Galaxy UV-luminosity function and reionization constraints on axion dark matter

Abstract

If the dark matter (DM) were composed of axions, then structure formation in the Universe would be suppressed below the axion Jeans scale. Using an analytic model for the halo mass function of a mixed DM model with axions and cold dark matter, combined with the abundance-matching technique, we construct the UV-luminosity function. Axions suppress high-z galaxy formation and the UV-luminosity function is truncated at a faintest limiting magnitude. From the UV-luminosity function, we predict the reionization history of the universe and find that axion DM causes reionization to occur at lower redshift. We search for evidence of axions using the Hubble Ultra Deep Field UV-luminosity function in the redshift range z = 6-10, and the optical depth to reionization, τ , as measured from cosmic microwave background polarization. All probes we consider consistently exclude m a 10 −23 eV from contributing more than half of the DM, with our strongest constraint ruling this model out at more than 8σ significance. In conservative models of reionization a dominant component of DM with m a = 10 −22 eV is in 3σ tension with the measured value of τ , putting pressure on an axion solution to the cusp-core problem. Tension is reduced to 2σ for the axion contributing only half of the DM. A future measurement of the UV-luminosity function in the range z = 10-13 by JWST would provide further evidence for or against m a = 10 −22 eV. Probing still higher masses of m a = 10 −21 eV will be possible using future measurements of the kinetic Sunyaev-Zel'dovich effect by Advanced ACTPol to constrain the time and duration of reionization.

Unbiased constraints on ultralight axion mass from dwarf spheroidal galaxies

“…This suggest that ULAs, like WDM, may suffer from a Catch 22 in that "if you want large cores, you don't get enough dwarfs; if you want enough dwarfs, you don't get big enough cores". Existing cosmological bounds also appear to rule out a ULA origin for the WP11 cores: high-z galaxies rule out ma 1 × 10 −22 eV (Bozek et al 2015;Schive et al 2016). Constraints from reionization, such as the CMB optical depth τ , are less conclusive, and may even favour low axion mass.…”

“…Figure C1. The optical depth to reionization, τ , computed in concordance models for ULAs, where the error band represents systematic modelling uncertainty (Bozek et al 2015). The horizontal bands represent 1 and 2-σ constraints on τ from different CMB polarization power spectrum measurements.…”

A free-form mass model of the Hubble Frontier Fields cluster AS1063 (RXC J2248.7−4431) with over one hundred constraints

“…A significant absence of such galaxies is not predicted for the LCDM model, where several galaxies are expected per HFF cluster in the range 9 < z < 10 on the basis of the standard LCDM model, by extrapolating the luminosity function (e.g Coe, Bradley & Zitrin 2015;Schive et al 2015). This may have profound implications for the nature of dark matter as this absence at z > 9.0 is a distinct prediction of the wave-DM scenario where light bosons such as axions lie in a ground state, and for which the inherent Jeans scale in this context suppresses the formation of low mass galaxies thereby delaying galaxy formation relative to LCDM Schive et al 2015;Bozek et al 2015). This scenario has only one Figure 1.…”

“…The circles mark the positions of the multiply lensed systems with spectroscopic redshift that are used to build the preliminary (or driver) lens model. free parameter, the boson mass, which is constrained to be 10 −22 eV by the local dwarf cores and which translates into a sharp onset of galaxy formation at z ∼ 9 − 10 (Bozek et al 2015;Schive et al 2015). This precise prediction means this model is readily falsifiable if significant numbers of galaxies were to be found at z > 10, and hence the new constraints provided by the HFF in this redshift regime provides a very crucial, timely means of discrimination between the wave-DM model and standard heavy particle interpretation of CDM.…”

Scalar field (wave) dark matter

“…8 M suppressing structure formation of low mass dark matter halos 7,29,42,44 . Moreover, there is particular interest in finding equilibrium configurations of the system of equations that describe the field (Einstein-Klein-Gordon system) and of its weak field approximation (Schrödinger-Poisson(SP) system), different authors have obtained solutions interpreted as boson stars or later as dark matter halos showing agreement with rotation curves in galaxies and velocity dispersion profiles in dwarf spheroidal galaxies 4,18,27,36,38,39,43,55,56 .…”