J/A+A/635/A107 Spectroscopy of the Eri 2 cluster (Zoutendijk+, 2020)
The MUSE-Faint survey.
I. Spectroscopic evidence for a star cluster in Eridanus 2 and constraints on
MACHOs as a constituent of dark matter.
Zoutendijk S.L., Brinchmann J., Boogaard L.A., Gunawardhana M.L.P.,
Husser T.-O., Kamann S., Ramos Padilla A.F., Roth M.M., Bacon R.,
den Brok M., Dreizler S., Krajnovic K.
<Astron. Astrophys. 635, A107 (2020)>
=2020A&A...635A.107Z 2020A&A...635A.107Z (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Radial velocities ; Abundances, [Fe/H]
Keywords: dark matter - galaxies: individual: Eridanus 2 -
galaxies: star clusters: individual: Eridanus 2 cluster -
techniques: imaging spectroscopy
Abstract:
It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may
host a stellar cluster in its centre. If this cluster is shown
to exist, it can be used to set constraints on the mass and abundance
of massive astrophysical compact halo objects (MACHOs) as a form of
dark matter. Previous research has shown promising expectations in the
mass range of 10-100M☉, but lacked spectroscopic measurements of
the cluster. We aim to provide spectroscopic evidence regarding the
nature of the putative star cluster in Eridanus 2 and to place
constraints on MACHOs as a constituent of dark matter.
We present spectroscopic observations of the central square arcminute
of Eridanus 2 from MUSE-Faint, a survey of ultrafaint dwarf galaxies
with the Multi Unit Spectroscopic Explorer on the Very Large
Telescope. We derived line-of-sight velocities for possible member
stars of the putative cluster and for stars in the centre of
Eridanus 2. We discuss the existence of the cluster and determine new
constraints for MACHOs using the Fokker-Planck diffusion
approximation.
Out of 182 extracted spectra, we identify 26 member stars of Eridanus
2, seven of which are possible cluster members. We find intrinsic mean
line-of-sight velocities of 79.7+3.13.8km/s and
76.0+3.23.7km/s for the cluster and the bulk of Eridanus 2,
respectively, as well as intrinsic velocity dispersions of <7.6km/s
(68-% upper limit) and 10.3+3.93.2km/s, respectively. This
indicates that the cluster most likely exists as a distinct dynamical
population hosted by Eridanus 2 and that it does not have a surplus of
dark matter over the background distribution. Among the member stars
in the bulk of Eridanus 2, we find possible carbon stars, alluding to
the existence of an intermediate-age population.We derived constraints
on the fraction of dark matter that can consist of MACHOs with a given
mass between 1-105M☉. For dark matter consisting purely of MACHOs,
the mass of the MACHOs must be less than 7.6M☉ and 44M☉ at
a 68- and 95-% confidence level, respectively.
Description:
This table contains sources observed with the Multi Unit Spectroscopic
Explorer on the Very Large Telescope towards the centre of the
ultra-faint dwarf galaxy Eridanus 2 and its possible stellar cluster.
These measurements were used to determine the velocity distributions
of the putative cluster and the bulk of Eridanus 2, to assess the
nature of the cluster, and to derive constraints on massive
astrophysical compact halo objects. The sources in this table were
limited to those with a spectral signal to noise of at least 5, a
spectrum not showing galactic emission lines, and a measurement of
radial velocity; or those that we identified as potential carbon
stars. The positions have been calibrated against GAIA DR2.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
eri2.dat 127 35 Source list for Eridanus 2
--------------------------------------------------------------------------------
Byte-by-byte Description of file: eri2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 I7 --- ID Identifier
9- 16 F8.5 deg RAdeg Right ascension (J2000)
18- 26 F9.5 deg DEdeg Declination (J2000)
28- 31 F4.1 arcsec Sep Angular separation from centre of cluster
33- 36 F4.1 --- SNR Spectral signal-to-noise ratio
38- 42 F5.1 km/s RV Line-of-sight velocity (using spexxy)
44- 47 F4.1 km/s e_RV Error on line-of-sight velocity (using spexxy)
49- 53 F5.2 [Sun] [Fe/H] Metallicity (using spexxy)
55- 58 F4.2 [Sun] e_[Fe/H] Error on Metallicity (using spexxy)
60- 63 F4.2 mas plx ? GAIA DR2 parallax
65- 68 F4.2 mas e_plx ? Error on GAIA DR2 parallax
70- 74 F5.2 mag F606Wmag ? HST/ACS F606W apparent magnitude
76- 80 F5.2 mag F814Wmag HST/ACS F814W apparent magnitude
82- 87 F6.4 --- LikeIso ? Likelihood of photometry being consistent
with a broadened isochrone
89 I1 --- Member [0/1] Membership flag (0: not a member of
Eri 2, 1: member of Eri 2)
91- 97 F7.5 --- LikeCl ? Likelihood of star belonging to cluster
99-103 F5.1 km/s RV2 ? Line-of-sight velocity (using ULySS)
105-108 F4.1 km/s e_RV2 ? Error on line-of-sight velocity
(using ULySS)
110-122 A13 --- SpType2 Spectral type (using ULySS)
123-127 F5.2 [Sun] [Fe/H]2 ? Metallicity (using The Cannon)
--------------------------------------------------------------------------------
Acknowledgements:
Sebastiaan L. Zoutendijk, zoutendijk(at)strw.leidenuniv.nl
(End) Sebastiaan Zoutendijk [Leiden Obs.], Patricia Vannier [CDS] 04-Feb-2020