Galaxy Evolution Through the Cosmic Time (original) (raw)
Related papers
Chemical and photometric evolution of elliptical galaxies
Space Science Reviews, 1994
In this paper we present the new chemical-spectro-photometric models of population synthesis by Bressan, Chiosi & Fagotto (1993). The models are specifically designed for elliptical galaxies. They include the presence of dark matter and galactic winds triggered by the energy deposit from supernovae and winds of massive stars. The models are aimed at studying the UVexcess and its dependence on the metallicity, the color-magnitude relation, and the color evolution as a function of the redshift. It is shown that in order to explain the color-magnitude relation as a result of galactic winds, the energy input from massive stars is required. Supernovae alone cannot provide sufficient energy to start galactic wind before the metallicity and hence colors have got saturated. We show that the main source of the UV-excess are the old, hot HI3 and AGB manque stars of high metallicity present in varying percentages in the stellar content of a galaxy. Since in our model the mean and maximum metallicity are ultimately driven by the mass of the galaxy, this provides a natural explanation for the Observed correlation between UV-excess and metallicity. Finally, looking at the color evolution as function of the redshift, we suggest that a sudden change occurring in the color (1550-V) at the onset of the old, hot HB and AGB manque stars of high metallicity, is a good age indicator. The detection of this feature at a certain redshift would impose firm constraints on the underlying cosmological model of the universe.
Photochemical evolution of elliptical galaxies - I. The high-redshift formation scenario
Monthly Notices of the Royal Astronomical Society, 2004
In this paper we compute new multi-zone photo-chemical evolution models for elliptical galaxies, taking into account detailed nucleosynthetic yields, feedback from supernovae and an initial infall episode. By comparing model predictions with observations, we derive a picture of galaxy formation in which the higher is the mass of the galaxy, the shorter are the infall and the star formation timescales. Therefore, in this scenario, the most massive objects are older than the less massive ones, in the sense that larger galaxies stop forming stars at earlier times. Each galaxy is created outside-in, i.e. the outermost regions accrete gas, form stars and develop a galactic wind very quickly, compared to the central core in which the star formation can last up to ∼ 1.3 Gyr. In particular, we suggest that both the duration of the star formation and the infall timescale decrease with galactic radius. In order to convert theoretical predictions into line-strength indices, different calibrations are adopted and discussed, focussing in particular on their dependence on the α−enhancement.
The Astrophysical Journal Supplement Series, 1994
In this paper we present new chemo-spectrophotometric models of elliptical galaxies in which infall of primordial gas is allowed to occur. They aim to simulate the collapse of a galaxy made of two components, i.e. luminous material and dark matter. The mass of the dark component is assumed to be constant in time, whereas that of the luminous material is supposed to accrete at a suitable rate. They also include the effect of galactic winds powered by supernova explosions and stellar winds from massive, early-type stars. The models are constrained to match a number of properties of elliptical galaxies, i.e. the slope and mean colours of the colour-magnitude relation (CMR), V versus (V-K), the UV excess as measured by the colour (1550-V) together with the overall shape of the integrated spectral energy distribution (ISED) in the ultraviolet, the relation between the Mg 2 index and (1550-V), the mass to blue luminosity ratio M/L B as a function of the B luminosity, and finally the broad-band colours (U-B), (B-V), (V-I), (V-K), etc. The CMR is interpreted as a mass-metallicity sequence of old, nearly coeval objects, whose mean age is 15 Gyr. Assuming the law of star formation to be proportional to M k g (t) with k = 1, the rate of star formation as function of time starts small, grows to a maximum, and then declines thus easily avoiding the excess of metal-poor stars found by BCF with the closed-box scheme (the analog of the G-Dwarf Problem in the solar vicinity). Owing to their stellar content, infall models can easily reproduce all the basic data of the galaxies under examination. As far as the UV excess is concerned, the same sources proposed by BCF are found to hold also with the infall scheme. H-HB and AGB manqué stars of high metallicity play the dominant role, and provide a robust explanation of the correlation between the (1550-V) colour and the luminosity, mass and metallicity of the galaxies. Furthermore, these models con-⋆ Send offprint requests to: C. Chiosi firm the potential of the (1550-V) colour as an age indicator in cosmology as already suggested by BCF. In the rest frame of a massive and metal-rich elliptical galaxy, this colour suffers from one major variation: at the onset of the so-called H-HB and AGB-manqué stars (age about 5.6 Gyr). This transition occurs at reasonably small redshifts and therefore could be detected with the present-day instrumentation.
Late Stages of Stellar Evolution and their Impact on Spectrophotometric Properties of Galaxies
2007
The connection between AGB evolution of stellar populations and infrared vs. ultraviolet properties of the parent galaxies is reviewed relying on the updated lookout provided by population-synthesis theory. In particular, planetary-nebula events and hot horizontal-branch evolution are assessed in a unitary view to outline a plain general picture of galaxy spectrophotometric evolution. This will include a brief discussion of relevant phenomena such as the ``UV upturn'' in ellipticals and the stellar mass loss properties along the galaxy morphological sequence.
The Evolution of Stellar Populations
The Evolution of Galaxies, 2001
We summarize the discussion section on "Evolution of Stellar Populations" we led on May 27, 2000 in Granada, Spain, as part of the Euroconference on The Evolution of Galaxies. I-Observational Clues. The discussion was organized around two groups of topics. In the first, Population Synthesis, the accent was partially placed on the use of tools and techniques centered around the question of the unicity of the models, their sensitivity to input and the question of the age-metallicity degeneracy. In the second group, Stellar Systems a stronger accent was placed on astrophysical questions, although we included there the need for "truth tests" that apply spectral synthesis techniques to objects for which there is detailed a priori knowledge of their stellar populations. We also provide a partial comparison between the present knowledge of these topics and that which existed at the time of the Crete Conference of 1995.
The Astrophysical Journal Supplement Series, 1997
We have developed a new stellar population synthesis model designed to study earlytype galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations or follow the galaxy through its evolution from an initial gas cloud to the present time. The model incorporates the new isochrones of the Padova group and the latest stellar spectral libraries. We have applied our model to new data for a set of three early-type galaxies, to find out whether these can be fitted using single-age old metal-rich stellar populations, as is normal practice when one uses other stellar models of this kind. The model is extensively compared with previous ones in the literature to establish its accuracy as well as the accuracy of this kind of models in general. Using the evolutionary version of the model we find that we cannot fit the most metal-rich elliptical galaxies if we keep the IMF constant and do not allow infall of gas. We do however reproduce the results of Arimoto & Yoshii (1986) for the evolution of the gas, and produce colors, and, for the first time with this type of models, absorption line-strengths. It is in fact possible to fit the data for the elliptical galaxies by varying the IMF with time. Our numerical model is in good broad agreement with the analytical simple model. We prefer however to calculate the evolution of the gas numerically instead of using the simple model, since it offers more flexibility, and even improved insight, when comparing with observations. In the present paper we describe the model, and compare a few key observables with new data for three early-type standard galaxies. However the data, as well as our fits, will be discussed in much more detail in a second paper (Vazdekis et al. 1996), where some conclusions will be drawn about elliptical galaxies on the basis of this model.
Dwarf elliptical galaxies: structure, star formation and colour-magnitude diagrams
Monthly Notices of the Royal Astronomical Society, 2001
The aim of this paper is to cast light on the formation and evolution of elliptical galaxies by means of N-body hydrodynamical simulations that include star formation, feedback and chemical evolution. Particular attention is paid to the case of dwarf spheroidals of the Local Group which, thanks to their proximity and modern ground-based and space instrumentation, can be resolved into single stars so that independent determinations of their age and star formation history can be derived. Indeed, the analysis of the colour-magnitude diagram of their stellar content allows us to infer the past history of star formation and chemical enrichment, thus setting important constraints on galactic models. Dwarf galaxies are known to exhibit complicated histories of star formation ranging from a single very old episode to a series of bursts over most of the Hubble time. By understanding the physical process driving star formation in these objects, we might be able to infer the mechanism governing star formation in more massive elliptical galaxies. Given these premises, we start from virialized haloes of dark matter, and follow the infall of gas into the potential wells and the formation of stars. We find that in objects of the same total mass, different star formation histories are possible, if the collapse phase started at different initial densities. We predict the final structure of dwarf spheroidal galaxies, their kinematics, their large-scale distribution of gas and stars, and their detailed histories of the star formation and metal enrichment. Using a population synthesis technique, star formation and metal enrichment rates are then adopted to generate the present colour-magnitude diagrams of the stellar populations hosted by dwarf spheroidal galaxies. The simulations are made assuming the redshift of galaxy formation z for ¼ 5 and varying the cosmological parameters H 0 and q 0. The resulting colour-magnitude diagrams are then compared with the observational ones for some dwarf spheroidals of the Local Group.
The star formation histories of elliptical galaxies across the Fundamental Plane
Monthly Notices of the Royal Astronomical Society, 2007
We present the first results from a study designed to test whether, given high-quality spectrophotometry spanning the mid-ultraviolet-optical wavelength regime, it is possible to distinguish the metal content and star-formation history of individual elliptical galaxies with sufficient accuracy to establish whether their formation history is linked to their detailed morphology and position on the Fundamental Plane.
A New Chemo-evolutionary Population Synthesis Model for Early-Type Galaxies. I. Theoretical Basis
The Astrophysical Journal Supplement Series, 1996
We have developed a new stellar population synthesis model designed to study earlytype galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations or follow the galaxy through its evolution from an initial gas cloud to the present time. The model incorporates the new isochrones of the Padova group and the latest stellar spectral libraries. We have applied our model to new data for a set of three early-type galaxies, to find out whether these can be fitted using single-age old metal-rich stellar populations, as is normal practice when one uses other stellar models of this kind. The model is extensively compared with previous ones in the literature to establish its accuracy as well as the accuracy of this kind of models in general. Using the evolutionary version of the model we find that we cannot fit the most metal-rich elliptical galaxies if we keep the IMF constant and do not allow infall of gas. We do however reproduce the results of Arimoto & Yoshii (1986) for the evolution of the gas, and produce colors, and, for the first time with this type of models, absorption line-strengths. It is in fact possible to fit the data for the elliptical galaxies by varying the IMF with time. Our numerical model is in good broad agreement with the analytical simple model. We prefer however to calculate the evolution of the gas numerically instead of using the simple model, since it offers more flexibility, and even improved insight, when comparing with observations. In the present paper we describe the model, and compare a few key observables with new data for three early-type standard galaxies. However the data, as well as our fits, will be discussed in much more detail in a second paper (Vazdekis et al. 1996), where some conclusions will be drawn about elliptical galaxies on the basis of this model.
The Stellar Population Histories of Local Early-Type Galaxies. I. Population Parameters
2000
Accepted for publication in the Astronomical Journal This paper commences a series of investigations into the stellar populations of local elliptical galaxies as determined from their integrated spectra. The goal of the series is to determine the star formation and chemical evolution histories of present-day elliptical galaxies. The primary galaxy sample analyzed is that of González (1993, G93), which consists of 39 ellipticals drawn primarily from the local field and nearby groups, plus the bulge of Messier 31. Single-stellar-population (SSP) equivalent ages, metallicities, and abundance ratios are derived from Hβ, Mgb, and 〈Fe 〉 line strengths using an extension of the Worthey (1994) models that incorporates non-solar line-strength “response functions ” by Tripicco & Bell (1995). These functions account for changes in the Lick/IDS indices caused by non-solar abundance ratios, allowing us to correct the Worthey (1994) models for the enhancements of Mg and other α-like elements rela...