Galactic stellar haloes in the CDM model

Abstract

We present six simulations of galactic stellar haloes formed by the tidal disruption of accreted dwarf galaxies in a fully cosmological setting. Our model is based on the Aquarius project, a suite of high resolution N-body simulations of individual dark matter haloes. We tag subsets of particles in these simulations with stellar populations predicted by the Galform semi-analytic model. Our method self-consistently tracks the dynamical evolution and disruption of satellites from high redshift. The luminosity function and structural properties of surviving satellites, which agree well with observations, suggest that this technique is appropriate. We find that accreted stellar haloes are assembled between 1<z<7 from less than 5 significant progenitors. These progenitors are old, metal-rich satellites with stellar masses similar to the brightest Milky Way dwarf spheroidals. In contrast to previous stellar halo simulations, we find that several of these major contributors survive as self-bound systems to the present day. Both the number of these significant progenitors and their infall times are inherently stochastic. This results in great diversity among our stellar haloes, which amplifies small differences between the formation histories of their dark halo hosts. The masses and density/surface-brightness profiles of the stellar haloes are consistent with expectations from the Milky Way and M31. Each halo has a complex structure, consisting of well-mixed components, tidal streams, shells and other subcomponents. This structure is not adequately described by smooth models. We find one example of an accreted thick disk. Contrasts in age and metallicity between halo stars and those in surviving satellites are in broad agreement with recent observations. [Abridged]Comment: 24 pages, 19 figures; accepted for publication in MNRAS, minor changes; version with high resolution images at http://www.virgo.dur.ac.uk/aquariu

New Spectroscopic Technique Based on Coaddition of Surface Brightness Fluctuations: NGC 4449 and Its Stellar Tidal Stream

“…These smaller halos are severely affected by the larger potential well of the host and are tidally stripped or fully disrupted, appearing on the sky as substructures in the form of streams and satellites (e.g., Bullock & Johnston 2005;Springel et al 2006;Cooper et al 2010). Observationally, the detection of substructures in the halos of massive galaxies agrees with this scenario (e.g., Martínez-Delgado et al 2010;Atkinson et al 2013;Martin et al 2014).…”

The orbital PDF: general inference of the gravitational potential from steady-state tracers

“…The parameters of the DF include the mass, M, and concentration, c, of the NFW halo, the tracer velocity anisotropy, β, and the double-power-law slopes and pivot radius of the tracer density profile, α, γ and r p . Their values are chosen to best match the distribution of mock stars inside an MW-sized halo in the Aquarius simulation (Cooper et al 2010), with M = 1.83 × 10 12 M , c = 16.2, β = 0.715, r p = 69.0 kpc, α = 2.30, γ = 7.47. The mock tracers generated according to this f (E, L) are expected to be a self-consistent, yet simplified, realization of the distribution of stars in the MW.…”

“…In particular, Wang et al (2015) applied the f (E, L) method to mock stellar haloes (Cooper et al 2010) constructed from the Aquarius simulations of cold dark matter ( CDM) galactic haloes (Springel et al 2008) and found significant biases in the fitted masses. These biases suggest that the proposed f (E, L) DF does not describe well the observed phasespace distribution of the mock stars.…”

The SLUGGS survey: combining stellar and globular cluster metallicities in the outer regions of early-type galaxies

“…In present-day ETGs, these stars contribute to lowering the metallicity in the regions where they have been accreted, i.e., at large galactocentric radii. These outermost regions are expected to show generally shallow metallicity gradients because of the dynamical mixing of pre-existing and accreted stars (Kobayashi 2004;Di Matteo et al 2009;Cooper et al 2010;Font et al 2011).…”