MID-IR LUMINOSITIES AND UV/OPTICAL STAR FORMATION RATES AT z < 1.4
- National Optical Astronomy Observatory, 950 North Cherry Ave., Tucson, AZ 85719 (United States)
- Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)
- Institut d'Astrophysique de Paris, CNRS, 98 bis boulevard Arago, F-75014 Paris (France)
- Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
- Department of Astronomy, Columbia University, New York, NY 10027 (United States)
- Departamento de AstrofIsica, Facultad de CC. FIsicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
- University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)
- UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
- Infrared Processing and Analysis Center, California Institute of Technology 100-22, Pasadena, CA 91125 (United States)
- University of Arkansas, Fayetteville, AR 72701 (United States)
- Spitzer Science Center, California Institute of Technology 220-6, Pasadena, CA 91125 (United States)
- Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)
Ultraviolet (UV) nonionizing continuum and mid-infrared (IR) emission constitute the basis of two widely used star formation (SF) indicators at intermediate and high redshifts. We study 2430 galaxies with z < 1.4 in the Extended Groth Strip with deep MIPS 24 {mu}m observations from FIDEL, spectroscopy from DEEP2, and UV, optical, and near-IR photometry from the AEGIS. The data are coupled with dust-reddened stellar population models and Bayesian spectral energy distribution (SED) fitting to estimate dust-corrected star formation rates (SFRs). In order to probe the dust heating from stellar populations of various ages, the derived SFRs were averaged over various timescales-from 100 Myr for 'current' SFR (corresponding to young stars) to 1-3 Gyr for long-timescale SFRs (corresponding to the light-weighted age of the dominant stellar populations). These SED-based UV/optical SFRs are compared to total IR luminosities extrapolated from 24 {mu}m observations, corresponding to 10-18 {mu}m rest frame. The total IR luminosities are in the range of normal star-forming galaxies and luminous IR galaxies (10{sup 10}-10{sup 12} L{sub sun}). We show that the IR luminosity can be estimated from the UV and optical photometry to within a factor of 2, implying that most z < 1.4 galaxies are not optically thick. We find that for the blue, actively star-forming galaxies the correlation between the IR luminosity and the UV/optical SFR shows a decrease in scatter when going from shorter to longer SFR-averaging timescales. We interpret this as the greater role of intermediate age stellar populations in heating the dust than what is typically assumed. Equivalently, we observe that the IR luminosity is better correlated with dust-corrected optical luminosity than with dust-corrected UV light. We find that this holds over the entire redshift range. Many so-called green valley galaxies are simply dust-obscured actively star-forming galaxies. However, there exist 24 {mu}m detected galaxies, some with L{sub IR}>10{sup 11} L{sub sun}, yet with little current SF. For them a reasonable amount of dust absorption of stellar light (but presumably higher than in nearby early-type galaxies) is sufficient to produce the observed levels of IR, which includes a large contribution from intermediate and old stellar populations. In our sample, which contains very few ultraluminous IR galaxies, optical and X-ray active galactic nuclei do not contribute on average more than {approx}50% to the mid-IR luminosity, and we see no evidence for a large population of 'IR excess' galaxies.
- OSTI ID:
- 21313910
- Journal Information:
- Astrophysical Journal, Vol. 700, Issue 1; Other Information: DOI: 10.1088/0004-637X/700/1/161; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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