Dust in galaxies throughout cosmic time

One of the most fundamental observational probes of galaxy evolution is determining the build-up of stellar mass. However, around half of all energy ever emitted from galaxies has been absorbed and reprocessed by dust, which is an end-product of stellar evolution. In order to obtain a more complete understanding of galaxy evolution, sensitive observations in the far-infrared and submillimetre are required where the dust emission peaks. Previous surveys have found galaxies were significantly dustier at earlier times, but the cause of this evolution, and the origin of the dust, are hotly debated topics in astrophysics. With the Herschel Space Observatory, a complete census of the dusty galaxy population has now recently been obtained. In this thesis I investigate the properties of the diverse dusty galaxy population via a panchromatic approach, utilising data from the UV to the submillimetre to study galaxy evolution. Using the first unbiased survey of dust in the local Universe, I explore the properties of galaxies in the local Universe as a function of morphology and highlight particularly interesting populations which are traditionally thought to be passive. The star-formation histories, dust content and environments of dusty early-type galaxies and passive spirals are investigated. I show that dusty early-type galaxies comprise a small minority of the general early-type galaxy population (5.5%), and harbour on average 5.5x10^7 M_sun of dust, which is comparable to that of some spiral galaxies in our sample. I compare these dusty populations to control samples to investigate how these galaxies are different to the general galaxy population. High redshift submillimetre galaxies are the most actively star-forming and dusty galaxies in the Universe. Constraining the properties of these galaxies is important for understanding the evolution of massive galaxies and galaxy evolution models in general. Using panchromatic data from the UV to the submillimetre, I explore the physical properties of a sample of ~250um rest-frame selected galaxies at high redshift, and compare them to dusty galaxies at low redshift selected in a similar way, to investigate the differences in the dusty galaxy populations over cosmic time. I find high redshift dusty galaxies have significantly higher star-formation rates and dust masses than z<0.5 dusty galaxies selected to have a similar stellar mass. Galaxies which are as highly star forming and dusty as those at z~2 are rare in the local Universe. My results support the idea that the most dusty galaxies at high redshift are a heterogeneous population, with around 60% of our sample consistent with secular evolution, and the other 40% of galaxies are starbursting, possibly merger-driven systems. The origin of dust in galaxies at both low and high redshifts presents a challenge to current theories of galaxy evolution. Recent work has revealed a `dust budget crisis', whereby the mass of dust observed in galaxies at low and high redshift cannot be accounted for by stellar mass loss from low-intermediate mass stars. I tackle this challenge using chemical evolution modelling of the high redshift submillimetre galaxies, with a detailed treatment of the star-formation histories and the dust sources and sinks in these galaxies. It is clear that a significant mass of dust must be from supernovae and/or grain growth; however, the origin of dust in high redshift dusty galaxies remains uncertain. I also consider the impact of inflows and outflows of gas, and the effect of changing the IMF on the physical properties of high redshift dusty galaxies

Dust in galaxies throughout cosmic time

One of the most fundamental observational probes of galaxy evolution is determining the build-up of stellar mass. However, around half of all energy ever emitted from galaxies has been absorbed and reprocessed by dust, which is an end-product of stellar evolution. In order to obtain a more complete understanding of galaxy evolution, sensitive observations in the far-infrared and submillimetre are required where the dust emission peaks. Previous surveys have found galaxies were significantly dustier at earlier times, but the cause of this evolution, and the origin of the dust, are hotly debated topics in astrophysics. With the Herschel Space Observatory, a complete census of the dusty galaxy population has now recently been obtained. In this thesis I investigate the properties of the diverse dusty galaxy population via a panchromatic approach, utilising data from the UV to the submillimetre to study galaxy evolution. Using the first unbiased survey of dust in the local Universe, I explore the properties of galaxies in the local Universe as a function of morphology and highlight particularly interesting populations which are traditionally thought to be passive. The star-formation histories, dust content and environments of dusty early-type galaxies and passive spirals are investigated. I show that dusty early-type galaxies comprise a small minority of the general early-type galaxy population (5.5%), and harbour on average 5.5x10^7 M_sun of dust, which is comparable to that of some spiral galaxies in our sample. I compare these dusty populations to control samples to investigate how these galaxies are different to the general galaxy population. High redshift submillimetre galaxies are the most actively star-forming and dusty galaxies in the Universe. Constraining the properties of these galaxies is important for understanding the evolution of massive galaxies and galaxy evolution models in general. Using panchromatic data from the UV to the submillimetre, I explore the physical properties of a sample of ~250um rest-frame selected galaxies at high redshift, and compare them to dusty galaxies at low redshift selected in a similar way, to investigate the differences in the dusty galaxy populations over cosmic time. I find high redshift dusty galaxies have significantly higher star-formation rates and dust masses than z<0.5 dusty galaxies selected to have a similar stellar mass. Galaxies which are as highly star forming and dusty as those at z~2 are rare in the local Universe. My results support the idea that the most dusty galaxies at high redshift are a heterogeneous population, with around 60% of our sample consistent with secular evolution, and the other 40% of galaxies are starbursting, possibly merger-driven systems. The origin of dust in galaxies at both low and high redshifts presents a challenge to current theories of galaxy evolution. Recent work has revealed a `dust budget crisis', whereby the mass of dust observed in galaxies at low and high redshift cannot be accounted for by stellar mass loss from low-intermediate mass stars. I tackle this challenge using chemical evolution modelling of the high redshift submillimetre galaxies, with a detailed treatment of the star-formation histories and the dust sources and sinks in these galaxies. It is clear that a significant mass of dust must be from supernovae and/or grain growth; however, the origin of dust in high redshift dusty galaxies remains uncertain. I also consider the impact of inflows and outflows of gas, and the effect of changing the IMF on the physical properties of high redshift dusty galaxies

Dust in galaxies throughout cosmic time

One of the most fundamental observational probes of galaxy evolution is determining the build-up of stellar mass. However, around half of all energy ever emitted from galaxies has been absorbed and reprocessed by dust, which is an end-product of stellar evolution. In order to obtain a more complete understanding of galaxy evolution, sensitive observations in the far-infrared and submillimetre are required where the dust emission peaks. Previous surveys have found galaxies were significantly dustier at earlier times, but the cause of this evolution, and the origin of the dust, are hotly debated topics in astrophysics. With the Herschel Space Observatory, a complete census of the dusty galaxy population has now recently been obtained. In this thesis I investigate the properties of the diverse dusty galaxy population via a panchromatic approach, utilising data from the UV to the submillimetre to study galaxy evolution. Using the first unbiased survey of dust in the local Universe, I explore the properties of galaxies in the local Universe as a function of morphology and highlight particularly interesting populations which are traditionally thought to be passive. The star-formation histories, dust content and environments of dusty early-type galaxies and passive spirals are investigated. I show that dusty early-type galaxies comprise a small minority of the general early-type galaxy population (5.5%), and harbour on average 5.5x10^7 M_sun of dust, which is comparable to that of some spiral galaxies in our sample. I compare these dusty populations to control samples to investigate how these galaxies are different to the general galaxy population. High redshift submillimetre galaxies are the most actively star-forming and dusty galaxies in the Universe. Constraining the properties of these galaxies is important for understanding the evolution of massive galaxies and galaxy evolution models in general. Using panchromatic data from the UV to the submillimetre, I explore the physical properties of a sample of ~250um rest-frame selected galaxies at high redshift, and compare them to dusty galaxies at low redshift selected in a similar way, to investigate the differences in the dusty galaxy populations over cosmic time. I find high redshift dusty galaxies have significantly higher star-formation rates and dust masses than z<0.5 dusty galaxies selected to have a similar stellar mass. Galaxies which are as highly star forming and dusty as those at z~2 are rare in the local Universe. My results support the idea that the most dusty galaxies at high redshift are a heterogeneous population, with around 60% of our sample consistent with secular evolution, and the other 40% of galaxies are starbursting, possibly merger-driven systems. The origin of dust in galaxies at both low and high redshifts presents a challenge to current theories of galaxy evolution. Recent work has revealed a `dust budget crisis', whereby the mass of dust observed in galaxies at low and high redshift cannot be accounted for by stellar mass loss from low-intermediate mass stars. I tackle this challenge using chemical evolution modelling of the high redshift submillimetre galaxies, with a detailed treatment of the star-formation histories and the dust sources and sinks in these galaxies. It is clear that a significant mass of dust must be from supernovae and/or grain growth; however, the origin of dust in high redshift dusty galaxies remains uncertain. I also consider the impact of inflows and outflows of gas, and the effect of changing the IMF on the physical properties of high redshift dusty galaxies

The evolution of post-starburst galaxies from z=2 to 0.5

We present the evolution in the number density and stellar mass functions of photometrically selected post-starburst galaxies in the UKIDSSUltraDeep Survey,with redshifts of 0.510. We find that this transitionary species of galaxy is rare at all redshifts, contributing ∼5 per cent of the total population at z ∼ 2, to <1 per cent by z ∼ 0.5. By comparing the mass functions of quiescent galaxies to post-starburst galaxies at three cosmic epochs, we show that rapid quenching of star formation can account for 100 per cent of quiescent galaxy formation, if the post-starburst spectral features are visible for ∼250 Myr. The flattening of the low-mass end of the quiescent galaxy stellar mass function seen at z ∼ 1 can be entirely explained by the addition of rapidly quenched galaxies. Only if a significant fraction of post-starburst galaxies have features that are visible for longer than 250 Myr, or they acquire new gas and return to the star-forming sequence, can there be significant growth of the red sequence from a slower quenching route. The shape of the mass function of these transitory post-starburst galaxies resembles that of quiescent galaxies at z ∼ 2, with a preferred stellar mass of log (M/M�) ∼10.6, but evolves steadily to resemble that of star-forming galaxies at z /~ 2 they are exclusively massive galaxies that have formed the bulk of their stars during a rapid assembly period, followed by complete quenching of further star formation; (2) at z </~1 they are caused by the rapid quenching of gas-rich star-forming galaxies, independent of stellar mass, possibly due to environment and/or gas-rich major mergers

Massive post-starburst galaxies at z > 1 are compact proto-spheroids

We investigate the relationship between the quenching of star formation and the structural transformation of massive galaxies, using a large sample of photometrically-selected poststarburst galaxies in the UKIDSS UDS field. We find that post-starburst galaxies at highredshift (z > 1) show high Sérsic indices, significantly higher than those of active star-forming galaxies, but with a distribution that is indistinguishable from the old quiescent population. We conclude that the morphological transformation occurs before (or during) the quenching of star formation. Recently quenched galaxies are also the most compact; we find evidence that massive post-starburst galaxies (M_ > 1010:5 M_) at high redshift (z > 1) are on average smaller than comparable quiescent galaxies at the same epoch. Our findings are consistent with a scenario in which massive passive galaxies are formed from three distinct phases: (1) gas-rich dissipative collapse to very high densities, forming the proto-spheroid; (2) rapid quenching of star formation, to create the “red nugget” with post-starburst features; (3) a gradual growth in size as the population ages, perhaps as a result of minor mergers

Picture This! Reflecting on the Use of Posters as Expressions of PhD Research Projects

The presentation of posters at scientific conferences to visually represent research projects is a widespread international practice. The main purpose of this paper is to offer reflections relating to posters as visual representations of research studies conducted by PhD candidates. As the basis for our reflections, we consider the main purposes and intended learning outcomes linked to posters and reflect on some of the design and assessment issues associated with the multi-faceted purposes of posters in contexts such as postgraduate research conferences. Notably, the paper includes a set of illustrative vignettes written by a group of PhD students from the Faculty of Humanities at the University of Manchester who were required to design and exhibit posters at an annually held postgraduate research conference. This reflexive dialogue raises a series of issues for consideration by those who are actively involved with the design, presentation, observation and assessment of posters produced by PhD candidates.Exploring Visual Representation of Concepts in Learning and Teaching in Higher Educatio

The identification of post-starburst galaxies at z∼1 using multiwavelength photometry: a spectroscopic verification

Despite decades of study, we still do not fully understand why some massive galaxies abruptly switch off their star formation in the early Universe, and what causes their rapid transition to the red sequence. Post-starburst galaxies provide a rare opportunity to study this transition phase, but few have currently been spectroscopically identified at high redshift (z > 1). In this paper, we present the spectroscopic verification of a new photometric technique to identify post-starbursts in high-redshift surveys. The method classifies the broad-band optical–nearinfrared spectral energy distributions (SEDs) of galaxies using three spectral shape parameters (supercolours), derived from a principal component analysis of model SEDs. When applied to the multiwavelength photometric data in the UKIDSS Ultra Deep Survey, this technique identified over 900 candidate post-starbursts at redshifts 0.5 5 angstrem) and Balmer break, characteristic of post-starburst galaxies.We conclude that photometric methods can be used to select large samples of recently-quenched galaxies in the distant Universe

Identification of common genetic variation that modulates alternative splicing

Alternative splicing of genes is an efficient means of generating variation in protein function. Several disease states have been associated with rare genetic variants that affect splicing patterns. Conversely, splicing efficiency of some genes is known to vary between individuals without apparent ill effects. What is not clear is whether commonly observed phenotypic variation in splicing patterns, and hence potential variation in protein function, is to a significant extent determined by naturally occurring DNA sequence variation and in particular by single nucleotide polymorphisms (SNPs). In this study, we surveyed the splicing patterns of 250 exons in 22 individuals who had been previously genotyped by the International HapMap Project. We identified 70 simple cassette exon alternative splicing events in our experimental system; for six of these, we detected consistent differences in splicing pattern between individuals, with a highly significant association between splice phenotype and neighbouring SNPs. Remarkably, for five out of six of these events, the strongest correlation was found with the SNP closest to the intron-exon boundary, although the distance between these SNPs and the intron-exon boundary ranged from 2 bp to greater than 1,000 bp. Two of these SNPs were further investigated using a minigene splicing system, and in each case the SNPs were found to exert cis-acting effects on exon splicing efficiency in vitro. The functional consequences of these SNPs could not be predicted using bioinformatic algorithms. Our findings suggest that phenotypic variation in splicing patterns is determined by the presence of SNPs within flanking introns or exons. Effects on splicing may represent an important mechanism by which SNPs influence gene function

The redshift evolution of major merger triggering of luminous AGN:a slight enhancement at z∼2

TH was supported by STFC grant ST/M503812/1 during the course of this work. VW, JM-A, MP and KR acknowledge support from the European Research Council Starting Grant SEDmorph (P.I. V. Wild).Active galactic nuclei (AGN), particularly the most luminous AGN, are commonly assumed to be triggered through major mergers, however observational evidence for this scenario is mixed. To investigate any influence of galaxy mergers on AGN triggering and luminosities through cosmic time, we present a sample of 106 luminous X-ray selected type 1 AGN from the COSMOS survey. These AGN occupy a large redshift range (0.5 < z < 2.2) and two orders of magnitude in X-ray luminosity (∼1043 - 1045 erg s-1). AGN hosts are carefully mass and redshift matched to 486 control galaxies. A novel technique for identifying and quantifying merger features in galaxies is developed, subtracting galfit galaxy models and quantifying the residuals. Comparison to visual classification confirms this measure reliably picks out disturbance features in galaxies. No enhancement of merger features with increasing AGN luminosity is found with this metric, or by visual inspection. We analyse the redshift evolution of AGN associated with galaxy mergers and find no merger enhancement in lower redshift bins. Contrarily, in the highest redshift bin (z∼2) AGN are ∼4 times more likely to be in galaxies exhibiting evidence of morphological disturbance compared to control galaxies, at 99% confidence level (∼2.4σ) from visual inspection. Since only ∼15% of these AGN are found to be in morphologically disturbed galaxies, it is implied that major mergers at high redshift make a noticeable but subdominant contribution to AGN fuelling. At low redshifts other processes dominate and mergers become a less significant triggering mechanism.PostprintPeer reviewe