INSPIRE: INvestigating Stellar Population In RElics VIII. Emission lines and UV colours in ultracompact massive galaxies
Year: 2025
Type: article
Abstract: ABSTRACT We report the discovery of emission lines in the optical spectra of ultracompact massive galaxies (UCMGs) from INSPIRE including relics, which are the oldest galaxies in the Universe. Emission-lines diagnostic diagrams suggest that all these UCMGs, independently of their star formation histories, are ‘retired galaxies’. They are inconsistent with being star-forming but lie in the same region of shock-driven emissions or photoionization models, incorporating the contribution from post-asymptotic giant branch (pAGB) stars. Furthermore, all but one INSPIRE objects have a high [O ii]/H$\alpha$ ratio, resembling what has been reported for normal-size red and dead galaxies. The remaining object (J1142+0012) is the only one to show clear evidence for strong active galactic nucleus activity from its spectrum. We also provide near-UV (far-UV) fluxes for 20 (5) INSPIRE objects that match in GALEX. Their ${\rm NUV}-r$ colours are consistent with those of galaxies lying in the UV green valley, but also with the presence of recently ($\le 0.5$ Gyr) formed stars at the sub-per cent fraction level. This central recent star formation could have been ignited by gas that was originally ejected during the pAGB phases and then re-compressed and brought to the core by the ram-pressure stripping of Planetary Nebula envelopes. Once in the centre, it can be shocked and re-emit spectral lines.
Authors: Chiara Spiniello, Mario Radovich, Anna Ferré-Mateu, Roberto De Propris, Magda Arnaboldi, Francesco La Barbera, Johanna Hartke, Giuseppe D’Ago, Crescenzo Tortora, Davide Bevacqua, Michalina Maksymowicz-Maciata, John Mills, Nicola R Napolitano, Claudia Pulsoni, Paolo Saracco, Diana Scognamiglio
Institutions: University of Oxford, Osservatorio Astronomico di Padova, National Institute for Astrophysics, Universidad de La Laguna, Instituto de Astrofísica de Canarias, University of Turku, Botswana International University of Science and Technology, European Southern Observatory, Astronomical Observatory of Capodimonte, University of Cambridge, University of Insubria, Brera Astronomical Observatory, University of Bristol, University of Naples Federico II, Max Planck Institute for Extraterrestrial Physics, California Institute of Technology, Jet Propulsion Laboratory
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Awards: G170708805, G2197447341, G2262748287, Cambridge Astronomical Survey Unit (CASU) (2023-2026): Powering Next Generation Survey Analysis and Processing, G3438924983, G3480869486, G425668148, G4753320163, Cambridge Astronomical Survey Unit (CASU): Filling the Astronomical Data Lake (2020-2024), G5809860598, G586857820, G7084143925, G7094801989, G8622543885
OpenAlex ID: W6940587727