GMRTLHCAT3 - Giant Metrewave Radio Telescope Lockman Hole 610-MHz Radio Source Catalog 3

Overview

In the run-up to routine observations with the upcoming generation of radio facilities, the nature of the sub-mJy radio population has been hotly debated. In this paper, the authors describe multi-frequency data designed to probe the emission mechanism that dominates in these faint radio sources. Their analysis is based on observations of the Lockman Hole (LH) using the Giant Metrewave Radio Telescope (GMRT) near Pune, India - the deepest 610-MHz imaging yet reported - together with 1.4-GHz imaging from the Very Large Array (VLA), which are well matched in resolution and sensitivity to the GMRT data: sigma_610MHz ~ 15 µJy/beam (µJy/beam), sigma}_1.4GHz ~ 6 µJy/beam, and full width at half-maximum (FWHM) ~ 5 arcseconds. The GMRT and VLA data are cross-matched to obtain the radio spectral indices for the faint radio emitters.

During six 12-hr sessions in 2006 February and July, the authors obtained data at 610 MHz for three pointings (FWHM ~ 43 arcminutes) in the LH (see Table 1 of the reference paper for full details), separated by 11 arcminutes (the LOCKMAN-E, LOCK-3 and LHEX-4 fields), typically with 28 of the 30 antennas that comprise the GMRT. The total integration time in each field, after overheads, was 16 hr. The final image had a noise level in the central 100 arcmin² of 14.7 µJy/beam, the deepest map reported at 610 MHz as of the date of publication, despite the modest integration time. New and archival data were obtained at the same three positions using the National Radio Astronomy Observatory's VLA, largely in its B configuration.

This table contains 1585 sources found in the LH field at 610 MHz by the GMRT. For 19 of the sources which have multiple components, the 34 individual components are listed as well. Thus, the final table contains 1619 (1585 + 34) entries. Source extraction was based on criteria of peak brightness > 5 times the local rms and integrated flux density > 3 times the local rms.

Catalog Bibcode

2009MNRAS.397..281I

References

Deep multi-frequency radio imaging in the Lockman Hole using the GMRT and VLA.
I. The nature of the sub-mJy radio population.
    Ibar E., Ivison R.J., Biggs A.D., Lal D.V., Best P.N., Green D.A.
   <Mon. Not. R. Astron. Soc., 397, 281-298 (2009)>
   =2009MNRAS.397..281I

Provenance

This table was created by the HEASARC in February 2012 based on CDS Catalog J/MNRAS/397/281 file table3.dat.

Parameters

Name
The name of the radio source or component using the IAU-style designation based on its truncated J2000.0 equatorial coordinates, viz., '[IIB2009] LH610MHz JHHMMSS.s+DDMMSSa', as recommended by the CDS Dictionary of Nomenclature of Celestial Objects, where the '[IIB2009]' prefix stands for 'Ibar, Ivison, Biggs 2009' and the suffixes 'a', 'b' and 'c' are used to designate components of multiple sources.

RA
The Right Ascension of the 610-MHz radio source or component in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table. The authors note in Section 3.5 of the reference paper that there is an astrometric offset of the VLA sources with respect to the GMRT sources, Delta (RA) = -0.60 +/- 0.03 and Delta(Dec) = 0.40 +/- 0.03 arcseconds (mean offset in RA and Dec, respectively). For double and triple systems, the position given is that of the brightest component. For extended sources, the position given is that of the most central component.

Dec
The Declination of the 610-MHz radio source or component in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table. The authors note in Section 3.5 of the reference paper that there is an astrometric offset of the VLA sources with respect to the GMRT sources, Delta (RA) = -0.60 +/- 0.03 and Delta(Dec) = 0.40 +/- 0.03 arcseconds (mean offset in RA and Dec, respectively). For double and triple systems, the position given is that of the brightest component. For extended sources, the position given is that of the most central component.

LII
The Galactic Longitude of the radio source or component.

BII
The Galactic Latitude of the radio source or component.

SNR_610_MHz
The peak flux to local noise ratio, PNR, of the radio source or component.

Bw_Smear_Corr
The bandwidth smearing correction factor calculated as discussed in Section 3.2.1 of the reference paper whch was applied to the radio source or component.

Maximum_Angular_Size
The observed maximum angular size of the radio source or component, in arcseconds. These values are not the deconvolved source sizes but are those fitted from the observed mosaic. For single sources, this value corresponds to twice the maximum FWHM. For multiple sources, it is given by the distance between the furthest components plus the FWHMs of each of them, in the direction they define in the sky (the 'position angle'). (See Sect. 3.3 of the reference paper for more details).

Position_Angle
The orientation angle (position angle) of the maximum extension of the source, with respect to North, in degrees.

Flux_610_MHz
The integrated flux density of the radio source or component at 610 MHz, in mJy, as obtained from the AIPS task SAD.

Flux_610_MHz_Error
The rms uncertainty in the integrated flux density of the radio source or component at 610 MHz, in mJy, as obtained from the AIPS task SAD.

Source_Type
The morphological classification of the 610-MHz radio source or component, coded as follows:

     S  = single Gaussian source without close neighbors
     SD = single Gaussian source with one close neighbor
     ST = single Gaussian source with two close neighbors
     SE = single Gaussian source with multiple close neighbors
     D  = double Gaussian source without close neighbors (the components are
            indicated as d1 & d2)
     T  = triple Gaussian source without close neighbors (the components are
            indicated as t1, t2 & t3)
     M  = extended source composed of more than 3 Gaussians

Source_Type_Flag
This flag parameter is set to 'TSQ2' for sources which were extracted from the Area_beam * sqrt(2) convolved images: this was done to include extended emission sources which were missed by the initial selection process. 16 new 610-MHz sources were found in this way.

Spectral_Index_Limit
This parameter is set to '<' if the corresponding parameter value is the 68.3% confidence range upper limit rather than an actual value.

Spectral_Index
The spectral index Alpha of the radio source or component between 610 MHz and 1.4 GHz. A null value means that the source was outside of the cross-matching region.

Spectral_Index_Pos_Err
The upper 68.3% confidence range uncertainty in the spectral index of the radio source or component based on the SAD flux density errors.

Spectral_Index_Neg_Err
The lower 68.3% confidence range uncertainty in the spectral index of the radio source or component based on the SAD flux density errors.

Spectral_Index_Quality
This flag parameter on the quality of the spectral index is set to 'O' if the radio source is outside the cross-match region or to 'U' if the value of the spectral index is considered to be unreliable.

Spectral_Index_Flag
This flag parameter on the spectral index has the following special non-blank codes, meaning as follows:

   1 = quoted value is an upper limit
   2 = source which has split the counterpart's flux density in a
       relative contribution
   3 = estimation which has used the original SAD extraction before
       multiple classification
   4 = cross-matched sources separated by a distance > 3"
   5 = counterparts having a fitted area ratio more than twice that
       expected from point sources
       (A^610MHz_source/A^1.4GHz_source > 2 * A^610MHz_beam/A^1.4GHz_beam)
   6 = estimation based on a cross-match involving more than one counterpart
   7 = spectral index affected by close companion
   8 = source affected by overlapping facets in the 3-D imaging approach

Contact Person

Questions regarding the GMRTLHCAT3 database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:28:17 EDT