Hydra II: a faint and compact Milky Way dwarf galaxy found in the Survey of the Magellanic 
Stellar History

Authors: SMASH Collaboration: Nicolas F. Martin , David L. Nidever , Gurtina Besla , Knut 
Olsen , Alistair R. Walker , A. Katherina Vivas, Robert A. Gruendl, Ricardo R. Muņoz, Robert 
D. Blum, Abhijit Saha, Blair C. Conn, Eric F. Bell , You-Hua Chu, Maria-Rosa L. Cioni, Thomas 
de Boer, Carme Gallart, Shoko Jin,  Andrea Kunder , Steven R. Majewski , David Martinez-
Delgado , Antonela Monachesi , Matteo Monelli, Lara Monteagudo, Noelia E. D. Noel, Edard 
W. Olszewski, Guy S. Stringfellow, Roeland van der Marel, Denis Zaritsky

We present the discovery of a new dwarf galaxy, Hydra II, found serendipitously within the data 
from the ongoing Survey of the MAgellanic Stellar History (SMASH) conducted with the Dark 
Energy Camera on the Blanco 4m Telescope. The new satellite is compact (r_h = 68 +/- 11 pc) 
and faint (M_V = -4.8 +/- 0.3), but well within the realm of dwarf galaxies. The stellar 
distribution of Hydra II in the color-magnitude diagram is well-described by a metal-poor ([Fe/H] 
= -2.2) and old (13 Gyr) isochrone and shows a distinct blue horizontal branch, some possible 
red clump stars, and faint stars that are suggestive of blue stragglers. At a heliocentric 
distance of 134 +/- 10 kpc, Hydra II is located in a region of the Galactic halo that models have 
suggested may host material from the leading arm of the Magellanic Stream. A comparison 
with N-body simulations hints that the new dwarf galaxy could be or could have been a satellite 
of the Magellanic Clouds.