GMRT radio continuum study of Wolf Rayet galaxies I: NGC 4214 and NGC 4449

Abstract

We report low frequency observations of Wolf-Rayet galaxies, NGC 4214 and NGC 4449 at 610, 325 and 150 MHz, using the Giant Meterwave Radio Telescope (GMRT). We detect diffuse extended emission from NGC 4214 at and NGC 4449. NGC 4449 is observed to be five times more radio luminous than NGC 4214, indicating vigorous star formation. We estimate synchrotron spectral index after separating the thermal free-free emission and obtain ${\alpha }_{nt}=-0.63\pm 0.04$ (S$\propto {\nu }^{{\alpha }_{nt}}$) for NGC 4214 and $-0.49\pm 0.02$ for NGC 4449. About $22\%$ of the total radio emission from NGC 4214 and $\sim 9\%$ from NGC 4449 at 610 MHz is thermal in origin. We also study the spectra of two compact star-forming regions in NGC 4214 from 325 MHz to 15 GHz and obtain ${\alpha }_{nt}=-0.32\pm 0.02$ for NGC 4214-I and ${\alpha }_{nt}=-0.94\pm 0.12$ for NGC 4214-II. The luminosities of these star-forming regions ($\sim 10^{19}\mathrm{W}\mathrm{H}{\mathrm{z}}^{-1}$) appear to be similar to those in circumnuclear rings in normal disk galaxies observed with similar linear resolution. We detect the supernova remnant SNR J1228+441 in NGC 4449 and estimate the spectral index of the emission between 325 and 610 MHz to be $-1.8$ in the epoch 2008-2009. The galaxies follow the radio-FIR correlation slopes suggesting that star formation in Wolf - Rayet galaxies, which are low-metallicity systems, are similar to that of normal disk galaxies.

14 pages, 9 figures, 5 tables, Revised version submitted to MNRAS after incorporating the referee's comments

References in corpus (5)

• Magnetic Fields in Starburst Galaxies and The Origin of the FIR-Radio Correlation
• High-resolution radio continuum survey of M33 II. Thermal and nonthermal emission
• Emerging Massive Star Clusters Revealed: High Resolution Imaging of NGC 4449 from the Radio to the Ultraviolet
• Multiwavelength star formation indicators: Observations
• VLA Observations of J1228+441, a Luminous Supernova Remnant in NGC 4449

Cited by in corpus (6)

• The Radio Spectral Energy Distribution and Star Formation Rate Calibration in Galaxies
• Science with the Murchison Widefield Array: Phase I Results and Phase II Opportunities
• PNe and H II regions in the starburst irregular galaxy NGC 4449 from LBT MODS data
• Spatially Resolved Dust, Gas, and Star Formation in the Dwarf Magellanic Irregular NGC4449
• Comment on "Constraining the annihilating dark matter mass by the radio continuum spectral data of NGC4214 galaxy"
• Low radio frequency observations of seven nearby galaxies with GMRT