INSPIRE: INvestigating Stellar Population In RElics VIII. Emission lines and UV colours in ultra-compact massive galaxies
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| Format: | Preprint |
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2025
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| author | Spiniello, Chiara Radovich, Mario Ferré-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 Rosario Pulsoni, Claudia Saracco, Paolo Scognamiglio, Diana |
| author_facet | Spiniello, Chiara Radovich, Mario Ferré-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 Rosario Pulsoni, Claudia Saracco, Paolo Scognamiglio, Diana |
| contents | We report the discovery of emission lines in the optical spectra of ultra-compact 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 photoionisation models, incorporating the contribution from post-asymptotic giant branch (pAGB) stars. Furthermore, all but one INSPIRE objects have a high [OII]/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-percent 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_20980 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | INSPIRE: INvestigating Stellar Population In RElics VIII. Emission lines and UV colours in ultra-compact massive galaxies Spiniello, Chiara Radovich, Mario Ferré-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 Rosario Pulsoni, Claudia Saracco, Paolo Scognamiglio, Diana Astrophysics of Galaxies We report the discovery of emission lines in the optical spectra of ultra-compact 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 photoionisation models, incorporating the contribution from post-asymptotic giant branch (pAGB) stars. Furthermore, all but one INSPIRE objects have a high [OII]/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-percent 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. |
| title | INSPIRE: INvestigating Stellar Population In RElics VIII. Emission lines and UV colours in ultra-compact massive galaxies |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2503.20980 |