Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA

• Main Authors: O'Neill, Theo J, Indebetouw, Remy, Sandstrom, Karin, Bolatto, Alberto D, Jameson, Katherine E, Carlson, Lynn R, Finn, Molly K, Meixner, Margaret, Sabbi, Elena, Sewilo, Marta
• Format: Journal Article
• Language: English
• Published: 29-08-2022
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2208.13768

NGC 602 is a young, low-metallicity star cluster in the "Wing" of the Small
Magellanic Cloud. We reveal the recent evolutionary past of the cluster through
analysis of high-resolution ($\sim$0.4 pc) Atacama Large
Millimeter/submillimeter Array observations of molecular gas in the associated
$\textrm{H}\scriptstyle\mathrm{II}$ region N90. We identify 110 molecular
clumps ($R <$ 0.8 pc) traced by CO emission, and study the relationship between
the clumps and associated young stellar objects (YSOs) and pre-main-sequence
(PMS) stars. The clumps have high virial parameters (typical $\alpha_{\rm{vir}}
= $ 4-11) and may retain signatures of a collision in the last $\lesssim$8 Myr
between $\textrm{H}\scriptstyle\mathrm{I}$ components of the adjacent
supergiant shell SMC-SGS 1. We obtain a CO-bright-to-H$_2$ gas conversion
factor of $X_{CO,B} = (3.4 \pm 0.2) \times 10^{20}$ cm$^{-2}$ (K km
s$^{-1}$)$^{-1}$, and correct observed clump properties for CO-dark H$_2$ gas
to derive a total molecular gas mass in N90 of $16,600 \pm 2,400 \ M_\odot$. We
derive a recent ($\lesssim 1$ Myr) star formation rate of $130 \pm 30 \
M_{\odot}$ Myr$^{-1}$ with an efficiency of 8 $ \pm$ 3\% assessed through
comparing total YSO mass to total molecular gas mass. Very few significant
radial trends exist between clump properties or PMS star ages and distance from
NGC 602. We do not find evidence for a triggered star formation scenario among
the youngest ($\lesssim$2 Myr) stellar generations, and instead conclude that a
sequential star formation process in which NGC 602 did not directly cause
recent star formation in the region is likely.