VizieR Online Data Catalog: AGN photoionization of gas in companion galaxies (Keel+, 2019)

We compiled a finding list of AGNs with companion galaxies based on our redshift and geometric criteria, largely through the efforts of volunteer participants in the Galaxy Zoo project (Lintott et al. 2008MNRAS.389.1179L). A post on the project forum setting out the desired kinds of galaxy pairs led to responses beginning both from objects seen in the normal course of classification for Galaxy Zoo and from SQL queries of the SDSS photometric and spectroscopic catalogs. This initial query selected object pairs projected within 15arcsec with both redshifts in SDSS DR8, where one had an AGN spectroscopic class and the other had a non-AGN galaxy spectroscopic class. The cut-off in projected separation corresponds to 17.5kpc at the median sample redshift z=0.060. To this we added additional pairs found by Galaxy Zoo volunteers that satisfied the same criteria except for not having both redshifts available from the SDSS, or fulfilling the linear separation criterion at lower redshifts. In some cases the missing redshift had been measured and was available from sources referenced in NED, and in others, tidal structure made physical association between the galaxies virtually certain (which was confirmed by our spectroscopy). Similarly, we also included nearby systems passing these tests, previously known outside the SDSS imaging region (i.e. Keel 1996ApJS..106...27K, Cat. J/ApJS/106/27 building on the catalogue by Lipovetsky, Neizvestny & Neizvestnaya 1988SoSAO..55....5L, Cat. VII/173): NGC 2992, NGC 6786, Kaz 63, and Kaz 199.

This set of pairs was further refined by our inspection of spectra to confirm the clear presence of a spectroscopic AGN. We required a Seyfert nucleus; originally we started compiling LINER AGN as well, but as their inferred ionizing luminosities all fell below our threshold for observation, we ceased collecting them for this program. When only the AGN redshift is known, tidal distortion was taken as secondary evidence that two galaxies are physically associated. These factors led us to a finding list of 212 AGN/companion pairs (table A1), incorporating Galaxy Zoo forum postings between 2012 January 16 and 2014 March 15.

We obtained spectra of 32 candidate pairs, some multiple times for confirmation or at different position angles, using the Kast double spectrograph (Miller J. S., Stone R. P. S., 1992, Lick Obs. Technical Report 66. Lick Observatory, Santa Cruz, CA) at the 3-m Shane telescope of Lick Observatory during 13 nights from 2013 to 2015. For each session, the D46 dichroic beamsplitter separated light into blue and red optical paths, with a nominal split centred at 4600Å. The wavelength settings were roughly 3400-4600Å in the blue side and 4600-7400Å on the red side. The slit width was 2.0arcsec. Flux calibration used observations of 1-3 standard stars per night. Clouds prohibited observing standards on 2015 April 23, so we used the response curve derived for April 26, and scaled line fluxes in the case of SDSS 1354+1327 to match earlier data where the slits crossed at the nucleus.

(1 data file).