Spectral and photometric evolution of simple stellar populations at various metallicities

Schulz, Jan; Alvensleben, Uta Fritze v.; Möller, Claudia; Fricke, K. J.

doi:10.1051/0004-6361:20020657

Cited by 130 publications

(217 citation statements)

References 34 publications

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“…Using GALEV SSP models (Schulz et al 2002), AnalySED compares the observed spectral energy distributions with a library of models to find the best fit. We used GALEV models based on a Kroupa IMF (Kroupa 2002) in the mass range 0.1 to 100 M , Padova isochrones (Girardi et al 2002), and different metallicities, depending on the galaxy.…”

Section: Cluster Ages and Massesmentioning

confidence: 99%

The star cluster – field star connection in nearby spiral galaxies

Silva-Villa

Larsen

2011

A&A

109

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Context. Recent studies have started to cast doubt on the assumption that most stars are formed in clusters. Observational studies of field stars and star cluster systems in nearby galaxies can lead to better constraints on the fraction of stars forming in clusters. Ultimately this may lead to a better understanding of star formation in galaxies, and galaxy evolution in general. Aims. We aim to constrain the amount of star formation happening in long-lived clusters for four galaxies through the homogeneous, simultaneous study of field stars and star clusters. Methods. Using HST/ACS and HST/WFPC2 images of the galaxies NGC 45, NGC 1313, NGC 5236, and NGC 7793, we estimate star formation histories by means of the synthetic CMD method. Masses and ages of star clusters are estimated using simple stellar population model fitting. Comparing observed and modeled luminosity functions, we estimate cluster formation rates. By randomly sampling the stellar initial mass function (SIMF), we construct artificial star clusters and quantify how stochastic effects influence cluster detection, integrated colors, and age estimates. Results. Star formation rates appear to be constant over the past 10 7 −10 8 years within the fields covered by our observations. The number of clusters identified per galaxy varies, with a few detected massive clusters (M ≥ 10 5 M ) and a few older than 1 Gyr. Among our sample of galaxies, NGC 5236 and NGC 1313 show high star and cluster formation rates, while NGC 7793 and NGC 45 show lower values. We find that stochastic sampling of the SIMF has a strong impact on the estimation of ages, colors, and completeness for clusters with masses ≤10 3 −10 4 M , while the effect is less pronounced for high masses. Stochasticity also makes size measurements highly uncertain at young ages (τ 10 8 yr), making it difficult to distinguish between clusters and stars based on sizes. Conclusions. The ratio of star formation happening in clusters (Γ) compared to the global star formation appears to vary for different galaxies. We find similar values to previous studies (Γ ≈ 2%-10%), but we find no obvious relation between Γ and the star formation rate density (Σ SFR ) within the range probed here (Σ SFR ∼ 10 −3 −10 −2 M yr −1 kpc −2 ). The Γ values do, however, appear to correlate with the specific U-band luminosity (T L (U), the fraction of total light coming from clusters compared to the total U-band light of the galaxy).

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Section: Cluster Ages and Massesmentioning

confidence: 99%

The star cluster – field star connection in nearby spiral galaxies

Silva-Villa

Larsen

2011

A&A

109

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“…We have adopted the updated GALEV simple stellar population (SSP) models (Schulz et al 2002;Anders & Fritze v. Alvensleben 2003) as our templates to derive ages, extinction values, and masses for each of the observed clusters in M 51. These models use the isochrones from the Padova group, which seem to fit the data better than the Geneva tracks (Whitmore & Zhang 2002).…”

Section: Adopted Cluster Modelsmentioning

confidence: 99%

The star cluster population of M 51

Gieles¹,

Bastian²,

Lamers³

2005

A&A

196

277

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Abstract. We use archival Hubble Space Telescope observations of broad-band images from the ultraviolet (F255W-filter) through the near infrared (NICMOS F160W-filter) to study the star cluster population of the interacting spiral galaxy M 51. We obtain age, mass, extinction, and effective radius estimates for 1152 star clusters in a region of ∼7.3 × 8.1 kpc centered on the nucleus and extending into the outer spiral arms. In this paper we present the data set and exploit it to determine the age distribution and relationships among the fundamental parameters (i.e. age, mass, effective radius). We show the critical dependence of the age distribution on the sample selection, and confirm that using a constant mass cut-off, above which the sample is complete for the entire age range of interest, is essential. In particular, in this sample we are complete only for masses above 5 × 10 4 M for the last 1 Gyr. Using this dataset we find: i) that the cluster formation rate seems to have had a large increase ∼50−70 Myr ago, which is coincident with the suggested second passage of its companion, NGC 5195; ii) a large number of extremely young (<10 Myr) star clusters, which we interpret as a population of unbound clusters of which a large majority will disrupt within the next ∼10 Myr; and iii) that the distribution of cluster sizes can be well approximated by a power-law with exponent, −η = −2.2 ± 0.2, which is very similar to that of Galactic globular clusters, indicating that cluster disruption is largely independent of cluster radius. In addition, we have used this dataset to search for correlations among the derived parameters. In particular, we do not find any strong trends between the age and mass, mass and effective radius, nor between the galactocentric distance and effective radius. There is, however, a strong correlation between the age of a cluster and its extinction, with younger clusters being more heavily reddened than older clusters.

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“…The code accounts for the increasing initial metallicities of successive stellar generations and naturally reproduces the observed broad stellar metallicity distributions of local galaxies. It is based on isochrones for 5 different metallicities −1.7 ≤ [Fe/H] ≤ +0.4 from the Padova group that include the thermal-pulsing AGB phase, which has been shown by Schulz et al (2002) to have an important effect on colors like (V − I) and (V − K) at ages from 100 Myr through a few Gyr for single-burst, single-metallicity stellar populations like star clusters.…”

Section: Undisturbed Galaxiesmentioning

confidence: 99%

The impact of starbursts and post-starbursts on the photometric evolution of high redshift galaxies

Alvensleben¹,

Bicker

2006

A&A

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We present evolutionary synthesis models for galaxies of spectral types Sa through Sd with starbursts of various strengths triggered at various redshifts and study their photometric evolution before, during, and after their bursts in a cosmological context. We find that bursts at high redshift, even very strong ones, only cause a small blueing of their intrinsically blue young parent galaxies. At lower redshift, in contrast, even small bursts cause a significant blueing of their intrinsically redder galaxies. While the burst phase is generally short, typically a few hundred Myr in normal-mass galaxies, the postburst stage with its red colors and, in particular the very red ones for early bursts at high redshift, lasts much longer, on the order of several Gyr. We find that, even without any dust, which in the postburst stage is not expected to play an important role anyway, models easily reach the colors of EROs in the redshift range z ∼ 2 through z ∼ 0.5 after starbursts at redshifts between 2 and 4. We therefore propose a third alternative for the ERO galaxies beyond the two established ones of passive galaxies vs. dusty starbursts: the dust-free post-(strong-)starbursts. A very first comparison of our models to HDF data with photometric redshifts shows that almost all of the outliers that could not be described with our chemically consistent models for undisturbed normal galaxy types E through Sd can now be explained very well. Galaxies in the redshift range from z ∼ 2.5 to z ∼ 0.5 that are redder, and in some cases much redder, than our reddest undisturbed model for a high-metallicity classical elliptical are well described by post-starburst models after starbursts at redshifts between 2 and 4. Galaxies bluer than our bluest low metallicity Sd model, most of which have redshifts lower than 1, are well explained by ongoing starbursts.

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Spectral and photometric evolution of simple stellar populations at various metallicities

Cited by 130 publications

References 34 publications

The star cluster – field star connection in nearby spiral galaxies

The star cluster – field star connection in nearby spiral galaxies

The star cluster population of M 51

The impact of starbursts and post-starbursts on the photometric evolution of high redshift galaxies

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