Euclid: Disky titans - surprisingly high star formation activity and gas content in two brightest group galaxies at z~0.75

@misc{gentile2026euclid,
  title = {{Euclid: Disky titans - surprisingly high star formation activity and gas content in two brightest group galaxies at z~0.75}},
  author = {F. Gentile and E. Daddi and D. Elbaz and A. Enia and F. Vito and P. -A. Duc and M. Franco and H. Fu and R. Giuffrida and D. Roberts and F. Shankar and S. Lu and P. Awad and J-B. Billand and M. Baes and L. Bisigello and E. Duran-Camacho and G. Castignani and O. Cucciati and G. De Lucia and C. D'Eugenio and D. Donevski and M. Fossati and M. Fumagalli and R. Gobat and C. Gruppioni and M. Magliocchetti and B. Magnelli and G. Papini and L. Pozzetti and V. Sangalli and J. G. Sorce and L. Spinoglio and V. Strazzullo and M. Tarrasse and G. Toni and G. Zamorani and J. Lewis and B. Altieri and S. Andreon and N. Auricchio and C. Baccigalupi and M. Baldi and S. Bardelli and P. Battaglia and A. Biviano and M. Bolzonella and E. Branchini and M. Brescia and S. Camera and V. Capobianco and C. Carbone and J. Carretero and M. Castellano and S. Cavuoti and A. Cimatti and C. Colodro-Conde and G. Congedo and L. Conversi and Y. Copin},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2606.02687},
  eprint = {2606.02687},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2606.02687},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Euclid: Disky titans - surprisingly high star formation activity and gas content in two brightest group galaxies at z~0.75
AU  - F. Gentile
AU  - E. Daddi
AU  - D. Elbaz
AU  - A. Enia
AU  - F. Vito
AU  - P. -A. Duc
AU  - M. Franco
AU  - H. Fu
AU  - R. Giuffrida
AU  - D. Roberts
AU  - F. Shankar
AU  - S. Lu
AU  - P. Awad
AU  - J-B. Billand
AU  - M. Baes
AU  - L. Bisigello
AU  - E. Duran-Camacho
AU  - G. Castignani
AU  - O. Cucciati
AU  - G. De Lucia
AU  - C. D'Eugenio
AU  - D. Donevski
AU  - M. Fossati
AU  - M. Fumagalli
AU  - R. Gobat
AU  - C. Gruppioni
AU  - M. Magliocchetti
AU  - B. Magnelli
AU  - G. Papini
AU  - L. Pozzetti
AU  - V. Sangalli
AU  - J. G. Sorce
AU  - L. Spinoglio
AU  - V. Strazzullo
AU  - M. Tarrasse
AU  - G. Toni
AU  - G. Zamorani
AU  - J. Lewis
AU  - B. Altieri
AU  - S. Andreon
AU  - N. Auricchio
AU  - C. Baccigalupi
AU  - M. Baldi
AU  - S. Bardelli
AU  - P. Battaglia
AU  - A. Biviano
AU  - M. Bolzonella
AU  - E. Branchini
AU  - M. Brescia
AU  - S. Camera
AU  - V. Capobianco
AU  - C. Carbone
AU  - J. Carretero
AU  - M. Castellano
AU  - S. Cavuoti
AU  - A. Cimatti
AU  - C. Colodro-Conde
AU  - G. Congedo
AU  - L. Conversi
AU  - Y. Copin
PY  - 2026
DA  - 2026/09/28
PB  - arXiv
DO  - 10.48550/arxiv.2606.02687
UR  - https://arxiv.org/abs/2606.02687
AB  - We present the discovery of two disky titans in the first data release of the Euclid satellite. These sources are massive (M>10^11 Msun) star-forming (SFR~20 Msun/yr) discs located in strong over-densities at intermediate redshift (z~0.75). They represent an small fraction of the massive galaxies in over-dense regions (just four candidates in more than 20 deg2 analysed in this study), and their existence is puzzling considering the abundance of passive and bulge-dominated sources commonly found at the centre of groups and clusters at low redshift. Firstly, our analysis shows that these objects are located in massive groups (Mh~10^13.8 Msun), where rapid accretion of cold gas should be prevented from the formation of a static hot halo. Despite this, a millimetre follow-up with NOEMA shows significant cold gas reservoirs (M_h2~10^10.3 Msun) within these sources. Secondly, our morphological analysis shows the presence of a massive and passive bulge in these galaxies, which is expected to stabilise the disc against fragmentation thereby suppressing further star formation. However, these sources lie on the Schmidt-Kennicutt relation or even slightly above. Building on these observations, we propose a scenario where these disky titans are the product of a merger-induced rejuvenation episode, in which the most massive galaxy of a group accretes cold gas from another member and briefly restarts star-formation. Such scenario is supported by a comparison with the TNG300 simulation and easily explains the surviving of star-formation activity in massive galaxies in over-dense environments as temporary stages in a more complex evolution. More in general, our study showcases the ability of Euclid to find rare objects thanks to the unprecedented statistics offered by its surveys and the scientific potential residing in the synergy between Euclid and other facilities observing at longer wavelengths.
ER  -