Starburst galaxies in the Hydra I cluster

¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
² Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
³ ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Department of Astronomy, University of Wisconsin-Madison, 475 N Charter St, Madison, WI 53706, USA
⁵ Research Center for Astronomical Computing, Zhejiang Laboratory, Hangzhou 311100, China
⁶ Department of Astronomy, University of Cape Town, Private Bag X3, 7701 Rondebosch, South Africa
⁷ Institute for Astronomy, University of Hawaii at Hilo, 640 N Aohoku Pl 209, Hilo HI 96720, USA
⁸ Western Sydney University, Locked Bag 1797, Penrith South DC NSW 1797, Australia
⁹ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, John Street, Hawthorn 3122, Australia
¹⁰ Department of Physics and Astronomy, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, South Africa
¹¹ Dpto. de Física Teórica y del Cosmos, University of Granada, Facultad de Ciencias (Edificio Mecenas), 18071 Granada, Spain
¹² Institut de Radioastonomie Millimétrique (IRAM), Av. Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
¹³ Département de physique, Université de Montréal, Complexe des sciences MIL, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Qc H2V 0B3, Canada
¹⁴ Laboratoire de Physique et de Chimie de l’Environnement, Observatoire d’Astrophysique de l’Université Ouaga I Pr Joseph Ki-Zerbo (ODAUO), BP 7021 Ouaga 03, Burkina Faso
¹⁵ Département de physique, de génie physique et d’optique, Université Laval, Québec (QC) G1V 0A6, Canada

^★ Corresponding author: clarac@iaa.es

Received: 20 January 2025
Accepted: 1 October 2025

Abstract

Studying the impact of environment on star formation and quenching pathways requires statistically relevant samples of galaxies in a wide mass range. We present a new catalog of 196 galaxies of the nearby Hydra I cluster out to ∼1.75r₂₀₀, consisting of broad u,g,r,i,z along with narrowband Hα measurements. These deep optical images were obtained with the DECam camera (CTIO) and reach down to a surface brightness limit of μ(3σ; 10″ × 10″) = 26.9 mag arcsec² in the g band. We also report the HI properties for 89 cluster members detected with MeerKAT. A color magnitude diagram (CMD) shows a bimodal distribution typical of a cluster population, more evolved than those found in isolation. We combined optical Hα and WISE infrared data to compare the star formation history at two distinct timescales. Differences in the star-forming activity depicted by both populations manifest as a starburst in 24 found members. Of these, 18 starburst galaxies have neutral gas measurements, and they show disturbed HI disks that suggest an environmentally triggered boost in star formation within the last 10⁷ yrs. Processes such as ram pressure stripping or tidal interactions may underlie their enhanced star-forming activity and asymmetric disks. Since Hydra’s dynamical history is unclear, we examine the spatial and velocity distribution of the sample. We reveal a possible link between the large-scale structure feeding the Hydra I cluster and the heightened star-forming activity of the starburst galaxies. This feeding pattern matches the few substructures that have been identified in Hydra in previous works, and this may explain their origin. Our results portray a picture of a cluster with an evolved nature, plus a population of new infalling galaxies that manifest the impact of their first contact with the cluster environment through star formation, color, morphology, and gas content transformations.