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Galaxy Formation The Big (and Little) Picture

Galaxy Formation The Big (and Little) Picture. Julianne Dalcanton University of Washington. This is your Universe on Dark Matter. This is your Universe. Galaxies are our link to the dark sector. Spirals M halo >10 10 M  V~200km/s. Dwarfs M halo >10 8 M  V~30km/s Weakly Clustered

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Galaxy Formation The Big (and Little) Picture

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  1. Galaxy FormationThe Big (and Little) Picture Julianne Dalcanton University of Washington

  2. This is your Universe on Dark Matter This is your Universe Galaxies are our link to the dark sector

  3. Spirals Mhalo>1010M V~200km/s Dwarfs Mhalo>108M V~30km/s Weakly Clustered Young stars Numerous Galaxies: Ellipticals Mhalo>1011M V~350km/s Highly Clustered Old stars Rare-ish

  4. Dark Matter

  5. Large scale structure rotation

  6. Structure forms hierarchically • Dark matter collects into halos • Small halos form first • Lots of merging, especially at early times Scale-free, so galaxy halo similar

  7. Galaxy Clusters Abell 1689 ??? V. Springel

  8. Galaxy Formation: The Short Course • Dark matter virializes. • Gas heats & cools. • Or it doesn’t. • Dense gas forms stars.

  9. The slighly longer version: • Infalling gas shock heats to the virial temperature of the dark matter halo. Stars X-Rays T~10K T~106K NGC 4649

  10. Some gas cools & contracts • Gas that comes in with high angular momentum forms a rotating disk. Neutral Hydrogen Stars NGC 2403

  11. When gas gets dense, it forms stars Molecular Gas Young Stars

  12. Stars are collisionless • They tend to preserve the motion with which they were formed. Courtesy K. Johnston

  13. M31 Bullock & Johnston 2005 Ferguson et al

  14. Gas can be ejected: “Feedback” Stars Ionized Gas (104K) Really Ionized Gas (5x106K) Strickland et al 2004

  15. Simulated galaxies are starting to look really promising! • rotation • ages • sizes F. Governato

  16. Is CDM compatible with our understanding of galaxy formation? • CDM • Heirarchical • Lots of small scale power • Small stuff first • Large stuff last • Nature • Too Few low mass galaxies • Young low mass galaxies & old high mass galaxies • Massive objects at high redshift. • Anti-Heirarchical? Surprisingly, yes

  17. log(number-o-galaxies) Mass Milky Way data is “missing” galaxies if LCDM is correct Hiding Low Mass Halos: Moore et al

  18. Making dwarf galaxies disappear: • “Feedback” • Supernova blowout • Ethermal;EKE >Egrav • “Squelching” • Reionization • Ethermal>Egrav • “Tidal Disruption” • Egrav,host>Egrav Dwarf galaxies have small gravitational potentials

  19. Smaller fraction of baryons wound up in massive galaxies • Star formation feedback & reionization won’t work for deep potential wells ? Similar problems for massive galaxies: underluminous log(Halo Mass / Luminosity) SN Feedback from disks van den Bosch et al 2004

  20. Merging = GasBH = Outflow V. Springel et al

  21. AGN Feedback: • Bigger spheroid = Bigger Black Hole • Feedback stronger in more massive galaxies • Star formation shuts down earlier and more completely in massive galaxies underluminous log(Halo Mass / Luminosity) SN Feedback from disks AGN Feedback from spheroids van den Bosch et al 2004

  22. AGN Feedback makes galaxies appear “anti-hierarchical” High mass Star formation rate Low mass • In massive galaxies: • Stars form early • Mass assembles late Low mass Star formation rate High mass Lucia et al 2005 Lookback time

  23. Putting it all together: Courtesy G. Stinson & F. Governato

  24. Problems remain • Predicting internal structure • Internal kinematics • Numbers/Masses at high redshift? • Compatibility with reionization? But, given our success of making the impossible possible, I’d be optomistic.

  25. But really, this is all a fairy tale. We’ve proven that LCDM is not necessarily wrong. This doesn’t mean it’s right! Theorist

  26. Why galaxy formation is not constraining cosmological models* CDM Theory starts with LCDM as an a prioriassumption Tunes “gastrophysics” to match observations WDM *in the era of precision cosmology Moore et al

  27. Start with predicted dark matter distribution Adust star formation and SN “feedback” to suppress the “right number” of galaxies

  28. What are the odds? Real Gas Real Outflows Real Star Formation Red = ionized

  29. Where could non-LCDM physics be lurking? Not on large (>Mpc) scales 5% normal matter 25% dark matter 70% dark energy Tegmark

  30. On intermediate (~1-10Mpc) scales? • Fix shape of the linear power spectrum • s8Wm0.6 is lower when measured on small scales, than for CMB+SN s8=0.9 True average M/L (Note: derived behavior of baryons vs mass is qualitatively similar) s8=0.6 Tinker et al 2005

  31. On smaller (~1 kpc) scales? Compared to the real universe LCDM simulations have: • Too many small lumps • Too high a central density LCDM log(Mean Density) • Too much small scale power • Too high initial phase space density Real Galaxies

  32. 5% normal matter 25% dark matter 70% dark energy Tegmark Galaxy formation provides far more freedom than people are exploiting CDM is an absurdly minimal description of dark matter

  33. What to do? • Don’t ignore theories whose power spectra deviate at small scales. • Improve constraints on gastrophysics. • Look for better observational tests. • Increase dynamic range of simulations. • Aggressively pursue dark-dark halos

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