Star formation in nearby galaxies

Ford, George Philip 2014. Star formation in nearby galaxies. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This work uses multiwavelength observations of nearby galaxies to explore the relationship between star formation and the interstellar medium in galaxies of various sizes and morphology. Galaxies in the Herschel Reference Survey are divided into barred and unbarred spirals to test for differences in dust temperature, dust mass, star formation rate, farinfrared luminosity, NUV-r colour and stellar mass between the two populations. The only significant observed difference is with stellar mass, where barred spirals are generally less massive. I suggest this is due to the speed of bar creation depending on galaxy mass, although this is counter to some previous observations. Trends with Hubble-type and environment are consistent with previous work. The resolved star formation law is studied in the two largest extragalactic sources in the local group, Andromeda (M31) and the Triangulum (M33). The two are measured to have global star formation rates (SFR) of 0.25M⊙ yr−1 and 0.16M⊙ yr−1 respectively using far-ultraviolet and 24 mm emission as star formation tracers. M33 has a higher mean surface density of star formation, as expected as it is later type than M31, and a higher star formation efficiency. Both galaxies appear consistent with the globally averaged SFR and gas surface density of normal spirals studied in previous work, with M31 at the low end in terms of SFR. When looking at smaller scales, both galaxies show evidence of saturation of neutral monatomic hydrogen at §Gas = 10M⊙ pc−2 when looking at the star formation law with total gas. They also appear to follow close to linear star formation laws with molecular gas only, consistent with previous work on resolved galaxies. M31 shows evidence of a sub-linear star formation law with molecular gas, indicating that star formation efficiency is lower in the highest density regions. Testing the relationship in M31 on different pixel scales does not effect the measured Kennicutt-Schmidt index, as has been suggested in previous work. M33 shows a significant portion of the galaxy has a relatively high SFR surface density, but little molecular gas as traced by CO. I suggest this could be evidence of CO-free molecular hydrogen in these regions.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Uncontrolled Keywords:	Galaxies, galaxy evolution, spiral galaxies, bars, star formation, interstellar medium (ISM), gas, Local Group, Herschel, infrared (IR), submillimeter (sub-mm), ultraviolet (UV), M31, Andromeda, M33, The Triangulum.
Funders:	Department funding
Date of First Compliant Deposit:	30 March 2016
Last Modified:	19 Mar 2016 23:45
URI:	https://orca.cardiff.ac.uk/id/eprint/63670

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