Eric S. Perlman et al. 2007 ApJ 663 808 doi:10.1086/518781
Eric S. Perlman1,2, R. E. Mason3, Christopher Packham4, N. A. Levenson5, Moshe Elitzur5, Justin J. Schaefer4, Masatoshi Imanishi6, William B. Sparks7 and James Radomski8
Show affiliationsWe discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87 in the mid-infrared (mid-IR) from 5 to 35 μm. These observations allow us to investigate mid-IR emission mechanisms in the core of M87 and to establish that the flaring, variable jet component HST-1 is not a major contributor to the mid-IR flux. The Spitzer data include a high signal-to-noise ratio 15-35 μm spectrum of the knot A/B complex in the jet, which is consistent with synchrotron emission. However, a synchrotron model cannot account for the observed nuclear spectrum, even when contributions from the jet, necessary due to the degrading of resolution with wavelength, are included. The Spitzer data show a clear excess in the spectrum of the nucleus at wavelengths longer than 25 μm, which we model as thermal emission from cool dust at a characteristic temperature of 55 ± 10 K, with an IR luminosity ~1039 ergs s-1. Given Spitzer's few arcsecond angular resolution, the dust seen in the nuclear spectrum could be located anywhere within ~5'' (390 pc) of the nucleus. In any case, the ratio of active galactic nucleus (AGN) thermal to bolometric luminosity indicates that M87 does not contain the IR-bright torus that classical unified AGN schemes invoke. However, this result is consistent with theoretical predictions for low-luminosity AGNs.
galaxies: active; galaxies: elliptical and lenticular, cD; galaxies: individual (M87); galaxies: jets; infrared: galaxies
Issue 2 (2007 July 10)
Received 2006 October 18, accepted for publication 2007 April 9
Eric S. Perlman et al. 2007 ApJ 663 808
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