%0 Generic %1 simpson2017imperfectly %A Simpson, J. M. %A Smail, Ian %A Wang, Wei-Hao %A Riechers, D. %A Dunlop, J. S. %A Ao, Y. %A Bourne, N. %A Bunker, A. %A Chapman, S. C. %A Chen, Chian-Chou %A Dannerbauer, H. %A Geach, J. E. %A Goto, T. %A Harrison, C. M. %A Hwang, H. S. %A Ivison, R. J. %A Kodama, Tadayuki %A Lee, C. H. %A Lee, H. M. %A Lee, M. %A Lim, C. F. %A Michalowski, M. J. %A Rosario, D. J. %A Shim, H. %A Shu, X. W. %A Swinbank, A. M. %A Tee, W. L. %A Toba, Y. %A Valiante, E. %A Wang, Junxian %A Zheng, X. Z. %D 2017 %K dust formation passive star system %T An imperfectly passive nature: Bright sub-millimeter emission from dust-obscured star formation in the z=3.717 "passive" system, ZF20115 %U http://arxiv.org/abs/1704.03868 %X 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 redshift. In this letter, we analyse deep ALMA/870um and SCUBA-2/450um imaging of the claimed "post-starburst" galaxy ZF-20115 at z=3.717 that exhibits a strong Balmer break and absorption lines. The far-infrared imaging reveals a luminous starburst located 0.4+/-0.1 arcsec (~3kpc in projection) from the position of the rest-frame ultra-violet/optical emission, with an obscured star-formation rate of 100 Mo/yr. This star-forming component is undetected in the rest-frame ultraviolet but contributes significantly to the lower angular resolution photometry at restframe wavelengths >3500A, significantly complicating the determination of a reliable stellar mass. Importantly, in the presence of dust obscuration, strong Balmer features are not a unique signature of a post-starburst galaxy and are indeed frequently observed in infrared-luminous galaxies. We conclude that the ZF20015 system does not pose a challenge to current models of galaxy formation and that deep sub-/millimeter observations are a prerequisite for any claims of quiescence. The multi-wavelength observations of ZF20115 unveil a complex system with an intricate and spatially-varying star-formation history. ZF20115 demonstrates that understanding high-redshift obscured starbursts will only be possible with multi-wavelength studies that include high-resolution observations, available with the JWST, at mid-infrared wavelengths.

@misc{simpson2017imperfectly, abstract = {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 redshift. In this letter, we analyse deep ALMA/870um and SCUBA-2/450um imaging of the claimed "post-starburst" galaxy ZF-20115 at z=3.717 that exhibits a strong Balmer break and absorption lines. The far-infrared imaging reveals a luminous starburst located 0.4+/-0.1 arcsec (~3kpc in projection) from the position of the rest-frame ultra-violet/optical emission, with an obscured star-formation rate of 100 Mo/yr. This star-forming component is undetected in the rest-frame ultraviolet but contributes significantly to the lower angular resolution photometry at restframe wavelengths >3500A, significantly complicating the determination of a reliable stellar mass. Importantly, in the presence of dust obscuration, strong Balmer features are not a unique signature of a post-starburst galaxy and are indeed frequently observed in infrared-luminous galaxies. We conclude that the ZF20015 system does not pose a challenge to current models of galaxy formation and that deep sub-/millimeter observations are a prerequisite for any claims of quiescence. The multi-wavelength observations of ZF20115 unveil a complex system with an intricate and spatially-varying star-formation history. ZF20115 demonstrates that understanding high-redshift obscured starbursts will only be possible with multi-wavelength studies that include high-resolution observations, available with the JWST, at mid-infrared wavelengths.}, added-at = {2017-04-13T09:14:49.000+0200}, author = {Simpson, J. M. and Smail, Ian and Wang, Wei-Hao and Riechers, D. and Dunlop, J. S. and Ao, Y. and Bourne, N. and Bunker, A. and Chapman, S. C. and Chen, Chian-Chou and Dannerbauer, H. and Geach, J. E. and Goto, T. and Harrison, C. M. and Hwang, H. S. and Ivison, R. J. and Kodama, Tadayuki and Lee, C. H. and Lee, H. M. and Lee, M. and Lim, C. F. and Michalowski, M. J. and Rosario, D. J. and Shim, H. and Shu, X. W. and Swinbank, A. M. and Tee, W. L. and Toba, Y. and Valiante, E. and Wang, Junxian and Zheng, X. Z.}, biburl = {https://www.bibsonomy.org/bibtex/212a89265e35843dd01bf743fbb08bd64/miki}, description = {[1704.03868] An imperfectly passive nature: Bright sub-millimeter emission from dust-obscured star formation in the z=3.717 "passive" system, ZF20115}, interhash = {d9e7a7d7820b5729ecc2bd1d8ca2eba5}, intrahash = {12a89265e35843dd01bf743fbb08bd64}, keywords = {dust formation passive star system}, note = {cite arxiv:1704.03868Comment: ApJ submitted. Comments welcome}, timestamp = {2017-04-13T09:14:49.000+0200}, title = {An imperfectly passive nature: Bright sub-millimeter emission from dust-obscured star formation in the z=3.717 "passive" system, ZF20115}, url = {http://arxiv.org/abs/1704.03868}, year = 2017 }