Defining the (Black Hole)-Spheroid Connection with the Discovery of Morphology-Dependent Substructure in the $M_{\rm BH}$--$\rm n_{sph}$ and $M_{\rm BH}$--$\rm R_{e, sph}$ Diagrams: New Tests for Advanced Theories and Realistic Simulations

TL;DR

This study investigates the relationships between black hole mass and host galaxy spheroid properties, revealing morphology-dependent differences and providing new tests for galaxy evolution theories through detailed analysis of 123 local galaxies.

Contribution

It introduces morphology-dependent $M_{BH}$--$ m n_{sph}$ and $M_{BH}$--$ m R_{e,sph}$ relations, and compares these across galaxy types, disks, and core structures, offering new insights into galaxy-black hole co-evolution.

Findings

Different $M_{BH}$--$ m n_{sph}$ relations for ETGs and LTGs.

A near-linear $M_{*,sph}$--$ m R_{e,sph}$ relation for all galaxy types.

Distinct $M_{BH}$--$ m R_{e,sph}$ relations for ETGs and LTGs, offset by about 1 dex.

Abstract

For 123 local galaxies with directly-measured black hole masses ($M_{\rm BH}$), we provide the host spheroid's S\'ersic index ($\rm n_{sph}$), effective half-light radius ($\rm R_{e,sph}$), and effective surface brightness ($\mu_e$), obtained from careful multi-component decompositions, and we use these to derive the morphology-dependent $M_{\rm BH}$--$\rm n_{sph}$ and $M_{\rm BH}$--$\rm R_{e,sph}$ relations. We additionally present the morphology-dependent $M_{\rm *,sph}$--$\rm n_{sph}$ and $M_{\rm *,sph}$--$\rm R_{e,sph}$ relations. We explored differences due to: early-type galaxies (ETGs) versus late-type galaxies (LTGs); S\'ersic versus core-S\'ersic galaxies; barred versus non-barred galaxies; and galaxies with and without a stellar disk. We detect two different $M_{\rm BH}$--$\rm n_{sph}$ relations due to ETGs and LTGs with power-law slopes $3.95\pm0.34$ and $2.85\pm 0.31$. We additionally quantified the correlation between $M_{\rm BH}$ and the spheroid's central concentration index, which varies monotonically with the S\'ersic index. Furthermore, we observe a single, near-linear $M_{\rm *,sph}$--$\rm R_{e,sph}^{1.08\pm 0.04}$ relation for ETGs and LTGs, which encompasses both classical and alleged pseudobulges. In contrast, ETGs and LTGs define two distinct $M_{\rm BH}$--$\rm R_{e,sph}$ relations with $\Delta_{\rm rms|BH}\sim\rm 0.60~dex$ (cf.\ $\sim$0.51~dex for the $M_{\rm BH}$--$\sigma$ relation and $\sim$0.58~dex for the $M_{\rm BH}$--$M_{\rm *,sph}$ relation), and the ETGs alone define two steeper $M_{\rm BH}$--$\rm R_{e,sph}$ relations, offset by $\sim$1~dex in the $\log M_{\rm BH}$-direction, depending on whether they have a disk or not and explaining their similar offset in the $M_{\rm BH}$--$M_{\rm *,sph}$ diagram. This trend holds using $10 \%$, $50 \%$, or $90 \%$ radii.(Abridged)