Galaxy Formation in a Λ Cold Dark Matter Universe

1. Galaxy Formation in a Λ Cold Dark Matter Universe Mario G. Abadi Instituto de Astronomía Teórica y Experimental Observatorio Astronómico de la Universidad Nacional de Córdoba Consejo de Investigaciones Científicas y Técnicas, Argentina In collaboration with Julio Navarro, Matthias Steinmetz, Vince Eke Amina Helmi, Laura Sales and Andres Meza XII Reunion Regional Latinoamericana de Astronomía de la IAU Isla de Margarita, Venezuela October 22-26 2007

2. Milky Way Galaxy

3. Surviving Satellites Duncan Forbes 2007

4. Merging Satellites • Sagittarius stream: warp around the entire MW nearly perpendicular to the midplane (Ibata et al. 2001). Progenitor=Sagittarius dwarf • Monoceros ring: a proposed ring of stars around the galactic plane (Yanny et al 2003 & Ibata et al 2003). Progenitor=Canis Major dwarf? • Orphan stream: a tidal stream that extends over 50° in the north galactic cap (Belokurov et al 2007). Progenitor=Ursa Major II?? • Andromeda stream: a giant stream of stars uncovered in the halo of M31 (Ibata et al. 2001) • External galaxy: a dwarf satellite galaxy in the process of being torn apart by gravitational tidal forces (Forbes et al 2003)

5. Merged Satellites • Substructure in the galactic halo (Helmi et al. 1999) • Arcturus stream (Eggen 1971, Navarro et al. 2004) • Debris from omega Cen parent galaxy in the solar neighborhood (Meza et al. 2005) • Substructure in the galactic disk (Helmi et al. 2005)

7. Orbital Classification of Satellites Surviving: Rgalaxy<Rsatellite<Rvirial Merged: 0<Rsatellite<Rgalaxy Escaping Rvirial<Rsatellite<∞ Distance Time

8. R-band Simulated Galaxy 40 kpc

9. Stellar halo and Satellites 600 kpc

10. Dark Matter Halo 600 kpc

11. Photometric Properties • I-band surface brightness profile of the simulated galaxy seen projected face-on • The surface density profile agrees very well with an observed Sab galaxy (UGC615) • Also colours are in agreement with UGC615 Surface Brightness Distance

12. Photometric Properties • I-band surface brightness profile of the simulated galaxy seen projected face-on • The surface density profile agrees very well with an observed Sab galaxy (UGC615) • Also colours are in agreement with UGC615 Surface Brightness Distance

13. Kinematics Properties • There is a poor agreement between the spheroid-dominated, declining rotation curve of the simulated galaxy and the observed galaxy. Velocity Distance

14. Kinematics Properties • There is a poor agreement between the spheroid-dominated, declining rotation curve of the simulated galaxy and the observed galaxy. Velocity Distance

15. Tully Fisher Relation • Angular momentum problem: Simulated disk galaxies only marginally agree with the observed TF relation for late-type spirals. They fit rather well in the relation appropriated for S0 due to the net angular momentum transfer from the gas to the dark matter halo during the galaxy formation process. • Solutions: involve some sort of feedback processes that regulate the gas supply to the galaxy. But, Governato et al ascribed the problem to poor numerical resolution. I-band Absolute Magnitude Rotation Speed

16. Feedback Solution The shapes of the CDM halo mass function and the luminosity function are very different (Baugh 2006) Simulations with no or week feedback tend to overpredict the cosmic star formation history substantially (Springel 2006)

17. Feedback Solution Weak Strong • Feedback effects regulate the delicate balance between gas supply and morphology • Identical initial conditions with different feedback recipe and star formation produce different galaxies • Strong (weak) feedback produce disk (bulge)-like galaxies Zavala Okamoto & Frenk 2007

18. Dynamical Components • Distribution function of circularity • Spheroid: no net rotation • Thick disk: slow rotation • Thin disk: fast rotation Counter-rotating stars Co-rotating stars

19. Age Distribution • Inefficient feedback leads to high rates of star formation at high-redshift. • Subsequent mergers form a massive spheroid • Galactic disks date from the time of the last major merger and form from the inside out Star formation rate (solar masses per year) Old Stellar Age Young

20. Natives and Immigrants The spheroid is old. There are no young stars in this component The thin disk contains a significant number of old stars (15% are older than 10 Gyrs) More than 90% of this old thin disk is a result of satellite accretion events The thick disk is old The old thick disk is not a former thin disk thickened by a minor merger but actually the debris from satellite accretion events Mass Fraction Fraction of Natives Old Stellar Age Young

21. Density Profiles • Luminous satellites are resilient to disruption by tides and they can survive as self-bound entities closer to the primary, where substructure in dark-matter only simulations may quickly disrupt (White & Rees 1978) • Stellar halos are much more concentrated than dark matter halos Number density Profile Distance to the centre

22. Cumulative Profiles • Simulated and observed Milky Way and Andromeda satellites have very similar profiles Cumulative number fraction Distance to the centre

23. Cumulative Profiles Simulated satellites trace very well the underlying dark matter distribution and are the best dark matter tracers in the outer parts of the galaxy • Milky Way globular clusters and simulated stellar halo have very similar distributions which are much more concentrated. Cumulative number fraction Distance to the centre

24. Anisotropy Velocity Dispersion • The simulated stellar halo consists almost exclusively of accreted stars • Satellites are only slightly more radially anisotropic than the dark matter β~0.4 • The anisotropy of the stellar halo is much more pronounced β~0.8 • The fact that the stellar halo is made of disrupted satellites suggests that there is an intrinsic difference between merged and surviving satellites =1-T2/(r2) Fraction of Natives Radial Isotropic Distance to the centre

25. Accretion Mass Distribution Any satellite more massive than ~10% Mhost is not able to survive. Number Large mass satellites are very likely to merge with the host Light Satellite Mass Heavy

26. Accretion Redshift Distribution • Merged satellites are more massive and have been accreted earlier than surviving one • Surviving satellites are predominantly low-mass systems and have been accreted recently • The building blocks of the stellar halo were on average more massive and were accreted (and disrupted) earlier than de population of satellites that survive until the present • These results may help to explain the difference between the abundance patterns of halo star in the solar neighborhood and in galactic dwarfs Fraction Accretion Redshift

27. Conclusions 1)Photometric properties of simulated galaxies agree with observations 2)Simulated galaxies marginally agree with Tully Fisher relation, but stronger feedback alleviate this problem 3)Spheroid by mergers, disk by gas accretion 4)Satellite density profile similar to dark matter halo but much more extended that the stellar halo 5)Satellite kinematics: also similar to dark matter and MW but different from stellar halo 6)Satellite Orbits: more massive satellites are accreted earlier and merge. Less massive satellite are accreted later and survive

28. Papers • Dynamical and Photometric properties • Fine Structure of galactic disks • Tidal torques • Omega Cen • Stellar halo • Substructure in the galactic disk • Surviving and merging satellite • Satellite on extreme orbits

29. Bibliografia • 2002 Freeman K. and Bland-Hawthorn J. The New Galaxy:Signatures of its Formation • 2003 Kauffmann G. The Formation and Evolution of Galaxies • 2006 Baugh C.M. A prime on hierarchical Galaxy Formation: the Semi-Analytical Approach • 2006 Avila-Reese V. Understanding Galaxy Formation and Evolution • 2007 Cecil G. and Rose J.A. Constraints on Galaxy Structure and Evolution from the Light of Nearby Systems

30. Ωtotal=100$ Ωlambda=76$ ΩmateriaOscura=20$ Ωgas=$3 con 80cts Ωgalaxias=20cts Escenario Cosmologico

31. Challenges to CDM on Galactic Scales • Too much dark matter in halo centers? • Halo substructure issues • Halo and galaxy merging history? • Halo occupation statistics ok? • Angular momentum issues • Does CDM correctly predict galaxy • number density (luminosity function)? • morphology, kinematics, and colors? • formation and evolution?

32. Galaxy Centers • Problem first recognized by Flores and me, and Moore, but HI errors were underestimated • (Swaters).. Small galaxies are mainly dark matter so the complications of baryonic physics are minimized. The only case where Blitz group see no radial motions is consistent with CDM r-γ with γ≈1. • The non-circular motions could becaused by nonspherical halos (Navarro).

33. Too Many Halos • “missing satellites”? Squelching • (Somerville) and properly identifying halos hosting satellites • (Gnedin, Klypin, Kravtsov, Zentner) seem to agree with • data. Enough subhalos at small radii to explain anomalous • flux ratios in radio gravitational lenses?

34. Halo Occupation Distribution • HALO OCCUPATION DISTRIBUTION Agree with • observations (as a function of mass, redshift)? • Predicted inner steep part of correlation function seen at • high redshift (SUBARU).

35. Merging History • Are there too many galaxy mergers to account for the numbers of (classical) bulges seen in disk galaxies (Kormendy)? • How important are major and minor • mergers in forming stars, spheroids, and AGN? In accounting for the brightest optical and IR galaxies at z > 2? • Do predicted mergers agree with numbers of peculiar galaxies and galaxy pairs seen (as a function of galaxy • luminosity, redshift, environment, …)?

36. Angular Momentum Issues • Catastrophic loss of angular momentum due to overcooling hydrodynamic simulations (Navarro, Steinmetz). • Spiral galaxies would be hard to form if ordinary matter has the same specific angular momentum distribution as dark matter (Bullock). • How do the disk baryons get the right angular momentum? • Mergers give halos angular momentum – too little for halos that host disks, too much for halos that host spheroids? • Role of AGN and other energy inputs? Role of cold inflows (Birnboim, Dekel, Katz, Weinberg …)? • Can simulated disks agree with observed Tully-Fisher relation and Luminosity Function at all redshifts?

37. Luminosity Function .

38. Bimodality

42. SUMMARY • We now know the cosmic recipe. Most of the universe is invisible stuff called “nonbaryonic dark matter” (25%) and “dark energy” (70%). • Everything that we can see makes up only about 1/2% of the cosmic density, and invisible atoms about 4%. The earth and its inhabitants are made of the rarest stuff of all: heavy elements (0.01%). • The ΛCDM Cold Dark Matter Double Dark theory based on this appears to be able to account for all the large scale features of the observable universe, including the details of the heat radiation of the Big Bang and the large scale distribution of galaxies. • Constantly improving data are repeatedly testing this theory. The main ingredients have been checked several different ways. There exist no convincing disagreements, as far as I can see. Possible problems may be due to the poorly understood physics of gas, stars,and massive black holes. • But we still don’t know what the dark matter and dark energy are, nor really understand how galaxies form and evolve. Let’s get back to work, so we can solve these problems before another 21 years elapse!

43. Fundamental Observational Properties of Galaxies 1) Galaxy contribution to the total density of the Universe: Why star formation is such an inefficient process? 2) Luminosity Function : Why there is a characteristic mass for galaxies?‏ 3) Bimodality: Why are there 2 distinct populations or a bimodality in properties such as colour? 4) Spatial Distribution (Correlation Function, Morphology Density Relation): What role does the environment play in galaxy formation? 5) Scaling Laws in size, luminosity and velocity: Why are there remarkably tight correlations between certain galaxy properties? 6) High redshift

44. Satellite Luminosity Function

45. Satellite Luminosity Function

46. Density Profile • Dark matter halo follows an “NFW” density profile ρ~rˉ¹(1+r)ˉ² • Number density profile of satellites, after rescaling their positions to the virial radius of each host and stacking all 8 simulations • There is little difference in the shape of the dark matter and satellite profiles. • Half mass radius very similar: R½=0.3 for dark matter particles and R½=0.37 for satellites • Simulated satellites differ from substructure halos, whose density profile is known to be significantly shallower than the dark matter • (Ghigna et al. 1998,2000 Diemand Moore & Stadel 2004 Gao et al 2004). • Luminous satellites are resilient to disruption by tides and they can survive as self-bound entities closer to the primary, where substructure in dark-matter only simulations may quickly disrupt (White & Rees 1978)‏ • The stellar halo is much more centrally concentrated R½=0.05

47. Density Profile • Dark matter halo follows an “NFW” density profile ρ~rˉ¹(1+r)ˉ² • Number density profile of satellites, after rescaling their positions to the virial radius of each host and stacking all 8 simulations • There is little difference in the shape of the dark matter and satellite profiles. • Half mass radius very similar: R½=0.3 for dark matter particles and R½=0.37 for satellites • Simulated satellites differ from substructure halos, whose density profile is known to be significantly shallower than the dark matter • (Ghigna et al. 1998,2000 Diemand Moore & Stadel 2004 Gao et al 2004). • Luminous satellites are resilient to disruption by tides and they can survive as self-bound entities closer to the primary, where substructure in dark-matter only simulations may quickly disrupt (White & Rees 1978)‏ • The stellar halo is much more centrally concentrated R½=0.05

48. Density Profile • Dark matter halo follows an “NFW” density profile ρ~rˉ¹(1+r)ˉ² • Number density profile of satellites, after rescaling their positions to the virial radius of each host and stacking all 8 simulations • There is little difference in the shape of the dark matter and satellite profiles. • Half mass radius very similar: R½=0.3 for dark matter particles and R½=0.37 for satellites • Simulated satellites differ from substructure halos, whose density profile is known to be significantly shallower than the dark matter • (Ghigna et al. 1998,2000 Diemand Moore & Stadel 2004 Gao et al 2004). • Luminous satellites are resilient to disruption by tides and they can survive as self-bound entities closer to the primary, where substructure in dark-matter only simulations may quickly disrupt (White & Rees 1978)‏ • The stellar halo is much more centrally concentrated R½=0.05

49. Satellite Orbit

50. Stellar Halo