On the Dark Matter Halos of Optical and IR-selected AGN in the Local Universe

TL;DR

This study investigates the dark matter halos of optical and infrared-selected active galactic nuclei (AGN) in the local universe, revealing that AGN host halos are generally more massive than non-active galaxies, with differences influenced by stellar age and selection method.

Contribution

It introduces the use of total satellite luminosity to compare dark matter halos of different AGN populations, highlighting the impact of selection methods and host galaxy properties.

Findings

AGN host halos are twice as massive as non-active galaxies when controlling for stellar mass.

WISE-selected AGN have higher satellite luminosity than optical AGN, but this difference diminishes when controlling for stellar age.

Differences in star formation properties do not fully account for the halo mass differences between AGN types.

Abstract

We use the technique of total satellite luminosity, L_sat, to probe the dark matter halos around active galactic nuclei in the SDSS Main Galaxy Sample. Our results focus on galaxies and AGN that are the central galaxy of their halo. Our two AGN samples are constructed from optical emission-line diagnostics and from WISE infrared colors. Both optically-selected and WISE-selected AGN have L_sat values twice as high as non-active galaxy samples when controlling for stellar mass and mean stellar age. This implies that the halos are twice as massive, but we cannot rule out that the increase in L_sat is due to these AGN residing in younger halos at the same mass. When only controlling for host galaxy stellar mass, WISE-selected AGN also have higher L_sat values than optical AGN at the factor of two level, consistent with previous results comparing the clustering of obscured and unobscured AGN. However, controlling for stellar age in the two populations of host galaxies removes half of this difference, attenuating the statistical significance of the difference. We perform permutation tests to quantify the different in the halo populations of each sample. The difference in star formation properties does not fully explain the difference in the two AGN populations, however. Although AGN luminosity correlates with mean stellar age, the difference in stellar age between the WISE and optical samples cannot be fully explained by differences in their AGN luminosity distributions.