MID-INFRARED SPECTROSCOPY OF TWO LENSED STAR-FORMING GALAXIES
- Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 (United States)
- Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510 (United States)
- Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, D-85741 Garching (Germany)
- Department of Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90024 (United States)
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Department of Physics and Astronomy, Austin Peay State University, P.O. Box 4608, Clarksville, TN 37044 (United States)
We present low-resolution, rest-frame {approx}5-12 {mu}m Spitzer/IRS spectra of two lensed z {approx} 2 UV-bright star-forming galaxies, SDSS J120602.09+514229.5 and SDSS J090122.37+181432.3. Using the magnification boost from lensing, we are able to study the physical properties of these objects in greater detail than is possible for unlensed systems. In both targets, we detect strong polycyclic aromatic hydrocarbon (PAH) emission at 6.2, 7.7, and 11.3 {mu}m, indicating the presence of vigorous star formation. For J1206, we find a steeply rising continuum and significant [S IV] emission, suggesting that a moderately hard radiation field is powering continuum emission from small dust grains. The strength of the [S IV] emission also implies a sub-solar metallicity of {approx}0.5 Z{sub sun}, confirming published rest-frame optical measurements. In J0901, the PAH lines have large rest-frame equivalent widths (>1 {mu}m) and the continuum rises slowly with wavelength, suggesting that any active galactic nucleus (AGN) contribution to L{sub IR} is insignificant, in contrast to the implications of optical emission-line diagnostics. Using [O III] line flux as a proxy for AGN strength, we estimate that the AGN in J0901 provides only a small fraction of its mid-infrared continuum flux. By combining the detection of [Ar II] with an upper limit on [Ar III] emission, we infer a metallicity of {approx}>1.3 Z{sub sun}. This work highlights the importance of combining rest-frame optical and mid-IR spectroscopy in order to understand the detailed properties of star-forming galaxies at high redshift.
- OSTI ID:
- 21467173
- Journal Information:
- Astrophysical Journal, Vol. 723, Issue 1; Other Information: DOI: 10.1088/0004-637X/723/1/729; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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