molecular cloud and a

Transcription

1 A molecular cloud and a Stop me if you ve heard this one before star cluster walk into a bar... Florent Renaud Lund Observatory with E. Emsellem, N. Guillard et al.

2 A complex scale-coupling environment Renaud et al. (2013) Large scale flows from kpc-scale structures e.g. bar(s), connected spirals Flows regulated by resonances (ILRs) Coupling with the nuclear cluster and the SMBH (and potentially AGN)

3 Leading / trailing asymmetry Renaud et al. (2015) Gaseous overdensities on the leading sides Athanassoula (1992) leading trailing Due to shocks Fragmentation along the edges of the bar trailing leading

4 Orbital motions (1) Gas dives inside the bar or (2) Gas circulates along the edge Renaud et al. (2015)

5 Suppression of star formation Renaud et al. (2013), Emsellem et al. (2015) Steep velocity curve inside the bar strong shear smooth out overdensities non-collapsing, non-star forming dense gas 107 M of molecular gas at high surface density SFR ~20 lower than expected Morris et al. (1989) Longmore et al. (2013) weak strong shear / gravity

6 Resonances and intermittent fueling Gas piles up at ILR Garcia-Burillo & Combes (2012) Eventually fragments Forms stars Left-overs fall onto SMBH delayed AGN fueling 200 pc Emsellem et al. (2015)

7 Feedback and vertical structure Emsellem et al. (2015) Star form in clumps inside ILR feedback Fountains vertical structure

8 Circulation and orbital crowding at the tips Along the edge on x1 orbits Contopoulos & Grosbol (1989) > 200 km/s (20 Myr between both ends) Tips of the bar = apocenters Material slows down Orbital crowding Kenney & Lord (1991) Renaud et al. (2015)

9 Cloud-cloud collisions and GMAs Tidal interactions and collisions Giant molecular associations (W43-like) Carlhoff et al. (2013) Motte et al. (2004) Known to trigger SF Loren (1976) Tan (2000) Tasker & Tan (2009) Inoue & Fukui (2013) Massive star formation? Anathpindika (2010) Motte et al. (2014) Takahira, Tasker & Habe (2014) Renaud et al. (2015)

10 SFE boost from turbulence Renaud et al. (2015) Collision induces turbulent compression increase SFR and SFE Mach = 1.3 Mach = 0.8 Same as in interacting galaxies (starbursts) Renaud et al. (2012, 2014) Mach = 0.8 (dense gas only)

11 Star cluster formation Renaud et al. (2015) Young clusters form at the tips Preferencially found on the leading side Feedback + tides destroy the least dense clusters / associations < 20 Myr 20-40Myr Myr

12 Star-gas decoupling Large-scale dynamics affect gas and stars differently Renaud et al. (2015) Stars decouple from gaseous left-overs (e.g. asymmetric drift) Bash, Green & Peters (1977) Bash (1979) Renaud et al. (2013) How fast depends on local physics (feedback, shear, tides) Fastest at the tips more efficient feedback (lower density environment) efficient removal of low angular momentum? Brook et al. (2012) Agertz & Kravtsov (2015)

13 Nuclear cluster formation (1) In situ formation Nuclear gas inflows in-situ formation Milosavljevic (2004) Torques from a bar or galaxy interactions help (but are not necessary) Beware quenching from AGN! Di Matteo et al. (2005) Hopkins et al. (2010)

14 Nuclear cluster formation (2) Migration scenario Ex-situ cluster formation Tremaine, Ostriker & Spitzer (1975) Andersen et al. (2008) Cluster-gas decoupling (feedback, drift, shear) Cluster migration + dry mergers (dynamical friction, ~ 1 Gyr) Antonini (2013) Arca-Sedda & Capuzzo-Dolcetta (2014)

15 Nuclear cluster formation (3) Wet merger scenario Ex-situ dense cluster formation Inefficient star-gas decoupling Retain gas if feedback < gravity Guillard et al. (submitted) Rahner et al. (2017) Wet merger + in situ formation (from gas left-overs) Guillard et al. (2016)

16 Feedback matters for cluster assembly Guillard et al. (submitted) Depends on feedback / ISM balance (gas mass, pressure, turbulence etc.) Important in: gas-rich dwarfs mergers high-z Need pred ict ive s i mula tions

17 Summary Large-scale dynamics rule gas flows (torques, shear, shocks, resonances) Strong shear inside the bar prevents SF Shocks on the leading edges Orbital crowding at the tips Cloud-cloud collisions, GMAs Young clusters on leading side Efficient gas-star decoupling at the tips Implications for feedback efficiency Dense enough clusters might retain/accrete gas and form NCs through wet mergers