WAVE GOODBYE TO COLD DARK MATTER ENOCH LEUNG (HKU) PROF. TOM BROADHURST (UPV/EHU) DR. JEREMY LIM (HKU) Hong Kong Astrophysical Society Annual Meeting 14 th November, 2015

OVERVIEW Cold dark matter (CDM) and Wave dark matter (ΨDM) give rise to different predictions of the high-z luminosity function (LF) We performed observational tests on the luminosity distribution of high-z galaxies behind four Hubble Frontier Fields (HFF) galaxy clusters Our preliminary results ruled out the CDM picture while being consistent with the ΨDM model

CDM VS ΨDM

STANDARD COLD DARK MATTER (CDM) Composed of heavy fermions e.g. WIMPs (Weakly Interacting Massive Particles) Smaller inhomogeneities of matter first collapse under self-gravity Later merge into larger structures Hierarchy of dark matter (DM) halos More small DM halos than large ones ⇒ More faint galaxies than bright ones

PREDICTED LF IN CDM Fainter luminosity (absolute magnitude) Luminosity function predicted by CDM at z = 4 (Schive et al. 2015) Increasing galaxy number density

HUNT FOR CDM PARTICLES Where are the WIMPs? Non-detections so far in the most sensitive direct-detection experiments (e.g. LUX, SuperCDMS, LHC) Why still can’t we detect it? Does it really exist? Another possible form of DM?

WAVE DARK MATTER (ΨDM) Composed of light bosons in a coherent, ground state Mass scale of ∼ eV Quantum effects play a significant role Governed by the evolution of the Schrödinger-Poisson equation Quantum pressure arising from the uncertainty principle counters gravity below a certain Jeans scale Suppresses and delays the formation of DM halos smaller than ∼ M ☉ ⇒ fewer less massive (faint) galaxies Predicts a turn over in the number density of galaxies towards the faint end of the LF, at some critical value dependent on the boson mass, the only free parameter in the ΨDM model (Schive et al. 2014)

PREDICTED LF IN ΨDM Fainter luminosity (absolute magnitude) Luminosity function predicted by CDM at z = 4 (Schive et al. 2015) Increasing galaxy number density

PREDICTED LF IN ΨDM Luminosity function predicted by ΨDM at z = 4 (Schive et al. 2015) Blue curve represents m Ψ = 0.8 × eV, which was determined from the observed kpc-scale cores of local dwarf spheroidal (dSph) galaxies Green and red curves represent two other possible boson masses that are consistent with current observed high-z LF

CURRENT STATUS Existing blank field surveys do not have sufficiently high sensitivities to probe the faint end of the high-z LF where different model predictions start to drift apart significantly (Schive et al. 2015)

GRAVITATIONAL LENSING!

GRAVITATIONAL LENSING Foreground mass in a gravitational lens magnifies background sources such that they are brightened up (more flux) Brings intrinsically faint galaxies that are originally undetectable up above the flux limit of our telescope Massive galaxy clusters act as the perfect lens candidates for our study

HUBBLE FRONTIER FIELDS CLUSTERS Targeted at four recently completed deep fields centering at strong lensing clusters Data products released from 2014 to 2015

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MAGNIFICATION CORRECTIONS Semi-parametric cluster lens models from our research group (Lam et al. 2014, Diego et al. 2014a, Diego et al. 2014b, Diego et al. 2015) Corrected for the local magnification of each individual galaxy to derive their unlensed absolute magnitudes Illustration of the effect of performing magnification corrections to obtain the intrinsic absolute magnitudes of high-z galaxies Blue bars: lensed absolute magnitudes Green bars: unlensed absolute magnitudes after correcting for their magnifications

MODEL PREDICTIONS Predicted the luminosity distribution of high-z galaxies at the four chosen cluster fields n lensed (>L 0 ) = (1/μ) n unlensed (>L 0 /μ) n is the number density of galaxies with luminosity L > L 0 L 0 is the luminosity limit (or equivalently, the flux limit) of our telescope μ is the magnification factor Competition between 1.Area expansion: actual source plane area is smaller than observed area by a factor of μ 2.Lowered luminosity/flux limit : galaxies in the source plane are brightened up by a factor of μ

PARALLEL BLANK FIELDS AS CONTROLS Parallel blank field observed by one of the two cameras of HST (ACS and WFC3/IR) while observing the cluster field with another camera Much lower, if any, magnifications at these cluster-free regions, i.e. μ ∼ 1

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UV LUMINOSITY DISTRIBUTION UV luminosity (1500 Å) distribution of galaxies at the parallel fields Vertical axis: number of galaxies in a given comoving volume within the unit redshift interval (z = 4 – 5) Roughly speaking, the galaxy number density as a function of luminosity Vertical error bars denote 1σ cluster variance Fainter luminosity (absolute magnitude)

UV luminosity distribution of galaxies at the parallel fields at z = Similar predictions for different models given the detection threshold of HST Not deep enough the distinguish between various model predictions

UV LUMINOSITY DISTRIBUTION I have just showed you the results from the parallel fields What about the cluster fields? Fainter luminosity (absolute magnitude)

UV luminosity distribution of galaxies at the cluster fields Obviously rules out the CDM model (black dotted curve) Favors the ΨDM model with a boson mass m Ψ = 0.8 × eV (blue dash-dotted curve) Consistent with the observed solitonic core properties of local dSph galaxies

CONCLUSION Utilized the gravitational lensing created by four massive HFF clusters which magnifies background high-z galaxies Demonstrated that the standard CDM is an inappropriate picture to describe the observed deficit of faint galaxies at high redshifts Strong indication for ΨDM with a boson mass of 0.8 × eV Coherent with several other independent observations 1.Solitonic core properties of local dSph galaxies (e.g. Fornax and Sculptor dwarf galaxies) 2.Thomson scattering optical depth to CMB reported by Planck 2015 results 3.High-z GRB event rates observed by SHOALS (Swift Gamma-Ray Burst Host Galaxy Legacy Survey) Possible explanation for the non-detections of CDM

I WILL MISS CDM! THANKS!

INTERNAL CONSISTENCY

REDSHIFT DISTRIBUTION

RADIAL SURFACE DENSITY PROFILE