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At least 73 records · Page 4

Statistical properties of IRAS galaxies

Statistical approaches to the study of galaxies seen by IRAS are reviewed, stressing the contrast between IR complete and optically complete samples. A statistical overview is given of the Cataloged Galaxies and Quasars Observed in the IRAS Survey. The bi-variate distribution of ESO/U galaxies as a function of 60 microns flux and optical size is used to predict the size of an IR complete sample from the optically complete sample. To within the uncertainties, both samples are found to belong to the same population, leaving little room for a fundamentally new class of extragalactic objects, besides IR bright galaxies like Arp220.

Helou, G.↗

Soft X-ray properties of Seyfert galaxies. I - Spectra

Results are presented from a study of soft X-ray spectra of 75 Seyfert galaxies observed by the Einstein Observatory IPC. The spectra in this sample (mostly high-luminosity Seyfert type 1s) are found to be consistent with a single power-law index alpha = 81. The AGN spectra observed with the IPC are compared with those from higher energy experiments, where AGN spectra have power law indices alpha = 0.7. It is found that the IPC spectra are systematically steeper than the HEAO 1 A-2 spectra of the same Seyfert galaxies, indicating a flattening toward higher energies.

Kruper, J. S.↗

The properties of infrared galaxies in the local universe

The 60-micron selected IRAS Bright Galaxy Sample is used as a starting point to derive additional complete flux-limited samples of extragalactic objects at 12, 25, and 100 microns. With these complete samples the luminosity functions at all IRAS wavelengths are derived for the local universe. These luminosity functions are used to determine the infrared emission of the local universe. The maximum in the energy output of galaxies occurs at 100 microns. The infrared emission of galaxies at 12 and 25 micron represents about 30 percent of the total infrared luminosity in the local universe. The mean infrared colors of infrared selected galaxies vary systematically with infrared luminosity; the ratio S sub nu (60 microns)/S sub nu(100 microns) increases and S sub nu(12 microns)/S sub nu(25 microns) decreases with increasing infrared luminosity.

Soifer, B. T.↗

The spatial correlation properties of dark galaxy halos in a CDM universe

We use the Hierarchical Particle Mesh (HPM) N-body code written by J. V. Villumsen (Villumsen, 1989) to investigate the two-point spatial correlation function, xi(r), of dark galaxy halos as a function of halo mass and local environment (i.e. high, low, or average mass density). We assume a standard cold dark matter (CDM) universe (omega = 1, delta = 0, H sub 0 = 50,km/sec/Mpc). Because of the large dynamic ranges in mass and length that can be obtained with the HPM code, it is well-suited to an investigation of this sort.

Brainerd, Tereasa G.↗

Synthetic properties of starburst galaxies

We present the results of an extensive grid of evolutionary synthesis models for populations of massive stars. The parameter space has been chosen to correspond to conditions typically found in objects like giant H II regions, H II galaxies, blue compact dwarf galaxies, nuclear starbursts, and infrared luminous starburst galaxies. The models are based on the most up-to-date input physics for the theory of stellar atmospheres, stellar winds, and stellar evolution. A population of massive stars is not only important in terms of its output of radiation but also via its deposition of mechanical energy. The output of radiative and mechanical luminosity is compared at various starburst epochs. In a supernova dominated instantaneous starburst, the mechanical luminosity can be as large as almost 10% of the total radiative luminosity. This occurs when most massive O stars have disappeared, and the synthetic spectrum in the optical and near-ultraviolet is dominated by B and A stars. During this epoch, the output of ionizing radiation below 912 A becomes very small, as indicated by a very large Lyman discontinuity and a very small ratio of ionizing over mechanical luminosity. We discuss the relevance of these results for the interpretation of starburst galaxies, active galactic nuclei, and the energetics of the interstellar medium.

Leitherer, Claus↗

X-ray properties of normal galaxies

In this paper I will first review briefly the results of the X-ray observations of early-type galaxies with the HEAO 2 (Eisnstein) satellite, published in the past ten years. I will then concentrate on more recent results stemming from a systematic re-analysis of the Einstein galaxy database, and I will also report on some very preliminary ROSAT results. Parts of this talk were given at the ESO Elba meeting on early-type galaxies in May 1992 and therefore there is a considerable overlap between this paper and that in the proceedings of that meeting. Some of this material was also reviewed by Fabbiano and Kim (1992) and Fabbiano (1992b).

Fabbiano, G.↗

Extent of warm haloes around medium-redshift galaxies

The properties of low-to-medium ionization gaseous haloes around galaxies are briefly reviewed. New observations concerning such haloes are presented. For the galaxy-QSO pair in the field of the radio source 3C303, the higher-redshift QSO has been found to show Mg II absorption at the lower redshift of the faint nearby galaxy. Secondly, new data are presented on one of the galaxies in the environment of the well-known BL Lac object AO 0235 + 164.

Burbidge, E. M.↗

A statistical analysis of the Einstein normal galaxy sample. III - Radio and X-ray properties of elliptical and S0 galaxies

Radioastronomy, optical and X-ray data were used to probe the cause of high X-ray luminosities of 28 radio-quiet elliptical galaxies (RQE) and S0 galaxies previously scanned by the Einstein Observatory. Comparisons were made with similar data on double-lobed 3CR galaxies. Radio luminosities were highly correlated with the X-ray luminosities, agreeing with models of radio nuclear sources in early-type galaxies as accreting compact objects. Additionally, 3CR galaxies seemed to be large-scale versions of normal RQE. The significance of interstellar medium/intracluster medium interactions for high correlations between the core and total radio power from X-ray emitting galaxies is discussed.

Fabbiano, G.↗

Quasars: Active nuclei of young galaxies

The hypothetical properties of 'young' galaxies and possible methods of observing them are discussed. It is proposed that star formation first takes place in the central regions of protogalaxies which may appear as quasar-like objects. An evolutionary scheme is outlined in which the radio quasars are transformed in time into the nuclei of radio galaxies.

Komberg, B. V.↗

IRAS observations of starburst galaxies

Far infrared properties of Starburst galaxies were analyzed using IRAS observations at 25, 60, and 100 micrometers. Seventy-nine of 102 Starburst galaxies from the list of Balzano were detected. These galaxies have high IR luminosities of up to a few 10 to the 12th power L sub 0 and concentrate in a small area of the IR color - color diagram. The IR power law spectral indices, alpha, lie within the ranges -2.5 <alpha(60,25)< -1.5 and -1.5 <alpha(100,60)< 0. These observed indices can be interpreted in terms of a cold disk component and a warm component. More than 80% of the 60 micrometer emission comes from the warm component. The fraction of the 60 micrometer emission attributable to the warm component can be used as an activity indicator.

Sekiguchi, Kazuhiro↗

Globular cluster formation in merging galaxies?

The properties of a population of luminous blue clusters in the merging galaxy NGC 3597 are discussed, and the observability of the signature of such a population in later evolutionary stages of a merger is assessed. NGC 3597 is an advanced merger which has already developed into an elliptical-like object with a de Vaucouleurs brightness distribution, but intense star formation is continuing in the central 4 kpc. A population of unresolved blue objects that are concentrated towards the central region is identified as clusters belonging to NGC 3597.

Lutz, D.↗

The photometric properties of brightest cluster galaxies. I - Absolute magnitudes in 116 nearby Abell clusters

Two-color aperture photometry of the brightest galaxies in a complete sample of nearby Abell clusters is presented. The results are used to anchor the bright end of the Hubble diagram; essentially the entire formal error for this method is then due to the sample of distant clusters used. New determinations of the systematic trend of galaxy absolute magnitude with the cluster properties of richness and Bautz-Morgan type are derived. When these new results are combined with the Gunn and Oke (1975) data on high-redshift clusters, a formal value (without accounting for any evolution) of q sub 0 = -0.55 + or - 0.45 (1 standard deviations) is found.

Hoessel, J. G.↗

The Swift Burst Alert Telescope Detected Seyfert 1 Galaxies: X-Ray Broadband Properties and Warm Absorbers

We present results from an analysis of the broadband, 0.3-195 keV, X-ray spectra of 48 Seyfert 1-1.5 sources detected in the very hard X-rays with the Swift Burst Alert Telescope (BAT). This sample is selected in an all-sky survey conducted in the 14-195 keV band. Therefore, our sources are largely unbiased toward both obscuration and host galaxy properties. Our detailed and uniform model fits to Suzaku/BAT and XMM-Newton/BAT spectra include the neutral absorption, direct power-law, reflected emission, soft excess, warm absorption, and narrow Fe I K[alpha] emission properties for the entire sample. We significantly detect O VII and O VIII edges in 52% of our sample. The strength of these detections is strongly correlated with the neutral column density measured in the spectrum. Among the strongest detections, X-ray grating and UV observations, where available, indicate outflowing material. The ionized column densities of sources with O VII and O VIII detections are clustered in a narrow range with Nwarm [approx] 1021 cm-2, while sources without strong detections have column densities of ionized gas an order of magnitude lower. Therefore, we note that sources without strong detections likely have warm ionized outflows present but at low column densities that are not easily probed with current X-ray observations. Sources with strong complex absorption have a strong soft excess, which may or may not be due to difficulties in modeling the complex spectra of these sources. Still, the detection of a flat [Gamma] [approx] 1 and a strong soft excess may allow us to infer the presence of strong absorption in low signal-to-noise active galactic nucleus spectra. Additionally, we include a useful correction from the Swift BAT luminosity to bolometric luminosity, based on a comparison of our spectral fitting results with published spectral energy distribution fits from 33 of our sources.

Winter, Lisa M.↗

H II regions as probes of galaxy evolution and the properties of massive stars

The use of H II regions as probes to study the chemical evolution of galaxies and the spectral properties of hot, massive stars is reviewed. The observable parameters for this task are the physical conditions, elemental abundances, and ionization balance in the ionized gas. Some outstanding uncertainties in the determination of these parameters and some approaches to remedy or circumvent the problems are discussed.

Garnett, Donald R.↗

Future X-ray observations of 'normal' galaxies

The study of the X-ray properties of galaxies is discussed in terms of existing observational results and the capacity for interpreting the data. The NASA Einstein Observatory data is first examined to describe the X-ray properties of spiral and irregular galaxies as well as elliptical and SO galaxies. Issues that remain to be addressed can be explored by studying the X-ray properties of very luminous 'super-Eddington' sources, starburst galaxies, and different phases of the interstellar medium. The specific requirements are set forth for the observatories conducting the research; particular conditions are given for detecting galaxies, high-resolution studies of individual galaxies, bandwidth, spectral studies, and time-variability studies. An ideal X-ray telescope is described based on these conditions, the primary features of which are a collecting area greater than 100 sq m, a large bandwidth, and the capacity for both photometric and spectroscopic investigation.

Fabbiano, Giuseppina↗

A Meeting on the AGN/Galaxy Connection

This grant was used for travel support of several junior astronomers to attend the meeting "The Actice Galactic Nuclei (AGN)/Normal Galaxy Connection", Session El.2 of the 32nd COSPAR Assembly held in Nagoya, Japan, 12-19 July 1998. This meeting included the contributions from both theoretical and observational astronomers to the following fundamental questions: What causes the activity in galaxies? What is the difference between normal and active galaxies? Which processes are responsible for fueling the AGN? Do all galaxies have central Black Holes? What is the difference between low and high luminosity AGN? The observational papers discussed themes like: the detection of the black hole at the nucleus of our Galaxy, as well as in other galaxies; results from surveys of AGN in local galaxies, the source of their activity and their cold gas content; the observations of quasar host galaxies; the properties of Ultraluminous Infrared Galaxies. These papers used data from ground based observatories and several space missions (e.g. ASCA, ROSAT, HST, ISO) in wavebands from radio through gamma-rays. The theoretical papers discussed issues like: mechanisms to fuel the AGN; the physics of the accretion process; the formation of black-holes, quasars and their jets.

Kinney, Anne↗