Super Star Clusters in the Central Starburst of NGC 4945
Journal article, 2020
The nearby (3.8Mpc) galaxy NGC 4945 hosts a nuclear starburst and Seyfert type 2 active galactic nucleus (AGN). We use the Atacama Large Millimeter/submillimeter Array (ALMA) to image the 93 GHz (3.2 mm) free-free continuum and hydrogen recombination line emission (H40 alpha and H42 alpha) at 2.2 pc (0 12) resolution. Our observations reveal 27 bright, compact sources with FWHM sizes of 1.4-4.0 pc, which we identify as candidate super star clusters. Recombination line emission, tracing the ionizing photon rate of the candidate clusters, is detected in 15 sources, six of which have a significant synchrotron component to the 93 GHz continuum. Adopting an age of similar to 5Myr, the stellar masses implied by the ionizing photon luminosities are log(10) (M*/M-circle dot) approximate to 4.7-6.1. We fit a slope to the cluster mass distribution and find beta = -1.8 +/-.0.4. The gas masses associated with these clusters, derived from the dust continuum at 350 GHz, are typically an order of magnitude lower than the stellar mass. These candidate clusters appear to have already converted a large fraction of their dense natal material into stars and, given their small freefall times of similar to 0.05 Myr, are surviving an early volatile phase. We identify a pointlike source in 93 GHz continuum emission that is presumed to be the AGN. We do not detect recombination line emission from the AGN and place an upper limit on the ionizing photons that leak into the starburst region of Q(0).<.10(52) s(-1).
Starburst galaxies
Star formation
Galaxies
Star clusters
Author
Kimberly L. Emig
Leiden University
Alberto D. Bolatto
University of Maryland
Adam K. Leroy
Ohio State University
Elisabeth A. C. Mills
University of Kansas
Maria J. Jimenez Donaire
Spanish National Observatory (OAN)
Alexander G. G. M. Tielens
Leiden University
University of Maryland
Adam Ginsburg
University of Florida
Mark Gorski
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Nico Krieger
Max Planck Society
Rebecca C. Levy
University of Maryland
David S. Meier
National Radio Astronomy Observatory Socorro
New Mexico Institute of Mining and Technology
Jurgen Ott
National Radio Astronomy Observatory Socorro
Erik Rosolowsky
University of Alberta
Todd A. Thompson
Ohio State University
Sylvain Veilleux
University of Maryland
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 903 1 50Subject Categories
Subatomic Physics
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
DOI
10.3847/1538-4357/abb67d