The Lower Limit of Dynamical Black Hole Masses Detectable in Virgo Compact Stellar Systems Using the JWST/NIRSpec IFU

TL;DR

This study investigates the minimum black hole mass detectable in compact stellar systems in the Virgo cluster using JWST/NIRSpec data and dynamical modeling, focusing on the influence of observational and modeling factors.

Contribution

It demonstrates that black holes constituting at least 1% of their host's stellar mass can be reliably detected with high-quality kinematic data and explores factors affecting measurement accuracy.

Findings

BH masses ≥1% of host stellar mass are accurately recoverable.

Higher-order velocity moments improve BH mass detection.

Measurement accuracy depends on data quality and modeling assumptions.

Abstract

Due to observational challenges, the mass function of black holes (BH) at lower masses is poorly constrained in the local universe. Understanding the occupation fraction of BHs in low-mass galaxies is crucial for constraining the origins of supermassive BH seeds. Compact stellar systems (CSSs), including ultra-compact dwarf galaxies (UCDs) and compact elliptical galaxies (cEs), are potential intermediate-mass BH hosts. Despite the difficulties posed by their limited spheres of influence, stellar dynamical modeling has been effective in estimating central BH masses in CSSs. Some CSSs may harbor a BH constituting up to 20% of their host stellar mass, while others might not have a central BH. In support of our ongoing efforts to determine the BH masses in select CSSs in the Virgo cluster using JWST/NIRSpec IFU observations and orbit-superposition dynamical models, we create mock kinematic data mimicking the characteristics of observed cEs/UCDs in the Virgo cluster with different BH masses. We then construct a series of dynamical models using the orbit-superposition code FORSTAND and explore the accuracy of recovering the BH mass. We find that the mass of BHs comprising 1% or more of the total host stellar mass can be accurately determined through kinematic maps featuring higher-order velocity moments. We also assess how BH mass measurement is affected by deprojection methods, regularization factors, anisotropy parameters, orbit initial conditions, the absence of higher-order velocity moments, spatial resolution, and the signal-to-noise ratio.