Calibrating stellar velocity dispersions based on spatially-resolved h-band spectra for improving the m-sigma relation

TL;DR

This study measures stellar velocity dispersions using high-quality H-band spectra for 31 nearby galaxies to calibrate and improve the black hole mass-stellar velocity dispersion relation, accounting for rotational effects.

Contribution

It introduces a method to calibrate velocity dispersions from near-IR spectra and corrects for rotational broadening to refine the MBH-sigma relation.

Findings

No significant difference between optical and H-band velocity dispersions.

80% of galaxies show a rotating stellar disk.

A correction method reduces aperture-dependent velocity dispersion variations.

Abstract

To calibrate stellar velocity dispersion measurements from optical and near-IR stellar lines, and to improve the black hole mass (MBH)- stellar velocity dispersion (sigma) relation, we measure stellar velocity dispersions based on high quality H-band spectra for a sample of 31 nearby galaxies, for which dynamical MBH is available in the literature. By comparing velocity dispersions measured from stellar lines in the H-band with those measured from optical stellar lines, we find no significant difference, suggesting that optical and near-IR stellar lines represent the same kinematics and that dust effect is negligible for early-type galaxies. Based on the spatially-resolved rotation and velocity dispersion measurements along the major axis of each galaxy, we find that a rotating stellar disk is present for 80% of galaxies in the sample. For galaxies with a rotation component, velocity dispersions measured from a single aperture spectrum can vary by up to ~20%, depending on the size of the adopted extraction aperture. To correct for the rotational broadening, we derive luminosity-weighted velocity dispersion within the effective radius of each galaxy, providing uniformly measured velocity dispersions to improve the MBH-sigma relation.