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Title: A census of dust in galaxies across 5 billion years of cosmic time
Author: Beeston, Rosemary Alice
ISNI:       0000 0004 8500 8406
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2019
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We present a census of dust in galaxies out to redshifts of 0.5, the most recent five billion years of cosmic history using the wealth of data from the Herschel Space Observatory and the Galaxy And Mass Assembly Survey (GAMA). A key goal of this Thesis is to try and quantify the dust component in galaxies, in galaxies of different morphological types, and derive the evolution of the dust content over recent cosmic history. We derive the dust mass function (DMF) of 15 750 galaxies with redshift z < 0.1, drawn from the overlapping area of the GAMA and H-ATLAS surveys. The DMF is derived using the density corrected Vmax method, where we estimate Vmax using: (i) the normal photometric selection limit (pVmax) and (ii) a bivariate bright- ness distribution (BBD) technique, which accounts for two selection effects. We fit the data with a Schechter function. We investigate potential sources of bias in our derived parameters and find that they are robust to uncertainties in the flux measurements of galaxies, the shape of the dust mass function and Eddington bias, though we see a strong dependence on the derived dust mass function parameters depending on the minimum mass used in the fit. The observed DMF does not agree with predictions from semi-analytic models or hydrodynamical cosmological simulations. The former attributes too much dust to high stellar mass galaxies. The latter underpredicts the high mass end of the DMF potentially due to long grain growth timescales. We find that the observed dust-to-stellar mass ratio is higher for low-mass disks than currently assumed in models. Comparing the DMFs and galaxy stellar mass functions (GSMF) we find there may be an approximate linear scaling from the late-type galaxy (LTG) GSMF to the LTG DMF. The LTG DMF can also be approximated by scaling the disk GSMF. We use a stacking analysis to investigate the evolution of dust properties as a function of both luminosity and redshift. We stack the FIR Herschel luminosities of galaxies in the H-ATLAS DR1 sample in luminosity-redshift bins and then fit the resulting SEDs with one and two component modified blackbodies (MBBs). At low redshift, we find that the mass-weighted and luminosity-weighted temperatures derived for the stacked SEDs both exhibit a trend for brighter galaxies to have warmer dust. In higher redshift bins we do see an evolution in both mass-weighted and luminosity-weighted temperature, but the effect is strongest for luminosity-weighted temperature. We are not able to determine whether the evolution is due to higher dust temperatures further back in cosmic time, or because the average luminosity of galaxies also evolves strongly over this redshift range. We derive 250 µm luminosity functions (LFs) and DMFs for this sample of galaxies in five redshift slices with a width of 0.1 out to redshift 0.5. We find that the low redshift DMF derived in this way has a different shape to the optically selected DMF from the GAMA sample. The uncertainty due to cosmic variance for this low-redshift sample is 14.5%. We find a strong evolution of both the luminosity and dust mass densities in our sample out to z = 0.5. We note that this Thesis extends our knowledge of the dust mass content of galaxies in the following ways (i) reducing the large uncertainty in measurements of the dust mass density from cosmic variance by using larger areas of the sky; (ii) using consistent, homogeneous measurements over these large volumes (via the GAMA and H-ATLAS surveys where photometry is derived consistently, and dust mass measurements are derived e.g. MAGPHYS for all of the sources in the same way); (iii) approaching the dust mass function from both an optically-selected and FIR-selected sample to determine if this makes a difference and finally (iv) investigating the dust content in galaxies and scaling relations with stellar mass for different morphological types (e.g. late-type/early type and bulge and disk-like galaxies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy