Examining the Influence of the Regions on Star Formation Surface Density

We analyzed the star formation surface density (Σ_SFR) between the global and H II regions in a sample of 69 low surface brightness galaxies (LSBGs) and 68 star-forming (SF) galaxies using data from the Hα images. The conventional global Σ_SFR, which is defined as the star formation rate (SFR) divided by the area of the global galaxy, may not accurately describe the star formation activity in LSBGs due to the lower number of H II regions compared to SF galaxies. To address this, we divide the global galaxy into two regions, the H II region and the diffuse region, and then study the Σ_SFR in each region. Our results show that both the SFR and area of the H II regions in LSBGs are lower than those in SF galaxies, resulting in the H II region's Σ_SFR (SFR/area) being slightly lower in LSBGs than in SF galaxies by 0.28 dex, although the global Σ_SFR is at least an order of magnitude lower in LSBGs than in SF galaxies. Furthermore, a significant difference exists between the global and H II regions in Σ_SFR. In LSBGs, Σ_SFR increased by 0.80 dex from the global region to the H II region, while SF galaxies demonstrate a 0.54 dex increase, highlighting the crucial aspect of carefully selecting an appropriate aperture for Σ_SFR calculations.