THE UNORTHODOX ORBITS OF SUBSTRUCTURE HALOS

By A. Ludlow, J. Navarro, Volker Springel, Adrian Jenkins, Carlos S. Frenk, A. Helmi. 2008

133 citations recorded by the source corpus.

We use a suite of cosmological N-body simulations to study the properties of substructure halos (subhalos) in galaxy-sized cold dark matter halos. We extend prior work on the subject by considering the whole population of subhalos physically associated with the main system. These are defined as subhalos that have at some time in the past been within the virial radius of the halo's main progenitor and that have survived as self-bound entities to z = 0. We find that this population extends beyond three times the virial radius, and contains objects on extreme orbits, including a few with velocities approaching the nominal escape speed from the system. We trace the origin of these unorthodox orbits to the tidal dissociation of bound groups of subhalos, which results in the ejection of some subhalos along tidal streams. Ejected subhalos are primarily low-mass systems, leading to mass-dependent biases in their spatial distribution and kinematics: the lower the subhalo mass at accretion time, the less centrally concentrated and kinematically hotter their descendant population. The bias is strongest among the most massive subhalos, but disappears at the low-mass end: below a certain mass, subhalos behave just like test particles in the potential of the main halo. Overall, our findings imply that subhalos identified within the virial radius represent a rather incomplete census of the substructure physically related to a halo: only about one half of all associated subhalos are found today within the virial radius of a halo, and many relatively isolated halos may have actually been ejected in the past from more massive systems. These results may explain the age dependence of the clustering of low-mass halos reported recently by Gao et al., and has further implications for (1) the interpretation of the structural parameters and assembly histories of halos neighboring massive systems; (2) the existence of low-mass dynamical outliers, such as Leo I and And XII in the Local Group; and (3) the presence of evidence for evolutionary effects, such as tidal truncation or ram-pressure stripping, well outside the traditional virial boundary of a galaxy system.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/94af8018e13ec68fb5f06bc968346e5421144b56

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Citations in the corpus

KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. II. A LACK OF DARK MATTER IN THE SOLAR NEIGHBORHOOD, (2012, background): “…sets of indices have been proposed in the literature, suggesting either “cuspy” (e.g., Navarro et al. 1997; Moore et al. 1999; Binney & Evans 2001; Ludlow et al. 2009) or “cored” profiles (e.g., de Boer et al. 2005; Narayan et al. 2005; Gentile et al. 2007; Salucci et al. 2007; Oh et al. 2008).”
THE SPACE MOTION OF LEO I: THE MASS OF THE MILKY WAY'S DARK MATTER HALO (2012, background): “These “ejected” subhalos always have very low mass at infall (0.1% of their host’s mass or less; Ludlow et al. 2009) and are usually found as the companion of a more massive infalling satellite (Sales et al. 2007).”
The mass–concentration–redshift relation of cold dark matter haloes (2013, background): “This is done in order to ensure that all subhalos “associated” with the main halo are excluded from the analysis (Ludlow et al. 2009), since their concentrations and masses were likely modified by the tidal field of the main object.”
The mass–concentration–redshift relation of cold and warm dark matter haloes (2016, background): “This selection ensures that systems previously accreted and expelled from the most massive halo in the simulation are excluded from the analysis (see Ludlow et al. 2009).”
A STELLAR MASS THRESHOLD FOR QUENCHING OF FIELD GALAXIES (2012, background): “Alternatively, these may be “backsplash” galaxies which have previously been within the host virial radius, but are on either highly eccentric orbits or have been dynamical ejected from the host halo (Ludlow et al. 2009; Wang et al. 2009).”
MAMPOSSt: Modelling Anisotropy and Mass Profiles of Observed Spherical Systems – I. Gaussian 3D velocities (2012, background): “While radial outer orbits are expected for structures in an expanding universe (e.g. Ascasibar & Gottlöber 2008 for dark matter particles and Ludlow et al. 2009 for subhaloes), the dissipative nature of the gas dynamics is expected to produce tangential orbits inthe inner regions of systems formed…”
The impact of dark matter cusps and cores on the satellite galaxy population around spiral galaxies (2010, background): “By definition, the distance from the host galaxy centre at accretion time, racc, equals the host virial radius, and closely correlates with orbital apocentre (Ludlow et al. 2009).”
Star formation and AGN activity in SDSS cluster galaxies (2009, background): “It has been suggested that an appreciable fraction of galaxies observed at∼ 1 − 3R200 previously passed through the cluster (e.g. Balogh et al. 2000; Gill et al. 2005; Ludlow et al. 2009).”
Galaxy evolution in groups and clusters: satellite star formation histories and quenching time-scales in a hierarchical Universe (2012, background): “The latter also naturally incorporates satellites that temporarily orbit beyond their host halo’s virial radius, Rvir, which we call ‘ejected satellites’, and then fall in again (Gill et al. 2005; Ludlow et al. 2009; Wang et al. 2009).”
THE SPLASHBACK RADIUS AS A PHYSICAL HALO BOUNDARY AND THE GROWTH OF HALO MASS (2015, background): “Thus, their reclassification as satellites can reduce the assembly bias of low-mass halos to some extent (see also Lacerna & Padilla 2011), but it does not explain the bulk of the effect (see also Ludlow et al. 2009; Wang et al. 2009).”
The Phoenix Project: the dark side of rich galaxy clusters (2012, methodology): “As discussed by Ludlow et al. (2009), the number density profile can be fitted accurately by an Einasto profile (eq.”
Galaxy evolution in groups and clusters: star formation rates, red sequence fractions and the persistent bimodality (2011, background): “At these radii, the enhancement is likely caused by (1) massive haloes being highly ellipsoidal and (2) satellites on orbits with apocentres beyond the virial radius (Gill, Knebe & Gibson 2005; Ludlow et al. 2009; Wang, Mo & Jing 2009b).”
Why does the environmental influence on group and cluster galaxies extend beyond the virial radius (2012, background): “…is what we refer to as ‘overshooting’: a non-negligiblefraction of infalling galaxies are on highly elliptical orbits (e.g., Benson 2005) that bring them well within r200 on first pericentric passage but back out beyond this radius later on (e.g., Gill, Knebe & Gibson 2005; Ludlow et al. 2009).”
SUBSTRUCTURE DEPLETION IN THE MILKY WAY HALO BY THE DISK (2009, background): “We see that the fraction of substructures that come in already as a subhalo in a larger group is actually quite small, only about 10-20% over the mass range considered, with a slight trend to increase towards smaller masses (see also Ludlow et al. 2009).”