TODDLERS: A new UV-millimeter emission library for star-forming regions

II. Star-formation rate indicators using Auriga zoom simulations

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281-S9, B-9000 Gent, Belgium
² The University of Texas at Dallas, 800 W Campbell Rd, Richardson, TX 75080, USA
³ Faculté des sciences et de génie, Université Laval, Pavillon Alexandre-Vachon, Québec G1V 0A6, Canada
⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, F-06000 Nice, France

^⋆ Corresponding author; anandutsavkapoor@gmail.com

Received: 21 June 2024
Accepted: 21 October 2024

Abstract

Context. The current generation galaxy formation simulations often approximate star formation, making it necessary to use models of star-forming regions to produce observables from such simulations. In the first paper of this series, we introduced TODDLERS, a physically motivated, time-resolved model for UV–millimeter (mm) emission from star-forming regions, implemented within the radiative transfer code SKIRT. In this work, we use the SKIRT-TODDLERS pipeline to produce synthetic observations.

Aims. We aim to demonstrate the potential of TODDLERS model through observables and quantities pertaining to star-formation. An additional goal is to compare the results obtained using TODDLERS with the existing star-forming regions model in SKIRT.

Methods. We calculated broadband and line emission maps for the 30 Milky Way-like galaxies of the Auriga zoom simulation suite at a redshift of zero. Analyzing far-ultraviolet (FUV) and infrared (IR) broadband data, we calculated kiloparsec (kpc)-resolved IR correction factors, k_IR, which allowed us to quantify the ratio of FUV luminosity absorbed by dust to reprocessed IR luminosity. Furthermore, we used the IR maps to calculate the kpc-scale mid-infrared (MIR) colors (8 μm/24 μm) and far-infrared (FIR) colors (70 μm/500 μm) of the Auriga galaxies. We used Hα and Hβ line maps to study the Balmer decrement and dust correction. We verified the fidelity of our model’s FIR fine structure lines as star formation rate (SFR) indicators.

Results. The integrated UV-mm spectral energy distributions (SEDs) exhibit higher FUV and near-ultraviolet (NUV) attenuation and lower 24 μm emission compared to the existing star-forming regions model in SKIRT, alleviating tensions with observations reported in earlier studies. The light-weighted mean k_IR increases with aperture and inclination, while its correlation with kpc-resolved specific star-formation rate (sSFR) is weaker than literature values from resolved SED fitting, potentially due to inaccuracies in local energy balance representation. The kpc-scale MIR-FIR colors show an excellent agreement with local observational data, with anti-correlation degree varying by galaxy morphology. We find that the Balmer decrement effectively corrects for dust, with the attenuation law varying with dust amount. The Hα emission attenuation levels in our models are comparable to those observed in the high-density regions of state-of-the-art radiation hydrodynamical simulations. The FIR fine-structure line emission-based luminosity-SFR relations are consistent with global observational relations, with the [C II] line displaying the best agreement.