The competing influences of ram pressure and tidal interaction in NGC 2276

¹ Department of Physics, Faculty of Science, University of Zagreb Bijenička Cesta 32 10000 Zagreb, Croatia
² INAF–Padova Astronomical Observatory Vicolo dell’Osservatorio 5 35122 Padova, Italy
³ Departamento de Fisica, Universidad Tecnica Federico Santa Maria Avenida España 1680 Valparaíso, Chile
⁴ Millenium Nucleus for Galaxies (MINGAL) Valparaíso, Chile
⁵ Georgia Institute of Technology North Avenue Atlanta GA 30332, USA
⁶ Waterloo Centre for Astrophysics & Department of Physics & Astronomy, University of Waterloo 200 University Ave W Waterloo ON N2L 3G1, Canada
⁷ Leiden Observatory, Leiden University PO Box 9513 2300 RA Leiden, The Netherlands
⁸ Physics Department & Institute of Theoretical and Computational Physics, University of Crete GR 71003 Heraklion, Greece
⁹ Institute of Astrophysics, Foundation for Research and Technology-Hellas GR 71110 Heraklion, Greece
¹⁰ Center for Astrophysics | Harvard & Smithsonian 60 Garden Street Cambridge MA 02138, USA
¹¹ Istituto Nazionale di Astrofisica (INAF) – Osservatorio Astronomico di Palermo Piazza del Parlamento 1 90134 Palermo, Italy
¹² Department of Physics, University of Florida Gainesville FL 32611-8440, USA

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Received: 5 May 2025
Accepted: 18 December 2025

Abstract

Context. The evolution of galaxies in groups is profoundly influenced by a variety of physical processes, with ram pressure and tidal interactions playing pivotal roles in shaping their structural and evolutionary pathways. The relative influences of these two processes are continuously debated with respect to groups compared to clusters, as ram pressure is less well understood in that case. In this work, we study NGC 2276, a nearby galaxy (z ≈ 0.0079), where the dominant process remains an open question.

Aims. We examined the distribution of stellar populations in NGC 2276 using multiwavelength data to assess potential evidence of tidal interactions and ram-pressure stripping.

Methods. We present the first HST WFC3/UVIS images of NGC 2276 and use them to investigate the distribution of stellar populations across the disk of NGC 2276, where we assume that the bluer broadband filters mainly trace younger stellar populations, while the redder filters trace mainly older stellar populations. Furthermore, by comparing HST images with maps of Hα emission from Calar Alto’s PMAS/PPAK integral field unit (IFU) and near-IR (NIR) maps from Spitzer’s IRAC, we identified arm-like overdensity features that trace the spiral structure of this galaxy and tracked the variation of their pitch angle with radius.

Results. Our results indicate that the distribution of the stellar populations is asymmetrical. The youngest stellar populations (up to ∼100 Myr) show a higher concentration on the leading side of the galaxy and are more diffuse on the trailing side, consistent with gas compression due to ram pressure. This asymmetry is visible in the red filters as well. We also show that the average pitch angles of the overdensity features increase with galactocentric distance. Our findings are consistent with the fact that ram pressure is the leading mechanism for the peculiar morphology of NGC 2276, but do not exclude the possibility that tidal interactions could have played a role.