Distance to the Sagittarius Dwarf Galaxy using MACHO Project RR Lyrae stars

TL;DR

This study measures the distance to the Sagittarius dwarf galaxy using RR Lyrae stars from the MACHO project, finding it closer than some previous estimates but consistent with others, and revealing the galaxy's extension inclined toward us.

Contribution

First differential distance measurement to the Sagittarius dwarf galaxy using MACHO RR Lyrae stars, providing a new estimate of its distance and spatial orientation.

Findings

Distance modulus difference of 2.41 mags at specified coordinates.

Distance to Sgr stars estimated at 24.8 ± 0.8 kpc.

Extension of Sgr inclined toward us.

Abstract

We derive the distance to the northern extension of the Sagittarius (Sgr) dwarf spheroidal galaxy from 203 Sgr RR0 Lyrae stars found in the MACHO database. Their distances are determined differentially with respect to 288 Galactic Bulge RR0 Lyrae stars also found in the MACHO data. We find a distance modulus difference of 2.41 mags at $l$ = 5$^{\circ}$ and $b$ = -8$^{\circ}$ and that the extension of the Sgr galaxy towards the galactic plane is inclined toward us. Assuming $\rm R_{GC}$ = 8 kpc, this implies the distance to these stars is $(m-M)_0$ = 16.97 $\pm$ 0.07 mags, which corresponds to D = 24.8 $\pm$ 0.8 kpc. Although this estimate is smaller than previous determinations for this galaxy and agrees with previous suggestions that Sgr's body is truly closer to us, this estimate is larger than studies at comparable galactic latitudes.