Betsy Mills: Hot Gas, Masers, and Cloud Collisions: The extreme properties of molecular gas at the heart of the Milky Way Galaxy

VLA Survey
  • DnC at 24-36 GHz

  • Brick NH3 + very high temperatures in brick: 100's of K + optically thin 4-4,5-5,7-7 + brightest, densest clumps have lowest temperatures + 300K gas, but no SF

    • CR heating?
    • Shock heating?
  • 36 GHz methanol maser + shock excited + dozens of point sources + 75 candidates, 29 T_B > 1000K (masing)

  • why so many masers? + large-scale shocks? + 80 km/s velocity gradient across cloud + methanol & ammonia emission dominated by convergence point of velocities

  • class I methanol masers usually show SF

SF in the Brick?
  • 7 VLA continuum sources + peaks in a more distributed set of continuum emission
  • 25 GHz continuum + most continuum outside of the molecular gas + external ionization
Rest of the CMZ
  • Pistol & Quintuplet continuum with streaks from the nonthermal filaments + second LBV seen in radio
  • NH3 near Sgr A* + NH3 traces edges of Sgr A East SNR + some SF in 50km/s cloud and 20km/s cloud
  • CND not in HC3N, weakly in ammonia
  • no NH3 or HC3N at brightest submm clump
  • nonthermal 3-3 line
Sgr B2
  • CH3OH only non-self-absorbed against hot core + shell structure
  • NH3 2-2 maser

Questions

  • Q Walsh: NH3 3-3 maser. Expected more of those. Were there others?
  • A: yes, there are at least 2 others
  • Q: Temperatures of ammonia. Is ammonia the only tracer that gives high temperature towards the Brick?
  • A: Yes, only one towards brick. 400-600K from H2 from Rodriguez-Fernandez. 400K in Sgr A from NH3 too.
  • Q: Formation pumping?
  • A: yes, possible. Need to form on short timescales.
  • Q: Need hefty CR for that heating. Can you expand on what VLA is good for?
  • A: CRs 10^-14, 10^-15. May happen. Hard to explain 100's K
  • A: VLA gets NH3 transitions for temperatures. ALMA gives density. VLA gives free-free. No overlap in frequency
  • Q: Is the brick a cloud? Is this really a transient colliding flow?
  • A: I don't claim that it's bound.

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