Galaxy evolution in the post-merger regime. V - Atomic gas evolution traced by ALFALFA stacks

@misc{ellison2026galaxy,
  title = {{Galaxy evolution in the post-merger regime. V - Atomic gas evolution traced by ALFALFA stacks}},
  author = {Sara L. Ellison and Manasvee Saraf and Leonardo Ferreira and Amelie Saintonge and Dirk Scholte and Jing Wang and Qifeng Huang},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.24925},
  eprint = {2609.24925},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.24925},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Galaxy evolution in the post-merger regime. V - Atomic gas evolution traced by ALFALFA stacks
AU  - Sara L. Ellison
AU  - Manasvee Saraf
AU  - Leonardo Ferreira
AU  - Amelie Saintonge
AU  - Dirk Scholte
AU  - Jing Wang
AU  - Qifeng Huang
PY  - 2026
DA  - 2026/09/21
PB  - arXiv
DO  - 10.48550/arxiv.2609.24925
UR  - https://arxiv.org/abs/2609.24925
AB  - (Abridged) In this work, we investigate the role of atomic hydrogen (HI) gas in the galaxy merger lifecycle. In order to both identify galaxies in mergers, as well as to predict their time since coalescence, we present an extension of the MUlti Model Merger Identifier (MUMMI) machine vision pipeline applied to Dark Energy Camera Legacy Survey (DECaLS) imaging. The new MUMMI-DECaLS catalog contains 19,951 post-mergers, of which 14,638 have robust time post-merger (T_PM) predictions. The MUMMI-DECaLS post-merger galaxy catalog is cross-matched with the Arecibo Legacy Fast ALFA (ALFALFA) survey. For the 752 post-mergers thus identified, as well as a matched control sample, we produce median spectral stacks of 21~cm emission, finding that the post-mergers are HI deficient by 0.11 dex compared with non-interacting galaxies. When divided into T_PM bins we find that the HI deficit (or excess) is strongly dependent on both the time since coalescence and whether the galaxies are star-forming or quenched. Star-forming post-mergers in particular show a strong HI evolution with T_PM, exhibiting a 0.1 dex MHI excess immediately after coalescence, a 0.3 dex MHI deficit at 0.16 < T_PM < 0.96 Gyr and normal gas masses by ~ 1.5 Gyr after coalescence. On the other hand, despite being matched in star formation rate, stellar mass and redshift, quenched post-mergers are HI deficient at both short and long post-coalescence times. Nonetheless, a significant mass of HI (>10^9 M_sun) remains even in these late-time quenched post-mergers, representing a resource which could potentially re-fuel star formation in the future. Our results demonstrate the complexity of quantifying the HI behaviour in mergers, which depends not only on timing, but also star-forming status, which can complicate comparisons between different studies and samples.
ER  -