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The Physical Nature of Cosmic Accretion of Baryons & Dark Matter into Halos and their Galaxies Andrew Wetzel Moore Fellow Carnegie Fellow in Theoretical Astrophysics Wetzel & Nagai 2014 arXiv:1412:0662 Spineto, Italy June 2015 Outline 1. Physical Cosmic Accretion of Dark Matter 2. Physical Cosmic Accretion of Baryons Andrew Wetzel Caltech - Carnegie 58 picture of cosmic accretion WECHSLER ET AL. Standard into halos 1.0 Wechsler et al 2002 1.0 M/M0 M/M0 0.5 0.1 0.1 1.0 0.5 a Scale factor = 1/(1+z) Andrew Wetzel Fig. 4.—Average mass accretion histories, normalized at a ¼ 1. Left: binned in three bins by final halo m Caltech - Carnegie log Physical Density Physical nature of cosmic accretion into galactic halos log Physical Radius see Diemand et al 2007, Cuesta et al 2008, Diemer et al 2013 Andrew Wetzel Caltech - Carnegie log Physical Density Physical nature of cosmic accretion into galactic halos 200 x background at given redshift “pseudo-evolution” 200 x background at given redshift log Physical Radius see Diemand et al 2007, Cuesta et al 2008, Diemer et al 2013 Andrew Wetzel Caltech - Carnegie spherical region is sufficiently overdense, its gr hin a halo. However, Physical Cosmic self-attraction overcomes the initial cosmolog me level of gas accresion, such that a mass shell reach a maxim ime, suggesting that Accretion ofwill Dark Matter and then collapse. Specifically, for flat ⇤CDM ay not extend to gas. (simulation of only dark matter) the radial acceleration around some overdens ure of cosmic accrefor the evolution of d2 r G m(< r) 8⇡G cosmic time, espe= + ⇢ r ⇤ 2 2 dt r 3 example, galaxies at 3 % of their mass since in which r is the physical radius from the ce to determine of the enclosed overdensity inside the splash- m(< Adhikari, Dalalenclosed & Chamberlain 2014 G is ate of decline the overdensity, r) is the mass, back radius, ∆ . Our results do not strongly depend on s our assumed mass profile inside the halo. For example, using an isothermal profile instead of NFW gives results that are consistent at the ∼ 10% level. Figure 2 shows the predicted values of the enclosed overdensity. Throughout this paper, we define overdensities relative to the mean matter density, not the critical density. In our model, ∆s depends only on the halo’s accretion rate s, along with the values of the background cosmological parameters ΩM and ΩΛ at the time the halo is observed. The behavior we find is unsurprising. As the accretion rate is increased (larger s), the potential deepens more quickly in time, resulting in splashback occuring at a smaller radius, or equivalently, at a larger enclosed overdensity ∆s . Similarly, at low redshift when ΩM diminishes and ΩΛ increases, the mean background density of the universe ρ̄m decreases more during the time between turnaround and splashback, again resulting in a larger ∆s . Finally, although the model presented here is exAndrewtremely Wetzel simple to evaluate, we also provide a very rough radius Caltech e=0.1 - Carnegie Physical Cosmic Accretion of Dark Matter from simulation with only dark matter Andrew Wetzel Caltech - Carnegie Outline 1. Physical Cosmic Accretion of Dark Matter 2. Physical Cosmic Accretion of Baryons Andrew Wetzel Caltech - Carnegie Physical accretion of gas & dark matter from simulation with gas - non-radiative Andrew Wetzel Caltech - Carnegie Physical accretion of baryons & dark matter from simulation with star formation + thermal feedback Andrew Wetzel Caltech - Carnegie Physical significance of R200m? Andrew Wetzel Caltech - Carnegie Physical accretion of baryons & dark matter from simulation with star formation + feedback Andrew Wetzel Caltech - Carnegie Physical Cosmic Accretion of Dark Matter & Baryons Dark matter growth is subject to pseudo-evolution at z <~ 1, no significant growth of mass at any radius Baryon growth is not subject to pseudo-evolution Physical growth at all radii because gas is dissipational Accretion rate at all r < R200m (nearly) tracks that at R200m Accretion radius of low-mass halos not increase at z <~ 1 Most meaningful radius to measure cosmic accretion of both dark matter and gas is ~2 R200m(z) Andrew Wetzel Caltech - Carnegie