The Origin of the 24-micron Excess in Red Galaxies Export

@article{citeulike:3503794, abstract = {Observations with the Spitzer Space Telescope have revealed a population of red-sequence galaxies with a significant excess in their 24-micron emission compared to what is expected from an old stellar population. We identify 900 red galaxies with 0.15\<z\<0.3 from the AGN and Galaxy Evolution Survey (AGES) selected from the NOAO Deep Wide-Field Survey Bootes field. Using Spitzer/MIPS, we classify 89 (\~{}10\%) with 24-micron infrared excess (f24\>0.3 mJy). We determine the prevalence of AGN and star-formation activity in all the AGES galaxies using optical line diagnostics and mid-IR color-color criteria. Using the IRAC color-color diagram from the Spitzer Shallow Survey, we find that 64\% of the 24-micron excess red galaxies are likely to have strong PAH emission features in the 8-micron IRAC band. This fraction is significantly larger than the 5\% of red galaxies with f24\<0.3 mJy that are estimated to have strong PAH emission, suggesting that the infrared emission is largely due to star-formation processes. Only 15\% of the 24-micron excess red galaxies have optical line diagnostics characteristic of star-formation (64\% are classified as AGN and 21\% are unclassifiable). The difference between the optical and infrared results suggest that both AGN and star-formation activity is occurring simultaneously in many of the 24-micron excess red galaxies. These results should serve as a warning to studies that exclusively use optical line diagnostics to determine the dominant emission mechanism in the infrared and other bands. We find that \~{}40\% of the 24-micron excess red galaxies are edge-on spiral galaxies with high optical extinctions. The remaining sources are likely to be red galaxies whose 24-micron emission comes from a combination of obscured AGN and star-formation activity.}, archivePrefix = {arXiv}, author = {Brand, Kate and Moustakas, John and Armus, Lee and Assef, Roberto J. and Brown, Michael J. I. and Cool, Richard R. and Desai, Vandana and Dey, Arjun and Le Floc\&\#x27;h, Emeric and Jannuzi, Buell T. and Kochanek, Christopher S. and Melbourne, Jason and Papovich, Casey J. and Soifer, B. T.}, citeulike-article-id = {3503794}, citeulike-linkout-0 = {http://arxiv.org/abs/0811.1398}, citeulike-linkout-1 = {http://arxiv.org/pdf/0811.1398}, day = {10}, eprint = {0811.1398}, keywords = {24-micron, excess, galaxies}, month = {Nov}, posted-at = {2008-11-19 21:47:16}, priority = {2}, title = {The Origin of the 24-micron Excess in Red Galaxies}, url = {http://arxiv.org/abs/0811.1398}, year = {2008} }

TY - JOUR ID - citeulike:3503794 L3 - citeulike-article-id:3503794 N2 - Observations with the Spitzer Space Telescope have revealed a population of red-sequence galaxies with a significant excess in their 24-micron emission compared to what is expected from an old stellar population. We identify 900 red galaxies with 0.15<z<0.3 from the AGN and Galaxy Evolution Survey (AGES) selected from the NOAO Deep Wide-Field Survey Bootes field. Using Spitzer/MIPS, we classify 89 (~10%) with 24-micron infrared excess (f24>0.3 mJy). We determine the prevalence of AGN and star-formation activity in all the AGES galaxies using optical line diagnostics and mid-IR color-color criteria. Using the IRAC color-color diagram from the Spitzer Shallow Survey, we find that 64% of the 24-micron excess red galaxies are likely to have strong PAH emission features in the 8-micron IRAC band. This fraction is significantly larger than the 5% of red galaxies with f24<0.3 mJy that are estimated to have strong PAH emission, suggesting that the infrared emission is largely due to star-formation processes. Only 15% of the 24-micron excess red galaxies have optical line diagnostics characteristic of star-formation (64% are classified as AGN and 21% are unclassifiable). The difference between the optical and infrared results suggest that both AGN and star-formation activity is occurring simultaneously in many of the 24-micron excess red galaxies. These results should serve as a warning to studies that exclusively use optical line diagnostics to determine the dominant emission mechanism in the infrared and other bands. We find that ~40% of the 24-micron excess red galaxies are edge-on spiral galaxies with high optical extinctions. The remaining sources are likely to be red galaxies whose 24-micron emission comes from a combination of obscured AGN and star-formation activity. TI - The Origin of the 24-micron Excess in Red Galaxies KW - 24-micron KW - excess KW - galaxies AU - Brand, Kate AU - Moustakas, John AU - Armus, Lee AU - Assef, Roberto AU - Brown, Michael AU - Cool, Richard AU - Desai, Vandana AU - Dey, Arjun AU - Le Floc'h, Emeric AU - Jannuzi, Buell AU - Kochanek, Christopher AU - Melbourne, Jason AU - Papovich, Casey AU - Soifer, BT PY - 2008/Nov/10/ UR - http://arxiv.org/abs/0811.1398 ER -