PROBING THE STAR FORMATION HISTORY AND INITIAL MASS FUNCTION OF THE z {approx} 2.5 LENSED GALAXY SMM J163554.2+661225 WITH HERSCHEL

Journal Article · Thu Dec 01 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/742/2/108· OSTI ID:22004610

Finkelstein, Keely D; Papovich, Casey; Finkelstein, Steven L ^[1]; Willmer, Christopher N. A.; Egami, Eiichi; Rieke, Marcia ^[2]; Rigby, Jane R ^[3]; Rudnick, Gregory ^[4]; Smith, J.-D. T. ^[5]

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1. George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843-4242 (United States)
2. Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States)
3. NASA Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States)
4. Department of Physics and Astronomy, 1251 Wescoe Hall Dr., University of Kansas, Lawrence, KS 66045-7582 (United States)
5. Ritter Observatory, Department of Physics and Astronomy, University of Toledo, MS 113, Toledo, OH 43606 (United States)

We present the analysis of Herschel Spectral and Photometric Imaging Receiver far-infrared (FIR) observations of the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and 500 {mu}m observations with existing data, we make an improved fit to the FIR spectral energy distribution of this galaxy. We find a total infrared (IR) luminosity of L(8-1000 {mu}m) = 6.9 {+-} 0.6 Multiplication-Sign 10{sup 11} L{sub Sun }, a factor of three more precise over previous L{sub IR} estimates for this galaxy, and one of the most accurate measurements for any galaxy at these redshifts. This FIR luminosity implies an unlensed star formation rate (SFR) for this galaxy of 119 {+-} 10 M{sub Sun} yr{sup -1}, which is a factor of 1.9 {+-} 0.35 lower than the SFR derived from the nebular Pa{alpha} emission line (a 2.5{sigma} discrepancy). Both SFR indicators assume an identical Salpeter initial mass function (IMF) with slope {Gamma} = 2.35 over a mass range of 0.1-100 M{sub Sun }; thus this discrepancy suggests that more ionizing photons may be necessary to account for the higher Pa{alpha}-derived SFR. We examine a number of scenarios and find that the observations can be explained with a varying star formation history (SFH) due to an increasing SFR, paired with a slight flattening of the IMF. If the SFR is constant in time, then larger changes need to be made to the IMF by either increasing the upper mass cutoff to {approx}200 M{sub Sun }, or a flattening of the IMF slope to 1.9 {+-} 0.15, or a combination of the two. These scenarios result in up to double the number of stars with masses above 20 M{sub Sun }, which produce the requisite increase in ionizing photons over a Salpeter IMF with a constant SFH.

• OSTI ID: 22004610
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 742; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ENERGY SPECTRA
GALAXIES
LUMINOSITY
MASS
PHOTONS
RED SHIFT
STARS