SSGSS: The Spitzer-SDSS-GALEX Spectroscopic Survey

Science Goals

The mid and far IR properties for large samples of galaxies have now been characterized using IRAC and MIPS photometry. Lookback studies of redshifted galaxies have facilitated the construction of stacked "hyper-resolved" SEDs using broadband photometry, but suffer from possible evolutionary effects that hamper their interpretation. Furthermore, the wide wavelength gap between IRAC 8 micron and MIPS 24 micron bands requires large interpolations. We remain in need of high quality mid-IR SEDs and spectroscopy for a representative sample in the local universe that may be applied to high-redshift studies.

We propose to use the Spitzer IRS to obtain SEDs from a representative sample of 100 galaxies imaged by GALEX, SDSS and Spitzer/SWIRE. We will use these data to study the global properties of SDSS galaxies using atomic and molecular nebular diagnostics measured from IR to UV. Among the key questions that we hope to address are:

• How can a full complement of UV optical and mid-IR photometry and spectroscopy be used to determine physical properties of "normal" galaxies such as SFR, SFH, dust content, and metallicity? What can we learn from the combination of optical and mid-IR signatures about AGN activity in bulges, Seyfert, LINERS, etc?
• How can the combination of optical+mid-IR spectroscopic diagnostics be used to probe the ISM structure (i.e. molecular clouds versus diffuse ISM), the relative heating of dust by young and old stars and the nebular conditions in star forming galaxies?

We are aiming to exploit the rich diagnostic information that can come from Mid-IR spectroscopy and for the first time, combine it with the powerful SDSS spectroscopic sample.

Our sample is representative of galaxies in the SDSS main spectroscopic sample, covering two orders of magnitude in stellar mass, color and dust attenuation. This survey provides a crucial link between mid-IR studies of nearby galaxies, such as those performed by ISO and SINGS, and on-going and future mid-IR studies of high redshift galaxies. The selected galaxies include "blue cloud" and "red sequence" galaxies as well as transition objects that fall between the two. These galaxies are also fairly well distributed in the Color-SFH space, suggesting that we will also be sampling the wide range of dust attenuations and star formation histories.