SIMBAD references

The state-of-the-art geometry models of stars/dust suggest that dust attenuation toward nebular regions (A_V,gas) is always larger than that of stellar regions (A_V,star). Utilizing the newly released integral field spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we investigate whether and how the A_V,star/A_V,gas ratio varies from subgalactic to galactic scales. On a subgalactic scale, we report a stronger correlation between A_V,star and A_V,gas for more active H II regions. The local A_V,star/A_V,gas is found to have moderate nonlinear correlations with three tracers of diffuse ionized gas (DIG), as well as indicators of gas-phase metallicity and ionization. The DIG regions tend to have larger A_V,star/A_V,gas compared to classic H II regions excited by young OB stars. Metal-poor regions with a higher ionized level suffer much less nebular attenuation and thus have larger A_V,star/A_V,gas ratios. A low-A_V,gas and high-A_V,star/A_V,gas sequence, which can be resolved into DIG-dominated and metal-poor regions, on the three BPT diagrams is found. Based on these observations, we suggest that besides the geometry of stars/dust, local physical conditions such as metallicity and ionized level also play an important role in determining the A_V,star/A_V,gas. On a galactic scale, the global A_V,star/A_V,gas ratio has strong correlations with stellar mass (M_*), moderate correlations with star formation rate (SFR) and metallicity, and weak correlations with inclination and specific SFR. Galaxies with larger M_* and higher SFR that are more metal-rich tend to have smaller A_V,star/A_V,gas ratios. Such correlations form a decreasing trend of A_V,star/A_V,gas along the star-forming main sequence and mass-metallicity relation. The dust growth process accompanied by galaxy growth might be one plausible explanation for our observations.