J/A+A/634/A10 Chemo-kinematic properties of Aquarius (Hermosa Munoz+, 2020)
Kinematical and metallicity properties of the Aquarius dwarf from FORS2 MXU
spectroscopy.
Hermosa Munoz L., Taibi S., Battaglia G., Iorio G., Rejkuba M., Leaman R.,
Cole A.A., Irwin M., Jablonka P., Kacharov N., McConnachie A.,
Starkenburg E., Tolstoy E.
<Astron. Astrophys. 634, A10 (2020)>
=2020A&A...634A..10H 2020A&A...634A..10H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Galaxies, rotation ;
Radial velocities ; Abundances, [Fe/H] ; Spectroscopy
Keywords: techniques: spectroscopic - galaxies: dwarf - Local Group -
galaxies: kinematics and dynamics - galaxies: abundances -
galaxies: stellar content
Abstract:
Dwarf galaxies found in isolation in the Local Group (LG) are unlikely
to have interacted with the large LG spirals, and therefore
environmental effects such as tidal and ram-pressure stripping should
not be the main drivers of their evolution.
We aim to provide insight into the internal mechanisms shaping LG
dwarf galaxies by increasing our knowledge of the internal properties
of isolated systems. Here we focus on the evolved stellar component of
the Aquarius dwarf galaxy, whose kinematic and metallicity properties
have only recently started to be explored.
Spectroscopic data in the region of the near-infrared Ca∼II triplet
lines has been obtained with FORS2 at the Very Large Telescope for 53
red giant branch (RGB) stars. These data are used to derive
line-of-sight velocities and [Fe/H] of the individual RGB stars.
We have derived a systemic velocity of -142.2+1.8-1.8km/s, in
agreement with previous determinations from both the HI gas and stars.
The internal kinematics of Aquarius appears to be best modelled by a
combination of random motions (l.o.s. velocity dispersion of
10.3+1.6-1.3km/s) and linear rotation (with a gradient
-5.0+1.6-1.9km/s/arcmin) along a P.A.=139-27+17deg,
broadly consistent with the optical projected major axis. This
rotation signal is significantly misaligned or even counter-rotating
to that derived from the HI gas. We also find the tentative presence
of a mild negative metallicity gradient and indications that the
metal-rich stars have a colder velocity dispersion than the metal-poor
ones. This work represents a significant improvement with respect to
previous measurements of the RGB stars of Aquarius, as it doubles the
number of member stars already studied in the literature. We speculate
that the misaligned rotation between the HI gas and evolved stellar
component might have been the result of recent accretion of HI gas, or
re-accretion after gas-loss due to internal stellar feedback.
Description:
We observed two slits with two different masks with VLT/FORS2 in the
region of the nIR CaII triplet lines for 53 candidate red giant branch
(RGB) stars. The temporal baseline spanned a period between 2013 June
7 and September 3. We used the 1028z+29 holographic grism in
conjunction with the OG590+32 order separation filter, to cover a
wavelength range of 7700-9500Å. This set-up, combined with the
slit widths of 1" (0.8" in some cases to avoid overlap between
adjacent stars), yielded a resolving power of about R∼2600 at
8600Å.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea2.dat 125 53 Properties of the observed VLT/FORS2 targets in
the Aquarius dwarf
sp/* . 110 Individual spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Field Field number (1)
8- 9 I2 --- Ap Slit aperture (2)
11- 19 F9.5 deg RAdeg Right ascension (J2000)
21- 29 F9.5 deg DEdeg Declination (J2000)
31- 37 F7.2 km/s HV Line-of-sight heliocentric velocity
39- 43 F5.2 km/s e_HV Error on the heliocentric velocity
45- 49 F5.2 pix-1 SNR Signal-to-noise ratio
51- 55 F5.2 [-] [Fe/H] Metallicity
57- 60 F4.2 [-] e_[Fe/H] Metallicity error
62- 67 F6.3 --- Vmag V-band magnitude
69- 73 F5.3 --- e_Vmag V-band magnitude error
75- 80 F6.3 --- Imag I-band magnitude
82- 86 F5.3 --- e_Imag I-band magnitude error
88 A1 --- Memb [N/Y] Membership
90-104 A15 --- Spectrum Name of the spectrum file,
in subdirectory sp (3)
107-125 A19 --- Sigma Name of the spectrum error file,
in subdirectory sp (3)
--------------------------------------------------------------------------------
Note (1): Fields number as follows:
aqu + 0/1 = Mask
c + 1/2 = Chip
Note (2): numbers <30 indicate targets from chip-1, otherwise from chip-2
numbers counted from bottom to top of the CCD.
Note (3): The spectra of the stars labelled as aqu1c1_ap13 and aqu1c1_ap17
are not quoted in the table, as their results have been combined
with the spectra of aqu0c1_ap11 and aqu0c1_ap16, respectively.
Those 2 stars have been measured twice in our sample.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambda Wavelength
10- 18 F9.6 --- RFlux Relative flux
--------------------------------------------------------------------------------
Acknowledgements:
Laura Hermosa Munoz, lhermosa(at)iaa.es
History:
28-Jan-2020: on-line version
28-Oct-2020: some Ap numbers corrected to be the same as those in the table
presented in the paper
(End) Patricia Vannier [CDS] 02-Dec-2019