Stellar populations and physical properties of starbursts in the antennae galaxy from self-consistent modelling of MUSE spectra

Abstract

We have modelled the stellar and nebular continua and emission-line intensity ratios of massive stellar populations in the Antennae galaxy using high resolution and self-consistent libraries of model HII regions around central clusters of aging stars. The model libraries are constructed using the stellar population synthesis code, Starburst99, and photoionisation model, Cloudy. The Geneva and PARSEC stellar evolutionary models are plugged into Starburst99 to allow comparison between the two models. Using a spectrum-fitting methodology that allows the spectral features in the stellar and nebular continua (e.g. Wolf-Rayet features, Paschen jump), and emission-line diagnostics to constrain the models, we apply the libraries to the high-resolution MUSE spectra of the starbursting regions in the Antennae galaxy. Through this approach, we were able to model the continuum emission from Wolf-Rayet stars and extract stellar and gas metallicities, ages, electron temperatures and densities of starbursts by exploiting the full spectrum. From the application to the Antennae galaxy, we find that (1) the starbursts in the Antennae galaxy are characterised by stellar and gas metallicities of around solar, (2) the star-forming gas in starbursts in the Western loop of NGC 4038 appears to be more enriched, albeit slightly, than the rest of galaxy, (3) the youngest starbursts are found across the overlap region and over parts of the western-loop, though in comparison, the regions in the western-loop appear to be at a slightly later stage in star-formation than the overlap region, and (4) the results obtained from fitting the Geneva and Parsec models are largely consistent.

The Paschen Jump as a Diagnostic of the Diffuse Nebular Continuum Emission in Active Galactic Nuclei

“…The results of our model fits show that a plausible explanation for the smoothness of the spectra across the jump is that the DC discontinuity is smoothed out by the pileup of high-order Paschen lines, as previously anticipated by Malkan & Sargent (1982), and also by the potential presence of gas at very high density (see below; Vincentelli et al 2021). In comparison with star-forming galaxies exhibiting a clear Paschen jump (e.g., Guseva et al 2006;Reines et al 2010;Gunawardhana et al 2020), the Doppler velocity broadening in broad-line AGN is also a key factor in smoothing out the jump. Our fits assume the same velocity broadening for the DC and the Paschen lines as both of them are expected to raise from the BLR, and the satisfactory fitting results across the Paschen jump are consistent with the DC and the Paschen lines originating from similar radii in the BLR.…”

Massive high-redshift quiescent galaxies with JWST

“…Brinchmann, Kunth, & Durret 2008). However, simultaneous modelling of a variety of spectral features that consider variations in stellar types, stellar/ISM abundances, and IMFs is complicated (Gunawardhana et al 2020). When this is combined with non-parametric SFHs to model the formation history, high-quality data and modular SED fitting codes become crucial (e.g.…”

Two interacting galaxies hiding as one, revealed by MaNGA

“…The irregular metallicity distribution can be compared with other merging systems, such as NGC 4038/4039. This system was studied by Gunawardhana et al (2020), who detected starforming regions with gas more enriched than the rest of the galaxy.…”