Very Compact Millimeter Sizes for Composite Star-forming/AGN Submillimeter Galaxies

Research output: Contribution to journalArticle




  • 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

Research units


We report the study of the far-infrared (IR) sizes of submillimeter galaxies (SMGs) in relation to their dustobscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined using mid-IR photometry. We determined the millimeter-wave (λobs = 1100 μm) sizes of 69 Atacama Large Millimeter/ submillimeter Array (ALMA)-identified SMGs, selected with ≥10 δ confidence on ALMA images (F1100 μm = 1.7-7.4 mJy). We found that all of the SMGs are located above an avoidance region in the sizeflux 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 Rc,e = 1.6-0.21 +0.34 and 1.5 -0.24 +0.93 kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median Rc,e1.0 -0.20 +0.20kpc. 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.

Original languageEnglish
Article numberL36
JournalAstrophysical Journal Letters
Issue number2
StatePublished - 10 Nov 2017

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