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Results for “early-type 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.

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NASA NTRS1986

Highly ionized atoms in cooling gas

The ionization of low density gas cooling from a high temperature was calculated. The evolution during the cooling is assumed to be isochoric, isobaric, or a combination of these cases. The calculations are used to predict the column densities and ultraviolet line luminosities of highly ionized atoms in cooling gas. In a model for cooling of a hot galactic corona, it is shown that the observed value of N(N V) can be produced in the cooling gas, while the predicted value of N(Si IV) falls short of the observed value by a factor of about 5. The same model predicts fluxes of ultraviolet emission lines that are a factor of 10 lower than the claimed detections of Feldman, Bruna, and Henry. Predictions are made for ultraviolet lines in cooling flows in early-type galaxies and clusters of galaxies. It is shown that the column densities of interest vary over a fairly narrow range, while the emission line luminosities are simply proportional to the mass inflow rate.

Edgar, Richard J.↗
NASA NTRS1989

Molecular gas, the interstellar medium, and star formation in S0 and Sa galaxies

The results are presented of a survey for CO J = 1 - 0 emission from S0 and S0/a galaxies. The results show that molecular gas is abundant within some early-type disk galaxies, and that the range in the ratio of molecular gas to atomic gas mass is similar to those in other disk galaxies. In the S0 and S0/a galaxies studied, estimated rates of star formation are substantially smaller than, but efficiencies of star formation are roughly the same as, those in Sb or Sc galaxies. Although the rate of cooling of the hot, X-ray emitting gas may be close to the estimated stellar mass return rate in the sample, the star formation rate probably exceeds both by a significant factor.

Thronson, Harley A., Jr.↗
NASA NTRS1987

Stellar bars and the spatial distribution of infrared luminosity

Ground-based 10 micron observations of the central region of over 100 infrared luminous galaxies are presented. A first order estimate of the spatial distribution of infrared emission in galaxies is obtained through a combination of ground-based and Infrared Astronomy Satellite (IRAS) data. The galaxies are nearby and primarily noninteracting, permitting an unbiased investigation of correlations with Hubble type. Approximately 40% of the early-type barred galaxies in this sample are associated with enhanced luminosity in the central (approximately 1 kpc diameter) region. The underlying luminosity source is attributed to both Seyfert and star formation activity. Late-type spirals are different in that the spatial distribution of infrared emission and the infrared luminoisty are not strongly dependent on barred morphology.

Devereux, Nicholas↗
NASA NTRS1985

A statistical analysis of the Einstein normal galaxy sample. I - Spiral and irregular galaxies

The results of a statistical analysis of 48 spiral and irregular galaxies observed with the Einstein Observatory are reported. It is found that the X-ray luminosity is not directly correlated with the mass of the galaxies, but is strongly correlated with the blue luminosity. This suggests that most X-ray sources, including low-mass binaries, are binary systems belonging to both old disk and young arm Population I components. A real bulge population of X-ray sources exists that can contribute significantly to the X-ray luminosity of early-type spirals. The X-ray emission from a sample of 29 relatively isolated, normal elliptical and S0 galaxies is also studied, and the results are compared to those for the above sample to investigate the origin of the X-ray emission in early-type galaxies and the possible emission mechanisms. The influence of a powerful radio source and the onset of nuclear activity are also examined.

Fabbiano, G.↗
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 NTRS1975

On the ionization of the intercloud medium by runaway O-B stars

H II regions around seven high-velocity stars of type O5 to B1 (lambda Cep, xi Per, 68 Cyg, alpha Cam, AE Aur, zeta Oph, mu Col) are investigated assuming 'on-the-spot' reabsorption of the diffuse UV and time-dependent cooling and recombination behind the stars. Ratios of column densities integrated through the H II regions are obtained for stationary and moving stars, and the ionization structure is calculated for an H II region around a runaway star moving perpendicular to the galactic plane. The total volume ionized is found to be practically independent of the star's velocity. Global properties of the intercloud medium are examined; it is found that the presence of clouds may reduce the volume ionized by as much as a factor of 7 and that as much as 30% of the total ionizing radiation from early-type stars may leak out of the galaxy. Copernicus satellite observations are shown to be consistent with lines of sight crossing only the H II regions around the observed stars and a neutral intercloud medium as well as with the existence of a 'hole' in the distribution of O-B5 stars in the vicinity of the sun.

Thuan, T. X.↗
NASA NTRS1987

The spatial distribution of 10 micron luminosity in spiral galaxies

The present ground-based 10-micron observations of 133 nearby luminous, noninteracting IR galaxies indicate that about 40 percent of the early-type barred spirals are associated with enhanced 10-micron luminosity in the central (about 1-kpc diameter) region. The luminosity source may be either Seyfert activity or star formation, or both. The difference in bar-central luminosity association in early- and late-type spirals indicates that the bulge/disk ratio may be an important parameter in the determination of central IR luminosity in barred spirals.

Devereux, Nicholas↗
NASA NTRS1978

Rocket ultraviolet imagery of the Andromeda galaxy

Far-UV electrographic imagery of M31 is presented which was obtained during a sounding-rocket flight with an electrographic Schmidt camera sensitive in the wavelength range from 1230 to 2000 A. The resolution in the imagery is such that 50% of the energy from a point source is confined within a circle 40 arcsec in radius. Two conspicuous features are observed in the UV image of M31: one corresponding to a bright association (NGC 206) in the SW region of the disk and one centered on the galactic nucleus. Indications of the general spiral-arm structure are also evident. Absolute photometry and brightness distributions are obtained for the observed features, and both the central region and NGC 206 are shown to be diffuse sources. It is found that the brightness distribution of the central region is a flat ellipse with its major axis closely aligned with the major axis of the galaxy, which favors a source model consisting of young early-type stars close to the galactic plane and constitutes strong evidence against a nonthermal point source at the galactic center.

Carruthers, G. R.↗
NASA NTRS1972

Preliminary results of OAO ultraviolet photoelectric photometry of galaxies

General results are presented based on nearly completed reductions of data for approximately 35 galaxies of all Hubble types. In general the visual and ultraviolet energy distributions are well correlated. The energy distribution in late-type galaxies appears to turn up sharply in the region around 2000 A, and this is tentatively interpreted as due to the presence of early-type stars whose energy distribution is modified by interstellar dust within these objects. Similar turnups may be present in several elliptical galaxies but the evidence at this time is not definitive.

Code, A. D.↗
NASA NTRS1985

Galactic interstellar abundance surveys with IUE. I - Neutral hydrogen

A survey is initiated of interstellar densities, abundances, and cloud structure in the Galaxy, using the International Ultraviolet Explorer. From high-resolution (0.1-A) spectra, interstellar column densities are derived toward 244 early-type stars by fitting the damping wings of the Ly-alpha absorption line. Published B-V photometry is used to derive E(B-V) color excesses, stellar distances r, and the mean hydrogen densities, n-bar = N(H I)/r. The data set includes stars out to r = 8.5 kpc and E(B-V) = 0.86, with 68 stars in the galactic halo (absolute b greater than 20 deg). The statistical sample consists of 205 stars of type O3-B2.5 within 5 kpc (53 stars in the halo). The column densities, log N(H I), range from less than 19.44 per square centimeter for alpha Vir to 21.81 for HD 37061. A statistical analysis of the E(B-V) distribution suggests variations in the line-of-sight cloud density and the mean reddening per cloud.

Shull, J. M.↗
NASA NTRS1980

Galaxies and far-infrared emission

The far-infrared luminosities of the central few hundred parsecs of many galaxies may exceed by more than an order of magnitude the amount expected from late-type stars. However, for the M82, NGC 253, NGC 1068 and several other galaxies studied in the present paper, the inferred mass-to-luminosity ratios are within the limits expected for stellar distributions containing early-type stars.

Telesco, C. M.↗
DOE OSTI2026

Low-mass Active Galaxies in the SAMI Galaxy Survey with Spatially Resolved Spectroscopy

The smallest supermassive black holes (BHs), which provide constraints on BH seeds, reside in low-mass galaxies. Here, we present a systematic analysis of 990 low-mass galaxies in the SAMI Galaxy Survey to identify emission from accreting BHs using integral field spectroscopy (IFS). Employing a novel automated scoring algorithm based on spatially resolved narrow emission-line diagnostics, we find signatures of active galactic nuclei (AGNs) in 41 galaxies, as well as an additional 46 (less secure) candidates. The galaxies have stellar masses between 10 9.4 ≲ M ⋆ /M ⊙ ≲ 10 10 (down to 10 8.5 , including less secure candidates), redshifts z ≲ 0.06, and morphologies ranging from early-type ellipticals to late-type spirals. Our AGN fraction of 4% (9% if we include the less secure candidates) is significantly higher than those reported by studies using single-fiber spectroscopy (≲1%–2%). Indeed, our additional analysis of single-fiber spectra of the objects in our sample demonstrates that many of our AGN candidates detected via IFS are missed. This work highlights the advantages of IFS, especially the ability to capture extended or decentralized emission from accreting BHs.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

A five-band study of spiral galaxies - X-ray, optical, near- and far-infrared, and radio continuum correlations

A statistical analysis is given of the relationships between global emission properties of spiral galaxies, including the radio continuum, far-infared, near-infrared H-band, optical (B), and X-ray emission. Different properties are observed in early-type and in late-type spiral galaxies, which can be ascribed to the presence of prominent bulges in the former. In late-type spirals, the statistical properties of the emission at different wavelengths are consistent with a common disk/arm origin. The power-law exponents of the correlations are consistent with a steeper IMF in low-luminosity galaxies and with the presence of an obscured starburst component in high-luminosity galaxies. The strongest correlation of the radio continuum luminosity with any other variable is with the far-infrared, suggesting that the radio emission is disjoint from the older low-mass stellar component.

Fabbiano, G.↗
NASA NTRS1979

Deep X-ray survey of the Small Magellanic Cloud

An extended survey of the Small Magellanic Cloud with the SAS 3 X-ray observatory detected SMC X-1 but no other source with a luminosity greater than 1.0 x 10 to the 37th ergs/sec. In particular, SMC X-2 and SMC X-3, observed one month earlier at luminosities of 7 x 10 to the 37th and 10 x 10 to the 37th ergs/sec, respectively, were not detected, which proves that they are both highly variable. The results indicate that the maximum luminosities of early-type X-ray stars in the SMC congregate near 10 to the 38th ergs/sec, which is about five times the maximum luminosity of similar sources in the Galaxy.

Clark, G.↗
NASA NTRS1984

The variation of galactic interstellar extinction in the ultraviolet

It has been found that the wavelength dependence of interstellar extinction is not the same for all stars in the Galaxy. The present investigation is concerned with a further demonstration of the degree of variation of interstellar extinction in the UV, taking into account new extinction measurements toward 29 early-type stars. The stars do not represent a random sample. Approximately 15 of them were chosen because they have either an unusually large or an unusually small ratio of the strength of the diffuse interstellar band at 4430 A to the color excess E(B-V). Five stars have a ratio of these quantities near average and nine additional stars are illuminating reflection nebulae. Attention is given to the deviation from the average galactic extinction law, dense versus diffuse cloud environments, and the galactic longitude dependence.

Witt, A. N.↗
NASA NTRS1988

Properties of clusters of galaxies

Recent results on clusters are reviewed and discussed in relation to cooling flows. Mergers of subclusters are apparently common in clusters. Such mergers will tend to disrupt cooling flows. The recently observed luminous arcs in clusters may be shocks generated by a subcluster merger in a cluster with a cooling flow. The peaked galaxy distributions and radial orbits suggested by recent studies of clusters will lead to a larger number of rapidly moving galaxies passing through the cooling flow region, and this may affect the cooling flow. Various ways in which the cooling flow environment (which appears to be ubiquitous in the early-type galactic systems which form the hosts for strong radio sources) may affect the origin and structure of the radio emitting regions are discussed.

Sarazin, Craig L.↗
NASA NTRS1988

Galactic interstellar abundance surveys with IUE. II - The equivalent widths and column densities

This paper continues a survey of interstellar densities, abundances, and cloud structure in the Galaxy, using the International Ultraviolet Explorer (IUE) satellite. Equivalent widths of 18 ultraviolet resonance transitions are presented and column densities for Si II, Mn II, Fe II, S II, and Zn II toward 261 early-type stars are derived. These equivalent widths and column densities agree within the stated errors of earlier Copernicus, BUSS, or IUE surveys of Mn II, Fe II, S II, and Zn II for 45 stars in common. The column densities are derived from single-component curves of growth with a common b-value based on that of Fe II and Si II.

Van Steenberg, Michael E.↗
NASA NTRS1988

Ultraviolet and optical spectrophotometry of the Seyfert 1.8 galaxy Markarian 609

Ultraviolet and optical observations of the Seyfert 1.8 galaxy Mrk 609 were collected simultaneously. The observations reveal strong line and continuum emission in the UV, an increase in the flux of H-beta and He I 5876, and a decrease in the H-alpha/H-beta value since the measurements by Osterbrock (1978, 1981), as well as an extended population of early-type stars, which is considered to be the source powering the larger part of the far-IR emission. Special attention is given to the origin of steep broad-line Balmer decrement measured by Osterbrock, since the strong UV continuum and the emission lines of Mrk 609 observed rule out reddening as the cause of the Balmer decrement. It is suggested that smaller-than-normal optical depths are likely to be the cause of the decrement.

Rudy, Richard J.↗