Abstract / Description of output
We present a deep photometric survey of the Andromeda galaxy, conducted
with the wide-field cameras of CFHT and INT, that covers the inner 50
kpc of the galaxy and the southern quadrant out to ~150 kpc and includes
an extension to M33 at >200 kpc. This is the first systematic
panoramic study of this very outermost region of galaxies. We detect a
multitude of large-scale structures of low surface brightness, including
several streams, and two new relatively luminous (MV~-9)
dwarf galaxies: And XV and And XVI. Significant variations in stellar
populations due to intervening stream-like structures are detected in
the inner halo, which is particularly important in shedding light on the
mixed and sometimes conflicting results reported in previous studies.
Underlying the many substructures lies a faint, smooth, and extremely
extended halo component, reaching out to 150 kpc, whose stellar
populations are predominantly metal-poor. We find that the smooth halo
component in M31 has a radially decreasing profile that can be fitted
with a Hernquist model of immense scale radius ~55 kpc, almost 4 times
larger than theoretical predictions. Alternatively a power law with
ΣV~R-1.91+/-0.11 can be fitted to the
projected profile, similar to the density profile in the Milky Way. If
it is symmetric, the total luminosity of this structure is
~109 Lsolar, again similar to the stellar halo of
the Milky Way. This vast, smooth, underlying halo is reminiscent of a
classical ``monolithic'' model and completely unexpected from modern
galaxy formation models. M33 is also found to have an extended
metal-poor halo component, which can be fitted with a Hernquist model
also of scale radius ~55 kpc. These extended slowly decreasing halos
will provide a challenge and strong constraints for further modeling.
Based on observations obtained with MegaPrime/MegaCam, a joint project
of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT),
which is operated by the National Research Council (NRC) of Canada, the
Institute National des Sciences de l'Univers of the Centre National de
la Recherche Scientifique of France, and the University of Hawaii.
Original language | English |
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Pages (from-to) | 1591-1623 |
Journal | Astrophysical Journal |
Volume | 671 |
Issue number | 2 |
DOIs | |
Publication status | Published - 1 Dec 2007 |
Keywords / Materials (for Non-textual outputs)
- Galaxies: Evolution
- Galaxies: Individual: Messier Number: M31
- Galaxies: Individual: Messier Number: M33
- Galaxies: Structure
- Galaxies: Local Group