A Pair of Boötes: A New Milky Way Satellite

By Shane Walsh, H. Jerjen, B. Willman. 2007

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As part of preparations for a southern sky search for faint Milky Way dwarf galaxy satellites, we report the discovery of a stellar overdensity in the Sloan Digital Sky Survey Data Release 5, lying at an angular distance of only 1.5° from the recently discovered Boötes dwarf. The overdensity was detected well above statistical noise by employing a sophisticated data-mining algorithm and does not correspond to any cataloged object. Overlaid isochrones using stellar population synthesis models show that the color-magnitude diagram of that region has the signature of an old (12 Gyr), metal-poor (Fe/H ≈ -2.0) stellar population at a tentative distance of 60 kpc, evidently the same heliocentric distance as the Boötes dwarf. We estimate the new object to have a total magnitude of MV ~ -3.1 ± 1.1 mag and a half-light radius of rh = 4.1′ ± 1.6′ (72 ± 28 pc), placing it in an apparent 40 pc < rh < 100 pc void between globular clusters and dwarf galaxies, occupied only by another recently discovered Milky Way satellite, Coma Berenices.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/10bcecb4837a149e1a96ece20d5ab5128262f6d0

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DWARF GALAXY ANNIHILATION AND DECAY EMISSION PROFILES FOR DARK MATTER EXPERIMENTS (2014, background): “Many such dwarf galaxies have been discovered in recent years (Willman et al. 2005; Zucker et al. 2006b,a; Walsh et al. 2007; Belokurov et al. 2007, 2008; Belokurov et al. 2009, 2010) with the prospect of more discoveries from ongoing and future sky surveys like Pan-Starrs (Kaiser et al. 2002), the…”
ACCURATE STELLAR KINEMATICS AT FAINT MAGNITUDES: APPLICATION TO THE BOÖTES I DWARF SPHEROIDAL GALAXY (2011, background): “…al. 2000), a three-times larger sample of dSph has been discovered, primarily of dSphs with lower intrinsic luminosities, extending to the ‘ultrafaint’ dSphs (Willman et al. 2005; Belokurov et al. 2006; Zucker et al. 2006a,b; Belokurov et al. 2007; Walsh et al. 2007; Belokurov et al. 2008, 2009).”
A MegaCam Survey of Outer Halo Satellites. III. Photometric and Structural Parameters (2018, background): “Discovered in SDSS DR5 imaging by Walsh et al. (2007), Boötes II lies just 1.”
MULTI-ELEMENT ABUNDANCE MEASUREMENTS FROM MEDIUM-RESOLUTION SPECTRA. III. METALLICITY DISTRIBUTIONS OF MILKY WAY DWARF SATELLITE GALAXIES (2010, background): “…except the least luminous objects (Willman 1, Willman et al. 2005; Segue 1, Belokurov et al. 2007; Segue 2, Belokurov et al. 2009; Boötes II, Walsh et al. 2007; Leo V, Belokurov et al. 2008; Pisces I, Watkins et al. 2009; and Pisces II and Segue 3, Belokurov et al. 2010) because they have…”
The properties of warm dark matter haloes (2013, background): “A number of new dwarf spheroidal (dSph) satellite galaxies have been discovered around the Milky Way and M31 (e.g. Willman et al. 2005; Walsh et al. 2007; Martin et al. 2009; Bell et al. 2011; Martin et al. 2013).”
CLUMPY STREAMS FROM CLUMPY HALOS: DETECTING MISSING SATELLITES WITH COLD STELLAR STRUCTURES (2010, methodology): “…using the Sloan Digital Sky Survey (SDSS, e.g. Willman et al. 2005; Belokurov et al. 2006a, 2007; Zucker et al. 2006; Irwin et al. 2007; Koposov et al. 2007; Walsh et al. 2007) but the number discrepancy between simulated dark-matter subhalos and observed satellite populations is still significant.”
Hundreds of Milky Way Satellites? Luminosity Bias in the Satellite Luminosity Function (2008, background): “…al. 2007) has revolutionized our view of the Milky Way and its environment, doubling the number of known dwarf spheroidal (dSph) galaxies over the last several years (e.g., Willman et al. 2005; Zucker et al. 2006a, 2006b; Belokurov et al. 2006; Grillmair 2006; Walsh et al. 2007; Irwin et al. 2007).”
CONFIRMATION OF FAINT DWARF GALAXIES IN THE M81 GROUP (2013, background): “…the Local Group (Irwin & Hatzidimitriou 1995; Mateo 1998; McConnachie & Irwin 2006; Simon & Geha 2007; Belokurov et al. 2007; Willman et al. 2005; Walsh et al. 2007; Zucker et al. 2006; Martin et al. 2006; Ibata et al. 2007; Irwin et al. 2008; McConnachie 2012) along with Centaurus and Hydra…”
Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1 (2019, methodology): “…automated search algorithms—have greatly increased the known population of Milky Way satellites (Willman et al. 2005a,b; Zucker et al. 2006a,b; Belokurov et al. 2006, 2007, 2008, 2009, 2010; Grillmair 2006, 2009; Sakamoto & Hasegawa 2006; Irwin et al. 2007; Walsh et al. 2007; Kim et al. 2015a).”
Cosmic Dawn (CoDa): the first radiation-hydrodynamics simulation of reionization and galaxy formation in the Local Universe (2015, background): “…that the ultra-faint dwarf galaxies (hereafter UFDs) discovered by the SDSS (Martin et al. 2004; Willman & et al. 2005; Zucker et al. 2006; Belokurov & et al. 2007; Irwin & et al. 2007; Walsh et al. 2007) are effectively reionisation fossils, living in dark matter sub-haloes of about 106−9M .”
ASSESSING THE MILKY WAY SATELLITES ASSOCIATED WITH THE SAGITTARIUS DWARF SPHEROIDAL GALAXY (2010, background): “Boötes II (ID=61, Λ⊙ = 277 ◦) Boötes II (Boo II; Walsh et al. 2007) is located in the direction (l, b) = (353.8◦,+68.9◦), and has a distance of 46 kpc and radial velocity vGSR = −116 km s −1 (Koch et al. 2009).”
EIGHT ULTRA-FAINT GALAXY CANDIDATES DISCOVERED IN YEAR TWO OF THE DARK ENERGY SURVEY (2015, background): “…2005b; Belokurov et al. 2006, 2007, 2008, 2009, 2010; Grillmair 2006, 2009; Sakamoto & Hasegawa 2006; Zucker et al. 2006a, 2006b; Irwin et al. 2007; Walsh et al. 2007) and dedicated spectroscopic follow-up observations (Kleyna et al. 2005; Muñoz et al. 2006; Martin et al. 2007; Simon & Geha…”
SAGITTARIUS II, DRACO II AND LAEVENS 3: THREE NEW MILKY WAY SATELLITES DISCOVERED IN THE PAN-STARRS 1 3π SURVEY (2015, background): “…Durham DH1 3LE, UK 9 GMTO Corporation, 251 S. Lake Ave, Suite 300, Pasadena, CA 91101, USA the Sloan Digital Sky Survey (SDSS; York et al. 2000) uncovered some 16 dwarf galaxies among the faintest ever found (e.g. Willman et al. 2005; Zucker et al. 2006; Belokurov et al. 2007; Walsh et al. 2007).”
A QUANTITATIVE EXPLANATION OF THE OBSERVED POPULATION OF MILKY WAY SATELLITE GALAXIES (2009, background): “We do not include two systems, BooII and LeoV (Walsh et al. 2007; Belokurov et al. 2008), which do not formally satisfy the very conservative selection limits from Koposov et al. (2008) These limits were chosen to avoid the issue of significant ’false positive’ detections, at the expense of leaving ”
PRE-REIONIZATION FOSSILS, ULTRA-FAINT DWARFS, AND THE MISSING GALACTIC SATELLITE PROBLEM (2008, background): “…of the halo around M31, resulting in the discovery of 12 new ultra-faint Milky Way satellites (Belokurov et al. 2006, 2007; Irwin et al. 2007; Walsh et al. 2007; Willman et al. 2005b, 2005a; Zucker et al. 2006b, 2006a; Geha et al. 2009) and six new companions for M31 (Ibata et al. 2007;…”
The Orbital Poles of Milky Way Satellite Galaxies: A Rotationally Supported Disk of Satellites (2008, background): “…satellite galaxies, of which the very faint ones were found most recently by systematic search campaigns (Willman et al. 2005; Sakamoto & Hasegawa 2006; Zucker et al. 2006a, 2006b; Belokurov et al. 2006, 2007; Walsh et al. 2007) in the Sloan Digital Sky Survey (SDSS; York et al. 2000) catalog data.”