The star formation histories of galaxies in different stages of pre-processing in the Fornax A group
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Date
2023Author
Loubser, S. I.
Mosia, K.
Serra, P.
Kleiner, D.
Peletier, R. F.
Kraan-Korteweg, R. C.
Iodice, E.
Loni, A.
Kamphuis, P.
Zabel, N.
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We study the recentstar formation histories of 10 galaxiesin the Fornax A galaxy group, on the outskirts of the Fornax cluster. The
group galaxies are gas-rich, and their neutral atomic hydrogen (H I) was studied in detail with observations from the MeerKAT
telescope. This allowed them to be classified into different stages of pre-processing (early, ongoing, advanced). We use long-slit
spectra obtained with the South African Large Telescope (SALT) to analyse stellar population indicators to constrain quenching
time-scales and to compare these to the H I gas content of the galaxies. The H α equivalent width, EW(H α), suggest that the
pre-processing stage is closely related to the recent (<10 Myr) specific Star Formation Rate (sSFR). The early-stage galaxy
(NGC 1326B) is not yet quenched in its outer parts, while the ongoing-stage galaxies mostly have a distributed population
of very young stars, though less so in their outer parts. The galaxies in the advanced stage of pre-processing show very low
recent sSFR in the outer parts. Our results suggest that NGC 1326B, FCC 35, and FCC 46 underwent significantly different
histories from secular evolution during the last Gyr. The fact that most galaxies are on the secular evolution sequence implies
that pre-processing has a negligible effect on these galaxies compared to secular evolution. We find EW(H α) to be a useful tool
for classifying the stage of pre-processing in group galaxies. The recent sSFR and H I morphology show that galaxies in the
Fornax A vicinity are pre-processing from the outside in.
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