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Rosa, I. G. de la; Coziol, R.; Carvalho, R. R. de; Zepf, Stephen E.

doi:10.1023/a:1017574202049

Cited by 6 publications

(9 citation statements)

References 14 publications

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“…they are on average older and possess higher [Fe/H] than their low‐density environment equivalents. This is consistent with the findings of de la Rosa et al (2001b) who also found such a difference in age and metallicity. However, the five early‐type galaxies that are the brightest in their respective compact groups (i.e.…”

Section: Resultssupporting

confidence: 93%

“…Our study also confirmed the previously reported finding (de la Rosa et al 2001b) that early‐type galaxies in HCGs are more metal poor than field galaxies. This again suggests that the star‐formation histories of early‐type galaxies in HCGs more closely resemble those of cluster galaxies than those in less dense environments such as small groups and the field.…”

Section: Discussionsupporting

confidence: 92%

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Ages and metallicities of Hickson compact group galaxies

Proctor

Forbes

Hau

et al. 2004

Monthly Notices of the Royal Astronomical Society

137

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Hickson Compact Groups (HCGs) constitute an interesting extreme in the range of environments in which galaxies are located, as the space density of galaxies in these small groups are otherwise only found in the centres of much larger clusters. The work presented here uses Lick indices to make a comparison of ages and chemical compositions of galaxies in HCGs with those in other environments (clusters, loose groups and the field). The metallicity and relative abundance of 'α-elements' show strong correlations with galaxy age and central velocity dispersion, with similar trends found in all environments. However, we show that the previously reported correlation between α-element abundance ratios and velocity dispersion disappears when a full account is taken of the the abundance ratio pattern in the calibration stars. This correlation is thus found to be an artifact of incomplete calibration to the Lick system.Variations are seen in the ranges and average values of age, metallicity and α-element abundance ratios for galaxies in different environments. Age distributions support the hierarchical formation prediction that field galaxies are on average younger than their cluster counterparts. However, the ages of HCG galaxies are shown to be more similar to those of cluster galaxies than those in the field, contrary to the expectations of current hierarchical models. A trend for lower velocity dispersion galaxies to be younger was also seen. This is again inconsistent with hierarchical collapse models, but is qualitatively consistent with the latest N-body-SPH models based on monolithic collapse in which star formation continues for many Gyr in low mass halos.

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Section: Resultssupporting

confidence: 93%

Section: Discussionsupporting

confidence: 92%

Ages and metallicities of Hickson compact group galaxies

Proctor

Forbes

Hau

et al. 2004

Monthly Notices of the Royal Astronomical Society

137

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“…The use of this technique has produced valuable insights into the history of large samples of galaxies in high-and low-density environments (Kuntschner et al 2002;Thomas et al 2005). There also exist a few stellar population studies with smaller samples of early-type galaxies in HCGs (de la Rosa et al 2001a;Proctor et al 2004;Mendes de Oliveira et al 2005, hereafter MCG05). Their common result is that early-type galaxies in HCGs are older and more metal-poor than their counterparts in the field.…”

Section: Introductionmentioning

confidence: 99%

Truncated Star Formation in Compact Groups of Galaxies: A Stellar Population Study

et al. 2006

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We present the results of a study comparing the stellar populations in the elliptical galaxies of Hickson compact groups ( HCGs) with those in low-density environments. We analyze a sample of intermediate-resolution (4.25 8 FWHM ) spectra of 22 galaxies in HCGs and 12 in the field or in loose groups. Three different population-synthesis models and stellar population analyses are used to make the results more robust. Great care has been taken to correct for the emission contamination of the Balmer lines, used to determine the mean luminosity-weighted ages of the galaxies. We find that, on average, galaxies in HCGs are systematically older and more metal-poor than in the field, in agreement with previous works. The most interesting finding is that the low-galaxies in HCGs show an enhanced [Mg/Fe] ratio and depleted metallicity [Z/H] with respect to their counterparts in the field. This anomalous behavior is interpreted as evidence for the action of a mechanism that truncates the star formation (SF). Hydrodynamic simulations of galaxy mergers ) support this interpretation by predicting the quenching of SF soon after the merger event. Combining this scenario and the evidence presented here, the HCGs, generally considered to be ideal environments for galaxy-galaxy interactions, become ideal places for SF truncation.

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“…Bernardi et al 1998; de la Rosa, de Carvalho & Zepf 2001a). Also, studies of the stellar population of early‐type systems indicate that they are older and more metal poor in CGs and clusters than in the field (Rose et al 1994; Proctor et al 2005; de la Rosa et al 2001b; Mendes et al 2005), suggesting that Es in dense systems experience a truncated period of star formation, which ultimately affects their chemical enrichment history, as opposed to their counterparts in the low‐density regime.…”

Section: Introductionmentioning

confidence: 99%

A principal component analysis approach to the star formation history of elliptical galaxies in compact groups

Ferreras

Pasquali

Carvalho

et al. 2006

Monthly Notices of the Royal Astronomical Society

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Environmental differences in the stellar populations of early-type galaxies are explored using principal component analysis (PCA), focusing on differences between elliptical galaxies in Hickson Compact Groups (HCGs) and in the field. The method is model-independent and purely relies on variations between the observed spectra. The projections (PC1,PC2) of the observed spectra on the first and second principal components reveal a difference with respect to environment, with a wider range in PC1 and PC2 in the group sample. We define a spectral parameter (ζ ≡ 0.36PC1−PC2) which simplifies this result to a single number: field galaxies have a very similar value of ζ, whereas HCG galaxies span a wide range in this parameter. The segregation is found regardless of the way the input SEDs are presented to PCA (i.e. changing the spectral range; using uncalibrated data; subtracting the continuum or masking the SED to include only the Lick spectral regions). Simple models are applied to give physical meaning to the PCs. We obtain a strong correlation between the values of ζ and the mass fraction in younger stars, so that some group galaxies present a higher fraction of them, implying a more complex star formation history in groups. Regarding "dynamically-related" observables such as a 4 or velocity dispersion, we find a correlation with PC3, but not with either PC1 or PC2. PCA is more sensitive than other methods based on a direct analysis of observables such as the structure of the surface brightness profile or the equivalent width of absorption lines. The latter do not reveal any significant variation between field and compact group galaxies. Our results imply that the presence of young stars only amounts to a fraction of a percent in its contribution to the total variance, reflecting the power of PCA as a tool to extract small variations in the spectra from unresolved stellar populations.

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Untitled

Cited by 6 publications

References 14 publications

Ages and metallicities of Hickson compact group galaxies

Ages and metallicities of Hickson compact group galaxies

Truncated Star Formation in Compact Groups of Galaxies: A Stellar Population Study

A principal component analysis approach to the star formation history of elliptical galaxies in compact groups

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