First ground-based CCD proper motions for Fornax II: Final results

Abstract

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, using CCD data acquired with the ESO 3.5 m NTT 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 ${\mu }_{\alpha }\cos \delta =0.62\pm 0.16$ $\masy$, and ${\mu }_{\delta }=-0.53\pm 0.15$ $\masy$. 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 unnacounted 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 $\sim$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 $\sim 950$ kpc. If this were the case, then Fornax would be a representative of an hypervelocity MW satellite in late infall.

Accepted by AJ. 25 pages, 9 figures, 9 tables. Interesting conclusions...Enjoy!

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Cited by in corpus (12)

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• Reproducing properties of MW dSphs as descendants of DM-free TDGs
• Insights from the Outskirts: Chemical and Dynamical Properties in the outer Parts of the Fornax Dwarf Spheroidal Galaxy
• The Fornax dwarf galaxy as a remnant of recent dwarf-dwarf merging in the Local Group
• The effect of tides on the Fornax dwarf spheroidal galaxy
• Analysis and interpretation of the Cramer-Rao lower-bound in astrometry: One dimensional case
• The Proper Motion of Pyxis: the first use of Adaptive Optics in tandem with HST on a faint halo object
• Tidal features of classical Milky Way satellites in a $\Lambda$CDM universe
• An XMM-Newton search for X-ray sources in the Fornax dwarf galaxy
• Direct geometrical measurement of the Hubble constant from galaxy parallax: predictions for the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope