Imaging Redshift Estimates for BL Lacertae Objects

TL;DR

This study uses high-quality imaging to detect host galaxies of BL Lac objects, providing redshift estimates and insights into their luminosity and evolution, especially for sources lacking spectroscopic redshifts.

Contribution

It offers a novel method of estimating redshifts for BL Lacs through host galaxy magnitudes, improving understanding of their distribution and evolution.

Findings

Hosts detected for 25 out of 49 objects.

Redshift estimates range from 0.2 to 1.0.

Higher mean redshift than previous spectroscopic solutions.

Abstract

We have obtained high dynamic range, good natural seeing i' images of BL Lacertae objects (BL Lacs) to search for the AGN host and thus constrain the source redshift. These objects are drawn from a sample of bright flat-spectrum radio sources that are either known (via recent Fermi LAT observations) gamma-ray emitters or similar sources that might be detected in continuing gamma-ray observations. All had spectroscopic confirmation as BL Lac sources, but no redshift solution. We detected hosts for 25/49 objects. As these galaxies have been argued to be standard candles, our measured host magnitudes provide redshift estimates (ranging from 0.2--1.0). Lower bounds are established on the redshifts of non-detections. The mean of the fit redshifts (and lower limits) is higher than those of spectroscopic solutions in the radio- and gamma-ray- loud parent samples, suggesting corrections may be needed for the luminosity function and evolution of these sources.