J/A+A/707/A221 ALMAGAL VI. Spatial distribution of cores (Schisano+, 2026)
ALMAGAL. VI. The spatial distribution of dense cores during the evolution of
cluster-forming massive clump.
Schisano E., Molinari S., Coletta A., Elia D., Schilke P., Traficante A.,
Sanchez-Monge A., Beuther H., Benedettini M., Mininni C., Klessen R.S.,
Soler J.D., Nucara A., Pezzuto S., van der Tak F., Hennebelle P.,
Beltran M.T., Moscadelli L., Rygl K.L.J., Sanhueza P., Koch P.M., Lis D.C.,
Kuiper R., Fuller G.A., Avison A., Bronfman L., Lebreuilly U., Moller T.,
Liu T., Pelkonen V.-M., Testi L., Zhang Q., Zhang T., Ahmadi A., Allande J.,
Battersby C., Wallace J., Brogan C.L., Clarke S., De Angelis F., Fontani F.,
Ho P.T.P., Hunter T.R., Jones B., Johnston K.G., Klaassen P.D., Liu S.J.,
Liu S.-Y., Maruccia Y., Rigby A.J., Su Y.-N., Tang Y., Walch S.,
Zinnecker H.
<Astron. Astrophys. 707, A221 (2026)>
=2026A&A...707A.221S 2026A&A...707A.221S (SIMBAD/NED BibCode)
ADC_Keywords: Interferometry ; Millimetric/submm sources
Keywords: star formation - stars: massive - stars: protostars - ISM: clouds -
submillimeter: ISM
Abstract:
High-mass stars and star clusters form from the fragmentation of
massive dense clumps driven by gravity, turbulence and magnetic
fields. The extent to which each of these agents impacts the
fragmentation depending on the clump mass, density and evolutionary
stage is still largely unknown. The ALMAGAL project,with ∼1000 clumps
observed at ∼1000 au resolution, allows a statistically significant
characterization of the fragmentation process over a large range of
clump physical parameters and evolutionary stages. Our goal is to
characterize where and how the dense cores revealed by ALMA are
distributed in massive potentially cluster-forming clumps to trace how
fragmentation is initially set and how it proceeds before gas
dispersal due to stellar feedback. We characterized the spatial
distribution of dense cores in the 514 ALMAGAL clumps that host at
least 4 cores, using a set of quantitative descriptors that we
evaluated against the clump bolometric luminosity-to-mass ratio, which
we adopted as an indicator of the evolution of the system. We measured
the separations between cores with the minimum spanning tree method
(MST), which we compared with the predictions of gravitational
fragmentation from Jeans theory. We investigated whether cores have
specific arrangements using the Q-parameter or variations due to their
masses with the mass segregation ratio, ΛMSR. ALMAGAL cores
are distributed throughout the entire area of the clump, usually
arranged in elliptical groups with an axis ratio e∼2.2, although high
values with e=>5 are also observed. We found a single characteristic
core separation per clump in ∼76% of cases, suggesting that multiple
fragmentation lengths may be frequently present. Typical core
separations are compatible with the clump-averaged thermal Jeans
length, lambdathJ. However, we found an additional population of
cores, typical of low-fragmented and young clumps, which are on
average more widely separated with l ≃ 3*λthJ. By stacking
the distributions of the core separations in clumps of similar
evolutionary stage, we also found that the separation decreases on
average from l∼22000 au in younger systems to l∼7000 au in more
evolved ones. The ALMAGAL cores are typically distributed in
fractal-type subclusters, while centrally concentrated patterns appear
only at later stages, but we do not observe a progressive transition
between these configurations with evolution. Finally, we also found
110 ALMAGAL systems with a signature of mass segregation, with an
occurrence that increases with evolution.
Description:
The ALMAGAL program provides an extended and homogeneous dataset to
study the fragmentation process in dense and massive clumps. In this
paper, we analyze the spatial distribution of the cores identified in
the ALMAGAL fields by Coletta et al. (2025A&A...696A.151C 2025A&A...696A.151C, Cat.
J/A+A/696/A151) to provide a robust characterization of where the
cores are located in massive and potentially cluster-forming clumps,
what their typical separation is, how they are distributed, and how
these properties vary across the early evolutionary phases. This work
is a complement to the comparison between the physical properties of
the ALMAGAL core population, specifically the level of fragmentation,
core masses, and efficiency, and the large-scale clump parameters
presented by Elia et al. (2025arXiv251110825E 2025arXiv251110825E). This ALMAGAL large
program (Molinari et al. 2025A&A...696A.149M 2025A&A...696A.149M, Cat. J/A+A/696/A149)
observed with ALMA in Band 6 (∼220GHz, ∼1.4mm) 1013 dense
massive clumps located close to the Galactic Plane, and selected from
the Hi-GAL and RMS surveys.
Descriptor for the spatial distribution of cores for the 514 dense
clumps of the ALMAGAL Large program where more than 4 sources were
detected. The table2.dat reports the positions and morphologies of the
groups of cores. The table3.dat includes statistical metrics of the
distribution of linear separations between cores and Jeans parameters
computed from clump-averaged properties. The table6.dat reports
diagnostics for the spatial statistics, i.e. Q-parameter and
parameters of the mass segregation (MS) ratio profile, for a
restricted subsample of 296 systems in which more than 8 sources were
identified (i.e see sections results and discussion).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 114 514 Metrics of ALMAGAL core clusters spatial distrib. as
position, sizes and shapes
table3.dat 171 514 Clump thermal Jeans parameters and reference values
of projected lcore distributions from MST analysis
table6.dat 77 296 Diagnostics of spatial statistics in clumps
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See also:
J/ApJ/950/148 : ASHES. IX. Massive clumps with ALMA observations
(Morii+, 2023)
J/ApJ/886/102 : ALMA obs. of 70um dark high-mass clumps (ASHES)
(Sanhueza+, 2019)
J/ApJ/815/130 : High-mass molecular clumps from MALT90 (Guzman+, 2015)
J/ApJ/787/107 : Spatial structure of young stellar clusters. I.
(Kuhn+, 2014)
J/A+A/696/A149 : ALMAGAL. I. Target clumps properties (Molinari+, 2025)
J/A+A/696/A151 : ALMAGAL III. Compact source catalog (Coletta+, 2025)
J/A+A/690/A33 : Core mass function in high-mass star formation
(Louvet+, 2024)
J/A+A/682/A81 : CORE Sample NIKA2 and SMA images (Beuther+, 2024)
J/A+A/649/A113 : ISOSS22478 and ISOSS23053 images (Beuther+, 2021)
J/A+A/648/A66 : CORE high-mass star-forming regions (Gieser+, 2021)
J/A+A/645/A94 : NGC 2264 clumps column densities (Nony+, 2021)
J/A+A/635/A2 : NGC6334 ALMA 87.6GHz continuum emission map
(Sadaghiani+, 2020)
J/A+A/615/A9 : Distribution of Serpens South protostars (Plunkett+, 2018)
J/A+A/615/A94 : ALMA massive protocluster gas clumps maps (Fontani+, 2018)
J/A+A/610/A77 : Orion Integral Filament ALMA+IRAM30m N2H+(1-0) data
(Hacar+, 2018)
J/A+A/600/A141 : Orion A integral shaped filament image (Kainulainen+, 2017)
J/A+A/600/L10 : Massive cluster progenitors from ATLASGAL (Csengeri+, 2017)
J/A+A/591/A149 : Hi-GAL. inner Milky Way: +68≥l≥70 (Molinari+, 2016)
J/A+A/584/A91 : Catalog of dense cores in Aquila from Herschel
(Konyves+, 2015)
J/ApJ/566/945 : Massive star forming regions at 1.2mm (Beuther+, 2002)
J/A+A/561/A83 : SDC13 infrared dark clouds spectra (Peretto+, 2014)
J/MNRAS/526/2278 : TEMPO. Fragmentation and emission properties (Avison+, 2023)
J/MNRAS/508/2964 : Study of clumps, cores and hubs with ALMA (Anderson+, 2021)
J/MNRAS/496/2790 : ATOMS I Description and a first look at G9.62+0.19
(Liu+, 2020)
J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)
J/A+A/481/345 : SED evolution in massive young stellar objects
(Molinari+, 2008)
J/MNRAS/473/849 : Mass segregation in Galactic stellar clusters (Dib+, 2018)
J/MNRAS/471/100 : Hi-GAL compact source catalog. -71.0<l<67.0 (Elia+, 2017)
J/ApJS/270/9 : ALMA obs. of 11 massive & luminous clumps protoclusters
(Xu+, 2024)
J/ApJS/208/11 : The Red MSX Source Survey: massive protostars
(Lumsden+, 2013)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/AJ/134/1368 : Proper motions in NGC 2244 and NGC 6530 (Chen+, 2007)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- Name ALMAGAL target name (AGLLL.llll+B.bbbb)
(Name)
19- 20 I2 --- Ncores Number of cores (Ncores)
22- 30 F9.5 deg RAdeg Cluster center right ascension (ICRS)
(RAmean) (1)
32- 40 F9.5 deg DEdeg Cluster center declination (ICRS)
(DECmean) (1)
42- 46 F5.2 arcsec Offset Offset from image center (Offset) (1)
48- 52 F5.2 arcsec RadCl Cluster radius Rcluster (RadCl) (2)
54- 61 E8.2 pc RadPhCl Linear size of the cluster Rphcluster
(RadPhCl) (2)
63- 68 F6.2 arcsec2 AreaCH Area of the convex hull (CH) polygon ACH
(AreaCH) (3)
70- 76 A7 arcsec2 AreaS Normalized CH area to number of cores inside
the polygon ACHnorm (AreaS) (3)
78- 79 I2 --- NvCH Number of vertices of the CH polygon
Nhullν (NvCH) (3)
81- 82 I2 --- NinCH Number of cores inside the CH polygon
Nhullin (NinCH) (3)
84- 89 F6.3 --- Xi Ratio of RadCl and RCH equivalent radius
(Xi) (4)
91- 95 F5.2 arcsec A Major axis of the fitted ellipse to CH
(Axis_A) (4)
97-101 F5.2 arcsec B Minor axis of the fitted ellipse to CH
(Axis_B) (4)
103-107 F5.2 --- A/B ? Axis ratio of the fitted ellipse to CH
(Elon) (4)
109-114 F6.1 deg PA [] Position Angle of the fitted ellipse to
CH (PA) (4)
--------------------------------------------------------------------------------
Note (1): Geometric center of the group of cores present in the ALMAGAL core
catalog (Coletta et al. 2025A&A...696A.151C 2025A&A...696A.151C, Cat. J/A+A/696/A151) and
its offset from the image center, which correspond to the clump center
measured in the Hi-GAL 250 µm maps.
Note (2): Cluster angular radius, Rcluster and corresponding linear size,
Rphcluster.
Note (3): Parameters of the convex hull (CH) polygon computed from the core
positions: area ACH , normalized area according to
ACHnorm = ACH/(1-Nhullν/Ncores) from Schmeja & Klessen
(2006A&A...449..151S 2006A&A...449..151S), number of cores at the CH vertices,
Nhullν, and inside the polygon, Nhullin.
Note (4): Elongation of the cluster: ratio between cluster radius and CH
equivalent radius defined as the radius of the circle with an area
equivalent to ACH, ξ, and ellipticity e and position angle PA of
the best fitting ellipse to the convex hull.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- Name ALMAGAL target name (AGLLL.llll+B.bbbb) (Name)
19- 20 I2 --- Ncores Number of cores (Ncores)
22- 25 F4.1 Msun Mth ? Clump-averaged thermal jeans mass (Mth_J) (1)
27- 38 F12.6 AU Lth ? Clump-averaged thermal jeans length
(Lth_J) (1)
40- 51 F12.6 AU lmin Minimum of projected linear core separations
(lmin)
53- 65 F13.6 AU lmax Maximum of projected linear core separations
(lmax)
67- 78 F12.6 AU lmean Mean of projected linear core separations
(lmean)
80- 91 F12.6 AU lstd Standard Deviation of projected linear core
separations (lstd)
93-104 F12.6 AU lmedian Median of projected linear core separations
(lmedian)
106-117 F12.6 AU lq1 First Quartile of projected linear core
separations (lq1)
119-131 F13.6 AU lq3 Third Quartile of projected linear core
separations (lq3)
133-144 F12.6 AU lmode ? Modal of the KDE-derived distribution of
projected linear core separations
(lmode) (2)
146-157 F12.6 AU l1 ? Inner edge at 68% peak-intensity of the
KDE-derived distribution (l1) (2)
159-171 F13.6 AU l2 ? Outer edge at 68% peak-intensity of the
KDE-derived distribution (l2) (2)
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Note (1): Clump-averaged quantities computed from properties reported in
Molinari et al. (2025A&A...696A.149M 2025A&A...696A.149M, Cat. J/A+A/696/A149).
Note (2): The lmode indicates the most frequently observed separation, as
l1(l-68%) and l2(l+68%) it has been determined from empirical
density distributions computed with the Gaussian Kernel Density
Estimate (KDE) method (Silverman 1986, Density Estimation for
Statistics and Data Analysis). The kernel bandwidth is derived from
the data applying the Scott's rule (Scott 1992, Multivariate Density
Estimation and Visualization).
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- Name ALMAGAL target name (AGLLL.llll+B.bbbb) (Name)
19- 20 I2 --- Ncores Number of cores (Ncores)
22- 26 F5.3 --- Q The Q parameter (Qpar) (1)
28- 32 F5.3 --- MeanEdge Mean edge length of cluster MST called m
(MeanEdge) (1)
34- 38 F5.3 --- ScorLen Cluster correlation length called s
(ScorLen) (1)
40 I1 --- NLamCrit ? Number of cores at the maximum of the MS
ratio profile (NLamCrit) (2)
42- 46 F5.2 --- LamPeak ? Peak value ΛmaxMSR of the MS
ratio profile (LamPeak) (2)
48 I1 --- NLamPeak ? Highest number of cores in MS ratio profile
greater than unity (NLamPeak) (2)
50- 54 F5.3 --- MSI Mass segregation integral IMSRλ for
MSR profile comparisons of different systems
defined by Xu et al. (2024ApJS..270....9X 2024ApJS..270....9X,
Cat. J/ApJS/270/9) (MSI)
56- 65 A10 --- f_MSI Mass segregation (MS) flag (MSFlag) (3)
67- 71 F5.3 --- Prob1 ? Probability of direct MS in Monte Carlo runs
(Prob1) (4)
73- 77 F5.3 --- Prob2 ? Probability of inverse MS in Monte Carlo
runs (Prob2) (4)
--------------------------------------------------------------------------------
Note (1): Mean edge length of cluster MST, m, the cluster correlation length, s,
and the Q parameter defined as Q = m/s, following
Cartwright & Whitworth (2004MNRAS.348..589C 2004MNRAS.348..589C).
Note (2): Quantities of the mass segregation ratio (MSR) profile: maximum
number of cores for which MSR profile is different than unity
NcritMST, the MSR maximum value ΛmaxMSR, and its
corresponding number of cores NmaxMST. These quantities are
measured only in the 110 systems where the mass segregation (MS)
is assessed.
Note (3): Meaning of Flag as follows:
Pos MS = MS ratio profile exceeds unity by more than 1-sigma
Pos Inv MS = MS ratio profile is smaller unity by more than
1-sigma
Rob MS = MS ratio profile exceeds unity by more than 1-sigma
and the probability from Monte Carlo simulation
exceeds 0.7
Rob Inv MS = MS ratio profile is smaller unity by more than 1-sigma
and the probability from Monte Carlo simulation exceeds
0.7
Flags reporting whether a signature of direct ('Pos MS') or
inverse ('Pos Inv MS') mass segregation is found and if it is robust
(additional flag 'Rob') against the Monte Carlo simulations described
in the text.
Note (4): Probability of presence of direct (Prob1) or inverse (Prob2) mass
segregation evaluated with Monte Carlo simulations.
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Acknowledgements:
Eugenio Schisano, eugenio.schisano(at)inaf.it
References:
Molinari et al. Paper I 2025A&A...696A.149M 2025A&A...696A.149M, Cat. J/A+A/696/A149
Sanchez-Monge et al. Paper II 2025A&A...696A.150S 2025A&A...696A.150S
Coletta et al. Paper III 2025A&A...696A.151C 2025A&A...696A.151C, Cat. J/A+A/696/A151
Mininni et al. Paper IV 2025A&A...699A..34M 2025A&A...699A..34M
Elia et al. Paper V 2025arXiv251110825E 2025arXiv251110825E
(End) Eugenio Schisano [INAF], Luc Trabelsi [CDS] 11-Dec-2025