Journal Article

Stellar population and dust extinction in an ultraluminous infrared galaxy at <i>z</i>= 1.135

K. Kawara, S. Oyabu, Y. Matsuoka, Y. Yoshii, T. Minezaki, H. Sameshima, N. Asami, N. Ienaka and T. Kozasa

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 1, pages 335-344
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI:
Stellar population and dust extinction in an ultraluminous infrared galaxy at z= 1.135

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We present the detailed optical to far-infrared (far-IR) observations of SST J1604+4304, an ultraluminous IR galaxy at z= 1.135. Analysing the stellar absorption lines, namely, the Ca ii H & K and Balmer H lines in the optical spectrum, we derive the upper limits of an age for the stellar population. Given this constraint, the minimum χ2 method is used to fit the stellar population models to the observed spectral energy distribution from 0.44 to 5.8 μm. We find the following properties. The stellar population has an age 40–200 Myr with a metallicity 2.5 Z. The starlight is reddened by E(BV) = 0.8. The reddening is caused by the foreground dust screen, indicating that dust is depleted in the starburst site and the starburst site is surrounded by a dust shell. The IR (8–1000 μm) luminosity is Lir= 1.78 ± 0.63 × 1012 L. This is two times greater than that expected from the observed starlight, suggesting either that 1/2 of the starburst site is completely obscured at UV-optical wavelengths, or that 1/2 of Lir comes from active galactic nucleus (AGN) emission. The inferred dust mass is 2.0 ± 1.0 × 108 M. This is sufficient to form a shell surrounding the galaxy with an optical depth E(BV) = 0.8. From our best stellar population model – an instantaneous starburst with an age 40 Myr – we infer the rate of 19 supernovae per year. Simply analytical models imply that 2.5 Z in stars was reached when the gas mass reduced to 30 per cent of the galaxy mass. The gas metallcity is 4.8 Z at this point. The gas-to-dust mass ratio is then 120 ± 73. The inferred dust production rate is 0.24 ± 0.12 M per SN. If 1/2 of Lir comes from AGN emission, the rate is 0.48 ± 0.24 M per SN. We discuss the evolutionary link of SST J1604+4304 to other galaxy populations in terms of the stellar masses and the galactic winds, including optically selected low-luminosity Lyman α-emitters and submillimeter selected high-luminosity galaxies.

Keywords: dust, extinction; galaxies: evolution; galaxies: high-redshift; galaxies: individual: SST J1604+4304; galaxies: starburst; galaxies: stellar content; cosmology: observations; infrared: galaxies

Journal Article.  8075 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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