# External Galaxies Commons™

## All Articles in External Galaxies

483 full-text articles. Page 1 of 19.

2020 San Jose State University

#### Computational Astronomy: Classification Of Celestial Spectra Using Machine Learning Techniques, Gayatri Milind Hungund

##### Master's Projects

Lightyears beyond the Planet Earth there exist plenty of unknown and unexplored stars and Galaxies that need to be studied in order to support the Big Bang Theory and also make important astronomical discoveries in quest of knowing the unknown. Sophisticated devices and high-power computational resources are now deployed to make a positive effort towards data gathering and analysis. These devices produce massive amount of data from the astronomical surveys and the data is usually in terabytes or petabytes. It is exhaustive to process this data and determine the findings in short period of time. Many details can be missed ...

2020 California Polytechnic State University, San Luis Obispo

#### Formation Pathways In Brightest Cluster Galaxies: Measuring The Distribution Of Ages, Metallicities, And Hydrodynamics Of Stellar Populations, Priscilla E. Holguin West

##### Physics

Brightest Cluster Galaxies (BCGs) are the most massive galaxies in the local universe and have had the full age of the universe to build. This makes their formation and evolution history particularly interesting as they offer a glimpse at potential evolutionary pathways for younger systems. We present the radial profile of ages, metallicities, and preliminary classification of companions to 23 BCGs observed using the SparsePak instrument on WIYN by running the STARLIGHT stellar population synthesis models. This analysis of the BCGs’ stellar populations is done by separating each BCG into different regions, and preliminary results of the stellar populations for ...

Automated Spectroscopic Detection And Mapping Using Alma And Machine Learningtechniques, 2020 Southern Methodist University

#### Automated Spectroscopic Detection And Mapping Using Alma And Machine Learningtechniques, Steven Cocke, Andrew Wilkins, Josephine Mcdaniel, John Santerre, Conor Nixon

##### SMU Data Science Review

In this paper we present a methodology for automating theclassification of spectrally resolved observations of multiple emissionlines with the Atacama Large Millimeter/submillimeter Array (ALMA).Molecules in planetary atmospheres emit or absorb different wavelengthsof light thereby providing a unique signature for each species. ALMAdata were taken from interferometric observations of Titan made be-tween UT 2012 July 03 23:22:14 and 2012 July 04 01:06:18 as part ofALMA project 2011.0.00319.S. We first employed a greedy set cover algorithm to identify the most probable molecules that would reproducethe set of frequencies with respective flux greater than ...

2020 University of Nevada, Las Vegas

#### Fast Radio Bursts From Interacting Binary Neutron Star Systems, Bing Zhang

##### Physics & Astronomy Faculty Publications

Recent observations of repeating fast radio bursts (FRBs) suggest that some FRBs reside in an environment consistent with that of binary neutron star (BNS) mergers. The bursting rate for repeaters could be very high and the emission site is likely from a magnetosphere. We discuss a hypothesis of producing abundant repeating FRBs in BNS systems. Decades to centuries before a BNS system coalesces, the magnetospheres of the two neutron stars start to interact relentlessly. Abrupt magnetic reconnection accelerates particles, which emit coherent radio waves in bunches via curvature radiation. FRBs are detected as these bright radiation beams point toward Earth ...

Asteroid Belt Survival Through Stellar Evolution: Dependence On The Stellar Mass, 2020 University of Nevada, Las Vegas

#### Asteroid Belt Survival Through Stellar Evolution: Dependence On The Stellar Mass, Rebecca G. Martin, Mario Livio, Jeremy L. Smallwood, Cheng Chen

##### Physics & Astronomy Faculty Publications

Polluted white dwarfs are generally accreting terrestrial-like material that may originate from a debris belt like the asteroid belt in the Solar system. ... See full text for complete abstract.

Extreme Ultraviolet Quasar Colours From Galex Observations Of The Sdss Dr14q Catalogue, 2020 Old Dominion University

#### Extreme Ultraviolet Quasar Colours From Galex Observations Of The Sdss Dr14q Catalogue, Daniel E. Vanden Berk, Sarah C. Wesolowski, Mary J. Yeckley, Joseph M. Marcinik, Jean M. Quashnock, Lawrence M. Machia, Jian Wu

##### Computer Science Faculty Publications

The rest-frame far to extreme ultraviolet (UV) colour–redshift relationship has been constructed from data on over 480,000 quasars carefully cross-matched between SDSS Data Release 14 and the final GALEX photometric catalogue. UV matching and detection probabilities are given for all the quasars, including dependencies on separation, optical brightness, and redshift. Detection limits are also provided for all objects. The UV colour distributions are skewed redward at virtually all redshifts, especially when detection limits are accounted for. The median GALEX far-UV minus near-UV (FUV − NUV) colour–redshift relation is reliably determined up to z ≈ 2.8, corresponding to rest-frame ...

New Foundation In The Sciences: Physics Without Sweeping Infinities Under The Rug, 2019 University of New Mexico

#### New Foundation In The Sciences: Physics Without Sweeping Infinities Under The Rug, Florentin Smarandache, Victor Christianto, Robert Neil Boyd

##### Mathematics and Statistics Faculty and Staff Publications

It is widely known among the Frontiers of physics, that “sweeping under the rug” practice has been quite the norm rather than exception. In other words, the leading paradigms have strong tendency to be hailed as the only game in town. For example, renormalization group theory was hailed as cure in order to solve infinity problem in QED theory. For instance, a quote from Richard Feynman goes as follows: “What the three Nobel Prize winners did, in the words of Feynman, was "to get rid of the infinities in the calculations. The infinities are still there, but now they can ...

2019 University of Massachusetts Amherst

#### The Bivariate Luminosity-Hi Distribution Function Of Galaxies, Zhon Butcher

##### Doctoral Dissertations

To investigate the correlation between optical luminosity and Hi mass, we obtained 21cm Hi line observations from the 100m class Nanç ay Radio Telescope of 2600 galaxies in the local universe (900 ≤ cz ≤ 12000 km s−1 ). We first present the observations and basic results of the Nanc¸ay Interstellar Baryons Legacy Extragalactic Survey (NIBLES), followed by Arecibo follow-up Hi line observations of 305 Nanç ay Hi undetected galaxies. Analysis of the low-luminosity follow-up sources indicates that they may have, on average, a more concentrated stellar mass distribution than the Nanc¸ay detected galaxies of corresponding luminosity.

Using the data ...

Galaxy And Mass Assembly: A Comparison Between Galaxy-Galaxy Lens Searches In Kids/Gama, 2019 University of Louisville

#### Galaxy And Mass Assembly: A Comparison Between Galaxy-Galaxy Lens Searches In Kids/Gama, Shawn Knabel, Benne Holwerda

##### Posters-at-the-Capitol

Strong gravitational lenses are cases where a distant background galaxy is located directly behind a massive foreground galaxy, whose gravity causes the light from the background galaxy to bend around the foreground galaxy. In addition to being visually stunning, these rare events are useful laboratories for furthering our understanding of gravity and cosmology and to determine properties, such as the mass and dark matter content, of the lensing galaxies themselves. The trouble is finding enough of these strong gravitational lenses for further study. The immensity of the catalogs being collected by state-of-the-art telescopes requires equally innovative methods for interpreting that ...

Photoionization Calculations Of The Radiation Force Due To Spectral Lines In Agns, 2019 University of Nevada, Las Vegas

#### Photoionization Calculations Of The Radiation Force Due To Spectral Lines In Agns, Randall C. Dannen, Daniel Proga, Timothy R. Kallman, Tim Waters

##### Physics & Astronomy Faculty Publications

One of the main mechanisms that could drive mass outflows in active galactic nuclei (AGNs) is radiation pressure due to spectral lines. Although straightforward to understand, the actual magnitude of the radiation force is challenging to compute because the force depends on the physical conditions in the gas, as well as the strength, spectral energy distribution (SED), and geometry of the radiation field. We present results from our photoionization and radiation transfer calculations of the force multiplier, M(ξ, t), using the same radiation field to compute the gas photoionization and thermal balance. We assume low gas density (n = 104 ...

Preparing A Database Of Extremely High Velocity Outflows In Quasars, 2019 Humboldt State University

#### Preparing A Database Of Extremely High Velocity Outflows In Quasars, Griffin Kowash, Carla P. Quintero, Sean S. Haas, Paola Rodriguez Hidalgo

##### IdeaFest: Interdisciplinary Journal of Creative Works and Research from Humboldt State University

No abstract provided.

Precise Ages Of Field Stars From White Dwarf Companions, 2019 Max-Planck-Institut f¨ur Astronomie

#### Precise Ages Of Field Stars From White Dwarf Companions, M. Fouesneau, H-W. Rix, T. Von Hippel, D. W. Hogg, H. Tian

##### Ted von Hippel

Observational tests of stellar and Galactic chemical evolution call for the joint knowledge of a star’s physical parameters, detailed element abundances, and precise age. For cool main-sequence (MS) stars the abundances of many elements can be measured from spectroscopy, but ages are very hard to determine. The situation is different if the MS star has a white dwarf (WD) companion and a known distance, as the age of such a binary system can then be determined precisely from the photometric properties of the cooling WD. As a pilot study for obtaining precise age determinations of field MS stars, we ...

New Halo White Dwarf Candidates In The Sloan Digital Sky Survey, 2019 University of Oklahoma

#### New Halo White Dwarf Candidates In The Sloan Digital Sky Survey, Kyra Dame, A. Gianninas, Mukremin Kilic, Jeffrey A. Munn, Warren R. Brown, Kurtis A. Williams, Ted Von Hippel, Hugh C. Harris

##### Ted von Hippel

We present optical spectroscopy and near-infrared photometry of 57 faint (g = 19–22) high proper motion white dwarfs identified through repeat imaging of ≈3100 deg2 of the Sloan Digital Sky Survey footprint by Munn et al. We use ugriz and JHphotometry to perform a model atmosphere analysis, and identify 10 ultracool white dwarfs with Teff < 4000 K, including the coolest pure H atmosphere white dwarf currently known, J1657+2638, with Teff = 3550 ± 100 K. The majority of the objects with cooling ages larger than 9 Gyr display thick disc kinematics and constrain the age of the thick disc to ≥11 Gyr. There are four white dwarfs in our sample with large tangential ...

Bayesian Hierarchical Modelling Of Initial-Final Mass Relations Across Star Clusters, 2019 Imperial College London

#### Bayesian Hierarchical Modelling Of Initial-Final Mass Relations Across Star Clusters, Shijing Si, David A. Van Dyk, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, David C. Stenning

##### Ted von Hippel

The initial-final mass relation (IFMR) of white dwarfs (WDs) plays an important role in stellar evolution. To derive precise estimates of IFMRs and explore how they may vary among star clusters, we propose a Bayesian hierarchical model that pools photometric data from multiple star clusters. After performing a simulation study to show the benefits of the Bayesian hierarchical model, we apply this model to five star clusters: the Hyades, M67, NGC 188, NGC 2168, and NGC 2477, leading to reasonable and consistent estimates of IFMRs for these clusters. We illustrate how a cluster-specific analysis of NGC 188 using its own ...

Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters – Iii. Analysis Of 30 Clusters, 2019 Bryant Space Center, Univeristy of Florida

#### Bayesian Analysis Of Two Stellar Populations In Galactic Globular Clusters – Iii. Analysis Of 30 Clusters, R. Wagner-Kaiser, D. C. Stenning, A Sarajedini, Ted Von Hippel, D. A. Van Dyk, E. Robinson, W. H. Jefferys

##### Ted von Hippel

We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of 30 Galactic globular clusters to characterize two distinct stellar populations. A sophisticated Bayesian technique is employed to simultaneously sample the joint posterior distribution of age, distance, and extinction for each cluster, as well as unique helium values for two populations within each cluster and the relative proportion of those populations. We find the helium differences among the two populations in the clusters fall in the range of ∼0.04 to 0.11. Because adequate models varying in carbon, nitrogen, and oxygen are not presently ...

Formation Of Ultra-Diffuse Galaxies In The Field And In Galaxy Groups, 2019 The Hebrew University

#### Formation Of Ultra-Diffuse Galaxies In The Field And In Galaxy Groups, Fangzhou Jiang, Avishai Dekel, Jonathan Freundlich, Aaron J. Romanowsky, Aaron A. Dutton, Andrea V. Macciò, Arianna Di Cintio

##### Aaron J. Romanowsky

We study ultra-diffuse galaxies (UDGs) in zoom in cosmological simulations, seeking the origin of UDGs in the field versus galaxy groups. We find that while field UDGs arise from dwarfs in a characteristic mass range by multiple episodes of supernova feedback (Di Cintio et al.), group UDGs may also form by tidal puffing up and they become quiescent by ram-pressure stripping. The field and group UDGs share similar properties, independent of distance from the group centre. Their dark-matter haloes have ordinary spin parameters and centrally dominant dark-matter cores. Their stellar components tend to have a prolate shape with a Sérsic ...

Hyper Wide Field Imaging Of The Local Group Dwarf Irregular Galaxy Ic 1613: An Extended Component Of Metal-Poor Stars, 2019 University of Arizona

#### Hyper Wide Field Imaging Of The Local Group Dwarf Irregular Galaxy Ic 1613: An Extended Component Of Metal-Poor Stars, Ragadeepika Pucha, Jeffrey L. Carlin, Beth Willman, Jay Strader, David J. Sand, Keith Bechtol, Jean P. Brodie, Denija Crnojević, Duncan A. Forbes, Christopher Garling, Jonathan Hargis, Annika H.G. Peter, Aaron J. Romanowsky

##### Aaron J. Romanowsky

Stellar halos offer fossil evidence for hierarchical structure formation. Since halo assembly is predicted to be scale-free, stellar halos around low-mass galaxies constrain properties such as star formation in the accreted subhalos and the formation of dwarf galaxies. However, few observational searches for stellar halos in dwarfs exist. Here we present gi photometry of resolved stars in isolated Local Group dwarf irregular galaxy IC 1613 (M sstarf ~ 108 M ⊙). These Subaru/Hyper Suprime-Cam observations are the widest and deepest of IC 1613 to date. We measure surface density profiles of young main-sequence, intermediate to old red giant branch, and ancient ...

Spatially Resolved Stellar Kinematics Of The Ultra-Diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, And Cold Dark Matter Halo Fits, 2019 Yale University

#### Spatially Resolved Stellar Kinematics Of The Ultra-Diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, And Cold Dark Matter Halo Fits, Pieter Van Dokkum, Asher Wasserman, Shany Danieli, Roberto Abraham, Jean Brodie, Charlie Conroy, Duncan A. Forbes, Christopher Martin, Matt Matuszewski, Aaron J. Romanowsky, Alexa Villaume

##### Aaron J. Romanowsky

We present spatially resolved stellar kinematics of the well-studied ultra-diffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hr of observations with the Keck Cosmic Web Imager. The luminosity-weighted dispersion within the half-light radius is ${\sigma }_{1/2}={33}_{-3}^{+3}$ km s−1, lower than what we had inferred before from a DEIMOS spectrum in the Hα region. There is no evidence for rotation, with ${V}_{\max }/\langle \sigma \rangle \lt 0.12$ (90% confidence) along the major axis, in possible conflict with models where UDGs are the high-spin tail of the normal dwarf galaxy ...

2019 University of New Mexico

#### Searching For Supermassive Binary Black Holes And Their Gravitational Waves, Karishma Bansal

##### Physics & Astronomy ETDs

The recent discovery of gravitational waves (GWs) by the LIGO collaboration has opened a new observing window on the universe, but it is limited to the GWs in the frequency range of 10-1000 Hz. The main motivation of this thesis is to consider the possibility of detecting low frequency (nHz) GWs. In the pursuit of these waves, we need to understand their source of origin and build a detector with the required sensitivity. Low-frequency waves are expected as a result of coalescing binary supermassive black holes (SMBBHs). We hope to detect these waves in the near future using pulsar timing ...

New Constraints On Early-Type Galaxy Assembly From Spectroscopic Metallicities Of Globular Clusters In M87, 2019 University of California, Santa Cruz

#### New Constraints On Early-Type Galaxy Assembly From Spectroscopic Metallicities Of Globular Clusters In M87, Alexa Villaume, Aaron J. Romanowsky, Jean Brodie, Jay Strader

##### Aaron J. Romanowsky

The observed characteristics of globular cluster (GC) systems, such as metallicity distributions, are commonly used to place constraints on galaxy formation models. However, obtaining reliable metallicity values is particularly difficult because of our limited means to obtain high quality spectroscopy of extragalactic GCs. Often, "color–metallicity relations" are invoked to convert easier-to-obtain photometric measurements into metallicities, but there is no consensus on what form these relations should take. In this paper we make use of multiple photometric data sets and iron metallicity values derived from applying full-spectrum stellar population synthesis models to deep Keck/LRIS spectra of 177 GCs centrally ...