Multicolour Optical Imaging of IR-Warm Seyfert Galaxies. I. Introduction and Sample Selection

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. 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 multi-colour broad and narrow band imaging for a sample of mid-IR ``warm'' Seyferts and for a control sample of mid-IR ``cold'' galaxies. In the present paper we describe the sample selection and briefly discuss their IR properties. We then give an overview of the data collected and present broad-band images for all our objects. Finally, we summarize the main issues that will be addressed with these data in a series of forthcoming papers.Comment: 18 pages including 3 figures and 5 tables (tables 1,4,5 are included as independent files

Extragalactic Large-Scale Structures behind the Southern Milky Way. -- II. Redshifts Obtained at the SAAO in the Crux Region

In our systematic optical galaxy search behind the southern Milky Way, 3760 (mostly unknown) galaxies with diameters D > 0.2 arcminutes were identified in the Crux region (287 < l < 318 degrees, |b| < 10 degrees, Woudt & Kraan-Korteweg 1997). Prior to this investigation, only 65 of these galaxies had known redshifts. In order to map the galaxy distribution in redshift space we obtained spectra for 226 bright (B_J < 18.0 mag) objects with the 1.9m telescope of the South African Astronomical Observatory (SAAO). Two main structures crossing the Galactic Plane in the Crux region have now become clear. A narrow, nearby filament from (l,b) = (340 deg, -25 deg) to the Centaurus cluster can be traced. This filament runs almost parallel to the extension of the Hydra-Antlia clusters found earlier and is part of what we have earlier termed the ``Centaurus Wall'' extending in redshift-space between 0 < v < 6000 km/s (Fairall & Paverd 1995). The main outcome of this survey however, is the recognition of another massive extended structure between 4000 < v < 8000 km/s. This broad structure, dubbed the Norma Supercluster (Woudt et al. 1997), runs nearly parallel to the Galactic Plane from Vela to ACO 3627 (its centre) from where it continues to the Pavo cluster. This massive structure is believed to be associated with the Great Attractor. The survey has furthermore revealed a set of cellular structures, similar to those seen in redshift space at higher galactic latitudes, but never before seen so clearly behind the Milky Way.Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, LaTex, 6 encapsulated postscript figures, requires l-aa.sty and epsf.sty. Original figures and tables are available upon request (E-mail: [email protected]

COLA II - Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies

We present optical spectroscopic observations of 93 galaxies taken from the infra-red selected COLA (Compact Objects in Low Power AGN) sample. The sample spans the range of far-IR luminosities from normal galaxies to LIRGs. Of the galaxies observed, 78 (84%) exhibit emission lines. Using a theoretically-based optical emission-line scheme we classify 15% of the emission-line galaxies as Seyferts, 77% as starbursts, and the rest are either borderline AGN/starburst or show ambiguous characteristics. We find little evidence for an increase in the fraction of AGN in the sample as a function of far-IR luminosity but our sample covers only a small range in infrared luminosity and thus a weak trend may be masked. As a whole the Seyfert galaxies exhibit a small, but significant, radio excess on the radio-FIR correlation compared to the galaxies classified as starbursts. Compact (<0.05'') radio cores are detected in 55% of the Seyfert galaxies, and these galaxies exhibit a significantly larger radio excess than the Seyfert galaxies in which cores were not detected. Our results indicate that there may be two distinct populations of Seyferts, ``radio-excess'' Seyferts, which exhibit extended radio structures and compact radio cores, and ``radio-quiet'' Seyferts, in which the majority of the radio emission can be attributed to star-formation in the host galaxy. No significant difference is seen between the IR and optical spectroscopic properties of Seyferts with and without radio cores. (Abridged)Comment: 24 pages, 4 figures, 6 tables. Accepted for publication in ApJ, February 200

Two New Planetary Nebulae Discovered in a Galaxy Search in the Southern Milky Way

Spectroscopic observations have been carried out for eleven objects believed to be planetary nebulae on the basis of their optical appearance. They were discovered in an ongoing deep search for galaxies in the Southern Milky Way (Kraan-Korteweg & Woudt 1994). The objects were observed with the 1.9m telescope of the South African Astronomical Observatory during our program for obtaining redshifts of obscured galaxies in the ``Zone of Avoidance''. Of the eleven objects, three proved too faint for a definite classification, four were galaxies with radial velocities between v=3920 km/s and v=14758 km/s, but four were confirmed as planetary nebulae (PNE). Their relative line strengths and radial velocities have been determined. The PNE are on average fairly large (23''-30''). Two of them (PNG 298.3+06.7 and PNG 323.6-04.5) were previously unknown; for these we show H_alpha and [OIII] images.Comment: A&A accepted, 7 pages, 3 tables, 2 postscript figures, 2 GIF figures, uses l-aa.sty, full paper including ps-figures available upon request at ftp://gin.obspm.fr/depot/kraan/pn.ps.gz (7.8Mb