Investigating the Environmental Properties of Galaxies in the SDSS-MaNGA Survey

This thesis presents a study of galaxy evolution in the local universe. I study how environments shape the structures of galaxies, and how internal and external processes affect star formation. I perform four investigations of galaxy properties: a study of the relations between size, mass and velocity dispersion of 124,524 galaxies from SDSS DR7; I estimate star formation rates using Hα and Dn4000 for galaxies in the MaNGA survey; a study of the spatial distribution of star formation in 1494 MaNGA galaxies; and finally, a study of 215 barred and 402 unbarred galaxies, to investigate how bars affect star formation. I find that environment plays a key role in the evolution of galaxies, both structurally and in terms of their star formation. Using core velocity dispersion to study the effects of minor mergers and tidal/ram pressure stripping, I find that central galaxies are up to 30% larger and more massive than satellites. I suggest that minor mergers play a crucial role in the increase in size and mass of centrals. In addition, I find that satellites have a uniform radial suppression of star formation, compared to centrals, which may be due to the strangulation of their cold gas supplies. I study the internal processes that affect star formation and find that specific star formation rate is suppressed at all radii for high mass galaxies. Massive galaxies are more likely to have suppressed star formation in their cores, which I determined is caused by a combination of morphological quenching and AGN feedback. Finally, I study the role of galaxy bars in regulating the cirumnuclear and disk star formation in late-type galaxies. I find that barred galaxies have lower star formation in their disks than unbarred galaxies, and that they are more likely to have enhanced star formation in their cores

Deep Learning Segmentation of Spiral Arms and Bars

We present the first deep learning model for segmenting galactic spiral arms and bars. In a blinded assessment by expert astronomers, our predicted spiral arm masks are preferred over both current automated methods (99% of evaluations) and our original volunteer labels (79% of evaluations). Experts rated our spiral arm masks as `mostly good' to `perfect' in 89% of evaluations. Bar lengths trivially derived from our predicted bar masks are in excellent agreement with a dedicated crowdsourcing project. The pixelwise precision of our masks, previously impossible at scale, will underpin new research into how spiral arms and bars evolve.Comment: Accepted at Machine Learning and the Physical Sciences Workshop, NeurIPS 202

The differing relationships between size, mass, metallicity and core velocity dispersion of central and satellite galaxies

We study the role of environment in the evolution of central and satellite galaxies with the Sloan Digital Sky Survey. We begin by studying the size-mass relation, replicating previous studies, which showed no difference between the sizes of centrals and satellites at fixed stellar mass, before turning our attention to the size-core velocity dispersion (σ0) and mass-σ0 relations. By comparing the median size and mass of the galaxies at fixed velocity dispersion we find that the central galaxies are consistently larger and more massive than their satellite counterparts in the quiescent population. In the star forming population we find there is no difference in size and only a small difference in mass. To analyse why these difference may be present we investigate the radial mass profiles and stellar metallicity of the galaxies. We find that in the cores of the galaxies there is no difference in mass surface density between centrals and satellites, but there is a large difference at larger radii. We also find almost no difference between the stellar metallicity of centrals and satellites when they are separated into star forming and quiescent groups. Under the assumption that σ0 is invariant to environmental processes, our results imply that central galaxies are likely being increased in mass and size by processes such as minor mergers, particularly at high σ0, while satellites are being slightly reduced in mass and size by tidal stripping and harassment, particularly at low σ0, all of which predominantly affect the outer regions of the galaxies

Deep Learning Segmentation of Spiral Arms and Bars

Machine Learning and the Physical Sciences Workshop, NeurIPS 2023. This is an open access conference contribution distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We present the first deep learning model for segmenting galactic spiral arms and bars. In a blinded assessment by expert astronomers, our predicted spiral arm masks are preferred over both current automated methods (99% of evaluations) and our original volunteer labels (79% of evaluations). Experts rated our spiral arm masks as `mostly good' to `perfect' in 89% of evaluations. Bar lengths trivially derived from our predicted bar masks are in excellent agreement with a dedicated crowdsourcing project. The pixelwise precision of our masks, previously impossible at scale, will underpin new research into how spiral arms and bars evolve.Peer reviewe

Contribution of a Single Host Genetic Locus to Mouse Adenovirus Type 1 Infection and Encephalitis

Susceptibility to mouse adenovirus type 1 (MAV-1) is mouse strain dependent; susceptible mice die from hemorrhagic encephalomyelitis. The MAV-1 susceptibility quantitative trait locus Msq1 accounts for ~40% of the phenotypic (brain viral load) variance that occurs between resistant BALB/c and susceptible SJL mice after MAV-1 infection. Using an interval-specific congenic mouse strain (C.SJL-Msq1SJL), in which the SJL-derived allele Msq1SJL is present in a BALB/c background, we demonstrate that Msq1SJL controls the development of high brain viral titers in response to MAV-1 infection, yet does not account for the total extent of brain pathology or mortality in SJL mice. C.SJL-Msq1SJL mice had disruption of the blood-brain barrier and increased brain water content after MAV-1 infection, but these effects occurred later and were not as severe, respectively, as those noted in infected SJL mice. As expected, BALB/c mice showed minimal pathology in these assays. Infection of SJL- and C.SJL-Msq1SJL-derived primary mouse brain endothelial cells resulted in loss of barrier properties, whereas BALB/c-derived cells retained their barrier properties despite being equally capable of supporting MAV-1 infection. Finally, we provide evidence that organ pathology and inflammatory cell recruitment to the brain following MAV-1 infection were both influenced by Msq1. These results validate Msq1 as an important host factor in MAV-1 infection and refine the major role of the locus in development of MAV-1 encephalitis. They further suggest that additional host factors or gene interactions are involved in the mechanism of pathogenesis in MAV-1-infected SJL mice

SDSS-IV MaNGA: the spatial distribution of star formation and its dependence on mass, structure, and environment

We study the spatially resolved star formation of 1494 galaxies in the SDSS-IV MaNGA Survey. Star formation rates (SFRs) are calculated using a two-step process, using H α in star-forming regions and Dn4000 in regions identified as active galactic nucleus/low-ionization (nuclear) emission region [AGN/LI(N)ER] or lineless. The roles of secular and environmental quenching processes are investigated by studying the dependence of the radial profiles of specific star formation rate on stellar mass, galaxy structure, and environment. We report on the existence of ‘centrally suppressed’ galaxies, which have suppressed Specific Star Formation Rate (SSFR) in their cores compared to their discs. The profiles of centrally suppressed and unsuppressed galaxies are distributed in a bimodal way. Galaxies with high stellar mass and core velocity dispersion are found to be much more likely to be centrally suppressed than low-mass galaxies, and we show that this is related to morphology and the presence of AGN/LI(N)ER like emission. Centrally suppressed galaxies also display lower star formation at all radii compared to unsuppressed galaxies. The profiles of central and satellite galaxies are also compared, and we find that satellite galaxies experience lower specific star formation rates at all radii than central galaxies. This uniform suppression could be a signal of the stripping of hot halo gas in the process known as strangulation. We find that satellites are not more likely to be suppressed in their cores than centrals, indicating that the core suppression is an entirely internal process. We find no correlation between the local environment density and the profiles of star formation rate surface density

Immigration and the Common Profit: Native Cloth Workers, Flemish Exiles, and Royal Policy in Fourteenth-Century London

Drawing on a wide variety of published and unpublished sources, this article reconstructs a crucial episode in the relationship between the English Crown, its native subjects and the kingdom’s immigrant population during the later Middle Ages. Determined that their presence would boost the development of the local textile industries, Edward III encouraged high numbers of skilled Flemish cloth workers who had been exiled from their home county at the start of the 1350s to settle in the realm. Most of them took up residence in London, where they produced higher-quality cloth for the domestic market and, probably, for export. Soon, however, the immigrants’ activities conflicted with the privileges that had structured the capital’s economic life for centuries. Their work was contested by London’s native weavers who, since the middle of the twelfth century, had enjoyed the sole right to produce cloth in the city. Hoping that the control over the immigrants’ activities would help them to overcome the crisis in the market for lower-quality textiles they were struggling with, the natives petitioned the king to obtain the incorporation of the Flemish weavers into their guild for over twenty-five years. Yet, arguing that the Flemings’ contribution benefited the common profit of the whole kingdom in a way that transcended the interests of any particular group, the Crown rejected all their requests and avoided every attempt at discussion. Each time political communication broke down, the native weavers took out their frustrations by physically attacking their Flemish counterparts. These incidents became increasingly violent during the years leading up to the Peasants’ Revolt in 1381 and came to a dramatic conclusion during the rebellion itself

The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment

The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in operation since July 2014. This paper describes the second data release from this phase, and the fourteenth from SDSS overall (making this, Data Release Fourteen or DR14). This release makes public data taken by SDSS-IV in its first two years of operation (July 2014-2016). Like all previous SDSS releases, DR14 is cumulative, including the most recent reductions and calibrations of all data taken by SDSS since the first phase began operations in 2000. New in DR14 is the first public release of data from the extended Baryon Oscillation Spectroscopic Survey (eBOSS); the first data from the second phase of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2), including stellar parameter estimates from an innovative data driven machine learning algorithm known as "The Cannon"; and almost twice as many data cubes from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous release (N = 2812 in total). This paper describes the location and format of the publicly available data from SDSS-IV surveys. We provide references to the important technical papers describing how these data have been taken (both targeting and observation details) and processed for scientific use. The SDSS website (www.sdss.org) has been updated for this release, and provides links to data downloads, as well as tutorials and examples of data use. SDSS-IV is planning to continue to collect astronomical data until 2020, and will be followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14 happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov 2017 (this is the "post-print" and "post-proofs" version; minor corrections only from v1, and most of errors found in proofs corrected

The Fifteenth Data Release of the Sloan Digital Sky Surveys: First Release of MaNGA-derived Quantities, Data Visualization Tools, and Stellar Library

Twenty years have passed since first light for the Sloan Digital Sky Survey (SDSS). Here, we release data taken by the fourth phase of SDSS (SDSS-IV) across its first three years of operation (2014 July–2017 July). This is the third data release for SDSS-IV, and the 15th from SDSS (Data Release Fifteen; DR15). New data come from MaNGA—we release 4824 data cubes, as well as the first stellar spectra in the MaNGA Stellar Library (MaStar), the first set of survey-supported analysis products (e.g., stellar and gas kinematics, emission-line and other maps) from the MaNGA Data Analysis Pipeline, and a new data visualization and access tool we call "Marvin." The next data release, DR16, will include new data from both APOGEE-2 and eBOSS; those surveys release no new data here, but we document updates and corrections to their data processing pipelines. The release is cumulative; it also includes the most recent reductions and calibrations of all data taken by SDSS since first light. In this paper, we describe the location and format of the data and tools and cite technical references describing how it was obtained and processed. The SDSS website (www.sdss.org) has also been updated, providing links to data downloads, tutorials, and examples of data use. Although SDSS-IV will continue to collect astronomical data until 2020, and will be followed by SDSS-V (2020–2025), we end this paper by describing plans to ensure the sustainability of the SDSS data archive for many years beyond the collection of data