Gustavo A. Bruzual

Exploring Cluster Elliptical Galaxies as Cosmological Standard Rods

We explore the possibility of calibrating massive cluster elliptical galaxies as cosmological standard rods using the fundamental plane relation combined with a correction for luminosity evolution. Although cluster ellipticals certainly formed in a complex way, their passive evolution out to redshifts of about 1 indicates that basically all major merging and accretion events took place at higher redshifts. Therefore, a calibration of their luminosity evolution can be attempted. We propose to use the Mg-? relation for that purpose because it is independent of distance and cosmology. We discuss a variety of possible caveats, ranging from dynamical evolution to uncertainties in stellar population models and evolution corrections to the presence of age spread. Sources of major random and systematic errors are analyzed as well. We apply the described procedure to nine elliptical galaxies in two clusters at z = 0.375 and derive constraints on the cosmological model. For the best-fitting ?-free cosmological model we obtain q0 ? 0.1, with 90% confidence limits being 0 < q0 < 0.7 (the lower limit being due to the presence of matter in the universe). If the inflationary scenario applies (i.e., the universe has flat geometry), then, for the best-fitting model, matter and ? contribute about equally to the critical cosmic density (i.e., ?m ? ?? ? 0.5). With 90% confidence, ?? should be smaller than 0.9.

Redshift Evolution of the Stellar Populations in Elliptical Galaxies

Velocity dispersions σ and Mg absorption line strengths Mgb have been measured for a sample of 16 ellipticals in three clusters at a redshift of 0.37. Like local cluster ellipticals, these objects show a correlation between Mgb and σ. However, at any given σ, the mean Mgb of the ellipticals at z = 0.37 is weaker than the mean Mgb of their local relatives in the Coma and Virgo clusters. The Mgb weakening is smallest for the most luminous ellipticals and larger for the fainter objects. This is unambiguous evidence for small but significant passive evolution of the stellar populations of elliptical galaxies with redshift. It requires that the bulk of the stars in cluster ellipticals has formed at z > 2. The most luminous objects may even have formed at z > 4. The Mgb-σ test is a very reliable estimator for the evolution of old stellar populations because it is virtually independent from the stellar initial mass function (IMF) and from the metallicities of the galaxies. Furthermore, the influence of selection effects is minimal. Consistent with the weakening of Mgb we find evidence for a B-band luminosity evolution of about 0.5 ± 0.1 mag at z = 0.37 from the Faber-Jackson relation. The combined information about the evolution of Mgb and luminosity allows us to constrain both the slope of the IMF in ellipticals and the cosmological deceleration parameter q0. Our present measurements are compatible with a standard Salpeter IMF and a q0 of 0.5 ± 0.5.

A Large‐Area CCD Camera for the Schmidt Telescope at the Venezuelan National Astronomical Observatory

We have designed, constructed, and put into operation a large-area CCD camera that covers a large fraction of the image plane of the 1 m Schmidt telescope at Llano del Hato in Venezuela. The camera consists of 16 CCD devices arranged in a 4 × 4 mosaic covering 23 × 35 of sky. The CCDs are 2048 × 2048 LORAL devices with 15 μm pixels. The camera is optimized for drift-scan photometry and objective-prism spectroscopy. The design considerations, construction features, and performance parameters are described in the following paper.

A Revised Age for the z = 1.55 Galaxy LBDS 53W091

Empirical evidence suggests that the stellar population in LBDS 53W091 is significantly younger than the dominant population in M32. We have used evolutionary population synthesis models to estimate the age of the dominant population in these stellar systems. The age of LBDS 53W091 is in the range from 1 to 2 Gyr and depends on the specific model. Older ages require sub-solar metallicity models. The estimates of the age of the dominant population in M32 range from 3 to 5 Gyr and depend not only on the model but also on the SED of this galaxy used in the fits. The same models predict an age of 11 to 13 Gyr for the stars in a typical old E/S0 galaxy. This age is consistent with the age of the metal-rich galactic bulge globular clusters NGC 6553, NGC 6528, and Terzan 5. Passive evolution seems an adequate scenario for the evolution of the stellar population in E galaxies from z = 1.6 to z = 0. The dominant population in M32 is genuinely young (3 to 5 Gyr), independently than an older stellar population may be present in this galaxy. Thus, M32 may not be representative of galaxies that evolve passively. The length of time for which these galaxies have existed as individual dynamical entities is not determined by our models. The age of the Λ = 0, Ω = 1 universe at z = 1.552 is 1.6 h –1 Gyr. Hence, a 1 to 2 Gyr old galaxy at z = 1.552 poses no problem for this universe as long as h ≤ 0.8. In this universe, the 13 Gyr limit for the E/S0 galaxy at z = 0 requires h ≤ 0.5. The most likely reason for the difference between our age estimate of 1 to 2 Gyr for LBDS 53W091 and the value of 3.5 Gyr derived by Dunlop et al. (1996) and Spinrad et al. (1997), is the fact that these authors did not require that the population synthesis models that they used fitted simultaneously the UV break amplitudes and the observed R – J, R – H , and R – K colors of this galaxy. This will be discussed in detail elsewhere. We thank H. Spinrad, A. Dey, and D. Stern for kindly sending to us their remarkable spectrum of LBDS 53W091.

Evolutionary Population Synthesis

A brief and non-exhaustive review of the main research papers on Evolutionary Population Synthesis is presented. The degree up to which these studies obey well known astrophysical constrains, such as the Fuel Consumption Theorem, is analyzed. A summary of the most significant results from the Isochrone Synthesis Spectral Evolution Models of Bruzual and Charlot (1992) concludes this presentation.

Inverse population synthesis using a dynamical basis

We introduce a new inverse population synthesis algorithm (DINBAS3D) which aims to recover the star formation and metallicity histories from galactic spectra. We investigate the use of a dynamical basis of three simple stellar population spectra that is specific for each galaxy. Our goal is to recover a robust star formation history that minimizes degeneracy effects which are very common in high resolution histories methods. In this work, we detail the method and present our findings when we apply DINBAS3D to synthetic spectra with known parameters, we compare our results with similar methods and find good agreement between them.

First Results from the UCM-CIDA-YALE Survey

The UCM-CIDA-YALE (UCY) survey for Hα emission line galaxies was designed as a deeper and wider extension of the successful Universi-dad Complutense de Madrid Survey (Zamorano et al., 1996, ApJS, 105, 343). It was aimed with three major goals: To obtain a statistically meaningful sample of star-forming galaxies in the local universe. To determine the properties of the faintest galaxies and its contribution in the luminosity function. To study the spatial distribution of these galaxies.

Star-Forming Galaxies from the UCM-CIDA-YALE Survey

The star formation rate (SFR) evolution with redshift is one of the key observational parameters in order to compare with current theories of formation and evolution of galaxies. The value for the SFR in the local universe is very dependent on the shape of the luminosity function and in particular on the a parameter. The UCM-CIDA-YALE survey (UCY) has grown to address this problem, among others. Using the objective-prism technique, we have been able to obtain a large sample of star-forming galaxy candidates in the local universe. The UCY survey aims to be the most extense colection of low luminosity star forming galaxies down to M B = −12. The global properties of the survey are presented.

Emission Lines in Star Forming Galaxies

Magris et al. (1993, Proceedings of the ESO/OHP Workshop on Dwarf Galaxies, ed. G. Meylan) have combined the spectral evolution population synthesis code of Bruzual & Chariot (1993, ApJ 405, 538) with the multipurpose photoionization-shock code MAPPINGS (Binette et al. 1993, AJ 105, 797) in order to calculate self-consistently the evolution of the nebular emission corresponding to the ionizing spectra produced by the synthetic population. In this poster we compare the redshift dependence of the EW[OII]3727 predicted by the Magris et al. models with the observations available (Colles et al. 1990, MNRAS 244, 408; Kennicutt 1992, ApJS 79, 255; Le Fevre et al. 1994, ApJ 423, L89). Models in which stars form following the Salpeter IMF according to the SFR ψ(t) = 1M⊙τ-1exp(-t/τ), for τ = 1,2,3,5,7, and ∞ Gyr have been considered. We assume H 0 = 50, Ω = 0, t g = 16 Gyr. About 2/3 of the galaxies in these samples have EW[OII]3727 from 2 to 5 times larger than the ones predicted by our models for steadily decreasing or even constant (τ = ∞) SFR. To cover the range of observed values of EW[OII]3727 we assume that instantaneous bursts (Salpeter IMF) of star formation take place in these galaxies, superimposed on the steady SFR used in the models. The mass added by the bursts as newly formed stars per unit mass of stars in the underlying galaxy is in the range 1 — 4 × 10-4. Depending on the rest-frame wavelength, the color of the galaxies may remain unaffected or become considerably bluer as a consequence of the bursting activity.

Infrared background models from galaxy evolution

Abstract Existing spectral evolutionary models of galaxies are supplemented in a semiempirical way in order to study the contribution of normal galaxies to the diffuse infrared background radiation. The predicted intensity of the infrared background produced by normal galaxies in the wavelength range from 1 to 250 μm is between one and two orders of magnitudes below the preliminary South Ecliptic Pole observations reported by the Diffuse Infrared Background Experiment (DIRBE) carried out on board the Cosmic Background Explorer (COBE) satellite. A difference in this sense is expected since the DIRBE results include foreground contamination from interplanetary and galactic sources. However, more refined galaxy models are needed in order to derive the normal galaxy contribution to the infrared background more precisely.