J/A+A/706/A85ivo://CDS.VizieR/J/A+A/706/A85CDSLassen A.E.Smith R.Vulcani B.Tonnesen S.Calderon-Castillo P.,Poggianti B.M.Fritz J.George K.Ignesti A.Jaffe Y.Marasco A.,Matijevic L.Moretti A.Radovich M.Tomicic N.2026-03-02T06:25:50Z2026-02-03T09:36:50ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgalaxiesvisible-astronomygalaxy-clustersinterstellar-mediumgalaxy-classification-systemsspectroscopyredshiftedIn dense environments, mechanisms like ram pressure stripping (RPS) and gravitational interactions can induce the formation of similar morphological features in galaxies, distinguishable only through a detailed study of the stellar properties. While RPS affects recently formed stars through the displacement of the gas disk from which they are formed, gravitational interactions perturb stars of all ages rather similarly. We present the first observational test of the Size-Shape Difference (SSD) measure, a novel approach, originally designed and validated for simulated galaxies, that quantifies morphological differences between young and intermediate-age stellar populations to distinguish RPS from gravitationally interacting galaxies. We analyze 67 galaxies from the GASP survey using spatially resolved star formation history derived from the SINOPSIS spectral fitting code. In our fiducial model, we compare stellar populations in two age bins (t<20Myr and 20Myr<=t<570Myr) to calculate SSD values. The sample includes confirmed cases of RPS with different stripping intensities, as well as undisturbed and gravitationally interacting galaxies. We find that the extreme cases of RPS show SSD values ~3.5x higher than undisturbed and gravitationally interacting galaxies (56^+24^_-15_) as compared to 16^+6^_-2_) and 16^+6^_-3_, respectively), confirming simulation predictions. This enhancement reflects RPS-induced asymmetries: the youngest stars are either compressed along the leading edge or displaced into extended tails of cold gas from which they are formed (or both), while older populations remain undisturbed. In contrast, gravitational interactions perturb all stars uniformly, producing lower SSD values. SSD robustly distinguishes strong RPS cases, even when different age bins are used. This holds even without correcting for disk inclination, or when single-band imaging are used to trace stellar distributions. This makes SSD a promising tool to select RPS candidates for spectroscopic follow-up in upcoming large-scale surveys.2026A&A...706A..85Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/706/A85CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/706/A85https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/706/A85http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/706/A85https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/706/A85https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/706/A85http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/706/A85GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/706/A85/table1 (SSD values of the 67 GASP galaxies derived in the paper)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/706/A85/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/706/A85/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/706/A85/table1?GETtext/xml+votable180.050000true66.96908333-60.903213890.0055555555555555566/8788 16434 16765 16767 17237 17448 18009 18014 18017 18038 18411 18607 19130 19608 19993 20021 20083 20483 24637 25956 26005 26027 26198 26202 26732 26966-26967 26982 27023 27029-27030 27072 27224-27225 27236 27238-27239 28005 33241 33628 43830 43836 43838-43839 43924 43939 43942 43945 43977 45981 45984 46910 46997https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/706/A85?format=asciiOpticaldefaultJ/A+A/706/A85/table1SSD values of the 67 GASP galaxies derived in the paperJtype? JType classification (1)meta.code.classfloatnullableSSDMeasured Size-Shape Differencesrc.morph.paramdoublee_SSDSize-Shape Difference uncertainty.stat.errordoubleGClassName of the group each galaxy has been assignedmeta.idcharIDGalaxy IDmeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainzGalaxy redshiftsrc.redshiftdouble