, with a centroid located at a most probable impact parameter of only {rho}~=1.4kpc. We argue that the line of sight is therefore likely passing through the interstellar medium of a galaxy, as opposed to the circumgalactic medium. The relation between the surface density of gas and that of star formation seems to follow the global empirical relation derived in the nearby Universe although our constraints on the star formation rate and on the galaxy extent remain too loose to be conclusive. We study the transition from atomic to molecular hydrogen using a theoretical description based on the microphysics of molecular hydrogen.We use the derived chemical properties of the cloud and physical conditions (Tk~=90K and n~=250cm^-3^) derived through the excitation of H_2_ rotational levels and neutral carbon fine structure transitions to constrain the fundamental parameters that govern this transition. By comparing the theoretical and observed HI column densities, we are able to bring an independent constraint on the incident UV flux, which we find to be in agreement with that estimated from the observed star formation rate.2018A&A...618A.184Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/618/A184CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/618/A184https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/618/A184http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/618/A184https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/618/A184https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/618/A184http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/618/A184GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/618/A184/list (List of spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/618/A184/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/618/A184/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/618/A184/list?GETtext/xml+votable180.050000true228.456333.869920.005555555555555556Associated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/A+A/618/A1846/8209https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/618/A184?format=asciiUVOpticaldefaultJ/A+A/618/A184/table2Column densities of H_2_ in different rotational levels at z_abs_=2.4636 towards J1513+0352recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSpeciesSpeciesmeta.notecharlogNColumn density of Specieslog(cm**-2)phys.columnDensityfloate_logNrms uncertainty on logNlog(cm**-2)stat.errorfloatJ/A+A/618/A184/table3Summary of column densities and abundancesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSpeciesSpeciesmeta.notecharlogNColumn density of Specieslog(cm**-2)phys.columnDensityfloate_logNrms uncertainty on logNlog(cm**-2)stat.errorfloat[X/H]? Observed gas-phase abundances (1)phys.abundfloatnullablee_[X/H]? rms uncertainty on [X/H]stat.error;phys.abundfloatnullablen_[X/H][f] Note on [X/H] (2)meta.notechar[X/Zn]? Depletion relative to Znphys.abundfloatnullablee_[X/Zn]? rms uncertainty on [X/Zn]stat.errorfloatnullableJ/A+A/618/A184/listList of spectraNxNumber of pointsmeta.numberintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNslitNumber of positions along slit in the spectrummeta.numberintObs.dateObservation datetime.epoch;obscharblambdaLower value of wavelength intervalnmem.wlfloatBlambdaUpper value of wavelength intervalnmem.wlfloatdlambdaSpectral resolutionnmspect.resolutionfloatsizeSize 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.fitscharAssocDataAssociated Data web pagemeta.ref.urlcharJ/A+A/618/A184/table1Journal of observationsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObs.DateObserving datetime.epochnullableWidthSlit widtharcsecspect.line.widthfloatInstArm name (UVB, VIS or NIR)meta.id;instrcharExpTimeExposure timestime.duration;obs.exposurecharSeeingDelivered seeing corrected by airmass in the VIS bandarcsecinstr.obsty.seeingfloatAirmassAirmass (recorded at start of exposure)obs.airMassfloatPA[] Position angle at the start of the observationdegpos.posAngint