The Peculiar Radio Source M17 JVLA 35

Abstract

M17 JVLA 35 is a radio source detected in projection against the M17 HII region. In recent observations, its spectrum between 4.96 and 8.46 GHz was found to be positive and very steep, with $\alpha \ge 2.9\pm 0.6$ ($S_{\nu }\propto {\nu }^{\alpha }$). Here we present Very Large Array observations made in the 18.5 to 36.5 GHz region that indicate a spectral turnover at $\sim$13 GHz and a negative spectral index ($\alpha \simeq -2.0$) at higher frequencies. The spectrum is consistent with that of an extragalactic High Frequency Peaker (HFP). However, M17 JVLA 35 has an angular size of $\sim 0\text{.}{}^{\prime \prime }5$ at 8.46 GHz, while HFPs have extremely compact, milliarcsecond dimensions. We discuss other possible models for the spectrum of the source and do not find them feasible. Finally, we propose that M17 JVLA35 is indeed an HFP but that its angular size becomes broadened by plasma scattering as its radiation travels across M17. If our interpretation is correct, accurate measurements of the angular size of M17 JVLA35 across the centimeter range should reveal the expected ${\nu }^{-2}$ dependence.

arXiv comment14 pages, 3 figures

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• GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
• Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way
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• A Protostellar Jet Emanating from a Hypercompact HII Region
• Surveying the Giant HII Regions of the Milky Way with SOFIA: I. W51A
• Surveying the Giant HII Regions of the Milky Way with SOFIA: II. M17
• JVLA Observations of Young Brown Dwarfs
• VLBA Observations of Strong Anisotripic Radio Scattering towards the Orion Nebula