J/ApJ/819/162ivo://CDS.VizieR/J/ApJ/819/162doi:10.26093/cds/vizier.18190162CDSPandya V.Mulchaey J.Greene J.E.2017-06-26T11:50:39Z2016-06-22T14:29:20ZCDS support team

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

cds-question@unistra.frgalaxiesvisible-astronomyradial-velocityx-ray-sourcesWe present the first comprehensive archival study of the X-ray properties of ultracompact dwarf (UCD) galaxies, with the goal of identifying weakly accreting central black holes in UCDs. Our study spans 578 UCDs distributed across 13 different host systems, including clusters, groups, fossil groups, and isolated galaxies. Of the 336 spectroscopically confirmed UCDs with usable archival Chandra imaging observations, 21 are X-ray-detected. Imposing a completeness limit of L_X_>2x10^38^erg/s, the global X-ray detection fraction for the UCD population is ~3%. Of the 21 X-ray-detected UCDs, seven show evidence of long-term X-ray time variability on the order of months to years. X-ray-detected UCDs tend to be more compact than non-X-ray-detected UCDs, and we find tentative evidence that the X-ray detection fraction increases with surface luminosity density and global stellar velocity dispersion. The X-ray emission of UCDs is fully consistent with arising from a population of low-mass X-ray binaries (LMXBs). In fact, there are fewer X-ray sources than expected using a naive extrapolation from globular clusters. Invoking the fundamental plane of black hole activity for SUCD1 near the Sombrero galaxy, for which archival Jansky Very Large Array imaging at 5GHz is publicly available, we set an upper limit on the mass of a hypothetical central black hole in that UCD to be <~10^5^M_{sun}_. While the majority of our sources are likely LMXBs, we cannot rule out central black holes in some UCDs based on X-rays alone, and so we address the utility of follow-up radio observations to find weakly accreting central black holes.2016ApJ...819..162Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/819/162CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/chandra : The Chandra Archive Log (CXC, 1999-2014)IX/45 : The Chandra Source Catalog, Release 1.1 (Evans+ 2012)J/A+A/586/A102 : UCDs in the halo of NGC1399 (Voggel+, 2016)J/ApJ/802/30 : NGVS VI. Ultra-compact dwarfs in M87 (Zhang+, 2015)J/MNRAS/443/1151 : AIMSS Project. I. Compact Stellar Systems (Norris+, 2014)J/AJ/148/32 : Globular cluster candidates in NGC 3115 (Jennings+, 2014)J/ApJS/204/14 : Deep Chandra observations of NGC 4649. I. (Luo+, 2013)J/MNRAS/422/885 : Ultracompact dwarf galaxies in Perseus (Penny+, 2012)J/ApJ/748/124 : AGN X-ray variability in the 4Ms catalog (Young+, 2012)J/AJ/142/199 : Sizes and luminosities of stellar systems (Brodie+, 2011)J/ApJ/737/86 : UCD galaxies in the Coma cluster (Chiboucas+, 2011)J/MNRAS/414/3699 : Study of hot stellar systems and galaxies (Misgeld+, 2011)J/A+A/531/A4 : Ultra compact dwarfs and globulars in Hya I (Misgeld+, 2011)J/ApJ/714/25 : AMUSE-Virgo survey. II. (Gallo+, 2010)J/AJ/137/498 : UCD and bright GC in Fornax (Gregg+, 2009)J/A+A/486/697 : Hydra I Cluster Catalogue (HCC) (Misgeld+, 2008)J/A+A/472/111 : Centaurus Compact Object Survey (Mieske+, 2007)J/A+A/464/L21 : Velocities of globular clusters in Fornax (Bergond+, 2007)J/A+A/418/445 : FCOS Ultra Compact Dwarf galaxies RVs (Mieske+, 2004)J/ApJ/613/279 : ACS Virgo Cluster Survey. III. M87 (Jordan+, 2004)J/ApJS/150/367 : Globular clusters in NGC 5128 (Peng+, 2004)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/819/162https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/819/162http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/819/162https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/819/162https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/819/162http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/819/162GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/819/162/table6 (Optical and X-ray properties of non-X-ray-detected UCDs)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/819/162/table6?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/819/162/table6?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/819/162/table6?GETtext/xml+votable180.050000true38.4183337.806390.005555555555555556Cone search capability for table J/ApJ/819/162/ucdgal (Optical and X-ray properties of X-ray-detected ultracompact dwarf (UCD) galaxies)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/819/162/ucdgal?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/819/162/ucdgal?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/819/162/ucdgal?GETtext/xml+votable180.050000true54.64083-35.432550.0055555555555555565/8633 6/1701 2369 2371 2372 2376 2377 2380 10379 17745 25083 26803 26809 27719 27737 27740 27743 27765 27767 27907 27913 27936 27938 28045 34540 36621 38852 38853 43262 43263 43626 43627 46987 47078https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/819/162?format=asciiOpticalX-raydefaultJ/ApJ/819/162/table6Optical and X-ray properties of non-X-ray-detected UCDsSimbadNameSimbad column added by the CDSmeta.idcharUCDAdopted UCD literature name (1)meta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSystUCD host systemmeta.id.parentcharRAJ2000Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.mainDist[3/105] Host system adopted distanceMpcpos.distance;pos.heliocentricfloatVMag[-16.2/-9.1]? Absolute V band magnitudemagphys.magAbs;em.opt.VfloatnullablelogM[5/9]? Log dynamical masslog(solMass)pos.parallax.dynfloatnullablerhl[2.6/101]? Optical half-light radiuspcphys.size.radiusfloatnullableHRV[300/9955]? Heliocentric radial velocitykm/sspect.dopplerVeloc;pos.heliocentricfloatnullablesigma[4/78]? Global stellar velocity dispersionkm/sphys.veloc.dispersionfloatnullableM/L[0.1/20]? Dynamical mass-to-light ratio in the V-bandlog(solMass.solLum**-1)phys.composition.massLightRatiofloatnullableExp[4/1494]? Total Chandra exposure timekstime.duration;obs.exposureintnullabletheta? Average off-axis angle (2)arcmininstr.offset;stat.meanfloatnullableRad[0/26.2]? Average radius of circular aperture (3)arcsecphys.angSize;srcfloatnullableCts[0/28921]? Total counts in source regionctphot.count;em.X-rayfloatnullableBkgd? Scaled background counts in background regionctinstr.background;obs.fieldfloatnullableU[0.9/393]? Number of counts expected (4)phot.countfloatnullablel_logFFLimit flag on logFFmeta.code.errorcharlogFF[-16/-13]? Log Full band (0.5-7 keV) flux upper limit (based on U counts)log(mW.m**-2)phot.flux;em.X-rayfloatnullablel_logLFLimit flag on LFmeta.code.errorcharlogLF[35/41]? Log Full band (0.5-7keV) luminosity upper limit (based on U counts)log(1e-07W)phys.luminosity;em.X-rayfloatnullableRefPrimary reference for UCD's optical properties (5)meta.ref;pos.framecharUCatDisplay reference catalogs (Gregg+, 2009, J/AJ/137/498; Chiboucas+, 2011, J/ApJ/737/86; Jennings+, 2014, J/AJ/148/32; Mieske+, 2007, J/A+A/472/111; Misgeld+, 2011, J/A+A/531/A4 and Penny+, 2012, J/MNRAS/422/885) within 3"meta.ref.urlintnullableJ/ApJ/819/162/ucdgalOptical and X-ray properties of X-ray-detected ultracompact dwarf (UCD) galaxiesSimbadNameSimbad column added by the CDSmeta.idcharUCDAdopted UCD literature namemeta.id;meta.maincharn_UCDNote on UCD (3)meta.notecharSystUCD host systemmeta.id.parentcharRefPrimary reference for UCD's optical properties (2)meta.ref;pos.framechargamma[0.9/1.8] Best-fit power law photon index (8)spect.indexfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintf_UCDFlag on UCD (G1)meta.codecharRAJ2000Right Ascension of the optical source (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of the optical source (J2000)degpos.eq.dec;meta.mainDist[3/21] Adopted distanceMpcpos.distance;pos.heliocentricfloatVMag[9.8/14.2]? Absolute V band magnitudemagphys.magAbs;em.opt.VfloatnullablelogM[6/9]? Log dynamical masslog(solMass)pos.parallax.dynfloatnullablee_logM[5/8]? Uncertainty in logMlog(solMass)stat.errorfloatnullablerhl[1.8/24.2]? Optical half-light radiuspcphys.size.radiusfloatnullablee_rhl[0.5/1.4]? Uncertainty in rhlpcstat.errorfloatnullableHRV[440/2024] Heliocentric radial velocitykm/sspect.dopplerVeloc;pos.heliocentricfloatsigma[8/68]? Global stellar velocity dispersionkm/sphys.veloc.dispersionfloatnullablee_sigma[1/6]? Uncertainty in sigmakm/sstat.errorfloatnullableM/L[0.9/5]? Dynamical mass-to-light ratio in the V-bandlog(solMass.solLum**-1)phys.composition.massLightRatiofloatnullablee_M/L[0.3/1.4]? Uncertainty in M/Llog(solMass.solLum**-1)stat.errorfloatnullablenLMXB[0.01/14]? Expected number of LMXBs (1)meta.numberfloatnullableExp[39/843] Total exposure timekstime.duration;obs.exposureintthetaAverage off-axis angle (4)arcmininstr.offset;stat.meanfloatsx[0.1/1.5]? Separation between optical X-ray positions (5)arcsecpos.angDistancefloatnullableRad[1.9/17] Average radius of circular aperture (6)arcsecphys.angSize;srcfloatNCF[5/3587] Net full band (0.5-7 keV) countsctphot.count;em.X-rayfloate_NCFThe 1{sigma} uncertainty in NCF (7)ctstat.errorfloatNCH[0.5/1313] Net hard band (2-7 keV) countsctphot.count;em.X-rayfloate_NCHThe 1{sigma} uncertainty in NCH (7)ctstat.errorfloatNCS[4/2287] Net soft band (0.5-2 keV) countsctphot.count;em.X-rayfloate_NCSThe 1{sigma} uncertainty in NCS (7)ctstat.errorfloatlogFF[-15.4/-13.1] Log Full band (0.5-7 keV) flux; in erg/s/cm^2^log(mW.m**-2)phot.flux;em.X-rayfloatE_logFFUpper 90% confidence interval in FFlog(mW.m**-2)stat.error;stat.maxfloate_logFFLower 90% confidence interval in FFlog(mW.m**-2)stat.errorfloatlogFH[-14.8/-13.3] Log Hard band (2-7 keV) flux; in erg/s/cm^2^log(mW.m**-2)phot.flux;em.X-rayfloatE_logFHUpper 90% confidence interval in FHlog(mW.m**-2)stat.error;stat.maxfloate_logFHLower 90% confidence interval in FHlog(mW.m**-2)stat.errorfloatlogFS[-15.8/-13.6] Log Soft band (0.5-2 keV) flux; in erg/s/cm^2^log(mW.m**-2)phot.flux;em.X-rayfloatE_logFSUpper 90% confidence interval in FSlog(mW.m**-2)stat.error;stat.maxfloate_logFSLower 90% confidence interval in FSlog(mW.m**-2)stat.errorfloatlogLF[36.4/38.8] Log Full band (0.5-7keV) luminosity; in erg/slog(1e-07W)phys.luminosity;em.X-rayfloatE_logLFUpper 90% confidence interval in LFlog(1e-07W)stat.error;stat.maxfloate_logLFLower 90% confidence interval in LFlog(1e-07W)stat.errorfloatlogLH[36.4/38.7] Log Hard band (2-7 keV) luminosity; in erg/slog(1e-07W)phys.luminosity;em.X-rayfloatE_logLHUpper 90% confidence interval in LHlog(1e-07W)stat.error;stat.maxfloate_logLHLower 90% confidence interval in LHlog(1e-07W)stat.errorfloatlogLS[36/38.3] Log Soft band (0.5-2 keV) luminosity; in erg/slog(1e-07W)phys.luminosity;em.X-rayfloatE_logLSUpper 90% confidence interval in LSlog(1e-07W)stat.error;stat.maxfloate_logLSLower 90% confidence interval in LSlog(1e-07W)stat.errorfloatHRClassical hardness ratio ((CH-CS)/(CH+CS))phot.flux;arith.ratiofloatE_gamma? Upper 90% confidence interval in gammastat.error;stat.maxfloatnullablee_gamma? Lower 90% confidence interval in gammastat.errorfloatnullableG09Display Gregg+, 2009, J/AJ/137/498, data within 3"meta.ref.urlintnullable