Day 1731

Wednesday, Thursday.

2007.02940

Non-equilibrium temperature evolution of ionization fronts during the Epoch of Reionization

Zeng, Hirata

The epoch of reionization (EoR) marks the end of the Cosmic Dawn and the beginning of large-scale structure formation in the universe. The impulsive ionization fronts (I-fronts) heat and ionize the gas within the reionization bubbles in the intergalactic medium (IGM). The temperature during this process is a key yet uncertain ingredient in current models. Typically, reionization simulations assume that all baryonic species are in instantaneous thermal equilibrium with each other during the passage of an I-front. Here we present a new model of the temperature evolution for the ionization front by studying non-equilibrium effects. In particular, we include the energy transfer between major baryon species ($e^{-}$, \HI, \HII, \HeI, and \HeII) and investigate their impacts on the post-ionization front temperature $T_{\mathrm{re}}$. For a better step-size control when solving the stiff equations, we implement an implicit method and construct an energy transfer rate matrix. We find that the assumption of equilibration is valid for a low-speed ionization front ($\lessapprox\ 10^9~\mathrm{cm}/\mathrm{s}$), but deviations from equilibrium occur for faster fronts. The post-front temperature $T_{\mathrm{re}}$ is lower by up to 19.7\% (at $3\times 10^9$ cm/s) or 30.8\% (at $10^{10}$ cm/s) relative to the equilibrium case.

2007.02946

The Ultimately Large Telescope -- what kind of facility do we need to detect Population III stars?

Schauer, Drory, Bromm

The launch of the James Webb Space Telescope will open up a new window for observations at the highest redshifts, reaching out to $z\approx 15$. However, even with this new facility, the first stars will remain out of reach, as they are born in small minihalos with luminosities too faint to be detected even by the longest exposure times. In this Letter, we investigate the basic properties of the "Ultimately Large Telescope", a facility that can detect Population III stars. Observations will take place in the near-infrared and therefore a moon-based facility is proposed. An instrument needs to reach magnitudes as faint as 39mag$_\mathrm{AB}$, corresponding to a primary mirror size of about 100m in diameter. Assuming JWST NIRCam filters, we estimate that Pop~III sources will have unique signatures in a colour-colour space and can be identified unambiguously.

2007.02964

Illuminating dark matter halo density profiles without subhaloes

Fielder, et al

Cold dark matter haloes consist of a relatively smooth dark matter component as well as a system of bound subhaloes. It is the prevailing practice to include all halo mass, including mass in subhaloes, in studies of halo density profiles. However, often in observational studies satellites are treated as having their own distinct dark matter density profiles in addition to the profile of the host. This difference makes comparisons between theoretical and observed results difficult. In this work we investigate density profiles of the smooth components of host haloes by excluding mass contained within subhaloes. We find that the density profiles of the smooth halo component (without subhaloes) differs substantially from the conventional halo density profile. Smooth profiles decline more rapidly at large radii and are not well characterised by the standard NFW profile. We also find that concentrations derived from smooth density profiles exhibit less scatter at fixed mass and a weaker mass dependence than standard concentrations. Both smooth and standard halo profiles can be described by a generalised Einasto profile, an Einasto profile with a modified central slope, with smaller residuals than either an NFW or Einasto profile. These results hold for both Milky Way-mass and cluster-mass haloes. This new characterisation of smooth halo profiles can be useful for many analyses, such as lensing and dark matter annihilation, in which the smooth and clumpy components of a halo should be accounted for separately.