Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “galaxies: fundamental parameters”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Fundamental parameters of brightest cluster galaxies

Photometry and spectroscopy of a sample of the brightest cluster galaxies (BCGs) are presented, and the relationships between scale length, surface brightness, velocity dispersion, and line strength are determined and compared with the relations determined for lower luminosity ellipticals (LLEs). It is found that the relation between log r(e), log sigma, and mean surface brightness reported by Dressler et al. for LLEs also describes the relation for BCGs fairly well. Fundamental plane solutions for BCGs are derived which can be used as distance indicators with a predicted error of about 21 percent per galaxy. Only a weak correlation is found between the Na D 5893 line strength and velocity dispersion for BCGs, in contrast to the significant correlation between these quantities reported for LLEs. It is found that the mean mass-to-light ratio for BCGs is a factor of about two greater than for the LLEs in the Virgo and Coma sample of Dressler et al.

Oegerle, William R.↗
NASA NTRS1995

Cosmological implications of ROSAT observations of groups and clusters of galaxies

We have combined ROSAT Position Sensitive Proportional Counter (PSPC) and optical observations of a sample of groups and clusters of galaxies to determine the fundamental parameters of these systems (e.g., the dark matter distribution, gas mass fraction, baryon mass fraction, mass-to-light ratio, and the ratio of total-to-luminous mass). Imaging X-ray spectroscopy of groups and clusters show that the gas is essentially isothermal beyond the central region, indicating that the total mass density (mostly dark matter) scales as rho(sub dark) varies as 1/r squared. The density profile of the hot X-ray emitting gas is fairly flat in groups with rho(sub gas) varies as 1/r and becomes progressively steeper in hotter richer systems, with rho(sub gas) varies as 1/r squared in the richest clusters. These results show, that in general, the hot X-ray-emitting gas is the most extended mass component in groups and clusters, the galaxies are the most centrally concentrated component, and the dark matter is intermediate between the two. The flatter density rofile of the hot gas compared to the dark matter produces a gas mass fraction that increases with radius within each object. There is also a clear trend of increasing gas mass fraction (from 2% to 30%) between elliptical galaxies and rich clusters due to the greater detectable extent of the X-ray emission in richer systems. For the few systems in which the X-ray emission can be traced to the virial radius (where the overdensity delta is approximately equal 200), the gas mass fraction (essentially the baryon mass fraction) approaches a roughly constant value of 30%, suggesting that this is the true primordial value. Based on standard big bang nucleosynthesis, the large baryon mass fraction implies that Omega = 0.1 - 0.2. The antibiased gas distribution suggests that feedback from galaxy formation and hydrodynamics play important roles in the formation of structure on the scale of galaxies to rich clusters. All the groups and clusters in our sample have mass-to-light ratios of M/L(sub V) approximately 100 - 150 solar mass/solar luminosity, which strongly contrasts with the traditional view that the mass-to-light ratio of rich clusters is significantly greater than individual galaxies or groups with M/L(sub V) approximately 250 - 300 solar mass/solar luminosity. We also show that M/L(sub V is essentially constant within the virial radius of clusters (where delta is greater than or approximately 200), which is consistent with the peaks formalism of biased galaxy formation. While the mass-to-light ratios of groups and clusters are comparable (indicating a constant mass fraction of optically luminous material), the ratio of the total mass-to-luminous mass (gas plus stars) monotonically decreases between galaxies and clusters. The decrease in M(sub total)/M(sub lum) arises from two factors: (1) the composition of baryonic matter varies from a predominance of optically luminous material (stars) on the scale of galaxies (approximately 10 kpc) to a predominance of X-ray luminous material (hot gas) on the scale of rich clusters (approximately 1 Mpc), and (2) the hot gas has a more extended spatial distribution than the gravitating matter. The observed decrease M(sub total)/M(sub lum) between galaxies and clusters indicates that the universe actually becomes `brighter' on mass scales between 10(exp 12) and 10(exp 15) solar mass, in the sense that a greater fraction of the gravitating mass is observable.

David, Laurence P.↗
NASA NTRS2012

Interactions in Massive Colliding Wind Binaries

The most massive stars (M> 60 Solar Mass) play crucial roles in altering the chemical and thermodynamic properties of their host galaxies. Stellar mass is the fundamental stellar parameter that determines their ancillary properties and which ultimately determines the fate of these stars and their influence on their galactic environs. Unfortunately, stellar mass becomes observationally and theoretically less well constrained as it increases. Theory becomes uncertain mostly because very massive stars are prone to strong, variable mass loss which is difficult to model. Observational constraints are uncertain too. Massive stars are rare, and massive binary stars (needed for dynamical determination of mass) are rarer still: and of these systems only a fraction have suitably high orbital inclinations for direct photometric and spectroscopic radial-velocity analysis. Even in the small number of cases in which a high-inclination binary near the upper mass limit can be identified, rotational broadening and contamination of spectral line features from thick circumstellar material (either natal clouds or produced by strong stellar wind driven mass loss from one or both of he stellar components) biases the analysis. In the wilds of the upper HR diagram, we're often left with indirect and circumstantial means of determining mass, a rather unsatisfactory state of affairs.

Corcoran, M.↗
NASA NTRS2011

What the UV SED Tells us About Stellar Populations and Galaxies

The UV SED parameter b as in f(sub 1) ~ 1(sup b), is commonly used to estimate fundamental properties of high-redshift galaxies including age and metallicity. However, sources and processes other than age and metallicity can influence the value of b. We use the local starforming dwarf galaxy, I Zw 18, in a case study to investigate uncertainties in age and metallicity inferred from b due errors or uncertainties in: mode of star formation (instantaneous starburst vs. continuous SF), dust extinction, nebular continuous emission (2-photon emission, Balmer continuum flux), and presence of older stars.

Heap, Sara R.↗
NASA NTRS2012

The Size Evolution of Passive Galaxies: Observations From the Wide-Field Camera 3 Early Release Science Program

We present the size evolution of passively evolving galaxies at z approximately 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z greater than approximately 1.5. We identify 30 galaxies in approximately 40 arcmin(sup 2) to H less than 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 micrometers less than approximately lambda (sub obs) 1.6 micrometers with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of approximately 0.033(1+z).We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M(sub ∗) approximately 10(sup 11) solar mass) undergo the strongest evolution from z approximately 2 to the present. Parameterizing the size evolution as (1 + z)(sup - alpha), we find a tentative scaling of alpha approximately equals (−0.6 plus or minus 0.7) + (0.9 plus or minus 0.4) log(M(sub ∗)/10(sup 9 solar mass), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of highredshift systems. We discuss the implications of this result for the redshift evolution of the M(sub ∗)-R(sub e) relation for red galaxies.

fundamental parameters↗
NASA NTRS2002

Ecological Niches for Space Missions in the Far-Infrared

The far-infrared and submillimeter region (30 micron-750 micron) has perhaps the greatest potential of all wavelengths for advancement in astronomy. When viewed in terms of the cosmic backgrounds, the far-IR is extremely important: half of the total luminosity in the Universe is emitted at rest wavelengths approximately 80-100 microns. At the highest known galaxy redshifts, this energy is redshifted to approximately 600 microns. Existing and planned missions have a broad range of capabilities defined in terms of their spectral coverage, spectral resolution, angular resolution, survey speed, and sensitivity. In this parameter space, the opportunity for future far-IR and submillimeter missions with great discovery potential is evident. Such missions will answer fundamental questions about the history of energy release in the Universe, the formation and evolution of galaxies, and formation of stellar and protoplanetary systems. We discuss the parameter space that can be filled by a few well-chosen space missions, specifically a submillimeter all-sky survey and a far-IR to submillimeter observatory.

Benford, D. J.↗
NASA NTRS1995

The fundamental plane correlations for globular clusters

In the parameter space whose axes include a radius (core, or half-light), a surface brightness (central, or average within the half-light radius), and the central projected velocity dispersion, globular clusters lie on a two-dimensional surface (a plane, if the logarithmic quantities are used). This is analogous to the 'fundamental plane' of elliptical galaxies. The implied bivariate correlations are the best now known for globular clusters. The derived scaling laws for the core properties imply that cluster cores are fully virialized, homologous systems, with a constant (M/L) ratio. The corresponding scaling laws on the half-light scale are differrent, but are nearly identical to those derived from the 'fundamental plane' of ellipticals. This may be due to the range of cluster concentrations, which are correlated with other parameters. A similar explanation for elliptical galaxies may be viable. These correlations provide new empirical constraints for models of globular cluster formation and evolution, and may also be usable as rough distance-indicator relations for globular clusters.

Djorgovski, S.↗
NASA NTRS2001

Ecological Niches for Space Missions in the Far-Infrared

The far-infrared and submillimeter region (30 micrometers-750 micrometers) has perhaps the greatest potential of all wavelengths for advancement in astronomy. When viewed in terms of the cosmic backgrounds, the fares is extremely important: half of the total luminosity in the Universe is emitted at rest wavelengths approximately 80 - 100 micrometers. At the highest known galaxy redshifts (z approximately equal to 6) this energy is redshifted to approximately 600 micrometers. Existing and planned survey missions have a broad range of capabilities, defined in terms of their spectral coverage, spectral resolution, survey area, and sensitivity. In this 4-dimensional parameter space, the flares is found to be substantially behind most other wavelength bands. The opportunity for future missions with great discovery potential is evident. Such missions will be wellsuited to answering fundamental questions about the history of energy release in the Universe, the formation and evolution of galaxies, and formation of stellar and protoplanetary systems. We discuss the parameter space that can be filled by a few well-chosen space missions, specifically a submillimeter all-sky survey and a far-IR to submillimeter observatory.

Benford, Dominic J.↗
NASA NTRS2004

Maximizing Science Capability for Far-Infrared Space Missions

The far-infrared and submillimeter region (20 microns-800 microns) has perhaps the greatest potential of all wavelengths for advancement in astronomy. When viewed in terms of the cosmic backgrounds, the far-IR is extremely important: half of the total luminosity in the Universe is emitted at rest wavelengths approximately 80-100 microns. At the highest known galaxy redshifts (z approximately equal to 6) this energy is redshifted to approximately 600 microns. Existing and planned missions have a broad range of capabilities, defined in terms of their spectral coverage, spectral resolution, angular resolution, mapping speed, and sensitivity. In this 5-dimensional parameter space, the far-IR is substantially be-hind most other wavelength bands. The opportunity for future missions with great discovery potential is evident. Such missions will be well-suited to answering fundamental questions about the history of energy release in the Universe, the formation and evolution of galaxies, and formation of stellar and protoplanetary systems. We discuss the parameter space that can be filled by a few well-chosen space missions, specifically a submillimeter all-sky survey and a far-IR to submillimeter observatory. Ultimately, a long baseline submillimeter interferometer is necessary to provide sensitivity and angular resolution.

Benford, Dominic↗
NASA NTRS1993

What determines the morphological fractions in clusters of galaxies?

A reexamination of Dressler's (1980) sample of nearly 6000 galaxies in 55 clusters shows that the morphology-clustercentric radius relation is more fundamental than the morphology-local density relation. This conclusion is supported by improved correlations when the projected clustercentric radius is used as the independent parameter, and by a comparison of galaxies with the same normalized clustercentric radii by different values of the projected local density.

Whitmore, Bradley C.↗
NASA NTRS1985

Self-regulating galaxy formation. I - H II disk and Lyman-alpha pressure

The nascent interstellar medium and star formation model are incorporated into a scenario for the formation epoch of spiral galaxies. The structure, star formation time scale, and luminosity of a self-gravitating isothermal disk are evaluated as functions of the disk surface density. The importance of radiation pressure, particularly that of Lyman-alpha, in maintaining an inflated disk and halting infall is discussed. The Lyman-alpha pressure also supports a considerable halo of material in the vicinity of the disk. A first-order infall scenario and the time-dependent properties of the system it constructs are presented. Disk properties are evaluated at the epoch at which further material is supportable against infall by Lyman-alpha pressure. The two-dimensional family of disk galaxies whose scales and surface density are expressible in terms of fundamental constants and which arise from the three parameter sets of perturbations in the Hubble flow are determined.

Cox, D. P.↗
NASA NTRS1993

Nuclear winds in active elliptical galaxies. I - Interaction

The interaction of a supersonic wind generated by an active nucleus, a nuclear wind, with the hot interstellar medium of an elliptical host galaxy is investigated. We survey the basic time and spatial scales of this interaction through a study covering the range of probable wind and galaxy parameters. The evolving wind/ISM interaction is detailed, with the conclusion that a true equilibrium state is never possible due to long cooling times. Alteration of the wind by mass loading is considered, and a relationship between nuclear winds and central stellar clusters in this context is outlined. The nuclear wind will fundamentally alter the interstellar medium of the host galaxy. Powerful radio galaxies and quasars can evacuate the entire ISM of their host galaxy. In an isolated elliptical galaxy, winds from moderately powerful radio galaxies will either be confined to within about a kpc or evacuate the entire hot ISM. Even in the relatively high pressure ISM of elliptical galaxies winds containing only 1 percent-10 percent of the radiant luminosity of the active nucleus will extend to the narrow-line region. Therefore, nuclear winds are likely to control the properties of the narrow-line emission.

Smith, Steven J.↗
NASA NTRS1992

Galaxy clusters and cold dark matter - A low-density unbiased universe?

Large-scale simulations of a universe dominated by cold dark matter (CDM) are tested against two fundamental properties of clusters of galaxies: the cluster mass function and the cluster correlation function. We find that standard biased CDM models are inconsistent with these observations for any bias parameter b. A low-density, low-bias CDM-type model, with or without a cosmological constant, appears to be consistent with both the cluster mass function and the cluster correlations. The low-density model agrees well with the observed correlation function of the Abell, Automatic Plate Measuring Facility (APM), and Edinburgh-Durham cluster catalogs. The model is in excellent agreement with the observed dependence of the correlation strength on cluster mean separation, reproducing the measured universal dimensionless cluster correlation. The low-density model is also consistent with other large-scale structure observations, including the APM angular galaxy-correlations, and for lambda = 1-Omega with the COBE results of the microwave background radiation fluctuations.

Bahcall, Neta A.↗
NASA NTRS1992

The efficiency of galaxy formation in clusters

Whether the observed trend in the efficiency of galaxy formation between poor and rich clusters is consistent with CDM-biased galaxy formation scenarios or with other hierarchical clustering scenarios described by a power-law fluctuation spectrum from galaxy to rich cluster scales in a universe with density parameter Omega = 1. A greater statistical correlation is found between galaxy and poor cluster masses than between galaxy and rich cluster masses due to the cluster proximity in filter length. This is the fundamental reason why galaxy formation is more efficient in poor clusters than in rich ones. It is found that the observed trend in the efficiency of galaxy formation and the observed values can be produced within the context of CDM-based galaxy formation scenarios or other scenarios involving flat spectra if X-ray luminous clusters are typically 2-3 sigma objects.

David, Laurence P.↗
NASA NTRS2002

Probing Galaxy Formation and Submillimeter Surveys

Multiwavelength observations of galaxies have revealed that a significant fraction of the their stellar or accretion luminosity is absorbed and reradiated by dust at far-infrared (FIR) and submillimeter (submm) wavelengths. Submillimeter (850 micron) surveys conducted by the SCUBA instrument on the JCMT have detected a population of high redshift (z approximately equal to 1-4) ultraluminous infrared galaxies, that dominate the luminosity densities at those redshifts. Their cumulative contribution to the cosmic infrared background (CIB) detected by the COBE satellite is comparable to the observations, suggesting that at 850 microns the CIB is resolved into its constituent sources. This suggests that the early universe was much more dust enshrouded than the present one. FIR and submm surveys can therefore address fundamental questions regarding the early processes of galaxy formation and their evolution in number and luminosity over cosmic history. The scientific information that can be obtained from such surveys depend on a number of parameters, the most important of which are the diameter of the telescope and the wavelengths of the survey. We summarize the effect of these parameters on the scientific return from such surveys.

Dwek, Eli↗
NASA NTRS2004

FUSE Observations of LMC and SMC 03-4 Stars: Physical Parameters of the Hottest Stars

The goal of the project is to analyze the spectra of the most massive stars in our neighbor Galaxies, to determine the physical parameters of temperature, mass, gravity, and Luminosity, together with the stellar wind properties. For this purpose, FUSE spectra, HST spectra (uv and optical) and high quality optical spectra obtained with ground-based telescopes need to be analyzed wing modern NLTE model atmosphere techniques. The combination of the use of spectra from different wavelength regions is a fundamental aspect of the project. Each spectral domain adds complementary important to the process of the spectral analysis. In this way the comparison of stellar properties between galaxies of different metallicity will become more significant.

Kudrtizki, Rolf-Peter↗
NASA NTRS1990

The kinematics of Abell clusters

Velocity histograms, galaxy positions, and velocity dispersions are presented for 69 nearby Abell clusters. The shape of the cumulative distribution for R = 1 or more clusters does not match the predictions of standard CDM models for any biasing parameter b. The only models consistent with the median and maximum dispersions of the sample are those of b about 1.6-2.0 and in which clusters are identified in three dimensions. Velocity dispersions of high-redshift systems appear fundamentally different from those of nearby clusters. The median dispersion of the subset of 25 cD clusters is similar to that of non-cD systems. A substantial fraction of the cD galaxies have velocities significantly different from the mean of their parent clusters. Three of these have 4 s or more measured redshifts. These last two results suggest that the formation of cD galaxies is dominated by the local, rather than global, cluster environment.

Zabludoff, Ann I.↗