J/MNRAS/477/298 Young star clusters in nearby molecular clouds (Getman+, 2018)
Young star clusters in nearby molecular clouds.
Getman K.V., Kuhn M.A., Feigelson E.D., Broos P.S., Bate M.R., Garmire G.P.
<Mon. Not. R. Astron. Soc., 477, 298-324 (2018)>
=2018MNRAS.477..298G 2018MNRAS.477..298G (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Clusters, open ; Stars, pre-main sequence ;
Morphology
Keywords: stars: early-type - stars: formation - stars: pre-main-sequence -
open clusters and associations: general - infrared: stars -
X-rays: stars
Abstract:
The SFiNCs (Star Formation in Nearby Clouds) project is an
X-ray/infrared study of the young stellar populations in 22
star-forming regions with distances ≲1kpc designed to extend
our earlier MYStIX (Massive Young Star-Forming Complex Study in
Infrared and X-ray) survey of more distant clusters. Our central goal
is to give empirical constraints on cluster formation mechanisms.
Using parametric mixture models applied homogeneously to the catalogue
of SFiNCs young stars, we identify 52 SFiNCs clusters and 19
unclustered stellar structures. The procedure gives cluster properties
including location, population, morphology, association with molecular
clouds, absorption, age (AgeJX), and infrared spectral energy
distribution (SED) slope. Absorption, SED slope, and AgeJX are age
indicators. SFiNCs clusters are examined individually, and
collectively with MYStIX clusters, to give the following results.
(1) SFiNCs is dominated by smaller, younger, and more heavily obscured
clusters than MYStIX. (2) SFiNCs cloud-associated clusters have the
high ellipticities aligned with their host molecular filaments
indicating morphology inherited from their parental clouds. (3) The
effect of cluster expansion is evident from the radius-age,
radius-absorption, and radius-SED correlations. Core radii increase
dramatically from ∼0.08 to ∼0.9pc over the age range 1-3.5Myr.
Inferred gas removal time-scales are longer than 1Myr. (4) Rich,
spatially distributed stellar populations are present in SFiNCs clouds
representing early generations of star formation. An appendix compares
the performance of the mixture models and non-parametric minimum
spanning tree to identify clusters. This work is a foundation for
future SFiNCs/MYStIX studies including disc longevity, age gradients,
and dynamical modelling.
Description:
The SFiNCs project is aimed at providing detailed study of the young
stellar populations and star cluster formation in nearby 22 SFRs. The
input lists of young stars, SPCMs, were obtained in our previous study
(Getman et al., 2017, Cat. J/ApJS/229/28). This study complements and
extends our earlier MYStIX survey of richer, more distant clusters.
Both efforts share consistent data sets, data reduction procedures,
and cluster identification methods. The latter are based on maximum
likelihood parametric mixture models, which differ from the
non-parametric procedures used in most previous studies.
We identify 52 SFiNCs clusters and 19 unclustered stellar components
in the 22 SFiNCs SFRs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 48 22 SFiNCs targets for cluster analysis
table2.dat 87 52 *SFiNCs clusters from mixture model
table3.dat 30 22 Mixture model goodness of fit.
table4.dat 110 8492 Membership of SFiNCs clusters
table5.dat 81 71 Properties of SFiNCs clusters
table6.dat 46 91 Properties of MYStIX clusters
tablea1.dat 50 14 Clusters in common between SFiNCs and
Gutermuth et al. (2009, Cat. J/ApJS/184/18, G09)
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Note on table2.dat: 52 ellipsoid cluster components from the best-fitting
mixture models for the 22 SFiNCs SFRs.
Highly uncertain parameter values are appended with ':'.
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See also:
J/ApJS/229/28 : SFiNCs: X-ray, IR and membership catalogs (Getman+, 2017)
J/ApJ/787/109 : Age estimates for NGC 2024 and ONC stars (Getman+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Region SFiNCs SFR (SFiNCs regions) (1)
17- 21 F5.3 kpc Distance Distance to SFR (SFiNCs regions) (1)
23- 26 I4 --- SPCMs Total number of SPCMs (SFiNCs regions) (1)
28- 33 F6.3 ph/s/cm2 logFXlim Apparent (0.5-8)keV X-ray photon flux limit
imposed for spatial uniformity
(SPCM subsample for cluster identification)
35- 38 I4 --- N* Total number of SPCMs used for the cluster
analysis
(SPCM subsample for cluster identification)
40- 42 I3 --- X-ray Number of X-ray selected SPCMs that lie within
the Chandra ACIS-I field and have their
X-ray photometric flux above the FX,lim
value
(SPCM subsample for cluster identification)
44- 46 I3 --- IRE Number of non-X-ray disc-bearing SPCMs that
lie within the Chandra ACIS-I field
(SPCM subsample for cluster identification)
48 I1 --- OB Number of OB-type stars within the SPCM
subsample used for the cluster identification
analysis
(SPCM subsample for cluster identification)
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Note (1): From Getman et al., 2017, Cat. J/ApJS/229/28
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Cluster Cluster component name,
labelled from west to east
19- 28 F10.6 deg RAdeg Ellipsoide centre right ascension (J2000)
29 A1 --- u_RAdeg Uncertainty flag RAdeg
32- 41 F10.6 deg DEdeg Ellipsoide centre declination (J2000)
42 A1 --- u_DEdeg Uncertainty flag on DEdeg
44- 46 I3 arcsec e_Pos ?=- Position error as 68 per cent error circle
48- 52 F5.3 pc Rc Core radius as an average between the
semimajor and semiminor axes of the
ellipsoid component
53 A1 --- u_Rc Uncertainty flag on Rc
55- 58 F4.2 --- e_Rc/Rc ?=- Core radius fractional statistical error
(68 per cent confidence interval)
60- 63 F4.2 --- eps Ellipticity
64 A1 --- u_eps Uncertainty flag on eps
66- 69 F4.2 --- e_eps/eps ?=- Ellipticity fractional statistical error
71- 73 I3 deg phi Orientation angle of the ellipse
(east from north)
74 A1 --- u_phi Uncertainty flag on phi
76- 79 I4 --- N Number of stars estimated by integrating the
model component out to four times the size
of the core
80 A1 --- u_N Uncertainty flag on N
82- 85 F4.2 --- e_N/N ?=- Number of stars fractional
statistical error
87 A1 --- Cloud [CR-] Relation to molecular clouds (1)
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Note (1): based on a visual inspection of far-infrared images discussed in
Section 6 and prior studies of the SFiNCs SFRs as follows:
C = likely embedded in a cloud
R = likely revealed
- = unclear case
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Region Star-forming region
17 I1 --- Nsubclt Number of clusters in the model
19- 22 F4.1 --- chi2 Pearson's chi2 value (1)
24- 25 I2 --- dof Degrees of freedom
27- 30 F4.2 --- Pchi2 Two-sided p-value for the null hypothesis that
the observed YSO distribution is drawn from
the model (2)
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Note (1): Pearson's chi-squared as a goodness-of-fit measure for the
best-fitting mixture models given in Table 2 based on the random tessellation
given in Fig. 3.
Note (2): If Pchi2<0.01, then the data are likely not drawn from the model.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Region SFiNCs SFR name
17- 34 A18 --- Desig Source IAU designation (HHMMSS.s+DDMMSS.s)
36- 45 F10.6 deg RAdeg Right ascension (J2000)
47- 56 F10.6 deg DEdeg Declination (J2000)
58- 60 I3 --- Flag Three-digit flag (1)
62- 65 F4.2 keV ME ?=- X-ray median energy in the (0.5-8)keV band
67- 71 F5.2 mag Jmag ?=- 2MASS J magnitude
73- 76 F4.2 mag e_Jmag ?=- 2MASS J magnitude error
78- 82 F5.2 mag Hmag ?=- 2MASS H magnitude
84- 87 F4.2 mag e_Hmag ?=- 2MASS H magnitude error
89- 93 F5.2 --- alphaIRAC ?=- Apparent SED slope (2)
95- 98 F4.2 --- e_alphaIRAC ?=- Apparent SED slope error
100-104 F5.2 [10-7W] logLXtc ?=- Intrinsic X-ray luminosity in
the (0.5-8)keV band
106-108 F3.1 Myr AgeJX ?=- Stellar age estimate using the method of
Getman et al. (2014, Cat. J/ApJ/787/109)
110 A1 --- Clus Cluster assignment (3)
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Note (1): The first digit indicates whether the source is located
inside (1) or outside (0) the Chandra ACIS-I field.
The second digit indicates whether the source is
an X-ray object (1) or not (0).
The third digit indicates whether the source is
an OB-type star (1) or not (0).
Note (2): alphaIRAC=dlog(λFλ)/dlog(λ) measured in the
IRAC wavelength range from 3.6 to 8.0um.
Note (3): cluster assignment: 'A'-'E' indicates the assigned SFiNCs cluster;
'U' indicates the unclustered stellar population;
'X' indicates uncertain assignment;
'-' indicates that no assignment is made for sources located outside the
Chandra ACIS-I field.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Cluster Cluster component name (1)
22- 24 I3 --- N4data Number of observed SPCMs
26- 28 I3 --- NJH ?=- Number of observed SPCMs with available
reliable J-H colour (2)
30- 33 F4.2 mag J-H ?=- J-H colour
35- 38 F4.2 mag e_J-H ? J-H colour error (3)
40- 42 I3 --- NME ?=- Number of observed SPCMs with available
X-ray median energy ME (2)
44- 47 F4.2 keV ME ?=- X-ray median energy in the (0.5-8)keV band
49- 52 F4.2 keV e_ME ? X-ray median energy error (3)
54- 56 I3 --- NIRAC ?=- Number of observed SPCMs with available
IRAC SED slope (alphaIRAC) (2)
58- 62 F5.2 --- alphaIRAC ?=- Median SED slope
64- 67 F4.2 --- e_alphaIRAC ? Median SED slope error (3)
69- 71 I3 --- NAgeJX ?=- Number of observed SPCMs with available
age estimates (AgeJX) (2)
73- 76 F4.2 Myr AgeJX ?=- Medium age
78- 81 F4.2 Myr e_AgeJX ? Medium age error (3)
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Note (1): In addition to the cluster components from Table 2 (A, B, C, D, and
E), the unclustered components (UnCl) are listed.
Note (2): the numbers are given for the SPCMs located within an ∼4xRc region
around the centre of the A-E components.
Note (3): the reported uncertainties on the medians are derived using the
bootstrap approach given in Getman et al. (2014, Cat. J/ApJ/787/109).
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Cluster MYStIX cluster component name
11- 13 I3 --- N4model Number of observed stars estimated by
integrating the model component out to four
times the size of the core
15- 19 F5.2 [pc] log(Rc) logarithm of cluster core radius
21- 24 F4.2 --- eps Cluster ellipticity
26- 29 F4.2 mag J-H Median J-H colour
31- 33 F3.1 keV ME X-ray median energy in the (0.5-8)keV band
35- 38 F4.2 [yr] log(AgeJX) ?=- log Age
40- 44 F5.2 --- alphaIRAC ?=- SED slope
46 A1 --- Cloud Relation to molecular clouds (1)
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Note (1): relation to molecular clouds, based on a visual inspection of fig. 7
in Getman et al. (2014, Cat. J/ApJ/787/109) as follows:
C = likely associated with a cloud, i.e. embedded in or emerging from a cloud
R = likely revealed, i.e. already emerged from a cloud
- = unclear case
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- SFR Star-forming region
17- 19 A3 --- m_SFR SFiNCs cluster component name
22- 25 F4.2 pc Size Cluster size (1)
27- 29 I3 --- Number Observed number of YSOs
31- 33 I3 pc-2 SIGMAmean Mean stellar density derived
from SFiNCs model (2)
35- 40 A6 --- Name Cluster name from G09
43- 46 F4.2 pc Rhull Cluster radius from G09 (3)
48- 50 I3 pc-2 sigmamean Mean stellar density inferred
from the analysis of G09 (3)
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Note (1): The reported size is a cluster radius four times the size of the
cluster core (Rc) given in Table 2.
Note (2): The mean density is estimated to be N4,data/π(4Rc)2, where the
total number of all SFiNCs YSOs observed within the cluster (N4, data) is taken
from Table 5.
Note (3): cluster radius and mean stellar density inferred from the analysis of
G09 (see their table 8). For SFO 2, NGC 1333, IC 348, LkHa 101, Serpens Main,
Sh 2-106, Cep A, and Cep C, the G09 values are adjusted to match the distances
adopted in SFiNCs; the distance values adopted in SFiNCs and G09 can be found
in Table 1 here and table 1 of G09, respectively.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 05-May-2021