2011A&A...526A.123R


C.D.S. - SIMBAD4 rel 1.7 - 2021.01.17CET15:18:38

2011A&A...526A.123R - Astronomy and Astrophysics, volume 526A, 123-123 (2011/2-1)

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

REJKUBA M., HARRIS W.E., GREGGIO L. and HARRIS G.L.H.

Abstract (from CDS):

NGC5128 (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. Our aims are to establish when the oldest stars formed in NGC 5128, and whether this galaxy formed stars over a long period. 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. 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 ∼10Gyr, 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 3-4Gyr. Two burst models, with 70-80% of the stars formed 12±1Gyr ago and with 20-30% younger contribution with 2-4Gyr 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 (∼1/10-1/4Z). The bulk of the halo stars in NGC 5128 must have formed at redshift z γ2 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 ∼2-4Gyr ago.

Abstract Copyright:

Journal keyword(s): galaxies: elliptical and lenticular, cD - galaxies: individual: NGC 5128 - galaxies: stellar content - galaxies: star formation

Simbad objects: 17

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Number of rows : 17

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 11151 1
2 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9647 1
3 NGC 891 H2G 02 22 32.907 +42 20 53.95 11.08 10.81 9.93 7.86   ~ 1545 2
4 LBN 659 GiG 02 36 35.469 +59 39 16.53   17       ~ 178 2
5 NAME Fornax Dwarf Spheroidal G 02 39 59.3 -34 26 57   9.02 7.4     ~ 1505 1
6 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 15112 1
7 M 81 Sy2 09 55 33.17306143 +69 03 55.0609270   7.89 6.94     ~ 4027 5
8 NGC 3377 GiP 10 47 42.400 +13 59 08.30 11.55 11.24 10.38     ~ 733 1
9 M 105 LIN 10 47 49.600 +12 34 53.87   10.56 9.76 9.12 8.18 ~ 1390 0
10 NAME M96 Group GrG 10 48 +13.3           ~ 282 0
11 NAME Vir I ClG 12 26 32.1 +12 43 24   10.00 8.49     ~ 5949 0
12 M 87 BiC 12 30 49.42338230 +12 23 28.0438581 10.16 9.59 8.63   7.49 ~ 6318 3
13 M 104 LIN 12 39 59.43185 -11 37 22.9954 9.51 9.55 8.00 8.05   ~ 1292 3
14 ACO 3526 ClG 12 48 51.8 -41 18 21           ~ 987 2
15 NAME Centaurus A Sy2 13 25 27.61509104 -43 01 08.8056025   8.18 6.84 6.66   ~ 4055 3
16 NAME Local Group GrG ~ ~           ~ 7137 0
17 NAME Galactic Bulge reg ~ ~           ~ 3516 0

    Equat.    Gal    SGal    Ecl

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2021.01.17-15:18:38

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