Evolution Of Early-type Galaxies Research Articles

Dust in high-redshift radio galaxies and the early evolution of spheroidal galaxies

Several lines of evidence suggest that early-type galaxies might have been very dusty during their initial evolutionary stages, characterized by intense star formation activity. The radio selection has provided, by far, the richest samples of high-$z$ galaxies, most likely of early type, which may therefore yield crucial direct information on the period when the bulk of stars were born. In order to investigate the role of dust in these phases, we have analyzed recent observations of a number of high-$z$ radio galaxies in the framework of a self-consistent scenario for the evolution of early type galaxies. The available data can be fully accounted for by ``opaque'' models similar to that already used by Mazzei and De Zotti (1994a) to fit the spectrum of the hyperluminous galaxy IRAS~F$10214+4724$. However, there is still considerable latitude for models. Good fits can be obtained with galactic ages ranging from 0.05 to 2 Gyr. Crucial constraints may be provided by ground-based sub-mm measurements and by observations with the forthcoming Infrared Space Observatory (ISO).

Models for the evolution of the spectral energy distribution of elliptical galaxies from ultraviolet to far-infrared wavelengths

We have worked out evolutionary synthesis models of the broad-band spectral energy distribution of elliptical galaxies over the whole frequency range from UV to far--IR. Internal extinction and far--IR re--emission by interstellar dust have been taken into account in a self--consistent way. Diffuse dust emission has been modelled in terms of two components: warm dust, located in regions of high radiation intensity, and cold dust, heated by the general radiation field. Emission from circumstellar dust clouds at different galactic ages was also taken into account. The models reproduce well the present average broad--band spectrum of nearby ellipticals over about four decades in frequency. Under the assumption of a dust--to--gas ratio proportional to the metallicity, the fraction of bolometric luminosity coming out at far-IR wavelengths strongly evolves during the galaxy lifetime, ranging from very low local values ($\lsim 0.5\%$) to $\sim 30\%$ or more in the first billion years. Some models even imply that early phases are optically thick; these models provide an excellent fit of the observed spectral energy distribution of the high redshift galaxy IRAS F10214$+$4724. Far--IR observations may thus play a key role in investigating the early evolution of elliptical galaxies. A strong far-IR evolution of early-type galaxies might be a crucial ingredient to explain the deep $60\mic$ IRAS counts.

Spectra of galaxies in clusters. II - Models for the spectra of postburst and stripped galaxies

view Abstract Citations (49) References (62) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectra of Galaxies in Clusters. II. Models for the Spectra of Postburst and Stripped Galaxies Newberry, Michael V. ; Boroson, Todd A. ; Kirshner, Robert P. Abstract We have computed models for the spectral evolution of early-type galaxies undergoing starbursts and for a model of a late-type galaxy where stripping halts star formation. The goal of this work is to investigate the peculiar combination of mean Balmer absorption strengths, (H) = 7-8 A, and relatively red color, B-V = 0.74 +/- 0.1, observed in the "E + A" spectra of galaxies in 3C 295 and other high-redshift rich clusters. We find that bursts consuming ~ 3%-8% of the luminous mass of the underlying galaxy match the observed <H> and B-V quite well. These values are also produced by a stripped model which terminates star formation over a time of ~0.1 Gyr or less. Since both types of models match the data, there is no strong reason to reject the stripping picture in favor of starbursts occurring in the densest clusters. We have computed a number of line and band absorption and continuum indices which can be measured in the optical spectra of faint high-redshift galaxies. Bursts having a constant star formation rate of ~ 0.5 Gyr duration cannot be distinguished from the stripped model in any of the indices that were compared. However, bursts that do not form O-B2 stars and have "delayed" star formation can be distinguished from the stripped model in comparisons between <H> and the 4000 A break, H+K, and G band indices. Since the 4000 A break is affected by the internal reddening in a galaxy, the H+K and G band indices are the best discriminators of star formation history. The separation between the various models is not large in any indices and a measurement precision of at least 5% is required to discriminate between them. We suggest that many of the E+A galaxies observed in high-redshift clusters might be recently stripped, while those in the high-redshift field are experiencing starbursts. Publication: The Astrophysical Journal Pub Date: February 1990 DOI: 10.1086/168413 Bibcode: 1990ApJ...350..585N Keywords: Astronomical Spectroscopy; Balmer Series; Galactic Clusters; Galactic Evolution; Star Distribution; Starburst Galaxies; Absorption Spectra; Galactic Radiation; Spectrum Analysis; Star Formation Rate; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: EVOLUTION; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (3) Related Materials (1) Part 1: 1988ApJ...335..629N

Spectral evolution of galaxies. I - Early-type systems

This work develops models for the spectral evolution of early-type galaxies using population synthesis techniques. Different choices of the initial mass function and the star formation rare allow the construction of models which at the present epoch cover the range of observed galaxy spectra. Special emphasis is given to the ultraviolet region of the spectrum. Ultraviolet spectra of late-type stars and early-type galaxies obtained with the International Ultraviolet Explorer satellite are used in this work. The evolving spectral energy distributions are used to compute galaxy colors, magnitudes, K-corrections, and evolutionary corrections as functions of redshift for different photometric systems.