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Formation and evolution of dusty ellipticals

Formation and evolution of dusty ellipticals. Laura Silva (INAF, Trieste, Italy). In collaboration with:. Gian Luigi Granato (INAF, Padova, Italy). Gianfranco De Zotti (INAF, Padova, Italy). Luigi Danese (SISSA, Trieste, Italy). STARTING POINT.

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Formation and evolution of dusty ellipticals

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  1. Formation and evolution of dusty ellipticals Laura Silva (INAF, Trieste, Italy) In collaboration with: Gian Luigi Granato (INAF, Padova, Italy) Gianfranco De Zotti (INAF, Padova, Italy) Luigi Danese (SISSA, Trieste, Italy)

  2. STARTING POINT Difficulty of simulations of galaxy formation in cosmological context: crucial simplifications are required to describe sub-grid physics (SF, SN feedback…). Different treatments can lead to very different predictions for the properties of the galaxy population. As a consequence many successes but several problems as well, in particular connected with properties of (large) E galaxies (e.g. Peebles 0201015)

  3. Summary of problems in SA models • Large E pop probably already in place at z1-1.5 (Im et al. 2001, Cohen 2001) • Not enough objects at z=0 with SED resembling E • The statistic ofsub-mm selected high z galaxies • The color-magnitude and/or the [/Fe]-M of E relations (Cole et al 2002, Thomas 1999, Thomas et al 2002, but see Kauffmann & Charlot 1998 for CM) • These evidences are more consistent with a view in which (stars in) large E are old and almost coeval

  4. Present day semi-analytical models match many observations, including IR (Granato et al 2000), but are challenged by counts and z-distrib. of sub-mm selected sources. Too many small SF events  a major revision of prescriptions used to approximate evolution of baryons seems required

  5. Suggestion: simulations ignore mutual feed-back between formation of E and high-z QSO activity, suggested by observations: • Local spheroids contain a central MDO (SMBH), with M= 106-109 • MBH Msph with scatter and MBH c4-5, tighter(e.g. Merritt & Ferrarese 2000, Gehardt et al 2001) • Spheroidal galaxies are the most common hosts of high-z QSOs(McLure et al,Dunlop et al ) • QSOs are associated to high metallicity, dusty environments(eg Hamann & Ferland 1999; Andreani, Franceschini & Granato, 1999) • In particular QSO may mark (cause?) the end of major episode of SF in spheroids.

  6. • Anti-hierarchical baryonic collapse scenario • Granato, Silva, et al 2001, MNRAS • Feed-back (SN + AGN) delay SF in smaller halos; • Large E form their stars as soon as their potential wells are in place  rapid chemical and dust enrichment  high-z sub-mm bright phase; • BH and L(QSO) grow, possibly contributing to stop the SF and expulsion of residual gas (0.5 to 2 Gyr); • QSO phase follows, (107--108 yrs) then (almost) passive evolution. Rapid reddening of colors (EROs). Intermediate and small sferoids shows up as LBGs.

  7. Test against sub-mm counts (Granato et al 2001, MNRAS) • “formation” rate of spheroids • SF duration (and time dependence) • SED evolution (GRASIL Silva, Granato, Bressan & Danese et al 1998)  Luminosity functions, number counts, redshift distribution

  8. 1 - FORMATION RATE of spheroids Two possible paths lead to equivalent results: 1) “end of formation” rate from evolution of QSO LF (QSOs as clocks of SF) 2) “beginning of formation” rate from PS or ST mass function of halos (Sasaki 94, Blain & Longair 93)

  9. 2- SFR(t,M) before QSOs shine computed taking into account collapse, heating, cooling and feedback in DM halos Tburst(Msph) Granato et al 2001

  10. short timescales for star-formation, decreasing with increasing mass, are suggested by • Chemical abundances (/Fe) in local ellipticals; • The statistic of QSOs in the PS formalism (Monaco, Salucci & Danese 2000) Parametrization:

  11. 3 - SED evolution is computed with GRASIL. Prediction for FIR-sub-mm is robust Tburst=2 Gyr Tburst=0.5 Gyr Granato et al 2001

  12. ABC scenario reproduces in a natural way sub-mm statistic (and chemistry of Ellipticals) MAMBO 1200 m SCUBA 850 m Granato et al 2001

  13. Various aspects and predictions in: • Monaco, Salucci & Danese, 2000, MNRAS • (statistic of QSOs and E in hierarchical clustering) • Granato, Silva, Monaco et al, 2001, MNRAS • (sub-mm statistic and E chemistry) • Magliocchetti, Moscardini et al, 2001, MNRAS • + Perrotta, Magliocchetti et al, 2002, astro-ph (clustering of SCUBA gal., LBG and EROs + effect of strong lensing + fluctuations in planck channels) • Romano, Silva, Matteucci & Danese, 2002, MNRAS (more details on chemistry of local E)

  14. SIRTF: predictions GOODS (0.1 sq deg): NEll 1500 ( 60% tot) SWIRE (70 sq deg): NEll 2 104 ( 20% tot) In both surveys star forming Ellipticals show up at 24 m S>450Jy (SWIRE) S>30Jy (GOODS) z

  15. GOODS  2 Jy SWIRE  30 Jy IRAC BANDS (3.6-8.0 m) dominated by passively evolving Ellipticals

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