J/ApJ/909/192 HST/ACS photometry of Eridanus II (Gallart+, 2021)
The star formation history of Eridanus II: on the role of supernova feedback in
the quenching of ultrafaint dwarf galaxies.
Gallart C., Monelli M., Ruiz-Lara T., Calamida A., Cassisi S., Cignoni M.,
Anderson J., Battaglia G., Bermejo-Climent J.R., Bernard E.J.,
Martinez-Vazquez C.E., Mayer L., Salvadori S., Monachesi A., Navarro J.F.,
Shen S., Surot F., Tosi M., Bajaj V., Strinfellow G.S.
<Astrophys. J., 909, 192 (2021)>
=2021ApJ...909..192G 2021ApJ...909..192G
ADC_Keywords: Galaxies, photometry; Photometry, HST; Photometry, UBVRI
Keywords: Dwarf galaxies ; Galaxy evolution ; Galaxy formation ;
Galaxy quenching ; Local Group
Abstract:
Eridanus II (Eri II) is an ultrafaint dwarf (UFD) galaxy (MV=-7.1)
located at a distance close to the Milky Way virial radius. Early
shallow color-magnitude diagrams (CMDs) indicated that it possibly
hosted an intermediate-age or even young stellar population, which is
unusual for a galaxy of this mass. In this paper, we present new
Hubble Space Telescope/Advanced Camera for Surveys CMDs reaching the
oldest main-sequence turnoff with excellent photometric precision and
derive a precise star formation history (SFH) for this galaxy through
CMD fitting. This SFH shows that the bulk of the stellar mass in EriII
formed in an extremely short star formation burst at the earliest
possible time. The derived star formation rate profile has a width at
half maximum of 500Myr and reaches a value compatible with null star
formation 13Gyr ago. However, tests with mock stellar populations and
with the CMD of the globular cluster M92 indicate that the star
formation period could be shorter than 100Myr. From the quantitative
determination of the amount of mass turned into stars in this early
star formation burst (∼2x105M☉) we infer the number of
supernova (SN) events and the corresponding energy injected into the
interstellar medium. For reasonable estimates of the Eri II virial
mass and values of the coupling efficiency of the SN energy, we
conclude that Eri II could be quenched by SN feedback alone, thus
casting doubts on the need to invoke cosmic reionization as the
preferred explanation for the early quenching of old UFD galaxies.
Description:
Deep photometric data for Eri II were obtained with the ACS/WFC aboard
the HST under program P.ID. 14224 (Cycle 23, P.I. C. Gallart).
Under this program, the galaxy was observed during six orbits,
organized in two visits of three orbits each. Short and long exposures
were taken in order to increase the dynamical range of our CMD. The
total exposure time was 7644s in F475W and 7900s in F814W.
Another ACS/WFC program was devoted to imaging the same galaxy in
cycle 23. GO program 14234 (P.I. J. Simon) used 13 orbits to observe
the central region of Eri II. A total of 10 and 16 exposures were
collected in the F606W and F814W bands, respectively, with individual
exposure times ranging from 1220 to 1390s. The total integration time
was 12830 and 20680s, respectively.
Objects:
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RA (ICRS) DE Designation(s)
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03 44 21.1 -43 32 00 Eri II = NAME Eridanus II
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig2.dat 86 19871 ACS/WFC F475W/F606W/F814W photometry of Eridanus II
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/ApJ/756/108 : HST VI phot. of variable stars in Leo T (Clementini+, 2012)
J/ApJ/812/158 : Leo P RR Lyrae candidates & cumulative SFH (McQuinn+, 2015)
J/A+A/635/A107 : Spectroscopy of the Eri 2 cluster (Zoutendijk+, 2020)
J/MNRAS/479/4136 : Morphological properties of galaxies (Karachentsev+, 2018)
J/ApJ/908/18 : HST stellar photometry of Eridanus II (Simon+, 2021)
Byte-by-byte Description of file: fig2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [1/19871] Sequential running number
7- 13 F7.3 mag F475W [20.1/31.1]?=100 ACS/WFC F475W band magnitude
15- 20 F6.4 mag e_F475W [0.0035/1.8]?=9.9999 Uncertainty in F475W
22- 28 F7.3 mag F606W [19.53/30.5]?=100 ACS/WFC F606W band magnitude
30- 35 F6.4 mag e_F606W [0.0036/1.4]?=9.9999 Uncertainty in F606W
37- 42 F6.3 mag F814W [17.38/30.4] ACS/WFC F814W band magnitude
44- 49 F6.4 mag e_F814W [0.0038/1] Uncertainty in F814W
51- 57 F7.4 --- chi [0.46/12] DAOPHOT IV/ALLFRAME chi parameter
59- 65 F7.4 --- sharp [-0.1/0.1] DAOPHOT IV/ALLFRAME sharp parameter
67- 75 F9.6 deg RAdeg [56/56.15] Right Ascension (ICRS)
77- 86 F10.6 deg DEdeg [-43.6/-43.49] Declination (ICRS)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Aug-2022