GOODS-Herschel : impact of active galactic nuclei and star formation activity on infrared spectral energy distributions at high redshift

Kirkpatrick, A.; Pope, A.; Alexander, D.M.; Charmandaris, V.; Daddi, E.; Dickinson, M.; Elbaz, D.; Gabor, J.; Hwang, H.S.; Ivison, R.; Mullaney, J.; Pannella, M.; Scott, D.; Altieri, B.; Aussel, H.; Bournaud, F.; Buat, V.; Coia, D.; Dannerbauer, H.; Dasyra, K.; Kartaltepe, J.; Leiton, R.; Lin, L.; Magdis, G.; Magnelli, B.; Morrison, G.; Popesso, P.; Valtchanov, I.

Abstract

We explore the effects of active galactic nuclei (AGNs) and star formation activity on the infrared (0.3-1000 μm) spectral energy distributions (SEDs) of luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample of 151 galaxies selected at 24 μm (S 24 >~ 100 μJy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-IR spectrum into contributions from star formation and AGN activity. A significant portion (~25%) of our sample is dominated by an AGN (>50% of the mid-IR luminosity) in the mid-IR. Based on the mid-IR classification, we divide our full sample into four sub-samples: z ~ 1 star-forming (SF) sources, z ~ 2 SF sources, AGNs with clear 9.7 μm silicate absorption, and AGNs with featureless mid-IR spectra. From our large spectroscopic sample and wealth of multi-wavelength data, including deep Herschel imaging at 100, 160, 250, 350, and 500 μm, we use 95 galaxies with complete spectral coverage to create a composite SED for each sub-sample. We then fit a two-temperature component modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust temperatures, regardless of the mid-IR power source, but display a marked difference in the warmer dust temperatures. We calculate the average effective temperature of the dust in each sub-sample and find a significant (~20 K) difference between the SF and AGN systems. We compare our composite SEDs to local templates and find that local templates do not accurately reproduce the mid-IR features and dust temperatures of our high-redshift systems. High-redshift IR luminous galaxies contain significantly more cool dust than their local counterparts. We find that a full suite of photometry spanning the IR peak is necessary to accurately account for the dominant dust temperature components in high-redshift IR luminous galaxies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Citation

Kirkpatrick, A., Pope, A., Alexander, D., Charmandaris, V., Daddi, E., Dickinson, M., …Valtchanov, I. (2012). GOODS-Herschel : impact of active galactic nuclei and star formation activity on infrared spectral energy distributions at high redshift. Astrophysical Journal, 759(2), Article 139. https://doi.org/10.1088/0004-637x/759/2/139

• Journal Article Type: Article
• Publication Date: Nov 1, 2012
• Deposit Date: Apr 8, 2013
• Publicly Available Date: Dec 23, 2013
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 759
• Issue: 2
• Article Number: 139
• DOI: https://doi.org/10.1088/0004-637x/759/2/139
• Keywords: Dust, Extinction, Active, Galaxies, Evolution, Star formation, Infrared.
• Public URL: https://durham-repository.worktribe.com/output/1457438