| Autor: |
Brand, Kate, Moustakas, John, Armus, Lee, Assef, Roberto J., Brown, Michael J. I., Cool, Richard R., Desai, Vandana, Dey, Arjun, Floc'h, Emeric Le, Jannuzi, Buell T., Kochanek, Christopher S., Melbourne, Jason, Papovich, Casey J., Soifer, B. T. |
| Rok vydání: |
2008 |
| Předmět: |
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| Zdroj: |
Astrophys.J.693:340-346,2009 |
| Druh dokumentu: |
Working Paper |
| DOI: |
10.1088/0004-637X/693/1/340 |
| Popis: |
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 0.150.3 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 IRAC 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.
Comment: ApJ, accepted; 11 pages, 7 figures; corrected reference to IRAC Shallow Survey in abstract |
| Databáze: |
arXiv |
| Externí odkaz: |
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