4 research outputs found
Observational signatures of forming young massive clusters: continuum emission from dense HII regions
Young massive clusters (YMCs) are the most massive star clusters forming in
nearby galaxies and are thought to be a young analogue to the globular
clusters. Understanding the formation process of YMCs leads to looking into
very efficient star formation in high-redshift galaxies suggested by recent
JWST observations. We investigate possible observational signatures of their
formation stage, particularly when the mass of a cluster is increasing via
accretion from a natal molecular cloud. To this end, we study the broad-band
continuum emission from ionized gas and dust enshrouding YMCs, whose formation
is followed by recent radiation-hydrodynamics simulations. We perform
post-process radiative transfer calculations using simulation snapshots and
find characteristic spectral features at radio and far-infrared frequencies. We
show that a striking feature is long-lasting, strong free-free emission from a
10pc-scale HII region with a large emission measure of , corresponding to the mean electron density of
. There is a turnover feature below 10
GHz, a signature of the optically-thick free-free emission, often found in
Galactic ultra-compact HII regions. These features come from the peculiar YMC
formation process, where the cluster's gravity effectively traps photoionized
gas for a long duration and enables continuous star formation within the
cluster. Such large and dense HII regions show distinct distribution on the
density-size diagram, apart from the standard sequence of Galactic HII regions.
This is consistent with the observational trend inferred for extragalactic HII
regions associated with YMCs.Comment: 12 pages, 10 figures, accepted for publication in MNRA
星団形成と輻射フィードバックによる分子雲破壊
京都大学新制・課程博士博士(理学)甲第23704号理博第4794号新制||理||1686(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 嶺重 慎, 教授 長田 哲也, 准教授 細川 隆史学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA