2006/10/13 by L. K. Hunt, T. X. Thuan, M. Sauvage +1 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Doubly ionized oxygen #Dwarf galaxy #Emission spectrum #Extinction (optical mineralogy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #H II region #Interstellar medium #Irregular galaxy #Lenticular galaxy #Luminosity #Metallicity #Physics #Spectral line #Star cluster #Star formation #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/508867
published as Astrophys.J.653:222-239,2006 · 42 pages, 10 figures, accepted for publication in the Astrophysical Journal
arxiv created 2006/10/13 · openalex publication_date 2006/12/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present Spitzer observations of the blue compact dwarf galaxy Haro 3, with an oxygen abundance of 12 + log(O/H) = 8.32. These data are part of a larger study of star formation and dust in low-metallicity environments. The IRS spectrum of Haro 3 shows strong narrow PAH emission, with high equivalent widths. Gaseous nebular fine-structure lines are also seen. Despite the absence of optical high-excitation lines, a faint high-ionization O IV line at 25.89 μm indicates the presence of radiation as hard as 54.9 eV. A CLOUDY model suggests that the MIR lines originate in two regions: a low-extinction optically emitting region, and an optically invisible one with much higher extinction. The morphology of Haro 3 changes with wavelength. IRAC 4.5 μm traces extended stellar photospheric emission from the body of the galaxy and hot dust continuum coming mainly from star-forming regions, 8 μm probes extended PAH emission coming mainly from the general ISM, MIPS 24 and 70 μm images map compact small-grain warm dust emission associated with active star formation, and 160 μm reflects cooler extended dust associated with older stellar populations. We have derived the optical-to-radio SED of the brightest star-forming region A in Haro 3. The best-fit DUSTY model of the SED gives a total luminosity of 2.8 × 10 9 L ☉ and a mass of 2.8 × 10 6 M ☉ for the ionizing clusters. We infer an extinction A V ≲ 3, intermediate between the optical A V ~ 0.5 and the radio A V ~ 8, consistent with the picture that longer wavelength observations probe more deeply into star-forming regions.