J/MNRAS/512/1294 HST study of star cluster in LEGUS galaxies (Hannon+, 2022)
H α morphologies of star clusters in 16 LEGUS galaxies Constraints on
H II region evolution time-scales.
Hannon S., Lee J.C., Whitmore B.C., Mobasher B., Thilker D., Chandar R.,
Adamo A., Wofford A., Orozco-Duarte R., Calzetti D., Della Bruna L.,
Kreckel K., Groves B., Barnes A.T., Boquien M., Belfiore F., Linden S.
<Mon. Not. R. Astron. Soc. 512, 1294-1316 (2022)>
=2022MNRAS.512.1294H 2022MNRAS.512.1294H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Interstellar medium ; Clusters, globular ;
Clusters, open ; Photometry, HST ; Ultraviolet ; Optical ;
H I data ; Morphology ; Positional data ; Galaxies, radius ;
Abundances ; Star Forming Region ; Stars, masses
Keywords: ISM: evolution - H II regions - galaxies: ISM -
galaxies: star clusters: general
Abstract:
The analysis of star cluster ages in tandem with the morphology of
their H II regions can provide insight into the processes that clear a
cluster's natal gas, as well as the accuracy of cluster ages and dust
reddening derived from Spectral Energy Distribution (SED) fitting. We
classify 3757 star clusters in 16 nearby galaxies according to their
Hα morphology (concentrated, partially exposed, no emission),
using Hubble Space Telescope (HST) imaging from the Legacy
ExtraGalactic Ultraviolet Survey (LEGUS). We find : (1) The mean SED
ages of clusters with concentrated (1-2 Myr) and partially exposed H
II region morphologies (2-3 Myr) indicate a relatively early onset of
gas clearing and a short (1-2 Myr) clearing time-scale. (2) The
reddening of clusters can be overestimated due to the presence of red
supergiants, which is a result of stochastic sampling of the IMF in
low mass clusters. (3) The age-reddening degeneracy impacts the
results of the SED fitting - out of 1408 clusters with M* => 5000
M☉, we find that at least 46 (3 per cent) have SED ages which
appear significantly underestimated or overestimated based on H
α and their environment, while the total percentage of poor age
estimates is expected to be several times larger. (4) Lastly, we
examine the dependence of the morphological classifications on spatial
resolution. At HST resolution, our conclusions are robust to the
distance range spanned by the sample (3-10 Mpc). However, analysis of
ground-based H α images shows that compact and partially exposed
morphologies frequently cannot be distinguished from each other.
Description:
Previous studies have examined correlations between Hα
morphology and star cluster properties, we use imaging from the Hubble
Space Telescope (HST) to study star clusters. We build upon the sample
from Hannon et al. (2019MNRAS.490.4648H 2019MNRAS.490.4648H), where this study quadruples
the number of young, massive clusters. By examining all clusters
regardless of SED age, this study may prove valuable in checking the
reliability of SED-fit ages, and obtaining new insights regarding
time-scales associated with gas clearing.
The data used in this study are taken from LEGUS (Calzetti et al.
2015AJ....149...51C 2015AJ....149...51C,
https://mast.stsci.edu/search/ui/#/hst/results?proposal_id=9796,10402,
13364 and
https://archive.stsci.edu/prepds/legus/dataproducts-public.html),
which combines WFC3 and archival ACS HST imaging to provide full
five-band NUV-U-B-V-I coverage for 50 nearby galaxies. The
LEGUS-Hα follow-up survey provides coverage of the Hα
emission-line with a narrow-band filter as well as a medium-band
filter sampling line-free continuum. General properties for our 16
selected galaxies including distance, position angle, inclination, and
diameter, are provided in table1.dat.
Then we extract cluster photometric data of the 21 galaxy fields (i.e
see section 2 for the procedure). Next, following the classification
process of Hannon et al. (2019MNRAS.490.4648H 2019MNRAS.490.4648H) (i.e see section 3). We
built Hα morphology classifications for 3815 detected star
clusters as presented in the tablea1.dat.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 61 16 General properties for our 16 LEGUS galaxies
tablea1.dat 64 3815 Hα morphology classifications for detected
star clusters in 16 LEGUS Galaxies
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See also:
VII/237 : HYPERLEDA. I. Catalog of galaxies (Paturel+, 2003)
J/ApJS/192/6 : A GALEX UV imaging survey of nearby galaxies (Lee+, 2011)
J/ApJ/889/154 : LEGUS & Ha-LEGUS obs. of NGC4449 star clusters
(Whitmore+, 2020)
J/MNRAS/498/4906 : Pressure components in the central HII regions
(Barnes+, 2020)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Field LEGUS galaxy name field (Field)
9 A1 --- n_Field Indicate the galaxies studied in Hannon
et al. 2019MNRAS.490.4648H 2019MNRAS.490.4648H
11- 17 A7 --- Mtype Morphological type as listed in
HyperLeda Makarov et al.
2014A&A...570A..13M 2014A&A...570A..13M, Cat. VII/237 (Type)
19- 23 F5.2 Mpc D Galactic distance from Calzetti et al.
2015AJ....149...51C 2015AJ....149...51C (Distance)
25- 27 I3 deg PA Position angle from Lee et al.
2011ApJS..192....6L 2011ApJS..192....6L, Cat. J/ApJS/192/6
(PositionAngle)
29- 32 F4.1 deg i Inclination angle from Lee et al.
2011ApJS..192....6L 2011ApJS..192....6L, Cat. J/ApJS/192/6
(Inclination)
34- 38 F5.2 [0.1arcmin] logD25 Apparent galactic diameter with system
at the isophote 25B-mag/arcsec2 from
HyperLeda Makarov et al.
2014A&A...570A..13M 2014A&A...570A..13M, Cat. VII/237 (D25)
40- 44 F5.3 --- Z Metallicity used to derive physical
properties as published in the LEGUS
star cluster catalogues (Z) (1)
46- 49 F4.2 Msun/yr SFR(UV) Star formation rate from Calzetti et al.
2015AJ....149...51C 2015AJ....149...51C (SFRUV)
51- 57 E7.2 Msun M* Stellar mass from Calzetti et al.
2015AJ....149...51C 2015AJ....149...51C (M*)
59- 61 I3 --- Nbr Number of clusters detected in the galaxy
and presented in the tablea1.dat
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Note (1): For NGC5457, Z = 0.02 for NGC 5457-NW1, Z = 0.008 for NGC 5457-NW2 and
NGC 5457-NW3.
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Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID Cluster object identifier number (ObjectID)
6- 13 F8.3 --- X X coordinate in the LEGUS mosaics (LEGUSX)
15- 23 F9.3 --- Y Y coordinate in the LEGUS mosaics (LEGUSY)
25- 34 F10.6 deg RAdeg Right ascension (J2000) (RA)
36- 45 F10.6 deg DEdeg Declination (J2000) (Dec)
47 I1 --- HaClass ?=0 Hα classifications (Hαclass)
(1)
49- 53 A5 --- Isolated [True False] Indicated if the cluster has
neighboring clusters within 75pc, 2077 True
and 1738 False cases (Isolated?)
55- 64 A10 --- Field LEGUS galaxy field (Field)
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Note (1): As detailed in the section 3 Hα Morphology classification, we
use the definition of each of the three Hα morphologies
introduced in Whitmore et al. (2011ApJ...729...78W 2011ApJ...729...78W) as follows:
1 = Hα class 1, concentrated where the target star cluster
has Hα emission covering it, and where there are no
discernible bubbles or areas around the cluster which lack
Hα emission, 499 objects in our sample
2 = Hα class 2, partially exposed where the Hα
surrounding the target cluster displays bubble like or
filamentary morphology covering part of the cluster, 372 objects
in our sample
3 = Hα class 3, no emission where the target cluster appears to
be clear of Hα, there is no Hα emission within ∼20pc
of the cluster. This includes those which have no visible
Hα emission in their entire 150pc wide postage stamps,
2886 objects in our sample
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 11-Mar-2025