J/MNRAS/521/3527 Andromeda XXV new member stars kinematics (Charles+, 2023)
Andromeda XXV - a dwarf galaxy with a low central dark matter density.
Charles E.J.E., Collins M.L.M., Rich R.M., Read J.I., Kim S.Y., Ibata R.A.,
Martin N.F., Chapman S.C., Balbinot E., Weisz D.R.
<Mon. Not. R. Astron. Soc. 521, 3527-3539 (2023)>
=2023MNRAS.521.3527C 2023MNRAS.521.3527C (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, dwarf ; Galaxies, nearby ; Stars, normal ;
Velocity dispersion ; Space velocities ; Spectroscopy ;
Photometry ; Optical ; Combined data
Keywords: galaxies: dwarf - galaxies: kinematics and dynamics -
galaxies: haloes - dark matter
Abstract:
Andromeda (And) XXV has previously been reported as a dwarf spheroidal
galaxy (dSph) with little-to-no dark matter. However, the
uncertainties on this result were significant. In this study, we
nearly double the number of member stars and re-derive the kinematics
and mass of And XXV. We find that And XXV has a systemic velocity of
vr = -107.7 ± 1.0 km/s and a velocity dispersion of
σv = 3.7+1.2-1.1 km/s. With this updated velocity
dispersion and a new literature measurement of the radial surface
brightness profile, we derive a mass contained within the half-light
radius of M(r < rh) = 4.79+3.0-2.9 * 106 M☉. This mass
corresponds to a mass-to-light ratio of
[M/L]rh = 25+17-16 M☉/L☉, demonstrating that And XXV
is most-likely dark matter dominated. We also measure the metallicity
of And XXV to be [Fe/H] = -1.9 ± 0.1 dex, which is in agreement with
previous results. Finally, we extend the analysis of And XXV to
include mass modelling using GravSphere. We find that And XXV has a
low central dark matter density,
ρDM(150 pc) = 2.3+1.4-1.1 * 107 M☉ kpc-3, which
makes And XXV a clear outlier when compared to other local group dSphs
of the similar stellar mass. In a companion paper, we will explore
whether some combination of dark matter cusp-core transformations
and/or tides can explain And XXV's low density.
Description:
Dwarf galaxies are typically dark matter dominated systems, with
mass-to-light ratios in the range 10-1000s making them ideal systems
for testing dark matter physics and cosmology. The ΛCDM model
which explains the cosmic microwave background radiation, and
structure formation on large scales albeit by invoking three
mysterious components: dark matter, dark energy, and inflation.
However, on galactic scales, particularly dwarf galaxies, there have
been a number of long-standing tensions between ΛCDM
predictions and observations. In this paper, we investigate another
potential outlier, Andromeda XXV a dSph satellite galaxy of M31 first
discovered as part of the Pan-Andromeda Archaeological Survey. And XXV
was previously identified as a potential outlier within the local
group in a 2013 study of Collins et al. (2013ApJ...768..172C 2013ApJ...768..172C, C13),
which performed a kinematic analysis of numerous M31 dSph satellites.
And XXV was found to have a low velocity dispersion. This is
consistent with a dark matter dominated system. However, due to the
small number of member stars (26) with stellar kinematics in their
sample, the uncertainty on this value is significant. As such, within
the uncertainties the presence of dark matter is not required and And
XXV could be described by a simple stellar system with no appreciable
dark matter component. C13 point out, more stellar velocities are
needed to confirm or rule out the presence of dark matter in this
system.
We present a revised kinematic analysis, using the spectroscopic data
set outlined in C13 combined with new observations to provide a larger
sample size, nearly double that used in C13, allowing us to critically
reassess if And XXV really is a dSph with no appreciable dark matter.
We will also extend the analysis to investigate the metallicity of And
XXV. Finally we use the dynamical mass modelling tool BINULATOR +
GravSphere to gain an insight into the dark matter content of And XXV.
We use spectroscopic data obtained using DEIMOS mounted on the Keck II
telescope. The observations are comprised of two masks. The first was
taken in September 2010 (previously presented in C13), and the second
mask was observed on 2018 August 18. The instrumental setup was the
same for both masks, using a resolution of 1.3 Å. To determine the
velocity and metallicity of each member star, we use the calcium
triplet Ca II lines in the region around ∼8500 Å, our observations
targeted the wavelength range of ∼5600-9800 Å with a central
wavelength of 7800 Å to resolve these lines. During data treatment
with a custom pipeline, velocities and uncertainties for all stars
were derived using the strong Ca II triplet feature found in spectra.
A MCMC fit a Gaussian to these features to extract offset of lines and
convert them to velocities. More, we obtained photometric data with
Large Binocular Cameras mounted on the Large Binocular Telescope in V
Bessel and i Sloan bands. We use morphologies to consider only stellar
objects, data were corrected using the dust maps and AV = 0.27 mag,
Ai = 0.171 mag. The photometric and spectroscopic observations were
combined by a 1" cross-match.
As desribed in section 3, members probability of stars are computed
before kinematic analysis of And XXV with equation 7 corresponding to
products of multiple probabilties components. After setting
probability cuts, we identified 49 members of And XXV. Next, the
kinematic analysis is realized likelihood function to product
distributions of velocities, velocity dispersion and membership
probabilities (i.e. section 4). We provide astrometrics, photometry,
velocities and membership probabilties a table fullkine.dat of stars
sample before cut-off which comprises 179 sources and after cut-off
with 49 stars with 0.828 => Pmemb => 0.117.
Objects:
----------------------------------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------------------------------
00 30 08.89 +46 51 07.0 Andromeda XXV = LEDA 5057228
----------------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fullkine.dat 56 179 The astrometrics, photometry and probability of
the full kinematics stars sample
membkine.dat 56 49 The astrometrics, photometry and probability of
identified Andromeda XXV member stars
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See also:
J/MNRAS/491/3496 : Andromeda XIX member stars (Collins+, 2020)
J/MNRAS/488/2743 : Giant Galactic dwarf satellite in Gaia DR2 (Torrealba+,2019)
J/MNRAS/485/2010 : Kinematics of the Tucana Dwarf Galaxy (Gregory+, 2019)
J/MNRAS/380/281 : Faint galactic satellites spectroscopic survey
(Martin+, 2007)
J/ApJ/895/78 : [Fe/H] and [α/Fe] in M31 dwarf galaxies (Wojno+, 2020)
J/ApJ/883/11 : Magellan/IMACS spectra of Crater II & Hercules (Fu+, 2019)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/ApJ/838/83 : Radial velocities, abundances & membership in TriII
(Kirby+, 2017)
J/ApJ/833/167 : PAndAS view of Andromeda satellites. II. (Martin+, 2016)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/798/77 : Metallicity of RGB stars in 6 M31 dwarf galaxies (Ho+, 2015)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/768/172 : Kinematic analysis of red giant in M31 dSphs (Collins+,2013)
J/ApJ/752/45 : SPLASH: Stellar spectroscopy of M31 satellites
(Tollerud+, 2012)
J/ApJ/738/186 : HST and DEIMOS measurements of NGC 2419 stars (Ibata+, 2011)
J/ApJ/733/46 : Velocity measurements in Segue 1 (Simon+, 2011)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: fullkine.dat membkine.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.4 deg RAdeg Right ascension (J2000) (RA)
10- 16 F7.4 deg DEdeg Declination (J2000) (dec)
18- 25 F8.2 km/s V Kinematic velocity (vel)
27- 31 F5.2 km/s e_V Uncertainty of V (vel_err)
33- 37 F5.2 mag Vmag Apparent magnitude in V optical band (Vmag)
39- 43 F5.2 mag imag Apparent magnitude in i optical band (imag)
45- 50 F6.3 --- S/N Signal to noise ratio (S/N)
52- 56 F5.3 --- Pmem Membership probability estimates (P_member)
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Luc Trabelsi [CDS] 05-Jun-2026