Download or read book Galaxy Merger Identification Methods and Investigations of the Role of Mergers in Galaxy Evolution written by Kiyoaki Christopher Omori and published by Springer. This book was released on 2024-11-29 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Star Formation and Merger Evolution of Interacting Galaxies written by Carrie Ruth Bridge and published by . This book was released on 2007 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hierarchical models and observations show that galaxy mergers and interactions play a key role in galaxy assembly and star formation, but to what extent is still unclear. This thesis attempts to quantify their contribution to galaxy evolution by probing the number of interactions and mergers, along with their star forming properties as a function of redshift. The presence of long tidal tails and bridges are robust signatures of recent merger activity. This completely dynamical phenomenon was used to develop a new classification scheme to identify interacting galaxies and probe the interaction fraction and merger rate. We applied this new technique to large area, multi-band imaging obtained via the Canada France Hawaii Telescope Legacy Survey (CFHTLS-Deep), yielding the first statistically secure, lower limit of the galaxy interaction fraction between 0.1 z 1.0. Optically, the fraction of galaxies undergoing an interaction evolves moderately with redshift as (1 + z)2.24+/-0.24The Spitzer 24mum coverage of both the Extragalactic First Look Survey (XFLS) and CFHTLSDeep Survey were used to carry out one of the first and largest merger studies of IR bright galaxies. Within the ACS component of the XFLS, interactions were identified over the full merger sequence using traditional techniques, finding a merger rate increase for 24microm galaxies of (1 + z) & sim;2. This result implies that merging is an increasingly important process in the evolution of luminous IR galaxies (LIRGs), contributing 40--60% of the IR luminosity density and at least 30--40% of the star formation rate density at z & sim; 1. Galaxy interactions at all stages are found to have elevated star formation rates greater than a factor of two-four (on average) and a higher incidence of AGN activity compared to non-interacting field galaxies. This result supports a causal connection between galaxy merging, induced star formation, and AGN activity. Ultimately, major mergers provide a moderate contribution to the evolution of the cosmic star formation rate density and IR luminosity density to z & sim; 1, with an increasing trend suggesting that merging plays a larger role at higher redshifts (z 1). It is also clear that merging plays a significant role in triggering the processes that power the IR emission of LIRG galaxies at z 0.5.
Download or read book Identifying Galaxy Mergers with Quantitative Morphological Parameters in Simulated James Webb Space Telescope Images written by Caitlin Rose and published by . This book was released on 2019 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mergers play an important role in the formation and evolution of galaxies by triggering starbursts, AGN activity, and morphological transitions from disks to ellipticals. They can also cause morphological disturbances in a galaxy’s appearance, such as double nuclei, tidal tails, and other asymmetries, which can appear before or after a merger has occurred. Therefore, one way to identify low redshift galaxy mergers is to search for these morphological signatures via quantitative morphological parameters, which quantify a galaxy’s light distribution (such as Sérsic profiles, or the CAS system, G and M20, and the MID statistics). However, for high redshift galaxies, these parameters can be affected by biases due to poor resolution and noisy images. The upcoming James Webb Space Telescope (JWST) will be able to probe higher redshifts than ever before for morphological studies with high spatial resolution. The Cosmic Evolution Early Release Science (CEERS) Survey will use JWST’s near-infrared camera to reveal detailed galaxy morphologies over a wide range of redshifts. In preparation for CEERS images, this works seeks to understand how well those common morphological statistics will be able to identify JWST mergers. Multiwavelength Sérsic profile fitting program Galapagos-2 and the nonparametric morphology program statmorph were run on simulated JWST images from Illustris, which were modified to match the specifications of CEERS imaging. Using Illustris merger history catalogs, plots of different combinations of the rest-frame morphologies of the simulated galaxies, binned by redshift, were made as functions of merger timescales. These plots do not separate mergers from non-mergers as cleanly as previous studies have found, regardless of redshift or merger timescale. This indicates that a more sophisticated analysis method, such as principal component analysis, will be required in order to effectively isolate JWST mergers from other galaxies."--Abstract.
Download or read book Constraining the Major Merging History of Massive Galaxies written by Kameswara Bharadwaj Mantha and published by . This book was released on 2021 with total page 241 pages. Available in PDF, EPUB and Kindle. Book excerpt: Major galaxy merging is a fundamental aspect of the hierarchical structure-growth scenario of the universe, and it is theoretical expected to contribute to several key aspects of galaxy evolution. As such, empirically identifying major mergers is a key methodological step towards assessing the ``merging -- galaxy evolution'' connection, and close-pair and morphology-based methods are established empirical merger identification techniques. Yet, the merger rate measurements from these methods vary up to a factor of five owing to their unique but analogous systematic biases, especially during the key epoch of galaxy growth (7-11 Gyr ago), highlighting that the merger contribution to galaxy growth remains poorly constrained. As a step towards addressing key open questions pertaining to empirical merger identification methodologies, we carryout comprehensive analysis of close pairs and merging induced tidal features (and in general galactic substructures) using forefront observational data from the Hubble Space Telescope (HST) and realistic mock observations from leading theoretical simulations. We analyze the incidence of major, similar-mass (mass ratio4) close pairs among a large sample of ~9800 massive galaxies (log Mstellar/Msun 10.3) from the HST-CANDELS survey and quantify the major merger rate evolution over 11 Gyr in cosmic history (published in Mantha et al., 2018). Using the mock light cone data from the leading SantaCruz Semi-Analytical Model (SAM), we systematically analyze the impact of different observational effects on the measurement of close-pair frequency and provide detailed statistical corrections to account for them. We also developed a new public software tool to extract and quantify different kinds of faint morphological substructures hosted by massive galaxies in the HST imaging and demonstrated its applicability in extracting tidal features using mock observations of a galaxy merger from a cosmological simulation (published in Mantha et al., 2019). Finally, using supervised and unsupervised deep-learning models, we also investigate the automated characterization of different morphological substructures hosted within the parametric light-profile subtracted residual images of 10,000 massive galaxies from the HST CANDELS survey.
Download or read book Galaxy Formation and Mergers with Stars and Massive Black Holes written by Chi-hun Kim and published by Stanford University. This book was released on 2011 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: While mounting observational evidence suggests the coevolution of galaxies and their embedded massive black holes (MBHs), a comprehensive astrophysical understanding which incorporates both galaxies and MBHs has been missing. To tackle the nonlinear processes of galaxy formation, we develop a state-of-the-art numerical framework which self-consistently models the interplay between galactic components: dark matter, gas, stars, and MBHs. Utilizing this physically motivated tool, we present an investigation of a massive star-forming galaxy hosting a slowly growing MBH in a cosmological LCDM simulation. The MBH feedback heats the surrounding gas and locally suppresses star formation in the galactic inner core. In simulations of merging galaxies, the high-resolution adaptive mesh allows us to observe widespread starbursts via shock-induced star formation, and the interplay between the galaxies and their embedding medium. Fast growing MBHs in merging galaxies drive more frequent and powerful jets creating sizable bubbles at the galactic centers. We conclude that the interaction between the interstellar gas, stars and MBHs is critical in understanding the star formation history, black hole accretion history, and cosmological evolution of galaxies. Expanding upon our extensive experience in galactic simulations, we are well poised to apply this tool to other challenging, yet highly rewarding tasks in contemporary astrophysics, such as high-redshift quasar formation.
Download or read book Merging Processes in Galaxy Clusters written by L. Feretti and published by Springer Science & Business Media. This book was released on 2006-04-18 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mergers are the mechanisms by which galaxy clusters are assembled through the hierarchical growth of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. Many of the observed properties of clusters depend on the physics of the merging process. These include substructure, shock, intra cluster plasma temperature and entropy structure, mixing of heavy elements within the intra cluster medium, acceleration of high-energy particles, formation of radio halos and the effects on the galaxy radio emission. This book reviews our current understanding of cluster merging from an observational and theoretical perspective, and is appropriate for both graduate students and researchers in the field.
Download or read book Studying the AGN merger Connection Through Visual Classification of CANDELS Galaxies written by Christina T. Magagnoli and published by . This book was released on 2020 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mergers play a vital role in galaxy evolution, having the potential to trigger Active Galactic Nucleus (AGN) activity, star formation, or changes in morphology. In this work, we investigate whether galaxy mergers have an effect on AGN activity in the galaxies involved. We used a visual classification scheme to classify the morphologies of nearly 50,000 galaxies and identify galaxy mergers in the CANDELS fields, a Multi-Cycle Treasury Program using the Hubble Space Telescope. We use IR and X-ray selection criteria to identify IR and X-ray AGN, and matched controls to both our AGN subsample and merger subsample. We investigated the fraction of mergers that host AGN, as well as the fraction of AGN that are found in merging systems, to study the AGN-merger connection from multiple angles. We also investigated the properties of mergers, such as the mass ratios of early-stage mergers, and their star forming properties. We find that galaxies involved in a merger or interaction are more likely than non-merging galaxies to host AGN. The fraction of merging systems that host AGN is 0.034±0.002,compared to an AGN fraction of 0.023±0.001 in non-merging systems. We also find that IR AGN are more likely to be found in merging systems, with a merger fraction of 0.353+0.021−0.019, compared to a merger fraction of 0.225+0.007−0.006 in control galaxies without AGN activity. This is likely because these are more dusty and obscured, and are expected to be observed earlier in the merger process, when merger signatures are more visible. The AGN detected in either the X-ray or both the IR and X-ray are even less likely to be found in merging systems, as the merger signatures are expected to fade later in the merging process. These results show that mergers play an important role in driving AGN activity."--Abstract.
Download or read book Stellar Populations in Nearby Merging Galaxies written by Alexander J. Mulia and published by . This book was released on 2015 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxy mergers were common in the early universe. To better understand this critical step in galaxy evolution, we perform detailed studies of three nearby merging systems. Using images from the Hubble Space Telescope, we identify hundreds of star clusters in these systems, most of which formed as a result of a merger. By studying these clusters, we are able to constrain the properties of their host galaxies. These properties include: the timescale of the interaction, morphology of the merger's progenitor galaxies, and the conditions in which stars and clusters formed. We find clusters in all tidal tails of our galaxy sample, even tails that were previously reported to be clusterless. Ages of clusters are similar to ages of their host tidal tails as predicted from simulations. We also find a color gradient across some tails, indicative of a gradient in ages that suggest star formation takes place primarily in the center of the tails, where gas is likely densest. In addition, cluster ages allow us to probe the star formation histories in these systems by predicting past SFRs in various regions of the galaxies using a new method involving the cluster mass function. The mergers also present an interesting environment to study star clusters themselves. We find that the formation and evolution of star clusters in mergers fits the "quasi-universal'' picture of clusters seen in many other galaxies.
Download or read book Probing Galaxy Evolution Through Numerical Simulations written by Maan H. Hani and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Large observational surveys have compiled substantial galaxy samples with an array of different properties across cosmic time. While we have a broad understanding of how galaxies grow and build their observable properties, the details of galaxy growth and evolution pose a fundamental challenge to galaxy evolution theories. Nonetheless, galaxy evolution is ultimately regulated by the properties of the gas reservoir. In this thesis I use numerical simulations to answer key questions related to the galactic gas reservoir, and galaxy mergers: a major transformational process. In Chapter 2 I present an analysis of 28 simulated L* galaxies to understand the physical processes that shape the massive gas reservoir surrounding galaxies (i.e. the circum-galactic medium; CGM). I show that (1) the gas and metal content of the CGM is driven by galaxy growth and the strength/presence of feedback processes, and (2) the ionisation and internal structures of the CGM are shaped by galactic outflows, and active galactic nucleus luminosity. Albeit dependent on internal galactic properties and the physical processes that shape them, the CGM remains greatly diverse, thus posing a challenge for observational surveys. As a follow-up to my study of normal L* galaxy gas halos, in Chapter 3 I present a theoretical study of the effect of galaxy mergers on the CGM. I demonstrate that galaxy mergers can leave a strong imprint on the CGM's gas and metal content, metallicity, and size. The merger can increase (1) the CGM's metallicity by 0.2-0.3 dex within 0.5 Gyr post-merge, and (2) the metal covering fractions by factors of 2-3. In spite of the increase in the CGM's metal content, the hard ionising field during the merger can drive a decline in the covering fractions of commonly observed ions. In Chapter 4 I shift focus to star formation, particularly the effects of galaxy mergers on star formation. While the effects of galaxy mergers have been proven observationally, theoretical predictions are limited to small binary merger suites and cosmological zoom-in studies. I present a statistical study of 27,691 post-merger galaxies from IllustrisTNG to quantify the effect of galaxy mergers on galactic star formation. I report a dependence in the merger-induced star formation rate (SFR) on mass ratio, stellar mass, gas fraction, and galaxy SFR. I also track the evolution of the effects of galaxy mergers demonstrating their decay over ~500 Myr. In Chapter 6, I leverage galactic scaling relations to extend my work on the effects of galaxy mergers to resolved scales. However, before using the simulated resolved scaling relations, I first examine their existence and robustness. In Chapter 5, I demonstrate the emergence of the kpc-scale star forming main sequence (rSFMS) in the FIRE-2 simulations. Nonetheless, the slope of the rSFMS is dependent on the (1) star formation tracer's timescale, and (2) observed resolution, which I propose is caused by the clumpiness of star formation. I develop a toy model that quantitatively captures the effects of clumpy star formation. I then illustrate how the model can be used to characterise the mass of star-forming clumps. Having demonstrated the existence and robustness of known scaling relations in numerical simulations, I explore the effects of galaxy mergers on resolved scales in Chapter 6. I generate synthetic observations for 1,927 post-mergers in IllustrisTNG and examine the radially-dependent merger-driven SFR enhancement, and metallicity suppression in post-mergers. Galaxy mergers preferentially boost star formation in the centres and suppress metallicities globally. The effects of the merger depends on galaxy properties such as stellar mass, SFR, mass ratio, and gas fraction.
Download or read book Merging Galaxies and Dark Matter Halos written by Andrew Rodger Wetzel and published by . This book was released on 2010 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mergers between distinct objects are a natural part of hierarchical structure formation. Mergers are also one of the most critical elements in the evolution of both galaxies and halos. I use high-resolution, cosmological volume simulations to explore galaxy and halo evolution and merging activity in a cosmological context, including environmental dependence, merger rates and dynamics, and how these processes in halos connect with those of galaxies. I first explore halo merging and evolution, focusing on its interplay with large-scale environment. While halo spatial clustering has been thought to depend only on mass, I ex- amine how spatial clustering depends on secondary parameters such as halo formation time, concentration, and recent merger history, a phenomenon known as "assembly bias". Next, I examine the extent to which close spatial pairs of objects can be used to predict mergers, finding limited utility to the pair-merger method arising from a competition between merger efficiency and completeness. I also explore the dependence of merging on environmental density, discovering that merging is less efficient in overdense environments. I then investigate how a massive galaxy/halo population at high redshift connects to a massive population of the same number density today, finding that scatter in mass growth and mergers between massive objects preclude a direct population mapping either forward or backward in time. In the latter part of this work, I explore the dynamics and mergers of galaxies in groups and clusters. I first examine the orbital distributions of satellite halos/galaxies at the time of infall onto a more massive host halo, finding that satellite orbits become more radial and penetrate deeper at higher host halo mass and higher redshift. I then track the evolution of galaxies in groups directly, examining the merger rates of galaxies over time and finding that galaxy mergers do not simply trace halo mergers. I also examine the small-scale environments of galaxy mergers, discovering that recently merged galaxies exhibit enhanced small-scale spatial clustering for a short time after a merger. Finally, by using abundance matching to assign stellar mass to subhalos, I explore the importance of merging vs. disruption processes for satellite galaxy evolution. I rigorously test the connection of galaxies to subhalos by comparing simulations against observed galaxy spatial clustering, satellite fractions, and cluster satellite luminosity functions, finding agreement in all cases.
Download or read book A Morphological Analysis of High Redshift Galaxy Mergers Using Machine Learning written by Caitlin Rose and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Galaxy mergers play an important role in the formation and evolution of galaxies. However, identifying mergers can be difficult, especially at high redshift, due to effects such as: cosmological surface brightness dimming, poor resolution of images, the shifting of optical light to the infrared, and the inherently more irregular morphologies of younger galaxies. The advent of JWST and new deep, high-resolution near-infrared NIRCam images from the Cosmic Evolution Early Release Science Survey (CEERS) will help mitigate some of these problems to better detect high redshift merger features. Simultaneously, sophisticated machine learning analysis techniques have the potential to more accurately identify mergers by exploiting complex multidimensional data (whether directly from multi-band images or from pre-computed quantitative measurements). In this dissertation, we investigate the use of machine learning techniques (random forests and convolutional neural networks) to identify high redshift galaxy mergers. We create simulated JWST CEERS NIRCam images in six filters and HST CANDELS/Wide WFC3/ACS images in four filters from IllustrisTNG and the Santa Cruz SAM. We use these simulated data to train the algorithms. We calculate morphology parameters for galaxies in those images using Galapagos-2 and statmorph, which are used as inputs for the random forests. We also cut stamps of uniform size for those galaxies, which are used as inputs to the convolutional neural networks. The input labels for the simulated galaxies were derived from Illustris merger history catalogs, such that “mergers” are galaxies that have experienced or will experience a merger within ±250 Myr and “non-mergers” are those that will not experience a merger within that time frame. We train random forests on simulated CEERS galaxies from 0.5
Download or read book Fundamentals of Galaxy Dynamics Formation and Evolution written by Ignacio Ferreras and published by UCL Press. This book was released on 2019-04-02 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxies, along with their underlying dark matter halos, constitute the building blocks of structure in the Universe. Of all fundamental forces, gravity is the dominant one that drives the evolution of structures from small density seeds at early times to the galaxies we see today. The interactions among myriads of stars, or dark matter particles, in a gravitating structure produce a system with fascinating connotations to thermodynamics, with some analogies and some fundamental differences. Ignacio Ferreras presents a concise introduction to extragalactic astrophysics, with emphasis on stellar dynamics, and the growth of density fluctuations in an expanding Universe. Additional chapters are devoted to smaller systems (stellar clusters) and larger ones (galaxy clusters). Fundamentals of Galaxy Dynamics, Formation and Evolution is written for advanced undergraduates and beginning postgraduate students, providing a useful tool to get up to speed in a starting research career. Some of the derivations for the most important results are presented in detail to enable students appreciate the beauty of maths as a tool to understand the workings of galaxies. Each chapter includes a set of problems to help the student advance with the material.
Download or read book Galaxy Formation and Evolution written by Houjun Mo and published by Cambridge University Press. This book was released on 2010-05-20 with total page 841 pages. Available in PDF, EPUB and Kindle. Book excerpt: A coherent introduction for researchers in astronomy, particle physics, and cosmology on the formation and evolution of galaxies.
Download or read book Unveiling Galaxies written by Jean-René Roy and published by Cambridge University Press. This book was released on 2018 with total page 311 pages. Available in PDF, EPUB and Kindle. Book excerpt: A thought provoking study of the powerful impact of images in guiding astronomers' understanding of galaxies through time.
Download or read book Observations and Modeling of Merging Galaxy Clusters written by Nathan Ryan Golovich and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Context: Galaxy clusters grow hierarchically with continuous accretion bookended by major merging events that release immense gravitational potential energy (as much as ~1065 erg). This energy creates an environment for rich astrophysics. Precise measurements of the dark matter halo, intra-cluster medium, and galaxy population have resulted in a number of important results including dark matter constraints and explanations of the generation of cosmic rays. However, since the timescale of major mergers (~several Gyr) relegates observations of individual systems to mere snapshots, these results are difficult to understand under a consistent dynamical framework. While computationally expensive simulations are vital in this regard, the vastness of parameter space has necessitated simulations of idealized mergers that are unlikely to capture the full richness. Merger speeds, geometries, and timescales each have a profound consequential effect, but even these simple dynamical properties of the mergers are often poorly understood. A method to identify and constrain the best systems for probing the rich astrophysics of merging clusters is needed. Such a method could then be utilized to prioritize observational follow up and best inform proper exploration of dynamical phase space. Task: In order to identify and model a large number of systems, in this dissertation, we compile an ensemble of major mergers each containing radio relics. We then complete a pan-chromatic study of these 29 systems including wide field optical photometry, targeted optical spectroscopy of member galaxies, radio, and X-ray observations. We use the optical observations to model the galaxy substructure and estimate line of sight motion. In conjunction with the radio and X-ray data, these substructure models helped elucidate the most likely merger scenario for each system and further constrain the dynamical properties of each system. We demonstrate the power of this technique through detailed analyses of two individual merging clusters. Each are largely bimodal mergers occurring in the plane of the sky. We build on the dynamical analyses of Dawson (2013b) and Ng et al. (2015) in order to constrain the merger speeds, timescales, and geometry for these two systems, which are among a gold sample earmarked for further follow up. Findings: MACS J1149.5+2223 has a previously unidentified southern subcluster involved in a major merger with the well-studied northern subcluster. We confirm the system to be among the most massive clusters known, and we study the dynamics of the merger. MACS J1149.5+2223 appears to be a more evolved system than the Bullet Cluster observed near apocenter. ZwCl 0008.8+5215 is a less massive but a bimodal system with two radio relics and a cool-core "bullet'' analogous to the namesake of the Bullet Cluster. These two systems occupy different regions of merger phase space with the pericentric relative velocities of ~2800 km s−1 and ~1800 km s−1 for MACS J1149.5+2223 and ZwCl 0008.8+5215, respectively. The time since pericenter for the observed states are ~1.2 Gyr and ~0.8 Gyr, respectively. In the ensemble analysis, we confirm that radio relic selection is an efficient trigger for the identification of major mergers. In particular, 28 of the 29 systems exhibit galaxy substructure aligned with the radio relics and the disturbed intra-cluster medium. Radio relics are typically aligned within 20° of the axis connecting the two galaxy subclusters. Furthermore, when radio relics are aligned with substructure, the line of sight velocity difference between the two subclusters is small compared with the infall velocity. This strongly implies radio relic selection is an efficient selector of systems merging in the plane of the sky. While many of the systems are complex with several simultaneous merging subclusters, these systems generally only contain one radio relic. Systems with double radio relics uniformly suggest major mergers with two dominant substructures well aligned between the radio relics. Conclusions: Radio relics are efficient triggers for identifying major mergers occurring within the plane of the sky. This is ideal for observing offsets between galaxies and dark matter distributions as well as cluster shocks. Double radio relic systems, in particular, have the simplest geometries, which allow for accurate dynamical models and inferred astrophysics. Comparing and contrasting the dynamical models of MACS J1149.5+2223 and ZwCl 0008.8+5215 with similar studies in the literature (Dawsonm 2013b; Ng et al., 2015; vam Weeren et al., 2017), a wide range of dynamical phase space ~1500-3000 km s−1 at pericenter and ~500-1500 Myr after pericenter) may be sampled with radio relic mergers. With sufficient samples of bimodal systems, velocity dependence of underlying astrophysics may be uncovered. Perspectives: With the gold sample identified from our ensemble analysis, our photometric observations will be used to constrain the dark matter distribution with gravitational lensing (in studies analogous to Jee et al., 2015, 2016). Furthermore, as new radio surveys identify additional radio relic systems, more may be added to this gold sample. These systems are best served to test self-interacting dark matter hypotheses, but observational based models much be complimented with detailed simulations, and in order to move forward with this work, more realistic initial conditions based on observations must be utilized. Collaborators and I are actively studying existing cosmological N-body simulations in search of analogs to these systems, which may then be re-simulated at higher resolution with new physics included.
Download or read book Star Formation in Merging Clusters of Galaxies written by Alison Seiler Mansheim and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis straddles two areas of cosmology, each of which are active, rich and plagued by controversy in their own right: merging clusters and the environmental dependence of galaxy evolution. While the greater context of this thesis is major cluster mergers, our individual subjects are galaxies, and we apply techniques traditionally used to study the differential evolution of galaxies with environment. Our first system (Chapter 2) is a cluster merger known as Musket Ball that is in a post-merging state. Our second system (Chapter 3), referred to as Cl J0910, is comprised of two clusters that have not yet merged. The order in which they are presented is intentional because, while it would have made more sense to study the pre-merger system first, our approach in Chapter 3 was shaped by what we learned by handling the significantly more difficult post-merger system. The body of this thesis is drawn from two papers: Mansheim et al. 2016a and Mansheim et al. 2016b, one on each system. Both projects benefited from exquisite data sets assembled as part of the Merging Cluster Collaboration (MC2), and Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey, allowing us to scrutinize the evolutionary states of galaxy populations in multiple lights. Multi-band optical and near-infrared imaging was available for both systems, allowing us to calculate photometric redshifts for completeness corrections, colors (red vs. blue) and stellar masses to view the ensemble properties of the populations in and around each merger. High-resolution spectroscopy was also available for both systems, allowing us to confirm cluster members by measuring spectroscopic redshifts, which are unparalleled in accuracy, and gauge star formation rates and histories by measuring the strengths of certain spectral features. We had the luxury of HST imaging for Musket Ball, allowing us to use galaxy morphology (late-type vs. early-type) as an additional diagnostic. For Cl J0910, 24 [mu]m imaging allowed us to defeat a most pernicious source of uncertainty (dusty starburst vs. quiescent). Details on the acquisition and reduction of multi-wavelength data for each system are found within each respective chapter. It is important to note that the research presented in Chapter 3 is based on a letter which had significant space restrictions, so much of the observational details are outsourced to papers written by ORELSE collaboration members. Below is a free-standing summary of each project, drawn from the abstracts of each paper. The Chapter 1 contains an introduction to the topic and motivation to fill a vacuum in knowledge using our hypothesis. Chapter 4, following the meat of the thesis in Chapters 2 and 3, gives closure and looks to the future. In Chapter 2, we investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z=0.53 that has progressed 1.1[superscript +1.3][subscript-0.4] Gyr since first pass-through. We attempt to reveal the effects a collision may have had on the evolution of the cluster galaxies by tracing their star formation history. We probe current and recent activity to identify a possible star formation event at the time of the merger using EW(H[delta]), EW[(OII)], and D[subscript n](4000) measured from the composite spectra of 64 cluster and 153 coeval field galaxies. We supplement Keck DEIMOS spectra with DLS and HST imaging to determine the color, stellar mass, and morphology of each galaxy and conduct a comprehensive study of the populations in this complex structure. Spectral results indicate the average cluster and cluster red sequence galaxies experienced no enhanced star formation relative to the surrounding field during the merger, ruling out a predominantly merger-quenched population. We find that the average blue galaxy in the North cluster is currently active and in the South cluster is currently post-starburst having undergone a recent star formation event. While the North activity could be latent or long-term merger effects, a young blue stellar population and irregular geometry suggest the cluster was still forming prior the collision. While the South activity coincides with the time of the merger, the blue early-type population could be a result of secular cluster processes. The evidence suggests that the dearth or surfeit of activity is indiscernible from normal cluster galaxy evolution. In Chapter 3, we examine the effects of an impending cluster merger on galaxies in the large scale structure (LSS) RX Cl J0910 at z =1.105. Using multi-wavelength data, including 102 spectral members drawn from the ORELSE survey and precise photometric redshifts, we calculate extinction-corrected star formation rates and map the specific star formation rate density of the LSS galaxies. These analyses along with an investigation of the color-magnitude properties of LSS galaxies indicate lower levels of star formation activity in the region between the merging clusters relative to the outskirts of the system. We suggest gravitational tidal forces due to the potential of merging halos may be the physical mechanisms responsible for the observed suppression of star formation in galaxies caught between the merging clusters.
Download or read book Astrophotonics written by Stefano Minardi and published by VCH. This book was released on 2012-04-04 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by well-known scientists in the field with vast experience in teaching astrophotonics, this is the first book to bridge astronomy and photonics for the benefit of developing new astronomical instrumentation. The textbook is clearly structured and covers four main methods relevant to observational astronomy: adaptive optics, photometry, interferometry and spectroscopy. It follows a progressive didactical path in photonics, starting from fundamentals of wave- and micro-optics and developing step-by-step the formalisms required for the treatment of optical multilayers, fiber optics and diffraction/holographic gratings. This approach allows students with a physics/engineering background to learn about the problematic of observational astronomy, while, conversely, students of astronomy are exposed to topics in modern photonics. Each chapter is divided into three main sections devoted to the discussion of astronomical concepts required to size an instrument designed for the particular method, the photonic concepts that most suit that instrument, and an analysis of existing, related photonic instruments. A set of exercises and a bibliography complete each chapter. Appendices include a short review of fundamentals of wave optics and photon detectors, plus an overview of project design and management using a real-life example of an astronomical instrumentation project. With its review of the latest instrumentation and techniques, this is invaluable for graduate and post-graduate students in astronomy, physics and optical engineering.
