Thesis Topic: Disks, stellar halos, and disk-halo interface in the Andromeda galaxy (M31) resolved with planetary nebulae

Thesis Supervisors:

Bhattacharya, Souradeep

Magda Arnaboldi (ESO)

Souradeep Bhattacharya (IUCCA)



Andromeda (M31)  is the nearest large spiral galaxy to our Milky Way.  The Triangulum galaxy (M33) is its largest and closest satellite. At mere 780 kpc distance these galaxies are ideal targets for studying the structures of their disks with individual stars. We are analyzing a sample of several thousand planetary nebulae in order to separate  thin disk, thick disk, substructures and stellar halo in M31 and M33, which the goals of mapping the kinematics and chemistry of the different components. We study whether their thin and thick disk components have similar or different structures from those in our Galaxy, and learn about their formations. M31, M33 and the Milky Way are the only large galaxies for which such comparative study is possible. In this thesis we will quantify the motions in the substructures of the disk-halo interface in the M31/M33 spirals. We wish to learn about the relative importance of accretion and in-situ processes in the formation of their stellar halo. This thesis requires active participation to the data reduction and analysis, and comparison between observations and the results from dynamical/cosmological simulations provided by computational groups based in the nearby institutes.


  • Bhattacharya, S., Arnaboldi, M., Caldwell, N., et al. (2019) "The survey of planetary nebulae in Andromeda (M 31). II. Age-velocity dispersion relation in the disc from planetary nebulae," A&A, 631, A56 - 2019A&A...631A..56B
  • Bhattacharya, S., Arnaboldi, M., Hartke, J., et al. (2019) "The survey of planetary nebulae in Andromeda (M 31). I. Imaging the disc and halo with MegaCam at the CFHT," A&A, 624, A132 - 2019A&A...624A.132B

Figure 1: The several thousand PNe identified by the CFHT survey (Bhattacharya et al. 2019 A&A, 624, 132; blue - PNe with m5007 brighter than 25.64 mag, green - PNe with m5007fainter than 25:64 mag and photometric depth varying with pointings) are overlaid on the map of RGB stars identified by the PAndAS survey. The Merrett+06 PNe re-identified by the CFHT survey are shown in yellow. The main M31 disk and the known substructures within the survey area are marked. The white circle shows the MMT Hectospec multi-fiber wide field spectrograph, currently being used to acquire spectra for the CFHT PN sample. These spectra provide the line-of-sight velocity information and the oxygen abundance of the stars.