Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGravitational lensing $H_0$ tension from ultralight axion galactic cores
75
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Gravitational lensing time delays offer an avenue to measure the Hubble parameter $H_0$, with some analyses suggesting a tension with early-type probes of $H_0$. The lensing measurements must mitigate systematic uncertainties due to the mass modelling of lens galaxies. In particular, a core component in the lens density profile would form an approximate local mass sheet degeneracy and could bias $H_0$ in the right direction to solve the lensing tension. We consider ultralight dark matter as a possible mechanism to generate such galactic cores. We show that cores of roughly the required properties could arise naturally if an ultralight axion of mass $msim10^{-25}$ eV makes up a fraction of order ten percent of the total cosmological dark matter density. A relic abundance of this order of magnitude could come from vacuum misalignment. Stellar kinematics measurements of well-resolved massive galaxies (including the Milky Way) may offer a way to test the scenario. Kinematics analyses aiming to test the core hypothesis in massive elliptical lens galaxies should not, in general, adopt the perfect mass sheet limit, as ignoring the finite extent of an actual physical core could lead to significant systematic errors.
rate research
Read More
It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_asim 10^{-22}text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here we use realistic kinematic mock data catalogs of Milky Way dSphs to show that the mass-anisotropy degeneracy in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSphs with reported stellar subcomponents, Fornax and Sculptor, and assuming that the halo profile has not been acted on by baryons, yields core radii $r_{c}>1.5$ kpc and $r_c> 1.2$ kpc respectively, and $m_a<0.4times 10^{-22}text{eV}$ at 97.5% confidence. These bounds are in tension with the number of observed satellites derived from simple (but conservative) estimates of the subhalo mass function in Milky Way-like galaxies. We discuss how baryonic feedback might affect our results, and the impact of such a small axion mass on the growth of structures in the Universe.
A number of proposed and ongoing experiments search for axion dark matter with a mass nearing the limit set by small scale structure (${cal O} ( 10 ^{ - 21 } {rm eV} ) $). We consider the late universe cosmology of these models, showing that requiring the axion to have a matter-power spectrum that matches that of cold dark matter constrains the magnitude of the axion couplings to the visible sector. Comparing these limits to current and future experimental efforts, we find that many searches require axions with an abnormally large coupling to Standard Model fields, independently of how the axion was populated in the early universe. We survey mechanisms that can alleviate the bounds, namely, the introduction of large charges, various forms of kinetic mixing, a clockwork structure, and imposing a discrete symmetry. We provide an explicit model for each case and explore their phenomenology and viability to produce detectable ultralight axion dark matter.
Riess et al (2018c) have claimed there exist seven problems in the analyses presented by Shanks et al (2018) where we argue that there is enough uncertainty in Cepheid distances and local peculiar velocity fields to explain the current tension in $H_0$. Here, we take each of the Riess et al (2018c) points in turn and suggest that either they do not apply or that the necessary caveats are already made by Shanks et al (2018). We conclude that the main point to be inferred from our analyses still stands which is that previous claims by Riess et al (2018b) that Gaia parallaxes confirm their Cepheid scale are, at best, premature in advance of further improvements in the Gaia astrometric solution.
There is an $approx9pm2.5$% tension between the value of Hubbles Constant, $H_0=67.4pm0.5$km,s$^{-1}$Mpc$^{-1}$, implied by the {it Planck} microwave background power spectrum and that given by the distance scale of $H_0=73.4pm1.7$km,s$^{-1}$Mpc$^{-1}$. But with a plausible assumption about a {it Gaia} DR2 parallax systematic offset, we find that {it Gaia} parallax distances of Milky Way Cepheid calibrators are $approx12-15$% longer than previously estimated. Similarly, {it Gaia} also implies $approx4.7pm1.7$% longer distances for 46 Cepheids than previous distances on the scale of Riess et al. Then we show that the existence of an $approx150$h$^{-1}$Mpc `Local Hole in the galaxy distribution implies an outflow of $approx500$km,s$^{-1}$. Accounting for this in the recession velocities of SNIa standard candles out to $zapprox0.15$ reduces $H_0$ by a further $approx1.8$%. Combining the above two results would reduce the distance scale $H_0$ estimate by $approx7$% from $H_0approx73.4pm1.7$ to $approx68.9pm1.6$ km,s$^{-1}$Mpc$^{-1}$, in reasonable agreement with the {it Planck} value. We conclude that the discrepancy between distance scale and {it Planck} $H_0$ measurements remains unconfirmed due to uncertainties caused by {it Gaia} systematics and an unexpectedly inhomogeneous local galaxy distribution.
It is currently thought that the early dark energy (EDE) resolution of the Hubble tension will inevitably suffer inconsistency with the large scale structure data (quantified as $S_8$). However, if this so-called $S_8$ tension is physical, it might be related only with the clustering property of dark matter at the corresponding scale. We find by performing Monte Carlo Markov Chain analysis that in the AdS-EDE model (with an Anti-de Sitter phase around recombination), if an axion field with mass $m_asimeq1.3times10^{-26}$ eV becomes dynamical at redshift $zsimeq 1.7times10^4$ and constitutes $7%$ of the total dark matter, both $H_0$ and $S_8$ will be consistent with local measurements within $1sigma$, while the model can fit PlanckCMB+SN+BAO+EFT dataset as well as $Lambda$CDM, which will possibly be tested with on-going CMB and galaxy surveys.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
