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Ionized Gas Kinematics at High Resolution. II: Discovery of a Double Infrared Cluster in II Zw 40

  • Beck, Sara
  • Turner, Jean
  • Lacy, John
  • Greathouse, Thomas
  • Lahad, Ohr
Publication Date
Feb 14, 2013
Submission Date
Feb 14, 2013
DOI: 10.1088/0004-637X/767/1/53
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The nearby dwarf galaxy II Zw 40 hosts an intense starburst. At the center of the starburst is a bright compact radio and infrared source, thought to be a giant dense HII region containing ~14,000 O stars. Radio continuum images suggest that the compact source is actually a collection of several smaller emission regions. We accordingly use the kinematics of the ionized gas to probe the structure of the radio-infrared emission region. With TEXES on the NASA-IRTF we measured the 10.5um [SIV] emission line with effective spectral resolutions, including thermal broadening, of ~25 and ~3 km/s and spatial resolution ~1". The line profile shows two distinct, spatially coextensive, emission features. The stronger feature is at galactic velocity and has FWHM 47 km/s. The second feature is ~44km/s redward of the first and has FWHM 32 km/s. We argue that these are two giant embedded clusters, and estimate their masses to be ~3x10^5Mo and ~1.5x10^5 Mo. The velocity shift is unexpectedly large for such a small spatial offset. We suggest that it may arise in a previously undetected kinematic feature remaining from the violent merger that formed the galaxy.

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