Secondary Infall in the Seyfert's Sextet: A Plausible Way Out of the Short Crossing Time Paradox

Omar López-Cruz*, Héctor Javier Ibarra-Medel, Sebastián F. Sánchez, Mark Birkinshaw, Christopher Añorve, Jorge K. Barrera-Ballesteros, Jesús Falcon-Barroso, Wayne A. Barkhouse, Juan P. Torres-Papaqui

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

2 Citations (Scopus)
140 Downloads (Pure)


We used integral field spectroscopy from CALIFA DR3 and multiwavelength publicly-available data to investigate the star-formation histories of galaxies in the Seyfert's Sextet (SS, HCG 79). The galaxies H79a, H79b, H79c, and H79f have low star-formation rates despite showing strong signs of interaction. By exploring their individual specific star formation histories (sSFH), we identified three earlier episodes of strong star formation common to these four galaxies. We use the last two episodes as markers of the epochs when the galaxies were crossing. We suggest that after the first turn-around, initially gas-rich galaxies crossed for the first time, consuming most of their gas. Hence after the second turn-around most mergers from second crossings would be mixed or dry. The exception would be gas-rich galaxies intruding for the first time. Therefore, we suggest that SS galaxies have survived one crossing during a Hubble time. Strong Balmer absorption lines and the presence of counter-rotating disks provide independent bounds to the second and first crossing, respectively. This scenario provides a plausible way out of the short crossing time paradox.
Original languageEnglish
Article numberL2
Number of pages11
JournalAstrophysical Journal Letters
Issue number1
Early online date28 Oct 2019
Publication statusPublished - 13 Nov 2019


  • Star formation
  • Stellar evolution
  • Disk galaxies
  • E+A galaxies
  • Stellar evolutionary models
  • Galaxy dynamics
  • Galaxies
  • Galaxy collisions
  • Galaxy mergers
  • Galaxy groups
  • Galactic and extragalactic astronomy
  • Hickson compact group


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