Abstract
NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda galaxy (M 31). With similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? We present the first reconstruction of the star formation histories of NGC 147 and NGC 185 using long-period variable stars (LPVs). LPVs are low- to intermediate-mass stars at the asymptotic giant branch, which their luminosity is related to their birth mass. Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC 185 we found that the main epoch of star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate. In the case of NGC 147, the star formation rate peaked only 7 Gyr ago, staying intense until ∼ 3 Gyr ago, but no star formation has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has evolved more slowly than NGC 185 initially, but more dramatically in more recent times.
Highlights
Dwarf galaxies are the most abundant type of galaxies in the universe; since they come in two main flavors: dwarf Irregulars and dwarf Spheroidal/Ellipticals
We have developed a novel method to use Long-Period Variable stars (LPVs) to reconstruct the Star Formation History (SFH) [4,5,6,7]
Max min fIMF(m)m dm m(t+dt) m(t) dm dn (t) δt where fIMF is the initial mass function, dn (t) and δt are a statement of numbers of LPVs and pulsation duration respectively
Summary
Dwarf galaxies are the most abundant type of galaxies in the universe; since they come in two main flavors: dwarf Irregulars (dIrrs) and dwarf Spheroidal/Ellipticals (dSph/dEs). The Star Formation History (SFH) is of the most important tracers of the galaxies’ evolution. We have developed a novel method to use Long-Period Variable stars (LPVs) to reconstruct the SFH [4,5,6,7].
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