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arXiv · 1710.09021

Very compact millimeter sizes for composite star-forming/AGN submillimeter galaxies

Soh Ikarashi·Karina Caputi·Kouji Ohta·R. J. Ivison·Claudia D. P. Lagos·Laura Bisigello·Bunyo Hatsukade·Itziar Aretxaga·James S. Dunlop·David H. Hughes·Daisuke Iono·Takuma Izumi·Nobunari Kashikawa·Yusei Koyama·Ryohei Kawabe·Kotaro Kohno·Kentaro Motohara·Kouichiro Nakanishi·Yoichi Tamura·Hideki Umehata·Grant W. Wilson·Kiyoto Yabe·Min S. Yun
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Abstract

We report the study of far-IR sizes of submillimeter galaxies (SMGs) in relation to their dust-obscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined using mid-IR photometry. We determined the millimeter-wave ($λ_{\rm obs}=1100 μ$m) sizes of 69 ALMA-identified SMGs, selected with $\geq10$$σ$ confidence on ALMA images ($F_{\rm 1100 μm}=1.7$--7.4 mJy). We found that all the SMGs are located above an avoidance region in the millimeter size-flux plane, as expected by the Eddington limit for star formation. In order to understand what drives the different millimeter-wave sizes in SMGs, we investigated the relation between millimeter-wave size and AGN fraction for 25 of our SMGs at $z=1$--3. We found that the SMGs for which the mid-IR emission is dominated by star formation or AGN have extended millimeter-sizes, with respective median $R_{\rm c,e} = 1.6^{+0.34}_{-0.21}$ and 1.5$^{+0.93}_{-0.24}$ kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median $R_{\rm c,e}=1.0^{+0.20}_{-0.20}$ kpc. The relation between millimeter-wave size and AGN fraction suggests that this size may be related to the evolutionary stage of the SMG. The very compact sizes for composite star-forming/AGN systems could be explained by supermassive black holes growing rapidly during the SMG coalescing, star-formation phase.

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Soh Ikarashi, Karina Caputi, Kouji Ohta, R. J. Ivison, Claudia D. P. Lagos, Laura Bisigello, Bunyo Hatsukade, Itziar Aretxaga, James S. Dunlop, David H. Hughes, Daisuke Iono, Takuma Izumi, Nobunari Kashikawa, Yusei Koyama, Ryohei Kawabe, Kotaro Kohno, Kentaro Motohara, Kouichiro Nakanishi, Yoichi Tamura, Hideki Umehata, Grant W. Wilson, Kiyoto Yabe, Min S. Yun. 2017-10-30. Very compact millimeter sizes for composite star-forming/AGN submillimeter galaxies. https://doi.org/10.3847/2041-8213%2Faa9572

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