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A multi-wavelength study of nearby starburst galaxy M 82

Nilkanth Vagshette, Satish S. Sonkamble, Madhav Patil, Sachindra Naik, Ilani Loubser

Abstract

We present a multi-wavelength study of the nearby starburst galaxy M 82 by combining high-resolution Far-ultraviolet (FUV) imaging from the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat and archival Chandra X-ray observations. Using FUV flux measurements, we estimate a spatially-resolved star formation rate (SFR) across several star-forming clumps within a radius of $\sim$3.6 kpc, finding a total SFR of 0.022 M$_{\odot}$ yr$^{-1}$. The H$_α$ recombination line flux yields an SFR of $\sim$0.010 M$_{\odot}$ yr$^{-1}$, while the infrared-based SFR derived from 24 $μ\mathrm{m}$ emission is significantly higher at 16 - 18 M$_{\odot}$ yr$^{-1}$, suggesting that a substantial fraction of star formation in M 82 is heavily dust-obscured. Morphological comparison of FUV, H$_α$, mid-infrared, and soft X-ray emission reveals a strong spatial correlation, tracing multi-phase outflows along the galaxy's minor axis. X-ray spectral analysis using a three-temperature $\texttt{VAPEC}$ model shows enhanced abundances of Ne, Mg, Si, and S, consistent with enrichment from Type-II supernovae. These results demonstrate the importance of combining UV, optical, IR, and X-ray observations to probe both obscured and unobscured star formation, the metal enrichment, and the outflow-driven evolution of starburst galaxies.

A multi-wavelength study of nearby starburst galaxy M 82

Abstract

We present a multi-wavelength study of the nearby starburst galaxy M 82 by combining high-resolution Far-ultraviolet (FUV) imaging from the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat and archival Chandra X-ray observations. Using FUV flux measurements, we estimate a spatially-resolved star formation rate (SFR) across several star-forming clumps within a radius of 3.6 kpc, finding a total SFR of 0.022 M yr. The H recombination line flux yields an SFR of 0.010 M yr, while the infrared-based SFR derived from 24 emission is significantly higher at 16 - 18 M yr, suggesting that a substantial fraction of star formation in M 82 is heavily dust-obscured. Morphological comparison of FUV, H, mid-infrared, and soft X-ray emission reveals a strong spatial correlation, tracing multi-phase outflows along the galaxy's minor axis. X-ray spectral analysis using a three-temperature model shows enhanced abundances of Ne, Mg, Si, and S, consistent with enrichment from Type-II supernovae. These results demonstrate the importance of combining UV, optical, IR, and X-ray observations to probe both obscured and unobscured star formation, the metal enrichment, and the outflow-driven evolution of starburst galaxies.
Paper Structure (7 sections, 3 equations, 7 figures, 1 table)

This paper contains 7 sections, 3 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Observations and Data Reduction
  3. Results and Discussion
  4. Star formation in M 82
  5. X-ray Spectroscopy
  6. Multiphase ISM
  7. Conclusion

Figures (7)

  • Figure 1: AstroSat$/$UVIT images of the M 82 galaxy. The left panel image shows 28 arcmin diameter field of view and the right panel shows the zoomed in view covering a $10 \times 10$ arcmin$^{2}$ region.
  • Figure 2: The figure shows the FUV Gaussian smoothed image of M 82, with the regions where flux were estimated indicated using green circles.
  • Figure 3: Luminosity and star formation rates estimated from the clumpy regions of the M 82 galaxy.
  • Figure 4: SDSS continuum subtracted H$_{\alpha}$ emission fitted with Gaussian 1D model.
  • Figure 5: Chandra X-ray spectrum of M 82 fitted with the best-fit model shown in blue. Bottom panel shows residual of the fit, illustrating the goodness of fit.
  • ...and 2 more figures