MIDIS: The Relation between Strong (Hβ + [O iii]) Emission, Star Formation, and Burstiness around the Epoch of Reionization
K. I. Caputi, Pierluigi Rinaldi, Edoardo Iani, Pablo G. Pérez‐González, Göran Östlin, L. Colina, T. R. Greve, H. U. Nørgaard‐Nielsen, G. S. Wright, Javier Álvarez-Márquez, A. Eckart, J. Hjorth, Á. Labiano, O. Le Fèvre, Fabian Walter, P. van der Werf, Leindert Boogaard, Luca Costantin, Alejandro Crespo Gómez, Steven Gillman, Iris Jermann, Danial Langeroodi, Jens Melinder, Florian Peißker, M. Güdel, Th. Henning, P. O. Lagage, T. P. Ray
Abstract
Abstract We investigate the properties of strong (H β + [O iii ]) emitters before and after the end of the “Epoch of Reionization” from z = 8 to z = 5.5. We make use of ultradeep JWST / NIRCam imaging in the parallel field (P2) of the MIRI Deep Imaging Survey (MIDIS) in the Hubble eXtreme Deep Field (H-XDF), in order to select prominent (H β + [O iii ]) emitters (with rest-frame equivalent width (EW 0 ) ≳ 100 Å) at z = 5.5–7, based on their flux density enhancement in the F356W band with respect to the spectral energy distribution continuum. We complement our selection with other (H β + [O iii ]) emitters from the literature at similar and higher ( z = 7−8) redshifts. We find (nonindependent) anticorrelations between EW 0 (H β + [O iii ]) and both galaxy stellar mass and age, in agreement with previous studies, and a positive correlation with specific star formation rate (sSFR). On the SFR– M ⋆ plane, the (H β + [O iii ]) emitters populate both the star formation main sequence and the starburst region, which become indistinguishable at low stellar masses ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>log</mml:mi> <mml:mn>10</mml:mn> </mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msup> <mml:mi>M</mml:mi> <mml:mo>⋆</mml:mo> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mo><</mml:mo> <mml:mn>7.5</mml:mn> </mml:math> ). We find tentative evidence for a nonmonotonic relation between EW 0 (H β + [O iii ]) and SFR, such that both parameters correlate with each other at SFR ≳ 1 M ⊙ yr −1 , while the correlation flattens out at lower SFRs. This suggests that low metallicities producing high EW 0 (H β + [O iii ]) could be important at low SFR values. Interestingly, the properties of the strong emitters and other galaxies (33% and 67% of our z = 5.5–7 sample, respectively) are similar, including, in many cases, high sSFR. Therefore, it is crucial to consider both emitters and nonemitters to obtain a complete picture of the cosmic star formation activity around the Epoch of Reionization.