J/A+A/592/A142ivo://CDS.VizieR/J/A+A/592/A142doi:10.26093/cds/vizier.35920142CDSRoehser T.Kerp J.Ben Bekhti N.Winkel B.2018-03-13T09:19:30Z2016-08-18T19:20:18ZCDS support team

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

cds-question@unistra.frmilky-way-galaxyinterstellar-mediumh-i-line-emissionco-line-emissionspectroscopyIntermediate-velocity clouds (IVCs) are HI halo clouds that are likely related to a Galactic fountain process. In-falling IVCs are candidates for the re-accretion of matter onto the Milky Way. Aims. We study the evolution of IVCs at the disk-halo interface, focussing on the transition from atomic to molecular IVCs. We compare an atomic IVC to a molecular IVC and characterise their structural differences in order to investigate how molecular IVCs form high above the Galactic plane. With high-resolution HI observations of the Westerbork Synthesis Radio Telescope and ^12^CO(1-0) and ^13^CO(1-0) observations with the IRAM 30m telescope, we analyse the small-scale structures within the two clouds. By correlating HI and far-infrared (FIR) dust continuum emission from the Planck satellite, the distribution of molecular hydrogen (H_2_) is estimated. We conduct a detailed comparison of the HI, FIR, and CO data and study variations of the XCO conversion factor. The atomic IVC does not disclose detectable CO emission. The atomic small-scale structure, as revealed by the high-resolution HI data, shows low peak HI column densities and low HI fluxes as compared to the molecular IVC. The molecular IVC exhibits a rich molecular structure and most of the CO emission is observed at the eastern edge of the cloud. There is observational evidence that the molecular IVC is in a transient and, thus, non- equilibrium phase. The average XCO factor is close to the canonical value of the Milky Way disk. We propose that the two IVCs represent different states in a gradual transition from atomic to molecular clouds. The molecular IVC appears to be more condensed allowing the formation of H_2_ and CO in shielded regions all over the cloud. Ram pressure may accumulate gas and thus facilitate the formation of H_2_. We show evidence that the atomic IVC will evolve also into a molecular IVC in a few Myr.2016A&A...592A.142Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/592/A142CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/592/A142https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/592/A142http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/592/A142https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/592/A142https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/592/A142http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/592/A142GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/592/A142/list (List of fits datacubes)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/592/A142/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/592/A142/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/592/A142/list?GETtext/xml+votable180.050000true178.7493120.882640.0055555555555555566/5184 28418 28424https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/592/A142?format=asciiRadiodefaultJ/A+A/592/A142/listList of fits datacubesNxNumber of pixels along X-axispixmeta.numberintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right ascension (J2000) of data cube centerdegpos.eq.ra;meta.mainDEJ2000Declination (J2000) of data cube centerdegpos.eq.dec;meta.mainNyNumber of pixels along Y-axispixmeta.numberintNzNumber of slicespixmeta.numberintObs.DateObservation date (YYYY-MM-DDThh:mm:ss.ssssss)time.epoch;obscharVLSRlLower value of LSR velocity intervalkm/sphys.veloc;time.interval;pos.lsrfloatVLSRuUpper value of LSR velocity intervalkm/sphys.veloc;time.interval;pos.lsrfloatdVLSRSpectral resolution in LSR velocitykm/sspect.resolutionfloatsizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of the FITS file in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the fits filemeta.title;meta.fitschar