J/ApJ/920/105 117 star clusters in poststarburst galaxy S12 (Chandar+, 2021) ================================================================================ The Star Formation History of a Post-starburst Galaxy Determined from Its Cluster Population. Chandar R., Mok A., French K.D., Smercina A., Smith J.-D.T. =2021ApJ...920..105C ================================================================================ ADC_Keywords: Galaxies; Clusters, open; Photometry, UBVRI Keywords: Galaxy formation Abstract: The recent star formation histories (SFHs) of post-starburst galaxies have been determined almost exclusively from detailed modeling of their composite starlight. This has provided important but limited information on the number, strength, and duration of bursts of star formation. In this work, we present a direct and independent measure of the recent SFH of the post-starburst galaxy S12 (plate-mjd-fiber for SDSS623-52051-207; designated EAS12 in Smercina et al.) from its star cluster population. We detect clusters from high-resolution, UBR optical images taken with the Hubble Space Telescope and compare their luminosities and colors with stellar population models to estimate the ages and masses of the clusters. No clusters younger than ~70Myr are found, indicating star formation shut off at this time. Clusters formed ~120Myr ago reach masses up to a ~fewx107M{sun}, several times higher than similar-age counterparts formed in actively merging galaxies like the Antennae and NGC3256. We develop a new calibration based on known properties for eight nearby galaxies to estimate the star formation rate (SFR) of a galaxy from the mass of the most massive cluster, Mmax. The cluster population indicates that S12 experienced an extremely intense but short-lived burst ~120Myr ago, with an estimated peak of 500_-250_^+500^M{sun}/yr and duration of 50{+/-}25Myr, one of the highest SFRs estimated for any galaxy in the modern universe. The cluster population also allows us to fill in more of the backstory of S12. Prior to the recent, intense burst, S12 was forming stars at a moderate rate of ~3-5M{sun}/yr, typical of spiral galaxies, but the system experienced an earlier burst at some point, approximately 1-3Gyr ago. While fairly uncertain, we estimate that the SFR during this earlier burst was ~20-30M{sun}/yr, similar to the current SFR in the Antennae and NGC3256. Description: We downloaded the reduced WFC3/UVIS images in the U, B, and R bands from the Hubble Legacy Archive, which corrects each exposure for dark current and bias, then flat-fields and drizzles them together through the standard WFC3 pipeline to a scale of 0.04"/pix. Objects: ------------------------------------------------------------------------ RA (ICRS) DE Designation(s) ------------------------------------------------------------------------ 16 13 32.22 +51 03 43.0 SDSS 6316-56483-722 = 2MASX J16133219+5103436 16 13 30.18 +51 03 35.6 SDSS 623-52051-207 = 2MASX J16133017+5103356 ------------------------------------------------------------------------ File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 66 117 *Catalog of Star Clusters in Poststarburst Galaxy S12 -------------------------------------------------------------------------------- Note on table2.dat : plate-mjd-fiber for SDSS 623-52051-207 from Smercina+, 2018ApJ...855...51S as designated EAS12 in Decker French+, 2015ApJ...801....1D. -------------------------------------------------------------------------------- See also: VII/195 : Globular Clusters in the Milky Way (Harris, 1996) VII/202 : Globular Clusters in the Milky Way (Harris, 1997) J/AJ/138/1243 : The star formation history of the LMC (Harris+, 2009) J/AJ/140/75 : Antennae galaxies (NGC 4038/4039) revisited (Whitmore+, 2010) J/ApJ/741/86 : XRBs and star clusters in NGC 4449 (Rangelov+, 2011) J/ApJ/826/32 : HST observations of star clusters in NGC 3256 (Mulia+, 2016) J/ApJ/862/2 : Post-starburst galaxy ages from SDSS (French+, 2018) J/ApJ/889/154 : LEGUS & Ha-LEGUS obs of NGC4449 star clusters (Whitmore+, 2020) http://hla.stsci.edu/ : Hubble Legacy Archive Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- Seq [1/117] Sequential Source ID 5- 14 F10.6 deg RAdeg [243/244] Right Ascension (J2000) 16- 25 F10.7 deg DEdeg [51/52] Declination (J2000) 27- 34 F8.3 mag Umag [20.2/30.6]?=-999.000 WFPC3 HST/UVIS F336W Vega-calibrated magnitude (1) 36- 40 F5.3 mag e_Umag [0.01/0.7] Uncertainty in Umag 42- 47 F6.3 mag Bmag [20.7/30.4] WFPC3 HST/UVIS F438W Vega-calibrated magnitude (1) 49- 53 F5.3 mag e_Bmag [0.01/0.2] Uncertainty in Bmag 55- 60 F6.3 mag Rmag [20.3/27.3] WFPC3 HST/UVIS F625W Vega-calibrated magnitude (1) 62- 66 F5.3 mag e_Rmag [0.009/0.05] Uncertainty in Rmag -------------------------------------------------------------------------------- Note (1): Instrumental magnitudes are converted to the VEGAMAG system by applying the following zeropoints from the WFC3 data handbook to our measured photometry: 23.46 (U), 24.98 (B), and 25.37 (R) mag. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Coralie Fix [CDS], 13-Feb-2024