J/MNRAS/495/3022 Stellar populations of the Ursa Minor dSph galaxy (Pace+, 2020)
Multiple chemodynamic stellar populations of the Ursa Minor dwarf spheroidal
galaxy.
Pace A.B., Kaplinghat M., Kirby E., Simon J.D., Tollerud E., Munoz R.R.,
Cote P., Djorgovski S.G., Geha M.
<Mon. Not. R. Astron. Soc., 495, 3022-3040 (2020)>
=2020MNRAS.495.3022P 2020MNRAS.495.3022P (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, dwarf ; Local group ; Positional data ;
Radial velocities ; Abundances, [Fe/H] ; Optical
Keywords: galaxies: evolution - galaxies: kinematics and dynamics -
Local Group - cosmology: dark matter -
galaxies: individual: Ursa Minor dSph
Abstract:
We present a Bayesian method to identify multiple (chemodynamic)
stellar populations in dwarf spheroidal galaxies (dSphs) using
velocity, metallicity, and positional stellar data without the
assumption of spherical symmetry. We apply this method to a new
Keck/Deep Imaging Multi-Object Spectrograph (DEIMOS) spectroscopic
survey of the Ursa Minor (UMi) dSph. We identify 892 likely members,
making this the largest UMi sample with line-of-sight velocity and
metallicity measurements. Our Bayesian method detects two distinct
chemodynamic populations with high significance (in logarithmic Bayes
factor, lnB∼33). The metal-rich ([Fe/H]=-2.05±0.03) population is
kinematically colder (radial velocity dispersion of
σv=4.9-1.0+0.8km/s) and more centrally concentrated than
the metal-poor ([Fe/H]=-2.29-0.06+0.05) and kinematically hotter
population (σv=11.5-0.8+0.9km/s). Furthermore, we apply
the same analysis to an independent Multiple Mirror Telescope
(MMT)/Hectochelle data set and confirm the existence of two
chemodynamic populations in UMi. In both data sets, the metal-rich
population is significantly flattened (ε=0.75±0.03) and the
metal-poor population is closer to spherical
(ε=0.33-0.09+0.12). Despite the presence of two
populations, we are able to robustly estimate the slope of the
dynamical mass profile. We found hints for prolate rotation of order
∼2km/s in the MMT data set, but further observations are required to
verify this. The flattened metal-rich population invalidates
assumptions built into simple dynamical mass estimators, so we
computed new astrophysical dark matter annihilation (J) and decay
profiles based on the rounder, hotter metal-poor population and
inferred log10(J(0.5°)/GeV2cm-5)∼19.1 for the Keck data set.
Our results paint a more complex picture of the evolution of UMi than
previously discussed.
Description:
Spectroscopic observations were carried out on 2009 February 22-23
(first presented by Kirby et al. 2010ApJS..191..352K 2010ApJS..191..352K, Cat.
J/ApJS/191/352), 2010 May 11-12 (first presented by Kirby et al.
2018ApJS..237...18K 2018ApJS..237...18K, Cat. J/ApJS/237/18), and 2012 April 20-22 (not
previously published) on the Keck/DEIMOS spectrograph (Faber et al.
2003SPIE.4841.1657F 2003SPIE.4841.1657F). All these observations used the 1200G
diffraction grating, which has a groove spacing of 1200mm-1 and a
blaze wavelength of 7760Å. The grating was tilted such that the
typical central wavelength of a spectrum was 7800Å, and the typical
wavelength range was about 2600Å.
Spectroscopic targets were selected from various photometric
catalogues. Where the slitmask design constraints forced a choice
among multiple candidates, we prioritized stars on the red giant
branch (RGB). Kirby et al. (2010ApJS..191..352K 2010ApJS..191..352K, Cat. J/ApJS/191/352)
described the slitmask design for the 2009 observations. Targets were
selected from Bellazzini et al.'s (2002AJ....124.3222B 2002AJ....124.3222B, Cat.
J/AJ/124/3222) photometric catalogue in the V and I filters. We used
the CMD in conjunction with Yonsei-Yale isochrones (Demarque et al.
2004ApJS..155..667D 2004ApJS..155..667D) to inform the selection.
Slitmasks from the 2010 observations were designed from Sloan Digital
Sky Survey (SDSS) ugriz photometry (Abazajian et al.
2009ApJS..182..543A 2009ApJS..182..543A, Cat. II/294). Stars were selected to lie within a
colour range around a 14.1Gyr, [Fe/H]=-1.63, Padova isochrone (Girardi
et al. 2004A&A...422..205G 2004A&A...422..205G). The allowed range was 0.4mag bluer and
0.3mag redder in (g-r)0 colour. We also selected HB stars from a box
in the CMD: 21>r0>20 and -0.4<(g-r)0<0.0. As for the 2009
observations, brighter stars were given higher priorities for
spectroscopic selection.
Objects:
----------------------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------------------
15 09 11.34 +67 12 51.7 NAME UMi Galaxy = Anon 1508+67 = DDO 199
----------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 144 1716 List of Keck/DEIMOS velocity and metallicity
measurements
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
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)
J/ApJS/237/18 : Cr, Co, and Ni abundances for metal-poor red giants
(Kirby+, 2018)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID [1/1538] Internal identifier
6- 24 I19 --- GaiaDR2 ? Gaia DR2 source identifier
26- 31 I6 --- Megacam ? Megacam identifier (Munoz et al.
2018ApJ...860...65M 2018ApJ...860...65M, Cat. J/ApJ/860/65)
33- 42 F10.6 deg RAdeg Right ascension (J2000)
44- 52 F9.6 deg DEdeg Declination (J2000)
54- 59 A6 --- Mask Slitmask
61- 67 F7.1 d MJD Modified Julian date
69- 74 F6.1 km/s vLOS Line of sight velocity
76- 79 F4.1 km/s e_vLOS Error on vLOS
81- 86 F6.1 km/s vLOSu Unique line of sight velocity for stars with
multiple measurements
88- 91 F4.1 km/s e_vLOSu Error on vLOSu
93- 97 F5.2 [-] [Fe/H] ? Fe/H abundance ratio
99- 102 F4.2 [-] e_[Fe/H] ? Error on [Fe/H]
104- 108 F5.2 [-] [Fe/H]u ? Unique Fe/H abundance ratio for stars with
multiple measurements
110- 113 F4.2 [-] e_[Fe/H]u ? Error on [Fe/H]u
115- 118 F4.2 --- PdSph ? Dwarf spheroidal galaxy membership
probability
120- 123 F4.2 --- PMR ? Metal-rich population membership
probability
125- 144 A20 --- Comments Comments (1)
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Note (1): Comments as follows:
CMD = excluded due to location on colour-magnitude diagram
GaiaNM = non-member due to non-zero parallax and/or large proper motion
RRLPS1 = RR Lyrae star in the PS1 catalogue
RRLGaia = RR Lyrae star in the Gaia catalogue
NA8190 = MW foreground star due to NaI doublet
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 19-Jun-2023