Detection of Hα emission from z > 3.5 submillimetre luminous galaxies with AKARI-FUHYU spectroscopy

Sedgwick, Chris; Serjeant, Stephen; Pearson, Chris; Smail, Ian; Im, Myungshin; Oyabu, Shinki; Takagi, Toshinobu; Matsuhara, Hideo; Wada, Takehiko; Lee, Hyung Mok; Jeong, Woong-Seob and White, Glenn J. (2013). Detection of Hα emission from z > 3.5 submillimetre luminous galaxies with AKARI-FUHYU spectroscopy. Monthly Notices of the Royal Astronomical Society, 436(1) pp. 395–400.

DOI: https://doi.org/10.1093/mnras/stt1572

URL: http://mnras.oxfordjournals.org/content/436/1/395....

Abstract

We present tentative Hα emission line detections of four submillimetre-detected galaxies at z > 3.5: the radio galaxies 8C1909+722 and 4C60.07 at signal-to-noise ratios (SNRs) of 3.1 and 2.5, and two submillimetre-selected galaxies (SMGs) near the first of these at SNRs of 10.0 and 2.4, made with the AKARI space telescope as part of the Follow-Up Hayai-Yasui-Umai mission programme. These are the highest redshift Hα detections in such galaxies, made possible by AKARI's unique near-infrared spectroscopic capability. The two radio galaxies had known redshifts and surrounding structure, and we have detected broad Hα components indicating the presence of dust-shrouded quasars. We conclude that powerful active galactic nuclei (AGNs) at z > 3.5 occur in peaks of the star formation density fields, supporting a close connection between stellar mass build-up and black hole mass assembly at this redshift. We also show that 4C60.07 is a binary AGN. The Hα detections of the two SMGs are the first redshift determinations for these sources, confirming their physical association around their companion radio galaxy. The Hα-derived star formation rates (SFRs) for the SMGs are lower than their far-infrared derived SFRs by a factor of ~10, suggesting a level of dust obscuration similar to that found in studies at ~1 < z < 2.7.

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