J/A+A/706/A185 Euclid. ERO. IC 10 and NGC 6822 (Howell+, 2026)
Euclid: Early Release Observations -
The star cluster systems of the Local Group dwarf galaxies IC 10 and NGC 6822.
Howell J.M., Ferguson A.M.N., Larsen S., Lancon A., Annibali F.,
Cuillandre J.-C., Hunt L.K., Martinez-Delgado D., Massari D., Saifollahi T.,
Voggel K., Altieri B., Andreon S., Auricchio N., Baccigalupi C., Baldi M.,
Bardelli S., Biviano A., Branchini E., Brescia M., Brinchmann J., Camera S.,
Canas-Herrera G., Candini G.P., Capobianco V., Carbone C., Carretero J.,
Castellano M., Castignani G., Cavuoti S., Cimatti A., Colodro-Conde C.,
Congedo G., Conselice C.J., Conversi L., Copin Y., Courbin F., Courtois H.M.,
Cropper M., Da Silva A., Degaudenzi H., De Lucia G., Dubath F.,
Duncan C.A.J., Dupac X., Dusini S., Escoffier S., Farina M., Farinelli R.,
Faustini F., Ferriol S., Finelli F., Frailis M., Franceschi E., Fumana M.,
Galeotta S., George K., Gillis B., Giocoli C., Gracia-Carpio J., Grazian A.,
Grupp F., Haugan S.V.H., Hoekstra H., Holmes W., Hormuth F., Hornstrup A.,
Jahnke K., Jhabvala M., Keihaenen E., Kermiche S., Kubik B., Kuemmel M.,
Kunz M., Kurki-Suonio H., Le Brun A.M.C., Le Mignant D., Ligori S.,
Lilje P.B., Lindholm V., Lloro I., Mainetti G., Maino D., Maiorano E.,
Mansutti O., Marggraf O., Martinelli M., Martinet N., Marulli F.,
Massey R.J., Medinaceli E., Mei S., Melchior M., Mellier Y., Meneghetti M.,
Merlin E., Meylan G., Mora A., Moresco M., Moscardini L., Nakajima R.,
Neissner C., Niemi S.-M., Padilla C., Paltani S., Pasian F., Pedersen K.,
Percival W.J., Pettorino V., Pires S., Polenta G., Poncet M., Popa L.A.,
Raison F., Renzi A., Rhodes J., Riccio G., Romelli E., Roncarelli M.,
Saglia R., Sakr Z., Sapone D., Sartoris B., Schirmer M., Schneider P.,
Schrabback T., Secroun A., Seidel G., Serrano S., Simon P., Sirignano C.,
Sirri G., Skottfelt J., Stanco L., Steinwagner J., Tallada-Crespi P.,
Taylor A.N., Teplitz H.I., Tereno I., Toft S., Toledo-Moreo R.,
Torradeflot F., Tutusaus I., Valenziano L., Valiviita J., Vassallo T.,
Wang Y., Weller J., Zamorani G., Zinchenko I.A., Martin-Fleitas J.,
Scottez V.
<Astron. Astrophys. 706, A185 (2026)>
=2026A&A...706A.185H 2026A&A...706A.185H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Clusters, globular ; Clusters, open
Keywords: galaxies: dwarf - galaxies: individual: NGC6822 -
galaxies: individual: IC 10 - Local Group -
galaxies: star clusters: general
Abstract:
Star clusters are valuable indicators of galaxy evolution, offering
insights into the buildup of stellar populations across cosmic time.
Understanding the intrinsic star cluster populations of dwarf galaxies
is particularly important given these systems' role in the
hierarchical growth of larger systems. We use data from Euclid's Early
Release Observation programme to study star clusters in two
star-forming dwarf irregular galaxies in the Local Group, NGC 6822 and
IC 10 [M*~(1-4)x108M☉]. With Euclid, star clusters are
resolved into individual stars across the main bodies and haloes of
both galaxies. Through visual inspection of the IE images, we uncover
30 new star cluster candidates in NGC 6822 and 16 in IC 10, ranging
from compact to diffuse extended clusters. We compile and re-evaluate
previously identified literature candidates, resulting in final
combined catalogues of 52 (NGC 6822) and 71 (IC 10) cluster candidates
with confidence-based classifications. We present homogeneous
photometry in IE, YE, JE, and HE, and in archival UBVRI data,
alongside size measurements and properties derived from the spectral
energy distribution fitting code BAGPIPES. Through synthetic cluster
injection, we conclude our sample is ∼50% complete to M≲103M☉
for ages ≲100Myr, and to M≲2x104M☉ for ages of ∼10Gyr. We
find that IC 10 has more young clusters than NGC 6822, and its young
clusters extend to higher masses, consistent with its starburst
nature. We find several old massive (≳105M☉) clusters in both
dwarfs, including an exceptional cluster in NGC 6822's outskirts with
a mass of 1.3x106M☉, nearly twice as massive as any other old
cluster in either galaxy. In NGC 6822, we also identify a previously
undetected, old, and extended cluster (Rh=12.4±0.11pc). Using
well-defined criteria, we identify 11 candidate GCs in NGC 6822 and
nine in IC 10. Both galaxies have high specific frequencies (S_N) for
their luminosities but remain consistent with the known GC scaling
relationships in the low-luminosity regime.
Description:
Catalogue of star cluster candidates in IC 10 (71 objects) and
NGC 6822 (52 objects), including both new clusters identified in this
work and clusters found in previous works. Tables 2 and 3 provide
equatorial coordinates, a classification flag indicating the
confidence of each object being a genuine cluster, a flag indicating
whether our cluster search recovered previously found literature
candidates, previous IDs and previous references. Tables B.1 and B.2
list photometric measurements including V and Y_E magnitudes and
derived colours spanning the UBVRI, Y_E, J_E, H_E, and I_E bands, in
addition to cluster half- light radii. Tables B.3. and B.4. give the
physical parameters for each cluster: ages, masses, metallicities, and
line-of-sight extinction estimates.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 82 78 Cluster coordinates & classifications NGC 6822
table3.dat 73 113 Cluster coordinates & classifications IC 10
tableb1.dat 150 52 Cluster photometry & half-light radii NGC 6822
tableb2.dat 150 71 Cluster photometry & half-light radii IC 10
tableb3.dat 86 51 Cluster physical properties NGC 6822
tableb4.dat 86 71 Cluster physical properties IC 10
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- EuclidID Cluster identifier used in this work
17- 27 F11.7 deg RAdeg Right Ascension (ICRS) at Ep=J2000
29- 40 F12.8 deg DEdeg Declination (ICRS) at Ep=J2000
42 I1 --- Class Morphological / confidence class (G1)
44- 58 A15 --- PrevIDs IDs from previous catalogues (2)
60- 62 A3 --- Recov? [Yes/No ] Recovered in this work?
64- 82 A19 --- Ref Literature reference (3)
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Note (2): IDs from previous catalogues as :
ESCC* = Euclid Identifier
Hubble* = Sources from Hubble, 1925ApJ....62..409H 1925ApJ....62..409H,
[H25] VNN in Simbad
C* = Sources from Hodge et al., 1977ApJS...33...69H 1977ApJS...33...69H,
[H77] Cl* NN in Simbad
SC* = Sources from Hwang et al., 2011ApJ...738...58H 2011ApJ...738...58H,
[HLL2011] NGC6822CN in Simbad or
Huxor et al. 2013MNRAS.429.1039H 2013MNRAS.429.1039H, [HFV2013] SCN in Simbad
NGC 6822-clKH* = Sources from Krienke et al., 2004PASP..116..497K 2004PASP..116..497K,
[H77] Cl* NN in Simbad
Note (3): References as follows:
Hodge (1977) = Hodge, 1977ApJS...33...69H 1977ApJS...33...69H
Hubble (1925) = Hubble, 1925ApJ....62..409H 1925ApJ....62..409H
Huxor et al. (2013) = Huxor et al., 2013MNRAS.429.1039H 2013MNRAS.429.1039H
Hwang et al. (2011) = Hwang et al., 2011ApJ...738...58H 2011ApJ...738...58H
Krienke (2004) = Krienke & Hodge, 2004PASP..116..497K 2004PASP..116..497K
This work = This work
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- EuclidID Cluster identifier used in this work
20- 30 F11.9 deg RAdeg Right Ascension (J2000)
32- 43 F12.8 deg DEdeg Declination (J2000)
45 I1 --- Class Morphological / confidence class (G1)
47- 59 A13 --- PrevIDs IDs from previous catalogues (2)
61- 63 A3 --- Recov? [Yes/No ] Recovered in this work? (Yes/No)
65- 73 A9 --- Ref Reference or source catalogue (3)
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Note (2): IDs from previous catalogues as :
ESCC* = Euclid Identifier
TG* = Sources from Tikhonov et al., 2009AstL...35..748T 2009AstL...35..748T,
[TG2009] NN in Simbad
S* or d* = Sources from Sharina et al., 2010MNRAS.405..839S 2010MNRAS.405..839S,
[SCP2010b] IC10 dNN in Simbad
C* = Sources from Karachentsev & Tikhonov, 1993A&AS..100..227K 1993A&AS..100..227K
H* = Sources from Hunter et al., 2001ApJ...559..225H 2001ApJ...559..225H,
[H2001] N-N in Simbad
L* = Sources from Lim & Lee, 2015ApJ...804..123L 2015ApJ...804..123L,
[LL2015] NN in Simbad
Note (3): Referneces as follows:
H01 = Hunter, 2001ApJ...559..225H 2001ApJ...559..225H
KT93 = Karachentsev & Tikhonov, 1993A&AS..100..227K 1993A&AS..100..227K
Lim15 = Lim & Lee, 2015ApJ...804..123L 2015ApJ...804..123L, Cat. J/ApJ/804/123
S10 = Sharina et al., 2010MNRAS.405..839S 2010MNRAS.405..839S
TG09 = Tikhonov & Galazutdinova, 2009AstL...35..748T 2009AstL...35..748T, Cat. J/PAZh/35/829
This work = This work
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Byte-by-byte Description of file: tableb1.dat tableb2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- EuclidID Cluster identifier used in this work
16 A1 --- n_EuclidID [*] Note on EuclidID
18- 30 F13.9 deg RAdeg Right ascension (J2000)
32- 43 F12.8 deg DEdeg Declination (J2000)
45- 49 F5.2 mag Vmag ?=- V-band integrated magnitude
51- 54 F4.2 mag e_Vmag ?=- Uncertainty in Vmag
56- 59 F4.2 mag B-V ?=- Integrated (B-V) colour
61- 64 F4.2 mag e_B-V ?=- Uncertainty in (B-V)
66- 70 F5.2 mag U-B ?=- Integrated (U-B) colour
72- 75 F4.2 mag e_U-B ?=- Uncertainty in (U-B)
77- 80 F4.2 mag V-R ?=- Integrated (V-R) colour
82- 85 F4.2 mag e_V-R ?=- Uncertainty in (V-R)
87- 90 F4.2 mag R-I ?=- Integrated (R-I) colour
92- 95 F4.2 mag e_R-I ?=- Uncertainty in (R-I)
97-101 F5.2 mag Yemag Euclid Ye-band magnitude
103-106 F4.2 mag e_Yemag Uncertainty in Yemag
108-112 F5.2 mag Ye-He (Ye-He) colour
114-117 F4.2 mag e_Ye-He Uncertainty in (Ye-He)
119-123 F5.2 mag Je-He (Je-He) colour
125-128 F4.2 mag e_Je-He Uncertainty in (Je-He)
130-134 F5.2 mag Ie-He (Ie-He) colour
136-139 F4.2 mag e_Ie-He Uncertainty in (Ie-He)
141-145 F5.2 pc Rh Half-light radius
147-150 F4.2 pc e_Rh Uncertainty in Rh
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Byte-by-byte Description of file: tableb3.dat tableb4.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- EuclidID Cluster identifier used in this work
17- 23 F7.4 Gyr Age Cluster age
25- 30 F6.4 Gyr e_Age Uncertainty on age
32- 37 F6.4 [Sun] logMass log10 total stellar mass
39- 44 F6.4 [Sun] e_logMass Uncertainty on log mass
46- 51 F6.4 [Sun] logLivingMass log10 living stellar mass
53- 58 F6.4 [Sun] e_logLivingMass Uncertainty on living mass
60- 65 F6.4 Sun Z Metallicity (Z/Zsun)
67- 72 F6.4 Sun e_Z Uncertainty on metallicity
74- 79 F6.4 mag Av Line-of-sight extinction
81- 86 F6.4 mag e_Av Uncertainty on extinction
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Global notes:
Note (G1): A numerical value indicating the outcome of visual classification by
three authors (AMNF, JH, SSL) as follows:
1 = Three likely classifications
2 = Two likely and one maybe
3 = One likely and two maybe
4 = Three maybe
5 = Any combination with unlikely
6 = Clusters from previous works clearly non-cluster like in Euclid
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Acknowledgements:
Jess Howell, jess.howell(at)ed.ac.uk
(End) Patricia Vannier [CDS] 25-Dec-2025