J/ApJ/768/77ivo://CDS.VizieR/J/ApJ/768/77doi:10.26093/cds/vizier.17680077CDSAdams E.A.K.Giovanelli R.Haynes M.P.2017-06-01T08:52:17Z2015-01-07T12:44:06ZCDS support team

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

cds-question@unistra.frdiffuse-molecular-cloudsradio-astronomyredshiftedsurveysh-i-line-emissionWe present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34Jy.km/s, median angular diameters of 10', and median velocity widths of 23km/s. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ~1Mpc, the UCHVCs have neutral hydrogen (HI) masses of ~10^5^-10^6^M_{sun}_, HI diameters of ~2-3kpc, and indicative dynamical masses within the HI extent of ~10^7^-10^8^M_{sun}_, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.2013ApJ...768...77Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/768/77CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVIII/73 : HI Parkes All Sky Survey Catalogue (HIPASS) (Meyer+, 2004)VIII/54 : Atlas of Galactic Neutral Hydrogen (Hartmann+, 1997)J/ApJS/209/12 : High-velocity clouds from GASS. I. (Moss+, 2013)J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)J/ApJ/758/44 : The GALFA-HI compact cloud catalog (Saul+, 2012)J/ApJ/756/79 : Opt. photometry in 3 Local Group dwarf galaxies (Sand+, 2012)J/MNRAS/415/1105 : Intermediate high-velocity clouds distances (Smoker+, 2011)J/AJ/142/170 : ALFALFA survey: {alpha}.40 HI source catalog (Haynes+, 2011)J/ApJ/722/367 : HI clouds in Quadrant I of the Milky Way (Ford+, 2010)J/ApJ/711/361 : Local Group dE galaxies. II. (Geha+, 2010)J/ApJ/702/940 : Radio and UV spectra of HVC toward the MC (Lehner+, 2009)J/AJ/133/2569 : Arecibo legacy fast ALFA survey III. (Giovanelli+, 2007)J/ApJ/653/240 : Low-mass SDSS dwarf galaxy properties (Geha+, 2006)J/ApJ/623/181 : Compact HVC photometry catalog (Siegel+, 2005)J/MNRAS/346/787 : HIDEEP survey (Minchin+, 2003)J/A+A/391/159 : A search for Compact High-Velocity Clouds (De Heij+, 2002)J/AJ/123/873 : HIPASS high-velocity clouds (Putman+, 2002)J/AJ/113/1197 : 21cm Spectra (Haynes+ 1997)J/ApJS/79/77 : Bell Lab. H I Survey - High Velocity Clouds (Stark+ 1992)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/768/77https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/768/77http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/768/77https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/768/77https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/768/77http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/768/77GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/768/77/uchvc (ALFALFA ultra-compact high velocity clouds (UCHVCs) in the {alpha}.40 survey and inferred cloud properties)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/768/77/uchvc?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/768/77/uchvc?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/768/77/uchvc?GETtext/xml+votable180.050000true1.4762531.3372220.005555555555555556Cone search capability for table J/ApJ/768/77/table2 (UCHVCs from Giovanelli+ (2010ApJ...708L..22G) that fail UCHVC criteria)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/768/77/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/768/77/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/768/77/table2?GETtext/xml+votable180.050000true162.208755.0719440.0055555555555555566/824 2126 2149 2211 2216 4585 4828 4842 4843 8244 8302 8303 8328 8348 8382 8388 8473 8512 8514 8932 12758 13350 13354 13422 13466 13473 13486 18414 19784 20014 20334 20373 22487 26073 26076 26102 26330 26338 26352 26363 26383 26523 26553 26570 26600 27101 27111 27117 27124 27413 27454 27673 27729 27733 27775 27808 27883 27904 28224 31483 31526 31691 31715 31720https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/768/77?format=asciiOpticalRadiodefaultJ/ApJ/768/77/uchvcALFALFA ultra-compact high velocity clouds (UCHVCs) in the {alpha}.40 survey and inferred cloud propertiesNotesNotes (7)meta.notecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHVCHVC designation (LLL.ll+BB.bb+Vlsr) (G1)meta.id;meta.maincharf_HVC[sabc, ] Flag on source (1)meta.codecharAGCArecibo General Catalog number (2)meta.idintRAJ2000Hour of right ascension (J2000) (3)pos.eq.ra;meta.mainDEJ2000Degree of declination (J2000) (3)pos.eq.dec;meta.maincz[-461/323] Heliocentric czkm/sphys.veloc;pos.heliocentricintVlsr[-454/327] LSR velocity (assumed solar motion of 20km/s toward l=57{deg}, b=25{deg})km/sphys.veloc;src.orbital.meanMotion;pos.lsrintVgsr[-282/298] Velocity in the Galactic standard of rest frame (GSR; Vgsr=Vlsr+225sinlcosb)km/sphys.veloc;pos.galacticintVLG[-294/264] Velocity with respect to the Local Group (LG) reference (4)km/smeta.ref;phys.veloc;pos.frameintW50[15/62] HI line FWHM (W50)km/sspect.line.widthinte_W50[1/15] W50 uncertaintykm/sstat.errorinta[4/29] Estimated cloud major diameter (5)arcminphys.angSizeintb[3/16] Estimated cloud minor diameter (5)arcminphys.angSizeintS21[0.2/8.6] 21cm integrated flux densityJy.km/sphot.fluxfloatS/N[4/44] Signal-to-noise ratio of the line (6)stat.snr;spect.lineintN3[0/5] The number of {alpha}.40 HVC neighbors within D=3{deg} (for f=0.2{deg}/km/s)meta.numberintN10[0/42] The number of {alpha}.40 HVC neighbors within D=10{deg} (for f=0.2{deg}/km/s)meta.numberintSimbadSimbad column added by the CDSmeta.ref.urlcharNEDSimbad column added by the CDSmeta.ref.urlcharDHI[1.2/6.2] HI diameter at d=1Mpc (Equation 9)kpcpos.distancefloatnHI[-3.7/-2.1] Log of the mean atomic HI density at d=1Mpc (Equation 5)log(cm**-3)phys.densityfloatlogNHI[18.3/19.3] Log of the mean HI column density (Equation 6)log(cm**-2)phys.columnDensity;stat.meanfloatlogMHI[5/6.3] Log of the HI mass at d=1Mpc (Equation 7)log(solMass)phys.massfloatlogMdyn[6.8/8.4] Log of the indicative dynamical mass within DHI at d=1Mpc (Equation 8)log(solMass)phys.massfloatJ/ApJ/768/77/table2UCHVCs from Giovanelli+ (2010ApJ...708L..22G) that fail UCHVC criteriarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHVCHVC designation (LLL.ll+BB.bb+Vlsr) (G1)meta.id;meta.maincharAGCArecibo General Catalog number (2)meta.idintRAJ2000Hour of right ascension (J2000) (3)pos.eq.ra;meta.mainDEJ2000Degree of declination (J2000) (3)pos.eq.dec;meta.maincz[-461/323] Heliocentric czkm/sphys.veloc;pos.heliocentricintVlsr[-454/327] LSR velocity (assumed solar motion of 20km/s toward l=57{deg}, b=25{deg})km/sphys.veloc;src.orbital.meanMotion;pos.lsrintVgsr[-282/298] Velocity in the Galactic standard of rest frame (GSR; Vgsr=Vlsr+225sinlcosb)km/sphys.veloc;pos.galacticintVLG[-294/264] Velocity with respect to the Local Group (LG) reference (4)km/smeta.ref;phys.veloc;pos.frameintW50[15/62] HI line FWHM (W50)km/sspect.line.widthinte_W50[1/15] W50 uncertaintykm/sstat.errorinta[4/29] Estimated cloud major diameter (5)arcminphys.angSizeintb[3/16] Estimated cloud minor diameter (5)arcminphys.angSizeintS21[0.2/8.6] 21cm integrated flux densityJy.km/sphot.fluxfloatS/N[4/44] Signal-to-noise ratio of the line (6)stat.snr;spect.lineintN3[0/5] The number of {alpha}.40 HVC neighbors within D=3{deg} (for f=0.2{deg}/km/s)meta.numberintN10[0/42] The number of {alpha}.40 HVC neighbors within D=10{deg} (for f=0.2{deg}/km/s)meta.numberintNotesNotesmeta.notecharNEDSimbad column added by the CDSmeta.ref.urlchar