J/ApJ/954/211 HST/WFC3 obs. of the Fireworks galaxy (NGC 6946) (Tran+, 2023)
Spatially resolved recent star formation history in NGC 6946.
Tran D., Williams B., Levesque E., Lazzarini M., Dalcanton J., Dolphin A.,
Koplitz B., Smercina A., Telford O.G.
<Astrophys. J., 954, 211 (2023)>
=2023ApJ...954..211T 2023ApJ...954..211T
ADC_Keywords: Galaxies, photometry; Photometry, HST; Ultraviolet; Optical
Keywords: Star formation ; Spiral galaxies ; Galaxy evolution ;
Stellar populations
Abstract:
The nearby face-on star-forming spiral galaxy NGC 6946 is known as the
Fireworks Galaxy due to its hosting an unusually large number of
supernovae. We analyze its resolved near-ultraviolet stellar
photometry measured from images taken with the Hubble Space
Telescope's Wide Field Camera 3 with the F275W and F336W filters. We
model the color-magnitude diagrams of the UV photometry to derive the
spatially resolved star formation history of NGC 6946 over the last
25Myr. From this analysis, we produce maps of the spatial distribution
of the young stellar population and measure the total recent star
formation rate (SFR) of nearly the entire young stellar disk. We find
the global SFR(age≤25Myr)=13.17-0.79+0.91M☉/yr. Over this
period, the SFR is initially very high (23.39-2.11+2.43M☉/yr
16-25Myr ago), then monotonically decreases to
5.31-0.17+0.19M☉/yr in the last 10Myr. This decrease in
global SFR over the last 25Myr is consistent with measurements made
with other SFR indicators. We discuss in detail two of the most active
regions of the galaxy, which we find are responsible for 3% and 5% of
the total star formation over the past 6.3Myr.
Description:
Observations for this program (GO-15877; PI: Levesque+ 2019hst..prop15877L)
were obtained between 2020 May 11 and 2021 November 21 using HST's
WFC3 ultraviolet-visible (UVIS) channel in filters F275W and F336W.
NGC 6946 was imaged in a 4x4 grid excluding the northernmost and
southernmost regions (Figure 1). This covers all of the UV-bright
regions and the locations of observed core-collapse supernovae (ccSN).
Using the high-quality photometry, we crossmatched our stellar catalog
to Gaia Data Release 2 (see I/345; superseded by I/355);
The photometric catalog (FUVS cat.) used in this paper can also be
found as a high-level science product in MAST (the Mikulski Archive
for Space Telescopes) via doi:10.17909/gveq-8820.
see Section 2.2.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
20 34 52.33 +60 09 13.2 NGC 6946 = UGC 11597
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 326 2638 Star formation rates (SFRs) over time
fuvscat.dat 290 669012 *The Fireworks Ultraviolet Survey (FUVS) photometric
catalog
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Note on fuvscat.dat: This catalog, prepared using the DOLPHOT package
(Dolphin 2000PASP..112.1383D 2000PASP..112.1383D ; 2016, http://ascl.net/1608.013), are
based on the reduced, calibrated, stacked, and mosaiced images of
NGC6946 (the Fireworks Galaxy) acquired with HST UVIS WFC3 (GO-15877;
PI Levesque). The catalog contains F336W and F275W photometry in the
Vega magnitude system. Each of the 14 fields were aligned with the
astrometric coordinate system from Gaia DR2 and thus the Gaia source
IDs of sources matched to Gaia are provided. Additionally, sources
that are likely foreground based on color are also flagged.
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/127/1531 : Star formation history of SMC (Harris+, 2004)
J/ApJS/173/185 : GALEX UV atlas of nearby galaxies (Gil de Paz+, 2007)
J/AJ/138/1243 : The star formation history of the LMC (Harris+, 2009)
J/A+A/537/A146 : Stellar models with rot. 0.8<M<120 (Ekstrom+, 2012)
J/other/Sci/337.444 : RV curves of Galactic massive O stars (Sana+, 2012)
J/A+A/545/A43 : HII regions in NGC 628 and NGC 6946 (Cedres+, 2012)
J/A+A/552/A19 : Radio-farIR correlation in NGC 6946 (Tabatabaei+, 2013)
J/ApJ/795/170 : Sample SNRs for M31 and M33 (Jennings+, 2014)
J/ApJS/215/9 : PHAT X. UV-IR photometry of M31 stars (Williams+, 2014)
J/A+A/601/A146 : M33 Mol. Clds & young stellar clusters (Corbelli+, 2017)
J/ApJ/915/92 : SOFIA CII and NII obs. of M101 and NGC6946 (Tarantino+, 2021)
J/ApJ/916/58 : HST obs. of supernova remnants in NGC6946 (Koplitz+, 2021)
J/ApJ/945/108 : Red supergiants from HST, Spitzer and Gaia (Johnson+, 2023)
J/A+A/694/A87 : NGC 3627, NGC 4321 & NGC 6946 [CII] mapping (Kovacic+, 2025)
http://archive.stsci.edu/hlsp/fuvs/ : The Fireworks Ultraviolet Survey (FUVS)
on MAST
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Index [0/2637] Grid index number
6- 17 F12.8 deg RA-NE [308.4/309.2] NE component Right
Ascension (J2000)
19- 29 F11.8 deg DE-NE [60/60.4] NE component Declination (J2000)
31- 42 F12.8 deg RA-NW [308.2/309] NW component Right Ascension
(J2000)
44- 54 F11.8 deg DE-NW [60/60.4] NW component Declination (J2000)
56- 67 F12.8 deg RA-SW [308.4/309.2] SW component Right
Ascension (J2000)
69- 79 F11.8 deg DE-SW [59.9/60.3] SW component Declination
(J2000)
81- 92 F12.8 deg RA-SE [308.2/309] SE component Right Ascension
(J2000)
94- 104 F11.8 deg DE-SE [59.9/60.3] SE component Declination
(J2000)
106- 108 I3 --- N [0/200] Number of stars
110- 117 F8.1 arcsec2 Area [10/165690] Grid size
119- 125 F7.5 Msun/yr SFR0-6.7 [0/0.05] Adjusted 0-6.7 star formation
rate
127- 133 F7.5 Msun/yr e_SFR0-6.7 [0/0.06] Lower uncertainty in SFR0-6.7
135- 141 F7.5 Msun/yr E_SFR0-6.7 [0/0.07] Upper uncertainty in SFR0-6.7
143- 149 F7.5 Msun/yr SFR6.7-6.8 [0/0.1] 6.7-6.8 star formation rate
151- 157 F7.5 Msun/yr e_SFR6.7-6.8 [0/0.07] Lower uncertainty in SFR6.7-6.8
159- 165 F7.5 Msun/yr E_SFR6.7-6.8 [0/0.05] Upper uncertainty in SFR6.7-6.8
167- 173 F7.5 Msun/yr SFR6.8-6.9 [0/0.11] 6.8-6.9 star formation rate
175- 181 F7.5 Msun/yr e_SFR6.8-6.9 [0/0.1] Lower uncertainty in SFR6.8-6.9
183- 189 F7.5 Msun/yr E_SFR6.8-6.9 [0/0.1] Upper uncertainty in SFR6.8-6.9
191- 197 F7.5 Msun/yr SFR6.9-7.0 [0/0.1] 6.9-7.0 star formation rate
199- 205 F7.5 Msun/yr e_SFR6.9-7.0 [0/0.1] Lower uncertainty in SFR6.9-7.0
207- 213 F7.5 Msun/yr E_SFR6.9-7.0 [0/0.1] Upper uncertainty in SFR6.9-7.0
215- 221 F7.5 Msun/yr SFR7.0-7.1 [0/0.2] 7.0-7.1 star formation rate
223- 229 F7.5 Msun/yr e_SFR7.0-7.1 [0/0.2] Lower uncertainty in SFR7.0-7.1
231- 237 F7.5 Msun/yr E_SFR7.0-7.1 [0/0.1] Upper uncertainty in SFR7.0-7.1
239- 245 F7.5 Msun/yr SFR7.1-7.2 [0/0.3] 7.1-7.2 star formation rate
247- 253 F7.5 Msun/yr e_SFR7.1-7.2 [0/0.2] Lower uncertainty in SFR7.1-7.2
255- 261 F7.5 Msun/yr E_SFR7.1-7.2 [0/0.2] Upper uncertainty in SFR7.1-7.2
263- 269 F7.5 Msun/yr SFR7.2-7.3 [0/1.6] 7.2-7.3 star formation rate
271- 277 F7.5 Msun/yr e_SFR7.2-7.3 [0/1.5] Lower uncertainty in SFR7.2-7.3
279- 285 F7.5 Msun/yr E_SFR7.2-7.3 [0/0.3] Upper uncertainty in SFR7.2-7.3
287- 293 F7.5 Msun/yr SFR7.3-7.4 [0/1] 7.3-7.4 star formation rate
295- 301 F7.5 Msun/yr e_SFR7.3-7.4 [0/0.9] Lower uncertainty in SFR7.3-7.4
303- 309 F7.5 Msun/yr E_SFR7.3-7.4 [0/1] Upper uncertainty in SFR7.3-7.4
311- 314 F4.2 mag Av [0/1.5] V band extinction
316- 319 F4.2 mag dAv [0/2.5] Differential V band extinction
321- 324 F4.1 Myr Age [4/22]? Mean age
326 A1 --- Reg Region? (1)
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Note (1): Code as follows:
h = Hodge Complex
t = Tip of NE spiral arm
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Byte-by-byte Description of file: fuvscat.dat
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Bytes Format Units Label Explanations
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1- 18 F18.14 deg RAdeg [308.48/309] Right ascension (J2000)
20- 37 F18.15 deg DEdeg [60/60.3] Declination (J2000)
39- 56 F18.15 mag F275Wmag [17.71/41.4] HST/WFC3 F275W band magnitude
58- 75 F18.16 mag e_F275Wmag [0.003/9.99] Uncertainty in F275Wmag
77- 94 F18.15 mag F336Wmag [16/39.2] HST/WFC3 F336W band magnitude
96- 113 F18.16 mag e_F336Wmag [0.002/9.99] Uncertainty in F336Wmag
115- 134 F20.16 --- SNR275 [-0.1/331] Signal-to-noise ratio in F275W
136- 155 F20.16 --- SNR336 [-0.1/698.6] Signal-to-noise ratio in F336W
157- 174 F18.16 mag Crowd275 [0/9.93] Crowding, WFC3_F275W
176- 193 F18.16 mag Crowd336 [0/9.98] Crowding, WFC3_F336W
195- 216 E22.17 --- Sharp275 [-9.999/9.999] Sharpness, WFC3_F275W
218- 236 F19.16 --- Sharp336 [-9.999/9.999] Sharpness, WFC3_F336W
238- 242 F5.2 --- Chi275 [0.34/89.9] Chi, WFC3_F275W
244- 248 F5.2 --- Chi336 [0.37/83.5] Chi, WFC3_F336W
250- 255 F6.3 --- Round275 [-9.999/9.999] Roundness, WFC3_F275W
257- 262 F6.3 --- Round336 [-9.999/9.999] Roundness, WFC3_F336W
264 I1 --- qf1 [0/1] Quality flag (1=high quality: SNR>4,
Crowding<0.7, sharpness2<0.2)
266 I1 --- fgd [0/1]? Foreground star flag (1)
268 I1 --- Match [0/1] Gaia DR2 flag (1=matched to Gaia source;
237 occurrences)
270- 288 I19 --- Gaia ?=0 Gaia DR2 identifier
290 I1 --- Blend [0/1] Blend flag (1=likely blend based on
F336W magnitude; 91 occurrences)
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Note (1): Flag as follows:
1 = likely foreground based on color (688 occurrences)
0 = likely not foreground
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History:
From electronic version of the journal for Table 3
* Photometric catalog downloaded at: doi:10.17909/gveq-8820 (via MAST)
Licences: cc-by
* The HLSP data products are licensed for use under CC BY 4.0 --
Please cite this paper and doi:10.17909/gveq-8820 (on MAST) if you use
these data.
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 15-Oct-2025