PASCHEN-alpha EMISSION IN THE GRAVITATIONALLY LENSED GALAXY SMM J163554.2+661225

Journal Article · Tue Oct 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/704/2/1506· OSTI ID:21367344

Papovich, Casey; Finkelstein, Steven L ^[1]; Rudnick, Gregory ^[2]; Rigby, Jane R ^[3]; Willmer, Christopher N. A.; Egami, Eiichi; Rieke, Marcia ^[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, Texas A and M University, College Station, TX 77843-4242 (United States)
2. Department of Physics and Astronomy, 1251 Wescoe Hall Dr., University of Kansas, Lawrence, KS 66045-7582 (United States)
3. Observatories, Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101 (United States)
4. Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States)
5. Ritter Observatory, University of Toledo, MS 113, Toledo, OH 43606 (United States)

We report the detection of the Paalpha emission line in the z = 2.515 galaxy SMM J163554.2+661225 using Spitzer spectroscopy. SMM J163554.2+661225 is a submillimeter-selected infrared-luminous galaxy maintaining a high star formation rate (SFR), with no evidence of an active galactic nucleus from optical or infrared spectroscopy, nor X-ray emission. This galaxy is lensed gravitationally by the cluster Abell 2218, making it accessible to Spitzer spectroscopy. We measure a line luminosity, L(Paalpha) = (2.05 +- 0.33) x 10{sup 42} erg s{sup -1}, corrected for gravitational lensing. Comparing the Halpha and Paalpha luminosities, we derive a nebular extinction, A(V) = 3.6 +- 0.4 mag. The dust-corrected luminosity, L(Paalpha) = (2.57 +- 0.43) x 10{sup 42} erg s{sup -1}, corresponds to an ionization rate, Q {sub 0} = (1.6 +- 0.3) x 10{sup 55} gamma s{sup -1}. The instantaneous SFR is psi = 171 +- 28 M {sub sun} yr{sup -1}, assuming a Salpeter-like initial mass function from 0.1 to 100 M {sub sun} yr{sup -1}. The total IR luminosity derived using 70, 450, and 850 mum data is L{sub IR} = (5-10) x 10{sup 11} L {sub sun}, corrected for gravitational lensing. This corresponds to psi = 90-180 M {sub sun} yr{sup -1}, where the upper range is consistent with that derived from the Paalpha luminosity. While the L(8 mum)/L(Paalpha) ratio is consistent with the extrapolated relation observed in local galaxies and star-forming regions, the rest-frame 24 mum luminosity is significantly lower with respect to local galaxies of comparable Paalpha luminosity. Thus, SMM J163554.2+661225 arguably lacks a warmer dust component (T{sub D} approx 70 K), which is associated with deeply embedded star formation, and which contrasts with local galaxies with comparable SFRs. Rather, the starburst in SMM J163554.2+661225 is consistent with star-forming local galaxies with intrinsic luminosities, L{sub IR} approx 10{sup 10} L {sub sun}, but 'scaled up' by a factor of approx10-100.

• OSTI ID: 21367344
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 704; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTROSCOPY
DUSTS
ELECTROMAGNETIC RADIATION
EMISSION
GALAXIES
INFRARED SPECTRA
IONIZATION
IONIZING RADIATIONS
LUMINOSITY
MASS
MILKY WAY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
RED SHIFT
SPECTRA
SPECTROSCOPY
STARS
X RADIATION