Dissecting the Perseus-Pisces supercluster observed with CFHT-MegaCam: Exploring late-type galaxy shape alignments within the local cosmic web
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| Autores principales: | , , , , |
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| Formato: | Preprint |
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2026
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| _version_ | 1866914591162761216 |
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| author | Mondelin, M. Codis, S. Cuillandre, J. -C. Paviot, R. de Boer, T. |
| author_facet | Mondelin, M. Codis, S. Cuillandre, J. -C. Paviot, R. de Boer, T. |
| contents | Intrinsic alignments of galaxy shapes are a major systematic for weak gravitational lensing and provide insight into how galaxies acquire orientations within the cosmic web. Most studies rely on large statistical samples; here, we probe this signal in a single nearby superstructure, extending to outer regions where secondary infall should dominate. We measure intrinsic alignments in the Perseus-Pisces supercluster as a function of galaxy morphology and radial extent into the low surface brightness regime. Using deep CFHT r-band imaging covering 367 deg2 (mainly from the UNIONS survey) and reaching 28 mag/arcsec2, we compute correlation functions at three isophotal radii for 2004 galaxies with log M*/Msun > 8.6, stratified by morphology and stellar mass in comoving coordinates. We detect positive intrinsic alignment signals for both early- and late-type galaxies out to 1 Mpc/h, including a clear signal for spirals. Shape-shape correlations are stronger than position-shape correlations, while comoving measurements increase the fraction of strongly correlated systems. Correlation profiles show little radial dependence across the three isophotes despite ellipticity variations in 10-20% of galaxies. We find strong morphology dependence: late-type galaxies dominate the shape-shape signal, preferentially inhabiting filaments and displaying higher ellipticities consistent with edge-on orientations. Early-type galaxies instead cluster near group and cluster centers, with no comparable excess in position-shape correlations. This segregation suggests distinct alignment mechanisms: tidal stretching for early-types in dense environments and tidal torquing for late-types in filaments. These local-Universe constraints inform intrinsic alignment modeling for Euclid, DESI, and LSST, highlighting the contribution of blue spiral galaxies to low-redshift cosmic shear contamination. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_23338 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Dissecting the Perseus-Pisces supercluster observed with CFHT-MegaCam: Exploring late-type galaxy shape alignments within the local cosmic web Mondelin, M. Codis, S. Cuillandre, J. -C. Paviot, R. de Boer, T. Cosmology and Nongalactic Astrophysics Intrinsic alignments of galaxy shapes are a major systematic for weak gravitational lensing and provide insight into how galaxies acquire orientations within the cosmic web. Most studies rely on large statistical samples; here, we probe this signal in a single nearby superstructure, extending to outer regions where secondary infall should dominate. We measure intrinsic alignments in the Perseus-Pisces supercluster as a function of galaxy morphology and radial extent into the low surface brightness regime. Using deep CFHT r-band imaging covering 367 deg2 (mainly from the UNIONS survey) and reaching 28 mag/arcsec2, we compute correlation functions at three isophotal radii for 2004 galaxies with log M*/Msun > 8.6, stratified by morphology and stellar mass in comoving coordinates. We detect positive intrinsic alignment signals for both early- and late-type galaxies out to 1 Mpc/h, including a clear signal for spirals. Shape-shape correlations are stronger than position-shape correlations, while comoving measurements increase the fraction of strongly correlated systems. Correlation profiles show little radial dependence across the three isophotes despite ellipticity variations in 10-20% of galaxies. We find strong morphology dependence: late-type galaxies dominate the shape-shape signal, preferentially inhabiting filaments and displaying higher ellipticities consistent with edge-on orientations. Early-type galaxies instead cluster near group and cluster centers, with no comparable excess in position-shape correlations. This segregation suggests distinct alignment mechanisms: tidal stretching for early-types in dense environments and tidal torquing for late-types in filaments. These local-Universe constraints inform intrinsic alignment modeling for Euclid, DESI, and LSST, highlighting the contribution of blue spiral galaxies to low-redshift cosmic shear contamination. |
| title | Dissecting the Perseus-Pisces supercluster observed with CFHT-MegaCam: Exploring late-type galaxy shape alignments within the local cosmic web |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2605.23338 |