Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Formation of Galaxies
Transcript
Formation of the Galaxies: Current Issues Joe Silk University of Oxford Gainesville, October 2006 Some remarks about star formation… mass, light, chemistry control galaxy evolution Low mass stars control M Solar mass stars control light in a spheroidal galaxy The most massive stars dominate the light in a disk galaxy Intermediate mass stars control chemical evolution THE INITIAL STELLAR MASS FUNCTION What determines the characteristic mass of a star? Is the IMF universal? Kroupa 2004 Stars Fundamental theory applied to a diffuse interstellar cloud that is collapsing under self-gravity 3 / 2 Minimum fragment mass ~ g mp ~ 0.01 M a robust but wrong result! Resolution: continuing accretion of cold gas, eventually halted by feedback that taps stellar energy via MHD turbulence3 vs Ý M gas ~ G first stars were massive In addition IMF most likely also involves fragmentation 3 PROCESSES PLAY A ROLE: FRAGMENTATION, ACCRETION, FEEDBACK Klessen 2006 NGC1333: Quillen et al. 2006 Shu 2006 Shu 2006 Pudritz et al. 2006 Disk galaxy star formation is inefficient, due to SN feedback Accretion and minor mergers renew gas supply Ellipticals are old because infall is quenched….by AGN outflows Efficient early star formation occurred in massive spheroids and ellipticals There are likely to be two modes of star formation: disks/pseudobulges AND elliptical/spheroid formation Accretion, mergers and AGN outflows are key ingredients (L ) theory (CDM-motivated) L ~ 3 1010 L Galaxies observations luminosity too many Dwarfs but they are fragile t m p 3 12 cool M cooledbaryons ~ 2 T g me t dyn ~ 0.5 too many Giants: a problem! nkT tcool ~ Gas cooling time-scale (T )n 2 t dyn ~ 1 Gmp n Dynamical time-scale A necessary condition for star formation is cooling: So the BIG ISSUE is astrophysical feedback Ultraluminous infrared galaxies and the galaxy luminosity function Sanders 1999 The red sequence evolves Bell et al. 2004 Blanton 2006 Star formation was efficient in the most massive galaxies Papovich et al. 2006 More evidence for a shorter timescale Maraston 2006 AN EFFICIENT MODE OF STAR FORMATION IS NEEDED FOR SPHEROID FORMATION: THE CASE FOR POSITIVE FEEDBACK D. Thomas D. Thomas 2006 THERE ARE PLAUSIBLY TWO MODES OF STAR FORMATION: REGULATED BY GAS SUPPLY, DYNAMICAL TIMESCALE DISK MODE: motivated by …. gravitational instability of cold disks star surface density gas surface density Star formation efficiency SFE = gas vcool m*,SN ESN initial 0.02 SPHEROID MODE: motivated by gas-rich mergers A GLOBAL STAR FORMATION LAW FOR DISKS Sajina et al. 2006 SFR=0.02 (GAS SURFACE DENSITY)/tdyn fits quiescent and starburst galaxies Need cold gas accretion via infall and/or minor mergers to maintain global disk instability Need low efficiency: due to SN feedback NGC 891 LOCAL COLD GAS FEEDING BY INFALL NGC 6946 HI contours Oosterloo et al. 2005 Boomsma et al 2005 The Rate of Star Formation number of SN bubbles porosity ~ generated per unit time maximum 4 - Volume of a bubble limited by ambient ISM pressure 1 ~ star formation rate 1.36 (pressure) Three-phase ISM Perhaps porosity self-regulates! SFR with SN feedback in a multiphase ISM Slyz et al. (2005) HISTORY OF STAR FORMATION Rocha-Pinto 2000: solar vicinity Allard et al. 2006: M100 Star Formation Rate Simulation The Mice (NGC 4676 a,b) old stars + gas density-dependent SFR shock-induced SFR Barnes (2004) GALAXY LUMINOSITY FUNCTION space density of galaxies AGN Feedback Bower et al. 2006 luminosity Massive spheroids form first K. Bundy et al. 2006 Cimatti et al. 2006 Build-up of luminosity and star formation rate Bouwens, Illingworth et al 2006 AGN ARE ANTI-HIERARCHICAL Hasinger et al. 2006 LEdd/c=GMMgas/r2 SMBH formation/feedback in galaxy spheroid formation LEddMSMBH 4 9 M 3 10 Msun km 300 s black hole Fits observed normalisation and slope mass King (2003), Silk & Rees (1998) Supernovae provide feedback in potential wells of low mass galaxies SMBH outflows provide positive feedback in massive protospheroids Blowout occurs/star formation terminates spheroid velocity dispersion Triggered global star formation? OUTFLOWS FROM SMBH OVERPRESSUR E ISM CLOUDS Saxton et al. 2005 star formation timescale tjet<<tgal yields high efficiency Labiano et al. 2005 z=0.27 radio galaxy star formation rate compared to renormalised black hole feeding rate Silverman et al. 2006 gravity-induced star formation jet-enhanced star formation in spheroids x 10-3 comoving star formation rate comoving SMBH accretion rate suppression by ouflows feedback redshift at z~2, SMBH fall below the relation Star formation suppressed Star formation triggered Borys et al 2006 AGN-induced outflows & star formation AGN AGN 3 Ý M gasoutflow ~ L /cv w SN 2.7 Ý Ý M gasoutflow M sfr SN AGN Ý Ý Msfr M sfr (t dyn / t jet ) M gas(v jet / ) / t dyn v w Boost by ~10! 3 Observed scaling! C. Martin 2005: KI and NaI line profiles OUTFLOWS FROM ULIRGS Morganti et al. 2005: HI absorption Swinbank et al. 2006 a SCUBA galaxy at z=2.385 multiplicative factor of AGNtriggered SN Everett & Murray 2006: extended injection of energy needed for NGC 4151 outflow X-ray absorbed QSOs in ULIRGs Ultraluminous starbursts associated with AGN absorption by ionised wind M. Page et al. 2006 A UNIFIED THEORY NEGATIVE POSITIVE H THEORETICAL INGREDIENTS ARE NEE
