J/ApJ/889/154 LEGUS & Ha-LEGUS obs. of NGC4449 star clusters (Whitmore+, 2020)
LEGUS and Hα-LEGUS observations of star clusters in NGC 4449:
improved ages and the fraction of light in clusters as a function of age.
Whitmore B.C., Chandar R., Lee J., Ubeda L., Adamo A., Aloisi A.,
Calzetti D., Cignoni M., Cook D., Dale D., Elmegreen B.G., Gouliermis D.,
Grebel E.K., Grasha K., Johnson K.E., Kim H., Sacchi E., Smith L.J.,
Tosi M., Wofford A.
<Astrophys. J., 889, 154 (2020)>
=2020ApJ...889..154W 2020ApJ...889..154W
ADC_Keywords: Clusters, globular; Photometry, HST; Optical; Galaxies, nearby;
Stars, ages; Stars, masses
Keywords: Galaxy stellar content ; Dwarf irregular galaxies ; Star clusters ;
Young massive clusters ; Globular star clusters
Abstract:
We present a new catalog and results for the cluster system of the
starburst galaxy NGC 4449, based on multiband imaging observations
taken as part of the LEGUS and Hα-LEGUS surveys. We improve
the spectral energy fitting method used to estimate cluster ages, and
find that the results, particularly for older clusters, are in better
agreement with those from spectroscopy. The inclusion of Hα
measurements, the role of stochasticity for low-mass clusters, the
assumptions about reddening, and the choices of SSP model and
metallicity all have important impacts on the age dating of clusters.
A comparison with ages derived from stellar color-magnitude diagrams
for partially resolved clusters shows reasonable agreement, but large
scatter in some cases. The fraction of light found in clusters
relative to the total light (i.e., TL) in the U, B, and V filters in
25 different ∼kiloparsec-size regions throughout NGC 4449 correlates
with both the specific region luminosity, RL, and the dominant age
of the underlying stellar population in each region. The observed
cluster age distribution is found to decline over time as
dN/dτ∝τγ, with γ=-0.85±0.15,
independent of cluster mass, and is consistent with strong, early
cluster disruption. The mass functions of the clusters can be
described by a power law with dN/dM∝Mβ and
β=-1.86±0.2, independent of cluster age. The mass and age
distributions are quite resilient to differences in age-dating
methods. There is tentative evidence for a factor of 2-3 enhancement
in both the star and cluster formation rate ∼100-300Myr ago,
indicating that cluster formation tracks star formation generally. The
enhancement is probably associated with an earlier interaction event.
Description:
We have selected NGC 4449, a nearby (distance=3.82Mpc) "starburst"
galaxy which is part of the LEGUS (Legacy Extragalactic UV Survey),
which has imaged 50 nearby star-forming galaxies in five broadband
filters using the Hubble Space Telescope (HST;
Calzetti+ 2015AJ....149...51C 2015AJ....149...51C). This galaxy also has narrowband
imaging that covers the Hα line (including the adjoining [NII]
lines), and is part of the Hα-LEGUS survey
(R. Chandar et al. 2020, in preparation).
NGC 4449 has been observed with three generations of cameras onboard
the HST. Figure 2 shows the coverage with the Wide Field Planetary
Camera 2 (WFPC2), Advanced Camera for Surveys (ACS), and Wide Field
Camera 3 (WFC3). In this work, we focus on the ACS and WFC3
observations. Note that many of the observations have been restricted
to the central star-forming portion of the galaxy (e.g., the WFC3
LEGUS observations, PI=Calzetti, proposal ID=13364); only the ACS
(F438W, F555W, F658N, F814W filters, PI=Aloisi, proposal ID=10585)
imaged the outer parts of the galaxy.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 183 594 Measured and derived properties of star clusters
in NGC 4449
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
II/342 : Hubble Source Catalog (V1 and V2) (Whitmore+, 2016)
J/AJ/109/960 : Young star clusters in The Antennae (Whitmore+ 1995)
J/A+AS/139/393 : Young Massive Star Clusters. II. (Larsen, 1999)
J/AJ/123/855 : Magellanic Clouds Photometric Survey: SMC (Zaritsky+, 2002)
J/AJ/127/1531 : Star formation history of SMC (Harris+, 2004)
J/AJ/138/1243 : The star formation history of the LMC (Harris+, 2009)
J/A+A/501/949 : Star cluster properties in five spiral galaxies (Mora+, 2009)
J/A+A/517/A50 : Ages & luminosities of young SMC/LMC clusters (Glatt+, 2010)
J/MNRAS/405/857 : Star clusters in NGC 3256 (Goddard+, 2010)
J/AJ/140/75 : Antennae galaxies (NGC 4038/4039) revisited (Whitmore+, 2010)
J/AJ/142/129 : HST photometry of NGC 4449 clusters (Annibali+, 2011)
J/ApJ/741/86 : XRBs and star clusters in NGC 4449 (Rangelov+, 2011)
J/ApJ/752/95 : PHAT stellar cluster survey. I. Year 1 (Johnson+, 2012)
J/ApJ/786/117 : M31 PHAT star clusters ages and masses (Fouesneau+, 2014)
J/ApJ/812/147 : Slug analysis of clusters in NGC 628 & 7793 (Krumholz+, 2015)
J/ApJ/827/33 : PHAT. XVI. Star cluster masses and ages (Johnson+, 2016)
J/ApJ/841/92 : Young massive star clusters in 2 LEGUS galaxies (Ryon+, 2017)
J/ApJ/845/56 : Star clusters automatically detected in LMC (Bitsakis+, 2017)
J/ApJ/853/104 : Ages of star clusters in SMC (Bitsakis+, 2018)
J/ApJS/235/23 : LEGUS galaxies1 observations (Sabbi+, 2018)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/595] Cluster id (1)
5- 12 F8.2 pix Xpix x coordinate
14- 21 F8.2 pix Ypix y coordinate
23- 34 F12.8 deg RAdeg [186.9/187.2] Right Ascension (J2000)
36- 46 F11.8 deg DEdeg [44/44.2] Declination (J2000)
48- 53 F6.3 mag F275Wmag [16/27]?=99.999 HST/WFC3 F275W magnitude (2)
55- 60 F6.3 mag e_F275Wmag [0.002/2.4]?=99.999 HST/WFC3 F275W error (2)
62- 67 F6.3 mag F336Wmag [16.4/25.5]?=99.999 HST/WFC3 F336W magnitude (2)
69- 74 F6.3 mag e_F336Wmag [0.002/0.3]?=99.999 HST/WFC3 F336W error (2)
76- 81 F6.3 mag F435Wmag [17.4/26.1]?=99.999 HST/ACS F435W magnitude (2)
83- 87 F5.3 mag e_F435Wmag [0.002/0.2]?=99.999 HST/ACS F435W error (2)
89- 94 F6.3 mag F555Wmag [17.18/25.2]?=99.999 HST/ACS F555W magnitude (2)
96-100 F5.3 mag e_F555Wmag [0.002/0.2]?=99.999 HST/ACS F555W error (2)
102-107 F6.3 mag F658Nmag [15.88/27.5]?=99.999 HST/ACS F658N magnitude (2)
109-114 F6.3 mag e_F658Nmag [0.001/10.2]?=99.999 HST/ACS F658N error (2)
116-121 F6.3 mag F814Wmag [16.3/24.4]?=99.999 HST/ACS F814W magnitude (2)
123-127 F5.3 mag e_F814Wmag [0.002/0.3]?=99.999 HST/ACS F814W error (2)
129-132 F4.2 mag CI [1.2/2.5] F555W Color Index (3)
134 I1 --- Nf [3/6] Number of filters
136 I1 --- Cat [1/3] Cluster category (4)
138 I1 --- Q [0/2] Quality: 1 = good, 2 = poor
140 I1 --- Morph [0/4] Ha morphology (5)
142-146 F5.2 [yr] logAge [6.4/10.3] log Age from Halpha-LEGUS (6)
148-155 F8.1 Msun Mass [162/896006] Mass from Halpha-LEGUS (6)
157-160 F4.2 mag E(B-V) [0/0.62] E(B-V) Halpha-LEGUS (6)
162-166 F5.2 [yr] logAgev1 [6/10.2] log Age from LEGUS, version 1 (7)
168-176 F9.1 Msun Massv1 [93.6/6.6e+6] Mass from LEGUS, version 1 (7)
178-181 F4.2 mag E(B-V)v1 [0/1.1] E(B-V) from LEGUS, version 1 (7)
183 I1 --- Add [0/1]? Added clusters (8)
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Note (1): Object 2 has been removed because it was discovered to be
a duplicate and removed, without renumbering.
Clusters are <[WCL2020] NGC 4449 NNN> in Simbad.
Note (2): Photometry in this file was measured in a 5 pixel aperture radius
& converted to the Vega system (zeropoints taken from the STScI
webpage). No correction for foreground extinction or aperture correction
is included.
Note (3): CI=mag(1px)-mag(3px) measured in the F555W frame.
Note (4): Cluster category as follows:
1 = symetric cluster (120 occurrences);
2 = asymetric cluster (261 occurrences);
3 = compact association (213 occurrences).
Note (5): Ha morphology (see Section 2.1) as follows:
1 = right on top;
2 = ring or clearly associated;
3 = possibly associated;
4 = no Hα.
Note (6): For the recommended Halpha-LEGUS age/mass estimates (described in
the text), we assume a distance modulus of 28.17mag (4.31Mpc) to
NGC4449; mass results assume an average aperture correction of -0.87mag.
Note (7): We include the current best-fit values of age, mass, and E(B-V)
from the LEGUS project as well, but these may change with subsequent
catalog releases.
Note (8): Added clusters as follows:
0 = in original catalog,
1 = added (See Section 2.1).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Jul-2021