Bibcode
Bouchard, A.; Prugniel, P.; Koleva, M.; Sharina, M.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 513, id.A54
Fecha de publicación:
4
2010
Revista
Número de citas
26
Número de citas referidas
26
Descripción
Context. NGC 404 is a nearly face-on, nearby low-luminosity lenticular
galaxy. Probing its characteristics provides a wealth of information on
the details of the possible evolution processes of dS0 galaxies, which
may not be possible in other, more distant objects. Aims: We
study the internal kinematics and the spatial distribution of the star
formation history in NGC 404. Methods: We obtained long-slit
spectroscopy at the OHP 1m93 telescope along the major and minor axes of
NGC 404. The spectra had a resolution R = 3600 covering a wavelength
range from 4600 to 5500 Å. The data were fitted against the
Pegase. HR stellar population models to derive the internal stellar
kinematics, ages, and metallicities simultaneously. All this was done
while taking any instrumental contamination to the line-of-sight
velocity distribution into account. First, the global properties of the
galaxy were analysed by fitting a single model to the data and looking
at the kinematic variations and SSP equivalent age and metallicities as
a function of radius. Afterwards, the stellar populations were
decomposed into 4 individually analysed components. Results: NGC
404 clearly shows two radial velocity inversions along its major axis.
The kinematically decoupled core rotates in the same direction as the
neutral hydrogen shell that surrounds the galaxy. We resolved the star
formation history in the core of the galaxy into 4 events: a very young
(< 150 Myr, and [Fe/H] = 0.4) component with constant ongoing star
formation, a second young (430 Myr) component with [Fe/H] = 0.1, an
intermediate population (1.7 Gyr) that has [Fe/H] = -0.05, and finally
an old (12 Gyr) component with [Fe/H] = -1.26. The two young components
fade very quickly with radius, leaving only the intermediate and old
population at a radius of 25´´ (370 pc) from the centre. Conclusions: We conclude that NGC 404 had a spiral morphology about 1
Gyr ago and that one or many merger events has triggered a morphological
transition. The interstellar medium in the galaxy has two components,
the cold molecular gas is most probably a remnant from its past spiral
incarnation and the outer neutral hydrogen layer that has probably been
acquired in one of the latest mergers.
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