SWIRE MIPS24 Single-Band 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:

The release includes both Spitzer IRAC and MIPS mid/far-infrared data products for all four fields as well as U, g', r', i', and Z optical data covering selected subregions of the data (McMahon et al. 2001, Gonzalez-Solares et al. 2004). The document "The SWIRE Data Release 2: Image Atlases and Source Catalogs for ELAIS-N1, ELAIS-N2, XMM-LSS, and the Lockman Hole" by Surace et al. describes the creation of these data products in detail [ SWIRE Delivery Document (PDF)]. The main SWIRE catalogs for 24 micron data are the Optical-IRAC-MIPS24 bandmerged catalogs. The bandmerged catalogs require a detection in the shortest IRAC band (3.6 microns). The column descriptions for those catalogs can be found here. The SWIRE project has produced single-band 24 micron catalogs to cover regions that lie outside the IRAC images, and to include sources that for some reason were not associated with a 3.6 micron detection. Below is a selected subset of the description of the columns found within the MIPS-24 single-band catalog. And, the MIPS-70 and MIPS-160 micron catalog column descriptions are available here.

SWIRE 24um-only Catalog Column Descriptions

Gator serves the SWIRE Spring 2005 EN1, EN2, Lockman, and XMM-LSS catalogs, and the Fall 2005 CDFS and ES1 catalogs. The column descriptions for the MIPS-24 single-band catalogs are listed below.

Column Name Data Type Units Description
  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 catalogs. However it is useful as a purely numerical source identifier within the Table.
  The name of the source, conforming to IAU standards. All sources in the catalogs are labeled "SWIRE", followed by an integer denoting the version of the SWIRE Data Products, and the string "_24_" to indicate the MIPS passband. The format for the numerical part of the name is the J2000 position of the object in hhmmss.s+ddmmss format. Sufficient precision is provided to ensure the names are unique.
The Right Ascension and Declination of the source in J2000 decimal degrees. The position is the resulting output of SExtractor, using the World Coordinate System keywords in the mosaic headers.
Positional uncertainties in arcseconds as derived by SExtractor. However, the actual positional uncertainties are dominated by systematic effects, and are larger than reflected here by about a factor of 2. Users should consult the data release document.
  A source identification number assigned to each 24 micron source detection. This may be used for correlating sources in the single-band MIPS24 catalog with sources appearing in the separately supplied combined optical-IRAC-MIPS24 catalog. The same source has the same ID number in both catalogs.
Aperture fluxes and their uncertainties for the 24 micron band. "N" refers to the aperture number, where smaller numbers indicate smaller apertures; the aperture radii are 5.25, 7.5, 10.5, and 15.0 arcseconds respectively.The fluxes are aperture-corrected and are quoted for a spectral shape proportional to the reciprocal of frequency. For point sources, aperture 2 has the least scatter.
Kron fluxes and uncertainties computed by SExtractor. Note that these values have had no "aperture correction" applied and are systematically low by 10-15% compared to the aperture measures.
Effective Kron radius, computed from SExtractor's derived shape parameters and the Kron factor.
Isophotal fluxes and uncertainties computed by SExtractor. Note that these values have had no "aperture correction" applied and are systematically low by 10-15% compared to the aperture measures.
Isophotal area used in derivation of the isophotal flux.
  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.
Semi-major and semi-minor radii and position angle.
  SExtractor generated status flags. The following indicates the meaning of the flag, as adapted from the Sextractor 2.3 User's Manual, by E. Bertin.
  • bit 0 - Bright Neighbors
  • bit 1 - Blended Object
  • bit 2 - Saturation
  • bit 4 - Bad Apertures
  • bit 5 - Bad Isophotes
  • bits 6-7 - Memory Overflow
  Average depth of coverage in units of independent images at the source location.
  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.
  Flag to indicate whether a source is included in the combined Optical-IRAC-MIPS24 catalog. A value of 1 indicates the source is in the combined catalog, while a 0 indicates this source appears only in the single-band MIPS24 catalog. Most 0 values are found in regions with no IRAC coverage.