The Interstellar Medium and Star Formation in Edge-On Galaxies. II. NGC 4157, 4565, and 5907

TL;DR

This study investigates the vertical structure and star formation properties of edge-on galaxies NGC 4157, 4565, and 5907, revealing smooth disk scale heights, consistent gravitational stability, and a distinct star formation law compared to face-on galaxies.

Contribution

It provides detailed measurements of disk thickness, velocity dispersions, and star formation laws in edge-on galaxies, highlighting differences from previous face-on galaxy studies.

Findings

Disk scale heights and velocity dispersions vary smoothly with radius.

The gravitational instability parameter Q remains above or equal to 1 across the disk.

Star formation law slope differs from that in face-on galaxy studies.

Abstract

We present a study of the vertical structure of the gaseous and stellar disks in a sample of edge-on galaxies (NGC 4157, 4565, and 5907) using BIMA/CARMA 12CO (J = 1 --> 0), VLA H I, and Spitzer 3.6 micron data. In order to take into account projection effects when we measure the disk thickness as a function of radius, we first obtain the inclination by modeling the radio data. Using the measurement of the disk thicknesses and the derived radial profiles of gas and stars, we estimate the corresponding volume densities and vertical velocity dispersions. Both stellar and gas disks have smoothly varying scale heights and velocity dispersions, contrary to assumptions of previous studies. Using the velocity dispersions, we find that the gravitational instability parameter Q follows a fairly uniform profile with radius and is greater than or equal to 1 across the star forming disk. The star formation law has a slope that is significantly different from those found in more face-on galaxy studies, both in deprojected and pixel-by-pixel plots. Midplane gas pressure based on the varying scale heights and velocity dispersions appears to roughly hold a power-law correlation with the midplane volume density ratio.