Galaxies with spectral energy distributions peaking near 60 micrometers. 1: Optical spectroscopy, infrared photometry, and radio continuum data

Details Galaxies with spectral energy distributions peaking near 60 micrometers. 1: Optical spectroscopy, infrared photometry, and radio continuum data Galaxies with spectral energy distributions peaking near 60 micrometers. 1: Optical spectroscopy, infrared photometry, and radio continuum data

Nov 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aj....106.1743v&link_type=abstract

Astronomical Journal (ISSN 0004-6256), vol. 106, no. 5, p. 1743-1770

Astronomy and Astrophysics

Astronomy

54

Continuums, Galactic Radiation, Infrared Photometry, Near Infrared Radiation, Radio Spectra, Spectral Energy Distribution, Visible Spectrum, Astronomical Catalogs, H Ii Regions, Infrared Astronomy Satellite, Optical Emission Spectroscopy, Radiant Flux Density, Seyfert Galaxies

Scientific paper

We present and discuss broadband infrared photometry in the 1-100 micrometer wavelength range, optical spectroscopy, and radio continuum observations of a sample of IRAS galaxies with unusual spectral energy distributions that peak near 60 micrometers. For inclusion in this sample of '60 PKs', the galaxies must have satisfied the following criteria: IRAS flux ratios f60/f100 greater than 1 and 1 less than f60/f25 less than 4, and galactic latitude absolute value of b greater than 10 deg. In this paper, which is the first of a series, we show that the 60PKs are relatively scarce objects that represent about 2% of the spatial density of 60 micrometer-selected galaxies in the range L(60 micrometers) = 109 to 1012 solar luminosity, but have a far-infrared luminosity function of nearly identical shape. They are detected up to redshifts of 0.2. Besides having the usual high percentage of active galaxies (approximately 30% H II-region like, 50% Seyfert 2, 10% Seyfert 1, 10% unknown) associated with a flat 25 to 60 micrometer spectral index, the sample also includes most of the galaxies that have been found to have a dust-obscured broadline region. We show that the additional f60/f100 greater than 1 constraint selects galaxies with dust that is more centrally concentrated and exposed to a more intense radiation field than in most other IRAS galaxies. In particular, the cirrus component of the far-infrared radiation, which is typically the dominant contributor to the 100 micrometer emission from spiral galaxies, is negligible or missing. This is consistent with the fact that the most distinctive optical signature of 60PKs is the absence of spiral structure: they tend to be peculiar and/or amorphous objects.

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