1804.05843
Astrophysical radio background cannot explain the EDGES signal: constraints from cooling of non-thermal electrons
Sharma
Recently the EDGES experiment has claimed the detection of an absorption feature centered at 78 MHz. When interpreted as a signature of cosmic dawn, this feature appears at the correct wavelength (corresponding to a range of z~15-20) but is larger by at least a factor of two in amplitude compared to the standard 21-cm models. One way to explain the excess radio absorption is by the enhancement of the diffuse radio background at nu=1.42 GHz (lambda=21cm) in the rest frame of the absorbing neutral H. Astrophysical scenarios, based on the acceleration of relativistic electrons by accretion on to SMBHs and by SN from first stars, have been proposed to produce the enhanced radio background via synchrotron emission. In this Letter, show that either the synchrotron or the inverse-compton (IC) cooling time for such electrons is at least 3 orders of magnitude shorter than the duration of the EDGES signal centered at z~17, irrespective of the magnetic field strength. This means that such electrons must be replenished on a timescale orders of magnitude shorter than allowed by the cosmic history of SF and growth of SMBHs. Thus astrophysical scenarios for excess radio background proposed to explain the EDGES signal are comfortably ruled out.
1804.05865
The Aemulus Project I: Numerical simulations for precision cosmology
DeRose, Wechsler, Tinker, et al
The rapidly growing statistical precision of galaxy surveys has lead to a need for ever-more precise predictions of the observables used to constrain cosmological and galaxy formation models. The primary avenue through which such predictions will be obtained is suites of numerical simulations. These simulations must span the relevant model parameter spaces, be large enough to obtain the precision demanded by upcoming data, and be thoroughly validated in order to ensure accuracy. In this paper, present one such suite of simulations, forming the basis for the AEMULUS project, a collaboration devoted to precision emulation of galaxy survey observables. Run a set of 75 (1.05 Gpc/h)^3 simulations with mass resolution and force softening of 3.51e10 (Omega_m/0.3) Msun/h and 20 kpc/h respectively at 47 different wCDM cosmologies spanning the range of parameter space allowed by the combination of recent CMB, BAO and SNIa results. Present convergence tests of several observables including spherical overdensity halo mass functions, galaxy projected correlation functions, galaxy clustering in z space, and matter and halo correlation functions and power spectra. Show that these statistics are covered to 1% (2%) for halos with more than 500 (200) particles respectively and scales of r>200 kpc/h in real space or k~3Mpc/h in harmonic space for z<=1. Find that the dominant source of uncertainty comes from varying the particle loading of the simulations. This leads to large systematic errors for statistics using haloes with fewer than 200 particles and scales smaller than k~4Mpc/h. Provide the halo catalogs and snapshots detailed in this work to the community at https://AemulusProject.github.io.
1804.05866
The Aemulus Project II: Emulating the halo mass funciton
McClintok, Rozo, et al
Existing models for the dependence of the halo mass function on cosmological parameters will become a limiting source of systematic uncertainty for cluster cosmology in the near future. Present a halo mass function emulator and demonstrate improved accuracy relative to state-of-the-art analytic models. In this work, mass is defined using an overdensity criteria of 200 relative to the mean background density. The emulator is constructed from the AEMULUS simulations, a suite of 40 N-body simulations with snapshots from z=3 to z=0. These simulations cover the flat wCDM parameter space allowed by recent CMB, BAO and SNIa results, varying the parameters w, Omega_m, Omega_b, sigma8, N_eff, N_s, and H_0. Validate the emulator using 5 realizations of 7 different cosmologies, for a total of 35 test simulations. These test simulations were not used in constructing the emulator, and were run with fully independent initial conditions. Use the test simulations to characterize the modeling uncertainty of the emulator, and introduce a novel way of marginalizing over the associated systematic uncertainty. Confirm non-universality in the halo mass function emulator as a function of both cosmological parameters and redshift. The emulator achieves better than 1% precision over much of the relevant parameter space, and demonstrate that the systematic uncertainty in the emulator will remain a negligible source of error for cluster abundance studies throughout at least the LSST Year 1 data set.
1804.05867
The Aemulus Project III: Emulation of the galaxy correlation function
Zhai, Tinker, et al
Using the N-body simulations of the AEMULUS project, construct an emulator for the NL clustering of galaxies in real and z space. Construct the model of galaxy bias using the halo occupation framework, accounting for possible velocity bias. The model includes 15 parameters, including both cosmological and galaxy bias parameters. Demonstrate that the emulator achieves ~1% precision at the scales of interest, 0.1<r<10 Mpc/h, and recovers the true cosmology when tested against independent simulations. The primary parameters of interest are related to the growth rate of structure, f, and its degenerate combination fsigma_8. Using this emulator, show that the constraining power on these parameters monotonically increases as smaller scales are included in the analysis, all the way down to 0.1 Mpc/h. For a BOSS-like survey, the constraints on fsigma_8 from r<30 Mpc/h scales alone are more than a factor of two tighter than those from the fiducial BOSS analysis of redshift-space clustering using perturbation theory at larger scales. The combination of real- and redshift-space clustering allows breaking of the degeneracy between f and sigma_8, yielding a 9% constraint on f alone for a BOSS-like analysis. The current AEMULUS simulations limit this model to surveys of massive galaxies. Future simulations will allow this framework to be extended to all galaxy target types, including emission-line galaxies.
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