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LOFHATLAS - LOFAR Radio Catalog of Herschel-ATLAS North Galactic Pole Field

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Overview

This table contains some of the results of Low-Frequency Array (LOFAR) High-Band Array (HBA) observations of the Herschel-ATLAS North Galactic Pole (NGP) survey area. The survey the authors carried out, consisting of four pointings covering around 142 deg2 of sky in the frequency range 126-173 MHz, does not provide uniform noise coverage but otherwise is representative of the quality of data to be expected in the planned LOFAR wide-area surveys, and has been reduced using recently developed 'facet calibration' methods at a resolution approaching the full resolution of the data sets (~10 x 6 arcsec) and an rms off-source noise that ranges from 100 µJy beam-1 in the center of the best fields to around 2 mJy/beam at the furthest extent of their imaging. In the reference paper, the authors describe the imaging, cataloguing and source identification processes, and present some initial science results based on a 5-sigma source catalog. These include (i) an initial look at the radio/far-infrared correlation at 150 MHz, showing that many Herschel sources are not yet detected by LOFAR; (ii) number counts at 150 MHz, including, for the first time, observational constraints on the numbers of star-forming galaxies; (iii) the 150-MHz luminosity functions for active and star-forming galaxies, which agree well with determinations at higher frequencies at low redshift, and show strong redshift evolution of the star-forming population; and (iv) some discussion of the implications of these observations for studies of radio galaxy life cycles.

The NGP field was observed in four separate pointings, chosen to maximize the area of sky covered, with the LOFAR HBA as part of the Surveys Key Science project. These observations used the HBA_DUAL_INNER mode, meaning that the station beams of core and remote stations roughly matched each other and giving the widest possible field of view. The first observation, which was made early on in LOFAR operations, was of slightly longer duration (~10 h) than the others (~8 h). International stations were included in some of the observations in 2014 but were not used in any of the authors' analysis, which uses only the Dutch array.

The author were interested in imaging in several separate frequency ranges (which are referred to hereafter as 'spectral windows'), since they wanted to be able to measure in-band spectral indices for detected sources. In addition, facet calibrating in different spectral windows could be done in parallel, speeding the processing up considerably. Accordingly, they chose to facet calibrate with six spectral windows, each made up of four bands and thus containing about 8 MHz of bandwidth:

Spectral   Nominal Frequency   Frequency Range
Window          (MHz)              (MHz)

1               130            126 - 134
2               138            134 - 142
3               146            142 - 150
4               154            150 - 158
5               161            158 - 166
6               169            166 - 173

The final source catalog was made by combining the four per-field catalogs. Ideally, the authors would have combined the images of each field and done source finding on a mosaicked image, but this proved computationally intractable given the very large image cubes that result from having six spectral windows. They therefore merged the catalogs by identifying the areas of sky where there is overlap between the fields and choosing those sources which are measured from the region with the best rms values. This should ensure that there are no duplicate sources in the final catalog. The final master catalogue contains 17,132 sources and is derived from images covering a total of 142.7 deg2 of independently imaged sky, with widely varying sensitivity. Total HBA-band (150-MHz) flux densities of catalogued sources detected using the PYBDSM software and a 5-sigma detection threshold range from a few hundred µJy to 20 Jy, with a median of 10 mJy. The authors examined all sources in the initial master catalog for associations with sources in other surveys, for rejection as artifacts, and for optical identifications, as described in detail in Section 3.5 of the reference paper. The final outcomes of this process were (a) an associated, artifact-free catalog of 15,292 sources, all of which the authors believe to be real physical objects which is contained in the present HEASARC table, and (b) a catalog of 6,227 objects with plausible, single optical identifications with Sloan Digital Sky Survey (SDSS) sources, representing an identification fraction of just over 40 per cent. (Note that around 50 sources with more than one equally plausible optical identification are excluded from this catalog; further observation would be required to disambiguate these sources).


Catalog Bibcode

2016MNRAS.462.1910H

References

LOFAR/H-ATLAS: a deep low-frequency survey of the
Herschel-ATLAS North Galactic Pole field.
    Hardcastle M.J., Gurkan G., van Weeren R.J., Williams W.L., Best P.N.,
    de Gasperin F., Rafferty D.A., Read S.C., Sabater J., Shimwell T.W.,
    Smith D.J.B., Tasse C., Bourne N., Brienza M., Bruggen M., Brunetti G.,
    Chyzy K.T., Conway J., Dunne L., Eales S.A., Maddox S.J., Jarvis M.J.,
    Mahony E.K., Morganti R., Prandoni I., Rottgering H.J.A., Valiante E.,
    White G.J.
   <Mon. Not. R. Astron. Soc., 462, 1910-1936 (2016)>
   =2016MNRAS.462.1910H    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in April 2018, based on CDS Catalog J/MNRAS/462/1910 file tablea1.dat.

Parameters

Name
The IAU-style J2000.0 position-based designation of the radio source, viz., 'ILT JHHMMSS.ss+DDMMSS.s', where the prefix stands for the International LOFAR Telescope, and is recommended by the Dictionary of Nomenclature of Celestial Objects for LOFAR-detected sources.

RA
The Right Ascension of the radio source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table. For a composite source, i.e. one created by associating more than one PYBDSM component, this is the mean Right Ascension of the associated sources.

RA_Error
The nominal (statistical) error in the Right Ascension of the radio source, in arcseconds (converted by the HEASARC from the degree units given in the original table). This does not take account of any systematic positional offsets.

Dec
The Declination of the radio source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table. For a composite source, i.e. one created by associating more than one PYBDSM component, this is the mean Declination of the associated sources.

Dec_Error
The nominal (statistical) error in the Declination of the radio source, in arcseconds (converted by the HEASARC from the degree units given in the original table). This does not take account of any systematic positional offsets.

LII
The Galactic Longitude of the radio source.

BII
The Galactic Latitude of the radio source.

Flux_150_MHz
The total flux density of the radio source at 150 MHz, in mJy (converted by the HEASARC from the Jy units used in the original table). For composite sources, the sum of the flux densities of all the associated components is given.

Flux_150_MHz_Error
The statistical error in the total flux density of the radio source at 150 MHz, in mJy (converted by the HEASARC from the Jy units used in the original table). No term is included to account for the uncertainty in the flux scale.

Component_Separation
The component separation, in arcseconds. This parameter, given for composite sources only, indicates the largest distance between the positions of two components that were associated to make the source.

Flux_130_MHz
The total flux density of the radio source in the 130-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_130_MHz_Error
The statistical error in the total flux density of the radio source in the 130-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_138_MHz
The total flux density of the radio source in the 138-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_138_MHz_Error
The statistical error in the total flux density of the radio source in the 138-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_146_MHz
The total flux density of the radio source in the 146-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_146_MHz_Error
The statistical error in the total flux density of the radio source in the 146-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_154_MHz
The total flux density of the radio source in the 154-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_154_MHz_Error
The statistical error in the total flux density of the radio source in the 154-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_161_MHz
The total flux density of the radio source in the 161-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_161_MHz_Error
The statistical error in the total flux density of the radio source in the 161-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_169_MHz
The total flux density of the radio source in the 169-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Flux_169_MHz_Error
The statistical error in the total flux density of the radio source in the 169-MHz spectral window, in mJy (converted by the HEASARC from the Jy units used in the original table).

Multiplicity
The radio source classification type: 'Single' for a single PYBDSM source, 'Multiple' for a composite source.

Number_Components
The number of individual components used to make a source, set to 1 for a single source, or to > 1 for a composite source.

Major_Axis
The major axis of the best-fitting elliptical Gaussian fitted by PYBDSM, in arcseconds (converted by the HEASARC from the degree units used in the original table). This parameter is given for single sources only.

Major_Axis_Error
The statistical error in the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM, in arcseconds (converted by the HEASARC from the degree units used in the original table).

Minor_Axis
The minor axis of the best-fitting elliptical Gaussian fitted by PYBDSM, in arcseconds (converted by the HEASARC from the degree units used in the original table). This parameter is given for single sources only.

Minor_Axis_Error
The statistical error in the minor axis of the best-fitting elliptical Gaussian fitted by PYBDSM, in arcseconds (converted by the HEASARC from the degree units used in the original table).

Position_Angle
The position angle of the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM, in degrees. This parameter is given for single sources only.

Position_Angle_Error
The statistical error in the position angle of the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM, in degrees.

Dc_Major_Axis
This parameter, given for single sources only, is the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM after deconvolution of the LOFAR beam, in arcseconds (converted by the HEASARC from the degree units used in the original table). It is set to zero for sources that are nominally unresolved.

Dc_Major_Axis_Error
The statistical error in the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM after deconvolution of the LOFAR beam, in arcseconds (converted by the HEASARC from the degree units used in the original table).

Dc_Minor_Axis
This parameter, given for single sources only, is the minor axis of the best-fitting elliptical Gaussian fitted by PYBDSM after deconvolution of the LOFAR beam, in arcseconds (converted by the HEASARC from the degree units used in the original table). It is set to zero for sources that are nominally unresolved.

Dc_Minor_Axis_Error
The statistical error in the minor axis of the best-fitting elliptical Gaussian fitted by PYBDSM after deconvolution of the LOFAR beam, in arcseconds (converted by the HEASARC from the degree units used in the original table).

Dc_Position_Angle
The position angle of the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM after deconvolution of the LOFAR beam, in degrees. This parameter is given for single sources only.

Dc_Position_Angle_Error
The statistical error in the position angle of the major axis of the best-fitting elliptical Gaussian fitted by PYBDSM after deconvolution of the LOFAR beam, in degrees.


Contact Person

Questions regarding the LOFHATLAS database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Tuesday, 03-Apr-2018 12:07:04 EDT