The lifetimes and properties of Little Red Dots in the AMBRA simulation

@misc{lachance2026lifetimes,
  title = {{The lifetimes and properties of Little Red Dots in the AMBRA simulation}},
  author = {Patrick LaChance and Yihao Zhou and Aklant Kumar Bhowmick and Rupert A. C. Croft and Tiziana Di Matteo and Laura Blecha and Fabio Pacucci and Paul Torrey and Simeon Bird},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.26999},
  eprint = {2609.26999},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.26999},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - The lifetimes and properties of Little Red Dots in the AMBRA simulation
AU  - Patrick LaChance
AU  - Yihao Zhou
AU  - Aklant Kumar Bhowmick
AU  - Rupert A. C. Croft
AU  - Tiziana Di Matteo
AU  - Laura Blecha
AU  - Fabio Pacucci
AU  - Paul Torrey
AU  - Simeon Bird
PY  - 2026
DA  - 2026/09/22
PB  - arXiv
DO  - 10.48550/arxiv.2609.26999
UR  - https://arxiv.org/abs/2609.26999
AB  - We identify and analyze the little red dots (LRDs) in the AMBRA cosmological hydrodynamic simulation, by producing mock observations of the galaxies and active galactic nuclei (AGN) between redshifts 5 and 8. We produce these mock observations with both a standard AGN emission model, and a ``gas-enshrouded'' model, and find that the presence of a gas-enshrouded AGN is instrumental to the reproduction of dim LRDs (F444W magnitude > 26.0). We find a steeper decrease in LRD density between z=5 and z=8 within AMBRA than seen in observations, resulting in a relative underproduction of LRDs beyond z∼6 in AMBRA. With the addition of unresolved AGN variability, the decline with redshift flattens, and the LRD redshift evolution in AMBRA becomes broadly consistent with other theoretical datasets, and closer to that seen in observations. We find that the LRDs in AMBRA are pre-existing black hole--galaxy systems that are undergoing an LRD phase, selected primarily by the brightness of the AGN relative to its host. While the exact duration of these LRD phases is not possible to determine due to the unresolved nature of the AGN environment, we use the available time-series data to place limits on the lifetimes of the LRDs in AMBRA. We find that the vast majority of LRDs in AMBRA have lifetimes between ∼3 and ∼ 300 Myr with LRD lifetime increasing with both black hole and host galaxy mass. The lower mass LRDs are more dependent on housing a gas-enshrouded AGN, and have shorter lifetimes (∼30 Myr). The higher mass LRDs are less sensitive to their AGN environment, but require more compact host galaxies, and have longer lifetimes (∼100 Myr).
ER  -