J/ApJ/938/82 CO molecular clumps and YSOs in NGC 602 region (O'Neill+, 2022)
Sequential star formation in the young SMC region NGC 602: insights from ALMA.
O'Neill T.J., Indebetouw R., Sandstrom K., Bolatto A.D., Jameson K.E.,
Carlson L.R., Finn M.K., Meixner M., Sabbi E., Sewilo M.
<Astrophys. J., 938, 82 (2022)>
=2022ApJ...938...82O 2022ApJ...938...82O
ADC_Keywords: Magellanic Clouds; H II regions; Molecular clouds; YSOs;
Interstellar medium; Carbon monoxide; Stars, masses;
Velocity dispersion; Infrared sources; Optical
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
αvir=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
XCO,B=(3.4±0.2)x1020cm-2 (K.km/s)-1, and correct observed
clump properties for CO-dark H2 gas to derive a total molecular gas
mass in N90 of 16600±2400M☉. We derive a recent (≲1Myr) star
formation rate of 130±30M☉/Myr with an efficiency of 8%±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 (≲2Myr) 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.
Description:
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 12CO, 13CO, and 12C18O 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 12CO 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 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.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 136 110 Clump properties
tablea2.dat 65 45 YSO properties
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See also:
J/ApJ/428/693 : Rosette Nebula & Maddalena Cloud structures (Williams+ 1994)
J/MNRAS/289/225 : SMC HI shells velocities (Staveley-Smith+ 1997)
J/ApJS/110/21 : Molecular clouds in Cepheus and Cassiopeia (Yonekura+ 1997)
J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)
J/ApJ/681/290 : HST/ACS photometry in the SMC (Schmalzl+, 2008)
J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)
J/ApJ/691/1560 : Dense core survey in the Orion B cloud (Ikeda+, 2009)
J/ApJ/730/78 : Hubble and Spitzer photometry of NGC 602 (Carlson+, 2011)
J/A+A/533/A109 : Pisa pre-main sequence tracks & isochrones (Tognelli+, 2011)
J/ApJ/745/173 : UV absorption sight lines of LMC and SMC (Welty+, 2012)
J/A+A/549/A70 : NGC 4214 multiband images (Hermelo+, 2013)
J/ApJ/774/73 : ALMA CO observations of 30 Dor (Indebetouw+, 2013)
J/AJ/146/62 : HERschel HERITAGE in Magellanic Clouds (Meixner+, 2013)
J/AJ/148/124 : Herschel key program Heritage (Seale+, 2014)
J/MNRAS/449/639 : VMC survey. XIV. SFR in SMC (Rubele+, 2015)
J/ApJ/811/78 : Elemental depletions in Magellanic Clds (Tchernyshyov+, 2015)
J/ApJ/833/229 : Star forming cloud-giant mocl complexes (Lee+, 2016)
J/A+A/589/A28 : N66, N88 & N25+N26 emission line maps (Requena-Torres+, 2016)
J/A+A/599/A9 : NGC 4214 [CII] line profile (Fahrion+, 2017)
J/ApJ/841/109 : Cloud decomposition & SFR measurements (Ochsendorf+, 2017)
J/ApJ/835/278 : Molecular clouds in the dwarf galaxy NGC6822 (Schruba+, 2017)
J/ApJ/853/175 : 12CO & 13CO cores & clumps in LHA 120-N 55 (Naslim+, 2018)
J/ApJ/854/154 : N159 12CO and 13CO (2-1) clumps (Nayak+, 2018)
J/ApJ/876/141 : ALMA obs. of giant moclds in Hen 2-10 (Imara+, 2019)
J/A+A/632/A106 : LMC-N11 (LHA 120-N11) [CII], HI, CO sp. (Lebouteiller+, 2019)
J/A+A/625/A104 : Stellar param. of OB stars in SMC wing (Ramachandran+, 2019)
J/A+A/643/A141 : Tracing total molecular gas in galaxies (Madden+, 2020)
J/A+A/641/A97 : ALMA Magellanic Bridge A mocl (Valdivia-Mena+, 2020)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/110] Clump running sequence identifier
5- 11 F7.4 deg RAdeg [22.3/22.5] Right Ascension (J2000)
13- 20 F8.4 deg DEdeg [-73.6/-73.5] Declination (J2000)
22- 26 F5.2 K Tpk12CO [2.2/22.6] 12CO peak antenna temperature
28- 31 F4.2 K Tpk13CO [0.5/7.2] 13CO peak antenna temperature
33- 40 F8.2 K.km/s W12 [59.6/13902] Total integrated 12CO
intensity
42- 45 F4.2 pc Reff [0.26/0.8] Effective radius from ellipse
fitting
47- 50 F4.2 pc e_Reff [0/0.4] Uncertainty in Reff
52- 57 F6.2 km/s Vlsr12Pk [159/180] Peak 12CO velocity
59- 62 F4.2 km/s sigv12 [0.2/1.1] CO velocity dispersion
64- 67 F4.2 km/s e_sigv12 [0/0.04] Uncertainty in sigv12
69- 73 F5.1 Msun mLTE [12/287]? LTE clump mass (1)
75- 78 F4.1 Msun e_mLTE [6/19.1]? Uncertainty in mLTE
80- 84 F5.1 Msun mXCO [1/281] X factor corrected, 12CO clump
mass
86- 89 F4.1 Msun e_mXCO [0.2/18] Uncertainty in mXCO
91- 95 F5.1 Msun/pc2 surfp [3.3/243.4] Surface density
97- 102 F6.1 Msun/pc3 rhoc [16.6/1217.1] Volume density at 0.1pc
104- 108 F5.1 Msun mvir12 [16.5/619.5] Virial mass
110- 114 F5.1 Msun e_mvir12 [0.7/256.3] Uncertainty in mvir12
116- 119 F4.1 --- aVir12 [1.3/39] Virial parameter, αvir
121- 124 F4.1 --- e_aVir12 [0.1/12.3] Uncertainty in aVir12
126- 134 A9 --- [CSM2011] YSO identifier(s) as in Table A2 (2)
136 A1 --- Group [r] Group (3)
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Note (1): Clumps without LTE mass estimates have 13CO S/N<3.
Note (2): YSO ID as given in Table 4 of Carlson+ (2011, J/ApJ/730/78)
and as used in Table A2 of this work.
Note (3): A denotation of "r" in Group indicates the clump is on the N90 rim.
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Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- [CSM2011] YSO identifier (YNNN) (1)
5 A1 --- f_[CSM2011] [i] "i" flag for source Y270 (1)(2)
8- 16 A9 --- --- [SSTNGC602]
18- 36 A19 --- SSTNGC602 IRAC designation (JHHMMSS.ss+DDMMSS.s)
(1)
38- 44 F7.4 deg RAdeg [22.17/22.6] Right Ascension (J2000)
(1)
46- 53 F8.4 deg DEdeg [-73.6/-73] Declination (J2000) (1)
55- 58 F4.2 Msun Mstar [1.2/7.8] Fit YSO Mass
60- 65 F6.2 10-6Msun/yr dM/dt [0.02/252] Fit envelope accretion rate
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Note (1): YSO identifier(s) and positions from Table 4 of
Carlson+ 2011, J/ApJ/730/78 (<[CSM2011] ANNN> in Simbad);
Note (2): Flag as follows:
i = the source Y270 fitting IRAC plus MIPS 24um (see Note (1)
for Table 4 in Carlson+ 2011, J/ApJ/730/78).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Aug-2024