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




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

PublisherOXFORD UNIV PRESS

OXFORD

2025

Monthly Notices of the Royal Astronomical Society

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

MON NOT R ASTRON SOC

539

2

1471

1479

9

0035-8711

1365-2966

DOIhttps://doi.org/10.1093/mnras/staf514(external)

https://academic.oup.com/mnras/article/539/2/1471/8101535(external)

https://research.utu.fi/converis/portal/detail/Publication/492309534(external)



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.


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’.


Last updated on 2025-09-06 at 12:10