LOTSSPRCAT - LOFAR 2-Meter Sky Survey Preliminary Data Release Source Catalog

Overview

The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a deep 120-168 MHz imaging survey that will eventually cover the entire Northern sky. Each of the 3,170 pointings will be observed for 8 hours, which, at most declinations, is sufficient to produce ~5-arcsec resolution images with a sensitivity of ~0.1 mJy/beam and accomplish the main scientific aims of the survey which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Due to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate sub-arcsecond imaging and spectral line studies. In this paper, The authors provide an overview of the LoTSS. They outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that they have released were created using a fully-automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44,000 sources are detected in the images that have a resolution of 25-arcseconds, typical noise levels of less than 0.5 mJy/beam, and cover an area of 381 square degrees in the region of the HETDEX Spring Field (Right Ascension 10^h 45^m 00^s to 15^h 30^m ^00^s and Declination +45^o 00' 00" to +57^o 00' 00").

Source detection on the mosaics that are centered on each pointing was performed with PyBDSM (See http://www.astron.nl/citt/pybdsm/ for more details). In an effort to minimize contamination from artifacts, the catalog was created using a conservative 7-sigma detection threshold. Furthermore, as the artifacts are predominantly in regions surrounding bright sources, the authors utilized the PyBDSM functionality to decrease the size of the box used to calculate the local noise when close to bright sources, which has the effect of increasing the estimated noise level in these regions. Their catalogs from each mosaic are merged to create a final catalogue of the entire HETDEX Spring Field region. During this process, the authors remove multiple entries for sources by only keeping sources that are detected in the mosaic centered on the pointing to which the source is closest to the center. In the catalog, they provide the type of source, for which they used PyBDSM to distinguish isolated compact sources, large complex sources, and sources that are within an island of emission that contains multiple sources. In addition, they attempted to distinguish between sources that are resolved and unresolved in their images.

The authors have provided a preliminary data release from the LOFAR Two-metre Sky Survey (LoTSS). This release contains 44,500 sources which were detected with a signal in excess of seven times the local noise in their 25" resolution images. The noise varies across the surveyed region but is typically below 0.5 mJy/beam and the authors estimate the catalog to be 90% complete for sources with flux densities in excess of 3.9 mJy/beam.

Catalog Bibcode

2017A&A...598A.104S

References

The LOFAR Two-metre Sky Survey.
I. Survey Description and Preliminary Data Release.
    Shimwell T.W., Rottgering H.J.A., Best P.N., Williams W.L., Dijkema T.J.,
    de Gasperin F., Hardcastle M.J., Heald G.H., Hoang D.N., Horneffer A.,
    Intema H., Mahony E.K., Mandal S., Mechev A.P., Morabito L., Oonk J.B.R.,
    Rafferty D., Retana-Montenegro E., Sabater J., Tasse C., van Weeren R.J.,
    Bruggen M., Brunetti G., Chyzy K.T., Conway J.E., Haverkorn M., Jackson N.,
    Jarvis M.J., McKean J.P., Miley G.K., Morganti R., White G.J., Wise M.W.,
    van Bemmel I.M., Beck R., Brienza M., Bonafede A., Calistro Rivera G.,
    Cassano R., Clarke A.O., Cseh D., Deller A., Drabent A., van Driel W.,
    Engels D., Falcke H., Ferrari C., Frohlich S., Garrett M.A., Harwood J.J.,
    Heesen V., Hoeft M., Horellou C., Israel F.P., Kapinska A.D.,
    Kunert-Bajraszewska M., McKay D.J., Mohan N.R., Orru E., Pizzo R.F.,
    Prandoni I., Schwarz D.J., Shulevski A., Sipior M., Smith D.J.B.,
    Sridhar S.S., Steinmetz M., Stroe A., Varenius E., van der Werf P.P.,
    Zensus J.A., Zwart J.T.L.
    <Astron. Astrophys. 598, A104 (2017)>
    =2017A&A...598A.104S        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in February 2017 based on CDS Catalog J/A+A/598/A104 file lotss.dat.

Parameters

Name
The J2000.0 position-based designation of the object, viz., ILT JHHMMSS.s+DDMMSS.s, where the significance of the prefix (given by the authors) is not known to the HEASARC. These names follow the general style recommendations for position-based names of the CDS Dictionary of Nomenclature of Celestial Objects,

RA
The Right Ascension of the source centroid in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10^-5 degrees (0.036 arcseconds) in the original table.

RA_Error
The formal 1-sigma statistical uncertainty in the Right Ascension of the source centroid, in arcseconds, as derived from the PyBDSM source fitting.

RA_Tot_Error
The 1-sigma total uncertainty in the Right Ascension of the source centroid, in arcseconds, including both the formal error from the PyBDSM source fitting (ra_error) and the 1.7" astrometric uncertainty added in quadrature.

Dec
The Declination of the source centroid in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10^-5 degrees (0.036 arcseconds) in the original table.

Dec_Error
The formal 1-sigma statistical uncertainty in the Declination of the source centroid, in arcseconds, as derived from the PyBDSM source fitting.

Dec_Tot_Error
The 1-sigma total uncertainty in the Declination of the source centroid, in arcseconds, including both the formal error from the PyBDSM source fitting (dec_error) and the 1.7" astrometric uncertainty added in quadrature.

LII
The Galactic Longitude of the source centroid.

BII
The Galactic Latitude of the source centroid.

Flux_150_MHz
The peak flux density of the source at 150 MHz, in mJy/beam.

Flux_150_MHz_Error
The formal 1-sigma statistical uncertainty in the peak 150-MHz flux density, in mJy/beam, as derived from the PyBDSM source fitting.

Flux_150_MHz_Tot_Error
The 1-sigma total uncertainty in the peak 150-MHz flux density, in mJy/beam, including both the formal error from the PyBDSM source fitting (flux_150_mhz_error) and the conservative 20% flux uncertainty, added in quadrature.

Int_Flux_150_MHz
The total (integrated) flux density of the source at 150 MHz, in mJy.

Int_Flux_150_MHz_Error
The formal 1-sigma statistical uncertainty in the integrated (total) 150-MHz flux density, in mJy, as derived from the PyBDSM source fitting.

Int_Flux_150_MHz_Tot_Err
The 1-sigma total uncertainty in the total (integrated) 150-MHz flux density, in mJy, including both the formal error from the PyBDSM source fitting (flux_150_mhz_error) and the conservative 20% flux uncertainty, added in quadrature.

Resolved_Flag
This flag parameter indicates whether the source is resolved (set to 'R' in such cases), or not resolved (set to 'U' in such cases)

RMS_150_MHz
The local noise (RMS) in the image at the position of the source, in mJy/beam. The noise varies across the surveyed region but is typically below 0.5 mJy/beam and the authors estimate the catalog to be 90% complete for sources with flux densities in excess of 3.9 mJy/beam. The authors utilized the PyBDSM functionality to decrease the size of the box used to calculate the local noise when close to bright sources, which has the effect of increasing the estimated noise level in these regions.

Structure_Code
The source structure code defining the multiplicity of the source structure in terms of Gaussian components, as follows:

    S = refers to an isolated single-Gaussian source
    C = refers to a single-Gaussian source partly overlapping with other sources
    M = is a source fit with multiple Gaussians

Mosaic_Image
The parent mosaic image in which the source detection was characterized. The mosaic images are provided through the LoTSS website http://lofar.strw.leidenuniv.nl/.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:30:13 EDT