SEIP Quick Start Guide
Posted by Justin Howell on 19 December 2013 01:44 PM
Quick Start Guide to using the Spitzer Enhanced Imaging Products
The Source List will be a table in IPAC Table Format. This is a simple space-delimited table, with simple headers. If you use IDL, there are some IPAC table readers at http://irsa.ipac.caltech.edu/tools/irsa_idl.html. Table readers in Topcat and AstroPy can also read this format.
The columns are described in Chapter 4 of the Explanatory Supplement. The ones of most interest, other than ra and dec, are flux columns (in microJy) i*_f_ap1, i*_df_ap1, m1_f_psf, m1_df_psf. The * indicates i1, i2, etc. for IRAC band 1, 2, etc. The “ap1” means an aperture flux in a 3.8 arcsec diameter aperture, with an aperture correction for a point-source already applied. The “psf” for “m1” (MIPS 24 microns) means a point-source fitted flux. The “df” means an uncertainty. Fluxes for a larger aperture for IRAC and an aperture flux for MIPS1 are also available, as well as bandfilled fluxes when something is detected at another wavelength, and 3sigma limits when appropriate, but these are the primary fluxes.
Along with the 2MASS flux columns, j (dj), h(dh), and k(dk) and WISE flux columns, wise1 (dwise1), etc., these should be enough to get you started with the Source List.
1. Getting the Most Reliable Fluxes
The SL contains only sources detected with a high signal-to-noise ratio in at least one band. The requirements for inclusion depend on whether the region is extragalactic or galactic. For extragalactic regions (obstype = 6), an object must be detected at the 10-sigma level in at least one channel (I1, I2, I3, I4, M1, J, H, K, W1, W2, W3, W4; see Table 1.3). For galactic regions (obstype = 3 or 4), an object must be detected at the 10-sigma level in at least two channels.
To retain only the most robust flux densities, apply the following cuts:
1. Make a SNR cut. Each source has 5 columns ending in “fluxtype”, four for each of the IRAC channels and one for MIPS-24. Flux densities with SNR>=3 for IRAC and >=10 for MIPS1 have *fluxtype=1.
2. Eliminate IRAC flux densities that may be affected by a nearby saturated source or a nearby extended source. There are four “fluxflag” columns, one for each IRAC channel. Choose *fluxflag=0.
3. Eliminate MIPS flux densities that may be affected by a nearby saturated source or a nearby extended source by choosing m1_brtfrac<0.5 and m1_extfrac<0.5.
4. Remove IRAC flux densities affected by soft saturation. There are four *softsatflag columns, one for each IRAC channel. Choose *softsatflag=0.
5. As long as you have filtered by *fluxtype = 1 (item #1 above), then you can use the following rules. For IRAC, use the 3.8 arcsec diameter aperture flux densities and the associated uncertainties (columns *f_ap1). For MIPS, use the PSF flux density and the associated uncertainties (m1_f_psf).
2. My object does not have an entry in the Source List!If you do not find the source(s) you expect, search for those positions in the IRAC and/or MIPS Coverage Tables. If the positions of interest are covered but your sources are not in the Source List, that indicates that your source was rejected from the Source List to ensure its overall reliability. This can happen for a variety of reasons. You may wish to measure your sources directly on the corresponding mosaics.