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26 April 2024 |
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Bootes II ReBooted: An MMT/MegaCam Study of An Ultra-Faint Milky Way Satellite | | S. M. Walsh
; B. Willman
; D. Sand
; J. Harris
; A. Seth
; D. Zaritsky
; H. Jerjen
; | | Date: |
19 Dec 2007 | | Abstract: | [Abridged] We present MMT/Megacam follow-up imaging in g and r of the
extremely low luminosity Bootes II Milky Way companion. These data were
obtained as part of a larger program to image with MMT/Megacam all of the Milky
Way dwarf satellites recently discovered in Sloan Digital Sky Survey data. We
use these data to measure Bootes II’s fundamental properties, including:
distance, luminosity, size, and stellar population. A comparison with empirical
globular cluster fiducials covering a range in [Fe/H] shows that Bootes II’s
stellar population is old and metal-poor ([Fe/H] < -2) and at a distance of 42
+/- 8 kpc, significantly closer than the initial published estimate of 60 kpc.
We find a revised physical half-light size of r_h ~ 38 +/- 12 pc and inferred
luminosity of M_V ~ -2.4 +/- 0.7 mag, assuming a Plummer profile. Although the
small number of stars in an object as low luminosity as Bootes II imposes
unavoidable uncertainty in its properties, the revised size and luminosity we
calculate move Bootes II squarely into the ambiguous region of size-luminosity
space intermediate between known globular clusters and dwarf galaxies, but also
occupied by the recently discovered Milky Way satellites Willman 1 and SEGUE 1.
We show that while the isodensity contours of Bootes II appear irregular, that
its apparently distorted morphology is not statistically significant given the
present data. We present several lines of circumstantial argument that support
a scenario where Bootes II is a dwarf galaxy (dark matter dominated) rather
than a globular cluster (not dark matter dominated). However, deeper,
wide-field imaging and/or spectroscopic data will be necessary to test the
speculations presented here. | | Source: | arXiv, 0712.3054 | | Services: | Forum | Review | PDF | Favorites | |
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