J/ApJ/773/67ivo://CDS.VizieR/J/ApJ/773/67doi:10.26093/cds/vizier.17730067CDSRoy S.2015-04-24T17:55:51Z2015-03-19T13:15:01ZCDS support team

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

cds-question@unistra.frradio-continuum-emissionmilky-way-galaxyWe have observed the Galactic center (GC) region at 0.154 and 0.255GHz with the Giant Metrewave Radio Telescope. A total of 62 compact likely extragalactic (EG) sources are detected. Their scattering sizes decrease linearly with increasing angular distance from the GC up to about 1{deg}. The apparent scattering sizes of the sources are more than an order of magnitude less than predicted earlier by the NE2001 model of Galactic electron distribution within 359.5{deg}<l<0.5{deg} and -0.5{deg}<b<0.5{deg} (Hyperstrong Scattering Region) of the Galaxy. High free-free optical depths ({tau}) are observed toward most of the extended non-thermal sources within 0.6{deg} from the GC. Significant variation of {tau} indicates that the absorbing medium is patchy at an angular scale of ~10' and n_e_ is ~10/cm3, which matches the NE2001 model. This model predicts the EG sources to be resolved out from 1.4GHz interferometric surveys. However, out of 10 EG sources expected in the region, 8 likely EG are present in the 1.4GHz catalog. Ionized interfaces of dense molecular clouds to the ambient medium are most likely responsible for strong scattering and low radio frequency absorption. However, dense GC clouds traced by CS J=1-0 emission are found to have a narrow distribution of ~0.2{deg} across the Galactic plane. Angular distribution of most EG sources seen through the so-called Hyperstrong Scattering Region are random in b, and typically ~7 out of 10 sources will not be seen through the dense molecular clouds, which explains why most of them are not scatter broadened at 1.4GHz.2013ApJ...773...67Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/773/67CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AZh/91/503 : Compact radio sources near Galactic center (Pynzar'+, 2014)J/A+A/535/A38 : Observations of NOAO Bootes field at 153MHz (Intema+, 2011)J/ApJ/699/186 : VLA observations of the Galactic center (Zhao+, 2009)J/ApJS/174/481 : 2LC Compact Radio Sources in the GC (Lazio+, 2008)J/MNRAS/371/38 : X-ray observations of the Galaxy center (Wang+, 2006)J/AJ/130/586 : Compact radio sources in the galactic plane (White+, 2005)J/MNRAS/360/1305 : Polarization of extragalactic sources (Roy+, 2005)J/AJ/128/1646 : The Galactic Center region at 330MHz (Nord+, 2004)J/A+AS/147/195 : Pulsar spectra of radio emission (Maron+, 2000)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/773/67https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/773/67http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/773/67https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/773/67https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/773/67http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/773/67GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/773/67/table1 (Flux density and source sizes near the Galactic center (GC))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/773/67/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/773/67/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/773/67/table1?GETtext/xml+votable180.050000true266.09596-31.276820.0055555555555555565/7207 6/28813 28818 28819 28822 28823 28824 28826 28827 28848 28849 28851 28852 28853 28854 288721.0204147082982102e-25 9.276497240453405e-25https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/773/67?format=asciiRadiodefaultJ/ApJ/773/67/table1Flux density and source sizes near the Galactic center (GC)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGLONGalactic longitudedegpos.galactic.lonGLATGalactic latitudedegpos.galactic.latS154[106/1895]? 0.154GHz flux densitymJyphot.flux.density;em.radio.100-200MHzintnullableS255[94/2170]? 0.255GHz flux densitymJyphot.flux.density;em.radio.200-400MHzintnullableS1400[51/1623] 1.4GHz flux densitymJyphot.flux.density;em.radio.750-1500MHzintalpha[-3/1.4]? Spectral index (1)spect.indexfloatnullableSexp[67/10585]? Expected flux density at 154MHz (2)phot.flux.densityintnullableSexp/S[0.09/2.9]? Ratio of expected to measured flux densities at 0.154GHzphot.flux;arith.ratiofloatnullablet154[0/59.1]? Angular size {theta} at 0.154GHzarcsecphys.angSize;em.radio.100-200MHzfloatnullablet255[0/44.6]? Angular size {theta} at 0.255GHzarcsecphys.angSize;em.radio.200-400MHzfloatnullablet1400[0/13]? Angular size {theta} at 1.4GHzarcsecphys.angSize;em.radio.750-1500MHzfloatnullableSize[0/31]? Scattering size at a fiducial wavelength of 1m (3)arcsecphys.angSizeintnullableRCatCross-match within 15" with the 330MHz catalog of Nord+, 2004, J/AJ/128/1646; the 1.4GHz catalog of White+, 2005, J/AJ/130/586 and the 1.4GHz catalog of Lazio+, 2008, J/ApJS/174/481meta.ref.urlintnullableSEDPlot the spectrum with SPECFIND (Vollmer et al. 2009, Cat. VIII/85)meta.ref.urlchar_RA.icrsRight ascension (ICRS) (computed by VizieR, not part of the original data)degpos.eq.ranullableindexed_DE.icrsDeclination (ICRS) (computed by VizieR, not part of the original data)degpos.eq.decnullableindexed