VLA Expansion Project Science Working Group:
Galactic (All but HI) Science
(13 November 1998)

Summary by M. Rupen.

Chaired by Miller Goss
Also present:
  Anantharamaiah, Peter Barnes, Tim Bastian, Chris Carilli, Mark Claussen,
  Ketan Desai, Dale Frail, Bob Hjellming, Michael Rupen, Jim Ulvestad,
  Joan Wrobel

Three major themes emerged:

1- Imaging thermal sources: protoplanetary disks, jets, and winds
  Follow-up: Luis Rodriguez will spearhead; Mark Claussen will be the NRAO
             contact
  * The transition between thermal (free-free) emission, going as nu^0.6,
    and dust emission, going as nu^2-3, occurs around 20-40 GHz
    ==> VLA has unique capability of imaging the f-f emission, and measuring
      the "turnover" frequency
  * MMA resolution @ 200 GHz is about 150 mas
    VLA upgrade at 40-50 GHz is 10 mas
    VLA upgrade sensitivity (rms) is 31 K in 12hrs in the continuuum (43 GHz)
    --> can map the cold dust
    --> can map the winds/jets down to the core
    --> 45 GHz resolution matched to submm resolution of MMA: map the
      cold and the hot dust at the same res'n, important for modelling
      the disks
    --> 10mas= 1AU at Taurus (140pc)
    VLA upgrade offers SENSITIVITY, imp. for disk modelling
                       RESOLUTION,  imp. for disk/outflow mapping
  * Luis says: can resolve & image hundreds of sources with dust masses
    above 0.01 Msun, out to 1 kpc
  * Local examples: HL Tau, L1551
  * Tie-ins:  SIRTF for proplyds
              MMA


2- The Galactic Center: mapping the three-dimensional dynamics & fields
  Follow-up: Anantha???
  * VLA Expansion Project provides proper motions of gas and stars on scales 
    ranging from 0.1 pc (???) to 100s of parsecs, as well as magnetic field
    orientations and strengths on similar scales
    --> the only possibility of getting such detailed information on ANY AGN
    --> watch the mass flow into the event horizon of a black hole
    --> the only prospect for real 3D mapping of the potential, anywhere
  * Needs SENSITIVITY to allow tracking faint sources (ionized gas etc.)
          RESOLUTION  to get highly accurate proper motions
          CORRELATOR  to get lots of masers in one shot, and to allow
                         efficient Zeeman splitting
  * Also note all will be tied to SgrA* directly
  * Random phrases
    : "movies of stars plunging into the galactic center"
    : "voyage to an AGN"
    : "entering the heart of darkness" (weelll....)
  * Tie-ins: Ghez et al., Genzel et al. for current work
  

3- Solar Mass Black Holes (Galactic superluminals)
  Follow-up: Hjellming, Rupen
  This one is a bit unclear at the moment -- needs a single Great Theme.
  Possibilities include
    * Imaging ADAF flows (i.e. quiescent black hole systems)
    * Mapping the accretion disk
    * Measuring mass loss from the binary companion
    * Temporal resolution which begins to match the X-ray satellites
    * Reliably and consistently image superluminals -- get rid of current
      limitations on figuring out which blob is which, actually recover all
      the flux, high enough sensitivity to map sources as they change
      (half-hour time scales!), etc.
    * Tracking magnetic field structure etc. from inception
    * Potentially, radio detections of many more BHs found by X-ray
      satellites --> why are some radio-loud?  are they all 0.3 or 0.9c ?
      etc.
    * Wild idea: can we see the interaction of the jet with the companion's
      wind?  with a high dynamic range...
  It's not clear which of these are actually do-able; the follow-up consists
  of figuring this out & coming up with The One Big Question we can answer.
  * Needs SENSITIVITY to allow rapid mapping and detection of faint sources
          RESOLUTION  to allow imaging
  * Tie-ins: X-ray and high-energy satellites
             only hope of imaging black hole systems on the scale of their
               accretion disks
             "mapping the accretion zones in quasars"
             "ins and outs of BH binaries"
             "feeding the Galactic superluminals"

4- Topics requiring more thought (might turn into Big Questions)
  * Using pulsars to map the potentials of globular clusters
    - can NGST do this?
    - how many could we hope to detect?
    - Miller: could probably get 1mas/yr motions, based on current studies
    - Is Lazio already doing this (GalCtr)?
    NEED A VOLUNTEER FOR THIS ONE -- Rupen will talk to Pton pundits
  
  * Interstellar medium -- is there anything we can contribute that's
    really new?  Suggestions included ammonia (density/temp. indicator all
    in one, at one frequency), mapping mag. field structures, origins of
    cosmic rays, etc.  None seemed spectacularly interesting.
    NEED SOMEONE TO THINK ABOUT THIS SOME MORE -- maybe science tea?

5- Topics which didn't seem too exciting for PR purposes (included to
  show what we thought about)
  * Scattering
  * Gal. magnetic fields
  * SNRs


VLA Expansion Project Science
VLA Expansion Project Home Page


Last modified 08 December 1999

mrupen@nrao.edu