Origin of 12 um Emission across Galaxy Populations from WISE and SDSS Surveys

DONOSO, E.; YAN, LIN; TSAI, CHAO-WEI; EISENHARDT, P.; ASSEF, R. J.; LEISAWITZ, D.; JARRETT, T.H.; STANDORD, S.A.

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Estados Unidos; Año: 2012 vol. 748 p. 80 - 90

0004-637X

We cross-matched Wide-field Infrared Survey Explorer sources brighter than 1 mJy at 12 um with the Sloan Digital Sky Survey galaxy spectroscopic catalog to produce a sample of 10^5 galaxies at z=0.08, the largest of its kind. This sample is dominated (70%) by star-forming (SF) galaxies from the blue sequence, with total IR luminosities in the range 10^8-10^12 L_sun. We identify which stellar populations are responsible for most of the 12 um emission. We find that most (80%) of the 12 um emission in SF galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast, the 12 um emission in weak active galactic nuclei (AGNs; L[OIII]10^7 L_sun), act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences. This suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. We also find that 4.6-12 um color is a useful first-order indicator of SF activity in a galaxy when no other data are available.