Sequential star formation in the young SMC region NGC 602 insights from ALMA. (2022)
Keywords :
Small Magellanic Cloud ; Interstellar medium ; Molecular clouds ; H II regions ; Star formation
Abstract: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 (~0.4pc) Atacama Large Millimeter/submillimeter Array observations of molecular gas in the associated HII region N90. We identify 110 molecular clumps (R<0.8pc) 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}_vir_=4-11) and may retain signatures of a collision in the last <~8Myr between HI components of the adjacent supergiant shell SMC-SGS 1. We obtain a CO-bright-to-H2 gas conversion factor of
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The NGC602/N90 region was observed by ALMA project 2016.1.00360.S. A
150 point mosaic was observed with a 48 antenna compact configuration
of the 12m array (MOUS uid://A001/X88f/X2a2), for 49 minutes on source
on 2016-Dec-30, with a mean precipitable water vapor (PWV) of 1.3mm.
A slightly larger region of the sky was observed in a 60 point mosaic
using the 7m Atacama Compact Array (ACA) eight times between
2016-Oct-12 and 24, for a total of 416 minutes on source, mostly at a
PWV of ~0.5mm.
The spectral setup contains three spectral windows with 122.07kHz
channels each, centered on the ^12^CO, ^13^CO, and ^12^C^18^O J=2-1
transitions. Additionally a 2GHz wide, 128 channel spectral window
centered at 232.86GHz was observed. The native spectral channel
spacing is 0.17km/s, with a resolution of ^12^CO of 0.184km/s.
See Section 2.1.
Two types of YSOs have been analyzed in the N90 region: solar-mass PMS
stars identified with high-resolution HST optical and near-IR
photometry, and YSO candidates with infrared excess emission
attributed to circumstellar dust identified using Spitzer and Herschel
Space Telescope (Herschel) data. We revisit these populations here.
We used HST F555W (~V) and F814W (~I) observations of N90 reduced by
Schmalzl+ (2008, J/ApJ/681/290) to study the distribution of
solar-mass PMS stars in the region, as selected by
Gouliermis+ 2012ApJ...748...64G. The data from HST GO program 10248
consist of 2156s and 2269s total integration time with the Advanced
Camera for Surveys (ACS) Wide Field Camera (WFC) in F555W and F814W,
respectively.
We also reanalyzed Spitzer-identified intermediate- and high-mass YSO
candidates in the region. Carlson+ (2011, J/ApJ/730/78; hereafter C11)
combined V, I, J, H, K, Spitzer IRAC 3.6-8.0um, and Spitzer MIPS 24um
photometry, using the high-resolution optical data to remove
background galaxies. Starting with the C11 combined photometry catalog
with galaxies removed, but including sources they classified as stars,
we added aperture photometry from the Herschel HERITAGE survey
(Meixner+ 2013, J/AJ/146/62 ; Seale+ 2014, J/AJ/148/124) at 100, 160,
250, and 350um using the Spectral and Photometric Imaging Receiver
(SPIRE) and Photodetector Array Camera and Spectrometer (PACS).
See Section 2.2.
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