Kinematics of SDSS subdwarfs: structure and substructure of the Milky Way halo

By Martin C. Smith, N. Evans II, V. Belokurov, Paul Hewett, D. Bramich, G. Gilmore, M. Irwin, S. Vidrih, D. Zucker. 2009

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We construct a new sample of ∼ 1700 solar neighbourhood halo subdwarfs from the Sloan Digital Sky Survey (SDSS), selected using a reduced proper-motion diagram. Radial velocities come from the SDSS spectra and proper motions from the light-motion curve catalogue of Bramich et al. Using a photometric parallax relation to estimate distances gives us the full phase-space coordinates. Typical velocity errors are in the range 30-50 km s ―1 . This halo sample is one of the largest constructed to date and the disc contamination is at a level of ≲1 per cent. This enables us to calculate the halo velocity dispersion to excellent accuracy. We find that the velocity dispersion tensor is aligned in spherical polar coordinates and that (σ r ,σ φ , σ θ ) = (143 ± 2, 82 ± 2, 77 ± 2) km s ―1 . The stellar halo exhibits no net rotation, although the distribution of υ φ shows tentative evidence for asymmetry. The kinematics are consistent with a mildly flattened stellar density falling with distance like r ―3.75 . Using the full phase-space coordinates, we look for signs of kinematic substructure in the stellar halo. We find evidence for four discrete overdensities localized in angular momentum and suggest that they may be possible accretion remnants. The most prominent is the solar neighbourhood stream previously identified by Helmi et al., but the remaining three are new. One of these overdensities is potentially associated with a group of four globular clusters (NGC 5466, NGC 6934, M2 and M13) and raises the possibility that these could have been accreted as part of a much larger progenitor.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/595982d7629eb7da038b24ebbaada0f785b43057

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Citations in the corpus

ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, background): “Generally, the velocity ellipsoid can have atilt, although it is evident from the recent studies by Smith et al. (2009a) and Bond et al. (2010) that the tilt with respect to the spherical coordinate system for the Galactic halo is consistent with zero so we ignore it.”
Co-formation of the disc and the stellar halo (2018, methodology): “Using the SDSS Stripe 82 proper motions, and thus going deeper, Smith et al. (2009) measured β = 0.69 using ∼ 2, 000 nearby sub-dwarfs.”
STRUCTURE AND KINEMATICS OF THE STELLAR HALOS AND THICK DISKS OF THE MILKY WAY BASED ON CALIBRATION STARS FROM SLOAN DIGITAL SKY SURVEY DR7 (2009, result): “Our results can also be compared with the recent analysis of SDSS subdwarfs by Smith et al. (2009).”
Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, unknown): “…1985; Preston, Shectman Beers 1991; Wetterer & McGraw 1996; Ivezić et al. 2000; Morrison et al. 2000; Yanny et al. 2000; Chiba & Beers 2000; Chen et al. 2001; Siegel et al. 2002; Vivas & Zinn 2006; Bell et al. 2008; Juŕıc et al. 2008; Smith et al. 2009; Sesar et al. 2011; Deason et al. 2011b).”
The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution (2016, unknown): “5 –0.7 (Kepley et al. 2007; Smith et al. 2009; Bond et al. 2010; Brown et al. 2010).”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “After excluding young stars, Binney finds that the velocity dispersion for a given stellar population increases as one moves vertically in z from the plane (cf. Smith et al. 2009).”
KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS (2012, methodology): “This result of radially biased inner halo concurs with the recent results by Smith et al. 2009b; Bond et al. 2010 using the proper motions.”
THE MILKY WAY TOMOGRAPHY WITH SDSS. III. STELLAR KINEMATICS (2009, methodology): “Past studies of halo stars alone were performed by Sirko et al. (2004), Allende Prieto et al. (2006), Carollo et al. (2007), and Smith et al. (2009), while disk samples ranging from nearby M stars to distant F/G stars have been studied by Bochanski et al. (2007b), West et al. (2008), and Fuchs et…”