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How are galaxies influenced by their environment?

Predictions & insights from hierarchical models. How are galaxies influenced by their environment?. rachel somerville STScI. with thanks to Eric Bell the COMBO/GEMS team Risa Wechsler Andrey Kravtsov Sandy Faber. what are observations telling us?.

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How are galaxies influenced by their environment?

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  1. Predictions & insights from hierarchical models How are galaxies influenced by their environment? rachel somerville STScI with thanks to Eric Bell the COMBO/GEMS team Risa Wechsler Andrey Kravtsov Sandy Faber

  2. what are observations telling us? • old wisdom: familiar correlations between galaxy observables • color-morphology • color-magnitude • luminosity-metallicity • new wisdom: correlation between intrinsic/physical properties , e.g. • stellar mass and star formation rate • stellar mass & metallicity • new wisdom: many fundamental galaxy properties have bimodal distributions, divided by a critical stellar mass

  3. SDSS: color and magnitude color Blanton et al. 2003 luminosity Baldry et al. 2003

  4. stellar mass and age… ~stellar age SDSS stellar mass Kauffmann et al. 2003, 2004

  5. stellar mass and relative star formation rate relative star formation rate stellar mass Brinchmann et al. 2004

  6. what imposes these relationships on galaxies (internal/external)? • the old wisdom: • morphology-density relation: early type fraction increases with density • Butcher-Oemler effect: early/blue fraction decreases with cosmic time • the new wisdom: (Hogg et al., Blanton et al., Balogh et al., Kauffmann et al.): • structural properties have weak dependence on environment • spectro-photometric properties have a stronger dependence on environment -- critical density?

  7. morphology-density as a function of redshift high density fraction of early types low density lookback time projected density Smith et al. 2004

  8. structure and density increasing density Kauffmann et al. 2004

  9. age and relative star formationand local density increasing N increasing N Kauffmann et al. 2004

  10. luminosity has a strong dependence on local density color has a weaker dependence on local density Hogg et al. 2003

  11. Balogh et al. 2004

  12. fraction of red galaxies increases with density but the mean color of the red and blue distributions changes little with density

  13. the color magnitude relation is in place at z~1 and evolution is consistent with passive color RDCS1252 z=1.24 magnitude Blakeslee et al. 2003 (ACS GTO team)

  14. …in the field as well as clusters (COMBO-17/ GEMS) age = 8.4Gyr rest U-V color age = 5.5 Gyr red dots: early type blue dots: late type rest V magnitude (luminosity) Bell et al. 2003

  15. do hierarchical models predict • this behaviour? • can they give us any insight into • what is going on? time

  16. cluster halo ‘Milky Way’ halo Wechsler et al.

  17. hierarchical simulations show a clear correlation between color/morphology and density, in qualitative agreement with observations Kauffmann et al. 1999 VIRGO/GIF simulations see also Benson et al. 2001; Springel et al. 2001

  18. dependence of mean color and morphological fraction on halo mass color fraction of bulge/disk galaxies Diaferio et al. 2001 log halo mass

  19. merger tree collisional heating radiative cooling star formation stellar feedback chemical enrichment stellar populations dust absorption & emission inflation primordial power spectrum galaxy observables

  20. specific model ingredients reheated gas ejected if Vc>150 km/s • major mergers (>4:1) trigger bursts of star formation • Bruzual & Charlot 2003 multi-metallicity stellar • population models

  21. SDSS & 2MASS luminosity functions u-band g-band r-band number per unit volume i-band z-band K-band magnitude (observed LF from Bell et al.

  22. luminosity functions by morphology bulge dominated disk dominated

  23. gas fraction SDSS Bell et al. log stellar mass

  24. gas fraction distributions increasing stellar mass -->

  25. color-magnitude relation r-band magnitude

  26. bright--> color histograms faint g-r color

  27. color of a passively evolving burst formed at z=5 u-r g-r Z=2xsolar Z=solar

  28. Global star formation history

  29. stellar mass assembly history new observational estimates from COMBO-17 and GOODS rss et al. 2004

  30. stellar mass assembly history estimates from Glazebrook et al. (GDDS) Rudnick et al. (FIRES) Dickinson et al. (HDFN) Fontana et al. (K20) rss et al. 2004

  31. color-magnitude and morphology at high redshift red: n>2 blue: n<2 red: B/T>0.5 blue: B/T<0.5

  32. missing EROs 13.5 5.8 3.2 1.0 0.5 0.1 KAB<22 GOODS rss et al. 2004 GOODS ApJL

  33. status: low redshift • hierarchical models can be made to reproduce global luminosity/stellar mass distributions at low redshift but don’t produce enough luminous red galaxies • color magnitude relation has correct slope (well, sort of) but distributions do not match data and are not bimodal

  34. status: high redshift • hierarchical models produce enough massive galaxies to z~2 • but, do not produce enough red galaxies • the mean stellar ages of the massive galaxies are old enough -- color problem is caused by ‘frosting’ of young stars

  35. what makes red galaxies red? • need a process that quenches star formation in the most massive galaxies without drastically altering the mass assembly/star formation history • environment: ram pressure or tidal stripping, harassment? • internal: SN or AGN driven wind? global instability?

  36. neighbor counts (R=2 Mpc) L=114 Mpc mp=3x108 M_sun r_force=1.5 kpc

  37. number of neighbors in 2 Mpc spheres cyan: 0-1 blue: 2-3 green: 4-6 rust: 7-11 red: >11

  38. number of neighbors vs. halo mass log halo mass log(1+N)

  39. color-magnitude by density g-r r-band mag

  40. N=0-1 N>17 Kauffmann et al. 2004

  41. increasing density--> N=0-1 N=2-3 N=4-6 N=7-11 N>11 -22.5 -21.5 decreasing luminosity --> -20.5 -19.5 -18.5

  42. increasing density--> decreasing luminosity--> u-r Balogh et al. 2004

  43. relative SFR vs. mass log(SFR/stellar mass) log stellar mass

  44. star formation/age as function of local density increasing N increasing N Kauffmann et al. 2004

  45. where does this leave us? • where do galaxies become red? • simulations: massive halos • real universe: all environments (though more often in dense ones) • how do galaxies become red? • simulations: whole distribution shifts • real universe: galaxies ‘hop’ from one distribution to the other • why do galaxies become red? • simulations: strangulation • real universe: ???

  46. internal processes • all gas driven out of galaxy after a merger by SN or AGN winds? • has almost no effect on colors because of continuous infall of fresh gas • star formation ‘turned off’ when a bulge (BH?) has grown beyond a critical mass?

  47. star formation shut off when m_bulge > 2 x 1010 M_sun better! g-r color r-band magnitude

  48. color distributions bimodal! bright faint g-r color

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