Méndez, René A.; Costa, Edgardo; Gallart, C.; Pedreros, Mario H.; Moyano, Maximiliano; Altmann, Martin
Bibliographical reference
The Astronomical Journal, Volume 142, Issue 3, article id. 93 (2011).
Advertised on:
9
2011
Citations
13
Refereed citations
12
Description
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
μαcos δ = 0.62 ± 0.16 mas
yr-1 and μδ = -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.
Based on observations made with ESO Telescopes at the La Silla
Observatory under programme. IDs lang060.A-9701rang, lang065.N-0472rang,
lang0.66.B-0276rang, lang074.B-0456rang, lang076.B-0528rang,
lang079.B-0379rang, lang080.B-0144rang, lang081.B-0534rang, and
lang082.B-0034rang.