The Close Environment of Seyfert Galaxies and Its Implication for Unification Models

This paper presents a statistical analysis of the circumgalactic environment of nearby Seyfert galaxies based on a computer-aided search of companion galaxies on the Digitized Sky Survey (DSS). An intrinsic difference between the environment of Seyfert 1 and Seyfert 2 galaxies, suggested by previous work, is confirmed as statistically significant. For Seyfert 2 galaxies we find a significant excess of large companions (diameter of companion >= 10 Kpc) within a search radius <= 100 Kpc of projected linear distance, as well as within a search radius equal to three times the diameter \ds of each Seyfert galaxy. For Seyfert 1 galaxies there is no clear evidence of any excess of companion galaxies neither within 100 Kpc, nor within 3\ds. For all samples the number of companions suggests a markedly non-Poissonian distribution for galaxies on scales <= 100 Kpc. This difference in environment is not compatible with the simplest formulation of the Unification Model for Seyferts: both types 1 and 2 should be intrinsicaly alike, the only difference being due to orientation of an obscuring torus. We propose an alternative formulation.Comment: 1 figure, accepted for publication in Astrophysical Journal Letter

The Circum-Galactic Environment of Bright IRAS Galaxies

This paper studies systematically, for the first time, the circumgalactic environment of bright IRAS galaxies as defined by Soifer et al. (1989). While the role of gravitational interaction for luminous and ultraluminous IRAS galaxies has been well established by various studies, the situation is by far more obscure in the IR luminosity range of the bright IRAS sample, 10^{10}Lsol < Lfir < 10^{11} Lsol. To easily identify nearby companion galaxies, the bright IRAS sample was restricted to 87 objects with redshift range 0.008 < z < 0.018 and galactic latitude > 30^{o}. A control sample, selected from the Center for Astrophysics redshift survey catalogue, includes 90 objects matching the Bright IRAS sample for distribution of isophotal diameter, redshift, and morphological type. From a search of nearby companion galaxies within 250 Kpc on the second-generation Digitized Sky Survey (DSS-II), we found that the circumgalactic environment of the Bright IRAS galaxies contains more large companions than the galaxies in the optically selected control sample, and is similar to that of Seyfert 2 galaxies. We found a weak correlation over a wide range of far IR luminosity (10^9 Lsol < Lfir < 10^{12.5}Lsol) between projected separation and Lfir, which confirms a very close relationship between star formation rate of a galaxy and the strength of gravitational perturbations. We also find that the far IR colors depend on whether a source is isolated or interacting. Finally, we discuss the intrinsic difference and evolution expectations for the bright IRAS galaxies and the control sample, as well as the relationship between starbursting and active galaxies.Comment: 10 pages, 5 figs, 2 tables. Accepted for publication in Ap

Arp 194: Evidence of Tidal Stripping of Gas and Cross-Fueling

We present new imaging and spectroscopic observations of the interacting system Arp 194 (= UGC 06945 = VV 126). The northern component (A194N) is a distorted spiral or ring galaxy likely disrupted by a collision or close encounter with a southern galaxy (A194S). There is evidence that a third galaxy with similar recession velocity is projected on A194N but its role is likely secondary. A194S is connected to A194N by a string of emission knots which motivates our interpretation that the former was the intruder. Three of the knots are easily discernible in B,R, and H-alpha images and are assumed to trace the path of the intruder following the encounter, which we estimate occurred a few 10^8 yr ago. Both A194S and N are experiencing strong bursts of star formation: the H-alpha luminosity indicates a total star formation rate ~ 10 solar masses per year. The lack of detectable J and K emission from the blobs, along with strong H-alpha emission, indicates that an evolved stellar population is not likely to be present. The brightest knot (closest to A194S) shows a star formation rate of ~1.2 solar masses per year which, if sustained over a time ~ 7 10^7 yr, could explain the spectral energy distribution. This suggests that the stripped matter was originally predominantly gaseous. The brightest knot is detected as a FIRST radio source and this is likely the signature of supernova remnants related to enhanced star formation. Motions in the gas between the brightest knot and A194S, traced by an emission line link of increasing radial velocity, suggests infall toward the center of the intruder. Arp 194 is therefore one of the few galaxies where evidence of ``cross-fueling'' is observed [LaTeX removed]