A1 Refereed original research article in a scientific journal
The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. IV. The Star Formation History of Andromeda VII Derived from Long-period Variable Stars
Authors: Navabi Mahdieh, Saremi Elham, Javadi Atefeh, Noori Majedeh, van Loon Jacco T, Khosroshahi Habib G, McDonald Iain, Alizadeh Mina, Danesh Arash, Gozaliasl Ghassem, Molaeinezhad Alireza, Parto Tahere, Raouf Mojtaba
Publisher: IOP PUBLISHING LTD
Publication year: 2021
Journal: Astrophysical Journal
Journal name in source: ASTROPHYSICAL JOURNAL
Journal acronym: ASTROPHYS J
Article number: ARTN 127
Volume: 910
Issue: 2
Number of pages: 16
ISSN: 0004-637X
eISSN: 1538-4357
DOI: https://doi.org/10.3847/1538-4357/abdec1
Abstract
We have examined the star formation history (SFH) of Andromeda VII (And
VII), the brightest and most massive dwarf spheroidal (dSph) satellite
of the Andromeda galaxy (M31). Although M31 is surrounded by several
dSph companions with old stellar populations and low metallicity, it has
a metal-rich stellar halo with an age of 6–8 Gyr. This indicates that
any evolutionary association between the stellar halo of M31 and its
dSph system is frail. Therefore, the question is whether And VII (a
high-metallicity dSph located ~220 kpc from M31) can be associated with
M31's young, metal-rich halo. Here we perform the first reconstruction
of the SFH of And VII employing long-period variable (LPV) stars. As the
most evolved asymptotic giant branch and red supergiant stars, the
birth mass of LPVs can be determined by connecting their near-infrared
photometry to theoretical evolutionary tracks. We found 55 LPV
candidates within two half-light radii, using multiepoch imaging with
the Isaac Newton Telescope in the i and V bands. Based on
their birth mass function, the star formation rate (SFR) of And VII was
obtained as a function of cosmic time. The main epoch of star formation
occurred
6.2 Gyr ago with an SFR of 0.006 ± 0.002 M⊙ yr−1. Over the past 6 Gyr, we find slow star formation, which continued until 500 Myr ago with an SFR ~ 0.0005 ± 0.0002 M⊙ yr−1. We determined And VII's stellar mass M = (13.3 ± 5.3) × 106 M⊙ within a half-light radius 
and metallicity Z = 0.0007, and we also derived its distance modulus of μ = 24.38 mag.
We have examined the star formation history (SFH) of Andromeda VII (And
VII), the brightest and most massive dwarf spheroidal (dSph) satellite
of the Andromeda galaxy (M31). Although M31 is surrounded by several
dSph companions with old stellar populations and low metallicity, it has
a metal-rich stellar halo with an age of 6–8 Gyr. This indicates that
any evolutionary association between the stellar halo of M31 and its
dSph system is frail. Therefore, the question is whether And VII (a
high-metallicity dSph located ~220 kpc from M31) can be associated with
M31's young, metal-rich halo. Here we perform the first reconstruction
of the SFH of And VII employing long-period variable (LPV) stars. As the
most evolved asymptotic giant branch and red supergiant stars, the
birth mass of LPVs can be determined by connecting their near-infrared
photometry to theoretical evolutionary tracks. We found 55 LPV
candidates within two half-light radii, using multiepoch imaging with
the Isaac Newton Telescope in the i and V bands. Based on
their birth mass function, the star formation rate (SFR) of And VII was
obtained as a function of cosmic time. The main epoch of star formation
occurred
6.2 Gyr ago with an SFR of 0.006 ± 0.002 M⊙ yr−1. Over the past 6 Gyr, we find slow star formation, which continued until 500 Myr ago with an SFR ~ 0.0005 ± 0.0002 M⊙ yr−1. We determined And VII's stellar mass M = (13.3 ± 5.3) × 106 M⊙ within a half-light radius and metallicity Z = 0.0007, and we also derived its distance modulus of μ = 24.38 mag.
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