Diversity of SEDs among the star-forming regions in NGC 1365

Journal article

Studying samples of young star-forming regions allows us to statistically examine the evolution of their natal gas and dust along with the associated time-scales in the volatile early stages of their lives. With the Physics at High Angular resolution in Nearby GalaxieS survey data, we analyse the diversity of spectral energy distributions (SEDs) for the rich sample of massive star-forming regions found in NGC 1365. By combining unique detections across a variety of data sets from Hubble Space Telescope (HST), James Web Space Telescope (JWST), and Atacama Large Millimeter/sub-millimeter Array (ALMA) images, we produce a catalogue of 85 star-forming regions located in the central starbursting region of NGC 1365. Prior to analysis, we observe clear saturation effects in our four JWST Mid-Infrared Instrument (MIRI) images, and implement a saturation-correction method which allows us to recover data for 23 of 32 saturation-affected regions in these images. We then perform photometry in 13 HST & JWST images which are convolved to match the resolution of MIRI/F2100W (64 pc), allowing us to probe star clusters as well as their immediate surroundings. Upon deriving their properties from SED-fitting using Code Investigating GALaxy Emission, we observe that regions selected with progressively redder wavebands are younger and generally more reddened. We also identify three SED features correlated with age: (1) sources with a positive near-infrared slope [(F300W + F360M)/(2F200W)] are by median half the age of those with negative near-infrared slopes; turnover occurs around 6 Myr, (2) the relative strength of dust emission (F2100W/F200W), and (3) polycyclic aromatic hydrocarbon emission (F335M/F300M) both show that larger such ratios correlate with younger ages. Considering our working resolution, these features are robust to the inclusion of nearby emission surrounding star clusters.

Authors: Hannon, S; Schinnerer, E; Whitmore, BC; Hassani, H; Liu, D

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 547
• Issue: 4
• Article number: stag266
• Publication date: 2026-03-27
• Acceptance date: 2025-12-22
• DOI: 10.1093/mnras/stag266
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: galaxies: star clusters: general; galaxies: individual: NGC 1365