J/ApJ/692/1464 Spectroscopy of Segue 1 (Geha+, 2009)
The least-luminous galaxy: spectroscopy of the Milky Way satellite Segue 1.
Geha M., Willman B., Simon J.D., Strigari L.E., Kirby E.N., Law D.R.,
Strader J.
<Astrophys. J., 692, 1464-1475 (2009)>
=2009ApJ...692.1464G 2009ApJ...692.1464G
ADC_Keywords: Galaxies, nearby ; Photometry, SDSS ; Radial velocities
Keywords: galaxies: dwarf - galaxies: individual (Segue 1) - galaxies:
kinematics and dynamics - Local Group
Abstract:
We present Keck/DEIMOS spectroscopy of Segue 1, an
ultra-low-luminosity (MV=-1.5+0.6-0.8) Milky Way satellite
companion. While the combined size and luminosity of Segue 1 are
consistent with either a globular cluster or a dwarf galaxy, we
present spectroscopic evidence that this object is a dark
matter-dominated dwarf galaxy. We identify 24 stars as members of
Segue 1 with a mean heliocentric recession velocity of 206±1.3km/s.
Although Segue 1 spatially overlaps the leading arm of the Sagittarius
stream, its velocity is 100km/s different from that predicted for
recent Sagittarius tidal debris at this position. Using spectral
synthesis modeling, we derive a metallicity for the single red giant
branch star in our sample of [Fe/H]=-3.3±0.2dex. We conclude that
Segue 1 is the least luminous of the ultra-faint galaxies recently
discovered around the Milky Way, and is thus the least-luminous known
galaxy.
Description:
Targets were selected for spectroscopy based on gri photometry of
Segue 1 from the SDSS DR6 public database.
One multislit mask was observed for Segue 1 using the Keck II 10m
telescope and the DEIMOS spectrograph on the night of 2007 November
12. The mask was observed for a total of 5400s through the 1200
line/mm grating covering a wavelength region 6400-9100Å and the
resulting spectral resolution is 1.37Å (FWHM).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 82 51 Keck/DEIMOS velocity measurements for stars in
Segue 1 sample
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See also:
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/ApJS/191/352 : Abundances in stars of Milky Way dwarf satellites (Kirby+,
2010)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Mm Sample type (members/non-members)
23- 29 I07 --- ID SDSS-DR6 source identification (the last seven
digits of "ObjId" identifying the object)
31- 32 I2 h RAh Hour of Right Ascension (J2000)
34- 35 I2 min RAm Minute of Right Ascension (J2000)
37- 40 F4.1 s RAs Second of Right Ascension (J2000)
42 A1 --- DE- Sign of the Declination (J2000)
43- 44 I2 deg DEd Degree of Declination (J2000)
46- 47 I2 arcmin DEm Arcminute of Declination (J2000)
49- 52 F4.1 arcsec DEs Arcsecond of Declination (J2000)
54- 57 F4.1 mag gmag SDSS-DR6 g band magnitude
59- 63 F5.2 mag g-r SDSS-DR6 (g-r) color index
65- 70 F6.1 km/s HRV Heliocentric radial velocity (1)
72- 75 F4.1 km/s e_HRV Error in HRV
77- 82 F6.1 km/s Vgsr Galactocentric velocity (1)
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Note (1): Radial velocities were measured by cross-correlating the observed
science spectra with a set of high signal-to-noise stellar templates.
The method is the same as that described in Simon & Geha,
2007ApJ...670..313S 2007ApJ...670..313S. We apply both a telluric and heliocentric
correction to all velocities. See section 2.3 for further details.
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History:
From electronic version of the journal
References:
Simon & Geha. The Kinematics of the Ultra-faint Milky Way Satellites:
Solving the Missing Satellite Problem. 2007ApJ...670..313S 2007ApJ...670..313S
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 07-Mar-2011