J/ApJ/883/11 Magellan/IMACS spectra of Crater II & Hercules (Fu+, 2019)
Dynamical histories of the Crater II and Hercules dwarf galaxies.
Fu S.W., Simon J.D., Jara A.G.A.
<Astrophys. J., 883, 11 (2019)>
=2019ApJ...883...11F 2019ApJ...883...11F
ADC_Keywords: Galaxies, spectra; Spectra, infrared; Optical; Surveys;
Radial velocities; Abundances, [Fe/H]; Equivalent widths
Keywords: galaxies: dwarf ; galaxies: individual (Crater II, Hercules) ;
galaxies: kinematics and dynamics ; Galaxy: halo ; Local Group
Abstract:
We investigate the possibility that the dwarf galaxies Crater II and
Hercules have previously been tidally stripped by the Milky Way. We
present Magellan/IMACS spectra of candidate member stars in both
objects. We identify 37 members of Crater II, 25 of which have
velocity measurements in the literature, and we classify three stars
within that subset as possible binaries. We find that including or
removing these binary candidates does not change the derived velocity
dispersion of Crater II. Excluding the binary candidates, we measure a
velocity dispersion of σVlos=2.7-0.4+0.5km/s,
corresponding to M/L=47-13+17M☉/L☉. We measure a mean
metallicity of [Fe/H]=-1.95-0.05+0.06, with a dispersion of
σ[Fe/H]=0.18-0.08+0.06. Our velocity dispersion and
metallicity measurements agree with previous measurements for Crater
II, and confirm that the galaxy resides in a kinematically cold
dark-matter halo. We also search for spectroscopic members stripped
from Hercules in the possible extratidal stellar overdensities
surrounding the dwarf. For both galaxies, we calculate proper motions
using Gaia DR2 astrometry, and use their full 6D phase space
information to evaluate the probability that their orbits approach
sufficiently close to the Milky Way to experience tidal stripping.
Given the available kinematic data, we find a probability of ∼40% that
Hercules has suffered tidal stripping. The proper motion of Crater II
makes it almost certain to be stripped.
Description:
We make our observations using the IMACS spectrograph on the Magellan
Baade telescope with R∼11000 and spectra covering the Ca triplet lines
in the near-infrared.
We observed a total of four slitmasks targeting candidate member stars
in Crater II on three nights in 2018 March.
We observed a total of three slitmasks targeting candidate member
stars in the extratidal densities surrounding Hercules. Our
observations targeted the overdensities (ODs) 13.2 and 16 as
designated in Roderick+ (2015ApJ...804..134R 2015ApJ...804..134R). We observed Hercules
during one night in 2016 June and two nights in 2017 June. Overall, we
observed two masks in OD13.2 and one mask in OD16.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 123 272 Spectroscopic measurements for Crater II and
Hercules targets -- from erratum published
in 2021, ApJ, 923, 281
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/131/2114 : Radial velocities in Fornax dSph (Walker+, 2006)
J/ApJ/704/898 : Photometry of the Hercules dwarf galaxy (Sand+, 2009)
J/ApJ/756/121 : Variable stars in Her dwarf galaxy (Musella+, 2012)
J/ApJ/752/45 : SPLASH: Stellar spec. of M31 satellites (Tollerud+, 2012)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/ApJ/768/172 : Kinematic of red giant in M31 dSphs (Collins+, 2013)
J/A+A/570/A61 : PM-selected stars of Hercules galaxy (Fabrizio+, 2014)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/833/167 : PAndAS view of Andromeda satellites. II. (Martin+, 2016)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/ApJ/861/23 : RR Lyrae stars in the Crater II dwarf galaxy (Joo+, 2018)
J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)
J/A+A/620/A155 : Gaia proper motions of 7 UFD galaxies (Massari+, 2018)
J/ApJ/863/25 : Deep Megacam obs. of 4 MW satellites (Mutlu-Pakdil+, 2018)
J/ApJ/863/89 : Gaia DR2 PMs in ultra-faint MW satellites (Simon, 2018)
J/AJ/156/257 : RGB stars spectroscopy in Draco & Ursa Minor (Spencer+, 2018)
J/A+A/616/A165 : K' images of star-forming dwarf galaxies (Vaduvescu+, 2018)
J/ApJ/875/77 : PMs of MW satellites with Gaia & DES (Pace+, 2019)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Gal Dwarf galaxy name
7- 30 A24 --- objID Unique object identifier in source catalog
(PSO JHHMMSS.ss+DDMMSS.s or
SDSS JHHMMSS.ss+DDMMSS.s)
32- 38 F7.1 d MJD [57567.0/58203.3]? Modified Julian Date of
spectrum (JD-2400000.5) (2)
40- 48 F9.5 deg RAdeg [177/247.6] Right Ascension (J2000)
50- 58 F9.5 deg DEdeg [-18.7/13] Declination (J2000)
60- 64 F5.2 mag gmag [13.3/23.2] g-band AB magnitude in filter
system (PS1 or SDSS) (1)
66- 70 F5.2 mag rmag [12.2/21.4] r-band AB magnitude in filter
system (PS1 or SDSS) (1)
72- 75 A4 --- Source Source catalog and filter system
(PS1 or SDSS) (1)
77- 81 F5.1 pix-1 SN [5/496.5] Signal-to-Noise ratio per pixel
83- 88 F6.1 km/s HRV [-487/400] Heliocentric radial velocity
90- 95 F6.1 km/s e_HRV [1/6.4] Uncertainty in HRV
97- 99 F3.1 0.1nm EWCa [1.3/7.3]? Equivalent Width,
five-parameter calcium triplet
101-103 F3.1 0.1nm e_EWCa [0/1]? Uncertainty in EWCa
105-109 F5.2 [-] [Fe/H] [-2.82/-1.74]? Metallicity, [Fe/H]
111-114 F4.2 [-] e_[Fe/H] [0.15/0.53]? Uncertainty in [Fe/H]
116-121 A6 --- Reg Region of Hercules overdensity (3)
123 I1 --- Mm [0/1]? Membership in dwarf galaxy (4)
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Note (1): Cataloged information for each Dwarf Galaxy depends upon the
source, where PS1 is the Pan-STARRS photometry for Crater II and SDSS is
the SDSS-III data for Hercules. The gr band photometry is in the
corresponding system and is not dereddened.
Note (2): Only Crater II targets and OC16 Hercules region targets have
Modified Julian Dates provided for the spectrum observed as the OD13.2
spectra are combined from two observations.
Note (3): Overdensities (ODs) 13.2 and 16 as designated in
Roderick+ (2015ApJ...804..134R 2015ApJ...804..134R).
Note (4): Membership code as follows:
0 = Non-member of Crater II or Hercules (235 occurrences);
1 = Member of Crater II (37 occurrences).
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Nomenclature note:
Objects from Pan-STARRS are in Simbad.
History:
From electronic version of the journal
05-Jul-2021:Insert into VizieR
21-Jan-2022:Table 2 corrected from erratum published in 2021, ApJ, 923, 281
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Feb-2021