SWIRE Optical-IRAC-MIPS24 Data Catalog Definition
SWIRE Overview
The Spitzer Wide-area InfraRed Extragalactic survey (SWIRE), the largest Spitzer Legacy program, is a wide-area, imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and AGN as a function of environment, from redshifts z~3 to the current epoch. SWIRE surveys 6 high-latitude fields, totaling ~50 sq. deg. in all 7 Spitzer bands: 3.6, 4.5, 5.8, and 8 microns with IRAC and 24, 70, and 160 microns with MIPS (Lonsdale et al. 2003). The SWIRE Legacy Extragalactic Source Catalogs will eventually contain in excess of 2 million IR-selected galaxies, from those dominated by the light of stellar populations detected primarily by IRAC, to starbursts, ultra-luminous infrared galaxies and AGN detected also by MIPS. The SWIRE project page can be found here.
The key scientific goals of SWIRE are to determine: (1) the evolution of actively star-forming and passively evolving galaxies to determine the history of galaxy formation in the context of cosmic structure formation; (2) the evolution of the spatial distribution and clustering of evolved galaxies, starbursts and AGN in the key redshift range, 0.5<z<1.5, when the sharp decline in star formation activity has occurred; (3) the evolutionary relationship between ``normal galaxies'' and AGN, and the contribution of AGN accretion energy vs. stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e. in the context of structure formation. The large volume is also optimised for finding rare objects.
SWIRE Fields
The Spitzer Wide-area InfraRed Extragalactic survey (SWIRE; Lonsdale et al. 2003) Versions 2.0 & 3.0 data products releases (Spring 2005 & Fall 2005) include an image atlas and source catalogs for most of the six SWIRE fields to be observed by Spitzer:
- ELAIS-N1 (European Large-Area ISO Survey) [images & catalogs released]
- ELAIS-N2 [images and catalogs released]
- XMM Large-Scale Structure Survey (LSS) [images and catalogs released]
- Lockman Hole (LH) [images and catalogs released]
- ELAIS-S1 [catalogs released]
- Chandra Deep Field South (CDFS) [catalogs released]
SWIRE Optical-IRAC-MIPS24 Catalog Column Descriptions
Gator serves the SWIRE Spring 2005 EN1 (156 columns, 282711 data rows), EN2 (156 columns, 126056 data rows), XMM-LSS (127 columns, 250733 data rows), LH (151 columns, 323044 data rows), Fall 2005 CDFS (156 columns, 221535 datarows), ES1 (146 columns, 186059 data rows) and catalogs. The column descriptions for all these catalogs are all very similar, except ES1, and are listed below. Please note that the XMM-LSS catalog contains fewer columns than the EN1, EN2, CDFS and LH catalogs; there are no columns related to optical magnitudes within the XMM-LSS catalog. The LH catalog has 5 fewer columns than the EN1, EN2 and CDFS catalogs because there are no optical z band data for that field and therefore no optical z photometry columns. The ES1 catalog has 10 fewer columns than EN1, EN2 and CDFS catalogs because the optical photometry is in a different system and therefore the there is a separate column description file for ES1.
| Column Name | Data Type | Units | Description |
| cntr |
int | An internal record number from the master database table from which the sources were selected. It is included in the released Catalog for database linkage reasons. It is not useful as a sequential record number because it does not increase monotonically with Right Ascension, and because there are gaps in a sequential listing of CNTR for the IRAC-24-Optical Catalog. However it is useful as a purely numerical source identifier within the Table. | |
| object |
character | The name of the source, conforming to IAU standards. All sources in the IRAC-24-Optical Catalogs are labeled "SWIRE", followed by the integer "2" to denote that they belong to Version 2.0 of the SWIRE Data Products. The format for the numerical part of the name is the J2000 position of the object in hhmmss.ss+ddmmss.s format. Sufficient precision is provided in case subsequent versions of the SWIRE Catalogs achieve sub-arcsecond separation between close sources. | |
| ra dec unc_ra unc_dec |
double | degrees arcsec |
The Right Ascension and Declination of the source in J2000 decimal degrees (position uncertainties are in units of arcseconds). The position is the resulting output of the Bandmerge processor, as described in the data Delivery Document (PDF), and it is usually dominated by the higher precision and higher SNR 3.6 and 4.5 microns source extractions. Positional uncertainties are as derived by SExtractor. However, the actual positional uncertainties are dominated by systematic effects, and are larger than reflected here. Users should consult the data release document. |
tile |
int | Numerical label denoting the IRAC 1x1 square degree tile which the source is found in. The first digit of the label refers to row number and the second refers to column within the tile layout. Thus, for example, tile_1_1, the lower-left-most tile, is labelled as tile "11" in the Table | |
| flux_apN_xx uncf_apN_xx |
double | microJy | Fluxes and their uncertainties for the 5 Spitzer wavelength bands, where "xx" is 36, 45, 58, 80 or 24 to denote the 4 IRAC bands 3.6, 4.5, 5.8, 8.0 microns and the MIPS 24 micron band. "N" refers to the aperture number, where smaller numbers indicate smaller apertures; the actual aperture sizes are given in the data release document. The fluxes are aperture-corrected. Null values for fluxes and their uncertainties are denoted by "-99.00". A null flux value does not necessarily mean a source has a flux below the SWIRE sensitivity limit in this band. There are three reasons a null value may exist: (1) non-detection to the limits of source extraction; or (2) failure of the detected source to meet the CSNR threshold criterion; or (3) lack of coverage in this band. The third criterion should not apply to null IRAC flux values since we have attempted to limit the IRAC-24-Optical Catalog to the full IRAC coverage area, but we do not guarantee this to be the case. |
| flux_kr_xx uncf_kr_xx |
double | microJy | Kron fluxes and uncertainties computed by SExtractor. |
| rad_kr_xx |
double | arcsec | Effective Kron radius, computed from SExtractor's derived shape parameters and the Kron factor. |
| flux_iso_xx uncf_iso_xx |
double | microJy | Isophotal fluxes and uncertainties computed by SExtractor. |
| area_iso_xx |
double | arcsec | Isophotal area used in derivation of the isophotoal flux. |
| stell_xx |
int | Single digit stellarity indices generated by the SExtractor software package, one per Spitzer band. They indicate how well the source resembles a point-like source [values range from 0 to 1, with zero being the least star-like and high values close to 1 indicating a high probability the source is star-like]. The reader is referred to the SExtractor documentation for further details. Users should note that the stellarity index is not reliable at low flux levels. An analysis of stellarity and star vs. galaxy colors for the IRAC-24-Optical Catalog is given in the data release document | |
| a_xx b_xx theta_xx |
double | arcsec,degrees | Semi-major and semi-minor radii and position angle. |
| flgs_xx |
character |
The first two characters indicate the flux measurement used,
either CA (compact, aperture) or EK (extended, Kron). The
numerical value is the SExtractor generated status flag. The following indicates
the meaning of the flag, as adapted from the Sextractor 2.3
User's Manual, by E. Bertin. Note that this flag is the sum of
all set bits, so no bits set would have a value of 0, while
bits 0 and 1 set would have a flag value of 3, for example.
|
|
| ext_fl_xx |
int | Source extension flag. A value of -1 indicates a definitely point-like object, a value of 2 indicates an object that is clearly extended, a value of 1 indicates an object that might be extended, and a value of 0 is indeterminate. In general, objects with this flag set equal to one or two will have poor aperture photometry, and the Kron flux will be preferable. Null for any source means no Sextractor detection; if a source is not listed with detected fluxes the flags associated with it are nulled. Note, the values of ext_fl_58, ext_fl_80, and ext_fl_24 can include -99 when the fluxes and other columns for those bands are set to -99; this indicates that the source's SNR is below our "nulling" thresholds. | |
| cov_avg_xx |
double | Average depth of coverage in units of independent images at the source location. | |
| cov_xx |
int | Flag indicating whether valid data at wavelength "xx" existed. The flag has a value of 1 if data existed, and 0 otherwise. This is useful for determining whether null flux values arise from a lack of data or a lack of detection. | |
| detid_24 |
int | A source identification number assigned to each 24 micron source detection. This may be used for correlating sources in the combined optical-IRAC-MIPS24 catalog with sources appearing in the separately supplied 24-micron only source list. The same source has the same ID number. | |
| ra_opt dec_opt |
double | degrees | Right Ascension and Declination of the optical source which has been matched to this Spitzer source, in J2000 decimal degrees. These coordinates are a refinement done on the position of the detected source using the combined WCS of the images in the 5 bands. |
| ap_m_x msig_x |
double | Vega mag | Aperture-corrected aperture magnitudes and their errors, measured in a fixed aperture of 1.2 arcseconds, for the five optical bands, where "x" is u, g, r, i, or z for the U, g', r', i', Z band set from the 2.5m Isaac Newton Telescope (INT) in La Palma, using the Wide Field Survey (WFS) data. Null values for fluxes and their uncertainties are denoted by "-99.00". A null flux value does not necessarily mean a source has a flux below the plate limit in this band. Instead there may be lack of coverage in this band. Users should consult the value of the flag cov_xx, which will indicate whether a given band had coverage at this location. |
| int_m_x |
double | Vega mag | Integrated magnitudes for the five optical bands, where "x" is u, g, r, i, or z for the U, g', r', i', and Z band set from the 2.5m Isaac Newton Telescope (INT) in La Palma, using the Wide Field Survey (WFS) data. The total fluxes were calculated using a curve-of-growth technique, as described by Hall \& Mackay (1984). Null values for integrated fluxes are denoted by "-99.00". A null flux value does not necessarily mean a source has a flux below the plate limit in this band. Instead there may be lack of coverage in this band. Users should consult the value of the flag cov_xx, which will indicate whether a given band had coverage at this location. |
| fl_x |
int | Stellarity flags generated by the Cambridge (UK) Astronomical Survey Unit (CASU) pipeline, one per band, as described in the data Delivery Document (PDF). Unlike the SExtractor stellarities measured for the Spitzer sources, the fl_x flags are coded flags. A value of -1 indicates a star; 0 denotes a noise source; 1 indicates an extended object such as a galaxy; -2 indicates possible non-stellar but too faint to be sure; -3 indicates possible stellar but too faint to be sure; -8 indicates a possible cross-match problem between bands; -9 indicates saturation, Users should consult the WFS documentation for detils. | |
| xid_dist |
double | arcsec | Distance in arcsec of the optical match from the Spitzer source. The search radius was 1.5\arcsec. |
| xid_p |
smallfloat | The NASA/IPAC Extragalactic Database (NED) p value for match. p is p(xD,yD) and can be defined as the expected-error density function evaluated for the observed separation, where the expected-error density function is the convolution of the error density functions for the two catalogs involved, assuming Gaussian errors; the density function has units of probability mass per steradian. p is a dimensionless measure of the probability of the optical source being a correct match to the Spitzer source, inversely proportional to the chi^2 goodness-of-match parameter. Please note that p should not be used to inter-compare optical match probabilities between Spitzer sources because it is not calibrated, and the correct calibration to a percentage probability will depend on the magnitude of the optical match. Further details on the reliability of Spitzer-optical matches are given in the SWIRE Delivery Document (PDF). | |
| fl_2mass | int | Flag used to identify sources which lie close to a bright 2MASS star (flag value set to 1). If a source is found to lie within a given radius of a bright star then there is a possibility that in one or more bands its flux may be affected by artifacts from the star, or it may have missed detection altogether due to the exclusion zone of the SExtractor software. Caution should therefore be used in interpreting the spectral energy distribution of such a source. The radius used for setting the flag varies by star brightness; details are given in the data release document. |