Unified kinematic scaling relation in the local Universe using Integral Field Spectroscopy surveys

Abstract

Mass-kinematics scaling relations have always been highly morphology-specific and the observational methods for the kinematic parameter have been specialised for the scaling relation of interest. Recently, thanks to the observational industrialisation provided by integral field spectroscopy (IFS) and the availability of large IFS galaxy surveys, the possibility of constructing a unified, morphology-independent, galaxy scaling relation has emerged.

In this thesis we study the dynamical scaling relation between galaxy mass (usually stellar mass, M*, but also baryonic and halo mass) and the generalised kinematic parameter S_K = \sqrt{K V_{rot}^2 + \sigma^2} that combines rotation velocity V_[rot} and velocity dispersion \sigma, and has previously shown potential for unifying galaxies of all morphologies in a single scaling relation.

For the construction of this scaling relation, we make use of the data from the Sydney-AAO Multi-object Integral-field-spectroscopy (SAMI) galaxy survey. We investigate the applicability of the M*-S_K scaling relation to galaxies ranging from elliptical galaxies to late-type spiral galaxies. We also investigate the effect of using either the stars or the gas component of galaxies as the kinematic tracer, optimise the combination of V_{rot} and \sigma by varying the K value in the S_K parameter, and compare the kinematic measurements from IFS survey to single-fibre spectroscopy with the intention of applying the findings to large-scale single-fibre surveys.

The linear galaxy scaling relation from SAMI shows a lower limit that may be due either to an intrinsic mass limit or to an instrumental resolution limit. To explore the origin of this apparent linearity limit, we initiated the Study of Ha from Dwarf Emissions (SHaDE), a high spectral resolution (R=13500) Ha integral field survey of 69 dwarf galaxies with stellar masses in the range 10^6<M*<10^9 M_\odot. We describe the SHaDE survey goals, design, observations and data reduction processes. We use SHaDE to extend the study of the M*-S_K scaling relation to include low-mass dwarf galaxies in an attempt to make the scaling relation truly universal. We find that the M*- V_{rot} Tully-Fisher relation is consistent with being linear down to the lowest masses we study. In contrast, the M*- \sigma Faber-Jackson relation appears to have a lower limit due to a floor in the internal velocity dispersion of the Ha-emitting gas of approximately 20\kms. Consequently, the M*- S_{0.5} scaling relation also has a lower limit at around a stellar mass of M*~10^{8.6}M_{\odot}.

One of the motivations for exploring a generalised scaling relation is to develop a powerful tool for measuring galaxy distances and peculiar velocities for cosmological studies, one that is applicable to all the galaxies in large-scale single-fibre spectroscopy surveys and in particular to the planned Taipan galaxy survey. A key step towards that goal is the development of the Taipan Live Data Reduction (TLDR) software. Although delays in commissioning the survey instrument have prevented this potential application of the generalised scaling relation being realised in time for this thesis, we use mock data to validate the functionalities and performance of TLDR and demonstrate its capabilities for measuring redshifts and both absorption-line and emission-line velocity dispersions. We outline the further work that needs to be done to tune TLDR to the as-built survey instrument and future extensions that could improve its performance and accuracy.

A generalised mass-kinematics scaling relation such as that studied in this thesis is a powerful tool. We expect that such scaling relations will soon be in common use for exploring the properties and formation histories of galaxies and for measuring galaxy distances and peculiar velocities in order to measure the mass distribution in the Universe and test the nature of gravity on large scales. Show more