"Invisible AGN" I: Sample Selection and Optical/Near-IR Spectral Energy Distributions

Abstract

In order to find more examples of the elusive high-redshift molecular absorbers, we have embarked on a systematic discovery program for highly obscured, radio-loud "invisible AGN" using the VLA Faint Images of the Radio Sky at Twenty centimeters (FIRST) radio survey in conjunction with Sloan Digital Sky Survey (SDSS) to identify 82 strong (> 300 mJy) radio sources positionally coincident with late-type, presumably gas-rich galaxies. In this first paper, the basic properties of this sample are described including the selection process and the analysis of the spectral-energydistributions (SEDs) derived from the optical (SDSS) + near-IR (NIR) photometry obtained by us at the Apache Point Observatory 3.5m. The NIR images confirm the late-type galaxy morphologies found by SDSS for these sources in all but a few (6 of 70) cases (12 previously well-studied or misclassified sources were culled). Among 70 sources in the final sample, 33 show galaxy type SEDs, 17 have galaxy components to their SEDs, and 20 have quasar power-law continua. At least 9 sources with galaxy SEDs have K-band flux densities too faint to be giant ellipticals if placed at their photometric redshifts. Photometric redshifts for this sample are analyzed and found to be too inaccurate for an efficient radio-frequency absorption line search; spectroscopic redshifts are required. A few new spectroscopic redshifts for these sources are presented here but more will be needed to make significant progress in this field. Subsequent papers will describe the radio continuum properties of the sample and the search for redshifted H I 21 cm absorption.

32 pages, 9 figures, accepted by AJ

References in corpus (3)

• Probing radio source environments via HI and OH absorption
• A survey for redshifted molecular and atomic absorption lines I
• Spitzer mid-infrared spectroscopy of compact symmetric objects: What powers radio-loud active galactic nuclei?

Cited by in corpus (9)

• A Search for Intrinsic HI 21 cm and OH 18 cm Absorption Toward Compact Radio Sources
• The evolution of neutral hydrogen over the past 11 Gyr via HI 21 cm absorption
• Invisible Active Galactic Nuclei. II Radio Morphologies & Five New HI 21 cm Absorption Line Detections
• Ionisation of the atomic gas in redshifted radio sources
• The HI absorption zoo: JVLA extension to $z\sim 0.4$
• Atomic and Molecular Absorption in Redshifted Radio Sources
• The mid-infrared properties and gas content of active galaxies over large look-back times
• Further Observational Evidence for a Critical Ionising Luminosity in Active Galaxies
• Intervening or associated? Machine learning classification of redshifted H I 21-cm absorption