A Variant Stellar-to-nebular Dust Attenuation Ratio on Subgalactic and Galactic Scales

Abstract

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.

Estimating Dust Attenuation From Galactic Spectra. II. Stellar and Gas Attenuation in Star-forming and Diffuse Ionized Gas Regions in MaNGA

“…At the lowest density, log 10 Σ Hα 38.5, the stellar attenuation is stronger than the gas attenuation, mainly because of the small amount of dust in the gas as seen from the rapid decrease of E(B − V ) gas in the low-density end. The negative correlation of E(B − V ) star /E(B − V ) gas with Σ Hα has recently been discussed in depth in Lin & Kong (2020), based on an earlier sample of MaNGA. Our results show in addition that the correlation is essentially a result of the dichotomy of the intrinsic properties of the ionized gas regions, Hii regions and DIG regions, divided at Σ Hα ∼ 10 39 erg s −1 kpc −2 as suggested by Zhang et al (2017).…”

“…Similar to [Nii]/[Sii], the [Oiii]/[Oii] also shows no correlation with the stellar attenuation, but a strong correlation with the gas attenuation (see Figure 13). Both [Nii]/[Sii] and [Oiii]/[Oii] have been used as indicators of the ionization level of gas (Dopita et al 2013;Lin & Kong 2020). In the ionization model of spherical Hii regions from Dopita et al (2013), the line ratio of [Oiii]/[Oii] increases as the ionization parameter (q) increases, when the gas-phase metallicity diagnostics (e.g.…”

“…Recently, using data of MaNGA galaxies in Sloan Digital Sky Survey Data Release 15 (SDSS DR15; Aguado et al 2019) and MaNGA value-added catalog (VAC) of the Pipe3D pipeline (Sánchez et al 2018), Lin & Kong (2020) investigated the variations of f from sub-galactic to galactic scales. They found that E(B − V ) star and E(B − V ) gas have a stronger correlation for more active Hii regions, while f is found to have a moderate correlation with tracers of DIG regions.…”

Dust Attenuation Curve for Local Subgalactic Star-forming Regions

“…In this work, we simply attribute non-AGN ionized gas to star-forming regions. However, such ionized gas also might have a nonnegligible contribution from DIG, which might be excited by mechanisms other than star formation, such as hot, low-mass evolved stars (Flores-Fajardo et al 2011;Zhang et al 2017) or shock (see Haffner et al 2009 for a review), and have a significant contribution to a sample of star-forming regions selected from the MaNGA survey (Lin & Kong 2020). DIG-dominated spaxels might not support the assumptions adopted in this work.…”

“…The second argument allows us to use nebular attenuation derived from the Balmer decrement to trace the stellar attenuation. Previous works showed that the color excesses derived from emission lines and stellar continuum are correlated with each other in either galactic (e.g., Calzetti 1997) or subgalactic (e.g., Kreckel et al 2013;Lin & Kong 2020) star-forming systems. Therefore, one can use τ B to represent the relative reddening of of stellar continuum.…”