Untangling galaxy components: the kinematics and stellar populations of bulges and disks

Tabor, Martha (2019) Untangling galaxy components: the kinematics and stellar populations of bulges and disks. PhD thesis, University of Nottingham.

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Abstract

Photometric bulge-disk decompositions have long been used as a way of separating out the central and extended components in a galaxy. However, whether these photometric components are made up of different stellar populations with distinct kinematics, or whether they are just a convenient way to fit a galaxy light profile, is not clear. By developing a method of bulge-disk decomposition that exploits both spectroscopic and photometric information available in integral field spectroscopy, we separate out bulges and disks based on their stellar populations and kinematics, to see if they are truly distinct. Tests of this new method on an initial sample of three S0 galaxies shows that the data are best fit when including two components with different kinematics, demonstrating that, at least in some of these systems, bulges and disks are indeed distinct and separable components. We therefore decided to apply the method to a larger sample from the MaNGA survey.

By applying this spectroscopic decomposition to this large sample of early-type galaxies, we extract information on the kinematics and stellar populations of bulges and disks, allowing us to compare the age, metallicity, specific angular momentum, j, and spin parameter, lambda_R, of the individual components. We find that bulges and disks have similar ages, but different metallicities, with bulges tending to have higher metallicity than their corresponding disks. Bulges and disks follow their own distinct kinematic relationships, both on the plane of the stellar spin parameter, lambda_R, and ellipticity, and in the relation between stellar mass, M, and specific angular momentum, j, with the location of the galaxy as a whole on these planes being determined by how much bulge and disk it contains.

As a check of the physical significance of the kinematic decompositions, we also dynamically model the individual galaxy components within the global potential of the galaxy. The resulting components exhibit kinematic parameters consistent with those derived from the spectroscopic decomposition, and though the dynamical modelling suffers from some degeneracies, the bulges and discs display systematically different intrinsic dynamical properties. An application to MUSE data, with higher spatial and spectral resolution, indicates that with high enough quality data it is possible to separate bulges and disks into distinct physically-meaningful components.

The work presented in this thesis demonstrates the value in considering the individual components of galaxies rather than treating them as a single entity, which neglects information that may be crucial in understanding where, when and how galaxies evolve into the systems we see today.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Merrifield, Michael
Aragon-Salamanca, Alfonso
Keywords: Photometric bulge-disk decompositions; Stellar populations; Kinematics; Kinematic decompositions; Galaxy evolution
Subjects: Q Science > QB Astronomy
Faculties/Schools: UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID: 57222
Depositing User: Tabor, Martha
Date Deposited: 31 Mar 2020 10:56
Last Modified: 06 May 2020 09:17
URI: http://eprints.nottingham.ac.uk/id/eprint/57222

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