New insights into the interstellar medium of the dwarf galaxy IC 10: connection between magnetic fields, the radio--infrared correlation and star formation

Abstract

We present the highest sensitivity and angular resolution study at 0.32 GHz of the dwarf irregular galaxy IC\,10, observed using the Giant Metrewave Radio Telescope, probing $\sim 45$ pc spatial scales. We find the galaxy-averaged radio continuum spectrum to be relatively flat, with a spectral index $\alpha =-0.34\pm 0.01$ ($S_{\nu }\propto {\nu }^{\alpha }$), mainly due to a high contribution from free--free emission. At 0.32 GHz, some of the H{\sc ii} regions show evidence of free--free absorption as they become optically thick below $\sim 0.41$ GHz with corresponding free electron densities of $\sim 11-22\mathrm{c}{\mathrm{m}}^{-3}$. After removing the free--free emission, we studied the radio--infrared relations on 55, 110 and 165 pc spatial scales. We find that on all scales the non-thermal emission at 0.32 and 6.2 GHz correlates better with far-infrared (FIR) emission at $70\mu$m than mid-infrared emission at $24\mu$m. The dispersion of the radio--FIR relation arises due to variations in both magnetic field and dust temperature, and decreases systematically with increasing spatial scale. The effect of cosmic ray transport is negligible as cosmic ray electrons were only injected $\lesssim 5$ Myr ago. The average magnetic field strength ($B$) of $12\mu$G in the disc is comparable to that of large star-forming galaxies. The local magnetic field is strongly correlated with local star formation rate ($\mathrm{SFR}$) as $B\propto {\mathrm{SFR}}^{0.35\pm 0.03}$, indicating a star-burst driven fluctuation dynamo to be efficient ($\sim 10$ per cent) in amplifying the field in IC\,10. The high spatial resolution observations presented here suggest that the high efficiency of magnetic field amplification and strong coupling with SFR likely sets up the radio--FIR correlation in cosmologically young galaxies.

19 pages, 14 figures, 3 tables. Accepted to be published in MNRAS

References in corpus (25)

• Cosmic Star Formation History
• Revised equipartition & minimum energy formula for magnetic field strength estimates from radio synchrotron observations
• The 0.4 < z < 1.3 star formation history of the Universe as viewed in the far-infrared
• High-resolution dark matter density profiles of THINGS dwarf galaxies: Correcting for non-circular motions
• FIGGS: Faint Irregular Galaxies GMRT Survey - Overview, observations and first results
• The Star Formation History of the Universe as Revealed by Deep Radio Observations
• Molecular Gas in the Low Metallicity, Star Forming Dwarf IC 10
• SLUG - Stochastically Lighting Up Galaxies. II: Quantifying the Effects of Stochasticity on Star Formation Rate Indicators
• On the Similarity between Cluster and Galactic Stellar Initial Mass Functions
• High-resolution radio continuum survey of M33 II. Thermal and nonthermal emission
• A multi-scale study of infrared and radio emission from Scd galaxy M33
• The Radio Continuum-Star Formation Rate Relation in WSRT SINGS Galaxies
• A multi-resolution analysis of the radio-FIR correlation in the Large Magellanic Cloud
• The dust un-biased cosmic star formation history from the 20 cm VLA-COSMOS survey
• The temperature dependence of the far-infrared-radio correlation in the Herschel-ATLAS
• Synchrotron spectral index and interstellar medium densities of star-forming galaxies
• Radio--Far infrared correlation in "blue cloud" galaxies with 0<z<1.2
• Untangling the Nature of Spatial Variations of Cold Dust Properties in Star Forming Galaxies
• SHIELD: Neutral Gas Kinematics and Dynamics
• The relation between atomic gas and star formation rate densities in faint irregular galaxies
• The far-infrared - radio correlation in dwarf galaxies
• The non-thermal superbubble in IC 10: the generation of cosmic ray electrons caught in the act
• Magnetic fields and star formation in low-mass Magellanic-type and peculiar galaxies
• A Large Scale, Low Frequency Murchison Widefield Array Survey of Galactic HII regions between 260< l <\340
• Cosmic-ray acceleration in supernova shocks

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