Chemical Evolution Of Galaxies Research Articles

Chemical Constraints, Baryonic Mass and the Chemical Evolution of Low Surface Brightness Galaxies

AbstractA brief review of primordial helium and deuterium abundances suggests a baryonic mass density of ΩB ≈ 0.04 – 0.045 (for Ho = 70). This mass may be dominated by intergalactic gas in clusters and groups of galaxies. The observed low chemical abundances in evolved dwarf galaxies might suggest that outflow was the origin for such gas, and we make general suggestions for the interpretation of the data from the next generation of X-ray spectroscopic satellites. The effects of both outflow and inflow on the chemical evolution of galaxies is discussed, particularly in the context of low surface brightness galaxies, and we comment on their dust content.

Investigations of Environmental Effects in Clusters of Galaxies Using N-Body Simulations

In order to investigate cluster evolutionary effects we present a new chemo-dynamical model. The model takes into account N-body simulations, modified for galaxy-galaxy binary encounters. The model incorporates also the codes for spectrophotometric and chemical evolution of galaxies. In the same time the calculations include the interaction between two merging subclusters.

Nucleosynthesis and chemical evolution of galaxies

Nucleosynthesis and chemical evolution of galaxies

Surveys for Metal-Poor Stars in the Galaxy: A New Window on the Low-Abundance Universe

Measurement of the abundances of the light and heavy elements in stars of the Milky Way galaxy is the cornerstone for the study of numerous aspects of chemical evolution in galaxies and the Universe. We stand poised to enter an era of rapid understanding, as new-generation telescopes with apertures in the 8m-10m class enable astronomers to obtain high-resolution, high-signal-to-noise near-UV, optical, and IR spectra of the stars which have locked up the chemical history of our Galaxy in their outer atmospheres. It is thus appropriate to review present surveys for the low-metallicity stars of our Galaxy, as the stars we uncover today will be studied so intensively in the coming decades.

Soft X‐Ray Lines and Gas Composition in NGC 1068

Previous X-ray and ultraviolet spectroscopy suggested that the Fe/O abundance ratio in NGC 1068 may be abnormally high. We have tested this suggestion by measuring and modeling the ASCA spectrum of NGC 1068. We have measured some 15 X-ray lines, to an accuracy better than a factor of 2, and modeled the continuum in two different ways. The first assumes that the hard X-ray continuum is the reflection of the nuclear source by two extended, photoionized gas components; a warm (T ~ 1.5 × 105 K) gas and a hot (T ~ 3 × 106 K) gas. All the observed emission lines are produced in this gas, and there is an additional, extended 0.6-3 keV pure continuum component. The model is similar to the one proposed by Marshall et al. (1993). The second model is a combination of a hard reflected continuum with a soft thermal plasma component. The calculations show that the emission lines in the photoionized gas model are in very good agreement with the observed ones assuming solar metallicity for all elements except for iron, which is more than twice solar, and oxygen, which is less than 0.25 solar. Models with solar oxygen are possible if the 0.5-1 keV continuum is weaker, but they do not explain the magnesium and silicon lines. The thermal model fit requires extremely low metallicity (0.04 solar) for all elements. We discuss these findings and compare them with the ASCA spectra of recently observed starburst galaxies. We argue that the apparent low metallicity of starburst galaxies, as well as of the extended nuclear source in NGC 1068, are inconsistent with galaxy chemical evolution. The explanation for this apparent anomaly is still unknown and may involve nonthermal continuum mechanisms and, in some cases, depletion onto grains. Given the strong H-like and He-like lines, as well as the prominent Fe L emission features, the origin of the soft X-ray lines in this source is more likely photoionized gas. We compare our model with the recent Iwasawa, Fabian, & Matt (1997) paper. We also show that fluorescence lines of low-Z elements in AGNs are likely to be stronger than previously assumed.

Extinction Effects on Galaxy Counts for Bulge‐Disk Galaxies

We examine extinction effects of interstellar dust on galaxy counts for bulge-disk galaxies. Evolution of dust mass is calculated simultaneously with galaxy chemical evolution equations under the context of the so-called infall model, and three-dimensional radiative transfer calculation is performed with scattering effects. Prevailing importance of the bulge on dust mass evolution and photometric appearance in the early formation epoch of spiral galaxies is demonstrated. We here present the galaxy number-magnitude relation, N(m), in the B and K bands and the number-redshift relation, N(z), in the B band with internal absorption taken into account. We confirm that N(m) is differently affected by evolution and extinction between the B and K bands, and that the K band is more suitable to distinguish q0 values. We find that in the B band the extinction effects give a drastic change in N(m) in such a way that N(m) looks as if galaxies show only mild luminosity evolution. Three kinds of models—evolutionary, evolutionary with dust, and nonevolutionary—can be most clearly distinguished from the observations of N(z) in z = 0.8-1.2 in the range of magnitude B = 20-24. We conclude that the dusty evolution model of galaxies with properly adopted parameters can better satisfy both N(m) and N(z) distributions simultaneously than the others.

The evolution of massive stars

Massive stars are the crossroads of many important astrophysical problems and thus a proper understanding of their evolution is very needed. They are the main sources of UV radiation, by heating the interstellar dust they produce the far-IR luminosities of galaxies. They are the precursors of Supernovae and also the main sources of nucleosynthesis. They are visible in distant galaxies and the recent observations of starbursts have shown their major role in the spectral and chemical evolution of galaxies. They begin to be observed in the galactic center and in regions of star formation around galactic nuclei.

The effects of cluster environment on the chemical evolution of galaxies -- III. NGC 753

We present new long-slit spectrophotometric measurements of 10 giant H II regions located in the Virgo spiral NGC 4254. Gradients in the emission-line ratios log R 23 , log [N II]/[O II] and log [S II]/[O II] are observed and provide the constraints for a photoionization analysis to determine disc abundance patterns for O/H, N/H and S/H. We find that log O/H+12=9.52(±0.1)−0.27(±0.05)ρ/ρ eff ; log N/H=8.62(±0.1)−0.38(±0.05)ρ/ρ eff ; and log S/H=7.70(±0.1)−0.27(±0.05)ρ/ρ eff . Adopting a distance of 18 Mpc to NGC 4254, the slopes become −0.06, −0.08 and −0.06 dex kpc −1 , respectively. The value of log O/H at the nucleus indicates that the disc of NGC 4254 has a very high metallicity relative to other spirals in its morphological class

Evolution of Spiral Galaxies. VI. Radial Distributions of Abundances in External Galaxies

The multiphase model of Ferrini and coworkers has been used to study the evolution of six spiral galaxies of different morphological types. This kind of model has been successfully applied to describe the chemical evolution of the solar neighborhood, the whole Galactic disk, and the bulge of the Galaxy in the first five papers of this series. The present study constitutes an extension of our previous work to spiral galaxies other than our own, with a twofold goal: the investigation of the possible relation between the chemical evolution of galaxies and their classification, and the possibility of applying a unique evolutionary scheme to all galaxies. The comparison of results with the observed abundance gradients indicates that these are determined by a fundamental imprint that arises from an early phase of the evolution of a given galaxy: the initial mass of the protogalaxy and its spatial dIstribution. This suggests a connection between the present abundance gradient and the formation process of a spiral galaxy through the collapse of material forming the disk.

Chemical and Dynamical History of the Milky Way

F-G dwarf stars of different metallicity are used as tracers of chemical and dynamical history of the Galaxy. Observed ratios of element abundances “[X/Fe] versus [Fe/H]” (where “X” is a some of chemical element) are compared with theoretical ones and allow us to make the choice between models (or parameters of theoretical models) of the Galaxy chemical evolution, nucleosynthesis and processes of star formation. Our experience has shown (Bikmaev, 1991, 1994a,b; Bikmaev et al., 1990) that in some cases classical approaches in abundance determination are affected by methodical uncertainties and the spread in [X/Fe] ratios may be large even if high quality spectra used.

The Rate of Supernovae in Normal Galaxies

The rate of supernovae (SNe) is a key number linking stellar evolution with galaxy evolution models. Stellar evolution theories predict life times, fates and nucleosysntesis yields of individual stars which are used to predicted the galaxy chemical evolution once the star formation history in the galaxy is known. Constraints to the models are the present chemical content of galaxies but also the present observed SN rate (Arimoto & Yoshi, 1987; Ferrini & Poggianti, 1993; Matteucci, 1994; Renzini et al., 1993; Bressan et al., 1994; Elbaz et al., 1995).

On the relation among metallicity, age, and galactocentric distance of globular clusters

Abstract Using the least-square solution, we have derived an equation relating metallidty of a globular cluster to its age and galactocentric distance. We discuss the possibility to use this equation for studies of the Galaxy's chemical evolution.

The First Generation of Stars: First Steps toward Chemical Evolution of Galaxies

We argue that extreme metal-poor stars show a high dispersion in metallicity, because their abundances are the outcome of very few supernova events. Abundance anomalies should appear because of the discrete range of progenitor masses. There is a natural metallicity threshold of Z/Z☉ ~ 10-4 below which one would expect to find very few, if any, halo stars. Similar reasoning is applied to lower mass systems, such as metal-poor compact blue galaxies and Lyman-alpha absorption-line clouds seen toward high-redshift quasars, where a somewhat higher threshold is inferred.

General constraints on the effect of gas flows in the chemical evolution of galaxies - II. Radial flows and abundance gradients

General constraints on the effect of gas flows in the chemical evolution of galaxies - II. Radial flows and abundance gradients

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 effects of cluster environment on the chemical evolution of galaxies - II. NGC 4254

The effects of cluster environment on the chemical evolution of galaxies - II. NGC 4254

Thresholds and the chemical evolution of galactic discs - II. Radial flows

We introduce radial flows into the chemical evolution models of Chamcham, Pitts & Tayler. In this work, the authors used a stability criterion in disc galaxies to define a threshold for star formation and to deduce a self-consistent star formation rate by combining an energy equation for the gas with the standard equations for the chemical evolution of galaxies. These models reproduced the general observable features of spiral galaxies and of the solar neighbourhood, but failed to reproduce the metallicity gradients observed in most galaxies. A biased infall rate increased the gradient, but not sufficiently to correspond with some observations. If the disc is formed out of centrifugal equilibrium, the resulting radial flows will also enhance the composition gradient, as is shown in the present paper

The chemical evolution of galaxies

The chemical evolution of galaxies is discussed starting with the simple box model. It is shown that this model with the additional assumption of metal-rich outflow provides a first useful insight into the chemical evolution of different stellar populations. More detailed models of galactic nucleosynthesis are then investigated which take into account galactic dynamics, noninstantaneous recycling and incomplete mixing. The implications of noninstantaneous recycling on the evolution of the element abundances in the galactic halo are discussed and constraints on the evolutionary time-scales of the halo are derived. Finally a model for the formation of the galactic halo is presented which takes into account local enrichment and incomplete mixing between different gas phases.

The effects of cluster environment on the chemical evolution of galaxies - I. NGC 4303

We present new spectrophotometric observations extending from 3610–9400 Å of 12 giant H II regions located in the disc of NGC 4303. The following three line ratios exhibit definite gradients across the disc: the metallicity index R23, [N II]/[O II], and [N II]/[S II]. By assuming a set of abundance gradients as input, we have computed a sequence of photoionization models which simultaneously predicts all three ratios over the observed portion of the galaxy disc, permitting us to infer accurate abundance information for nitrogen, oxygen, and sulphur. All three of these elements exhibit negative gradients with slope values which are close to those measured in many other spirals. In addition, N/O increases, and S/O decreases with an increase of O/H, respectively. The observed oxygen and sulphur gradients are explained well by a closed-box model of chemical evolution, while the gradient for nitrogen is steeper than simple model predictions. A comparison of R23 and O/H gradients derived in this paper with published values for two other Virgo spirals and five well-observed field objects indicates that the cluster and field spirals are indistinguishable in terms of their abundance properties.

The origin of the quasi-stellar object absorption lines

view Abstract Citations (15) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Origin of the Quasi-stellar Object Absorption Lines Viegas, S. M. ; Gruenwald, R. B. Abstract In recent years, several results concerning the QSO absorption-line systems indicate the possibility that they may be associated with star- forming regions in intervening galaxies. In this paper, we explore the hypothesis that the metal absorption lines are produced in H II regions of intervening galaxies. Our method of analysis is mainly based on the C IV and Si IV absorption lines. A comparison between observed and calculated equivalent widths fix the characteristics of the absorbing H II region (ionizing star, gas density, and chemical abundances). The calculated equivalent widths are obtained from column densities given by photoionization models. The column densities are calculated for different lines of sight crossing the H II region at different distances from the star. The analysis of 20 absorption line systems shows that H II regions in intervening galaxies can be the origin of the metal-line absorption systems. This model provides promising consequences concerning star formation rates and chemical evolution of galaxies. Publication: The Astrophysical Journal Pub Date: August 1991 DOI: 10.1086/170335 Bibcode: 1991ApJ...377...39V Keywords: Absorption Spectra; Galactic Evolution; H Ii Regions; Line Spectra; Quasars; Interacting Galaxies; Lyman Alpha Radiation; Star Formation Rate; Astrophysics; GALAXIES: EVOLUTION; NEBULAE: H II REGIONS; QUASARS full text sources ADS | data products NED (35) SIMBAD (15)