Modeling the Gas Flow in the Bar of NGC 1365

TL;DR

This study combines new observations and re-analysis of existing data to model gas flow in NGC 1365's bar, revealing complex kinematics and constraints on the galaxy's mass distribution and dark matter halo properties.

Contribution

It provides the first detailed hydrodynamic simulations of NGC 1365's bar flow, exploring different dark matter halo models and bar pattern speeds to understand the galaxy's mass structure.

Findings

Galaxy is bi-symmetric in light but asymmetric in dust and gas kinematics.

HII regions show velocities 60-80 km/s different from surrounding gas.

Models suggest a fast bar with corotation at ~1.2 times the bar radius.

Abstract

We present new observations of the strongly-barred galaxy NGC 1365, including new photometric images and Fabry-Perot spectroscopy, as well as a detailed re-analysis of the neutral hydrogen observations from the VLA archive. We find the galaxy to be at once remarkably bi-symmetric in its I-band light distribution and strongly asymmetric in the distribution of dust and in the kinematics of the gas in the bar region. The velocity field mapped in the H-alpha line reveals bright HII regions with velocities that differ by 60 to 80 km/s from that of the surrounding gas, which may be due to remnants of infalling material. We have attempted hydrodynamic simulations of the bar flow to estimate the separate disk and halo masses, using two different dark matter halo models and covering a wide range of mass-to-light ratios (Upsilon) and bar pattern speeds (Omega_p). None of our models provides a compelling fit to the data, but they seem most nearly consistent with a fast bar, corotation at sim 1.2r_B, and Upsilon_I simeq 2.0 +- 1.0, implying a massive, but not fully maximal, disk. The fitted dark halos are unusually concentrated, a requirement driven by the declining outer rotation curve.