Souradeep Bhattacharya

PhD student at the European Southern Observatory (ESO) in Garching, Germany

My Research

I am interested in understanding the formation and evolution of nearby galaxies. I utilise planetary nebulae (PNe) as discrete tracers of kinematics and chemical evolution of galaxies. My PhD thesis is on understanding the inner halo and disk of Andromeda (M31) using PNe. The close distance of M31 allows us to probe the kinematics of its structural components and unravel its formation history, especially its major merger thought to have happened 2-3 Gyr ago. It also allows us to study the relation of PNe with their parent stellar population, in the context of stellar evolution.
I have previously also worked on understanding the morphologies of open clusters, in particular the oldest open cluster Berkeley 17 and its Blue Straggler population. I have also worked on studying X-ray sources in the globular cluster 47 Tuc.

Survey of Planetary Nebulae in Andromeda (M31) - Imaging the disc and inner halo

For my PhD, I am carrying out a survey of Planetary Nebulae (PNe) in the disk and inner halo (~60 sq. deg.) of M31. This is the largest sample of PNe in any galaxy. We identify them as point-like sources by comparing [OIII] (narrow-band) and g (broad-band) images from the MegaCam imager at the 3.6m CFHT. For the PNe identified within the inner 16 sq. deg. (Bhattacharya et al. 2019b), we observe a rise in the faint-end of the PN luminosity function in M31 at all radial distances, possibly related with the star-formation history of M31. 

Survey of Planetary Nebulae in Andromeda (M31) II- Disk Kinematics

Spectroscopic follow-up of some of the PNe identified in the imaging survey was carried out with the HectoSpec multi-fibre spectrograph at the 6.5m MMT. The PNe are divided into high and low extinction samples, whose kinematics are fitted to obtain the rotation curves and rotational velocity dispersion profiles of the M31 disc. We obtain the age-velocity dispersion relation in different deprojected elliptical bins (Bhattacharya et. al 2019c, A&A, in submission).

Studies of open clusters

For my Masters thesis at IANCU with Dr. Wen-Ping Chen, I confirmed the core-tail shape of the oldest known open cluster Berkeley 17 with Pan-STARRS data, also finding that it exhibits mass segregation. We found that nearly half its expected Blue Straggler candidates (BSSs) could be field contaminants (Bhattacharya et al. 2017b). Recently with Gaia DR2, we confirm the number of BSSs and find that they show a bimodal radial distribution, similar to globular clusters of intermediate dynamical age undergoing dynamical relaxation. (Bhattacharya et al. 2019a).

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I also presented the maiden use of the DBSCAN algorithm to determine open cluster morphology for two Galactic open clusters, Czernik 20 and NGC 1857, from spatial distribution of near infrared (NIR) data from the UKIDSS and 2MASS surveys (Bhattacharya et al. 2017a).

Catalogue of X-ray sources in the globular cluster 47 Tuc

As a summer intern at the University of Alberta with Dr. Craig Heinke, I combined Chandra ACIS observations of the globular cluster 47 Tuc to create a deeper X-ray source list, and study some of its faint radio millisecond pulsars (MSPs). We are able to extract X-ray spectra of MSPs 47 Tuc aa, ab, Z, S and F.  We limit X-ray emission from the full surface of the rapidly spinning MSP 47 Tuc aa, and use this limit to put an upper bound for amplitude of r-mode oscillations in this pulsar constraining the shape of the r-mode instability window (Bhattacharya et al. 2017c).