The extended 12 micron galaxy sample

Abstract

We have selected an all-sky (|b| ≥ 25 • ) 12 µm flux-limited sample of 893 galaxies from the IRAS Faint Source Catalog, Version 2 (FSC-2). This new sample contains 2.3 times as many objects as an earlier selection (Spinoglio & Malkan 1989) based on the IRAS Point Source Catalog, Version 2. We have obtained accurate total fluxes in the IRAS wavebands by using the ADDSCAN procedure for all objects with FSC-2 12 µm fluxes greater than 0.15 Jy and increasing flux densities from 12 to 60 µm, and defined the sample by imposing a survey limit of 0.22 Jy on the total 12 µm flux. Its completeness is verified, by means of the classical Log N − Log S and V /V max tests, down to 0.30 Jy, below which we have measured the incompleteness down to the survey limit, using the Log N − Log S plot, for our statistical analysis. We have obtained redshifts (mostly from catalogs) for virtually all (98.4%) the galaxies in the sample.Using existing catalogs of active galaxies, we defined a subsample of 118 objects consisting of 53 Seyfert 1s and quasars, 63 Seyfert 2s, and 2 blazars-∼ 13% of the full sample), which is the largest unbiased sample of Seyfert galaxies ever assembled. Since the 12 µm flux has been shown to be about one-fifth of the bolometric flux for Seyfert galaxies and quasars, the subsample of Seyferts (including quasars and blazars) is complete not only to 0.30 Jy at 12 µm but also with respect to a bolometric flux limit of ∼ 2.0 × 10 −10 erg s −1 cm −2 . The average value of V /V max for the full sample, corrected for incompleteness at low fluxes, is 0.51 ± 0.04, expected for a complete sample of uniformly distributed galaxies, while the value for the Seyfert galaxy subsample is 0.46 ± 0.10, suggesting that several more galaxies are yet to be identified as Seyferts in our sample. We have derived 12 µm and far-infrared luminosity functions for the AGN, as well as for the entire sample. The AGN luminosity functions are more complete than those of the optically selected CfA Seyfert galaxies for all luminosities and AGN types.We extracted from our sample a complete subsample of 235 galaxies fluxlimited (8.3 Jy) at 60 µm. The 60 µm luminosity function computed for this subsample is in satisfactory agreement with the ones derived from the bright galaxy sample (BGS;Soifer et al. 1987) and the deep high-galactic latitude sample (Lawrence et al. 1986), both selected at 60 µm. Over the high luminosity range where our sample and the BGS overlap, however, our space densities are systematically lower by a factor of ∼ 1.5, whereas at low luminosities our space densities are higher by about the same amount. Comparable results are obtained when comparing the far-IR luminosity function of our entire sample with the one derived from the BGS. This is not unexpected, because of the bias towards high-luminosity spirals caused by selection at 60 µm.

X-ray observations of highly obscuredτ9.7μm > 1 sources: an efficient method for selecting Compton-thick AGN?

“…An ideal data set for this purpose is the Spitzer IRS spectroscopic sample of Wu et al (2009). These authors present low-resolution Spitzer 5.5−35 μm spectra for 103 galaxies from the 12 μm Seyfert sample (Rush et al 1993). This is a complete, unbiased, flux-limited sample of local Seyfert galaxies, selected from the IRAS Faint Source Catalog by means of optical spectroscopy.…”

“…The structure of the paper is as follows: we first compile a local sample of high optical-depth (τ 9.7 μm > 1) sources from the Wu et al (2009) flux-limited Spitzer-IRS observations of the 12 μm Seyfert sample of Rush et al (1993). We investigate the X-ray spectra available in the literature, to deduce how many of these high-τ objects are heavily obscured or Compton-thick.…”

Unveiling the nucleus of NGC 7172

“…From our data, the inclination of the torus structure cannot be assumed. Thean et al (2000) observed NGC 7172 as part of a sample of 87 mid-infrared selected AGN from Rush et al (1993) at 8.4-GHz with the VLA A-configuration. The radio map shows, as in our NIR observation, an elongation to the south-west.…”

Spectroscopic Cosmological Surveys in the Far-IR

“…To have an idea of the galaxies that could be observed by SAFARI in the far-IR in the redshift range 0.4<z<4.0, one has to look at the rich rest frame mid-IR spectra of local galaxies that have been recently observed by the Spitzer satellite. Figure 2 shows the average Spitzer IRS high-resolution mid-IR spectra (Tommasin et al, 2009) of the 12μm sample of Seyfert galaxies (Rush, Malkan & Spinoglio, 1993), compared to those of starburst galaxies (Brandl et al, 2006). The quality of the data is very high and shows the many features that can differentiate between AGN and star formation processes.…”