2018/09/26 by A. Maragkoudakis, Alexandros Maragkoudakis, Nina Ivkovich +6
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Galaxy #H II region #Irregular galaxy #Lenticular galaxy #Luminosity #Luminous infrared galaxy #Metallicity #Physics #Star formation #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.1093/mnras/sty2658
26 pages, 24 figures, 6 tables. Accepted for publication in MNRAS
arxiv created 2018/09/26 · openalex publication_date 2018/09/27 · arxiv updated 2018/10/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present mid-infrared (MIR) spectra of |\rmH \small II| regions within star-forming galaxies M83 and M33. Their emission features are compared with Galactic and extragalactic |\rmH \small II| regions, |\rmH \small II|-type galaxies, starburst galaxies, and Seyfert/LINER type galaxies. Our main results are as follows: (i) the M33 and M83 H ii regions lie in between Seyfert/LINER galaxies and |\rmH \small II|-type galaxies in the 7.7/11.3–6.2/11.3 plane, while the different sub-samples exhibit different 7.7/6.2 ratios; (ii) Using the NASA Ames PAH IR Spectroscopic database, we demonstrate that the 6.2/7.7 ratio does not effectively track PAH size, but the 11.3/3.3 PAH ratio does; (iii) variations on the 17 μm PAH band depends on object type; however, there is no dependence on metallicity for both extragalactic |\rmH \small II| regions and galaxies; (iv) the PAH/VSG intensity ratio decreases with the hardness of the radiation field and galactocentric radius (Rg), yet the ionization alone cannot account for the variation seen in all of our sources; (v) the relative strength of PAH features does not change significantly with increasing radiation hardness, as measured through the [|\rmNe \small III|]/[|\rmNe \small II|] ratio and the ionization index; (vi) We present PAH SFR calibrations based on the tight correlation between the 6.2, 7.7, and 11.3 μm PAH luminosities with the 24 μm luminosity and the combination of the 24 μm and H α luminosity; (vii) Based on the total luminosity from PAH and FIR emission, we argue that extragalactic |\rmH \small II| regions are more suitable templates in modelling and interpreting the large-scale properties of galaxies compared to Galactic |\rmH \small II| regions.