First Ground-based Charge-coupled Device Proper Motions for Fornax. II. Final Results

We present the first entirely ground-based astrometric determination of the proper motion for the Fornax Local Group dwarf spheroidal satellite galaxy of the Milky Way (MW), using charge-coupled device data acquired with the ESO 3.5 m New Technology Telescope at La Silla Observatory in Chile. Our un...

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Bibliographic Details
Published in:The Astronomical journal 2011-09, Vol.142 (3), p.93-jQuery1323897311926='48'
Main Authors: Méndez, René A, Costa, Edgardo, Gallart, Carme, Pedreros, Mario H, Moyano, Maximiliano, Altmann, Martin
Format: Article
Language:English
Subjects:
Astronomical instruments
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CALCULATION METHODS
CHARGE-COUPLED DEVICES
Computer simulation
COMPUTERIZED SIMULATION
COSMIC RADIO SOURCES
DISTANCE
GALAXIES
MILKY WAY
MONTE CARLO METHOD
Monte Carlo methods
MOTION
Orbitals
ORBITS
PHYSICS
PROPER MOTION
QUASARS
RADIAL VELOCITY
SATELLITES
SEMICONDUCTOR DEVICES
SIMULATION
STARS
TELESCOPES
VELOCITY
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Summary:We present the first entirely ground-based astrometric determination of the proper motion for the Fornax Local Group dwarf spheroidal satellite galaxy of the Milky Way (MW), using charge-coupled device data acquired with the ESO 3.5 m New Technology Telescope at La Silla Observatory in Chile. Our unweighted mean from five quasar fields in the background of Fornax, used as fiducial reference points, leads to Delta *m Delta *acos Delta *d = 0.62 ? 0.16 mas yr--1 and Delta *m Delta *d = --0.53 ? 0.15 mas yr--1. A detailed comparison with all previous measurements of this quantity seems to imply that there is still no convincing convergence to a single value, perhaps indicating the existence of unaccounted systematic effects in (some of) these measurements. From all available proper-motion and radial velocity measurements for Fornax, we compute Fornax's orbital parameters and their uncertainty using a realistic Galactic potential and a Monte Carlo simulation. Properties of the derived orbits are then compared to main star formation episodes in the history of Fornax. All published proper-motion values imply that Fornax has recently (200-300 Myr ago) approached perigalacticon at a distance of ~150 kpc. However, the derived period exhibits a large scatter, as does the apogalacticon. Our orbit, being the most energetic, implies a very large apogalactic distance of ~950 kpc. If this were the case, then Fornax would be a representative of a hypervelocity MW satellite in late infall.
ISSN:1538-3881
0004-6256
1538-3881
DOI:10.1088/0004-6256/142/3/93