Spitzer Mid-Infrared Spectroscopy of 70um-Selected Distant Luminous Infrared Galaxies
arXiv:0709.3119 · doi:10.1086/523938
Abstract
We present mid-infrared spectroscopy obtained with the Spitzer Space Telescope of a sample of 11 optically faint, infrared luminous galaxies selected from a Spitzer MIPS 70um imaging survey of the NDWFS Bootes field. These are the first Spitzer IRS spectra presented of distant 70um-selected sources. All the galaxies lie at redshifts 0.3<z<1.3 and have very large infrared luminosities of L_IR~ 0.1-17 x 10^12 solar luminosities. Seven of the galaxies exhibit strong emission features attributed to polycyclic aromatic hydrocarbons (PAHs). The average IRS spectrum of these sources is characteristic of classical starburst galaxies, but with much larger infrared luminosities. The PAH luminosities of L(7.7) ~ 0.4 - 7 x 10^11 solar luminosities imply star formation rates of ~ 40 - 720 solar masses per year. Four of the galaxies show deep 9.7um silicate absorption features and no significant PAH emission features (6.2um equivalent widths < 0.03um). The large infrared luminosities and low f70/f24 flux density ratios suggests that these sources have AGN as the dominant origin of their large mid-infrared luminosities, although deeply embedded but luminous starbursts cannot be ruled out. If the absorbed sources are AGN-dominated, a significant fraction of all far-infrared bright, optically faint sources may be dominated by AGN.
8 Pages, ApJ accepted
References in corpus (12)
- Mid-IR Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
- The distribution of silicate strength in Spitzer spectra of AGNs and ULIRGs
- Spitzer Mid-Infrared Spectroscopy of Infrared Luminous Galaxies at z~2 I: the Spectra
- A Spitzer IRS Low-Resolution Spectroscopic Search for Buried AGNs in Nearby Ultraluminous Infrared Galaxies - A Constraint on Geometry between Energy Sources and Dust -
- Spitzer Mid-Infrared Spectroscopy of Infrared Luminous Galaxies at z~2 II: Diagnostics
- Spitzer IRS spectra of a large sample of Seyfert galaxies: a variety of infrared SEDs in the local AGN population
- PAH Emission from Ultraluminous Infrared Galaxies
- AGN and Starburst Classification from Spitzer Mid-Infrared Spectra for High Redshift SWIRE Sources
- The AGN Contribution to the Mid-IR Emission of Luminous Infrared Galaxies
- A Spitzer Infrared Spectrograph Survey of Warm Molecular Hydrogen in Ultra-luminous Infrared Galaxies
- Spitzer IRS Spectra of Optically Faint Infrared Sources with Weak Spectral Features
- Spitzer Spectra of a 10 mJy Galaxy Sample and the Star Formation Rate in the Local Universe