Feeding and feedback in the active nucleus of Mrk 1157 probed with Gemini Near-Infrared Integral-Field Spectrograph

TL;DR

This study maps the stellar and gaseous kinematics of Mrk 1157's nucleus using near-infrared integral-field spectroscopy, revealing a rotating stellar disk, a bar, and complex gas outflows influenced by the active nucleus and radio jet.

Contribution

First detailed near-IR 2D kinematic mapping of Mrk 1157's nucleus, combining stellar and gas dynamics with emission-line analysis to understand AGN feedback mechanisms.

Findings

Detected stellar rotation and a bar structure.

Identified gas outflows with a mass rate of 6 solar masses per year.

Found molecular H2 emission dominated by X-ray heating.

Abstract

We have mapped the stellar and gaseous kinematics, as well as the emission-line flux distributions and ratios, from the inner 450pc radius of Mrk1157, using 2D near-IR spectra obtained with the Gemini NIFS at a spatial resolution of 35pc. The stellar velocity field shows a rotation pattern, with a discrete S-shaped zero velocity curve. The presence of a bar is also supported by the residual map between the observed rotation field and a model of circular orbits in a Plummer potential. The stellar velocity dispersion map presents a partial ring of low-sigma values (50-60km/s) at 250pc from the nucleus surrounded by higher sigma values from the galaxy bulge, originated in kinematically colder regions with recent star formation. The velocity dispersion of the bulge (100km/s) implies in a black hole mass of 8.3x10^6M_Sun. Emission-line flux distributions are most extended along PA=27/153deg, reaching at least 450pc from the nucleus and following the orientation observed in previous optical emission-line [OIII] imaging and radio jet. The molecular H_2 emission is dominated by thermal processes, mainly due to X-ray heating by the active nucleus. The [FeII] excitation has a larger contribution from shocks produced by the radio jet, as evidenced by the line-ratio maps and velocity dispersion map, which show spatial correlation with the radio structures. The gaseous kinematics shows two components, one due to gas located in the galaxy plane and another in outflow, which is oriented close to the plane of the sky, thus extending to high latitudes, as the galaxy plane is inclined by 45deg relative to the plane of the sky. The gas rotating in the plane dominates the H_2 and Pa-beta emission, while the gas in outflow is observed predominantly in [FeII] emission. From the outflow velocities and implied geometry, we estimate an outflow mass rate of 6M_sun/yr for the ionised gas.