Looking for Obscured Young Star Clusters in NGC 1313

Abstract

Using recently acquired Hubble Space Telescope NIR observations (J, Paβ, and H bands) of the nearby galaxy NGC 1313, we investigate the timescales required by a young star cluster to emerge from its natal cloud. We search for extincted star clusters, potentially embedded in their natal cloud as either (1) compact sources in regions with high Hα/Paβ extinctions or (2) compact H ii regions that appear as point-like sources in the Paβ emission map. The NUV-optical-NIR photometry of the candidate clusters is used to derive their ages, masses, and extinctions via a least-χ 2 spectral energy distribution broad- and narrowband fitting process. The 100 clusters in the final samples have masses in the range and moderate extinctions, E(B - V) ≲ 1.0 mag. Focusing on the young clusters (0-6 Myr), we derive a weak correlation between extinction and age of the clusters. Almost half of the clusters have low extinctions, E(B - V) < 0.25 mag, already at very young ages (≤3 Myr), suggesting that dust is quickly removed from clusters. A stronger correlation is found between the morphology of the nebular emission (compact, partial or absent, both in Hα and Paβ) and cluster age. Relative fractions of clusters associated with a specific nebular morphology are used to estimate the typical timescales for clearing the natal gas cloud, resulting in between 3 and 5 Myr, ∼1 Myr older than what was estimated from NUV-optical-based cluster studies. This difference hints at a bias for optical-only-based studies, which James Webb Space Telescope will address in the coming years. Show more