What are protoclusters? – Defining high-redshift galaxy clusters and protoclusters

We explore the structures of protoclusters and their relationship with high-redshift clusters using the Millennium Simulation combined with a semi-analytic model. We find that protoclusters are very extended, with 90 per cent of their mass spread across∼35 h−1 Mpc commoving at z =2 (∼30 arcmin). The ‘main halo’, which can manifest as a high-redshift cluster or group, is only a minor feature of the protocluster, containing less than 20 per cent of all protocluster galaxies at z = 2. Furthermore, many protoclusters do not contain a main halo that is massive enough to be identified as a high-redshift cluster. Protoclusters exist in a range of evolutionary states at high redshift, independent of the mass they will evolve to at z = 0. We show that the evolutionary state of a protocluster can be approximated by the mass ratio of the first and second most massive haloes within the protocluster, and the z = 0 mass of a protocluster can be estimated to within 0.2 dex accuracy if both the mass of the main halo and the evolutionary state are known. We also investigate the biases introduced by only observing star-forming protocluster members within small fields. The star formation rate required for line-emitting galaxies to be detected is typically high, which leads to the artificial loss of low-mass galaxies from the protocluster sample. This effect is stronger for observations of the centre of the protocluster, where the quenched galaxy fraction is higher. This loss of low-mass galaxies, relative to the field, distorts the size of the galaxy overdensity, which in turn can contribute to errors in predicting the z = 0 evolved mass

How to build a cluster: the formation and evolution of galaxies in high-redshift clusters and protoclusters

High redshift galaxy protoclusters are the precursors of today’s massive clusters; the sites of formation of the most massive galaxies in the present-day Universe. By studying these immature structures we can directly analyse the formation of galaxies in the densest environments without relying on extrapolations from low redshift. Finding protoclusters is challenging due to the need for very wide and deep surveys. Radio-loud active galactic nuclei (RLAGN) have been shown to preferentially reside in overdense environments at z > 1. By using these bright radio sources as beacons, protoclusters may be efficiently selected, without the need for large, blind surveys. In this thesis I study the properties of galaxies in high redshift (z > 1.3) clusters and protoclusters selected around RLAGN. Using a sample of 37 clusters and protoclusters from the Clusters Around Radio-Loud AGN (CARLA) survey, I show that the protocluster galaxies have an approximately unevolving, red observed-frame i'-[3.6] colour across 1.3 2 must have assembled within 0.5 Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in z > 2 protoclusters could have formed via dry mergers. Some of the CARLA structures exhibit signs of being mature, collapsed clusters. In a pilot project, I report on the discovery of a z = 1.58 cluster with a strong red sequence around the RLAGN 7C 1753+6311. I demonstrate that the cluster has an enhanced quiescent galaxy fraction that is three times that of the control field. I also show that this enhancement is mass dependent: 91 +/- 9% of the M* > 10^10.5 Msun cluster galaxies are quiescent, compared to only 36 +/- 2% of field galaxies, whereas the fraction of quiescent galaxies with lower masses is the same in the cluster and field environments. This is in contrast to low redshift studies which have shown that mass and environmental effects on quenching star formation are separable. In the literature there is some debate as to whether RLAGN preferentially reside in clusters of a certain stage of collapse. The presence of a dense core and a well-formed, quiescent red sequence suggest that 7C1753+6311 resides within a mature cluster. This means that distant RLAGN do not solely reside in young, uncollapsed protoclusters, rather they can be found in clusters in a wide range of evolutionary states. Finally I present results from surveys of Halpha emitters in the fields around three high redshift RLAGN. I find that there is more dust-obscured star formation in protocluster galaxies than in similarly-selected control field galaxies at z ~ 2.5 and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average I do not find a difference between the star formation rate (SFR)-mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ~ 2.5 is governed predominantly by galaxy mass and not the host environment. The stellar mass distribution of the protocluster galaxies is also skewed towards higher masses and there is a significant lack of low mass (M < 10^10 Msun) galaxies within the protocluster core. These results have implications for future protocluster surveys. The lack of low mass galaxies affects the level of overdensity which is detected. If only high mass galaxies are considered, the density of the protocluster field may be over-estimated. This means that it is important when quantifying protoclusters to compare their mass functions, rather than simply number overdensities. I also find that some radio galaxies do not reside in the centre, or densest region of the surrounding structure, meaning the overdensity measured in an aperture centred on the RLAGN will be underestimated. This means that future studies of (proto)clusters around RLAGN should use larger fields of view in order to establish the existence of a (proto)cluster

How to build a cluster: the formation and evolution of galaxies in high-redshift clusters and protoclusters

High redshift galaxy protoclusters are the precursors of today’s massive clusters; the sites of formation of the most massive galaxies in the present-day Universe. By studying these immature structures we can directly analyse the formation of galaxies in the densest environments without relying on extrapolations from low redshift. Finding protoclusters is challenging due to the need for very wide and deep surveys. Radio-loud active galactic nuclei (RLAGN) have been shown to preferentially reside in overdense environments at z > 1. By using these bright radio sources as beacons, protoclusters may be efficiently selected, without the need for large, blind surveys. In this thesis I study the properties of galaxies in high redshift (z > 1.3) clusters and protoclusters selected around RLAGN. Using a sample of 37 clusters and protoclusters from the Clusters Around Radio-Loud AGN (CARLA) survey, I show that the protocluster galaxies have an approximately unevolving, red observed-frame i'-[3.6] colour across 1.3 2 must have assembled within 0.5 Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in z > 2 protoclusters could have formed via dry mergers. Some of the CARLA structures exhibit signs of being mature, collapsed clusters. In a pilot project, I report on the discovery of a z = 1.58 cluster with a strong red sequence around the RLAGN 7C 1753+6311. I demonstrate that the cluster has an enhanced quiescent galaxy fraction that is three times that of the control field. I also show that this enhancement is mass dependent: 91 +/- 9% of the M* > 10^10.5 Msun cluster galaxies are quiescent, compared to only 36 +/- 2% of field galaxies, whereas the fraction of quiescent galaxies with lower masses is the same in the cluster and field environments. This is in contrast to low redshift studies which have shown that mass and environmental effects on quenching star formation are separable. In the literature there is some debate as to whether RLAGN preferentially reside in clusters of a certain stage of collapse. The presence of a dense core and a well-formed, quiescent red sequence suggest that 7C1753+6311 resides within a mature cluster. This means that distant RLAGN do not solely reside in young, uncollapsed protoclusters, rather they can be found in clusters in a wide range of evolutionary states. Finally I present results from surveys of Halpha emitters in the fields around three high redshift RLAGN. I find that there is more dust-obscured star formation in protocluster galaxies than in similarly-selected control field galaxies at z ~ 2.5 and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average I do not find a difference between the star formation rate (SFR)-mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ~ 2.5 is governed predominantly by galaxy mass and not the host environment. The stellar mass distribution of the protocluster galaxies is also skewed towards higher masses and there is a significant lack of low mass (M < 10^10 Msun) galaxies within the protocluster core. These results have implications for future protocluster surveys. The lack of low mass galaxies affects the level of overdensity which is detected. If only high mass galaxies are considered, the density of the protocluster field may be over-estimated. This means that it is important when quantifying protoclusters to compare their mass functions, rather than simply number overdensities. I also find that some radio galaxies do not reside in the centre, or densest region of the surrounding structure, meaning the overdensity measured in an aperture centred on the RLAGN will be underestimated. This means that future studies of (proto)clusters around RLAGN should use larger fields of view in order to establish the existence of a (proto)cluster

Frontal Plane Knee Alignment: A Call for Standardized Measurement

Evaluations of knee alignment are useful in the diagnosis of arthritic conditions affecting the knee joint, serving also as a guide for conservative management and surgical planning. They are also fundamental to various aspects of musculo-skeletal research. Recently, there has been great interest in frontal plane alignment measures related to the pathogenesis of knee osteoarthritis (OA). Several approaches have been proposed over the years to describe and measure alignment, but the differences between them have made it difficult to compare or correlate the results of independent studies. Toward a standard approach to the measurement and reporting of alignment data that may be equally applicable to clinicians and researchers, we discuss a system of measurements based on geometric analysis of the femur, tibia, and knee joint surfaces. We also discuss a standardized methodology for measurement and computation of these parameters

Functional plasticity in the type IV secretion system of Helicobacter pylori.

Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection

The structure and evolution of a forming galaxy cluster at z = 1.62

We present a comprehensive picture of the Cl 0218.3−0510 protocluster at z = 1.623 across 10 comoving Mpc. Using filters that tightly bracket the Balmer and 4000 Å breaks of the protocluster galaxies we obtain precise photometric redshifts resulting in a protocluster galaxy sample that is 89 ± 5 per cent complete and has a contamination of only 12 ± 5 per cent. Both star-forming and quiescent protocluster galaxies are located, which allows us to map the structure of the forming cluster for the first time. The protocluster contains six galaxy groups, the largest of which is the nascent cluster. Only a small minority of the protocluster galaxies are in the nascent cluster (11 per cent) or in the other galaxy groups (22 per cent), as most protocluster galaxies reside between the groups. Unobscured star-forming galaxies predominantly reside between the protocluster’s groups, whereas red galaxies make up a large fraction of the groups’ galactic content, so observing the protocluster through only one of these types of galaxies results in a biased view of the protocluster’s structure. The structure of the protocluster reveals how much mass is available for the future growth of the cluster and we use the Millennium Simulation, scaled to a Planck cosmology, to predict that Cl 0218.3−0510 will evolve into a 2.7+3.9 −1.7 × 1014M cluster by the present day

Type IIn supernovae at z ~ 2 from archival data

Supernovae have been confirmed to redshift z ~ 1.7 for type Ia (thermonuclear detonation of a white dwarf) and to z ~ 0.7 for type II (collapse of the core of the star). The subclass type IIn supernovae are luminous core-collapse explosions of massive stars and, unlike other types, are very bright in the ultraviolet, which should enable them to be found optically at redshifts z ~ 2 and higher. In addition, the interaction of the ejecta with circumstellar material creates strong, long-lived emission lines that allow spectroscopic confirmation of many events of this type at z ~ 2 for 3 - 5 years after explosion. Here we report three spectroscopically confirmed type IIn supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data using a method designed to exploit these properties at z ~ 2. Type IIn supernovae directly probe the formation of massive stars at high redshift. The number found to date is consistent with the expectations of a locally measured stellar initial mass function, but not with an evolving initial mass function proposed to explain independent observations at low and high redshift.Comment: 8 pages, 2 figures, includes supplementary informatio

The Lantern Vol. 11, No. 2, March 1943

• Hypnosis-A Study in Sleep • Ursinellins • Senorita Luna • Realization • The Days of Ofelia • Often a Bridesmaid • Unfinished Symphony • Interview with a Wood-Carver • A Wrong-Doing? • Our War Aims • Singleness • Departure • Soldier to a Worried Motherhttps://digitalcommons.ursinus.edu/lantern/1029/thumbnail.jp

The galaxy mass-size relation in CARLA clusters and proto-clusters at 1.4 < z < 2.8: larger cluster galaxy sizes

(Abridged) We study the galaxy mass-size relation in CARLA spectroscopically confirmed clusters at $1.4<z<2.8$, which span a total stellar mass $11.3<\mathrm{log}(M^c_*/M_{\odot})<12.6$ (halo mass $13.5 \lesssim \mathrm{log}(M^c_h/M_{\odot}) \lesssim 14.5$). Our main finding is that cluster passive ETG at $z \gtrsim 1.5$ with ${\rm log}(M/M_{\odot})>10.5$ are systematically $\gtrsim 0.2-0.3~{\rm dex}$ larger than field ETGs. The passive ETG average size evolution is slower at $1<z<2$ when compared to the field. This could be explained by differences in the formation and early evolution of galaxies in haloes of a different mass. Strong compaction and gas dissipation in field galaxies, followed by a sequence of mergers may have also played a significant role in the field ETG evolution, but not in the evolution of cluster galaxies. Our passive ETG mass-size relation shows a tendency to flatten at $9.6<{\rm log}(M/M_{\odot})<10.5$, where the average size is $\mathrm{log}(R_e/\mathrm{kpc}) = 0.05 \pm 0.22$. This implies that galaxies in the low end of the mass-size relation do not evolve much from $z\sim 2$ to the present, and that their sizes evolve in a similar way in clusters and in the field. BCGs lie on the same mass-size relation as satellites, suggesting that their size evolution is not different at redshift z $\gtrsim$ 2. Half of the active ETGs ($\sim 30\%$ of the ETGs) follow the field passive galaxy mass-size relation, and the other half follow the field active galaxy mass-size relation. These galaxies likely went through a recent merger or neighbor galaxy interaction, and would most probably quench at a later epoch and increase the fraction of passive ETGs in clusters. We do not observe a large population of compact galaxies, as is observed in the field at these redshifts, implying that the galaxies in our clusters are not observed in an epoch close to their compaction.Comment: 15 pages, 10 figures, accepted for publication in Astronomy & Astrophysic