Dr Lawrence Bilton

MPhil Astronomy
MPhil

Status Complete

Part Time No

Years 2014 - 2016

Project Title Tracing Star Formation around QSOs with Polycyclic Aromatic Hydrocarbons

Project Description The feedback processes linking quasar activity to galaxy stellar mass growth are not well understood. If star formation is closely causally linked to black hole accretion, one may expect star formation confined to nuclear regions rather than extended over several kpc scales. Since Polycyclic Aromatic Hydrocarbon (PAH) emission features are widely used as tracers of stellar formation, it is, therefore, possible to use PAH emission detected around QSOs to help resolve this question. PAH data from a sample of 63 QSOs procured from the Spitzer Space Telescope’s Infrared Spectrograph (IRS) is used, employing the Spectroscopic Modelling Analysis and Reduction Tool’s (SMART) Advanced Optimal (AdOpt) extraction routines. A composite spectrum was also produced to help determine the average conditions and compositions of star forming regions. It is found, from our high redshift (𝑧>1) sample of QSOs, there is a marginally significant extended star formation on average of 34 𝑘𝑝𝑐 scales. At low redshift, the median extension after deconvolving the instrumental point spread function is 3.2 𝑘𝑝𝑐, potentially showing evolutionary variations in star formation activity. However, limitations of the spatial resolving power constrain the ability to make any absolute conclusive remarks. It is also found that the QSO/AGN composite has more neutral PAHs than the starbursting and the main sequence galaxies, consistent with the AGN having no contribution to heating the PAH emission, and also consistent with the average PAH emission found on 𝑘𝑝𝑐 scales (i.e. not confined to the nuclear regions). A tentative detection of water vapour emission from the gravitationally lensed Einstein Cross quasar, QSO J2237+0305, is also presented suggesting a strong molecular outflow possibly driven by the active nucleus.

Awarding Institution Open University

Status	Complete
Part Time	No
Years	2014 - 2016
Project Title	Tracing Star Formation around QSOs with Polycyclic Aromatic Hydrocarbons
Project Description	The feedback processes linking quasar activity to galaxy stellar mass growth are not well understood. If star formation is closely causally linked to black hole accretion, one may expect star formation confined to nuclear regions rather than extended over several kpc scales. Since Polycyclic Aromatic Hydrocarbon (PAH) emission features are widely used as tracers of stellar formation, it is, therefore, possible to use PAH emission detected around QSOs to help resolve this question. PAH data from a sample of 63 QSOs procured from the Spitzer Space Telescope’s Infrared Spectrograph (IRS) is used, employing the Spectroscopic Modelling Analysis and Reduction Tool’s (SMART) Advanced Optimal (AdOpt) extraction routines. A composite spectrum was also produced to help determine the average conditions and compositions of star forming regions. It is found, from our high redshift (𝑧>1) sample of QSOs, there is a marginally significant extended star formation on average of 34 𝑘𝑝𝑐 scales. At low redshift, the median extension after deconvolving the instrumental point spread function is 3.2 𝑘𝑝𝑐, potentially showing evolutionary variations in star formation activity. However, limitations of the spatial resolving power constrain the ability to make any absolute conclusive remarks. It is also found that the QSO/AGN composite has more neutral PAHs than the starbursting and the main sequence galaxies, consistent with the AGN having no contribution to heating the PAH emission, and also consistent with the average PAH emission found on 𝑘𝑝𝑐 scales (i.e. not confined to the nuclear regions). A tentative detection of water vapour emission from the gravitationally lensed Einstein Cross quasar, QSO J2237+0305, is also presented suggesting a strong molecular outflow possibly driven by the active nucleus.
Awarding Institution	Open University

PhD Physics
PhD / DPhil

Status Complete

Part Time No

Years 2016 - 2020

Project Title The Motions of Galaxies within Large-Scale Structures

Project Description Galaxy clusters represent one of the largest-scale structures in the Universe, with their environments of varying density being ideal for inducing an increase in activity of the cluster galaxy members and the pervading Intracluster Medium (ICM) between them. However the precise drivers, thereby the inferred consequences, of differing states of galaxy cluster activity have not been adequately disentangled. If one can procure a sufficient dichotomic sample of cluster galaxies of differing sub-populations from relaxed and unrelaxed galaxy cluster dynamical states, one could analyse how these sub-populations `move' as a function of both radius and dynamical state. Specifically, using velocity dispersion profiles (VDPs) that weight against cluster galaxies across all radii with a Gaussian window function, one can determine how cluster galaxies of properties that pertain to galaxy evolutionary indicators respond to the cluster environment as a function of the clustocentric radius. In addition, analysing the rotational profiles of these sub-populations as a function of the clustocentric radius can help identify where the bulk of the kinetic energy lies. In view of these points, we have pooled data of galaxies from the Sloan Digital Sky Survey (SDSS) two composite galaxy clusters are assembled into unrelaxed and relaxed states, which are compared with one another through splitting their cluster galaxy populations by their evolutionary proxies (i.e. morphology, colour, mass and AGN), thus analysing their resultant VDPs and rotational profiles. It is therefore found that unrelaxed galaxy clusters possess increased interaction between cluster galaxies as the radius increases, driven by blue and red elliptical galaxies, suggesting an induction of activity by pre-processed groups. AGN-hosting cluster galaxy sub-populations within these unrelaxed environs however present increased activity as (R→0), indicating these are recent infallers, potentially triggered due to interactions with the ICM. Rotational profiles of unrelaxed clusters build upon the VDPs, showing significant bulk rotation of cluster galaxies with prominent core rotation driven by redder sub-populations.

Director of Studies Kevin Pimbblet

Thesis The motions of galaxies within large-scale structures

Status	Complete
Part Time	No
Years	2016 - 2020
Project Title	The Motions of Galaxies within Large-Scale Structures
Project Description	Galaxy clusters represent one of the largest-scale structures in the Universe, with their environments of varying density being ideal for inducing an increase in activity of the cluster galaxy members and the pervading Intracluster Medium (ICM) between them. However the precise drivers, thereby the inferred consequences, of differing states of galaxy cluster activity have not been adequately disentangled. If one can procure a sufficient dichotomic sample of cluster galaxies of differing sub-populations from relaxed and unrelaxed galaxy cluster dynamical states, one could analyse how these sub-populations `move' as a function of both radius and dynamical state. Specifically, using velocity dispersion profiles (VDPs) that weight against cluster galaxies across all radii with a Gaussian window function, one can determine how cluster galaxies of properties that pertain to galaxy evolutionary indicators respond to the cluster environment as a function of the clustocentric radius. In addition, analysing the rotational profiles of these sub-populations as a function of the clustocentric radius can help identify where the bulk of the kinetic energy lies. In view of these points, we have pooled data of galaxies from the Sloan Digital Sky Survey (SDSS) two composite galaxy clusters are assembled into unrelaxed and relaxed states, which are compared with one another through splitting their cluster galaxy populations by their evolutionary proxies (i.e. morphology, colour, mass and AGN), thus analysing their resultant VDPs and rotational profiles. It is therefore found that unrelaxed galaxy clusters possess increased interaction between cluster galaxies as the radius increases, driven by blue and red elliptical galaxies, suggesting an induction of activity by pre-processed groups. AGN-hosting cluster galaxy sub-populations within these unrelaxed environs however present increased activity as (R→0), indicating these are recent infallers, potentially triggered due to interactions with the ICM. Rotational profiles of unrelaxed clusters build upon the VDPs, showing significant bulk rotation of cluster galaxies with prominent core rotation driven by redder sub-populations.
Director of Studies	Kevin Pimbblet
Thesis	The motions of galaxies within large-scale structures

BSc Natural Sciences (Physics & Astronomy)
BSc

Status Complete

Part Time Yes

Years 2011 - 2014

Awarding Institution Open University

Dr Lawrence Bilton's Qualifications (3)