Multicolor optical imaging of infrared-warm Seyfert galaxies. I. Introduction and sample selection.
Abstract (from CDS):
The standard AGN unification models attempt to explain the diversity of observed AGN types by a few fundamental parameters, where orientation effects play a paramount role. Whether other factors, such as the evolutionary stage and the host galaxy properties are equally important parameters for the AGN diversity, is a key issue that we are addressing with the present data. Our sample of IR-selected Seyfert galaxies is based on the important discovery that their integrated IR spectrum contains an AGN signature, the ``warm'' 25-60 µm color index. This being an almost isotropic property, our sample is much less affected by orientation/obscuration effects compared to most Seyfert samples. It therefore provides a test-bed for the orientation-dependent models of Seyferts, involving dusty tori. We have obtained multicolor broadband and narrowband imaging for a sample of mid-IR ``warm'' (-1.5≤α(25,60)≤0) Seyferts and for a control sample of mid-IR ``cold'' (α(25,60)≤-1.5) galaxies. The two samples span similar ranges of far-IR colors (~-3.0≤α(60,100)≤0.5). The warm sample contains 21 Seyfert 1 and 33 Seyfert 2 galaxies with logLFIR=9.6-11.8 and z=0.01-0.08, including some of the most extreme warm sources (L60≥1011 L☉). The cold sample contains 16 IRAS sources selected to match the warm galaxies in redshift and luminosity range, but show a variety of nuclear types (Seyfert 1, Seyfert 2, and starburst). In the present paper we describe in some detail the sample selection and briefly discuss their IR properties. We then give an overview of the data collected and present broadband images for all our objects. Finally, we summarize the main issues that will be addressed with these data in a series of forthcoming papers: (i) the orientation versus evolutionary Seyfert unification schemes and (ii) the origin of mid-IR excess in the warm Seyfert sample.