Kinematic and metallicity properties od the Aquarius dwarf galaxy from FORS2 MXU spectroscopy

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 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. We focus on the evolved stellar component of the Aquarius dwarf, whose kinematic and metallicity properties have only recently started to be explored. We have obtained spectroscopic data in the the near-infrared CaII triplet lines region with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars, to derive line-of-sight velocities and [Fe/H] of the individual RGB stars. We have derived a systemic velocity of $-142.2_{-1.8}^{+1.8}$ km s${}^{-1}$, in agreement with previous measurements 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 $10.3_{-1.3}^{+1.6}$ km s${}^{-1}$) and linear rotation (with a gradient $-5.0_{-1.9}^{+1.6}$ km s${}^{-1}$ arcmin${}^{-1}$) along a P.A.=$139_{-27}^{+17}$ deg, 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 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.

Accepted for publication in A&A. 15 pages, 9 figures

References in corpus (16)

• Updated Nearby Galaxy Catalog
• High-resolution mass models of dwarf galaxies from LITTLE THINGS
• The DART imaging and CaT survey of the Fornax Dwarf Spheroidal Galaxy
• The NIR Ca II triplet at low metallicity - Searching for extremely low-metallicity stars in classical dwarf galaxies
• Analysis and calibration of CaII triplet spectroscopy of Red Giant Branch stars from VLT/FLAMES observations
• LITTLE THINGS in 3D: robust determination of the circular velocity of dwarf irregular galaxies
• Delayed Star Formation in Isolated Dwarf Galaxies: HST Star Formation History of the Aquarius Dwarf Irregular
• Chemistry and Kinematics of the Late-Forming Dwarf Irregular Galaxies Leo A, Aquarius, and Sagittarius DIG
• The Chemical Evolution of Dwarf Spheroidal Galaxies: Dissecting the Inner Regions and their Stellar Populations
• Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix
• The stellar content of the isolated transition dwarf galaxy DDO210
• The Dynamics and Metallicity Distribution of the Distant Dwarf Galaxy VV124
• Kinematics of the Tucana Dwarf Galaxy: An Unusually Dense Dwarf in the Local Group
• Complexity on dwarf galaxies scale: A bimodal distribution function in Sculptor
• From K giants to G dwarfs: stellar lifetime effects on metallicity distributions derived from red giants
• Denuded Dwarfs Demystified: Gas Loss from dSph Progenitors and Implications for the Minimum Mass of Galaxies

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• Galaxy populations in the Hydra I cluster from the VEGAS survey I. Optical properties of a large sample of dwarf galaxies