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
Pierluigi Rinaldi, K. I. Caputi, Luca Costantin, Steven Gillman, Edoardo Iani, Pablo G. Pérez‐González, Göran Östlin, L. Colina, T. R. Greve, H. U. Noorgard-Nielsen, G. S. Wright, A. Alonso‐Herrero, Javier Álvarez-Márquez, A. Eckart, M. García-Marín, J. Hjorth, O. Ilbert, Sarah Kendrew, Á. Labiano, O. Le Fèvre, J. P. Pye, Tuomo Tikkanen, Fabian Walter, P. van der Werf, M. J. Ward, Marianna Annunziatella, R. Azzollini, Arjan Bik, Leindert Boogaard, Sarah E. I. Bosman, Alejandro Crespo Gómez, Iris Jermann, Danial Langeroodi, Jens Melinder, R. A. Meyer, T. Moutard, Florian Peißker, M. Topinka, E. F. van Dishoeck, M. Güdel, Th. Henning, Pierre-Olivier Lagage, T. P. Ray, B. Vandenbussche, C. Waelkens, Rafael Navarro-Carrera, Vasily Kokorev
Abstract
Abstract We make use of JWST medium-band and broadband NIRCam imaging, along with ultradeep MIRI 5.6 μ m 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 (H β + [O iii ]) emitters, based on their enhanced fluxes in the F430M and F444W filters, with EW 0 (H β +[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 μ m, indicating the simultaneous presence of a prominent H α emission line with EW 0 (H α ) ≃200–3000 Å. This is the first time that H α emission can be detected in individual galaxies at z > 7. The H α line, when present, allows us to separate the contributions of H β and [O iii ] to the (H β +[O iii ]) complex and derive H α -based star formation rates (SFRs). We find that in most cases [O iii ]/H β > 1. Instead, two galaxies have [O iii ]/H β < 1, indicating that the NIRCam flux excess is mainly driven by H β . 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>SFR</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>Mpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≃</mml:mo> <mml:mo>−</mml:mo> <mml:mn>2.35</mml:mn> </mml:math> , which is about a quarter of the total value ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>SFR</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>tot</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>Mpc</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≃</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1.76</mml:mn> </mml:math> ) at z ≃ 7–8. Therefore, the strong H α emitters likely had a significant role in reionization.