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NASA NTRS1993

The nature of the evolution of galaxies by mergers

The merger theory for the formation of elliptical galaxies is examined by conducting a dynamical study of the expected frequency of merging galaxies on the basis of the collisional theory, using galaxy models without halos. The expected merger rates obtained on the basis of the collisional theory fall about a magnitude below the observational value in the present epoch. In the light of current observational evidence and the results obtained, a marked regularity in the formation of ellipticals is indicated, followed by secular evolution by mergers.

Chatterjee, Tapan K.↗
NASA NTRS2002

Probing Galaxy Formation and Evolution with Space Born Sub-Millimeter Telescopes

A major unresolved question in cosmology is how the complex system of galaxies we see in the present universe evolved from an almost perfectly smooth beginning. Multiwavelength observations of galaxies have revealed that a significant fraction of their UV-visible starlight is absorbed and reradiated by dust at infrared JR) and submillimeter wavelengths. The cumulative IR-submm. emission from galaxies since the epoch of recombination, the cosmic IR background, has recently been recorded by the COBE satellite. The COBE observations in combination with recent submm surveys conducted with the SCUBA on the 15 m JCMT have shown that most of the radiation from star formation that has taken place in the early stages of galaxy evolution is reradiated by dust at submm wavelengths. Therefore, submm telescopes offer a unique probe of the early stages of galaxy formation and evolution. This talk will: (1) consider the impact of telescope diameter on the depth of the survey (what redshift can be probed) at different wavelengths; (2) discuss the relative scientific merits of high-resolution narrow-field surveys versus lower resolution deep surveys; and (3) show how both strategies offer complementary information crucial to our understanding of the structure and evolution of galaxies in the universe.

Dwek, Eli↗
NASA NTRS2021

Powerful quasars with young jets in multi-epoch radio surveys

Energetic feedback driven by the large-scale (100’s of kpc) lobes of classical radio galaxies is known to play an important role in shaping galaxy evolution. However, the prevalence of young and compact jets – and their impact on the interstellar medium – remains an open question. Multi-epoch radio surveys with cadences of years to decades offer a promising means of identifying even faint (mJy-level) jets that are compact and potentially young on the basis of variability. Recently, a comparison of images from the Very Large Array Sky Survey (VLASS) and the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey has revealed a population of distant (0.2 < z < 3.2) quasars that have brightened dramatically in the past 1–2 decades. These quasars appear to have transitioned from “radio-quiet” nondetections in FIRST to “radio-loud” detections in VLASS. Extensive multiband follow-up observations with the VLA from 1 to 18GHz have revealed compact (sub-kpc) radio sources that are consistent with young jets that were recently triggered. Here, we summarize the status of our on-going study of quasars with newborn jets identified in the radio time domain.

galaxies↗
NASA NTRS2013

Uv-bright Nearby Early-type Galaxies Observed in the Mid-infrared: Eidence for a Multi-stage Formation History by Way of WISE and GALEX Imaging

In the local universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission than what is expected from their old, red stellar populations. Several origins for this ultraviolet excess (UVX) have been proposed including a population of hot young stars and a population of old, blue horizontal branch or extended horizontal branch (BHB or EHB) stars that have undergone substantial mass loss from their outer atmospheres. We explore the radial distribution of UVX in a selection of 49 nearby E/S0-type galaxies by measuring their extended photometry in the UV through mid-infrared (mid-IR) with the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the Wide-field Infrared Survey Explorer (WISE). We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis models, which allow for the inclusion of EHB stars. We find that combined WISE mid-IR and GALEX UV colors are more effective in distinguishing models than optical colors, and that the UV/mid-IR combination is sensitive to the EHB fraction. There are strong color gradients, with the outer radii bluer than the inner half-light radii by approx.1 mag. This color difference is easily accounted for with an increase in the BHB fraction of 0.25 with radius. We estimated that the average ages for the inner and outer radii are 7.0 +/- 0.3 Gyr, and 6.2 +/- 0.2 Gyr, respectively, with the implication that the outer regions are likely to have formed approx. 1 Gyr after the inner regions. Additionally, we find that metallicity gradients are likely not a significant factor in the color difference. The separation of color between the inner and outer regions, which agrees with a specific stellar population difference (e.g., higher EHB populations), and the approx. 0.5-2 Gyr age difference suggests multi-stage formation. Our results are best explained by inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with z approx. 1.

galaxies: elliptical and lenticular↗
NASA NTRS1986

The advanced X-ray Astrophysics Facility

The basic characteristics and capabilities of the Advanced X-ray Astrophysics Facility (AXAF) are described. The use of the AXAF to perform mass determinations in galaxies and in cluster of galaxies is discussed. The study of galaxy evolution, the interactions of galaxies with their environment, and the properties of galactic halos with the AXAF is proposed. The application of the facility to cosmological measurements, the estimation of the age of the universe, and the analysis of stars, galaxy clusters, and protogalaxies is examined.

Tananbaum, H.↗
NASA NTRS1993

The Evolution of Galaxies and Their Environment

The Third Teton Summer School on Astrophysics discussed the formation of galaxies, star formation in galaxies, galaxies and quasars at high red shift, and the intergalactic and intercluster medium and cooling flows. Observation and theoretical research on these topics was presented at the meeting and summaries of the contributed papers are included in this volume.

Hollenbach, David↗
NASA NTRS1993

Results on the evolution of galaxies and their environment from the Ultraviolet Imaging Telescope on Astro-1

The Ultraviolet Imaging Telescope (UIT), part of the Astro-1 Spacelab Mission, was used to obtain high-resolution surface brightness distribution data in six ultraviolet wavelength bands for the bright reflection nebula NGC 7023. The corresponding data from the visible leads us to conclude that the scattering in the near and far ultraviolet in this nebula is more strongly forward directed than it is in the visible. The UIT also obtained near-UV and far-UV images of the giant OB association NGC 206 in M32. Photometry was obtained for thirty massive stars. We analyzed UV imagery of two Sb bulges and two E galaxies obtained with UIT. For NGC 1275, the measured UV colors indicate a mass function which extends to eight solar masses but no higher. Other aspects of this investigation are discussed.

Stecher, Theodore P.↗
NASA NTRS2003

Gravitational Lenses and the Structure and Evolution of Galaxies

The grant has supported the completion of 16 papers and 4 conference proceedings to date. During the first year of the project we completed five papers, each of which represents a new direction in the theory and interpretation of gravitational lenses. In the first paper, "The Importance of Einstein Rings", we developed the first theory for the formation and structure of the Einstein rings formed by lensing extended sources like the host galaxies of quasar and radio sources. We applied the theory to three lenses with lensed host galaxies. For the time delay lens PG 1115+080 we found that the structure of the Einstein ring ruled out models of the gravitational potential which permitted a large Hubble constant (70 km/s Mpc). In the second paper, :Cusped Mass Models Of Gravitational Lenses", we introduced a new class of lens models where the central density is characterized by a cusp ( rho proportional to tau(sup -gamma), 1 less than gamma less than 2) as in most modern models and theories of galaxies rather than a finite core radius. In the third paper, "Global Probes of the Impact of Baryons on Dark Matter Halos", we made the first globally consistent models for the separation distribution of gravitational lenses including both galaxy and cluster lenses. We show that the key physics for the origin of the sharp separation cutoff in the separation distribution near 3 arc sec is the effect of the cooling baryons in galaxies on the density structure of the system.

Kochanek, Christopher↗
NASA NTRS2004

Gravitational Lenses and the Structure and Evolution of Galaxies

During the first year of the project we completed five papers, each of which represents a new direction in the theory and interpretation of gravitational lenses. In the first paper, The Importance of Einstein Rings, we developed the first theory for the formation and structure of the Einstein rings formed by lensing extended sources like the host galaxies of quasar and radio sources. In the second paper, Cusped Mass Models Of Gravitational Lenses, we introduced a new class of lens models. In the third paper, Global Probes of the Impact of Baryons on Dark Matter Halos, we made the first globally consistent models for the separation distribution of gravitational lenses including both galaxy and cluster lenses. The last two papers explore the properties of two lenses in detail. During the second year we have focused more closely on the relationship of baryons and dark matter. In the third year we have been further examining the relationship between baryons and dark matter. In the present year we extended our statistical analysis of lens mass distributions using a self-similar model for the halo mass distribution as compared to the luminous galaxy.

Oliversen, Ronald J.↗
NASA NTRS2009

The International X-ray Observatory

The International X-Ray Observatory, a joint NASA-ESA-JAXA effort, is a next generation X-ray telescope that will answer many fundamental questions in contemporary astrophysics such as how do supermassive black holes influence galaxy evolution and how do galaxy clusters evolve (and how does this constrain dark energy and dark matter)? As a powerful astronomical observatory, IXO will also address questions ranging from the neutron star equation of state to the distribution and dynamical state of intergalactic material. X-ray spectroscopy, polarimetry, and timing studies provided by IXO's instruments will give detailed measures of abundances, temperatures, densities, magnetic fields and gravitational potentials. These measurements will be complementary to the next generation of observatories such as ALMA, JWST, and future ground-based optical-NIR telescopes. This mission will be ready for launch in the 2020-2021 timeframe and will launch on an Atlas V or Ariane V launch vehicle to L2. It employs a deployable optical bench to achieve the 20 meter focal length and a suite of five instruments. This talk will describe the motivating science for this mission as well as the spacecraft, instruments and optics

Hornschemeier, A.↗
NASA NTRS2018

The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MegaSaura). II. Stacked Spectra

We stack the rest-frame ultraviolet spectra of N = 14 highly magnified gravitationally lensed galaxies at redshifts 1.6 < z < 3.6. The resulting new composite spans 900 < lambda rest < 3000 Angstrom, with a peak signal-to-noise ratio of 103 per spectral resolution element (approximately 100 km s (exp -1)). It is the highest signalto-noise ratio, highest spectral resolution composite spectrum of z approximately 2-3 galaxies yet published. The composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the James Webb Space Telescope (JWST). We report equivalent widths to aid in proposing for and interpreting JWST spectra. We examine the velocity profiles of strong absorption features in the composite, and in a matched composite of z approximately 0 COS/HST galaxy spectra. We find remarkable similarity in the velocity profiles at z approximately 0 and z approximately 2, suggesting that similar physical processes control the outflows across cosmic time. While the maximum outflow velocity depends strongly on ionization potential, the absorptionweighted mean velocity does not. As such, the bulk of the high-ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least approximately 2000 km s (exp -1). We interpret this tail as arising from the stellar wind and photospheres of massive stars. Starburst99 models are able to replicate this high-velocity absorption tail. However, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at z approximately 2. We publicly release our composite spectra.

Rigby, J. R.↗
NASA NTRS1994

Galaxy pairs in deep HST images: Evidence for evolution in the galaxy merger rate

We use four deep serendipitous fields observed with the Hubble Space Telescope (HST) Wide-Field Camera to constrain the rate of galaxy merging between the current epoch and z approximately equals 0.7. Since most mergers occur between members of bound pairs, the merger rate is given to a good approximation by (half) the rate of disappearance of galaxies in pairs. An objective criterion for pair membership shows that 34% +/- 9% of our HST galaxies with I = 18-22 belong to pairs, compared to 7% locally. This means that about 13% of the galaxy population has disappeared due to merging in the cosmic epoch corresponding to this magnitude interval (or 0.1 approximately less than z approximately less than 0.7). Our pair fraction is a lower limit: correction for pair members falling below our detection threshold might raise the fraction to approximately 50%. Since we address only two-galaxy merging, these values do not include physical systems of higher multiplicity. Incorporating I-band field-galaxy redshift distributions, the pair fraction grows with redshift as alpha(1 + z)(exp 3.5 +/- 0.5) and the merger rate as (1 + z)(exp 2.5 +/- 0.5). This may have significant implications for the interpretation of galaxy counts (disappearance of faint blue galaxies), the cosmological evolution of faint radio sources and quasars (which evolve approximately as (1 + z)(exp 3), the similarity in the power law is necessary but not sufficient evidence for a causal relation), statistics of QSO companions, the galaxy content in distant clusters, and the merging history of a 'typical' galaxy.

Burkey, Jordan M.↗
NASA NTRS2011

Evolution in the Continuum Morphological Properties of Ly alpha-Emitting Galaxies from Z=3.1 to Z=2.1

We present a rest-frame ultraviolet morphological analysis of 108 z = 2.1 Lyman Alpha Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S) and compare it to a similar sample of 171 LAEs at z = 3.1 . Using Hubble Space Telescope (HST) images taken as part of the Galaxy Evolution From Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field surveys, we measure the size and photometric component distributions, where photo- metric components are defined as distinct clumps of UV-continuum emission. At both redshifts, the majority of LAEs have observed half-light radii < 2 kpc, but the median half-light radius rises from 0.97 kpc at z = 3.1 to 1.41 kpc at z = 2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of mUlti-component systems. In the z = 2.1 LAE sample, we see clear correlations between the LAE size and other physical properties derived from its SED. LAEs are found to be larger for galaxies with larger stellar mass, larger star formation rate, and larger dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at that redshift, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Lya emission.

Bond, Nicholas A.↗
NASA NTRS1999

Galaxy Surveys with Future X-Ray Missions

The potential of large area imaging missions with good angular resolution will be demonstrated for galaxy evolution studies. X-rays are an important band in which to study galaxies, not least because the recycling of material out of galaxies (in 'superwinds') is an inherently X-ray subject. So the chemical evolution of the universe is profoundly affected by matter emitting in the X-ray band. Specific requirements on area, FWHM of the PSF and field-of- view will be shown. There is a need for deep imaging, some 100 times fainter than Chandra deep surveys, in order to properly explore galaxy evolution in X-rays.

Fabbiano, Giuseppina↗
NASA NTRS2013

GESE: A Small UV Space Telescope to Conduct a Large Spectroscopic Survey of Z-1 Galaxies

One of the key goals of NASA's astrophysics program is to answer the question: How did galaxies evolve into the spirals and elliptical galaxies that we see today? We describe a space mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at a redshift, z is approximately 1 (look-back time of approximately 8 billion years). GESE is a 1.5-meter space telescope with an ultraviolet (UV) multi-object slit spectrograph that can obtain spectra of hundreds of galaxies per exposure. The spectrograph covers the spectral range, 0.2-0.4 micrometers at a spectral resolving power, R approximately 500. This observed spectral range corresponds to 0.1-0.2 micrometers as emitted by a galaxy at a redshift, z=1. The mission concept takes advantage of two new technological advances: (1) light-weighted, wide-field telescope mirrors, and (2) the Next- Generation MicroShutter Array (NG-MSA) to be used as a slit generator in the multi-object slit spectrograph.

galaxy evolution↗