Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “GALAXIES”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

A Comparison of Rest-frame Ultraviolet and Optical Emission-Line Diagnostics in the Lensed Galaxy SDSS J1723+3411 at Redshift z = 1.3293

For the extremely bright lensed galaxy SDSS J1723+3411 at z = 1.3293, we analyze spatially integrated MMT, Keck, and Hubble Space Telescope spectra that fully cover the rest-frame wavelength range of 1400 ̊A to 7200 ̊A. We also analyze near-IR spectra from Gemini that cover Hαfor a portion of the lensed arc. We report fluxes for 42 detected emission lines, and upper limits for an additional22. This galaxy has extreme emission line ratios and high equivalent widths that are characteristic of extreme emission-line galaxies. We compute strong emission line diagnostics from both the rest-frame optical and rest-frame ultraviolet (UV), to constrain physical conditions and test the spectral diagnostics themselves. We tightly determine the nebular physical conditions using the most reliable diagnostics, and then compare to results from other diagnostics. We find disappointing performance from the UV–only diagnostics: they either are unable to measure the metallicity or dramatically under-estimate it; they over-estimate the pressure; and the UV diagnostic of ionization parameter has a strong metallicity dependence in this regime. Based on these results, we suggest that upcoming James Webb Space Telescope(JWST) spectroscopic surveys of galaxies in the reionization epoch should invest the additional integration time to capture the optical [O II] and [O III] emission lines, and not rely solely on the rest-frame UV emission lines. We make available the spectra; they represent one of the highest-quality emission line spectral atlases of star-forming galaxy available beyond the local universe, and will aid planning observations with JWST.

galaxies↗
NASA NTRS2019

Correlation between SFR Surface Density and Thermal Pressure of Ionized Gas in Local Analogs of High-redshift Galaxies

We explore the relation between the star formation rate (SFR) surface density (integration of SFR) and the interstellar gas pressure for nearby compact starburst galaxies. The sample consists of 17 green peas and 19 Lyman break analogs (LBAs). Green peas are nearby analogs of Ly alpha emitters at high redshift and LBAs are nearby analogs of Lyman break galaxies at high redshift. We measure the sizes of green peas using Hubble Space Telescope Cosmic Origins Spectrograph near-UV images with a spatial resolution of approximately 0.05 arcsec. We estimate the gas thermal pressure in H II regions by P equals N (sub total)Tk (sub B) approximately or equal to 2n (sub e)Tk (sub B). The electron density is derived using the [S II] doublet at 6716,6731 Angstroms and the temperature is calculated from the [O III] lines. The correlation is characterized by the integration of SFR equals 2.40 times 10 (sup -3) times solar mass per year per square kiloparsec times ((P divided by k (sub B)) divided by (10 ( sup 4) per cubic centimeter times K)) times (sup 1.33). Green peas and LBAs have high integration of SFR up to 1.2 solar masses per year per square kiloparsec and high thermal pressure in the H II region up to P divided by k (sub B) approximating 10 (sup 7.2) K cubic centimeters. These values are at the highest end of the range seen in nearby starburst galaxies. The high gas pressure and the correlation are in agreement with those found instar-forming galaxies at redshift approximating 2.5. These extreme pressures are shown to be responsible for driving galactic winds in nearby starbursts. These outflows may be crucial in enabling Ly alpha and Lyman-continuum to escape.

Galaxies: Evolution↗
NASA NTRS2014

The Atacama Cosmology Telescope: Dusty Star-Forming Galaxies and Active Galactic Nuclei in the Southern Survey

We present a catalogue of 191 extragalactic sources detected by the Atacama Cosmology Telescope (ACT) at 148 and/or 218 GHz in the 2008 Southern survey. Flux densities span 14 -1700 mJy, and we use source spectral indices derived using ACT-only data to divide our sources into two subpopulations: 167 radio galaxies powered by central active galactic nuclei (AGN) and 24 dusty star-forming galaxies (DSFGs). We cross-identify 97 per cent of our sources (166 of the AGN and 19 of the DSFGs) with those in currently available catalogues. When combined with flux densities from the Australia Telescope 20 GHz survey and follow-up observations with the Australia Telescope Compact Array, the synchrotron-dominated population is seen to exhibit a steepening of the slope of the spectral energy distribution from 20 to 148 GHz, with the trend continuing to 218 GHz. The ACT dust-dominated source population has a median spectral index, A(sub 148-218), of 3.7 (+0.62 or −0.86), and includes both local galaxies and sources with redshift around 6. Dusty sources with no counterpart in existing catalogues likely belong to a recently discovered subpopulation of DSFGs lensed by foreground galaxies or galaxy groups.

dusty star-forming galaxies (DSFGs)↗
NASA NTRS2014

Galaxy Evolution Spectroscopic Explorer (GESE): Science Rationale, Optical Design, and Telescope Architecture

One of the key goals of NASA’s astrophysics program is to answer the question: How did galaxies evolve into the spiral, elliptical, and irregular galaxies that we see today? We describe a space mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to help address this question by making a large ultraviolet spectroscopic survey of galaxies at a redshift, z approximately 1 (look-back time of approximately 8 billion years). GESE is a 1.5-m space telescope with an near-ultraviolet (NUV) multi-object slit spectrograph covering the spectral range, 0.2-0.4 micrometers (0.1-0.2 micrometers as emitted by galaxies at a redshift, z approximately 1) at a spectral resolution of delta lambda=6 A.

elliptical↗
NASA NTRS2015

Effective Power-Law Dependence of Lyapunov Exponents on the Central Mass in Galaxies

Using both numerical and analytical approaches, we demonstrate the existence of an effective power-law relation L alpha m(sup p) between themean Lyapunov exponent L of stellar orbits chaotically scattered by a supermassive black hole (BH) in the centre of a galaxy and the mass parameter m, i.e. ratio of the mass of the BH over the mass of the galaxy. The exponent p is found numerically to obtain values in the range p approximately equals 0.3-0.5. We propose a theoretical interpretation of these exponents, based on estimates of local 'stretching numbers', i.e. local Lyapunov exponents at successive transits of the orbits through the BH's sphere of influence. We thus predict p = 2/3 − q with q approximately equaling 0.1-0.2. Our basic model refers to elliptical galaxy models with a central core. However, we find numerically that an effective power-law scaling of L with m holds also in models with central cusp, beyond a mass scale up to which chaos is dominated by the influence of the cusp itself. We finally show numerically that an analogous law exists also in disc galaxies with rotating bars. In the latter case, chaotic scattering by the BH affects mainly populations of thick tube-like orbits surrounding some low-order branches of the x(sub 1) family of periodic orbits, as well as its bifurcations at low-order resonances, mainly the inner Lindblad resonance and the 4/1 resonance. Implications of the correlations between L and m to determining the rate of secular evolution of galaxies are discussed.

chaos aEuro" galaxies:↗
NASA NTRS2016

Going the Distance: Mapping Host Galaxies of LIGO and VIRGO Sources in Three Dimensions using Local Cosmography and Targeted Follow-Up

The Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) discovered gravitational waves (GWs) from a binary black hole merger in 2015 September and may soon observe signals from neutron star mergers. There is considerable interest in searching for their faint and rapidly fading electromagnetic (EM) counterparts, though GW position uncertainties are as coarse as hundreds of square degrees. Because LIGO's sensitivity to binary neutron stars is limited to the local universe, the area on the sky that must be searched could be reduced by weighting positions by mass, luminosity, or star formation in nearby galaxies. Since GW observations provide information about luminosity distance, combining the reconstructed volume with positions and redshifts of galaxies could reduce the area even more dramatically. A key missing ingredient has been a rapid GW parameter estimation algorithm that reconstructs the full distribution of sky location and distance. We demonstrate the first such algorithm, which takes under a minute, fast enough to enable immediate EM follow-up. By combining the three-dimensional posterior with a galaxy catalog, we can reduce the number of galaxies that could conceivably host the event by a factor of 1.4, the total exposure time for the Swift X-ray Telescope by a factor of 2, the total exposure time for a synoptic optical survey by a factor of 2, and the total exposure time for a narrow-field optical telescope by a factor of 3. This encourages us to suggest a new role for small field of view optical instruments in performing targeted searches of the most massive galaxies within the reconstructed volumes.

catalogs – galaxies: distances and redshifts –↗
NASA NTRS1974

Stellar content of the nuclei of elliptical galaxies determined from 2.3 micron CO band strengths

Observations of the luminosity sensitive CO absorption band at 2.3 micron are presented for the nuclei of 16 epsilon and SO galaxies. Preliminary data on the radial variation of the CO index in 6 galaxies are also given. The data show that the 2-u radiation from the nuclei is dominated by high luminosity stars of integrated spectral type later than K5. There is only a small variation in the CO absorption from galaxy to galaxy, and only a slight variation with measuring aperture size from 17.5 in. to 59 in. The data can be used to synthesize stellar populations for elliptical galaxy nuclei.

Frogel, J. A.↗
NASA NTRS1975

Optical and infrared spectrophotometry of 18 Markarian galaxies

Slit spectra, spectrophotometric scans and infrared broad band observations are presented. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal and stellar radiation components were present. One group of Seyfert galaxies was characterized both by the presence of a high density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which did not have a high density region of gas, were dominated by thermal radiation from dust and a stellar continuum. Ten of the galaxies, which are not Seyfert galaxies, are shown to be examples of extragalactic H 2 regions.

Becklin, E. E.↗
NASA NTRS1976

The non-thermal radiation in the galaxy

The distribution of nonthermal emissivity with height z above the galactic plane is examined. The main result is that recent observations of the distribution of brightness at intermediate latitudes in the galaxy and of the edge-on spiral galaxy NGC 891 indicate that the emissivity extends to heights of several kpc perpendicular to the plane. The relationship between the nonthermal emissivity and the neutral gas is also studied. In several galaxies the angular distributions of neutral hydrogen and nonthermal emission are roughly coextensive and show similar features such as spiral structure. If radio galaxies and normal galaxies with strong nuclear radio sources are excluded, there appears to be a proportionality between their total HI content and their nonthermal radio luminosity.

Baldwin, J. E.↗
NASA NTRS1977

The nonthermal radiation in the galaxy

Observations of the distribution of brightness at intermediate latitudes in the galaxy and of the edge-on spiral galaxy, NGC 891, indicate that the emissivity extends to heights of several kpc perpendicular to the plane. In several galaxies, the angular distributions of neutral hydrogen and nonthermal emission are roughly coextensive and show similar features such as spiral structure. If radio galaxies and normal galaxies with strong nuclear radio sources are excluded, there appears to be a proportionality between their total H(I) content and their nonthermal radio luminosity.

Baldwin, J. E.↗
NASA NTRS1977

The redshift and optical structure of the X-ray galaxy cluster A478

Observational results are reported concerning the optical properties of the X-ray cluster of galaxies A478. A cluster redshift of 0.09 is determined, which implies a cluster X-ray luminosity of 10 to the 45th power erg/s over the energy range from 2 to 6 keV. The cluster is classified as type cD, the center of the cluster is found to be consistent with the position of the cD galaxy, and it is shown that the surface distribution of the galaxies in the cluster is well described by a bounded isothermal gas-sphere model. The core radius of the galaxy distribution is estimated to be about 1.5 arcmin, corresponding to approximately 0.20 Mpc for a Hubble constant of 50 km/s per Mpc. It is noted that the observed galaxy distribution is somewhat asymmetric, being elongated along the NE-SW direction.

Bahcall, N. A.↗
NASA NTRS1977

Clusters of galaxies

Observational properties of clusters of galaxies and some theoretical interpretations are reviewed. The major subjects of the review include catalogs of clusters, the static properties of rich clusters, cluster dynamics, X-ray emission from clusters of galaxies, and cluster radio emission. Observed static properties discussed are: richness, classification schemes, galactic content, cD galaxies, density profiles, sizes, and the optical luminosity function. Several characteristic time scales of clusters of galaxies are examined along with mass segregation, the dynamical evolution of clusters, cluster masses, mass-to-light ratios, the missing-mass problem, and the mean galactic and cluster mass densities in the universe. The main characteristics of clusters that contain X-ray emission are summarized, emphasizing the relation of the X-ray emission to optical properties. The most important properties of cluster radio emission are outlined, the relation of this emission to the other cluster properties studied is indicated, and evidence suggesting the influence of an intracluster gas on the radio galaxies and their relativistic electrons is noted.

Bahcall, N. A.↗
NASA NTRS1977

X-ray clusters of galaxies - Correlation of X-ray luminosity with galactic content

All 14 X-ray clusters of galaxies detected by the Ariel 5 satellite at high galactic latitudes with redshifts of less than 0.05 are analyzed optically for galaxy content. A strong correlation is found between cluster X-ray luminosity and galaxy type: the fraction of spiral galaxies in a cluster decreases rapidly with increasing X-ray luminosity. The observed correlation is consistent with a combined model of thermal bremsstrahlung emission from a hot intracluster gas and stripping of the spiral galaxies caused by the ram pressure of the same intracluster gas.

Bahcall, N. A.↗
NASA NTRS1978

Protogalaxy interactions in newly formed clusters - Galaxy luminosities, colors, and intergalactic gas

The role of protogalaxy interactions in galactic evolution is studied during the formation of galaxy clusters. In the early stages of the collapse, coalescent encounters of protogalaxies lead to the development of a galactic luminosity function. Once galaxies acquire appreciable random motions, mutual collisions between galaxies in rich clusters will trigger the collapse of interstellar clouds to form stars. This provides both a source for enriched intracluster gas and an interpretation of the correlation between luminosity and color for cluster elliptical galaxies. Other observational consequences that are considered include optical, X-ray, and diffuse nonthermal radio emission from newly formed clusters of galaxies.

Silk, J.↗
NASA NTRS1979

General properties of HII regions in galaxies

The structure, electron density, and dimensions of HII regions in galaxies are discussed. These parameters are correlated to the chemical composition gradient along the galactic radius, the dimensions of the three largest HII regions in the galaxy, and the amount of hydrogen in the galaxy, as well as the mass, dimensions, and total optical luminosity of the galaxy. The relationships of HII regions to star formation and galactic nucleus activity are discussed and the kinematic properties of the SB and Sab galaxies are related to the size of HII regions.

Smirnov, M. A.↗
NASA NTRS1978

N galaxies - A new class of X-ray sources

It is shown that in addition to many Seyfert galaxies and quasars, N galaxies are also powerful X-ray sources. X-ray emission has been discovered from all six N galaxies in the 3C radio catalogue with redshifts less than 0.06 and from the N galaxy Pic A. Since many of the N galaxies possess compact radio components, it is suggested that the principle cause of X-ray emission may be the synchrotron self-Compton process. An alternate theory suggests that X-rays may be generated by gas clouds colliding with velocities of the order of the Doppler width of the broad lines.

Marshall, F. E.↗
NASA NTRS1978

On the contribution of normal galaxies to the diffuse X-ray background

A calculation has been made of the contribution of normal galaxies to the diffuse X-ray background, based on a model of the X-ray luminosity evolution of galaxies in which two populations of galactic X-ray sources are distinguished. With plausible estimates of the behavior of the galactic X-ray source populations with time, normal galaxies provide between 1.5% and 9% of the X-ray background between 2 and 10 keV. Unless massive halos exist around galaxies and their formation is accompanied by the production of early-type Population I X-ray binaries, a firm upper limit of about 25% can be set on the contribution of normal galaxies to the X-ray background between 2 and 10 keV.

Van Paradijs, J.↗
NASA NTRS1979

Photometric studies of composite stellar systems. III - UBVR and JHK observations of E and S0 galaxies

Infrared (JHK) photometry is presented for a sample of E and S0 galaxies. The sample comprises 80 field galaxies, 35 galaxies in the Virgo cluster, and 22 in the Coma cluster. The galaxies span a range of 6 mag in absolute magnitude. Multiaperture UBVR photometry for 107 field galaxies is also presented. The infrared data are combined with these optical data or with published optical data to give V-K colors. This paper describes the observational techniques and lists the data.

Persson, S. E.↗