# Do BL Lac Objects and FR I radiogalaxies inhabit the same galaxy environment?

## TL;DR

This study compares the galaxy environments of BL Lac objects and FR I radiogalaxies, revealing that FR I galaxies are surrounded by denser galaxy environments than BL Lacs, challenging previous assumptions about their relationship.

## Contribution

It provides the first direct comparison of the environments of BL Lac objects and FR I radiogalaxies using SDSS data, suggesting they may not share the same galaxy environment.

## Key findings

- FR I radiogalaxies have twice the galaxy excess density compared to BL Lacs within 0.5 Mpc.
- The results imply a need to reconsider the parent population hypothesis for BL Lac objects.
- The study uses SDSS i-band images to quantify galaxy environments around both types of objects.

## Abstract

We investigate the environments of galaxies around BL Lac objects and FR I radiogalaxies, the alleged parent populations of misaligned sources. We compare the environment of a sample of 50 BL Lac objects at 0.1<z<0.33 with that of a sample of 90 FR I galaxies at 0.1<z< 0.15. The galaxy environment is estimated using the SDSS images in the i-band. We find that the galaxy excess density within 0.5 Mpc around of FR I radiogalaxies is a factor ~ 2 larger than that around BL Lacs. This implies a reconsideration of the parent population of BL Lac objects.