The molecular H2 emission and the stellar kinematics in the nuclear region of the Sombrero galaxy

TL;DR

This study investigates the molecular hydrogen emission and stellar kinematics in the nuclear region of the Sombrero galaxy, revealing a rotating molecular disk and estimating the supermassive black hole's mass.

Contribution

It provides the first detailed analysis of H$_2$ emission and stellar kinematics in M104's nucleus, modeling the stellar dynamics and estimating black hole mass.

Findings

Detected H$_2$ emission line indicating a molecular torus/disk

Modeled stellar kinematics with a thin eccentric disk

Estimated black hole mass of approximately 9 x 10^8 solar masses

Abstract

We analyze the molecular H$_2$ emission and the stellar kinematics in a data cube of the nuclear region of M104, the Sombrero galaxy, obtained with NIFS on the Gemini-north telescope. After a careful subtraction of the stellar continuum, the only emission line we detected in the data cube was H$_2 \lambda 21218$. An analysis of this emission revealed the existence of a rotating molecular torus/disk, aproximately co-planar with a dusty structure detected by us in a previous work. We interpret these two structures as being associated with the same obscuring torus/disk. The kinematic maps provided by the Penalized Pixel Fitting method revealed that the stellar kinematics in the nuclear region of M104 appears to be the result of the superposition of a "cold" rotating disk and a "hot" bulge. Using a model of a thin eccentric disk, we reproduced the main properties of the maps of the stellar radial velocity and of the stellar velocity dispersion, specially within a distance of 0.2" from the kinematic axis (in regions at larger distances, the limitations of a model of a thin rotating disk become more visible). The general behavior of the $h_3$ map, which is significantly noisier than the other maps, was also reproduced by our model (although the discrepancies, in this case, are considerably higher). With our model, we obtained a mass of (9.0 +/- 2.0) x 10^8 Mo for the supermassive black hole of M104, which is compatible, at $1\sigma$ or $2\sigma$ levels, with the values obtained by previous studies.