Molecular Clouds in in the LMC at High Resolution The Importance

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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

  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

      Australia Telescope Compact
•   Six 22m antennas near
    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.

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