Leo V: A Companion of a Companion of the Milky Way Galaxy?

Abstract

We report the discovery of a new Milky Way satellite in the constellation Leo, identified in data from the Sloan Digital Sky Survey. It lies at a distance of ∼ 180 kpc, and is separated by 3 • from another recent discovery, Leo IV. We present follow-up imaging from the Isaac Newton Telescope and spectroscopy from the Hectochelle fiber spectrograph at the Multiple Mirror Telescope. Leo V's heliocentric velocity is ∼ 173.3 ± 3.1 kms −1 , offset by ∼ 40 kms −1 from that of Leo IV. A simple interpretation of the kinematic data is that both objects may lie on the same stream, though the implied orbit is only modestly eccentric (e ∼ 0.2)

The Highly Unusual Chemical Composition of the Hercules Dwarf Spheroidal Galaxy

“…At an [Fe/H] of Ϫ2.02 and Ϫ2.04 dex, both stars are slightly more metal-rich than the sample mean found from comparison with globular cluster fiducials (Belokurov et al 2007) and from low-resolution data, which yield a mean metallicity of Ϫ2.3 or Ϫ2.5 dex (Simon & Geha 2007;Kirby et al 2008). The latter work finds an intrinsic metallicity spread of at least 0.5 dex (rms), which would indicate that our stars are well within the Her metal-rich tail.…”

“…We note that the photometric values agree well with the temperatures derived from excitation equilibrium. The physical gravities were derived from the photometric data, adopting a distance to Her of 140 kpc (Belokurov et al 2007) and a stellar mass of 0.8 M , representative of the red giants (see also Koch , & McWilliam 2008). The Fe abundances from the ionized and neutral lines agree marginally within the uncertainties so that ionization equilibrium holds with the adopted surface gravities.…”

“…However, only little is known about the metal enrichment of the ultrafaint, presumably lowmass, systems recently discovered in the Sloan Digital Sky Survey (SDSS; Zucker et al 2006aZucker et al , 2006bBelokurov et al 2006Belokurov et al , 2007Belokurov et al , 2008Irwin et al 2007;Walsh et al 2007). Current low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor (e.g., Muñoz et al 2006;Belokurov et al 2007;Kirby et al 2008).…”

“…Are peculiar stars found in the Galactic halo related to those in dSphs? Hercules (hereafter Her) is one of the faintest (M V p Ϫ6.6 mag) and among the very metal-poor (∼Ϫ2.3 dex) dSph candidates discovered in the SDSS (Belokurov et al 2007). Its stellar mass is estimated to be (4-7) # 10 4 M , (Martin et al 2008).…”

Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

“…Thanks to Sloan Digital Sky Survey (SDSS, York et al 2000), such dwarf satellites and more dark matterdominated systems have been discovered by some observational studies (Willman et al 2005;Belokurov et al 2007Belokurov et al , 2008Belokurov et al , 2009Belokurov et al , 2010Zucker et al 2006a,b). More recently, using the Dark Energy Survey (Flaugher 2005) and Pan-STARRS 1 3π survey (Kaiser et al 2002), 12 faint dwarf galaxies were discovered (Bechtol et al 2015;Laevens et al 2015a,b).…”