Infrared power-law galaxies in the Chandra Deep Field South: AGN and ULIRGs
We investigate the nature of a sample of 92 Spitzer/MIPS 24 micron selected galaxies in the CDFS, showing power law-like emission in the Spitzer/IRAC 3.6-8 micron bands. The main goal is to determine whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical populat...
| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Journal article |
| Language: | English |
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Institute of Physics Publishing
2005
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| _version_ | 1826262824712667136 |
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| author | Alonso-Herrero, A Perez-Gonzalez, P Alexander, D Rieke, G Rigopoulou, D Floc'h, E Barmby, P Papovich, C Rigby, JR Bauer, F Brandt, W Egami, E Willner, S Dole, H Huang, J |
| author_facet | Alonso-Herrero, A Perez-Gonzalez, P Alexander, D Rieke, G Rigopoulou, D Floc'h, E Barmby, P Papovich, C Rigby, JR Bauer, F Brandt, W Egami, E Willner, S Dole, H Huang, J |
| author_sort | Alonso-Herrero, A |
| collection | OXFORD |
| description | We investigate the nature of a sample of 92 Spitzer/MIPS 24 micron selected galaxies in the CDFS, showing power law-like emission in the Spitzer/IRAC 3.6-8 micron bands. The main goal is to determine whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical population of obscured AGN not detected even in deep X-ray surveys. The majority of the IR power-law galaxies are ULIRGs at z>1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical to IR spectral energy distributions (SEDs) of the X-ray detected galaxies are almost equally divided between a BLAGN SED class (similar to an optically selected QSO) and a NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRG galaxies (e.g., Mrk231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter, and possibly more obscured. Moreover, the IR power-law galaxies have SEDs significantly different from those of high-z (z_sp>1) IR (24 micron) selected and optically bright (VVDS I_AB<=24) star-forming galaxies whose SEDs show a very prominent stellar bump at 1.6 micron. The galaxies detected in X-rays have 2-8 keV rest-frame luminosities typical of AGN. The galaxies not detected in X-rays have global X-ray to mid-IR SED properties that make them good candidates to contain IR bright X-ray absorbed AGN. If all these sources are actually obscured AGN, we would observe a ratio of obscured to unobscured 24 micron detected AGN of 2:1, whereas models predict a ratio of up to 3:1. Additional studies using Spitzer to detect X-ray-quiet AGN are likely to find more such obscured sources. |
| first_indexed | 2024-03-06T19:42:11Z |
| format | Journal article |
| id | oxford-uuid:210fa82f-eeb6-462b-b63c-76f995863f28 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T19:42:11Z |
| publishDate | 2005 |
| publisher | Institute of Physics Publishing |
| record_format | dspace |
| spelling | oxford-uuid:210fa82f-eeb6-462b-b63c-76f995863f282022-03-26T11:31:05ZInfrared power-law galaxies in the Chandra Deep Field South: AGN and ULIRGsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:210fa82f-eeb6-462b-b63c-76f995863f28EnglishSymplectic Elements at OxfordInstitute of Physics Publishing2005Alonso-Herrero, APerez-Gonzalez, PAlexander, DRieke, GRigopoulou, DFloc'h, EBarmby, PPapovich, CRigby, JRBauer, FBrandt, WEgami, EWillner, SDole, HHuang, JWe investigate the nature of a sample of 92 Spitzer/MIPS 24 micron selected galaxies in the CDFS, showing power law-like emission in the Spitzer/IRAC 3.6-8 micron bands. The main goal is to determine whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical population of obscured AGN not detected even in deep X-ray surveys. The majority of the IR power-law galaxies are ULIRGs at z>1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical to IR spectral energy distributions (SEDs) of the X-ray detected galaxies are almost equally divided between a BLAGN SED class (similar to an optically selected QSO) and a NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRG galaxies (e.g., Mrk231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter, and possibly more obscured. Moreover, the IR power-law galaxies have SEDs significantly different from those of high-z (z_sp>1) IR (24 micron) selected and optically bright (VVDS I_AB<=24) star-forming galaxies whose SEDs show a very prominent stellar bump at 1.6 micron. The galaxies detected in X-rays have 2-8 keV rest-frame luminosities typical of AGN. The galaxies not detected in X-rays have global X-ray to mid-IR SED properties that make them good candidates to contain IR bright X-ray absorbed AGN. If all these sources are actually obscured AGN, we would observe a ratio of obscured to unobscured 24 micron detected AGN of 2:1, whereas models predict a ratio of up to 3:1. Additional studies using Spitzer to detect X-ray-quiet AGN are likely to find more such obscured sources. |
| spellingShingle | Alonso-Herrero, A Perez-Gonzalez, P Alexander, D Rieke, G Rigopoulou, D Floc'h, E Barmby, P Papovich, C Rigby, JR Bauer, F Brandt, W Egami, E Willner, S Dole, H Huang, J Infrared power-law galaxies in the Chandra Deep Field South: AGN and ULIRGs |
| title | Infrared power-law galaxies in the Chandra Deep Field South: AGN and
ULIRGs |
| title_full | Infrared power-law galaxies in the Chandra Deep Field South: AGN and
ULIRGs |
| title_fullStr | Infrared power-law galaxies in the Chandra Deep Field South: AGN and
ULIRGs |
| title_full_unstemmed | Infrared power-law galaxies in the Chandra Deep Field South: AGN and
ULIRGs |
| title_short | Infrared power-law galaxies in the Chandra Deep Field South: AGN and
ULIRGs |
| title_sort | infrared power law galaxies in the chandra deep field south agn and ulirgs |
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