The Population of H ii Regions in NGC 7020

• Published in: The Astronomical journal 2021-04, Vol.161 (4), p.191
• Main Authors: Dottori, Horacio, Díaz, Rubén J., Grosbøl, Preben, Bueno, Amanda, Gimeno, Germán
• Format: Article
• Language: English
• Subjects: Apexes; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Clusters; EMISSION; Emissions; GALAXIES; GAS FLOW; H alpha line; H II regions; Initial mass function; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; METALLICITY; Narrowband; NUCLEI; TELESCOPES
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/1538-3881/abe30f

The galaxy NGC 7020 displays an exotic hexagonal ringlike central structure with conspicuous ansae located at two opposite vertices and a tenuous external ring populated by H ii regions. Inside and around the hexagonal structure, H α emission is also present at the inner disk. To characterize the population of the H ii regions, as well as their ionizing clusters, we imaged NGC 7020 with narrowband H α and nearby continuum filters attached to GMOS-S installed on the Gemini South telescope. We found 202 H ii regions or complexes of H ii regions evenly distributed between the outer ring and the central disk The nucleus and ansae also present H α emission. The equivalent width of the H α line ( W H α ) is systematically greater at the regions of the outer ring relative to those of the inner disk. We discuss the influence of the metallicity gradient of the disk and the upper limit of the masses of the initial mass function on W H α , and we conclude that the data are still consistent with the occurrence of a younger burst of H ii region formation in the outer ring. The central regions present more massive clusters, M ≥ 10 6 M ⊙ , than those of the outer ring ( M ≤ 10 6 M ⊙ ). Three clusters within 5″ of the nucleus present masses higher than 10 8 M ⊙ . The presence of diffuse H α emission in the inner 5″ suggests gas flows in the nuclear region.