Catalogue of compact radio sources in Messier-82 from e-MERLIN observations

This dataset presents a catalogue of compact radio sources identified in the central region of the starburst galaxy Messier 82 (M82) using 2016 L-Band (1–2 GHz) continuum data from the e-MERLIN interferometer. The observations were conducted at a central frequency of 1.5 GHz.

The data were processed using the e-MERLIN CASA pipeline for initial calibration. Subsequent data inspection, flagging, and automated calibration were performed using CASA (Common Astronomy Software Applications). The calibrated visibilities were then imaged using Briggs weighting, resulting in a synthesized beam size of 0.17 arcsec × 0.13 arcsec.

A total of 36 compact radio sources were identified in the central region of M82 from the resulting image (Figure 3.1) based on the following criteria: a signal-to-noise (S/N) ratio of at least 6, absence of contamination from diffuse emission (due to the uv-coverage of the e-MERLIN baselines, Figure 2.3), and a compact or slightly elongated morphology. Source finding was initially performed using Python Blob Detection and Source Finder (PyBDSF).

The dataset includes two tables detailing the properties of these 36 sources:

Table 3.1: CASA imfit Source Catalogue

This table contains source parameters derived using the CASA task imfit. For each source, an elliptical region was manually defined to encompass its emission, and a Gaussian fit was performed. The table includes the following columns:

(1) Source Number (sequential identifier)

(2) Source Name

(3) Right Ascension Offset (arcseconds from 09h55m00s J2000)

(4) Declination Offset (arcseconds from 69d40m00s J2000)

(5) Peak 1.5 GHz Flux Density (mJy/beam)

(6) Integrated 1.5 GHz Flux Density (mJy)

(7) Signal-to-Noise Ratio

Note: For a subset of sources (2, 12, 18, and 36), where the initial Gaussian fit yielded an integrated flux density lower than the peak flux density, the peak flux density was adopted as the representative integrated flux density for these entries.

Table 3.2: PyBDSF Source Catalogue

This table presents source parameters for the same 36 sources, as determined by the automated PyBDSF algorithm. The columns are analogous to Table 3.1, providing an independent set of measurements based on automated source detection and Gaussian fitting.

Figures:

Accompanying this dataset are contour images (Figure 3.2) for each of the 36 identified sources, visually representing their morphology and emission. The source numbers in the figure captions correspond to the Source Number column in both Table 3.1 and Table 3.2.

Data Access:

The reduced e-MERLIN continuum data used in this study is available at: https://www.e-merlin.ac.uk/distribute/CY3/CY3210/CY3210.html.