SYMPOSIUM SUMMARY. Mitch Begelman JILA, University of Colorado

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1 SYMPOSIUM SUMMARY Mitch Begelman JILA, University of Colorado

2 THANKS! Thank you Cornelia, Sera, and the whole SOC! Thank you Loránt and the whole LOC! Thank you NRAO staff! Thank you students running the mikes

3 Where does the GalacFc Center start? ILR, ends of the bar, molecular ring 2-3 kpc? CMZ few 100 pc defined how? amount of molecular gas? advent of extreme condifons? temperatures, densifes, hypersonic turbulence

4 Where does the GalacFc Center start? CMZ or ILR, ends of the bar, molecular ring 2-3 kpc? CMZ few 100 pc defined how? amount of molecular gas? advent of extreme condifons? temperatures, densifes, hypersonic turbulence

Vis- à- vis MW GMCs, CMZ is X- treme DensiFes 10-100 x GMCs Temps hundreds of K Turbulent speeds tens of km/s - HYPERSONIC!

5 Vis- à- vis MW GMCs, CMZ is X- treme DensiFes x GMCs Temps hundreds of K Turbulent speeds tens of km/s - HYPERSONIC! Vis- à- vis s, CMZ is wim- P x lower pressure 10-4 x gamma- rays (comp. to NGC 253) Much lower SFR than expected in either case! (Lower than S- K law predicfon)

6 What inhibits star formafon in the CMZ? Strong supersonic turbulence High temps Tidal forces (outer CMZ) * formafon intermifent (highly asymmetric) Requires cloud collisions? Clouds transient thermal instabilifes to form, destrucfon on < orbital Fme?

7 Bimodal star formafon rate? What s the trigger? Local vs. global condifons Local: cloud- cloud collisions current state of CMZ Global: ambient pressure (thermal, cosmic ray, magnefc ) Radial pressure gradient wind Is wind strength the trigger?

8 Toy model for bimodal star formafon THE TRIGGER Suppose density threshold ~ 10 x Fdal (for 100 K clouds) p/k~10 6 ( 150 /r 100 ) 2 L W ~10 c s2 3 /G ~5x10 39 T 100 ( 150 ) 3 erg/s POSITIVE FEEDBACK Once star formafon gets going it perpetuates a strong wind (unfl mass depleted) Could explain sharpness of bimodal behavior Trigger is therefore self- sustaining (could also be triggered by AGN acfvity? CMZ as residual torus? [PonF])

9 The CND More mysterious terminology Circumnuclear Disk? Central Nuclear Disk? Compact Nuclear Disk? Let s look it up No MW def. even on disambiguafon page but Both CNDs have the same symbol! Pro- nuclear movement

10 The CND 2-7 pc, few 10 4 solar masses Mostly Fdally unbound Clouds turbulent and warm transient? Inefficient star formafon on average Source of the massive stellar disks? But through triggered fragmentafon (cloud collision, etc.), not spontaneous local instability eccentricifes too high

11 Central Stars Young stars (few Myr, O/WR) in ragged ring(s) at pc B stars (S populafon) fill in the hole and extend beyond ring Include v. eccentric orbits formed by binary disrupfon of ring stars? S- stars fairly old Should include: Rejuvenated stars (blue stragglers) Hypervelocity escapers Source for TDEs In situ formafon increasingly difficult at << 1 pc, even if Fdal limit overcome! Increased Fdal density > cm - 3 implies decreased Jeans mass!

12 G2 Most economical hypothesis: contains a star Orbit similar to known (S) stars Difficult to form compact cloud with high dust content Extreme eccentricity easier if origin is at large r! K- band photometry ambiguous, but could hide T Tauri, maybe (Fdally stripped) giant Apply Occam s Razor (try to disprove it s a star). which (as pointed out by F. Lo) we will soon be able to do Mass and radius of emivng region suggests stellar wind with speed ~50 km/s and mass loss ~ 10-7 M /yr

13 Black Hole AccreFon Mass currently supplied by stellar winds, Ṁ~10-5 Ṁ Edd Luminosity ~ 10-9 L Edd so either: 1) 100% Ṁ accreted with v. low radiafve efficiency or 2) Only 10-4 of available Ṁ accreted (or something in- between) 1) X- rays are synchrotron, IC too weak 2) 2- temp. flow, but electrons receive their share (which is promptly radiated away). Allows SSC. OpFon 2 (radiafvely efficient accrefon) much more likely! Small fracfon of Ṁ likely to sfck at the circularizafon radius (JPO) R circ is outer boundary of ADIOS most mass supplied lost in wind mm- peak and Faraday rot. consistent w/~thermal synchrotron Prior acfvity ~100s yrs ago (K reverberafon) ~10 39 erg/s

14 Flares X- flares IR flares but not vice- versa X- flares can be intense! 100 x quiescent luminosity Most powerful flares dominate flaring power 1/3 total L X in flares Synchrotron origin most likely? Or can IC work? Energy requirements for X- flares are worrying Maybe modest bulk Lorentz factors not enough Maybe a Fpoff for reconnecfon, minijets, and kinefc beaming (Ceruv et al. 2012, 2013)

15 PolarizaFon High linear polarizafon ~10-40% Organized field orientalon toroidal in disk (or jet?) Pol. can t discriminate bet. unidirecfonal B and zero net flux Faraday rotafon can discriminate, but complicated Detailed field geometry OpFcal depth effects (90 o p.a. flip at synch. photosphere) B- n correlafons? Stable (high) circular polarizafon ~ 1.5% - important clue? Faraday conversion? Intrinsic circ. pol. from mildly rel. synch. emission?

16 The Future Fermi Bubbles energy source, emission mechanisms, jet or no jet? G2 star or no star, origin, other Fdal streams? EHT BH spin? Structure of the accrefon flow? What s flaring? And further out What maintains the turbulence/high temps of molecular gas? and how does it regulate star formafon? ALMA (and CCAT?) crucial measure small scale structure, cloud kinemafcs/dynamics, chemical/ionizafon states Fate of The Brick etc.

17 A Deluge of Data Boulder, CO, 9/12/13

19 See you at the G2 2 nd Periapse Symposium in 2151 (Gillessen et al. 2012) or 2289 (Phifer et al. 2013) or 2211 (Gillessen et al. 2013) or 2404 (MPE 2013) or 2277 (UCLA 2013)

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