Firenze (JPO: 28/07/17) Small Scale Crisis for CDM: Fatal or a Baryon Physics Fix

Transcription

1 Firenze (JPO: 28/07/17) Small Scale Crisis for CDM: Fatal or a Baryon Physics Fix

2 CBR Spectrum Planck and all-a Perfect Fit to the CDM Expectation Precise measurements of the CBR specify the cosmological model.

3 Perfect for all large scale info

4 In Detail: Representative Current Cosmological Model (prior: LCDM) W tot = 1 (assumption) [= ] W cdm = ± W baryon = ± W lambda = 0.71 ± 0.01 n = 0.97 ± 0.01 H 0 =69.3 ± 0.9 km/s/mpc s 8 = 0.83 ± 0.02 t scat =0.088 ± ; Spergel et al (WMAP9) precision cosmology??

5 A More Critical Look at the Low Red-Shift Tests: But 10 3 > Z > 6 6 > Z > > Z Photons CBR SZ Rdio Lns Baryons CBR GalForm LEN Dark Matter CBR StrGrth HlsClstrs Dark Energy CBR SN Ages,BAO etc l > 20Mpc/h CBR 20 > l >1 CBR? Cltrs,LyA, StrGrth Clstrs2pt SDSS GrLensing 1 > l??????? X?? XXX???

6 FIRST: Let us look at observed galaxy properties: dwarf spheroidals are a separate low density sequence and the lower the mass the lower the density (Kormendy, 2015 data) Elliptical Dwarf Spher.

7 Let us now look at low mass galaxies in the local group Coral Wheeler, 2015

8 Let us look at the familiar problems at small scales Too big to fail problem. Missing satellite problem. Absence of DM cusps in Dwarf Spheroidal Galaxies? Orbiting GCs in Dwarf Spheroidal Galaxies? Wrong red-shift evolution of low mass Galaxies? PERHAPS ALL OF THESE CAN BE FIXED BY DOING THE BARYONIC PHYSICS CAREFULLY. BUT

9 A Simple Question not often asked With FIVE orders of magnitude range in stellar mass for objects having halo mass _0.5 M solar, then what would we expect to see for halos for the ten times more numerous CDM halos of _0.5 M solar and the hundred times more numerous halos of mass _0.5 M solar??? If they had a similar range in the ratio of M*/M DM, then there would be vastly more satellites systems in the local group. Not exactly the same problem as the missing satellite or the too big to fail problems. It is the missing halo problem. And is serious for CDM.

10 An Alternative to Standard ( cold) DM: Fuzzy Dark Matter - Lam Hui, JPO, Scott Tremaine & Ed Witten Very light bosons axions w mass ev Quantum limit: ħ = m * v * λ implies large size when v is small: M * R = (ħ 2 /(G * m 2 )) Coupled with VT and cosmological formation give minimum halo mass vs redshift. Can explain dwarf spheroidal results. Testable predictions of reduced substructure.

11 Mass-Radius relation at low mass end: from QM v 2 = GM/R = ħ 2 /(m 2 R 2 ) èm * R = ħ 2 /(G * m 2 ) or R R min = 1 kpc * (M/10 9 M solar ) -1 * m -22-2

12 Mass-Radius relation at low end: combine w cosmology to get mass limit! ρ 200 ρ crit = 600 * H 2 /(8 π G) and ρ ~ M/R 3 ~ M 4 èm M min = (H 2 ħ 6 /(G 4 * m 6 )) 1/4 or M min = M solar * (1 + z) 3/4 * m -22-3/2

13 And the halos have a different shape: no cusp. Several papers show that the profiles match those of dwarf spheroidals better than does the standard NFW profile. Burkert profile??

14 Mass Function of Halos Computed: Bozek et al(2015)

15 Basic low redshift tests Cusp-core issue? Dwarf galaxy satellites? Dynamical friction in dwarf systems? Too big to fail problem? Sizes of small systems? Missing halo problem. Evolution of low mass galaxies?

16 Cusp-Core issue in dwarf systems We conclude that one or more of the following statements must be true: (i) the dark matter is more complex than envisaged by any current model; (ii) current simulations fail to reproduce the diversity in the effects of baryons on the inner regions of dwarf galaxies; and/or (iii) the mass profiles of inner mass deficit galaxies inferred from kinematic data are incorrect.

17 Some Predictions No dynamical friction in small systems. No cusps in small systems. No sub-halos smaller than 10 8 M solar at z = 0. By z = 10 minimum halo mass is 10 9 M solar and low mass galaxies form late. MW tidal streamers not broadened by interactions with sub-halos. Gravitational lensing by intervening subhalos is reduced.

18 Conclusions The standard CDM model works essentially perfectly on large scales (r > 5 kpc). Many familiar small scale problems. Most can be addressed by baryonic physics treatments. But some: Dynamical friction absence in low mass and ultra faint systems Missing low mass halo problem Can perhaps only be addressed by changing the nature of the DM to ultra-light axions, WDM etc