Star Formation across cosmic time Florent Renaud & Oscar Agertz Lund Observatory
Polaris (André et al. 2010) Universality ... • Filamentary structure • Diameter (~0.1 pc) • Knots = pre-stellar cores Taurus (Palmeirim et al. 2013) • Extinction threshold (A v > 7) • Cluster formation at intersections • Universal IMF IC 5146 (Arzoumanian et al. 2012) Where it can be resolved = solar neighborhood = one single environment
isolated disk: M83 (HST) ... and diversity • Different star cluster formation (open, massive, globular, nuclear ...) merger: Antennae (HST) • IMF variations from galaxy to galaxy § within galaxies § • Disk sub-structures (e.g. spirals, bars) clumpy galaxy ( z ~2): UDF 6462 (ACS) • Galaxy interactions / mergers • Galaxy formation
Cosmic star formation history Evolution of the cosmic SFR density • with gas content • turbulence • disk formation • merger rate (~ expansion of the Universe) • quenching Madau & Dickinson (2014) (starvation, stripping, feedback etc.)
Beware of quenching Satellites get quenched faster than centrals • à different processes van den Bosch et al. (2008), Bahe & McCarthy (2015) Tinker et al. (2013)
Evolution of MW-like galaxies Proto-galaxy • Low-mass (= fragile) Interaction-driven Growth by major mergers • Formation of the disk • Rotation-support Highly turbulent Episodic mergers Possible clumpy phase • Formation of the disks • Quiet, steady phase Formation of the bar •
PDFs and KS laws Analytical model from Renaud et al. (2012) Numerical confirmation in Kraljic et al. (2014) Observations from Kennicutt et al. (1998, 2007) Bigiel et al. (2008) • Increased turbulence Tacconi et al. (2010) Daddi et al. (2010) à increase SFR and remain on Kennicutt's law • Make turbulence compressive à increase SFE See also Padoan & Nordlund (2011) and move to the starburst regime Hennebelle & Chabrier (2011) Renaud et al. (2014)
Starbursts • Most of SF in central regions (in advanced mergers) Sanders & Mirabel (1996) • Due to gas inflows (negative torques inside co-rotation) Keel (1985) Barnes & Hernquist (1991) NGC 7252 • But also a non-negligible off-nuclear activity Wang et al. (2004) Hancock et al. (2009) Chien & Barnes (2010) Smith et al. (2014) Moreno et al. (2015) Elmegreen et al. (2016,2017) ... NGC 2207
Off-nuclear starbursts • Tidal and turbulent compression where/when potentials overlap Renaud et al. (2008, 2014) Jog (2015) • Increase turbulence and change its nature Irwin (1994) NGC 4093/39 Elmegreen et al. (1995) • Form denser structures Hennebelle & Falgaronne (2012) Federrath et al. (2014) isolated interacting galaxies galaxies • Trigger starburst Renaud et al. (2014) Solenoidal-dominated Compression-dominated (energy equipartition) (comp. tidal forcing)
In interactions Antennae-like galaxies
In interactions Cartwheel-like galaxy
Same SFR, different physics Bournaud et al. (2015) • A starburst and a disk: same SFR but different ISM à different star (cluster) formation Renaud et al. (in prep.)
Star formation at very high redshift Renaud, Agertz et al. (in prep.) Density of the Universe • Fornax dwarf galaxy, Larsen et al. increases with redshift 20 kpc ∝ (1 + z ) 3 z = 5 More interactions • More tidal + turbulent • compression Formation of massive • clusters (globulars?) In galactic outskirts • red = compressive tides
At very high redshift z = 9.3 Cosmological simulation Resolve formation sites (~1 pc) But short... (z > 8) 500 pc 20 kpc Renaud et al. (in prep)
Formation of the first clusters z = 9.3 Young massive clusters Formation triggered by galactic interaction Same physics than 2x10 7 M � at low z? In galaxy outskirts Survival? 4x10 6 M � ~ 5 pc Eagle 200 pc Renaud et al. (in prep) Illustris
Summary • Several stages in galaxy formation = several stages in star formation • Different sources of turbulence (injection at kpc scale) • Including mergers (but not only) • Compression (tides + turbulence) induces starbursts and the formation of young massive clusters • Possibly important for formation of globular clusters at high redshift • How/where/when galaxies get their stellar populations
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