INSPIRE: INvestigating Stellar Population In RElics VIII. Emission lines and UV colours in ultracompact massive galaxies - UTU Research Portal

A1 Refereed original research article in a scientific journal

INSPIRE: INvestigating Stellar Population In RElics VIII. Emission lines and UV colours in ultracompact massive galaxies

Authors: Spiniello, Chiara; Radovich, Mario; Ferre-Mateu, Anna; De Propris, Roberto; Arnaboldi, Magda; La Barbera, Francesco; Hartke, Johanna; D'Ago, Giuseppe; Tortora, Crescenzo; Bevacqua, Davide; Maksymowicz-Maciata, Michalina; Mills, John; Napolitano, Nicola R.; Pulsoni, Claudia; Saracco, Paolo; Scognamiglio, Diana

Publisher: OXFORD UNIV PRESS

Publishing place: OXFORD

Publication year: 2025

Journal: Monthly Notices of the Royal Astronomical Society

Journal name in source: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Journal acronym: MON NOT R ASTRON SOC

Volume: 539

Issue: 2

First page : 1471

Last page: 1479

Number of pages: 9

ISSN: 0035-8711

eISSN: 1365-2966

DOI: https://doi.org/10.1093/mnras/staf514

Web address : https://academic.oup.com/mnras/article/539/2/1471/8101535

Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/492309534

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]/Hα 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 NUV-r colours are consistent with those of galaxies lying in the UV green valley, but also with the presence of recently (≤ 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.

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Funding information in the publication:
CS, CT, FLB, DB, and PS acknowledge funding from the INAF PRIN-INAF 2020 programme 1.05.01.85.11. JH and CS acknowledge the financial support from the mobility programme of the Finnish Centre for Astronomy with ESO (FINCA), funded by the Academy of Finland grant nr 306531. AFM has received support from RYC2021-031099-I and PID2021-123313NA-I00 of MICIN/AEI/10.13039/501100011033/FEDER,UE, NextGenerationEU/PRT. CT acknowledges the INAF grant 2022 LEMON. GD acknowledges support by UKRI-STFC grants: ST/T003081/1 and ST/X001857/1. MR acknowledges financial support from the INAF mini-grant 2022 ‘GALCLOCK’.