J/ApJ/768/172 Kinematic analysis of red giant in M31 dSphs (Collins+, 2013)
A kinematic study of the Andromeda dwarf spheroidal system.
Collins M.L.M., Chapman S.C., Rich R.M., Ibata R.A., Martin N.F.,
Irwin M.J., Bate N.F., Lewis G.F., Penarrubia J., Arimoto N., Casey C.M.,
Ferguson A.M.N., Koch A., McConnachie A.W., Tanvir N.
<Astrophys. J., 768, 172 (2013)>
=2013ApJ...768..172C 2013ApJ...768..172C
ADC_Keywords: Photometry, ugriz ; Stars, giant ; Radial velocities ;
Galaxies, nearby ; Velocity dispersion ; Abundances, [Fe/H]
Keywords: dark matter; galaxies: dwarf; galaxies: fundamental parameters;
galaxies: kinematics and dynamics; Local Group
Abstract:
We present a homogeneous kinematic analysis of red giant branch stars
within 18 of the 28 Andromeda dwarf spheroidal (dSph) galaxies,
obtained using the Keck I/LRIS and Keck II/DEIMOS spectrographs. Based
on their g-i colors (taken with the CFHT/MegaCam imager), physical
positions on the sky, and radial velocities, we assign probabilities
of dSph membership to each observed star. Using this information, the
velocity dispersions, central masses, and central densities of the
dark matter halos are calculated for these objects, and compared with
the properties of the Milky Way dSph population. We also measure the
average metallicity ([Fe/H]) from the co-added spectra of member stars
for each M31 dSph and find that they are consistent with the trend of
decreasing [Fe/H] with luminosity observed in the Milky Way
population. We find that three of our studied M31 dSphs appear as
significant outliers in terms of their central velocity dispersion,
And XIX, XXI, and XXV, all of which have large half-light radii
(≳700pc) and low velocity dispersions (σv<5km/s). In
addition, And XXV has a mass-to-light ratio within its half-light
radius of just [M/L]half=10.3-6.77.0, making it consistent with
a simple stellar system with no appreciable dark matter component
within its 1σ uncertainties. We suggest that the structure of
the dark matter halos of these outliers have been significantly
altered by tides.
Description:
The Canada-France-Hawaii Telescope Pan-Andromeda Archaeological Survey
(PAndAS) survey (McConnachie et al. 2009Natur.461...66M 2009Natur.461...66M), conducted
using the 3.6m CFHT, maps out the stellar density of the disc and halo
regions of the M31-M33 system over a projected area of ∼350deg2,
resolving individual stars to depths of g=26.5 and i=25.5 with a
signal-to-noise ratio (S/N) of 10.
The data for the dwarf spheroidal (dSph) galaxies were taken between
2006 September and 2012 September with the DEep-Imaging Multi-Object
Spectrograph (DEIMOS), situated on the Nasmyth focus of the Keck II
telescope (R∼1.3Å) in the 5600-9800Å range. For four dSphs (And
XI, XII, XIII, and XXIV) the lower resolution (R∼3.5Å FWHM) was used.
Andromeda V (And V) was observed using the LRIS instrument on Keck I
rather than the DEIMOS instrument on Keck II on 2009 Aug 16, with R∼3Å.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 66 18 *Details of the structural properties for each dwarf
table2.dat 89 22 Details of spectroscopic observations
table3.dat 86 295 Details of probable dSph members
table4.dat 90 18 Kinematic properties of Andromeda dSph galaxies as
derived from Keck I/LRIS, and Keck II/DEIMOS data
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Note on table1.dat: As derived from CFHT photometry by Ibata et al.
(2007ApJ...671.1591I 2007ApJ...671.1591I), Letarte et al. (2009MNRAS.400.1472L 2009MNRAS.400.1472L), Irwin et al.
(2008ApJ...676L..17I 2008ApJ...676L..17I), McConnachie et al. (2008ApJ...688.1009M 2008ApJ...688.1009M),
Martin et al. (2009, J/MNRAS/380/281), Collins et al. (2010MNRAS.407.2411C 2010MNRAS.407.2411C,
2011MNRAS.417.1170C 2011MNRAS.417.1170C), Brasseur et al. (2011ApJ...743..179B 2011ApJ...743..179B),
Richardson et al. (2011ApJ...732...76R 2011ApJ...732...76R), and McConnachie (2012, J/AJ/144/4),
updated for distances presented in Conn et al. (2012, J/ApJ/758/11).
The photometry for And VI is derived from Subaru SuprimeCam photometry
(Collins et al. 2011MNRAS.417.1170C 2011MNRAS.417.1170C), and the values for And XXVIII come from
SDSS photometry (Slater et al. 2011ApJ...742L..14S 2011ApJ...742L..14S).
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See also:
J/ApJ/758/11 : Bayesian distances to M31 satellites (Conn+, 2012)
J/ApJ/752/45 : SPLASH: Stellar spectroscopy of M31 satellites (Tollerud+, 2012)
J/AJ/144/4 : Properties of dSph in the Local Group (McConnachie+, 2012)
J/MNRAS/390/1437 : Stellar streams in Andromeda (M31) (Chapman+, 2008)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/MNRAS/380/281 : Faint galactic satellites spectrosc. survey (Martin+, 2007)
J/MNRAS/375/831 : Draco MegaCam, INT and HST photometry (Segall+, 2007)
J/AJ/124/1464 : Variable stars in Andromeda VI (Pritzl+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Gal Dwarf galaxy name
11 A1 --- n_Gal [c] And XXX = Cas II
13- 14 I2 h RAh Hour of right ascension (J2000)
16- 17 I2 min RAm Minute of right ascension (J2000)
19- 22 F4.1 s RAs Second of right ascension (J2000)
24 A1 --- DE- Sign of declination (J2000)
25- 26 I2 deg DEd Degree of declination (J2000)
28- 29 I2 arcmin DEm Arcminute of declination (J2000)
31- 34 F4.1 arcsec DEs Arcsecond of declination (J2000)
36- 40 F5.1 mag VMag [-10.6/-6.3] Absolute V-band magnitude
42- 45 I4 pc rh [114/1481] Half-light radius
47- 49 I3 pc E_rh [9/112] Positive uncertainty on rh
51- 53 I3 pc e_rh [12/271] Negative uncertainty on rh
55- 58 I4 kpc Dist [650/1255] Distance
60- 62 I3 kpc E_Dist [21/218] Positive uncertainty on Dist
64- 66 I3 kpc e_Dist [21/474] Negative uncertainty on Dist
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Gal Field (dwarf spheroidal) name
11 A1 --- m_Gal [ab] Index in case of multiple observations
14- 24 A11 "Y-M-D" Date Observation date
25- 27 A3 --- n_Date Observation on several days
30- 42 A13 --- Inst Instrument and grating
46- 48 F3.1 0.1nm Res [1.3/3.5] Resolution in Å
51- 52 I2 h RAh Hour of Right Ascension (J2000)
54- 55 I2 min RAm Minute of Right Ascension (J2000)
57- 61 F5.2 s RAs Second of Right Ascension (J2000)
63 A1 --- DE- [+] Sign of Declination (J2000)
64- 65 I2 deg DEd Degree of Declination (J2000)
67- 68 I2 arcmin DEm Arcminute of Declination (J2000)
70- 73 F4.1 arcsec DEs Arcsecond of Declination (J2000)
75- 77 I3 deg PA [0/315] Slit position angle
79- 82 I4 s Exp [1200/5400] Exposure time
84- 86 I3 --- Ntar [33/196] Number of targets observed
88- 89 I2 --- Nmem [1/43] Number of member stars observed
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Gal Field (dwarf spheroidal) name
11 A1 --- m_Gal [ab] Index in case of multiple observations
13- 15 I3 --- ID [1/172] Star identifier in Gal
17- 18 I2 h RAh Hour of Right Ascension (J2000)
20- 21 I2 min RAm Minute of Right Ascension (J2000)
23- 28 F6.3 s RAs Second of Right Ascension (J2000)
30 A1 --- DE- [+] Sign of Declination (J2000)
31- 32 I2 deg DEd Degree of Declination (J2000)
34- 35 I2 arcmin DEm Arcminute of Declination (J2000)
37- 42 F6.3 arcsec DEs Arcsecond of Declination (J2000)
44- 49 F6.3 mag gmag [21.4/25] The CFHT/MegaCam g-band magnitude
51- 56 F6.3 mag imag [20.3/24] The CFHT/MegaCam i-band magnitude
58- 65 F8.3 km/s HRV [-604.5/918.2] Heliocentric radial velocity
67- 73 F7.3 km/s e_HRV [1.2/227] Error in HRV
75- 80 F6.3 --- S/N [0.3/17] Signal-to-noise (per Angstrom)
82- 86 F5.3 --- Pi [0/1] Likelihood of membership (1)
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Note (1): Likelihood of membership as (equation 1):
Pi∝PCMD*Pdist*Pvel
where PCMD is the probability based on CMD position,
Pdist is the probability based on distance, and
Pvel is the probability based on velocity).
See section 3 for further details.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Gal Dwarf galaxy name
11 A1 --- n_Gal [c] And XXX = Cas II
13- 15 F3.1 --- eta [1.5/5] Free parameter η (1)
17- 22 F6.1 km/s RV [-558/-107] Radial velocity
24- 26 F3.1 km/s E_RV [0.9/6] Positive error on RV
28- 30 F3.1 km/s e_RV [0.9/7] Negative error on RV
32- 35 F4.1 km/s sigV [0/15] Velocity dispersion σV
37- 39 F3.1 km/s E_sigV Positive error on sigV
40 A1 --- f_sigV [*] non-reliable sigV (2)
42- 44 F3.1 km/s e_sigV [1/8.1] Negative error on sigV
46- 49 F4.2 10+7Msun Mh [0/8.3] Mass contained within the half-light
radius
51- 54 F4.2 10+7Msun E_Mh [0.08/5] Positive error on Mh
56- 59 F4.2 10+7Msun e_Mh [0.06/5] Negative error on Mh
61- 66 F6.1 Msun/Lsun [M/L] [0/1391] Dynamical central mass-to-light ratio
68- 73 F6.1 Msun/Lsun E_[M/L] [4.2/1039] Positive error on [M/L]
75- 80 F6.1 Msun/Lsun e_[M/L] [3.9/1128] Negative error on [M/L]
82- 85 F4.1 [Sun] [Fe/H] [-2.2/-1.4] Spectroscopic [Fe/H]
87- 90 F4.2 [Sun] e_[Fe/H] [0.1/0.6] [Fe/H] uncertainty
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Note (1): In Section 3.3, we tested that our velocity probability criteria was
not overly biasing our final measurements of velocity dispersion to
artificially lower values with the introduction of an extra parameter,
η, that allows us to add additional weight to stars in the tails
of the Gaussian velocity distribution.
Note (2):
* = Velocity dispersions derived from fewer than eight members stars, and
require confirmation from further follow-up.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 28-Nov-2014