J/MNRAS/397/1748 Spectroscopic study of Segue 2 (Belokurov+, 2009)
The discovery of Segue 2: a prototype of the population of satellites of
satellites.
Belokurov V., Walker M.G., Evans N.W., Gilmore G., Irwin M.J., Mateo M.,
Mayer L., Olszewski E., Bechtold J., Pickering T.
<Mon. Not. R. Astron. Soc., 397, 1748-1755 (2009)>
=2009MNRAS.397.1748B 2009MNRAS.397.1748B
ADC_Keywords: Galaxies, nearby ; Photometry, SDSS ; Radial velocities
Keywords: galaxies: dwarf - galaxies: individual: Segue 2 - Local Group
Abstract:
We announce the discovery of a new Milky Way satellite Segue 2 found
in the data of the Sloan Extension for Galactic Understanding and
Exploration (SEGUE). We followed this up with deeper imaging and
spectroscopy on the Multiple Mirror Telescope (MMT). From this, we
derive a luminosity of Mv=-2.5, a half-light radius of 34pc and a
systemic velocity of ~-40km/s. Our data also provide evidence for a
stream around Segue 2 at a similar heliocentric velocity, and the
SEGUE data show that it is also present in neighbouring fields. We
resolve the velocity dispersion of Segue 2 as 3.4km/s and the possible
stream as ∼7km/s. This object shows points of comparison with other
recent discoveries, Segue 1, Boo II and Coma. We speculate that all
four objects may be representatives of a population of satellites of
satellites - survivors of accretion events that destroyed their larger
but less dense parents. They are likely to have formed at redshifts
z>10 and are good candidates for fossils of the reionization epoch.
Description:
Follow-up imaging of Segue 2 was carried out on 2007 October 7 using
the Megacam imager on the Multiple Mirror Telescope (MMT).
On 2008 October 22-23 and 26, we obtained high-resolution spectra of
352 targets around Segue 2 using three independent fibre
configurations with the Hectochelle spectrograph at the MMT.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 73 422 Hectochelle spectroscopy of Segue 2
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See also:
J/ApJ/694/L144 : Spectroscopic study of Leo V (Walker+, 2009)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- --- [Seg2-]
6- 8 I03 --- Seq Number in galaxy
10- 11 I2 h RAh Rihgt ascension (J2000)
13- 14 I2 min RAm Rihgt ascension (J2000)
16- 20 F5.2 s RAs Rihgt ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 32 F4.1 arcsec DEs Declination (J2000)
34- 37 F4.1 arcmin R Angular radius from Segue 2 center
39- 43 F5.2 mag gmag g magnitude
45- 49 F5.2 mag imag i magnitude
51- 56 F6.1 km/s HV Heliocentric velocity
58- 60 F3.1 km/s e_HV rms uncertainty on HV
62- 66 F5.2 0.1nm sigMg ? Composite magnesium index (1)
68- 71 F4.2 0.1nm e_sigMg ? rms uncertainty on sigMg
73 A1 --- Mm [BSY?N] Membership status (2)
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Note (1): Weighted sum of pseudo-equivalent widths for each individual line
of the Mg-I/Mg-b triplet (see Walker et al., 2007ApJS..171..389W 2007ApJS..171..389W).
Note (2): Membership flag as follows:
Y = member, on the bright part of the RGB (5 stars)
N = no association with Segue 2
? = possible member from the fainter region of the RGB (3 stars)
B = blue horizontal branch (BHB) member (3 stars)
S = stream candidate (15 stars)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 16-Nov-2009