Download or read book Evolution of the Galaxy Merger Rate Using Deep HST WFC Images written by Jordan Michael Burkey and published by . This book was released on 1993 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 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 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 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 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 Science with the Hubble Space Telescope written by Piero Benvenuti and published by . This book was released on 1992 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Clues to Galaxy Evolution from the Major Merger Rate at High Redshift written by Russell E. Ryan and published by . This book was released on 2008 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Evolution of Galaxies in the Hubble Deep Fields written by Stephen Donald Jermy Gwyn and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is a study of several aspects of the evolution of galaxies using photometric redshifts in the Hubble Deep Fields (HDF's). The photometric redshift method is used in the HDF's down to a magnitude limit of I = 28. The large sample and the unprecedented depth of the Hubble Deep Fields allow one to trace the evolution of several properties of galaxies from z = 5 to the present in a statistical manner. This thesis studies four such aspects: (1) The clustering of galaxies is examined. When the redshift distributions of the HDF-North and the HDF-South are compared, one finds a significantly greater number of galaxies around z = 0.5. This suggests the presence of a structure (a very weak cluster or a very strong group) in the HDF-North. (2) The star formation rate density (SFRD) is determined by measuring the UV-luminosity density. After correcting for dust extinction, the star formation rate is found to decrease exponentially with time with an e-folding period of about 4 Gyr. (3) The difference between the rate of declines of the B band galaxy number density and the luminosity densities are used to examine the merging history of the Universe. While the total B band luminosity density of the Universe decreases only slightly with time since z = 5, the number density of galaxies drops considerably more. On average, a present day galaxy is the product of ∼3 progenitors. (4) The morphology of galaxies is quantified using a "lumpiness" parameter, L, which measures the number of local maxima in the image of a galaxy. Rest-frame B band images are made of both HDF's by k-correcting each pixel of each galaxy in the frames using the photometric redshifts of the parent galaxies. It is found that L increases with increasing absolute brightness and increasing redshift, albeit only slightly.

Download or read book Close Pairs of Galaxies and Merger Rate Evolution written by David Robert Patton and published by . This book was released on 1999 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: New techniques are developed for relating the statistics of close galaxy pairs to the galaxy merger and accretion rates. Unlike the traditional pair fraction approach, these methods are shown to be robust to a number of selection effects related to the depth and completeness of the sample. These techniques are applied to the large, well-defined SSRS2 (z ∼ 0) and CNOC2 (0.1 ≤ ± ≤ 0.55) redshift surveys, yielding the first secure measurements of close pair statistics at low and moderate redshift. These results imply that the galaxy merger and accretion rates increase with redshift, approximately as (1 + z)2±1.5, for galaxies brighter than MB = -18. The CNOC2 survey is used to carry out a detailed comparison between close companions and field galaxies. Paired galaxies are found to be of slightly earlier spectral type, with a larger spread in properties. In particular, the spectral indices of close companions imply a more complex star formation history, as would be expected if galaxy interactions and mergers are prevalent.

Download or read book Evolution of the Universe of Galaxies written by Richard G. Kron and published by . This book was released on 1990 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Morphological and Kinematic Indicators of Structural Transformation in Galaxies written by Connor Bottrell and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The observed properties of galaxies are intricately connected to their respective evolutionary histories. Establishing these connections - tying the morphologies, dynamics, and other properties of galaxies to the dominant events and processes from which they originate - is the central challenge in creating a self-consistent framework for how galaxies form and evolve. Overcoming this challenge requires that two criteria be satisfied: (1) accurate characterization of the physical states of galaxies; and (2) creation of models that connect the observed features of galaxies to their evolutionary histories. This thesis chiefly concerns the identification and characterization of morphological and kinematic indicators for structural transformation in galaxies and their connections to galaxy mergers - including merger status (merger or non-merger) and merger stage. Accurate measurement of the morphological structures of galaxies is a cornerstone for making connections to their evolutionary pathways. However, without significant overlap between the observational footprints of deep and shallow galaxy imaging surveys, the extent to which structural measurements for large galaxy samples are robust to image quality (e.g. depth, spatial resolution) cannot be established. Deep images from the Sloan Digital Sky Survey (SDSS) Stripe 82 co-adds provide a unique solution to this problem - offering 1.6 − 1.8 magnitudes improvement in depth with respect to SDSS Legacy images. Having similar spatial resolution to Legacy, the co-adds make it possible to examine the sensitivity of parametric morphologies to depth alone. Using the GIM2D surface-brightness decomposition software, I provide public morphology catalogs for 16,908 galaxies in the Stripe 82 ugriz co-adds. The methods and selection are completely consistent with those of previous analyses in the shallow images. Measurements in the deep and shallow images are rigorously compared. No systematics in total magnitudes and sizes are found except for faint galaxies in the u-band and the brightest galaxies in each band. However, characterization of bulge-to-total fractions is significantly improved in the deep images. Furthermore, statistics used to determine whether single-Sérsic or two-component (e.g. bulge+disc) models are required become more bimodal in the deep images. Lastly, I show that morphological asymmetries (commonly linked to mergers) are enhanced in the deep images and that the enhancement is positively correlated with the asymmetries measured in Legacy images. Recently, machine learning has become a popular tool to quantify galaxy morphologies and identify mergers - exploiting the often disturbed and asymmetric morphological features present in merging galaxies. However, this technique relies on using an appropriate set of training data to be successful. By combining hydrodynamical simulations, synthetic observations and convolutional neural networks (CNNs), I quantitatively assess how realistic simulated galaxy images must be in order to reliably classify real mergers. Specifically, I compare the performance of CNNs trained with two types of galaxy images, stellar maps and images with full radiative transfer through internal dust, each with three levels of observational realism: (1) no observational effects (idealized images), (2) realistic sky and point spread function (semi-realistic images), (3) insertion into a real sky image (fully realistic images). I show that networks trained on either idealized or semi-real images have poor performance when applied to survey-realistic images. In contrast, networks trained on fully realistic images achieve 87.1% classification performance. Importantly, the level of realism in the training images is much more important than whether the images included radiative transfer, or simply used the stellar maps (87.1% compared to 79.6% accuracy, respectively). Therefore, one can avoid the large computational and storage cost of running radiative transfer with a relatively modest compromise in classification performance. Making photometry-based networks insensitive to colour incurs a very mild penalty to performance with survey-realistic data (86.0% with r-only compared to 87.1% with gri). This result demonstrates that while colour can be exploited by colour-sensitive networks, it is not necessary to achieve high accuracy and so can be avoided if desired. I provide the public release of the statistical observational realism suite, RealSim, as a companion to this work. Galaxy kinematics derived from observational integral field spectroscopy (IFS) may offer an orthogonal and highly-complimentary basis to photometry for accurately identifying and characterizing observed galaxy mergers. As with morphology, mergers can trigger kinematic disturbances in galaxies resulting in irregular and asymmetric kinematic structure. However, these kinematic disturbances are not always reflected in the morphologies. The current and future state-of-the-art IFS instruments which provide spatially-resolved kinematics for many thousands of galaxies make kinematic merger studies statistically viable. Anticipating the demand for realistic synthetic IFS and kinematic data for calibrating merger classification models with simulations, I present RealSim-IFS: a novel tool that emulates the instrumental response of current and future fibre-based IFS instruments. Components of RealSim-IFS are tested on real IFS data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to demonstrate the high precision that is achieved by RealSim-IFS. In a further demonstration with RealSim-IFS, I generate realistic synthetic MaNGA kinematic observations for a sample of galaxies from the IllustrisTNG cosmological hydrodynamical simulations. The survey-realistic kinematic maps for post-merger galaxies are compared with non-merging galaxies to illustrate the potential role of kinematics in enabling more accurate identification and characterization of galaxy mergers - either independently or in tandem with photometry.

Download or read book Morphological Perspectives on Galaxy Evolution Since Z 1 5 written by Michael Rutkowski and published by . This book was released on 2013 with total page 193 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxies represent a fundamental catalyst in the ``lifecycle'' of matter in the Universe, and the study of galaxy assembly and evolution provides unique insight into the physical processes governing the transformation of matter from atoms to gas to stars. With the Hubble Space Telescope, the astrophysical community is able to study the formation and evolution of galaxies, at an unrivaled spatial resolution, over more than 90% of cosmic time. Here, I present results from two complementary studies of galaxy evolution in the local and intermediate redshift Universe which used new and archival HST images. First, I use archival broad-band HST WFPC2 optical images of local (d

Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gravitational Lensing Strong Weak and Micro written by Peter Schneider and published by Springer Science & Business Media. This book was released on 2006-12-30 with total page 565 pages. Available in PDF, EPUB and Kindle. Book excerpt: The observation, in 1919 by A.S. Eddington and collaborators, of the gra- tational de?ection of light by the Sun proved one of the many predictions of Einstein’s Theory of General Relativity: The Sun was the ?rst example of a gravitational lens. In 1936, Albert Einstein published an article in which he suggested - ing stars as gravitational lenses. A year later, Fritz Zwicky pointed out that galaxies would act as lenses much more likely than stars, and also gave a list of possible applications, as a means to determine the dark matter content of galaxies and clusters of galaxies. It was only in 1979 that the ?rst example of an extragalactic gravitational lens was provided by the observation of the distant quasar QSO 0957+0561, by D. Walsh, R.F. Carswell, and R.J. Weymann. A few years later, the ?rst lens showing images in the form of arcs was detected. The theory, observations, and applications of gravitational lensing cons- tute one of the most rapidly growing branches of astrophysics. The gravi- tional de?ection of light generated by mass concentrations along a light path producesmagni?cation,multiplicity,anddistortionofimages,anddelaysp- ton propagation from one line of sight relative to another. The huge amount of scienti?c work produced over the last decade on gravitational lensing has clearly revealed its already substantial and wide impact, and its potential for future astrophysical applications.

Download or read book American Astronomer Bulletin written by William D. McPherson and published by . This book was released on 1907 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: