MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at <i>z</i> ≃ 6.6

Abstract We present Virgil, a Mid-Infrared Instrument (MIRI) extremely red object detected with the F1000W filter as part of the MIRI Deep Imaging Survey observations of the Hubble Ultra Deep Field. Virgil is an Ly α emitter (LAE) at z spec = 6.6312 ± 0.0019 (from the Very Large Telescope/MUSE) with a rest-frame UV-to-optical spectral energy distribution (SED) typical of LAEs at similar redshifts. However, MIRI observations reveal an unexpected extremely red color at rest-frame near-infrared (NIR) wavelengths, F444W − F1000W = 2.33 ± 0.06. Such a steep rise in the NIR, completely missed without MIRI imaging, is poorly reproduced by models including only stellar populations and hints toward the presence of an active galactic nucleus, although alternative explanations such as extreme dust obscuration and strong nebular continuum and emission lines contribution due to young stellar ages cannot be completely ruled out. According to the shape of its overall SED, Virgil belongs to the recently discovered population of little red dots but displays an extended rest-frame UV-optical wavelength morphology following a 2D-Sérsic profile with an average index of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.9</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.31</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.85</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.11</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> pkpc. Only at MIRI wavelengths, Virgil is unresolved due to the coarser point-spread function. This discovery demonstrates the crucial importance of deep MIRI surveys to reveal the true nature and properties of high- z galaxies that otherwise would be misinterpreted and raises the question of how common Virgil-like objects could be in the early Universe.

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Journal
The Astrophysical Journal
Published
2025-08-12
DOI
https://doi.org/10.3847/1538-4357/ade5a6
Citations
6
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
6.93

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article

MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at z ≃ 6.6

J. Hjorth, Sarah Kendrew, K. I. Caputi, Fabian Walter et al.
6 citations
The Astrophysical Journal
Galaxies: Formation, Evolution, Phenomena
6.93
article

MIDIS: MIRI Uncovers Virgil, the First Little Red Dot with Clear Detection of Its Host Galaxy at z ≃ 6.6

J. Hjorth, Sarah Kendrew, K. I. Caputi, Fabian Walter, M. Guêdel, T. R. Greve, A. Alonso‐Herrero, Alvaro Labiano, Tuomo Tikkanen, Luca Costantin, L. Colina, Göran Östlin, Pablo G. Pérez‐González, Arjan Bik, Alejandro Crespo Gómez, Marianna Annunziatella, Leindert Boogaard, Edoardo Iani, Pierluigi Rinaldi, J. P. Pye, Javier Álvarez-Márquez, Sarah E. I. Bosman, T. Moutard, P. van der Werf, Jens Melinder, Thomas Henning, Steven Gillman, Danial Langeroodi, Gillian Wright
article en
6 citations

Abstract

Abstract We present Virgil, a Mid-Infrared Instrument (MIRI) extremely red object detected with the F1000W filter as part of the MIRI Deep Imaging Survey observations of the Hubble Ultra Deep Field. Virgil is an Ly α emitter (LAE) at z spec = 6.6312 ± 0.0019 (from the Very Large Telescope/MUSE) with a rest-frame UV-to-optical spectral energy distribution (SED) typical of LAEs at similar redshifts. However, MIRI observations reveal an unexpected extremely red color at rest-frame near-infrared (NIR) wavelengths, F444W − F1000W = 2.33 ± 0.06. Such a steep rise in the NIR, completely missed without MIRI imaging, is poorly reproduced by models including only stellar populations and hints toward the presence of an active galactic nucleus, although alternative explanations such as extreme dust obscuration and strong nebular continuum and emission lines contribution due to young stellar ages cannot be completely ruled out. According to the shape of its overall SED, Virgil belongs to the recently discovered population of little red dots but displays an extended rest-frame UV-optical wavelength morphology following a 2D-Sérsic profile with an average index of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>n</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0.9</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.31</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.85</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.11</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> pkpc. Only at MIRI wavelengths, Virgil is unresolved due to the coarser point-spread function. This discovery demonstrates the crucial importance of deep MIRI surveys to reveal the true nature and properties of high- z galaxies that otherwise would be misinterpreted and raises the question of how common Virgil-like objects could be in the early Universe.

The Astrophysical JournalVol. 989(2)
Leiden University (NL), University of Copenhagen (DK), Space Telescope Science Institute (US), University of Vienna (AT), University of Arizona (US), University of Leicester (GB), Institute of Science and Technology Austria (AT), Stockholm University (SE), University of Groningen (NL), Heidelberg University (DE), ETH Zurich (CH), European Space Astronomy Centre (ES), Royal Observatory (GB), Max Planck Institute for Astronomy (DE), Centro de Astrobiología (ES), AlbaNova (SE), University College London (GB), UK Astronomy Technology Centre (GB), Heidelberg Institute for Theoretical Studies (DE), Technical University of Denmark (DK)
National Aeronautics and Space Administration, Northrop Grumman, Utah State University, Villum Fonden, Space Telescope Science Institute, European Space Agency, University of Leicester, University College London, Cardiff University, National Research Foundation, Dublin Institute for Advanced Studies, Universiteit Leiden, Rijksuniversiteit Groningen, Danmarks Grundforskningsfond, Universiteit van Amsterdam, Chalmers Tekniska Högskola, Eidgenössische Technische Hochschule Zürich, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Paul Scherrer Institut, Ministerio de Ciencia e Innovación, Universität zu Köln, Instituto Nacional de Técnica Aeroespacial, Max-Planck-Institut für Astronomie, Ames Research Center, Jet Propulsion Laboratory, Goddard Space Flight Center, Science and Technology Facilities Council, Consejo Superior de Investigaciones Científicas, European Regional Development Fund, Agencia Estatal de Investigación
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