Abstract / Description of output
We present a spectroscopic survey of the giant stellar stream found in
the halo of the Andromeda galaxy. Taken with the DEIMOS multi-object
spectrograph on the Keck2 telescope, these data display a narrow
velocity dispersion of 11 +/- 3 km s-1, with a steady radial
velocity gradient of 245 km s-1 over the 125-kpc radial
extent of the stream studied so far. This implies that the Andromeda
galaxy possesses a substantial dark matter halo. We fit the orbit of the
stream in different galaxy potential models. In a simple model with a
composite bulge, disc and halo, where the halo follows a universal
profile that is compressed by the formation of the baryonic components,
we find that the kinematics of the stream require a total mass inside
125 kpc of M125= 7.5+2.5-1.3×
1011 Msolar, or M125 > 5.4 ×
1011 Msolar at the 99 per cent confidence level.
This is the first galaxy in which it has been possible to measure the
halo mass distribution by such direct dynamical means over such a large
distance range. The resulting orbit shows that if M32 or NGC 205 is
connected with the stream, they must either trail or lag the densest
region of the stream by more than 100 kpc. Furthermore, according to the
best-fitting orbit, the stream passes very close to M31, causing its
demise as a coherent structure and producing a fan of stars that will
pollute the inner halo, thereby confusing efforts to measure the
properties of genuine halo populations. Our data show that several
recently identified planetary nebulae, which have been proposed as
evidence for the existence of a new companion of M31, are likely members
of the Andromeda stream.
Original language | English |
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Pages (from-to) | 117-124 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 351 |
Issue number | 1 |
DOIs | |
Publication status | Published - 1 Jun 2004 |
Keywords / Materials (for Non-textual outputs)
- galaxies: individual: M31
- galaxies: kinematics and dynamics