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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Astronomy

Year Degree Awarded

2014

Month Degree Awarded

February

First Advisor

Prof. Daniela Calzetti

Subject Categories

External Galaxies

Abstract

Thanks to the Spitzer Space Telescope, the infrared (IR) emission have been better studied in the past decades, as well as its relations to star formation rates (SFR) and the calibrations of IR emissions as SFR indicators. However, the far infrared (FIR) emission are still understudied, especially at the sub-galactic region scales. In this dissertation, I present new ground--based observations in the light of the infrared hydrogen recombination line Br[gamma] (2.16~mu m) of a sample of KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) galaxies. The Br[gamma] emission line offers the double advantage of directly tracing ionizing photons and of being relatively insensitive to the effects of dust attenuation. It is therefore a relatively unbiased reference star formation rate (SFR) indicator that I use to establish the calibrations of the Herschel PACS 70, 100 and 160~mu m emission as SFR tracers on sub--galactic scales. I confirm with higher statistical accuracy the dependence of the SFR calibrations on metallicity and star formation timescale. I also provide calibrations for SFR indicators for HII regions that combine the observed H[alpha] with one of the three IR bands. I find significant diffuse IR emission not related to current star formation activity in galaxies, implying major impact of diffuse stellar population on the dust heating in nearby galaxies. I make comparisons among different SFR(IR) indicators and provide interpretations on the comparisons.

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