TY - JOUR
T1 - A Keck/DEIMOS spectroscopic survey of the faint M31 satellites AndXV and AndXVI
AU - Letarte, B.
AU - Chapman, S. C.
AU - Collins, M.
AU - Ibata, R. A.
AU - Irwin, M. J.
AU - Ferguson, A. M. N.
AU - Lewis, G. F.
AU - Martin, N.
AU - McConnachie, A.
AU - Tanvir, N.
AU - Ferguson, Annette
PY - 2009/12/1
Y1 - 2009/12/1
N2 - We present the results of a spectroscopic survey of the recently
discovered M31 satellites AndXV and AndXVI, lying at projected distances
from the centre of M31 of 93 and 130 kpc, respectively. These satellites
lie to the south of M31, in regions of the stellar halo which wide-field
imaging has revealed as relative voids (compared to the ~degree-scale
coherent stream-like structures). Using the Deep Imaging Multi-Object
Spectrograph mounted on the Keck II telescope, we have defined probable
members of these satellites, for which we derive radial velocities as
precise as ~6kms-1 down to i ~ 21.5. While the distance to
AndXVI remains the same as previously reported (525 +/- 50 kpc), we have
demonstrated that the brightest three stars previously used to define
the tip of the red giant branch in AndXV are in fact Galactic, and AndXV
is actually likely to be much more distant at 770 +/- 70 kpc (compared
to the previous 630 kpc), increasing the luminosity from MV ~
-9.4 to -9.8. The AndXV velocity dispersion is resolved with
vr = -339+7-6kms-1 and
σv = 11+7-5kms-1. The
AndXVI dispersion is not quite resolved at 1σ with vr =
-385+5-6kms-1 and σ =
0+10-indef kms-1. Using the photometry
of the confirmed member stars, we find metallicities of AndXV (median
[Fe/H] = -1.58, interquartile range +/-0.08) and AndXVI (median [Fe/H] =
-2.23, interquartile range +/-0.12). Stacking the spectra of the member
stars, we find spectroscopic [Fe/H] = -1.8 (-2.1) for AndXV (AndXVI),
with an uncertainty of ~0.2 dex in both cases. Our measurements of AndXV
reasonably resolve its mass (~108Msolar) and
suggest a polar orbit, while the velocity of AndXVI suggests it is
approaching the M31 escape velocity given its large M31 centric
distance.
AB - We present the results of a spectroscopic survey of the recently
discovered M31 satellites AndXV and AndXVI, lying at projected distances
from the centre of M31 of 93 and 130 kpc, respectively. These satellites
lie to the south of M31, in regions of the stellar halo which wide-field
imaging has revealed as relative voids (compared to the ~degree-scale
coherent stream-like structures). Using the Deep Imaging Multi-Object
Spectrograph mounted on the Keck II telescope, we have defined probable
members of these satellites, for which we derive radial velocities as
precise as ~6kms-1 down to i ~ 21.5. While the distance to
AndXVI remains the same as previously reported (525 +/- 50 kpc), we have
demonstrated that the brightest three stars previously used to define
the tip of the red giant branch in AndXV are in fact Galactic, and AndXV
is actually likely to be much more distant at 770 +/- 70 kpc (compared
to the previous 630 kpc), increasing the luminosity from MV ~
-9.4 to -9.8. The AndXV velocity dispersion is resolved with
vr = -339+7-6kms-1 and
σv = 11+7-5kms-1. The
AndXVI dispersion is not quite resolved at 1σ with vr =
-385+5-6kms-1 and σ =
0+10-indef kms-1. Using the photometry
of the confirmed member stars, we find metallicities of AndXV (median
[Fe/H] = -1.58, interquartile range +/-0.08) and AndXVI (median [Fe/H] =
-2.23, interquartile range +/-0.12). Stacking the spectra of the member
stars, we find spectroscopic [Fe/H] = -1.8 (-2.1) for AndXV (AndXVI),
with an uncertainty of ~0.2 dex in both cases. Our measurements of AndXV
reasonably resolve its mass (~108Msolar) and
suggest a polar orbit, while the velocity of AndXVI suggests it is
approaching the M31 escape velocity given its large M31 centric
distance.
M3 - Article
SN - 1365-2966
VL - 400
SP - 1472
EP - 1478
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
ER -