Revisiting Attenuation Curves: the Case of NGC 3351

Abstract

Multi-wavelength images from the farUV (∼0.15 µm) to the sub-millimeter of the central region of the galaxy NGC 3351 are analyzed to constrain its stellar populations and dust attenuation. Despite hosting a ∼1 kpc circumnuclear starburst ring, NGC 3351 deviates from the IRX-β relation, the relation between the infrared-to-UV luminosity ratio and the UV continuum slope β that other starburst galaxies follow. To understand the reason for the deviation, we leverage the high angular resolution of archival nearUV-to-nearIR HST images to divide the ring into ∼60-180 pc size regions and model each individually. We find that the UV slope of the combined intrinsic (dust-free) stellar populations in the central region is redder than what is expected for a young model population. This is due to the region's complex star formation history, which boosts the nearUV emission relative to the farUV. The resulting net attenuation curve has a UV slope that lies between those of the starburst attenuation curve (Calzetti et al. 2000) and the Small Magellanic Cloud extinction curve; the total-to-selective attenuation value, R (V)=4.93, is larger than both. As found for other star-forming galaxies, the stellar continuum of NGC 3351 is less attenuated than the ionized gas, with E(B-V) star =0.40 E(B-V) gas . The combination of the 'red' intrinsic stellar population and the new attenuation curve fully accounts for the location of the central region of NGC 3351 on the IRX-β diagram. Thus, the observed characteristics result from the complex mixture of stellar populations and dust column densities in the circumnuclear region. Despite being a sample of one, these findings highlight the difficulty of defining attenuation curves of general applicability outside the regime of centrally-concentrated starbursts.

The UV 2175Å attenuation bump and its correlation with PAH emission at z ∼ 2

“…To interpret UV photometry, it is necessary to correct the observed light for dust attenuation, which requires knowledge of the dust attenuation curve as a function of wavelength (Salim & Narayanan 2020). Often, the uncertainties ★ E-mail: ishivaei@arizona.edu † E-mail: boogaard@mpia.de ‡ E-mail: tanio.diaz@mail.udp.cl in the UV-inferred SFR estimates are dominated by the uncertainties in the shape of the UV attenuation curve (e.g., Kennicutt & Evans 2012;Reddy et al 2012;Shivaei et al 2018Shivaei et al , 2020aCalzetti et al 2021).…”