|Título||The elliptical galaxy NGC 720 : an unequal-mass galaxy merger remnant
Rembold, Sandro Barboza
Pastoriza, Miriani Griselda
Bruzual A., G.
|Abstract||The stellar population of the central region of the galaxy NGC 720 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 Mg₂ index presents a gradient of d Mg₂ / d log r = −0.079 which behaves similarly to the Fe I lines, indicating no enhancement of Mg₂ in relation to Fe I. 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 NGC 720. In the central region a 13 Gyr and solar metallicity stellar population dominates the flux at 5870 Å; the contribution of this component vanishes at a radius of 0.73 kpc, where the total flux is accounted for by a younger, 5 Gyr and solar metallicity stellar population. For distances larger than 1 kpc a 2.5 Gyr component becomes very important. Moreover, NGC 720 is probably overabundant in CN in the center with respect to the solar abundance. The estimated total mass (3.29×10¹¹ Mѳ) and theMg₂ 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 (13–5 Gyr), 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 4 Gyr ago.
|Contido em||Astronomy and astrophysics. Vol. 436, no. 1 (June 2005), p. 57-65
[en] Galaxies: elliptical and lenticular, cD
[en] Galaxies: individual: NGC720
[en] Galaxies: kinematics and dynamics
[en] Galaxies: stellar content
|Tipo||Artigo de periódico
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