J/MNRAS/390/1437 Stellar streams in Andromeda (M31) (Chapman+, 2008)
The kinematic footprints of five stellar streams in Andromeda's halo.
Chapman S.C., Ibata R., Irwin M., Koch A., Letarte B., Martin N.,
Collins M., Lewis G.F., McConnachie A., Penarrubia J., Rich R.M.,
Trethewey D., Ferguson A., Huxor A., Tanvir N.
<Mon. Not. R. Astron. Soc., 390, 1437-1452 (2008)>
=2008MNRAS.390.1437C 2008MNRAS.390.1437C
ADC_Keywords: Abundances, [Fe/H] ; Radial velocities ; Photometry, VRI ;
Galaxies, nearby ; Spectroscopy ; Stars, normal
Keywords: stars: kinematics - galaxies: haloes - galaxies: individual: M31
Abstract:
We present a spectroscopic analysis of five stellar streams ("A", "B",
"Cr", "Cp" and "D") as well as the extended star cluster, EC4, which
lies within Stream "C", all discovered in the halo of M31 from our
Canada-France-Hawaii Telescope/MegaCam survey. These spectroscopic
results were initially serendipitous, making use of our existing
observations from the DEep Imaging Multi-Object Spectrograph mounted
on the Keck II telescope, and thereby emphasizing the ubiquity of
tidal streams that account for ∼70 per cent of the M31 halo stars in
the targeted fields. Subsequent spectroscopy was then procured in
Stream "C" and Stream "D" to trace the velocity gradient along the
streams. Nine metal-rich ([Fe/H]~-0.7) stars at vhel=-349.5km/s,
σv,corr∼5.1±2.5km/s are proposed as a serendipitous
detection of Stream "Cr", with follow-up kinematic identification at a
further point along the stream. Seven metal-poor ([Fe/H]~-1.3) stars
confined to a narrow, 15km/s velocity bin centred at vhel=-285.6,
σv,corr=4.3+1.7-1.4km/s represent a kinematic detection of
Stream "Cp", again with follow-up kinematic identification further
along the stream. For the cluster EC4, candidate member stars with
average [Fe/H]~-1.4, are found at vhel=-282 suggesting it could be
related to Stream "Cp". No similarly obvious cold kinematic candidate
is found for Stream "D", although candidates are proposed in both of
two spectroscopic pointings along the stream (both at ~-400km/s).
Spectroscopy near the edge of Stream "B" suggests a likely kinematic
detection at vhel~-330, σv,corr∼6.9km/s, while a candidate
kinematic detection of Stream "A" is found (plausibly associated to
M33 rather than M31) with vhel~-170, σv,corr=12.5km/s. The
low dispersion of the streams in kinematics, physical thickness and
metallicity makes it hard to reconcile with a scenario whereby these
stream structures as an ensemble are related to the giant southern
stream. We conclude that the M31 stellar halo is largely made up of
multiple kinematically cold streams.
Description:
The spectroscopic fields cover the four stellar streams presented in
the Ibata et al. (2007ApJ...671.1591I 2007ApJ...671.1591I) M31 extended halo analysis,
called Stream "D", "C", "B" and "A", respectively. Multi-object
spectroscopic observations with the Keck II telescope and the DEIMOS
were obtained in photometric conditions with ∼0.8" seeing in 2004 and
2005 September. On 2007 October 8, additional DEIMOS masks were
obtained further along the Stream "C" and Stream "D" under ∼1" seeing,
and cloudy conditions (see Fields F36 and F37 in table 1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 98 9 Properties of DEIMOS fields in the M31 stellar
streams "A","B","C" and "D".
stars.dat 73 115 Properties of candidate M31 halo stars in fields
F7 (table 2), F37 (table 3), F25/26 (table 4),
F36 (table 5), M6 (table 6) and M8 (table 7)
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See also:
J/AJ/112/491 : Late-Type Stars in M31. II. (Brewer+ 1996)
J/AJ/124/234 : M31 outer halo UBVRI photometry and metallicity (Reitzel+,
2002)
J/AJ/127/2738 : ACS VI photometry of M31 halo RR Lyrea (Brown+, 2004)
J/MNRAS/369/120 : Kinematic survey of planetary nebulae in M31 (Merrett+, 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Str Stream designation (added by CDS)
4- 12 A9 --- Stream Target name
14- 21 A8 --- Field Field designation
23- 24 I2 h RAh Hour of right ascension (J2000)
26- 27 I2 min RAm Minute of right ascension (J2000)
29- 33 F5.2 s RAs Second of right ascension (J2000)
35 A1 --- DE- Declination sign (J2000)
36- 37 I2 deg DEd Degree of declination (J2000)
39- 40 I2 arcmin DEm Arcminute of declination (J2000)
42- 45 F4.1 arcsec DEs Arcsecond of declination (J2000)
47- 52 F6.1 km/s HRV Stream radial velocity
54 A1 --- u_sigma [∼ ] Uncertainty flag on sigma
55- 58 F4.1 km/s sigma ? Velocity dispersion (1)
60- 62 F3.1 km/s E_sigma ? Positive uncertainty on sigma
64- 66 F3.1 km/s e_sigma ? Negative uncertainty on sigma
68- 71 F4.1 [-] [Fe/H] Mean [Fe/H] (2)
73- 75 F3.1 [-] e_[Fe/H] Uncertainty in [Fe/H]
77- 80 F4.1 [-] [Fe/H]p ? Statistical photometric [Fe/H] from Ibata
et al., 2007ApJ...671.1591I 2007ApJ...671.1591I
82- 84 F3.1 kpc FWHM ? Stream width (3)
86- 87 I2 kpc Rperi ? Rperi model parameter (4)
89- 91 I3 10+7Msun Mstr ? Structural estimation of stream mass (5)
92 A1 --- --- [/]
93 I1 10+7Msun Msv ? Kinematical estimation of stream mass (5)
95- 98 F4.1 10+6Lsun Lstr ? Stream luminosity (6)
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Note (1): Velocity dispersions, estimated through a maximum-likelihood
analysis taking into account the measurement errors in the velocities
(or in the case of Stream "A", Stream "B", Stream "D", a subtraction
in quadrature of the measurement error).
Note (2): For certain streams (notably Stream "A" and Stream "D"), it is
arguable that the [Fe/H]phot measurements are estimated from sets of
stars which may not actually be a kinematic detection of "the stream".
For this reason, we also quote the statistical [Fe/H]phot estimate
from Ibata et al. (2007ApJ...671.1591I 2007ApJ...671.1591I) in [Fe/H]p column. In
particular, the Stream "D" values are quoted for the combination of
six stars in the two separated pointings along the stream, and
therefore the numbers in the table are simply duplicated.
Note (3): Stream widths derived from Gaussian fits (quoted FWHM) to
the integrated profile in the region defined in Ibata et al.
(2007ApJ...671.1591I 2007ApJ...671.1591I) (their fig. 31). At the distance of M31
(785kpc - McConnachie et al. 2005MNRAS.356..979M 2005MNRAS.356..979M) 1°=13kpc.
Note (4): Rperi estimated as 1/5Dstream as discussed in section 4.
Note (5): Mass of stream width estimated from structural parameters (first
entry) and from σv (second entry).
Note (6): Lstream from Ibata et al. (2007ApJ...671.1591I 2007ApJ...671.1591I), except for
Stream "Cp" and Stream "Cr" which are discussed in the text.
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Str Stream designation, as in table1
4- 5 I2 h RAh Hour of right ascension (J2000)
7- 8 I2 min RAm Minute of right ascension (J2000)
10- 14 F5.2 s RAs Second of right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Degree of declination (J2000)
20- 21 I2 arcmin DEm Arcminute of declination (J2000)
23- 26 F4.1 arcsec DEs Arcsecond of declination (J2000)
28- 33 F6.1 km/s HRV Heliocentric radial velocity
35- 40 F6.3 km/s e_HRV HRV uncertainty
42- 47 F6.2 [-] [Fe/H]p ? Photometric [Fe/H]
49- 55 F7.4 [Sun] [Fe/H] ? Spectroscopic [Fe/H] calculated from the
CaII triplet lines equivalent width
57- 61 F5.2 mag Vmag V-band magnitude (Johnson-Cousins)
63- 67 F5.2 mag Imag I-band magnitude (Johnson-Cousins)
69- 73 F5.2 arcmin Dist ? Distance from the centre of EC4 (only for
table 4) (1)
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Note (1): At the distance of EC4, 13kpc=1°
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Nomenclature note:
Tables 2-5: stars are <[CII2008] JHHMMSS.ss+DDMMSS.s> in Simbad.
Tables 6-7: stars are <[CII2008] JHHMMSS.s+DDMMSS.s> in Simbad.
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 31-Jan-2011