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Half-Light Radius Measurements of Andromeda Dwarf Satellites from the Isaac Newton Telescope Survey Using Exponential, Plummer, and Sérsic Fits

Hedieh Abdollahi

TL;DR

This study measures half-light radii for Andromeda's dwarf satellites using multi-epoch INT/WFC imaging in the i and V bands, complemented by the identification of long-period variables as probes of stellar populations. TRGB-based distances are derived and cross-validated against RR Lyrae and Cepheid distances, while radial-profile fitting with Exponential, Plummer, and Sérsic models yields robust structural parameters, with Sérsic fits providing the best description. A catalog of photometric and LPV data is prepared for public release, enabling future investigations of stellar content, star-formation histories, and dust production in M31's satellite system. Overall, the results demonstrate structural diversity among the satellites and establish reliable distance and size measurements to underpin population and evolutionary analyses in the M31 halo.

Abstract

We present half-light radius measurements for the dwarf satellites of Andromeda, based on multi-epoch imaging from the Isaac Newton Telescope (INT) Monitoring Survey of Local Group dwarf galaxies. This analysis is conducted within a larger study to identify long-period variable (LPV) stars in these galaxies. The survey was performed with the Wide Field Camera on the 2.5-m INT and covers multiple epochs obtained between 2015 and 2018 in the i (Sloan) and V (Harris) bands. To determine the half-light radii, we derived surface brightness and number density profiles for each system and fitted them with Exponential, Plummer, and Sérsic models. The resulting half-light radii are in good agreement with literature values but reveal subtle variations linked to differences in stellar distribution and morphology. Distances were independently estimated using the Tip of the Red Giant Branch (TRGB) method, yielding values consistent with previous determinations. The complete photometric and variability catalogs will be made publicly available through CDS/VizieR, providing a valuable resource and foundation for future studies of the structure, stellar populations, and evolution of Andromeda's dwarf companions.

Half-Light Radius Measurements of Andromeda Dwarf Satellites from the Isaac Newton Telescope Survey Using Exponential, Plummer, and Sérsic Fits

TL;DR

This study measures half-light radii for Andromeda's dwarf satellites using multi-epoch INT/WFC imaging in the i and V bands, complemented by the identification of long-period variables as probes of stellar populations. TRGB-based distances are derived and cross-validated against RR Lyrae and Cepheid distances, while radial-profile fitting with Exponential, Plummer, and Sérsic models yields robust structural parameters, with Sérsic fits providing the best description. A catalog of photometric and LPV data is prepared for public release, enabling future investigations of stellar content, star-formation histories, and dust production in M31's satellite system. Overall, the results demonstrate structural diversity among the satellites and establish reliable distance and size measurements to underpin population and evolutionary analyses in the M31 halo.

Abstract

We present half-light radius measurements for the dwarf satellites of Andromeda, based on multi-epoch imaging from the Isaac Newton Telescope (INT) Monitoring Survey of Local Group dwarf galaxies. This analysis is conducted within a larger study to identify long-period variable (LPV) stars in these galaxies. The survey was performed with the Wide Field Camera on the 2.5-m INT and covers multiple epochs obtained between 2015 and 2018 in the i (Sloan) and V (Harris) bands. To determine the half-light radii, we derived surface brightness and number density profiles for each system and fitted them with Exponential, Plummer, and Sérsic models. The resulting half-light radii are in good agreement with literature values but reveal subtle variations linked to differences in stellar distribution and morphology. Distances were independently estimated using the Tip of the Red Giant Branch (TRGB) method, yielding values consistent with previous determinations. The complete photometric and variability catalogs will be made publicly available through CDS/VizieR, providing a valuable resource and foundation for future studies of the structure, stellar populations, and evolution of Andromeda's dwarf companions.

Paper Structure

This paper contains 8 sections, 6 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observations and Data
  3. Identification of Long-Period Variables
  4. Results
  5. Tip of the Red Giant Branch
  6. Distances Moduli
  7. Half-light Radius
  8. Conclusions

Figures (3)

  • Figure 1: Distance results for Andromeda's satellite galaxies. The range depicted in this plot is derived from 2012ApJ...758...11C.
  • Figure 2: Comparison of half-light radius measurements of And II, derived from three different fitting functions.
  • Figure 3: Spatial distribution of Andromeda’s dwarf satellite galaxies. The semi-major axis of the galaxies is represented proportionally to their actual sizes based on data from Table \ref{['table:objects']}.