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Herschel observations and a model for IRAS 08572+3915: a candidate for the most luminous infrared galaxy in the local (z < 0.2) Universe

A. Efstathiou, C. Pearson, D. Farrah, D. Rigopoulou, J. GraciŠ Carpio, A. Verma, H. W. W. Spoon, J. Afonso, J. Bernard-Salas, D. L. Clements, A. Cooray, D. Cormier, M. Etxaluze, J. Fischer, E. GonzŠlez-Alfonso, P. Hurley, V. Lebouteiller, S. Oliver, M. Rowan-Robinson, E. Sturm

Abstract
We present Herschel photometry and spectroscopy, carried out as part of the Herschel ultraluminous infrared galaxy (ULIRG) survey, and a model for the infrared to submillimetre emission of the ULIRG IRAS 08572+3915. This source shows one of the deepest known silicate absorption features and no polycyclic aromatic hydrocarbon emission. The model suggests that this object is powered by an active galactic nucleus (AGN) with a fairly smooth torus viewed almost edge-on and a very young starburst. According to our model, the AGN contributes about 90 per cent of the total luminosity of 1.1 × 1013 L, which is about a factor of 5 higher than previous estimates. The large correction of the luminosity is due to the anisotropy of the emission of the best-fitting torus. Similar corrections may be necessary for other local and high-z analogues. This correction implies that IRAS 08572+3915 at a redshift of 0.058 35 may be the nearest hyperluminous infrared galaxy and probably the most luminous infrared galaxy in the local (z < 0.2) Universe. IRAS 08572+3915 shows a low ratio of [C ii] to IR luminosity (log L[Cii]/LIR < −3.8) and a [O i]63 μm to [C ii]158 μm line ratio of about 1 that supports the model presented in this Letter.

Keywords
radiative transfer - galaxies: active - galaxies: individual (IRAS 08572+3915) - infrared: galaxies

Monthly Notices of the Royal Astronomical Society
Volume 437, Issue 1, Page L16
2014 January

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia