Chemical Evolution Of Elliptical Galaxies Research Articles

The effects of the initial mass function on the chemical evolution of elliptical galaxies

We describe the use of our chemical evolution model to reproduce the abundance patterns observed in a catalog of elliptical galaxies from the SDSS DR4. The model assumes ellipticals form by fast gas accretion, and suffer a strong burst of star formation followed by a galactic wind which quenches star formation. Models with fixed IMF failed in simultaneously reproducing the observed trends with the galactic mass. So, we tested a varying IMF; contrary to the diffused claim that the IMF should become bottom heavier in more massive galaxies, we find a better agreement with data by assuming an inverse trend, where the IMF goes from being bottom heavy in less massive galaxies to top heavy in more massive ones. This naturally produces a downsizing in star formation, favoring massive stars in largest galaxies. Finally, we tested the use of the Integrated Galactic IMF, obtained by averaging the canonical IMF over the mass distribution function of the clusters where star formation is assumed to take place. We combined two prescriptions, valid for different SFR regimes, to obtain the IGIMF values along the whole evolution of the galaxies in our models. Predicted abundance trends reproduce the observed slopes, but they have an offset relative to the data. We conclude that bottom-heavier IMFs do not reproduce the properties of the most massive ellipticals, at variance with previous suggestions. On the other hand, an IMF varying with galactic mass from bottom-heavier to top-heavier should be preferred

The chemical evolution of elliptical galaxies with stellar and QSO dust production

The presence of dust strongly affects the way we see galaxies and also the chemical abundances we measure in gas. It is therefore important to study he chemical evolution of galaxies by taking into account dust evolution. We aim at performing a detailed study of abundance ratios of high redshift objects and their dust properties. We focus on Lyman-Break galaxies (LBGs) and Quasar (QSO) hosts and likely progenitors of low- and high-mass present-day elliptical galaxies, respectively. We have adopted a chemical evolution model for elliptical galaxies taking account the dust production from low and intermediate mass stars, supernovae Ia, supernovae II, QSOs and both dust destruction and accretion processes. By means of such a model we have followed the chemical evolution of ellipticals of different baryonic masses. Our model complies with chemical downsizing. We made predictions for the abundance ratios versus metallicity trends for models of differing masses that can be used to constrain the star formation rate, initial mass function and dust mass in observed galaxies. We predict the existence of a high redshift dust mass-stellar mass relationship. We have found a good agreement with the properties of LBGs if we assume that they formed at redshift z=2-4. In particular, a non-negligible amount of dust is needed to explain the observed abundance pattern. We studied the QSO SDSS J114816, one of the most distant QSO ever observed (z=6.4), and we have been able to reproduce the amount of dust measured in this object. The dust is clearly due to the production from supernovae and the most massive AGB stars as well as from the grain growth in the interstellar medium. The QSO dust is likely to dominate only in the very central regions of the galaxies and during the early development of the galactic wind.

JD8 - Hot Interstellar Matter in Elliptical Galaxies

The physical properties of the hot interstellar matter in elliptical galaxies are directly related with the formation and evolution of elliptical galaxies via star formation episodes, environmental effects such as stripping, infall, and mergers, and growth of super-massive black holes. The recent successful Chandra and XMM-Newton X-ray space missions have provided a large amount of high spatial/spectral resolution observational data on the hot ISM in elliptical galaxies. At the same time, theoretical studies with numerical simulations and analytical modeling of the dynamical and chemical evolution of elliptical galaxies have made a significant progress and start to predict various observable quantities.

A possible theoretical explanation of metallicity gradients in elliptical galaxies

ABSTRA C T Models of chemical evolution of elliptical galaxies taking into account different escape velocities at different galactocentric radii are presented. As a consequence of this, the chemical evolution develops differently in different galactic regions; in particular, we find that the galactic wind, powered by supernovae (of Type II and I) starts, under suitable conditions, in the outer regions and successively develops in the central ones. The star formation is assumed to stop after the onset of the galactic wind in each region. The main result found in the present work is that this mechanism is able to reproduce metallicity gradients, namely the gradients in the Mg2 index, in good agreement with observational data. We also find that in order to honour the constant ΩhMg=Feiy ratio with galactocentric distance, as inferred from metallicity indices, a variable initial mass function as a function of galactocentric distance is required. This is only a suggestion, as trends on abundances inferred purely from metallicity indices are still uncertain.

Stellar Populations in Gas‐rich Galaxy Mergers. I. Dependence on Star Formation History

We investigate the nature of stellar populations of major galaxy mergers between late-type spirals with considerably abundant interstellar medium by performing numerical simulations designed to solve both the dynamical and chemical evolution of the mergers in a self-consistent manner. We particularly consider that the star formation history of galaxy mergers is a crucial determinant of the nature of stellar populations of merger remnants, and therefore we investigate how the difference in star formation history between galaxy mergers affects the chemical evolution of galaxy mergers. We found that the rapidity of star formation, which is defined as the ratio of the dynamical timescale to the timescale of gas consumption by star formation, is the most important determinant for a number of fundamental characteristics of stellar populations of merger remnants. The main results obtained in this study are the following. 1. A galaxy merger with more rapid star formation becomes elliptical with larger mean metallicity. This is primarily because, in the merger with more rapid star formation, a smaller amount of metal-enriched gas is tidally stripped away during merging, and, consequently, a larger amount of the gas can be converted to stellar components. This demonstrates that the cause of the color-magnitude relation of elliptical galaxies can be closely associated with the details of merging dynamics that depend on the rapidity of star formation in galaxy mergers. 2. A negative metallicity gradient fitted reasonably well by a power law can be reproduced by a dissipative galaxy merger with star formation. The magnitude of the metallicity gradient is larger for an elliptical galaxy formed by a galaxy merger with less rapid star formation. 3. The absolute magnitude of the metallicity gradient correlates with that of the age gradient in galaxy mergers in the sense that a merger remnant with a steeper negative metallicity gradient is more likely to show a steeper age gradient. 4. The outer part of a stellar population is both older and less metal-enriched than the nucleus in an elliptical galaxy formed by a galaxy merger with less rapid star formation. Moreover, the metallicity of the outer part of the gaseous component for some models with less rapid star formation is appreciably smaller than the stellar metallicity. This result implies that the origin of metal-poor hot gaseous X-ray halos in real elliptical galaxies can essentially be ascribed to the dynamics of dissipative galaxy merging. 5. Irrespective of the rapidity of star formation, the epoch of galaxy merging affects both the mean stellar metallicity and the mean stellar age of merger remnants: later galaxy mergers are more likely to become ellipticals with both younger and more metal-enriched stellar populations. This result reflects the fact that in the later mergers, a larger amount of more metal-enriched interstellar gas is preferentially converted into stars during the later period of star formation triggered by galaxy merging. These five results clearly demonstrate that even the chemical evolution of elliptical galaxies can be strongly affected by the details of dynamical evolution of galaxy merging, which are furthermore determined by the rapidity of star formation of galaxy mergers. In particular, tidal stripping of interstellar gas and the total amount of gaseous dissipation during galaxy merging are demonstrated to play vital roles in determining a number of chemical properties of merger remnants. Based on these results, we adopt a specific assumption of luminosity dependence on rapidity of star formation and thereby discuss how successfully the present merger model can reproduce a number of fundamental chemical, photometric, and spectroscopic characteristics of elliptical galaxies.

Metal enrichment in elliptical galaxies and globular clusters through the study of iron and H-Beta spectral indices

view Abstract Citations (71) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Metal enrichment in elliptical galaxies and globular clusters through the study of iron and H-beta spectral indices. Buzzoni, A. ; Mantegazza, L. ; Gariboldi, G. Abstract Chemical evolution of elliptical galaxies and globular clusters is addressed through a combined study of the iron indices at 5270 and 5335 A, and of the H-Beta line strength. The observational database of 74 standard stars (both dwarfs and giants) referred to in a previous paper (Buzzoni et al. (1992)) complemented with the data of Faber et al. (1985) and Gorgas et al. (1993) allowed us to explore here Fe and H-Beta index dependence on stellar temperature, gravity, and metallicity. The derived fitting functions were then included into Buzzoni's (1989) code for population synthesis in order to derive expected integrated indices for simple stellar populations and compare with observations. Partition of metals in the current chemical mix of galaxies and globulars has been constrained supporting the claim that light alpha elements might be enhanced in the globular cluster metal-poor population. An alternative conclusion resting on the standard framework with (alpha/Fe) = 0 would require a systematically larger age, about 18-20 Gyr. Iron and magnesium in ellipticals are found in average solar but a systematic trend of (Mg/Fe) vs global metallicity does exist with iron more deficient with respect to magnesium at high Z. We conclude that this effect might indicate that Fe abundance per unit mass in the galaxies is constant (suggesting a constant rate per unit mass of SN I events) while light metals supplied by SNe II should have been more effectively enriched with increasing galactic total mass. Publication: The Astronomical Journal Pub Date: February 1994 DOI: 10.1086/116873 Bibcode: 1994AJ....107..513B Keywords: Chemical Evolution; Dwarf Stars; Elliptical Galaxies; Galactic Evolution; Giant Stars; Globular Clusters; H Beta Line; Iron; Metallicity; Stellar Composition; Stellar Gravitation; Stellar Spectra; Stellar Temperature; Astronomical Spectroscopy; Galactic Mass; Mass Distribution; Stellar Models; Astronomy full text sources ADS | data products SIMBAD (93)

The influence of dark matter on the chemical evolution of elliptical galaxies

We have computed detailed models for the chemical evolution of elliptical galaxies in the presence of dark matter. These models assume that a galactic wind develops as a result of the energy injection into the gas by supernovae, and that no star formation takes place afterward. We have found that the occurrence of galactic winds is strongly affected by the presence of dark matter if this is distributed like the luminous one

Synthetic colors and the chemical evolution of elliptical galaxies

Detailed photometric and chemical evolution models for elliptical galaxies of various initial masses are presented. The observed color-magnitude diagrams and the mass-metallicity relation are well reproduced. In particular, the mass-metallicity relation is obtained by computing the detailed evolution of the abundances of Fe. Particular attention is given to interpreting the UV excess observed in ellipticals and its behavior as a function of the metal content of these galaxies. It is suggested that the UV excess in ellipticals is determined mainly by metal-rich stars, which do not experience any thermal pulsing phase during their advanced evolution following the horizontal branch phase and which leave the AGB well before the onset or the thermal pulses. It is shown that this scenario is well-grounded, and that above a critical metallicity the masses of the stars in the post-early AGB phase are lower for larger metallicities. 76 refs.

The metal abundance range in the Ursa Minor dwarf galaxy

A small sample of red giants in the Ursa Minor dwarf spheroidal galaxy has been observed with the multichannel scanner and the digital spectrograph of the Hale 5 m telescope. These observations confirm the large width of the giant branch in the color-magnitude diagram and indicate that it is caused by a range in metal abundance of approx.1 dex (i.e., -2.55< or approx. =(Fe/H)< or approx. =-1.36, according to Cohen's scale for globular clusters). Ursa Minor and the Draco dwarf spheroidal appear to have very similar ranges in metal abundance. These observations and those of the other dwarf spheroidal galaxies are compared with the models of the chemical evolution of elliptical galaxies that include mass loss. The models are consistent with the dispersions in metal abundance that are found in the dwarf spheroidals, but now with the lack of detectable dispersions in globular clusters that are comparable in mass to Ursa Minor and Draco (e.g., M92). Some explanations for this difference between the galaxies and the clusters are discussed.