Understanding formation of galaxies from their environments

1. Understanding formation of galaxies from their environments Yipeng Jing Shanghai Astronomical Observatory

2. A brief overview of structure formation • A concordance LCDM model emerged; • Structures form from bottom up; • Most basic properties of dark matter halos well understood now, • Number density approximately by PS; • Internal structure by NFW profile; • Halos are triaxial with larger halos being more elongated; • Halos are pointed along nearby filaments; also pointed preferentially to each other; • Halos are slowly rotating with the spin parameter 0.05; spin parameters are log-normal distributed; • Rotation preferentially along the minor axis of halos

3. Structure formation

4. Physical processes of galaxy formation • Gas cooling and disk galaxy formation; • Galaxies falling into bigger halos with halos merges; ram pressure and tidal stripping may take away hot gas and even cold gas from satellite galaxies; • Mergers of gaseous galaxies lead to starbursts; • dry mergers are important as well; formation of E galaxies • Black holes grow with merges and accretion; • Supernova feedback and AGN feedback

5. JYP & Suto, Y. 2000, ApJ, 529, L69

6. Okamoto et al. 2005, MNRAS, 363,129 Formation of galactic disk depends on the formation of stars and the feedback; much more complicated than the conventional disk formation scenario by Fall and Efstathiou (1980)

7. Physical processes of galaxy formation • Gas cooling and disk galaxy formation; • Galaxies falling into bigger halos with halos merges; ram pressure and tidal stripping may take away hot gas and cold gas from satellite galaxies; • Mergers of gaseous galaxies lead to starbursts; • dry mergers are important as well; formation of E galaxies • Black holes grows with merges and accretion; • Supernova feedback and AGN feedback

8. Strangulation: hot gas stripping Gravitational tidal force can remove cold gas and even part of stellar mass of a satellite galaxy Wang, H.Y., Jing et al., in preparation

9. Physical processes of galaxy formation • Gas cooling and disk galaxy formation; • Galaxies falling into bigger halos with halos merges; ram pressure and tidal stripping may take away hot gas and even cold gas from satellite galaxies; • Mergers of gaseous galaxies lead to starbursts; • dry mergers are important as well; formation of E galaxies • Black holes grows with merges and accretion; • Supernova feedback and AGN feedback

10. Hierarchical formation, galaxies falling into bigger halos, and galaxies mergers

11. Physical processes of galaxy formation • Gas cooling and disk galaxy formation; • Galaxies falling into bigger halos with halos merges; ram pressure and tidal stripping may take away hot gas and even cold gas from satellite galaxies; • Mergers of gaseous galaxies lead to starbursts; • dry mergers are important as well; formation of E galaxies • Black holes grows with merges and accretion; • Supernova feedback and AGN feedback

13. Spectroscopic (redshift) survey of 10**6 galaxies Sloan Digital Sky Survey (SDSS)

14. Orientation of central galaxies relative to host halos • Yang X.H., et al. astroph/0601040, MN, 2006 • Kang X., et al. , MN, 2007

15. Isodensity Surfaces of halos • Use SPH method to get the density for each particle and form the isodensity surfaces (Jing & Suto 2002)

16. Why do we do this? • Understanding disk formation • Relation with the rotation (spin) of the dark matter halos; • Dynamical evolution; • Understanding elliptical formation • Major merges

17. Observational Sample • SDSS DR2 • Halo based groups (unique!); selected from SDSS (Yang et al. 2005 MNRAS 356, 1293) • Useful information • Central and satellites; • Mass of the halos • Color of the group members

19. Alignment for the whole sample • f= N(θ) /N_ran(θ) • 24,728 pairs

20. Dependences on the color

21. Dependences on group mass

22. Which satellites contributed ?

23. Summary for the observation • Satellites align with the major axis of the centrals, in contrast with the classic Holmberg(1969) effect; • The effect stronger for red centrals/satellites; vanishes for blue centrals; have chance to have our Milky Way • Stronger for richer systems; • Stronger for satellites at smaller halo-centric distance

24. Jing & Suto 2002

25. Jing & Suto 2002

26. Jing & Suto (2002) Radius R

27. Semi-analytical modeling of galaxy formation based on N-body simulations • Physical processes: heating, cooling, star formation and feedback, chemical evolution, dust extinction, SSP, galaxy mergers and morphology transformation; (quite complete compared with previous works) • Subhalos well resolved; Galaxy mergers are dealt with much better than previous works； • Cooling time scale is longer than standard; flat faint end of LF; • Cut off cooling in massive halos with AGN formation and feedback • Kang X., YPJ, H.J.Mo, G. Boerner (2005) • Kang, Jing, Silk, 2006

28. Predictions from Semi-analytical model + Numerical Simulation • Difficulty to predict the orientation of the central galaxies • Spiral galaxies: may not be related to halo spin from recent simulations • Ellipticals: detailed simulation of mergers • Useful constraints from the observation

29. Assumption on the orietation of the central galaxy • Central galaxy aligns perfectly with the dark matter within r_vir or within 0.3 r_vir

30. Predictions from Semi-analytical model + Numerical Simulation • Difficulty to predict the orientation of the central galaxies • Spiral galaxies: may not be related to halo spin from recent simulations • Ellipticals: detailed simulation of mergers • Useful constraints from the observation

31. If some misalignment between the central galaxy and its host halo • Gaussian distribution with the width • 60 degrees for blue • 30 degrees for red

32. Dependence on halo mass

33. Schematic picture to explain the alignment

34. Conclusions from the modeling • The alignment effect is explained if • the red central has some mis-alignment with the host halo(Gaussian width 30degrees) • the blue central has more (60 degrees) • Color and halo mass dependences explained; • Important Implications: Is the disk of spirals determined by the spin of the host? Intrinsic alignment for weak lensing?

35. Color of centrals and satellites • To understand • Hot gas stripping • Cold gas and stars stripping by tides • AGN activity

36. Fraction of blue galaxies Weinmann et al. 2006 More severe for more massive clusters But hot gas not stripped immediately!

37. Astroph/0709.1354; downsizing

38. Monaco et al. 2006, ApJ Downsizing requires satellite galaxies to lose a significant amount of stars before merging into the central galaxies

39. A few points for the future work • Hot gas stripped not immediately after falling into the host; need more work to quantify this; • Stars of satellites must be stripped out by tides; existence of the IC stars; • In order to keep the central galaxies red, blue components of satellites must be removed

40. Interaction-induced star formation enhancement (Li et al. 2008a) • Sample selection • SDSS DR4; 400,000 galaxies r<17.7 • Use emission line diagram to select star-forming galaxies r<17.6 • Use SFR/M*, specific star formation rate as the star formation strength

41. Clustering propertiesOverall comparison for different types Brinchmann et al. 2004

42. Methods • cross correlation function with spectroscopic sample of all galaxies ; neighbour counts • Enhancement function with reference to galaxies in a photometric sample to limiting magnitude 19; other limits18.5 and 19.5 also used, to study the effect of companion’s mass; • Morphology --- sign of interaction

44. Clustering propertieshigh/low SFR/M* Projected cross-correlation function

45. Clustering propertiesAs a function of SFR/M*, at different scales

46. Interaction-induced enhancement function dependence on mass of the SF galaxy Average boot of SFR/M* as a function of the distance to the nearest neighbor in r<19 but r-r_sfg<1.4

47. Weak dependence on mass of the companion

48. Dependence on the concentration of star-forming galaxies

49. Highly concentrated star forming galaxies, as ellipticals

50. neighbour counts of SF galaxies; <30% have a neighbor at r_p<100 kpc/h