The Pristine survey – VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars

Abstract

We use the Pristine survey CaHK narrow-band photometry, combined with the SDSS ugr photometry, to provide a cleaner sample of blue horizontal branch stars in the Galactic halo out to large distances. We demonstrate a completeness of 91% and a purity of 93% with respect to available spectroscopic classifications. We subsequently use our new clean sample of these standard candles to investigate the substructure in the Galactic halo over the Pristine footprint. Among other features, this allows for a careful tracing of multiple parts of the Sagittarius stream, providing a measurement independent from other tracers used and reaching larger distances. Moreover, we demonstrate with this clean and complete sample that the halo follows a density profile with a negative power-law slope of 3.5-4.0. As the relatively shallow SDSS u-band is the limiting factor in this technique, we foresee large potential for combining Pristine survey photometry with the much deeper u-band photometry from the Canada-France-Imaging Survey.

The artemis simulations: stellar haloes of Milky Way-mass galaxies

“…In terms of the outer slope, some studies also find a steeper decline in the density profile at large radii, with a slope of ≈ −6 outside ≈ 50 kpc (Ivezić 2000;Deason et al 2014). However, other studies of outer regions (≥ 50 kpc) of the halo find that the density profile extends out to ≈ 100 kpc without an obvious cut off (Fukushima et al 2019) and with shalower slopes (Thomas et al 2018;Starkenburg et al 2019).…”

Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics

“…In addition, while it is likely that debris from an early, massive accretion event dominates the inner halo (i.e., the Gaia Sausage/ Gaia-Enceladus, ∼10 Gyr ago; e.g., Belokurov et al 2018;Helmi et al 2018), the current consensus is that the MW has had a fairly quiescent recent accretion history. This consensus has emerged based on numerous studies, including studies of the structure and kinematics of stars of the Galactic disk plane (e.g., Gilmore et al 2002;Hammer et al 2007;Ruchti et al 2015), the steep stellar density profile beyond ∼25 kpc in the halo (e.g., Deason et al 2013;Pillepich et al 2014;Deason et al 2018;Fukushima et al 2018Fukushima et al , 2019Thomas et al 2018;Starkenburg et al 2019), and the amount of substructure in the halo relative to predictions from simulations (e.g., Lancaster et al 2019a). An alternative scenario is one in which the MW has experienced more recent lowluminosity or radial accretion events with debris that is harder to find observationally; for example, Donlon et al (2019) suggest that a recent (∼2 Gyr), radial merger (with  M M 10 9 ) that mixes efficiently could explain the Virgo Overdensity (Vivas et al 2001).…”

The miniJPAS survey: A preview of the Universe in 56 colors

“…The J-spectra are sufficiently detailed to allow for the derivation of stellar parameters and to address a range of important topics in stellar astrophysics, including the search for metal-poor stars (Youakim et al 2017;Yoon et al 2018;Placco et al 2018Placco et al , 2019, blue horizontal branch stars (Santucci et al 2015b;Whitten et al 2019a;Starkenburg et al 2019), blue stragglers (Santucci et al 2015a), ultracool dwarfs, and white dwarfs. They also allow for the identification and chemical characterization of Galactic stellar streams, classical dwarf galaxies, and ultra-faint dwarf galaxies (e.g., Longeard et al 2018;Shipp et al 2018Shipp et al , 2019Chiti et al 2020;Longeard et al 2020).…”