RT Journal Article T1 A multi-wavelength analysis of M 81: insight on the nature of Arp's loop A1 Sollima, A. A1 Gil de Paz, Armando A1 Martínez Delgado, D. A1 Gabany, R. J. A1 Gallego Laborda, J. J. A1 Hallas, T. AB Context. The optical ring-like structure detected by Arp (1965) around M81 (commonly referenced as "Arp's loop") represents one of thethe most spectacular features observed in nearby galaxies. Arp's loop is commonly interpreted as a tail resulting from the tidal interaction between M81 and M82. However, since its discovery the nature of this feature has remained controversial. Aims. Our primary purpose was to identify the sources of optical and infrared emission observed in Arp's loop. Methods. The morphology of Arp's loop has been investigated with deep wide-field optical images. We also measured its colors using IRAS and Spitzer-MIPS infrared images and compared them with those of the disk of M81 and Galactic dust cirrus that fills the area where M81 is located. 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We are grateful to Ignacio Trujillo, Michele Bellazzini, Julianne Dalcanton, and Juan Carlos Muñoz Mateos for helpful discussions. We also thank Steve Mandel for providing us their wide field deep images of the M81 sky area. NO Ministerio de Ciencia e Innovación (MICINN), España DS Docta Complutense RD 18 may 2024