m * high m* High-mass Low-mass galaxies Athigh high-redshift, cold gas At z>2, SF proceeds at extremely high rates by feedback effectively expelled Suppressed at high in –z Feedback is SF ineffective suppressing star formation At lower z, haloes grow and feedback less effective Rapid gas becomes consumption m * low m* Coldgas gasexhausting left available at low-z Cold at z~2 Starformation formationdrops still active at low Star thereafter Smooth SF history Local galaxies are gas poor with old stars large mass small mass Observations show: A sharp transition in the physical properties of galaxies at M* ~ 3 1010 Mʘ (see, e.g., Kauffmann et al. 2003) Tully, Mould, Aaronson 1982 • Massive galaxies are redder • Contain older stars • star formation much larger at high redshitfs Bimodal Color Distribution Bright Red Galaxies Faint Blue Galaxies Baldry et al. 2004 Color Distribution Dependence on luminosity BLUE RED The cold gas fraction log Number log Number Local galaxies with u-r<1 -20.5 < Mr <-19.5 Local galaxies with u-r>1.5 vc2 feedback 0 ESN 100 km / s M=109 Mʘ at z=4.5 Mprog=109 Mʘ Colore Distribution: Dependence on the environment t1 t2 small mass halo t3 Large mass halo Z=0 Galaxies endng up in clusters originate from the merging of clumps which have collapsed in biased, high-density regions of the density field, hence at higher redshift. The star formation histories of the population contained (today) in dense environments (groups/clusters) peaks at higher redshift compared to that of smaller galaxies. Bimodality extends at least up to z ≈ 0.8 Bell et al. 03 The Evolution of luminosity and mass functions i) density evolution, typical of hierarchical clustering clustering, (mass of galaxies increases with time) ii) luminosity evolution (SFR increasing with z from z=1 to z=2.5, flat at higher z) estimates from Glazebrook et al. (GDDS) Rudnick et al. (FIRES) Dickinson et al. (HDFN) Fontana et al. (K20) Bell et al. (COMBO) The Luminosity Evolution I:Luminosity evolution: B and UV - B-band and UV luminosity ~ instanteneous star form. rate - The number of massive objects decreases with z (hierarchical clustering) - Star Formation strongly increases with z N Z=3 Z=0 * LB Mm II: Luminosity evolution: K MZ<25 - K-band luminosity ~ total mass in stars formed at current time At z ~ 1.5 simple models underpredict the total amount of stars formed in massive haloes Additional mechanism MUST BE triggering star formation at z≥4 t Starbursts S m * (t t ' ) (t ' ) dt ' Pozzetti et al. 2003 0 t (t ' ) const S m * (t t ' ) dt ' m* 0 Data: Fontana et al ‘”tidal forces during encounters cause otherwise stable disks to develop bars, and the gas in such barred disks, subjected to strong gravitational torques, flows toward the central regions “ Mihos & Hernquist 1996 See also Noguchi 1987 Barnes & Hernquist 1991 Gas Angular Momentum Part of the available galactic cold gas is detabilized and funnelled toward the centre Cavaliere 1 j 1 m' rd vd Vittorini f ( v, V ) 2000 2 j 2 mbV Rate: 2 1 n ( rtidal ) Vrel FlyBy Duration: 1 r Vrel / rtidal Part of the available cold gas is detabilized and funnelled toward the centre 1 j 1 m' rd vd f ( v, V ) 2 j 2 mbV Cavaliere Vittorini 2000 (Sanders & Mirabel 96) Starbursts Freqency Starbursts Mass Conversion rate 2 1 n ( rtidal ) Vrel FlyBy Strongly increases with z 2 FlyBy 3 4 f mcold n 1 / R3 Strongly increases with z 2 larger m’/m ratios r Vrel r 1 dyn R R R 1 * ( v, t ) m Larger vd/V ratio Larger r/R ratio Smaller r~(1+z)-1/2 Smaller r~(1+z)-1/2 Larger cold gas mass r Larger f ≥ 0.01 The Bursts EROs AGN activity triggered by destabilization of gas during encounters: Would naturally explain 1) They are already in place at high z (at least at z=2, see McLure talk) while the stellar content of galaxies is still growing II) Their activity drops at lower z Burst constitute only one mode of star formation addig to quiescent star formation BUT for AGN constitute the whole feeding mechanism The effect of Starbursts on the Galaxy Lum. Function. Cold Gas destabilization from Fly-by interactions strongly decreases from z=3 to z=0 Somerville Primack & Faber 2001 At high z a large amount of cold gas is destabilized Strong starbursts are expected at z > 3-4 MZ < 25.5 L > 0.2 L* Data from Giavalisco et al. 03 The effect of Starbursts induced by fly-by events in the K-band observables NM et al 2004 K-band z-counts K-band Lumin. Functions Stellar Mass function at high z z=1-1.6 z=1.6-2 z=2-3 The Big Picture At z > 2.5 – 3 -Effective cooling (low virial T≈105 K, high densities) -rapid merging, frequent encounters allow continuous refueling of gas in the growing galactic haloes. Large B/ UV -High SFR (≈102 Mʘ/yr), especially in clumps formed in BIASED regions of the density field Emission (progenitors of large-mass galaxies / cluster members. Ly-break glxs 9 -Self-regulated SF: in small-mass clumps (M<10 Mʘ) feedback yields a self-regulated star-formation preferentially in massive -Frequent encounters continuously destabilize an appreciable fraction of such a gas triggering: haloes with larger cross - fast BH accretion: QSO at full Eddington rate section for interactions. - Powerful starbursts (up to 103 Mʘ / yr) - Building-up of the stellar mass conent 1/3 of the stellar mass in galaxies with M >1010 M is in place at by z≈2 * ʘ What about z≈3 ? At z < 2. i) Construction of galaxies and merging rate decline ii) Accretion of smaller lumps by major progenitors iii) decline of fraction f ≈ j / j of gas accreted by BH or converted in SBursts Arising of bimodality in the iv) exaustion of cold gas in massive galaxies properties of galaxy pop. (originated from the merging of clumps collapsed in biased, high-density regions where most of the gas has already been converted into stars) v) Lower-mass haloes (MDM > 5 1011 Mʘ) still star forming • Massive galaxies (MDM > 1013 Mʘ) vi) Starbursts activity drops especially in massive systems undergo an almost passive evolution redder - QSO only occasionally refueled by encounters colors. - Emission drops down to L~ 10-2 LEddington • Residual star formation in less massive - QSO Lum. Funct. steepens at bright end galaxies (rates 0.1 – 1 Mʘ/yr) still retaining part of theircold gas reservoir (blue colors) Bibliografia I. Evoluzione delle Perturbazioni Cosmologiche 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. E. Bertschinger, Annu. Rev. Astron. Astrophys. 1998. 36: 599-654 Coles, P., Lucchin, F."Cosmology - The origin and evolution of Cosmic Structure", 1995, Wiley, Chichester. Efstathiou, G., Silk, J.I., 1983, Foundamental Cosmic Phys., 9, 1 Lucchin, F. 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J.; Cannon, D. B.; Navarro, J. F., 1999, Nature, 397, 135 Part of the available cold gas is detabilized and funnelled toward the centre Cavaliere Vittorini 2000 1 j 1 m' rd vd f ( v, V ) 2 j 2 mbV (Sanders & Mirabel 96) 3/4 feeds circumnuclear starbursts QSO Properties m acc (v, t ) 1 f mcold 4 r c 2 macc L ( v, t ) t mBH (1 ) m acc (v, t ' ) dt ' 0 Starbursts Properties 3 f mcold m * (v, t ) 4 r t * (t t ' ) (t ' ) dt ' S m 0 Pre-collision t ~ 0.01(rinit/h)3/2 trot As the galaxies fall in towards each other for the first time, they move on simple parabolic orbits until they are close enough that they have entered each others' dark halos, and the gravitational force becomes non-Keplerian. During this infall, the galaxies hardly respond to one another at all, save for their orbital motion. Impact t ~ 0.3 (rp/h)3/2 trot As the galaxies reach perigalacticon, they feel the strong tidal force from one another. The galaxies become strongly distorted, and the tidal tails are launched from their back sides. Strong shocks are driven in the galaxies' ISM due to tidal caustics in the disks as well as direct hydrodynamic compression of the colliding ISM. Gravitational Response t ~trot As the galaxies separate from their initial collision, the disk self-gravity can amplify the tidal distortions into a strong $m=2$ spiral or bar pattern. This self-gravitation response is strongly coupled to the internal structure of the galaxies as well as their orbital motion, resulting in a variety of dynamical responses z=3 z=1 z=0.4 Menci et al. 04 MBH~s4 Cold gas mass ~ s2.5 Interactions favour large galact. masses s3.5 SN feedback disfavours small galact. masses s4 Data from Gebhardt et al. 2000 (circles) Ferrarese & Merrit 2000 (squares) -21< Mr < -19 Local Blue Galaxy Pop. u-r < 1.3 Local Red Galaxy Pop. u-r >1.8 log MBH (Mʘ ) The normalization of the QSO LFs - increases from z=0 to z=2 - decreases for z>2 z=2 z=1.2 z=0.5 The shape of the QSO LFs progressively flattens for z>2.5 The rise with z of the normalization is due to the increasing fraction of destabilized cold gas feeding the BH BECAUSE z=3 z=4.2 The encounter rate and the hence the accretion rate increases with z The flattening is due to the rapid exaustion of galactic cold gas in larger galaxies, whose star formation is peaked at higher z Data from Hartwick & Shade 1990, Boyle et al 2000, Fan et al 2001 The rapid decrease at z<2.5 is due to 3 concurring factors 1) The decrease with time of the merging rate of galaxies 2) The decrease with time of the galactic cold gas left available for accretion 3) The decrease with time of the encounter rate stimulating the cold gas funneling toward the nucleus Previous works adopting SAMs treated the accreted fraction f as a free parameter constant with z (missed process #3) Data from Hartwick & Shade 1990, Warren, Hewitt, Osmer 1994, Goldschmidt & Miller 1998, Boyle et al 2000, Fan et al 2001 The effect of Starbursts on the Galaxy Lum. Function. Cold Gas destabilization from Fly-by interactions strongly decreases from z=3 to z=0 At high z a large amount of cold gas is destabilized Strong starbursts are expected at z > 3-4 NM et al. 2004 Data from Steidel et al. 99 The effect of Starbursts induced by fly-by events in the K-band observables NM et al 2004 K-band z-counts K-band Lumin. Functions The stellar Mass Function (Fontana et al. 04) Data from Fontana et al. 03 The Global Picture At z > 2.5 - 3 rapid merging, frequent encounters allow continuous refueling of gas in the growing galactic haloes. Frequent encounters continuously destabilize appreciable fraction of such a gas triggering: an fast BH accretion: QSO at full Eddington rate - powerful starbursts Such processes are produced preferentially in massive haloes due to their larger cross section for interactions. At z < 2.5 - 3 i) Construction of galaxies and merging rate decline ii) decline of accreted fraction f ≈ j / j iii) exaustion of cold gas particulary in massive galaxies (originated from the merging of clumps collapsed in biased, high-density regions where most of the gas has already been converted into stars) - QSO only occasionally refueled by encounters - Emission drops down to L~ 10-2 LEddington - QSO Lum. Funct. steepens at bright end Starbursts activity drops Massive galaxies (MDM > 1013 M⊙) undergo an almost passive evolution redder colors Residual star formation in less massive galaxies which still retain part of their cold gas Evolutinary Tracks Galaxies with DM mass of: M=1013 M⊙ M=1012 M⊙ M=2.5 1011 M⊙ M=5 1010 M⊙