2005A&A...436...57R -
Astronomy and Astrophysics, volume 436, 57-65 (2005/6-2)
The elliptical galaxy NGC720: An unequal-mass galaxy merger remnant.
REMBOLD S.B., PASTORIZA M.G. and BRUZUAL G.
Abstract (from CDS):
The stellar population of the central region of the galaxy
NGC720 has been investigated through longslit optical spectroscopy. The velocity dispersion and 13 Lick indices were obtained as a function of the radius along the semimajor axis of the galaxy. The Mg
2 index presents a gradient of dMg
2/dlogr=-0.079 which behaves similarly to the FeI lines, indicating no enhancement of Mg
2 in relation to FeI. The stellar population ages and metallicities were derived by a population synthesis method using available evolutive spectrophotometric models. The synthesis indicates a strong age gradient along the semimajor axis of
NGC720. In the central region a 13Gyr and solar metallicity stellar population dominates the flux at 5870Å; the contribution of this component vanishes at a radius of 0.73kpc, where the total flux is accounted for by a younger, 5Gyr and solar metallicity stellar population. For distances larger than 1kpc a 2.5Gyr component becomes very important. Moreover,
NGC720 is probably overabundant in CN in the center with respect to the solar abundance. The estimated total mass (3.29x10
11M
☉) and the Mg
2 gradient values suggest that this galaxy might have undergone a merger event. The correspondence between the J-band brightness profile decomposition and the result of the spectral synthesis shows that this galaxy is formed by an old (13-5Gyr), bulge-like, small-scale and massive spheroid and a younger (5-2.5Gyr), large-scale disk component. We discuss our results in comparison with available numerical simulations and propose that the merger event must have occurred about 4Gyr ago.
Abstract Copyright:
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Journal keyword(s):
galaxies: elliptical and lenticular, cD - galaxies: individual: NGC720 - galaxies: kinematics and dynamics - galaxies: stellar content
Simbad objects:
6
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