Dragon's Lair: on the large-scale environment of BL Lac objects

TL;DR

This paper investigates the large-scale environments of BL Lac objects and challenges the unification scenario by showing they differ from radio galaxies but are consistent with FR0 sources, suggesting jets are common in various AGN types.

Contribution

It provides new insights into the environments of BL Lacs, proposing they are similar to FR0s, which impacts understanding of jet formation and AGN unification models.

Findings

BL Lacs and radio galaxies inhabit different large-scale environments.

BL Lacs have environments similar to FR0 radio sources.

Results challenge the traditional unification scenario of AGNs.

Abstract

The most elusive and extreme sub-class of active galactic nuclei (AGNs), known as BL Lac objects, shows features that can only be explained as the result of relativistic effects occurring in jets pointing at a small angle with respect to the line of sight. A long standing issue is the identification of the BL Lac parent population, having jets oriented at larger angles. According to the "unification scenario" of AGNs, radio galaxies with low luminosity and edge-darkened radio morphology are the most promising candidates to be the parent population of BL Lacs. Here we compare the large-scale environment, an orientation independent property, of well-defined samples of BL Lacs with samples of radio-galaxies all lying in the local Universe. Our study reveals that BL Lacs and radio galaxies live in significantly different environments, challenging predictions of the unification scenario. We propose a solution to this problem proving that large-scale environments of BL Lacs is statistically consistent with that of compact radio-sources, known as FR0s, sharing similar properties. This implies that highly relativistic jets are ubiquitous and are the natural outcome of the accretion of gas into the deep gravitational potential well produced by supermassive black holes.