Explaining two circumnuclear star forming rings in NGC5248

TL;DR

This study uses high-resolution CO observations to analyze the molecular gas distribution in NGC5248, revealing a gas ring at 100pc but not at 370pc, and discusses the nature of its two circumnuclear star forming rings.

Contribution

First detailed molecular gas mapping of NGC5248's central region, clarifying the structure and dynamics of its circumnuclear rings.

Findings

Molecular gas forms a ring at 100pc from the nucleus.

No ring structure detected at 370pc in molecular gas.

Discussion on the nature and formation scenarios of the two rings.

Abstract

The distribution of gas in the central kiloparsec of a galaxy has a dynamically rapid evolution. Nonaxisymmetries in the gravitational potential of the galactic disk, such as a large scale stellar bar or spiral, can lead to significant radial motion of gaseous material from larger radii to the central region. The large influx of gas and the subsequent star formation keep the central region constantly changing. However, the ability of gas to reach the nucleus proper to fuel an AGN phase is not guaranteed. Gas inflow can be halted at a circumnuclear star forming ring several hundred parsec away. The nearby galaxy NGC5248 is especially interesting in this sense since it is said to host 2 circumnuclear star forming rings at 100pc and 370pc from its quiescent nucleus. Here we present new subarcsecond PdBI+30m CO(2-1) emission line observations of the central region. For the first time the molecular gas distribution at the smallest stellar ring is resolved into a gas ring, consistent with the presence of a quiescent nucleus. However, the molecular gas shows no ring structure at the larger ring. We combine analyses of the gaseous and stellar content in the central kiloparsec of this galaxy to understand the gas distribution and dynamics of this star forming central region. We discuss the probability of two scenarios leading to the current observations, given our full understanding of this system, and discuss whether there are really two circumnuclear star forming rings in this galaxy.