SIT 45: An interacting, compact, and star-forming isolated galaxy triplet Grajales-Medina, D. Argudo Fernández, María del Carmen Verley, Simon Duarte Puertas, Salvador Lisenfeld, Ute Espada Fernández, Daniel Galaxies: general Galaxies: formation Galaxies: evolution Galaxies: interactions galaxies: star formation Acknowledgements. We thank our referee whose valuable comments have certainly contributed to improve and clarify this paper. MAF and PVB acknowledge financial support by the DI-PUCV research project 039.481/2020. MAF also acknowledges support from FONDECYT iniciación project 11200107 and the Emergia program (EMERGIA20_38888) from Consejería de Transformación Económica, Industria, Conocimiento y Universidades and University of Granada. UL and DE acknowledge support from project PID2020-114414GB- 100, financed by MCIN/AEI/10.13039/501100011033. DE also acknowledges support from Beatriz Galindo senior fellowship (BG20/00224) financed by the Spanish Ministry of Science and Innovation, and project PID2020-114414GB- 100 financed by MCIN/AEI/10.13039/501100011033. UL, SV and DE acknowledge support from project P20_00334 financed by the Junta de Andalucía and from FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades/Proyecto A-FQM-510-UGR20. MB gratefully acknowledges support by the ANID BASAL project FB210003 and from the FONDECYT regular grant 1211000. SDP is grateful to the Fonds de Recherche du Québec – Nature et Technologies and acknowledges financial support from the Spanish Ministerio de Economía y Competitividad under grants AYA2016-79724-C4-4-P and PID2019-107408GB-C44, from Junta de Andalucía Excellence Project P18-FR-2664, and also acknowledges support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). This research made use of Astropy, a community-developed core Python (http://www.python.org) package for Astronomy (Astropy Collaboration 2013); Ipython (Pérez & Granger 2007); Matplotlib (Hunter 2007); Numpy (Walt et al. 2011); Scipy (Jones et al. 2001); and Topcat (Taylor 2005). This research made use of Astrodendro, a Python package to compute dendrograms of Astronomical data (http:// www.dendrograms.org/). This research has made use of the NASA/IPAC Extragalactic Database, operated by the Jet Propulsion Laboratory of the California Institute of Technology, un centract with the National Aeronautics and Space Administration. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy O ce of Science. The SDSS-III Web site is http://www.sdss3.org/. The SDSS-IV site is http://www.sdss. org. Based on observations made with the NASA Galaxy Evolution Explorer (GALEX). GALEX is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory /California Institute of Technology, funded by the National Aeronautics and Space Administration. Context. The underlying scenario of the formation and evolution of galaxy triplets is still uncertain. Mergers of galaxies in isolated triplets give us the opportunity to study the already complex merging process, with minimal contamination of other environmental effects that potentially allow and accelerate galaxy transitions from active star-forming to passive galaxies. Aims. The merging system SIT 45 (UGC 12589) is one of 315 systems in the SDSS-based catalogue of Isolated Triplets (SIT); it is an unusual isolated galaxy triplet, consisting of three merging late-type galaxies. The main aims of this work are to study the dynamical evolution and star formation history (SFH) of SIT 45, as well as its dependence on its local and large-scale environment. Methods. To study its dynamics, parameters such as the velocity dispersion (σv), the harmonic radius (RH), the crossing time (H0tc), and the virial mass (Mvir), along with the compactness of the triplet (S) were considered. To investigate the possible dependence of these dynamical parameters on the environment, the tidal force Q parameters (both local and large-scale) and the projected local density (ηk) were used. To constrain the SFH, we used CIGALE to fit its observed spectral energy distribution using multiwavelength data from the ultraviolet to the infrared. Results. SIT 45 is one of the most compact triplets in the SIT, and it is also more compact than triplets in other samples. According to its SFH, SIT 45 presents star formation, where the galaxies also present recent (∼200 Myr) star formation increase, indicating that this activity may have been triggered by the interaction. Its dynamical configuration suggests that the system is highly evolved in comparison to the SIT. However, this is not expected for systems composed of star-forming late-type galaxies, based on observations in compact groups. Conclusions. We conclude that SIT 45 is a system of three interacting galaxies that are evolving within the same dark matter halo; its compact configuration is a consequence of the ongoing interaction rather than being due to a long-term evolution (as suggested from its H0tc value). We consider two scenarios for the present configuration of the triplet, one where one of the members is a tidal galaxy, and another where this galaxy arrives to the system after the interaction. Both scenarios need further exploration. The isolated triplet SIT 45 is therefore an ideal system to study short timescale mechanisms (∼108 yr), such as starbursts triggered by interactions which are more frequent at higher redshift. 2023-02-14T11:38:53Z 2023-02-14T11:38:53Z 2022-12-22 journal article D. Grajales-Medina et al.: SIT 45: An interacting, compact, and star-forming isolated galaxy triplet. A&A 669, A23 (2023) [https://doi.org/10.1051/0004-6361/202244492] https://hdl.handle.net/10481/79924 10.1051/0004-6361/202244492 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional EDP Sciences