Supermassive black hole mass measurement in the spiral galaxy NGC 4736 Using JWST/NIRSpec stellar kinematics

TL;DR

This study accurately measures the supermassive black hole in NGC 4736 using JWST/NIRSpec stellar kinematics, resolving previous inconsistencies and demonstrating the instrument's capability for such measurements.

Contribution

First dynamical measurement of SMBH in NGC 4736 using JWST/NIRSpec stellar kinematics, confirming the black hole mass aligns with established scaling relations.

Findings

SMBH mass in NGC 4736 is (1.60±0.16)×10^7 M⊙.

NIRSpec can detect SMBHs with masses around 5×10^6 M⊙ within 5 Mpc.

The measurement resolves previous discrepancies based on emission-line tracers.

Abstract

We present accurate mass measurements of the central supermassive black hole (SMBH) in NGC 4736 (M 94).\ We used the ``gold-standard" stellar absorption features (CO band heads) at $\sim$2.3 ${\rm \mu m}$, as opposed to gas emission lines, to trace the dynamics in the nuclear region, easily resolving the SMBH's sphere of influence. The analysis uses observations made with the integral field unit of the Near-Infrared Spectrograph (NIRSpec) on the {\it James Webb} Space Telescope and a surface brightness profile derived from {\it Hubble} Space Telescope archival images. We used Jeans anisotropic models within a Bayesian framework, and comprehensive Markov chain Monte Carlo optimization, to determine the best-fit black hole mass, orbital anisotropy, mass-to-light ratio, and nucleus kinematical inclination. We obtained a SMBH mass $M_{\rm BH}=(1.60\pm0.16)\times10^7$ M$_\odot$ (1$\sigma$ random error), which is consistent with the $M_{\rm BH}$-$\sigma$ and $M_{\rm BH}$-$M_\star$ relations. This is the first dynamical measurement of a $M_{\rm BH}$ in NGC 4736 based on the stellar kinematics observed with NIRSpec. We thus settle a longstanding inconsistency between estimates based on nuclear emission-line tracers and the $M_{\rm BH}$-$\sigma$ relation. Our analysis shows that NIRSpec can detect SMBHs with $M_{\rm BH,min}\approx 5\times10^6$ M$_\odot$ in galaxies within 5 Mpc and $\sigma\approx100$ km s$^{-1}$