Gas compression and stellar feedback in the tidally interacting and ram-pressure stripped Virgo spiral galaxy NGC 4654

TL;DR

This study investigates how gas compression and stellar feedback influence star formation in the Virgo galaxy NGC 4654, revealing the interplay between external interactions, gas dynamics, and star formation regulation.

Contribution

The paper combines new CO observations with analytical and dynamical models to elucidate the effects of ram-pressure stripping and gravitational interactions on the ISM and star formation in NGC 4654.

Findings

Gas surface densities exceed canonical values near the galaxy's edge.

A Toomre Q parameter of ~0.8 and increased velocity dispersion reproduce observed gas and SFR profiles.

Stellar feedback regulates star formation by increasing turbulence and moderately enhancing gas density.

Abstract

NGC 4654 is a Virgo galaxy seen almost face-on, which undergoes nearly edge-on gas ram pressure stripping and a fly-by gravitational interaction with another massive galaxy, NGC 4639. NGC 4654 shows a strongly compressed gas region near the outer edge of the optical disk, with HI surface densities (HSDR), exceeding the canonical value of 10-15 Msun/pc2. New IRAM 30m HERA CO(2-1) data of NGC 4654 are used to study the physical conditions of the ISM. The CO-to-H$_2$ conversion factor was estimated and found to be one to two times the Galactic value with significant decrease in the ratio between the molecular fraction and the total ISM pressure in the HSDR, self-gravitating gas, a Toomre parameter below $Q=1$ and star-formation efficiency 1.5-2 times higher. Analytical models were used to reproduce radial profiles of the SFR and the atomic and molecular surface densities. A Toomre parameter of $\rm Q \sim 0.8$ combined with an increase in the velocity dispersion of 5 km/s are necessary conditions to simultaneously reproduce the gas surface densities and the SFR. A dynamical model was used to reproduce the gas distribution of NGC 4654. The comparison between the velocity dispersion given by the moment 2 map and the intrinsic 3D velocity dispersion from the model were used to discriminate between regions of broader linewidths caused by a real increase in the velocity dispersion and those caused by an unresolved velocity gradient only. We found that the 5 km/s increase in the intrinsic velocity dispersion is compatible with observations. During a period of gas compression through external interactions, the gas surface density is enhanced, leading to an increased SFR and stellar feedback. Under the influence of stellar feedback, the gas density increases only moderately. The stellar feedback acts as a regulator of star-formation, increasing the turbulent velocity within the region.