Deep ACS Imaging of the Halo of NGC 5128: Reaching the Horizontal Branch

Rejkuba, M.; Greggio, L.; Harris, William E.; Harris, G. L. H.; Peng, Eric W.

doi:10.1086/432462

Cited by 127 publications

(253 citation statements)

References 71 publications

(156 reference statements)

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“…The possibility that most of the metal-rich clusters in elliptical galaxies formed through major mergers (Ashman & Zepf 1992) does not, by itself, solve the original 'S N problem' because such large amounts of incoming gas are needed to make the thousands of GCs in giant ellipticals at any plausible formation efficiency that this version of their origin becomes similar to basic hierarchical merging (see Harris 2001). The Woodley et al 2010) and for a sample of halo field stars (dotted line, Rejkuba et al 2005).…”

Section: The Specific-frequency 'Problems' and Formation Issuesmentioning

confidence: 99%

Massive star clusters in galaxies

Harris

2010

Phil. Trans. R. Soc. A.

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The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

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Section: The Specific-frequency 'Problems' and Formation Issuesmentioning

confidence: 99%

Massive star clusters in galaxies

Harris

2010

Phil. Trans. R. Soc. A.

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“…In Paper I (Rejkuba et al 2005), we presented HST ACS/WFC photometry of the stars in an outer-halo field of NGC 5128. The photometric limits of the data, resulting from A&A 526, A123 (2011) component (Soria et al 1996;Marleau et al 2000;Rejkuba et al 2003), similar to what is deduced for more distant field elliptical galaxies .…”

Section: Introductionmentioning

confidence: 99%

“…For more distant galaxies the mean age can be obtained from the fits to the age and metallicity sensitive luminosity features such as red clump, asymptotic giant branch bump and red giant branch bump. Rejkuba et al (2005) derived luminosity weighted mean age of 8 +3 −3.5 Gyr for NGC 5128 halo, and Durrell et al (2010) obtained a mean age of M81 halo stars of 9 ± 1 Gyr. In all three galaxies (M 31,M 81 and NGC 5128) there are stars younger than < ∼ 8 Gyr, but the bulk of the population is old.…”

Section: Introductionmentioning

confidence: 99%

How old are the stars in the halo of NGC 5128 (Centaurus A)?

Rejkuba¹,

Harris

Greggio

et al. 2011

A&A

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Context. NGC 5128 (Centaurus A) is, at the distance of just 3.8 Mpc, the nearest easily observable giant elliptical galaxy. Therefore it is the best target to investigate the early star formation history of an elliptical galaxy. Aims. Our aims are to establish when the oldest stars formed in NGC 5128, and whether this galaxy formed stars over a long period. Methods. We compare simulated colour−magnitude diagrams with the deep ACS/HST photometry. The simulations assume in input either the observed metallicity distribution function, based on the colour distribution of the upper red giant branch stars, or the closed box chemical enrichment. Simulations are constructed for single age bursts using BASTI evolutionary isochrones; more complex star formation histories are constructed as well by combining several individual simulations. Comparisons with data are made by fitting the whole colour−magnitude diagram as well as the the luminosity functions in V and I band. In addition we inspect carefully the red clump and asymptotic giant branch bump luminosities and number counts, since these features are the primary constraints on the ages of the observed stars. Results. We find that that the observed colour−magnitude diagram can be reproduced satisfactorily only by simulations that have the bulk of the stars with ages in excess of ∼10 Gyr, and that the alpha-enhanced models fit the data much better than the solar scaled ones. Data are not consistent with extended star formation over more than 3−4 Gyr. Two burst models, with 70−80% of the stars formed 12 ± 1 Gyr ago and with 20−30% younger contribution with 2−4 Gyr old stars provide the best agreement with the data. The old component spans the whole metallicity range of the models (Z = 0.0001−0.04), while for the young component the best fitting models indicate higher minimum metallicity (∼1/10−1/4 Z ). Conclusions. The bulk of the halo stars in NGC 5128 must have formed at redshift z > ∼ 2 and the chemical enrichment was very fast, reaching solar or even twice-solar metallicity already for the ∼11−12 Gyr old population. The minor young component, adding ∼20−30% of the stars to the halo, and contributing less than 10% of the mass, may have resulted from a later star formation event ∼2−4 Gyr ago.

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“…At a distance of 18 Mpc, the brightest stars of an old stellar population, which are at the Tip of the RGB, have J ≃ 26 mag. For our simulations we adopt the same model stellar population as in Greggio et al (2012), namely a flat age distribution between 10 and 12 Gyr, and a metallicity distribution determined for a halo field in the elliptical galaxy Centaurus A (Rejkuba et al 2005) (see Fig. 1).…”

Section: The Science Casementioning

confidence: 99%

“…A thorough study of this kind has been performed for the nearby elliptical galaxy Centaurus A (Harris & Harris 2000;Rejkuba et al 2005), through the analysis of CMDs obtained from HST data in different regions of the galaxy, sampling the stellar populations from ≃ 8 to ≃ 38 Kpc from the center . The results show that the metallicity distribution is very wide in all the examined fields, with very little variations of the peak and width.…”

Section: Introductionmentioning

confidence: 99%

Studying the metallicity gradient in Virgo ellipticals with European-Extremely Large Telescope photometry of resolved stars

Schreiber

Greggio

Falomo

et al. 2013

Monthly Notices of the Royal Astronomical Society

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The next generation of large aperture ground based telescopes will offer the opportunity to perform accurate stellar photometry in very crowded fields. This future capability will allow one to study in detail the stellar population in distant galaxies. In this paper we explore the effect of photometric errors on the stellar metallicity distribution derived from the color distribution of the Red Giant Branch stars in the central regions of galaxies at the distance of the Virgo cluster. We focus on the analysis of the Color-Magnitude Diagrams at different radii in a typical giant Elliptical galaxy obtained from synthetic data constructed to exemplify observations of the European Extremely Large Telescope. The simulations adopt the specifications of the first light high resolution imager MICADO and the expected performance of the Multi-Conjugate Adaptive Optics Module MAORY. We find that the foreseen photometric accuracy allows us to recover the shape of the metallicity distribution with a resolution 0.4 dex in the inner regions (µ B = 20.5 mag arcsec −2 ) and ≃ 0.2 dex in regions with µ B = 21.6 mag arcsec −2 , that corresponds to approximately half of the effective radius for a typical giant elliptical in Virgo. At the effective radius (µ B ≃ 23 mag arcsec −2 ), the metallicity distribution is recovered with a resolution of ≃ 0.1 dex. It will thus be possible to study in detail the metallicity gradient of the stellar population over (almost) the whole extension of galaxies in Virgo. We also evaluate the impact of moderate degradations of the Point Spread Function from the assumed optimal conditions and find similar results, showing that this science case is robust.

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Deep ACS Imaging of the Halo of NGC 5128: Reaching the Horizontal Branch

Cited by 127 publications

References 71 publications

Massive star clusters in galaxies

Massive star clusters in galaxies

How old are the stars in the halo of NGC 5128 (Centaurus A)?

Studying the metallicity gradient in Virgo ellipticals with European-Extremely Large Telescope photometry of resolved stars

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