Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userChemically consistent evolution of galaxies: II. Spectrophotometric evolution from zero to high redshift
58
0
0.0
(
0
)
Authors
Jens Bicker
Ask ChatGPT about the research
No Arabic abstract
We present a new generation of chemically consistent evolutionary synthesis models for galaxies of various spectral types from E through Sd. The models follow the chemical enrichment of the ISM and take into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary isochrones, spectra and yields. Our first set of closed-box 1-zone models does not include any spatial resolution or dynamics. For a Salpeter initial mass function (IMF) the star formation rate(SFR) and its time evolution are shown to successfully parameterise spectral galaxy types E, ..., Sd. We show how the stellar metallicity distribution in various galaxy types build up with time to yield after $sim 12$ Gyr agreement with stellar metallicity distributions observed in our and other local galaxies. The models give integrated galaxy spectra over a wide wavelength range (90.9AA - 160$mu$m), which for ages of $sim 12$ Gyr are in good agreement not only with observed broad band colours but also with template spectra for the respective galaxy types. Using filter functions for Johnson-Cousins, as well as for HST broad band filters in the optical and Bessel & Bretts NIR filter system, we calculate the luminosity and colour evolution of model galaxies over a Hubble time. Including a standard cosmological model and the attenuation by intergalactic hydrogen we present evolutionary and cosmological corrections as well as apparent luminosities in various filters over the redshift range from z $sim 5$ to the present for our galaxy types and compare to earlier models using single (=solar) metallicity input physics only. We also present a first comparison of our cc models to HDF data.(Abridged abstract)
rate research
Read More
We explore the implications for the high redshift universe of ``state-of-the-art models for the chemical and spectrophotometric evolution of spiral galaxies. The models are based on simple ``scaling relations for discs, obtained in the framework of Cold Dark Matter models for galaxy formation, and were ``calibrated as to reproduce the properties of the Milky Way and of nearby discs (at redshift z~0). In this paper, we compare the predictions of our ``hybrid approach to galaxy evolution to observations at moderate and high redshift. We find that the models are in fairly good agreement with observations up to z~1, while some problems appear at higher redshift (provided there is no selection bias in the data); these discrepancies may suggest that galaxy mergers (not considered in this work) played a non negligible role at z>1. We also predict the existence of a ``universal correlation between abundance gradients and disc scalelengths, independent of redshift.
We study the chemical and spectro-photometric evolution of galactic disks with detailed models calibrated on the Milky Way and using simple scaling relations, based on currently popular semi-analytic models of galaxy formation. We compare our results to a large body of observational data on present day galactic disks, including: disk sizes and central surface brightness, Tully-Fisher relations in various wavelength bands, colour-colour and colour-magnitude relations, gas fractions vs. magnitudes and colours, abundances vs. local and integrated properties, as well as spectra for different galactic rotational velocities. Despite the extremely simple nature of our models, we find satisfactory agreement with all those observables, provided the timescale for star formation in low mass disks is longer than for more massive ones. This assumption is apparently in contradiction with the standard picture of hierarchical cosmology. We find, however, that it is extremely successfull in reproducing major features of present day disks, like the change in the slope of the Tully-Fisher relation with wavelength, the fact that more massive galaxies are on average ``redder than low mass ones (a generic problem of standard hierarchical models) and the metallicity-luminosity relation for spirals. It is concluded that, on a purely empirical basis, this new picture at least as successful as the standard one. Observations at high redshifts could help to distinguish between the two possibilities.
We present new deep optical spectra of 9 high-z radio galaxies (HzRGs) at z > 2.7 obtained with FORS2 on VLT. These rest-frame ultraviolet spectra are used to infer the metallicity of the narrow-line regions (NLRs) in order to investigate the chemical evolution of galaxies in high-z universe. We focus mainly on the CIV/HeII and CIII]/CIV flux ratios that are sensitive to gas metallicity and ionization parameter. Although the NV emission has been widely used to infer the gas metallicity, it is often too weak to be measured accurately for NLRs. By combining our new spectra with data from the literature, we examine the possible redshift evolution of the NLR metallicity for 57 HzRGs at 1 < z < 4. Based on the comparison between the observed emission-line flux ratios and the results of our photoionization model calculations, we find no significant metallicity evolution in NLRs of HzRGs, up to z ~ 4. Our results imply that massive galaxies had almost completed their chemical evolution at much higher redshift (z > 5). Finally, although we detect strong NV emission lines in 5 HzRGs at z > 2.7, we point out that high NV/HeII ratios are not indicative of high metallicities but correspond to high ionization parameters of gas clouds in NLRs.
In this contribution we briefly describe our recent results on the properties of Lyman break galaxies at z~5 obtained from deep and wide blank field surveys using Subaru telescope, and through the comparison with samples at lower redshift ranges we discuss the evolution of star-forming galaxies in the early universe.
Absorption-line spectroscopy is a powerful tool used to estimate element abundances in the nearby as well as distant universe. The accuracy of the abundances thus derived is, naturally, limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform the new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state-of-the-art quantal calculations. Here we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts (GRBs). We report new extensive calculations of a large number of energy levels of S II, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree-Fock framework, and utilize both non-ralativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes (~0.04 dex) to the metallicities estimated from S II in past studies. These results will be readily applicable to other studies of S II in the Milky Way and other galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
