2008/03/31 by Amy E. Reines, Kelsey E. Johnson, W. M. Goss · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Cluster (spacecraft) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Hubble space telescope #Radio galaxy #Star cluster #Star formation #Stellar, planetary, and galactic studies #Supernova #astro-ph
paper · pdf · doi:10.1088/0004-6256/135/6/2222
Accepted for publication in the Astronomical Journal. 20 pages, 14 figures
arxiv created 2008/03/31 · openalex publication_date 2008/05/13 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a multi-wavelength study of embedded massive clusters in the nearby (3.9 Mpc) starburst galaxy NGC 4449 in an effort to uncover the earliest phases of massive cluster evolution. By combining high-resolution imaging from the radio to the ultraviolet, we reveal these clusters to be in the process of emerging from their gaseous and dusty birth cocoons. We use Very Large Array (VLA) observations at centimeter wavelengths to identify young clusters surrounded by ultra-dense H ii regions, detectable via their production of thermal free–free radio continuum. Ultraviolet, optical and infrared observations are obtained from the Hubble and Spitzer Space Telescope archives for comparison. We detect 39 compact radio sources toward NGC 4449 at 3.6 cm using the highest resolution (1 3) and sensitivity (∼12 μJy) VLA image of the galaxy to date. We reliably identify 13 thermal radio sources and derive their physical properties using both nebular emission from the H ii regions and spectral energy distribution fitting to the stellar continuum. These radio-detected clusters have ages ≲5 Myr and stellar masses of order 10 4 M ☉ . The measured extinctions are quite low: 12 of the 13 thermal radio sources have A V ≲ 1.5, while the most obscured source has A V ≈ 4.3. By combining results from the nebular and stellar emission, we find an I -band excess that is anti-correlated with cluster age and an apparent mass–age correlation. Additionally, we find evidence that local processes such as supernovae and stellar winds likely play an important role in triggering the current bursts of star formation within NGC 4449.