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AT20GHARC - Australia Telescope 20-GHz (AT20G) High-Angular Resolution Catalog

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Overview

This table contains the high-angular-resolution catalog for the Australia Telescope 20-GHz (AT20G) survey, using the high-angular-resolution 6-km antenna data at the baselines of ~4500 m of the Australia Telescope Compact Array (ATCA). The authors have used the data to produce the visibility catalog that separates the compact active galactic nuclei (AGNs) from the extended radio sources at the 0.15-arcsecond angular scale, corresponding to the linear size scale of 1 kpc at redshifts higher than 0.7. They find the radio population at 20 GHz to be dominated by compact AGNs constituting 77% of the total sources in the AT20G. In the paper, they introduce the visibility-spectra diagnostic plot, produced using the AT20G cross-matches with lower frequency radio surveys at 1 GHz [the NRAO VLA Sky Survey (NVSS: Condon et al. 1998, AJ, 115, 1693) and the Sydney University Molonglo Sky Survey (SUMSS: Mauch et al. 2003, MNRAS, 342, 1117)], that separates the 20-GHz population into distinct sub-populations of the compact AGNs, the compact steep-spectrum (CSS) sources, the extended AGN-powered sources and extended flat-spectrum sources. The extended flat-spectrum sources include a local thermal emitting population of high-latitude planetary nebulae and also gravitational lens and binary black hole candidates among the AGNs. The authors find a smooth transition in properties between the CSS sources and the AGN populations. The visibility catalog, together with the main AT20G survey, provides an estimate of angular size scales for sources in the AT20G and an estimate of the flux arising from central cores of extended radio sources. The identification of the compact AGNs in the AT20G survey provides high-quality calibrators for high-frequency radio telescope arrays and very large baseline interferometry observations.

Catalog Bibcode

2013MNRAS.434..956C

References

The AT20G high-angular-resolution catalogue

    Chhetri R., Ekers R. D., Jones P. A., Ricci R.
   <Mon. Not. R. Astron. Soc., 434, 956-965 (2013)>
   =2013MNRAS.434..956C

Provenance

This table was created by the HEASARC in December 2013 based on machine-readable versions of Tables 2 and 3 from the reference paper which were obtained from the MNRAS web site.

Parameters

Name
The IAU-style AT20G radio source designation (AT20G JHHMMSS+DDMMSS). Notice that the CDS Dictionary of Nomenclature of Celestial Objects recommends a more detailed naming convention (AT20G JHHMMSS.s+DDMMSS) than the one that is used herein.

RA
The Right Ascension of the radio source in the selected equinox. The RA was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table.

Dec
The Declination of the radio source in the selected equinox. The Dec was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table.

LII
The Galactic Longitude of the radio source.

BII
The Galactic Latitude of the radio source.

Flux_20_GHz
The AT20G flux density of the radio source at 20 GHz, in mJy.

Flux_8p6_GHz
The AT20G flux density of the radio source at 8.6 GHz, in mJy.

Flux_4p8_GHz
The AT20G flux density of the radio source at 4.8 GHz, in mJy.

Flux_1p4_GHz
The NVSS flux density of the radio source at 1.4 GHz, in mJy.

Flux_0p8_GHz
The SUMSS or MGPS-2 (second epoch Molonglo Galactic Plane Survey: Murphy et al. 2007, MNRAS, 382, 382) flux density of the radio source at 0.8 GHz, in mJy.

Alpha_1_4p8_GHz
The spectral index of the radio source between 1 and 4.8 GHz. For sources with flux densities in both SUMSS/MGPS-2 and NVSS, the NVSS value is used for the 1-GHz flux density.

Alpha_1_8p6_GHz
The spectral index of the radio source between 1 and 8.6 GHz. For sources with flux densities in both SUMSS/MGPS-2 and NVSS, the NVSS value is used for the 1-GHz flux density.

Alpha_1_20_GHz
The spectral index of the radio source between 1 and 20 GHz. For sources with flux densities in both SUMSS/MGPS-2 and NVSS, the NVSS value is used for the 1-GHz flux density.

Alpha_4p8_8p6_GHz
The spectral index of the radio source between 4.8 and 8.6 GHz.

Alpha_4p8_20_GHz
The spectral index of the radio source between 4.8 and 20 GHz.

Alpha_8p6_20_GHz
The spectral index of the radio source between 8.6 and 20 GHz.

Vis_1
The lowest measured 6-km visibility of the radio source, after bias correction according to equation (2) of the reference paper. Unresolved sources have a maximum visibility of 1, so the 6-km visibility values greater than 1 are due to noise.

The authors calculated the 3-sigma value of 0.14 for the distribution of the visibilities for sources with values > 1 (see also Chhetri et al. 2012, MNRAS, 422, 2274). Using this, they arrive at the lower limit of 0.86 for the 6-km visibilities of unresolved sources with 3-sigma confidence. Hence, all sources with 6-km visibility >= 0.86 can be considered compact and sources with 6-km visibility < 0.86 can be considered extended. For a source with a Gaussian brightness distribution, the value of 0.86 corresponds to a spatial resolution of 0.15 arcseconds.

Since the extended sources will be more resolved in the Hour Angle with resolution along the major axis, the visibilities are sorted in ascending order so that the first listed (vis_1) is closest to the major axis size. The authors note that this will introduce a small noise bias of the order of the rms noise error of 3.6 mJy in the visibility amplitude (different from that discussed in Section 3.2 of the reference paper) when only the minimum value is used. To avoid this bias, the authors have used all available values for their statistical analyses.

Vis_2
The second 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_3
The third 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_4
The fourth 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_5
The fifth 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_6
The sixth 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_7
The seventh 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_8
The eighth 6-km visibility of the radio source. See the description of the vis_1 parameter above for more details.

Vis_Error
The uncertainty in all of the 6-km visibilities of the radio source.

Source_Flags
This parameter contains flags which indicate that there is further information about the source updated from Murphy et al. (2010, MNRAS, 402, 2403: the AT20G Catalog) as follows:

    n - there are no 6-km visibilities for this source.
    v - more than two 6-km visibilities are present.
    e - the source is flagged as 'extended' in the AT20G survey and corresponds
        to an angular size greater than ~5 arcseconds.
    h - the source is identified as an H II region.
    p - the source is identified as a planetary nebula (Parker et al. 2006,
        MNRAS, 373, 79; Miszalski et al. 2008, MNRAS. 384, 525).
    m - the source is identified as part of the Magellanic Clouds.
    l - the source has no match in the lower frequency surveys (NVSS and SUMSS).
    b - the source is flagged as large and extended in the AT20G survey.
  

Contact Person

Questions regarding the AT20GHARC database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 18-Dec-2013