Evolutionary Population Synthesis Models Research Articles

Hard X-ray-to-radio energy distributions in starburst galaxies

We present in this contribution the predictions on the multiwavelength spectral energy distribution of our evolutionary population synthesis models including single and binary stellar systems. The high energy computations include the emission associated to X-ray binaries and supernovae remnants, as well as the mechanical energy released into the interstellar medium, which can be partially reprocessed into thermal X-rays. With these components we compute the spectral energy distribution of starburst galaxies from X-ray to radio ranges, and analyze finally the effects of the high energy emission on the H and He ionizing continuum.

Far‐Ultraviolet and Visible Imaging of the Nucleus of M32

We have imaged the nucleus of M32 at 1600 A (FUV) and 5500 A (V) using the Wide-Field/Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope. We detected the nucleus at 1600 A using the redleak-free Woods filter on WFPC2. The far-ultraviolet (FUV) light profile can be fitted with a Gaussian of FWHM 046 (4.6 pixels) but cannot be resolved into individual stars; no UV-bright nuclear structure was detected. The (FUV - V) color of the nucleus is 4.9 ± 0.3, which is consistent with earlier observations. We are unable to confirm any radial variation in (FUV - V) within 08 of the nucleus; beyond that radius the FUV surface brightness drops below our detection threshold. We also performed surface photometry in V and found our results to be in excellent agreement with deconvolved WFPC1 results. M32's light profile continues to rise in a nuclear cusp even within 01 of its center. No intermediate-age stellar population is required by evolutionary population synthesis models to reproduce the (FUV - V) color of the nucleus, although these data and current models are insufficient to resolve this issue.

The K-band Hubble diagram for the brightest cluster galaxies: a test of hierarchical galaxy formation models

We analyse the K-band Hubble diagram for a sample of brightest cluster galaxies (BCGs) in the redshift range 0 2) that is evolving passively. We can thus use evolutionary population synthesis models to estimate the rate of growth in stellar mass for these systems. We find that the stellar mass in a typical BCG has grown by a factor ~ 2 since z=1 if q_0=0.0 or by factor ~ 4 if q_0=0.5. These results are in good agreement with the predictions of semi-analytic models of galaxy formation and evolution set in the context of a hierarchical scenario for structure formation. The models predict a scatter in the luminosities of the BCGs that is somewhat larger than the observed one, but that depends on the criterion used to select the model clusters.

The VRI colours of H II galaxies

We present a high spatial resolution CCD surface photometry study in the optical V, R and I broadband filters of a sample of 15 HII galaxies. The colours of the starburst continuum and of the underlying galaxy are measured. The distribution of colours of the underlying galaxy in HII galaxies is similar to the colours of other late type low surface brightness galaxies which suggests a close kinship of these with the quiescent phases of HII galaxies. However, comparison with recent evolutionary population synthesis models shows that the observational errors and the uncertainties in the models are still too large to put strict constraints on their past star formation history.

THE STRUCTURE AND ENVIRONMENT OF H II GALAXIES

ABSTRACT H II galaxies are dwarf star forming galaxies found in objective prism surveys through their strong emission lines. They have been targets of extensive studies of their spectroscopic properties such as chemical abundances, physical conditions and kinematics. Little surface photometry work has been done on H II galaxies up to now. This thesis is primarily a CCD surface photometry study of the structural properties, optical colors and a statistical analysis of the environment of H II galaxies. In the chapter "The Morphology of H II Galaxies" I have used a sample of 39 H II galaxies with CCD images for a study of their overall morphology and luminosity profiles. The results show that H II galaxies can be classified in two main types: type I H II galaxies are luminous and have disturbed and irregular outer shapes while type II H II galaxies are less luminous and have regular shapes. The outer parts of profiles of all HIi galaxies are well represented by an exponential as in other types of known dwarf galaxies. In "The Dynamics of H II Galaxies" I have investigated the relation between the linear size of the starburst, luminosity and velocity dispersion. It is found that H II galaxies have similar relations as virialized systems which supports the gravitational origin of their overall kinematics. The possible bi-parametric behavior ("fundamental plane") of H II galaxies is also investigated. However, a conclusive answer to this question still requires more and better data. In "The Colors of H II Galaxies" I have presented a high spatial resolution CCD surface photometry study. The colors of the underlying stellar continuum within the starburst are obtained by removing the flux contribution of the emission lines in the broad band filters. Comparison with recent evolutionary population synthesis models show that the observational errors and the uncertainties in the models are still too large to put strict constraints on their past star formation history. However, the distribution of colors of the underlying galaxy in H II galaxies is similar to the colors of some dwarf galaxies which suggests a kinship of these with the quiescent phases of H II galaxies. In "The Environment of H II Galaxies" I have studied the environment of 51 H II galaxies for which I have CCD images, H-beta luminosity, velocity dispersion, H-beta equivalent width and oxygen abundance. The aim of the study is to check the tidal origin of the starburst in H II galaxies and the effect of the environment on their intrinsic properties. It is found that only 12 H II galaxies have a bright neighbour within a projected distance of 1 Mpc and 250 km s-1 in velocity difference. Surprisingly, isolated H II galaxies tend to be of high luminosity and disturbed morphology while H II galaxies with neighbours tend to be low luminosity regular H II galaxies. Furthermore, the metal abundance and the equivalent width of the emission lines in H II galaxies do not depend on the presence of a companion. These results are opposed to what is expected if interaction with a luminous companion is the main mechanism triggering the starbursts. It is also found a loose group of four H II galaxies with no luminous companion. For this, there is the additional difficulty of understanding how these starbursts are synchronized on time scales of less than 107 yrs in systems separated by ~1-2 Mpc.

Stellar Population Models of Distant Radio Galaxies

Stellar populations of high redshift radio galaxies (HzRG) (z up to 4.2) are the oldest stellar systems known, that is the ones formed at the earliest cosmological epochs. Therefore they are the best objects for providing us with information about the epoch of galaxy formation. The information on the stellar populations in HzRG are obtained from the study of their Integrated Spectral Energy Distribution (ISED) which are gathered both from spectra and integrated magnitudes. The most common approach for the interpretation of colors and spectral features of the energy distribution of galaxies is the Evolutionary Population Synthesis (EPS), which has been introduced for the first time by Tinsley in 1972. EPS models have often been used in the past to interpret the ISED of HzRG (Chambers & Charlot 1990; Lilly & Longair 1984; di Serego Alighieri et al. 1994) in order to draw conclusions on the age of the stellar populations and therefore on the epoch of galaxy formation. The results are sometimes conflicting and a number of very recent EPS models have become available (Bressan et al. 1995; Bruzual & Charlot 1993; Buzzoni 1989; Guiderdoni & Rocca-Volmerange 1987): we are therefore analysing the differences between the various EPS models with the aim of assessing their suitability to study the stellar population at early epochs. The EPS models assume for stars a given Initial Mass Function(IMF) as well as a Star Formation Rate (SFR). Then one can compute the number of stars with given mass present in the galaxy as a function of time. The position of each star in the HR diagram is determined by means of the isochrones, which are calculated from stellar evolutionary models. The ISED of a galaxy is obtained from the superposition of the spectra of single stars obtained from a stellar spectral library. Thus these models describe the galaxy ISED as a function of the time, giving a complete evolutionary picture.

Self-Consistent Evolution of Ring Galaxies

view Abstract Citations (12) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Self-Consistent Evolution of Ring Galaxies Mazzei, P. ; Curir, A. ; Bonoli, C. Abstract Ring galaxies are commonly known as objects where a burst of star formation was triggered by a close encounter with an intruder, maybe a satellite galaxy. BVRI CCD observations of five ring galaxies have been performed. Here we present the results of a self-consistent approach to reproduce their observed morphology and spectral energy distribution using updated N-body simulations and evolutionary population synthesis models extending from UV to far-IR wavelengths. Some suggestions about the evolutionary properties of these starburst galaxies are then derived. Publication: The Astronomical Journal Pub Date: August 1995 DOI: 10.1086/117542 arXiv: arXiv:astro-ph/9506109 Bibcode: 1995AJ....110..559M Keywords: GALAXIES: STARBURST; GALAXIES: EVOLUTION; Astrophysics E-Print: MNRAS accepted full text sources arXiv | ADS | data products SIMBAD (8) NED (5)

STAR FORMATION IN GIANT EXTRAGALACTIC H II REGIONS

ABSTRACT Star formation properties in Giant Extragalactic H II Regions (GEHRs) are investigated using optical photometry and evolutionary population synthesis models. Photometric data in BVR bands and in the emission line of H-alpha are obtained by CCD imaging at Vainu Bappu Observatory, Kavalur. Aperture photometry is performed for 180 GEHRs in galaxies NGC 1365, 1566, 2366, 2903, 2997, 3351, 4303, 4449, 4656 and 5253. Thirty six of these GEHRs having published spectroscopic data are studied for star formation properties. The population synthesis model is constructed based on Maeder's stellar evolutionary and Kurucz stellar atmosphere models, to synthesize observational quantities of embedded clusters in GEHRs. The observed H-alpha luminosity is a measure of the number of massive stars while the contribution to BVR bands is from intermediate mass (5-15 solar mass) stars when the cluster is young and from evolving supergiants when the cluster is old (age >/= 6~Myr). Differential reddening between gas and embedded stars is essential to constrain the dereddened cluster colors within the range of youngest clusters. Obscuring dust closely associated with gas, which is distributed in filaments and clumps, as in the case of 30 Doradus, is the most likely configuration giving rise to net reduction of extinction towards stars. The fraction of the stellar photons escaping the nebula unattenuated is estimated to be 50%. GEHRs are rarely found to be simple systems containing stars from single generation. In the present sample such regions in addition to being older than 3~Myr, have their Lyman continuum luminosity reduced by as much as 60%, compared to the observed B band luminosity for a normal IMF. The missing ionizing photons may be escaping the nebula, leading to the ionization of extra-H II region ionized medium. Co-existence of young (age </= 5 Myr; stars producing ionizing photons) and old populations (~10~Myr; Red Supergiants) is found to be common in GEHRs. The emission and continuum knots are seen spatially separated (40-100 pc) on CCD images in NGC 2997, 4303 and 4449 and may be direct evidences for the co-existence of young and old populations in giant star forming complexes. Triggering of star formation from earlier bursts is the most likely cause of new generation of stars, and may be a common phenomenon in GEHRs. Spatial separation between the young and old stars (~30 pc) had been earlier reported in 30 Doradus. Thus GEHRs in nearby galaxies share many of the properties shown by 30 Dor, the nearest GEHR.

Population synthesis in starburst galaxies: Mkn 710

Evolutionary population synthesis models have been built to study the properties of the starforming processes taking place in starburst regions. BothZ ⊙ andZ ⊙/10 stellar evolutionary tracks have been used to take into account that starburst galaxies are generally metal deficient. A very small time step allows us to follow the evolution of the cluster even during very short phases. Three parameters have been synthesized: the ratio of the Siiv (1400 A) andCiv (1550 A) UV absorption lines, that characterize the predominant massive stars in the cluster, the ratio of the WRbump over the Hβ luminosity, tracer of WR stars and the FIR luminosity, directly related to the extinction due to dust in the cluster. The predictions have been compared with observations of the burst taking place in the galaxy Mkn 710. The burst age is 5–6 Myr. The stars seem to have formed simultaneously with a mass spectrum whose slope is in the range (1,2) for massive stars. The upper mass limit has to be ≥60M ⊙. We have performed a systematic study of a sample of 17 starburst galaxies searching for differences in the star formation process that may be related to different metallicities or morphological types.