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IRASFSC: Help

IRASFSC - IRAS Faint Source Catalog, Version 2.0


Overview

The Faint Source Survey (FSS) is the definitive Infrared Astronomical Satellite (IRAS) data set for faint point sources. The FSS was produced by point-source filtering the individual detector data streams and then coadding those data streams using a trimmed-average algorithm. The resulting images, or plates, give the best estimate from the IRAS survey data of the point source flux density at every surveyed point of the sky. The Faint Source Catalog (FSC) is a compilation of the sources extracted from the FSS plates that have met reasonable reliability requirements. Averaged over the whole catalog, the FSC is at least 98.5% reliable at 12 and 25 microns, and ~94% at 60 microns. For comparison, the IRAS Point Source Catalog (PSC) is >99.997% reliable, but the sensitivity of the FSC exceeds that of the PSC by about a factor of 2.5. This increase in sensitivity results from the co-adding of the three separate hours-confirming (HCON) passes over the sky which were used for confirmation and not added together for the Point Source Catalog. The FSC also contains 99,973 infrared sources which are not in the PSC. The FSC contains data for 173,044 point sources in unconfused regions with flux densities typically above 0.2 Jy at 12, 25, and 60 microns, and above 1.0 Jy at 100 microns. The FSS plates are somewhat more sensitive but less reliable than the FSC; typically, only sources with SNR > 5 - 6 in the plates are contained in the FSC. The data products, the processing methods used to produce them, results of an analysis of these products, and cautionary notes are given in the Explanatory Supplement to the IRAS Faint Source Survey.

This database table contains the IRAS Faint Source Catalog (FSC) (Version 2.0, released in September 1990) non-associations data. The associations data for the IRAS FSC is contained in the file ftp://cdsarc.u-strasbg.fr/pub/cats/II/156A/assoc.dat.gz

The FSC is limited in galactic latitude to the unconfused regions of sky in which the absolute value of BII is greater than or equal to 10 degrees at 12 and 25 microns and greater than or equal to 20 degrees at 60 microns. Because of the presence of the infrared "cirrus" at 100 microns, the FSC does not contain sources detected ONLY at 100 microns. Sources with a 100 micron detection were included in the catalog if they were bandmerged with high reliability detections at other spectral bands. For the faintest sources, the reliability exceeds 90% at 12 and 25 microns, and 80% at 60 microns.


Catalog Bibcode

1990IRASF.C......0M

References

General information about the IRAS Faint Sources Catalog can be found in an article by Mehrdad Moshir in the May 1991 issue of the IPAC Newsletter.

Most of the parameter definitions and explanations were excerpted from the original "Explanatory Supplement to the IRAS Faint Source Survey, Version 1" (Moshir et al, 1989). Some of the text was adjusted to accommodate version 2.0.

IRAS Faint Source Catalog, |b| > 10 Degrees, Version 2.0
  Moshir, M., Copan, G., Conrow, T., McCallon, H., Hacking, P., Gregorich, D.,
  Rohrbach, G., Melnyk, M., Rice, W., Fullmer, L., and Chester, T.J.
  <Infrared Processing and Analysis Center (1989)>
  =1990IRASF.C......0M

Provenance

The HEASARC recreated this database table in August 2005, based on the CDS table, in an effort to modernize its parameter names and documentation, as well as to add Galactic coordinates.

Parameters

Name
The IRAS source name is derived from its position by combining the hours, minutes and tenths of minutes of right ascension and the sign, degrees and minutes of the declination. In obtaining the minutes of right ascension and declination for the name, the positions were truncated. This quantity is preceded by the letter `F` to designate a FSC source. The letters 'A' and 'B' are appended to names of sources which are so close together that they would otherwise have had identical names. Due to the large number of duplicate sources caused by plate overlap, the convention used in the PSC has been changed and the `A` for the first such source with a duplicate name has been eliminated. Names were uniquely assigned to catalog sources, including duplicate sources.

RA
The Right Ascension of the source at epoch 1983.5 in the selected equinox. Positions in the originating catalog table were given in B1950.0 equinox to a precision of 0.1 seconds of time.

Dec
The Declination of the source at epoch 1983.5 in the selected equinox. Positions in the originating catalog table were given in B1950.0 equinox to a precision of 1 arcseconds.

LII
The Galactic Longitude of the source.

BII
The Galactic Latitude of the source.

Error_Major_Axis
The semi-major axis of the 1-sigma positional uncertainty ellipse, in arcseconds. The uncertainty in the position for a source depends primarily on its brightness in the various wavelength bands and the number of sightings. The final uncertainty is expressed as an ellipse whose semimajor and semi-minor axes are the 1-sigma errors given in seconds of arc. The orientation (position angle) of the ellipse on the sky is expressed in terms of the angle between the major axis of the ellipse and the local equatorial meridian. It is expressed in degrees east of north.

Error_Minor_Axis
The semi-minor axis of the 1-sigma positional uncertainty ellipse, in arcseconds. The uncertainty in the position for a source depends primarily on its brightness in the various wavelength bands and the number of sightings. The final uncertainty is expressed as an ellipse whose semimajor and semi-minor axes are the 1-sigma errors given in seconds of arc. The orientation (position angle) of the ellipse on the sky is expressed in terms of the angle between the major axis of the ellipse and the local equatorial meridian. It is expressed in degrees east of north.

Error_Ellipse_PA
The position angle of the 1-sigma positional uncertainty ellipse, in degrees. The orientation (position angle) of the ellipse on the sky is expressed in terms of the angle between the major axis of the ellipse and the local equatorial meridian. It is expressed in degrees east of north.

Number_Obs_12um
The number of individual detector sightings at the peak-flux pixel in the 12-micron band.

Number_Obs_25um
The number of individual detector sightings at the peak-flux pixel in the 25-micron band.

Number_Obs_60um
The number of individual detector sightings at the peak-flux pixel in the 60-micron band.

Number_Obs_100um
The number of individual detector sightings at the peak-flux pixel in the 100-micron band.

Flux_12um
The 12-micron, non-color-corrected flux density in units of Janskies (1 Jy = 10^-26 W m^-2 Hz^-1). The flux densities have been calculated assuming an intrinsic source energy distribution such that the flux density f_(nu) is proportional to (nu)^-1. Note that the flux density quoted for some sources could be zero if there were not enough data available to derive a good upper limit.

Flux_25um
The 25-micron, non-color-corrected flux density in units of Janskies (1 Jy = 10^-26 W m^-2 Hz^-1). The flux densities have been calculated assuming an intrinsic source energy distribution such that the flux density f_(nu) is proportional to (nu)^-1. Note that the flux density quoted for some sources could be zero if there were not enough data available to derive a good upper limit.

Flux_60um
The 60-micron, non-color-corrected flux density in units of Janskies (1 Jy = 10^-26 W m^-2 Hz^-1). The flux densities have been calculated assuming an intrinsic source energy distribution such that the flux density f_(nu) is proportional to (nu)^-1. Note that the flux density quoted for some sources could be zero if there were not enough data available to derive a good upper limit.

Flux_100um
The 100-micron, non-color-corrected flux density in units of Janskys (1 Jy = 10^-26 W m^-2 Hz^-1). The flux densities have been calculated assuming an intrinsic source energy distribution such that the flux density f_(nu) is proportional to (nu)^-1. Note that the flux density quoted for some sources could be zero if there were not enough data available to derive a good upper limit.

Flux_12um_Error
The 1-sigma uncertainty in the flux density at 12 microns, in Jy. This parameter was created by the HEASARC based on the tabulated values of the flux and its relative percentage uncertainty.

Flux_25um_Error
The 1-sigma uncertainty in the flux density at 25 microns, in Jy. This parameter was created by the HEASARC based on the tabulated values of the flux and its relative percentage uncertainty.

Flux_60um_Error
The 1-sigma uncertainty in the flux density at 60 microns, in Jy. This parameter was created by the HEASARC based on the tabulated values of the flux and its relative percentage uncertainty.

Flux_100um_Error
The 1-sigma uncertainty in the flux density at 100 microns, in Jy. This parameter was created by the HEASARC based on the tabulated values of the flux and its relative percentage uncertainty.

Quality_Flag_12um
The 12-micron flux density quality flag. A flux density measurement can be either high quality (FQUAL=3), moderate quality (FQUAL=2) or an upper limit (FQUAL=1). See Section II.F.4 of the Explantory Supplement for more details.

Quality_Flag_25um
The 25-micron flux density quality flag. A flux density measurement can be either high quality (FQUAL=3), moderate quality (FQUAL=2) or an upper limit (FQUAL=1). See Section II.F.4 of the Explantory Supplement for more details.

Quality_Flag_60um
The 60-micron flux density quality flag. A flux density measurement can be either high quality (FQUAL=3), moderate quality (FQUAL=2) or an upper limit (FQUAL=1). See Section II.F.4 of the Explantory Supplement for more details.

Quality_Flag_100um
The 100-micron flux density quality flag. A flux density measurement can be either high quality (FQUAL=3), moderate quality (FQUAL=2) or an upper limit (FQUAL=1). See Section II.F.4 of the Explantory Supplement for more details.

Rel_Error_Flux_12um
The 12-micron relative flux density uncertainty expressed as a percentage of the measured value. Each flux density measurement other than an upper limit has an associated uncertainty expressed as a 1-sigma value in units of 100 x [delta(f_(nu))/f_(nu)].

Rel_Error_Flux_25um
The 25-micron relative flux density uncertainty expressed as a percentage of the measured value. Each flux density measurement other than an upper limit has an associated uncertainty expressed as a 1-sigma value in units of 100 x [delta(f_(nu))/f_(nu)].

Rel_Error_Flux_60um
The 60-micron relative flux density uncertainty expressed as a percentage of the measured value. Each flux density measurement other than an upper limit has an associated uncertainty expressed as a 1-sigma value in units of 100 x [delta(f_(nu))/f_(nu)].

Rel_Error_Flux_100um
The 100-micron relative flux density uncertainty expressed as a percentage of the measured value. Each flux density measurement other than an upper limit has an associated uncertainty expressed as a 1-sigma value in units of 100 x [delta(f_(nu))/f_(nu)].

Min_Src_Reliability
The percent minimum source reliability. The minimum reliability for a source is the maximum of the reliabilities calculated individually for each band. See Section III.D of the Explantory Supplement for more details.

SNR_12um
The 12-micron signal-to-noise ratio calculated through the use of a noise (68% quantile) calculated over an area of roughly 79.25 arcmin x 79.25 arcmin, which is accurate to approximately 3%.

SNR_25um
The 25-micron signal-to-noise ratio calculated through the use of a noise (68% quantile) calculated over an area of roughly 79.25 arcmin x 79.25 arcmin, which is accurate to approximately 3%.

SNR_60um
The 60-micron signal-to-noise ratio calculated through the use of a noise (68% quantile) calculated over an area of roughly 99.5 arcmin x 99.5 arcmin, which is accurate to approximately 3%.

SNR_100um
The 100-micron signal-to-noise ratio calculated through the use of a noise (68% quantile) calculated over an area of roughly 99.5 arcmin x 99.5 arcmin, which is accurate to approximately 3%.

Local_SNR_12um
The 12-micron local signal-to-noise ratio is calculated using the noise for the pixel containing the peak flux density of the source.

Local_SNR_25um
The 25-micron local signal-to-noise ratio is calculated using the noise for the pixel containing the peak flux density of the source.

Local_SNR_60um
The 60-micron local signal-to-noise ratio is calculated using the noise for the pixel containing the peak flux density of the source.

Local_SNR_100um
The 100-micron local signal-to-noise ratio is calculated using the noise for the pixel containing the peak flux density of the source.

Area_12um
The area of the source calculated as the number of contiguous pixels with a 12-micron flux density above three times the noise after possible re-thresholding.

Area_25um
The area of the source calculated as the number of contiguous pixels with a 25-micron flux density above three times the noise after possible re-thresholding.

Area_60um
The area of the source calculated as the number of contiguous pixels with a 60-micron flux density above three times the noise after possible re-thresholding.

Area_100um
The area of the source calculated as the number of contiguous pixels with a 100-micron flux density above three times the noise after possible re-thresholding.

Number_Nearby_Srcs
The number of nearby catalog sources within a radius of 6 arcminutes.

Number_12um_Exts
The number of extractions within a radius of 6 arcminutes at 12 microns.

Number_25um_Exts
The number of extractions within a radius of 6 arcminutes at 25 microns.

Number_60um_Exts
The number of extractions within a radius of 6 arcminutes at 60 microns.

Number_100um_Exts
The number of extractions within a radius of 6 arcminutes at 100 microns.

Cirrus_Flag
Over nearly the entire sky, portions of the FSS plates are affected by the infrared cirrus. Cirrus can seriously hamper efforts to extract point sources from the data and can also produce structure on a point source scale that can masquerade as true point sources. The CIRRUS flag gives the number of 100-microns-only sources or cold 60- and 100-micron sources (defined by the logarithm of the ratio of 60- to 100-micron flux densities <= -0.75) in the extraction database within a radius of 30 arcmin. It is a coarse discriminant that warns the user that cirrus which contains structure on a point source scale is present in a given region. Values above 2 usually indicate contamination.

Confusion_Flag
The bandmerger process attempted to identify sources that were confused with neighboring sources in one or more bands. This flag is set in a given band if any instance of confusion was present in that band. The resulting individual band flags are combined into a single value.

Noise_Corr_12um
The noise correction factor at 12 microns, being the ratio of noise (68% quantile) to the median instrumental noise. This provides a global measure of cirrus contamination, especially at 100 microns. See Section III.C.4 of the Explanatory Supplement for more details.

Noise_Corr_25um
The noise correction factor at 25 microns, being the ratio of noise (68% quantile) to the median instrumental noise. This provides a global measure of cirrus contamination, especially at 100 microns. See Section III.C.4 of the Explanatory Supplement for more details.

Noise_Corr_60um
The noise correction factor at 60 microns, being the ratio of noise (68% quantile) to the median instrumental noise. This provides a global measure of cirrus contamination, especially at 100 microns. See Section III.C.4 of the Explanatory Supplement for more details.

Noise_Corr_100um
The noise correction factor at 100 microns, being the ratio of noise (68% quantile) to the median instrumental noise. This provides a global measure of cirrus contamination, especially at 100 microns. See Section III.C.4 of the Explanatory Supplement for more details.

Number_ID
Much of the utility of the FSC comes from the association of infrared objects with sources known to exist from other astronomical catalogs. A large number of catalogs have been searched for positional matches. The total number of matches found is given by this parameter.

ID_Type
This parameter, the ID type, ranges from 1 to 15 and states whether an association was found in a stellar catalog (bit 0), an extragalactic catalog (bit 1), catalogs with other types of objects (bit 2), or in a catalog with mixed types or derived partially/completely from IRAS data (bit 3). This differs from the convention used in previous IRAS data products where only the total of the association types was given. For example, if associations were found to both an extragalactic catalog and a stellar catalog, the ID type was "multiple". The information as to which type of catalogs were matched is now being preserved.

Noise_Ratio_12um
This parameter provides another global measure of cirrus, being the ratio of the 85% to 68% quantiles of the positive values from the flux density grid at 12 microns. See Section III.G.7 of the Explanatory Supplement for more details.

Noise_Ratio_25um
This parameter provides another global measure of cirrus, being the ratio of the 85% to 68% quantiles of the positive values from the flux density grid at 25 microns. See Section III.G.7 of the Explanatory Supplement for more details.

Noise_Ratio_60um
This parameter provides another global measure of cirrus, being the ratio of the 85% to 68% quantiles of the positive values from the flux density grid at 60 microns. See Section III.G.7 of the Explanatory Supplement for more details.

Noise_Ratio_100um
This parameter provides another global measure of cirrus, being the ratio of the 85% to 68% quantiles of the positive values from the flux density grid at 100 microns. See Section III.G.7 of the Explanatory Supplement for more details.


Contact Person

Questions regarding the IRASFSC database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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