Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe splashback boundary of haloes in hydrodynamic simulations
110
0
0.0
(
0
)
Authors
Stephanie ONeil
Ask ChatGPT about the research
No Arabic abstract
The splashback radius, $R_{rm sp}$, is a physically motivated halo boundary that separates infalling and collapsed matter of haloes. We study $R_{rm sp}$ in the hydrodynamic and dark matter only IllustrisTNG simulations. The most commonly adopted signature of $R_{rm sp}$ is the radius at which the radial density profiles are steepest. Therefore, we explicitly optimise our density profile fit to the profile slope and find that this leads to a $sim5%$ larger radius compared to other optimisations. We calculate $R_{rm sp}$ for haloes with masses between $10^{13-15}{rm M}_{odot}$ as a function of halo mass, accretion rate and redshift. $R_{rm sp}$ decreases with mass and with redshift for haloes of similar $M_{rm200m}$ in agreement with previous work. We also find that $R_{rm sp}/R_{rm200m}$ decreases with halo accretion rate. We apply our analysis to dark matter, gas and satellite galaxies associated with haloes to investigate the observational potential of $R_{rm sp}$. The radius of steepest slope in gas profiles is consistently smaller than the value calculated from dark matter profiles. The steepest slope in galaxy profiles, which are often used in observations, tends to agree with dark matter profiles but is lower for less massive haloes. We compare $R_{rm sp}$ in hydrodynamic and N-body dark matter only simulations and do not find a significant difference caused by the addition of baryonic physics. Thus, results from dark matter only simulations should be applicable to realistic haloes.
rate research
Read More
We have explored the outskirts of dark matter haloes out to 2.5 times the virial radius using a large sample of halos drawn from Illustris, along with a set of zoom simulations (MUGS). Using these, we make a systematic exploration of the shape profile beyond R$_{vir}$. In the mean sphericity profile of Illustris halos we identify a dip close to the virial radius, which is robust across a broad range of masses and infall rates. The inner edge of this feature may be related to the virial radius and the outer edge with the splashback radius. Due to the high halo-to-halo variation this result is visible only on average. However, in four individual halos in the MUGS sample, a decrease in the sphericity and a subsequent recovery is evident close to the splashback radius. We find that this feature persists for several Gyr, growing with the halo. This feature appears at the interface between the spherical halo density distribution and the filamentary structure in the environment. The shape feature is strongest when there is a high rate of infall, implying that the effect is due to the mixing of accreting and virializing material. The filamentary velocity field becomes rapidly mixed in the halo region inside the virial radius, with the area between this and the splashback radius serving as the transition region. We also identify a long-lasting and smoothly evolving splashback region in the radial density gradient in many of the MUGS halos.
We obtain predictions for the properties of cold dark matter annihilation radiation using high resolution hydrodynamic zoom-in cosmological simulations of Milky Way-like galaxies (APOSTLE project) carried out as part of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) programme. Galactic halos in the simulation have significantly different properties from those assumed in the standard halo model often used in dark matter detection studies. The formation of the galaxy causes a contraction of the dark matter halo, whose density profile develops a steeper slope than the Navarro-Frenk-White (NFW) profile between $rapprox1.5$ kpc and $rapprox10$ kpc. At smaller radii, $rlesssim1.5$ kpc, the halos develop a flatter than NFW slope. This unexpected feature may be specific to our particular choice of subgrid physics model but nevertheless the dark matter density profiles agree within 30% as the mass resolution is increased by a factor 150. The inner regions of the halos are almost perfectly spherical (axis ratios $b/a > 0.97$ within $r=1$ kpc) and there is no offset larger than 45 pc between the centre of the stellar distribution and the centre of the dark halo. The morphology of the predicted dark matter annihilation radiation signal is in broad agreement with $gamma$-ray observations at large Galactic latitudes ($bgtrsim3^circ$). At smaller angles, the inferred signal in one of our four galaxies is similar to that which is observed but it is significantly weaker in the other three.
We present a new technique for creating mock catalogues of the individual stars that make up the accreted component of stellar haloes in cosmological simulations and show how the catalogues can be used to test and interpret observational data. The catalogues are constructed from a combination of methods. A semi-analytic galaxy formation model is used to calculate the star formation history in haloes in an N-body simulation and dark matter particles are tagged with this stellar mass. The tags are converted into individual stars using a stellar population synthesis model to obtain the number density and evolutionary stage of the stars, together with a phase-space sampling method that distributes the stars while ensuring that the phase-space structure of the original N-body simulation is maintained. A set of catalogues based on the $Lambda$CDM Aquarius simulations of Milky Way mass haloes have been created and made publicly available on a website. Two example applications are discussed that demonstrate the power and flexibility of the mock catalogues. We show how the rich stellar substructure that survives in the stellar halo precludes a simple measurement of its density profile and demonstrate explicitly how pencil-beam surveys can return almost any value for the slope of the profile. We also show that localized variations in the abundance of particular types of stars, a signature of differences in the composition of stellar populations, allow streams to be easily identified.
The correlation between the spins of dark matter halos and the large-scale structure (LSS) has been studied in great detail over a large redshift range, while investigations of galaxies are still incomplete. Motivated by this point, we use the state-of-the-art hydrodynamic simulation, Illustris-1, to investigate mainly the spin--LSS correlation of galaxies at redshift of $z=0$. We mainly find that the spins of low-mass, blue, oblate galaxies are preferentially aligned with the slowest collapsing direction ($e_3$) of the large-scale tidal field, while massive, red, prolate galaxy spins tend to be perpendicular to $e_3$. The transition from a parallel to a perpendicular trend occurs at $sim10^{9.4} M_{odot}/h$ in the stellar mass, $sim0.62$ in the g-r color, and $sim0.4$ in triaxiality. The transition stellar mass decreases with increasing redshifts. The alignment was found to be primarily correlated with the galaxy stellar mass. Our results are consistent with previous studies both in N-body simulations and observations. Our study also fills the vacancy in the study of the galaxy spin--LSS correlation at $z=0$ using hydrodynamical simulations and also provides important insight to understand the formation and evolution of galaxy angular momentum.
Self-gravitating astronomical objects often show a central plateau in the density profile (core) whose physical origin is hotly debated. Cores are theoretically expected in N-body systems of maximum entropy, however, they are not present in the canonical N-body numerical simulations of cold dark matter (CDM). Our work shows that despite this apparent contradiction between theory and numerical simulations, they are fully consistent. Simply put, cores are characteristic of systems in thermodynamic equilibrium, but thermalizing collisions are purposely suppressed in CDM simulations. When collisions are allowed, N-body numerical simulations develop cored density profiles, in perfect agreement with the theoretical expectation. We compare theory and two types of numerical simulations: (1) when DM particles are self-interacting (SIDM) with enough cross-section, then the effective two-body relaxation timescale becomes shorter than the Hubble time resulting in cored DM haloes. The haloes thus obtained, with masses from dwarf galaxies to galaxy clusters, collapse to a single shape after normalization, and this shape agrees with the polytropic density profile theoretically expected. (2) The inner radii in canonical N-body numerical simulations are always discarded because the use of finite-mass DM particles artificially increases the two-body collision rate. We show that the discarded radii develop cores that are larger than the employed numerical softening and have polytropic shapes independently of halo mass. Our work suggests that the presence of cores in simulated (or observed) density profiles can used as evidence for systems in thermodynamic equilibrium.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
