MIDIS: Strong (Hβ+[O III]) and Hα Emitters at Redshift z ≃ 7-8 Unveiled with JWST NIRCam and MIRI Imaging in the Hubble eXtreme Deep Field
Ilbert, O.; Östlin, G.; Güdel, M.; Colina, L.; Kokorev, V.; Greve, T. R.; Walter, F.; Henning, Th.; van der Werf, P.; Ward, M.; Le Fèvre, O.; Kendrew, S.; Melinder, J.; Bik, A.; Annunziatella, M.; Caputi, K. I.; Hjorth, J.; Iani, E.; Pérez-González, P. G.; Rinaldi, P.; Eckart, A.; Alonso-Herrero, A.; Labiano, A.; Vandenbussche, B.; Lagage, P. -O.; Waelkens, C.; Tikkanen, T.; Wright, G. S.; Crespo Gómez, A.; Álvarez-Márquez, J.; Boogaard, L.; Peissker, F.; García-Marín, M.; Costantin, L.; Gillman, S.; Jermann, I.; Langeroodi, D.; Moutard, T.; Topinka, M.; Ray, T.; Pye, J.; van Dishoeck, E.; Noorgard-Nielsen, H. U.; Azzollini, R.; Bosman, S. E. I.; Meyer, R. A.; Navarro-Carrera, R.
Netherlands, Denmark, Spain, Sweden, United Kingdom, Germany, United States, France, Italy, Ireland, Austria, Switzerland, Belgium
Abstract
We make use of JWST medium-band and broadband NIRCam imaging, along with ultradeep MIRI 5.6 μm imaging, in the Hubble eXtreme Deep Field to identify prominent line emitters at z ≃ 7-8. Out of a total of 58 galaxies at z ≃ 7-8, we find 18 robust candidates (≃31%) for (Hβ + [O III]) emitters, based on their enhanced fluxes in the F430M and F444W filters, with EW0(Hβ +[O III]) ≃87-2100 Å. Among these emitters, 16 lie in the MIRI coverage area and 12 exhibit a clear flux excess at 5.6 μm, indicating the simultaneous presence of a prominent Hα emission line with EW0(Hα) ≃200-3000 Å. This is the first time that Hα emission can be detected in individual galaxies at z > 7. The Hα line, when present, allows us to separate the contributions of Hβ and [O III] to the (Hβ +[O III]) complex and derive Hα-based star formation rates (SFRs). We find that in most cases [O III]/Hβ > 1. Instead, two galaxies have [O III]/Hβ < 1, indicating that the NIRCam flux excess is mainly driven by Hβ. Most prominent line emitters are very young starbursts or galaxies on their way to/from the starburst cloud. They make for a cosmic SFR density ${\mathrm{log}}_{10}({\rho }_{{\mathrm{SFR}}_{{\rm{H}}\alpha }}/({M}_{\odot }\,{\mathrm{yr}}^{-1}\,{\mathrm{Mpc}}^{-3}))\simeq -2.35$ , which is about a quarter of the total value ( ${\mathrm{log}}_{10}({\rho }_{{\mathrm{SFR}}_{\mathrm{tot}}}/({M}_{\odot }\,{\mathrm{yr}}^{-1}\,{\mathrm{Mpc}}^{-3}))\simeq -1.76$ ) at z ≃ 7-8. Therefore, the strong Hα emitters likely had a significant role in reionization.