The interstellar medium and star formation in edge-on galaxies

This thesis presents a study of the vertical disk structure and star formation in four edge-on spiral galaxies (NGC 891, 4157, 4565, and 5907) observed in CO with BIMA/CARMA, HI with VLA, and IR (3.6 and 24 µm) with Spitzer. We first derive the radial density distributions for the edge-on galaxies using our PVD method for the radio data and GIPSY task RADPROF for IR data. The derived radial profiles are used to verify the correlation between star formation rate (SFR) and gas surface densities (ΣH2 and Σgas ), and between the ΣH2 /ΣHI ratio and the hydrostatic midplane pressure that have been found in face-on galaxies by previous studies. In addition, we examine the relationship between SFR and the molecular gas based on a pixel-by-pixel method. In order to estimate the volume densities of gas and stars, we measure the disk thickness as a function of radius, taking into account projection effects for less edge-on galaxies (NGC 4157, 4565, and 5907) by determining and correcting for the disk inclination. We also infer the vertical velocity dispersions with radius using the derived volume densities and disk thicknesses. Overall, the disk thicknesses increase with radius and the velocity dispersions decrease as a function of radius. We test the importance of gravitational instability parameter Q in determining massive star forming regions and the importance of interstellar gas pressure in controlling the ρH2 /ρHI ratio for two cases: varying and constant velocity dispersions. The Q parameter does not show a clear correlation with massive star formation although Q using varying velocity dispersion shows marginal instability in some galaxies. Both velocity dispersion models seem to show a well defined power-law relationship between the pressure and the ρH2 /ρHI ratio, although their relationship is tighter for the constant values. We conclude that the ρH2 /ρHI ratio is more closely related to the gas volume density than to the pressure.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Astronomy

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2013

Author dc:creator

• Yim, Ki Jeong

Contributors dc:contributor

• Wong, Tony
• Chu, You-Hua
• Gammie, Charles F.
• Looney, Leslie W.

• Galaxies
• Interstellar Medium (ISM)
• edge-on
• kinematics and dynamics
• individual (NGC 891, NGC 4157, NGC 4565, NGC 5907)
• stars
• formation

Statement dc:rights

• Copyright 2012 Ki Jeong Yim

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/42266

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/42266