NASA-Sloan Atlas

The NASA-Sloan Atlas is a catalog of images and parameters of local galaxies derived from Sloan Digital Sky Survey imaging, and with the addition of Galaxy Evolution Explorer (GALEX) data for the ultraviolet part of the spectrum. The primary documentation can be found at the NASA-Sloan Atlas website.

The version of the NASA-Sloan Atlas used by MaNGA for its targeting is v1_0_1. This version contains some new features relative to the previous publicly released version (v0_1_2). These include an expanded redshift range (to z = 0.15),
and the calculation of elliptical Petrosian aperture photometry.

As part of DR13 we are releasing the summary catalog file for v1_0_1: nsa_v1_0_1.fits (2.5 Gbytes; datamodel). A table is available in CAS corresponding to this data (nsa).

The object detection, deblending, and other details regarding the image analysis can be found in Blanton et al. (2011). Broadly speaking, this process is better tuned for large, bright galaxies than the standard SDSS processing. Nevertheless, it is still susceptible to some of the similar failure modes (over or underdeblending).

The elliptical Petrosian aperture photometry is a new addition since that paper, and is considered the most reliable photometry available in this catalog. The definition of the Petrosian radius used for the apertures is based on the SDSS r-band and is identical to the usual SDSS definition except using elliptical instead of circular apertures. The position angle and axis ratio of the ellipses used are determined from the second moments of the light distribution at around the 90% light radius (as determined using the circular Petrosian fluxes). Based on simulations, these magnitudes avoid the dependence on ellipticity of the circular Petrosian magnitudes and avoid the biases associated with the single-component Sérsic fits released in v0_1_2. They do have the expected dependence of Petrosian magnitudes on profile shape, leading to an underestimate of the total flux for pure de Vaucouleurs galaxies.

We have also applied aperture corrections to the photometry, to account for the variation in point spread function between the bandpasses, particularly for GALEX. We do so by using the measured curve-of-growth to predict the aperture correction for an ideal elliptical galaxy, and applying this correction to the real data. For GALEX, these corrections can be of order 30% to 50% for galaxies with half-light radii around an arcsec; for SDSS they are always negligible.

All absolute magnitudes in the NASA-Sloan Atlas are given with H0 = 100 h km s-1 Mpc-1, so should be interpreted as M – 5 log10 h.