Presentation on theme: "Challenges for the Standard Cosmology Tom Shanks Durham University."— Presentation transcript:
Challenges for the Standard Cosmology Tom Shanks Durham University
New Age of Precision Cosmology? Boomerang + WMAP CMB experiments detect acoustic peak at l=220(≈1deg) Spatially flat, CDM Universe (de Bernardis et al. 2000, Spergel et al 2003, 2006) SNIa Hubble Diagram requires an accelerating Universe with a term CDM also fits galaxy clustering power spectrum (e.g. Cole et al 2005)
Astrophysical Problems for CDM Too much small scale power in mass distribution? Mass profile of LSB galaxies less sharply peaked than predicted by CDM (Moore et al, 1999a) Instability of spiral disks to disruption by CDM sub- haloes (Moore et al, 1999b) Observed galaxy LF is much flatter than predicted by CDM - even with feedback (Cole et al, 1999). CDM Massive galaxies form late vs. “downsizing” Slope of galaxy correlation function is flatter than predicted by CDM mass anti-bias simple high peaks bias disallowed (eg Cole et al, 1998) L X -T relation galaxy clusters not scale-free?
CDM Mass Function v Galaxy LF CDM halo mass function is steeper than faint galaxy LF Various forms of feedback are invoked to try and explain this issue away Gravitational galaxy formation theory becomes a feedback theory! (from Benson et al 2003) CDM haloes
No evolution seen for z<1 early-types Brown et al (2007) Observe “downsizing” - but CDM predicts late epoch of galaxy formation and hence strong dynamical evolution in the range 0<z<1. Wake et al (2007)
Fundamental Problems for CDM CDM requires 2 pieces of undiscovered physics!!! makes model complicated+fine-tuned is small - after inflation, / rad ~ 1 in 10 102 Also, today ~ Matter - Why? To start with one fine tuning (flatness) problem and end up with several - seems circular! anthropic principle ?!? CDM Particle - No Laboratory Detection Optimists like search for neutrino! Pessimists like search for E-M ether!
Fundamental Problems for CDM Even without , CDM model has fine tuning since CDM ~ baryon (Peebles 1985) Baryonic Dark Matter needed anyway! Nucleosynthesis baryon ~ 10 x star Also Coma DM has significant baryon component
Coma galaxy cluster gas Coma contains hot X-ray gas (~20%) X-ray map of Coma from XMM-Newton (Briel et al 2001) If M/L=5 then less plausible to invoke cosmological density of exotic particles than if M/L=60-600!
H 0 route to a simpler model X-Ray gas becomes Missing Mass in Coma. In central r<1h -1 Mpc:- Virial Mass 6 10 14 h -1 M o M vir /M X =15h 1.5 X-ray Gas Mass 4 10 13 h -2.5 M o Thus M vir /M X =15 if h=1.0, 5 if h=0.5, 1.9 if h=0.25
3 Advantages of low H 0 Shanks (1985) - if H o <30kms -1 Mpc -1 then: X-ray gas becomes Dark Matter in Coma Inflationary baryon =1 model in better agreement with nucleosynthesis Light element abundances baryon h 2 <0.06 baryon 1 starts to be allowed if h 0.3 Inflation+EdS => =1 => Globular Cluster Ages of 13-16Gyr require H o <40kms -1 Mpc -1 But the first acoustic peak is at l=330, not l=220
Escape routes from CDM Galaxy/QSO P(k) - scale dependent bias - abandon the assumption that galaxies trace the mass ! SNIa Hubble Diagram - Evolution WMAP - cosmic foregrounds? Epoch of Reionisation at z~10 Galaxy Clusters - SZ inverse Compton scattering of CMB Galaxy Clusters - lensing of CMB
The 2dF QSO Redshift Survey 23340 QSOs observed
2dF QSO Lensing SDSS Galaxy Groups and Clusters in 2QZ NGC area
Strong QSO-group lensing Strong anti- correlation between 2dF QSOs and foreground galaxy groups (Myers et al 2003) If caused by lensing magnification… then high group masses M ≈1 and/or anti-bias b~0.2 (But see Hoekstra et al 2003)
QSO-group/galaxy lensing Myers et al 2003, 2005, Mountrichas & Shanks 2007
CMB Lensing - CDM Lensing smoothing functions computed for various models including standard CDM model - linear and non- linear (Seljak 1996)
CMB Lensing - CDM Standard model predicts only small lensing effects on CMB (Seljak, 1996) But standard model also predicts much smaller lensing effect than observed with confirmed 2QZ QSOs……..
Implications for CMB Lensing CMB lensing smoothing functions, ( )/ Only one that improves WMAP fit is ( )=constant (black line) Requires mass r -3 or steeper Also requires anti- bias at b~0.2 level
Foregrounds move 1st peak WMAP z~10 Reionisation + QSO lensing effects of galaxies and groups from Myers et al (2003, 2005) l=330 l=220 Need SZ for 2nd peak other models can be fine-tuned to fit WMAP first peak? Shanks, 2007, MNRAS, 376, 173 (see also Lieu + Mittaz, 2005, ApJ, 628, 583)
SZ effect decreases with z! WMAP SZ at 94GHz Bielby + Shanks 2007 astro-ph/ 0703407 Lieu et al 2006, ApJ, 648, L176 Z=0.02 Z~0.1 Z~0.2Z~0.4 172 Abell Clusters 235 Abell Clusters38 OVRO/BIMA Clusters Coma cluster (arcmin) TT
Conclusions CDM gains strong support from WMAP, SNIa, P(k) But assumes “undiscovered physics” + very finely- tuned + problems in many other areas eg “downsizing” To move to other models need to abandon assumption that galaxies trace mass QSO lensing galaxy groups have more mass than expected from virial theorem Lensing (+reionisation) of CMB may give escape route to simpler models than CDM SZ CMB contamination - extended, z dependent? Fine tuning CMB foregrounds - may allow Baryon =1, low H 0 model……plus others?