J/ApJ/944/43 HST/ACS stellar photometry for Reticulum II (Simon+, 2023)
Timing the r-process enrichment of the ultra-faint dwarf galaxy Reticulum II.
Simon J.D., Brown T.M., Mutlu-Pakdil B., Ji A.P., Drlica-Wagner A.,
Avila R.J., Martinez-Vazquez C.E., Li T.S., Balbinot E., Bechtol K.,
Frebel A., Geha M., Hansen T.T., James D.J., Pace A.B., Aguena M.,
Alves O., Andrade-Oliveira F., Annis J., Bacon D., Bertin E., Brooks D.,
Burke D.L., Rosell A.C., Kind M.C., Carretero J., Costanzi M.,
da Costa L.N., De Vicente J., Desai S., Doel P., Everett S., Ferrero I.,
Frieman J., Garcia-Bellido J., Gatti M., Gerdes D.W., Gruen D.,
Gruendl R.A., Gschwend J., Gutierrez G., Hinton S.R., Hollowood D.L.,
Honscheid K., Kuehn K., Kuropatkin N., Marshall J.L., Mena-Fernandez J.,
Miquel R., Palmese A., Paz-Chinchon F., Pereira M.E.S., Pieres A.,
Malagon A.A.P., Raveri M., Rodriguez-Monroy M., Sanchez E., Santiago B.,
Scarpine V., Sevilla-Noarbe I., Smith M., Suchyta E., Swanson M.E.C.,
Tarle G., To C., Vincenzi M., Weaverdyck N., Wilkinson R.D.
<Astrophys. J., 944, 43 (2023)>
=2023ApJ...944...43S 2023ApJ...944...43S
ADC_Keywords: Galaxies, photometry; Local group ; Photometry, HST; Optical
Keywords: Dwarf galaxies ; Local Group ; Stellar populations ; Galaxy ages ;
HST photometry ; Nucleosynthesis ; R-process
Abstract:
The ultra-faint dwarf galaxy Reticulum II (Ret II) exhibits a unique
chemical evolution history, with 72-12+10% of its stars strongly
enhanced in r-process elements. We present deep Hubble Space Telescope
photometry of Ret II and analyze its star formation history. As in
other ultra-faint dwarfs, the color-magnitude diagram is best fit by a
model consisting of two bursts of star formation. If we assume that
the bursts were instantaneous, then the older burst occurred around
the epoch of reionization, forming ∼80% of the stars in the galaxy,
while the remainder of the stars formed ∼3Gyr later. When the bursts
are allowed to have nonzero durations, we obtain slightly better fits.
The best-fitting model in this case consists of two bursts beginning
before reionization, with approximately half the stars formed in a
short (100Myr) burst and the other half in a more extended period
lasting 2.6Gyr. Considering the full set of viable star formation
history models, we find that 28% of the stars formed within
500±200Myr of the onset of star formation. The combination of the
star formation history and the prevalence of r-process-enhanced stars
demonstrates that the r-process elements in Ret II must have been
synthesized early in its initial star-forming phase. We therefore
constrain the delay time between the formation of the first stars in
Ret II and the r-process nucleosynthesis to be less than 500Myr. This
measurement rules out an r-process source with a delay time of several
Gyr or more, such as GW170817.
Description:
We obtained a 12-tile mosaic of Ret II with the Wide Field Channel of
the Advanced Camera for Surveys (ACS) on HST, through program GO-14766
(PI: Simon). The observations were carried out between 2016 November 9
and 2016 November 26.
Each mosaic tile was observed for a single orbit, consisting of two
F606W exposures and two F814W exposures, with total integration times
of 980s in F606W and 1140s in F814W.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
03 35 42.10 -54 02 56.9 Ret II = NAME Reticulum II
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 52 17947 Ret II stellar photometry
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See also:
J/AJ/129/2714 : JHK photometry of M92 variable stars (Del Principe+, 2005)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/ApJ/778/149 : Abundances for 3 stars in Sgr dSph (McWilliam+, 2013)
J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/802/93 : Abundance analysis of 5 stars in Sculptor (Simon+, 2015)
J/ApJ/830/93 : Abund. of the Ret II brightest red giant members (Ji+, 2016)
J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
J/AJ/151/82 : The 4 brightest red giants in Ret 2 (Roederer+, 2016)
J/ApJ/838/44 : Abund. of the brightest member of Tuc III (Hansen+, 2017)
J/ApJ/850/137 : ISLAndS project. III. Var. stars (Martinez-Vazquez+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/ApJ/863/25 : Deep Magellan obs. of 4 MW satellites (Mutlu-Pakdil+, 2018)
J/ApJ/882/40 : Lanthanide fraction in metal-poor stars (Ji+, 2019)
J/ApJ/882/177 : Abundances of 4 member stars of Tucana III (Marshall+, 2019)
J/ApJ/885/53 : Sp. & HST phot. of galaxy Leo V (Mutlu-Pakdil+, 2019)
J/ApJ/903/88 : Ions individual abund. in LAMOST J1109+0754 (Mardini+, 2020)
J/MNRAS/499/4040 : RR Lyrae pop. in the Draco dwarf galaxy (Muraveva+, 2020)
J/ApJ/902/106 : HST Gaia data of Hercules dwarf gal. (Mutlu-Pakdil+, 2020)
J/ApJ/906/96 : Dwarfs gal. in DC Justice League Simul. (Applebaum+, 2021)
J/AJ/162/229 : 13 Magellanic Clouds metal-poor stars (Reggiani+, 2021)
J/ApJ/908/18 : HST stellar photometry of Eridanus II (Simon+, 2021)
J/A+A/657/A54 : Local Group Gaia eDR3 systemic motions (Battaglia+, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [1/17947] Stellar index number
7- 15 F9.6 deg RAdeg [53.68/54.2] Right Ascension (J2000) (1)
17- 26 F10.6 deg DEdeg [-54.2/-53.9] Declination (J2000) (1)
28- 33 F6.3 mag F606mag [18.34/28.64] HST/ACS F606W band apparent
magnitude (STMAG system)
35- 39 F5.3 mag e_F606mag [0.001/0.3] Uncertainty in F606mag
41- 46 F6.3 mag F814mag [19/28.91] HST/ACS F814W band apparent
magnitude (STMAG system)
48- 52 F5.3 mag e_F814mag [0.001/0.3] Uncertainty in F814mag
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Note (1): Astrometry is calibrated to Gaia DR3
(Gaia Collaboration+ 2023A&A...674A...1G 2023A&A...674A...1G; see I/355).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Jan-2025