Sara C. Beck Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv, Israel and Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Michiel R. Hogerheijde Steward Observatory, The University of... more
Sara C. Beck Department of Physics and Astronomy, Tel Aviv University, Ramat Aviv, Israel and Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Michiel R. Hogerheijde Steward Observatory, The University of Arizona, 933 North Cherry ...
ABSTRACT 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... more
ABSTRACT 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.
