A PAndAS view of M31 dwarf elliptical satellites: NGC147 and NGC185

Abstract

We exploit data from the Pan-Andromeda Archaeological Survey (PAndAS) to study the extended structures of M31's dwarf elliptical companions, NGC147 and NGC185. Our wide-field, homogeneous photometry allows to construct deep colour-magnitude diagrams (CMDs) which reach down to $\sim 3$ mag below the red giant branch (RGB) tip. We trace the stellar components of the galaxies to surface brightness of ${\mu }_g\sim 32$ mag arcsec${}^{-2}$ and show they have much larger extents ($\sim 5$ kpc radii) than previously recognised. While NGC185 retains a regular shape in its peripheral regions, NGC147 exhibits pronounced isophotal twisting due to the emergence of symmetric tidal tails. We fit single Sersic models to composite surface brightness profiles constructed from diffuse light and star counts and find that NGC147 has an effective radius almost 3 times that of NGC185. In both cases, the effective radii that we calculate are larger by a factor of $\sim 2$ compared to most literature values. We also calculate revised total magnitudes of $M_g=-15.36\pm 0.04$ for NGC185 and $M_g=-16.36\pm 0.04$ for NGC147. Using photometric metallicities computed for RGB stars, we find NGC185 to exhibit a metallicity gradient of [Fe/H]$\sim -0.15$ dex/kpc over the radial range 0.125 to 0.5 deg. On the other hand, NGC147 exhibits almost no metallicity gradient, $\sim -0.02$ dex/kpc from 0.2 to 0.6 deg. The differences in the structure and stellar populations in the outskirts of these systems suggest that tidal influences have played an important role in governing the evolution of NGC147.

17 pages, 13 figures; MNRAS accepted

References in corpus (6)

• The Dartmouth Stellar Evolution Database
• The mass-metallicity gradient relation of early-type galaxies
• Simulations of the formation and evolution of isolated dwarf galaxies
• The Chemical Evolution of Dwarf Spheroidal Galaxies: Dissecting the Inner Regions and their Stellar Populations
• The internal dynamics of the Local Group dwarf elliptical galaxies NGC147, NGC185, and NGC205
• The chemical content of nearby galaxies from planetary nebulae: NGC 147

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• DUSTiNGS III: Distribution of Intermediate-Age and Old Stellar Populations in Disks and Outer Extremities of Dwarf Galaxies
• The stellar metallicity gradients of Local Group dwarf galaxies
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• Star formation history of And XVIII: a dwarf spheroidal galaxy in isolation
• The intrinsic ellipticity of dwarf spheroidal galaxies: constraints from the Andromeda system
• The Strikingly Metal-Rich Halo of the Sombrero Galaxy
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• Unlocking Discovery Potential for Decaying Dark Matter and Faint X-ray Sources with XRISM
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• NGC 147 Corroborates the Break in the Stellar Mass-Stellar Metallicity Relation for Galaxies