Investigating star-formation and supernovae in Messier-82

Abstract

Context: Messier 82 (M82) is a well-studied nearby starburst galaxy, home to numerous compact radio sources, including supernova remnants (SNRs) and HII regions. The high star formation rate (SFR) in M82 leads to frequent supernovae (SNe), making it an ideal laboratory for studying compact radio sources in a dense starburst environment.

Aims: This thesis aims to catalog and analyze compact radio sources in the central region of M82 using new 1.5 GHz e-MERLIN observations. The study provides updated classifications for previously known sources and identifies new objects, contributing to our understanding of supernova (SN) activity and star formation (SF) in M82.

Methods: The dataset was obtained from e-MERLIN L-band observations in 2016, processed using CASA for calibration and imaging. Compact sources were detected using PyBDSF. Sources were selected based on a signal-to-noise ratio (S/N) threshold of 6, ensuring reliable detections. Spectral indices were derived from multi-frequency subband imaging and combined with existing C-band (5 GHz) flux measurements to refine classifications. Morphological analysis was also performed to distinguish between SNRs and HII regions.

Results: A total of 36 compact sources were identified, including 31 previously known objects and four newly detected sources. A key finding of this study is the reclassification of source 38.76+53.5, previously thought to be an HII region, as an SNR based on its steep spectral index (-1.054). This demonstrates the importance of multi-frequency spectral analysis in accurately identifying radio sources in starburst environments. Additionally, comparisons with previous studies from 2008 C-band observation confirmed the persistence of known sources while revealing discrepancies in classification. The spectral properties of 41.95+57.5 were further analyzed, contributing to the ongoing debate about its nature, while observations of SN 2008iz suggest it has now transitioned into a SNR. These findings refine existing classifications and contribute to a deeper understanding of the radio source population in M82. While this study does not establish a complete catalogue, it provides an updated dataset that enhances our knowledge of the physical processes shaping radio emission in starburst galaxies. Future multi-wavelength and long-term monitoring studies will be essential for further constraining the nature and evolution of these sources.