Molecular Clouds in in the LMC at High Resolution The Importance

Document Sample
Molecular Clouds in in the LMC at High Resolution The Importance Powered By Docstoc
					          Molecular Clouds in in the
         LMC at High Resolution: The
          Importance of Short ALMA
                  Baselines


  T. Wong1,2,4, J. B. Whiteoak1, M. Hunt2, J. Ott1, Y.-N. Chin3

1CSIRO  Australia Telescope National Facility
2School of Physics, University of New South Wales, Australia

3Tamkang University, Taiwan

4Contact: Tony.Wong@csiro.au
      Australia Telescope Compact
•   Six 22m antennas near
                         Array
    Narrabri, NSW, five
    moveable on rail tracks.
• National Facility open to
  proposers worldwide.
• Operates in 5 frequency
  bands from 1-25 GHz.
• 3mm (85-105+ GHz)
  upgrade in progress for 5
  antennas (due late June).
• Wide-bandwidth (2 GHz x
  4 IF) correlator under
                               Longitude 150° E, Latitude 30° S
  development (mid-2006).
     The ATCA Millimetre Upgrade
• 3 elements currently
  have dual linear
  polarization 3mm
  receivers, 5 by July.
• 2 observing bands:
  84.9-87.3 and 88.5-
  91.3 GHz. Full          (above) 3mm low-
  coverage of 85-105      noise amplifiers
                          based on InP
  GHz expected by
                          MMIC technology
  July, extension to
  115 GHz planned.        (left) Both 3mm
                          and 12mm systems
• A~0.35, Tsys~300 K     are housed in a
  (above atmosphere).     single dewar.
Molecular Clouds in the LMC
                A unique nearby, low-metallicity
                star formation environment.
                Contours: CO at 2.6’ resolution
                from NANTEN (Mizuno et al.)


                        N113 HII region




                     SEST spectra (Chin et al. 1997)
       Mapping of N113 in 4 transitions
   HCO+ (1-0)                      HCN (1-0)                   • We observed N113 in
                                                                 HCO+, HCN, HNC, C2H,
                                                                 and 87 GHz continuum.
                                                               • Observations conducted
                                                                 in 2003 July & August in
                                                                 two E-W configurations
                                                                 of 3 antennas (baselines
   C2H (N=1-0)                     HNC (1-0)                     30-135 m).
                                                               • RMS noise ~30 mJy in a
                                                                 2 km s-1 channel.
                                                               • Reference pointing on
                                                                 SiO maser R Dor, phase
                                                                 calibration using PKS
Integrated intensity images for 4 lines. Contour levels: 0.5     B0537-441 (25° away).
  Jy bm-1 km s-1 for top panels and 0.2 for bottom panels.
Comparison in u-v plane
             • Assuming a SEST gain of
               25 Jy/K, the total HCO+
               and HCN fluxes are 80 and
               60 Jy km s-1 (Chin et al.
               1997) respectively.
             • Thus only ~15% of flux is
               detected on the shortest
               (30m) ATCA baseline.
             • The relative sizes of the
               emission regions differ:
               HCO+ is more extended
               than HCN, which in turn is
               more extended than HNC.
             • Possible explanations:
               HCO+ associated with an
               extended PDR, HNC/HCN
               enhanced in dense cores.
       Implications for ALMA DRSP
• Emission from abundant
  species like HCO+ and HCN is
  heavily resolved, even on a
  30m baseline.
• Information on abundances &
  cloud structure will require
  observations from an array of
  smaller dishes (ACA).
• Lack of small-scale emission
  implies high-resolution
  observations will require
  much greater sensitivity.
• Note that ATCA’s field of view
  at 90 GHz (36”, see figure) is
  similar to ALMA’s at 230 GHz
  (~10 pc at LMC distance) —
  mosaicking clearly needed.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:8/13/2012
language:
pages:7