J/ApJ/733/46 Velocity measurements in Segue 1 (Simon+, 2011)
A complete spectroscopic survey of the Milky Way satellite Segue 1: the darkest
galaxy.
Simon J.D., Geha M., Minor Q.E., Martinez G.D., Kirby E.N., Bullock J.S.,
Kaplinghat M., Strigari L.E., Willman B., Choi P.I., Tollerud E.J., Wolf J.
<Astrophys. J., 733, 46 (2011)>
=2011ApJ...733...46S 2011ApJ...733...46S
ADC_Keywords: Galaxies, nearby ; Stars, normal ; Radial velocities ;
Equivalent widths ; Photometry, SDSS ; Spectroscopy
Keywords: dark matter - galaxies: dwarf - galaxies: individual (Segue 1) -
galaxies: kinematics and dynamics - Local Group
Abstract:
We present the results of a comprehensive Keck/DEIMOS spectroscopic
survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have
obtained velocity measurements for 98.2% of the stars within 67pc
(10', or 2.3 half-light radii) of the center of Segue 1 that have
colors and magnitudes consistent with membership, down to a magnitude
limit of r=21.7. Based on photometric, kinematic, and metallicity
information, we identify 71 stars as probable Segue 1 members,
including some as far out as 87pc. After correcting for the influence
of binary stars using repeated velocity measurements, we determine a
velocity dispersion of 3.7+1.4-1.1km/s. The mass within the
half-light radius is 5.8+8.2-3.1x105M☉. The stellar
kinematics of Segue 1 require very high mass-to-light ratios unless
the system is far from dynamical equilibrium, even if the period
distribution of unresolved binary stars is skewed toward implausibly
short periods. With a total luminosity less than that of a single
bright red giant and a V-band mass-to-light ratio of
3400M☉/L☉, Segue 1 is the darkest galaxy currently known.
Description:
We observed 12 new slit masks, including at least one slit placed on
each of the 112 candidate member stars (plus repeat observations of 18
of the 24 members from Geha et al., 2009, Cat. J/ApJ/692/1464), with
the DEIMOS spectrograph on the Keck II telescope. The observations
took place on the nights of 2009 February 18, 26, and 27 and 2010
February 12 and 13.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 94 522 Velocity measurements in Segue 1
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See also:
II/306 : The SDSS Photometric Catalog, Release 8 (Adelman-McCarthy+, 2011)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJ/692/1464 : Spectroscopy of Segue 1 (Geha+, 2009)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- --- [SDSS]
5- 23 A19 --- SDSS SDSS-DR5 identification (JHHMMSS.ss+DDMMSS.s)
25- 30 F6.1 km/s Vel [-180.2/394.9] Heliocentric velocity
32- 35 F4.1 km/s e_Vel [2.2/37.8] Uncertainty in Vel
37- 40 F4.1 0.1nm EW Weighted sum of CaT line equivalent widths (1)
42- 45 F4.1 0.1nm e_EW ?=-9.9 Uncertainty in EW (1)
47- 50 F4.1 arcmin Rad [0/17.8] Radial distance from Segue 1
52- 60 F9.3 d MJD [54416.5/55240.5] Modified Julian Date of
observation
62- 66 F5.2 mag gmag ? SDSS-DR5 g band magnitude
68- 72 F5.2 mag rmag ? SDSS-DR5 r band magnitude
74- 78 F5.2 mag imag [13.22/22]? SDSS-DR5 i band magnitude
80 I1 --- Mm [0/1]? Member status (0=no, 1=member) (2)
82- 87 F6.3 --- EMpr [0/1]? Member probability from the
EM (Expectation Maximization) algorithm (3)
89- 94 F6.3 --- Bpr [0/1]? Bayesian member probability (4)
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Note (1): Where EW=0.5*EW8498+1.0*EW8542+0.6*EW8662. For a few stars
our spectra did not cover any of the CaT lines, so we did not measure
the EW (their velocities were determined with other features). These
objects are listed with equivalent widths of -9.9.
Note (2): According to the criteria established at the beginning of Section 3.1.
1 = member;
0 = non-member.
Note (3): The algorithm is run on the subset of stars whose colors and
magnitudes are consistent with membership, so photometric non-members
are indicated by probability -9.999.
Note (4): From the Bayesian approach. As with the EM algorithm, these
calculations are run on the subset of stars whose colors and
magnitudes are consistent with membership, so photometric non-members
are indicated by probability -9.999.
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History:
From electronic version of the journal
References:
Martinez et al. Paper II. 2011ApJ...738...55M 2011ApJ...738...55M
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 06-Nov-2012