J/A+A/589/A139 Stellar populations of NGC 3311 (Barbosa+, 2016)
The Hydra I cluster core. I. Stellar populations in the cD galaxy NGC 3311.
Barbosa C.E., Arnaboldi M., Coccato L., Hilker M., Mendes de Oliveira C.,
Richtler T.
<Astron. Astrophys. 589, A139 (2016)>
=2016A&A...589A.139B 2016A&A...589A.139B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Galaxies, optical ; Abundances
Keywords: galaxies: clusters: individual: Hydra I -
galaxies: individual: NGC 3311 - galaxies: halos -
galaxies: evolution - galaxies: formation - galaxies: stellar content
Abstract:
The history of the mass assembly of brightest cluster galaxies may be
studied by mapping the stellar populations at large radial distances
from the galaxy centre, where the dynamical times are long and
preserve the chemodynamical signatures of the accretion events.
To provide extended and robust measurements of the stellar population
parameters in NGC 3311, the cD galaxy at the centre of the Hydra I
cluster, and out to three effective radius. We wish to characterise
the processes that drove the build up of the stellar light at all
these radii.
We obtained the spectra from several regions in NGC 3311 covering an
area of ∼3arcmin2 in the wavelength range 4800<lambda(Å)<5800,
using the FORS2 spectrograph at the Very Large Telescope in the MXU
mode. We measured the equivalent width of seven absorption-features
defined in the Lick/IDS system, which were modelled by single stellar
populations, to provide luminosity-weighted ages, metallicities, and
alpha element abundances.
The trends in the Lick indices and the distribution of the stellar
population parameters indicate that the stars of NGC3311 may be
divided in two radial regimes, one within and the another beyond one
effective radius, Re=8.4kpc, similar to the distinction between
the inner galaxy and the external halo derived from the NGC3311
velocity dispersion profile. The inner galaxy (R<Re) is old (age
∼14Gyr), has negative metallicity gradients and positive alpha element
gradients. The external halo is also very old, but has a negative age
gradient. The metal and element abundances of the external halo both
have a large scatter, indicating that stars from a variety of
satellites with different masses have been accreted. The region in the
extended halo associated with the off-centred envelope at
0<P.A.(°)<90 (Arnaboldi et al., 2012A&A...545A..37A 2012A&A...545A..37A) has higher
metallicity with respect to the symmetric external halo.
The different stellar populations in the inner galaxy and extended
halo reflect the dominance of in situ stars in the former and the
accreted origin for the large majority of the stars in the latter. The
low value of the velocity dispersion in the inner galaxy indicates
that its stars are bound to the galaxy's gravitational potential, and
the abundances and gradients suggest that the inner galaxy is formed
in an outside-in scenario of merging gas-rich lumps, reminiscent of
the first phase of galaxy formation. The external halo has a higher
velocity dispersion, it is dynamically hotter than the galaxy and its
stars are gravitationally driven by the cluster's gravitational
potential. The stars in the external halo were removed from their
parent galaxies, either disks with truncated star formation, or the
outer regions of early-type galaxies. Late mass accretion at large
radii is now coming from the tidal stripping of stars from dwarfs and
S0 galaxies. These results provide supporting evidence for the recent
theoretical models of formation of massive ellipticals as a two-phase
process.
Description:
We have observe the stellar halo over NGC 3311, the central galaxy of
the Hydra I cluster, using 118 small slits avoiding point sources. The
data was obtained with FORS2 spectrograph at the Very Large Telescope
using the spectroscopic mask mode (MXU). Equivalent width of
absorption line features were measured in the Lick/IDS sytem, and
stellar population parameters, ie. age, metallicity and alpha-element
abundances, were calculated using single stellar populations with
models from Thomas et al. (2011MNRAS.412.2183T 2011MNRAS.412.2183T).
Objects:
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RA (2000) DE Designation(s)
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10 36 36.0 -27 31 04 Hydra I = ACO 1060
10 36 42.82 -27 31 42.0 NGC 3311 = LEDA 31478
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 152 119 Equivalent width of Lick indices for the Hydra I
cluster core and stellar population parameters
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See also:
J/ApJS/85/249 : Surface Photometry of Hydra I Galaxies. I. (Hamabe 1993)
J/A+A/486/697 : Hydra I Cluster Catalogue (HCC) (Misgeld+, 2008)
J/A+A/531/A4 : Ultra compact dwarfs and globulars in Hya I (Misgeld+, 2011)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- ID Identification of the slit (1)
10- 13 F4.1 kpc Rad Projected distance to the center of
NGC 3311 (2)
15- 20 F6.1 deg PA [] Position angle in relation to NGC 3311
22- 26 F5.1 10/nm S/N Signal-to-Noise ratio
28- 32 F5.2 0.1nm Hbeta ?=- Hβ equivalent width
34- 38 F5.2 0.1nm e_Hbeta ?=- Error in the Hbeta equivalent width
40- 44 F5.2 0.1nm Fe5015 ?=- Fe 5015Å equivalent width
46- 49 F4.2 0.1nm e_Fe5015 ?=- Error in the Fe5015 equivalent width
51- 55 F5.2 0.1nm Mgb ?=- Mgb equivalent width
57- 60 F4.2 0.1nm e_Mgb ?=- Error in the Mgb equivalent width
62- 66 F5.2 0.1nm Fe5270 ?=- Fe 5270Å equivalent width
68- 71 F4.2 0.1nm e_Fe5270 ?=- Error in the Fe5270 equivalent width
73- 77 F5.2 0.1nm Fe5335 ?=- Fe 5335Å equivalent width
79- 82 F4.2 0.1nm e_Fe5335 ?=- Error in the Fe5335 equivalent width
84- 88 F5.2 0.1nm Fe5406 ?=- Fe 5406Å equivalent width
90- 93 F4.2 0.1nm e_Fe5406 ?=- Error in the Fe5406 equivalent width
95- 99 F5.2 0.1nm Fe5709 ?=- Fe 5709Å equivalent width
101-104 F4.2 0.1nm e_Fe5709 ?=- Error in the Fe5709 equivalent width
106-110 F5.2 [yr] Age Luminosity weighted age
112-115 F4.2 [yr] e_Age Lower error in age
117-120 F4.2 [yr] E_Age Upper error in age
122-126 F5.2 [Sun] [Z/H] Luminosity weighted total metallicity
128-131 F4.2 [Sun] e_[Z/H] Lower error in total metallicity
133-136 F4.2 [Sun] E_[Z/H] Upper error in total metallicity
138-142 F5.2 [Sun] [alpha/Fe] Luminosity weighted alpha element abundance
144-147 F4.2 [Sun] e_[alpha/Fe] Lower error in alpha element abundance
149-152 F4.2 [Sun] E_[alpha/Fe] Upper error in alpha element abundance
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Note (1): Slits names as cen1sNN, cen2sNN,inn1sNN, inn2sNN, out1sNN and out2sNN.
Note (2): Radial distances to the center of NGC 3311 are calculated assuming
a distance of 50.7Mpc to the core of the Hydra I cluster.
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Acknowledgements:
Carlos Eduardo Barbosa, carlos.barbosa(at)usp.br
(End) Carlos Eduardo Barbosa [IAG-USP], Patricia Vannier [CDS] 22-Mar-2016