Durham University

Department of Physics

Staff profile

Publication details for Professor Ian Smail

Simpson, J. M., Smail, Ian, Wang, Wei-Hao, Riechers, D., Dunlop, J. S., Ao, Y., Bourne, N., Bunker, A., Chapman, S. C., Chen, Chian-Chou, Dannerbauer, H., Geach, J. E., Goto, T., Harrison, C. M., Hwang, H. S., Ivison, R. J., Kodama, Tadayuki, Lee, C.-H., Lee, H.-M., Lee, M., Lim, C.-F., Michałowski, M. J., Rosario, D. J., Shim, H., Shu, X. W., Swinbank, A. M., Tee, W.-L., Toba, Y., Valiante, E., Wang, Junxian & Zheng, X. Z. (2017). An Imperfectly Passive Nature: Bright Submillimeter Emission from Dust-obscured Star Formation in the z = 3.717 “Passive” System, ZF 20115. The Astrophysical Journal Letters 844(1): L10.

Author(s) from Durham


The identification of high-redshift, massive galaxies with old stellar populations may pose challenges to some models of galaxy formation. However, to securely classify a galaxy as quiescent, it is necessary to exclude significant ongoing star formation, something that can be challenging to achieve at high redshifts. In this Letter, we analyze deep ALMA/870 μm and SCUBA-2/450 μm imaging of the claimed "post-starburst" galaxy ZF 20115 at z = 3.717 that exhibits a strong Balmer break and absorption lines. The rest-frame far-infrared imaging identifies a luminous starburst 0farcs4 ± 0farcs1 (~3 kpc in projection) from the position of the ultraviolet/optical emission and is consistent with lying at the redshift of ZF 20115. The star-forming component, with an obscured star formation rate of ${100}{-70}^{+15}\,{M}{\odot }\,{\mathrm{yr}}^{-1}$, is undetected in the rest-frame ultraviolet but contributes significantly to the lower angular resolution photometry at rest-frame wavelengths gsim3500 Å. This contribution from the obscured starburst, especially in the Spitzer/IRAC wavebands, significantly complicates the determination of a reliable stellar mass for the ZF 20015 system, and we conclude that this source does not pose a challenge to current models of galaxy formation. The multi-wavelength observations of ZF 20115 unveil a complex system with an intricate and spatially varying star formation history. ZF 20115 demonstrates that understanding high-redshift obscured starbursts will only be possible with multi-wavelength studies that include high-resolution observations, available with the James Webb Space Telescope, at mid-infrared wavelengths.