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arXiv · 2610.29683

Euclid Quick Data Release (Q1). The shape of cluster haloes revealed by intracluster light

Euclid Collaboration·T. Kolcu·N. A. Hatch·A. Fernandez·S. P. Bamford·H. Gao·J. B. Golden-Marx·G. Martin·Y. M. Bahé·S. L. Ahad·C. Bellhouse·J. Butler·S. de Nicola·F. Durret·A. Ellien·A. H. Gonzalez·H. Gully·M. Kluge·M. Maturi·M. Montes·L. Moscardini·R. Ragusa·A. Saro·M. Urbano·N. Aghanim·B. Altieri·S. Andreon·N. Auricchio·C. Baccigalupi·M. Baldi·S. Bardelli·P. Battaglia·R. Bender·A. Biviano·M. Bolzonella·E. Branchini·M. Brescia·S. Camera·G. Cañas-Herrera·V. Capobianco·C. Carbone·J. Carretero·S. Casas·M. Castellano·G. Castignani·S. Cavuoti·K. C. Chambers·A. Cimatti·C. Colodro-Conde·G. Congedo·C. J. Conselice·L. Conversi·Y. Copin·F. Courbin·H. M. Courtois·M. Cropper·J. -C. Cuillandre·A. Da Silva·H. Degaudenzi·G. De Lucia·C. Dolding·H. Dole·F. Dubath·X. Dupac·S. Escoffier·M. Farina·R. Farinelli·S. Ferriol·F. Finelli·P. Fosalba·S. Fotopoulou·M. Frailis·E. Franceschi·M. Fumana·L. Gabarra·S. Galeotta·K. George·B. Gillis·C. Giocoli·P. Gómez-Alvarez·J. Gracia-Carpio·A. Grazian·F. Grupp·S. V. H. Haugan·S. Hemmati·H. Hoekstra·W. Holmes·F. Hormuth·A. Hornstrup·M. Huertas-Company·K. Jahnke·M. Jhabvala·B. Joachimi·S. Kermiche·A. Kiessling·B. Kubik·M. Kümmel·M. Kunz·H. Kurki-Suonio·R. Laureijs
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Abstract

Intracluster light (ICL) offers a luminous route for measuring the shapes and orientations of cluster haloes. We used Euclid Quick Data Release (Q1) images to quantify ICL shapes for 205 clusters at $0.1 \leq z \leq 0.8$ selected from the eROSITA All-Sky Survey and the Dark Energy Survey. We measured the ICL properties across five bands ($I_\mathrm{E}$, $Y_\mathrm{E}$, $J_\mathrm{E}$, $H_\mathrm{E}$ and the coadded $YJH_\mathrm{E}$), and find that the shape parameters are consistent across the filters, with the $H_\mathrm{E}$ band probing the profiles to the largest cluster-centric distances ($0.1R_{200\mathrm{c}}\sim100$ kpc). The ICL ellipticity ($e=1-b/a$) distribution peaks at 0.5, consistent with halo ellipticities inferred from strong and weak lensing studies, suggesting that the ICL traces the large-scale structure of the clusters. Cluster cores, dominated by brightest cluster galaxy (BCG) light, are round ($e\sim0.2$), while the ICL becomes progressively more elongated at large radii, reaching an ellipticity of $\sim0.5$ by $0.1R_{200\mathrm{c}}$. We find that the ICL is closely aligned with the BCG (87% lie within 30$^\circ$), but shows a weaker alignment with the satellite galaxy distribution (61% within 30$^\circ$). Robust position angles could be measured using the ICL for 63% of the sample, whereas position angles could be measured for only 30% of the sample using the satellite galaxies. Stacking clusters in redshift bins allows measurements of the ICL surface brightness to $0.6$-$0.8R_{200\mathrm{c}}$ and ellipticity beyond $0.3$-$0.4R_{200\mathrm{c}}$ (300-400 kpc), but we observed a plateau in the ICL ellipticity beyond $0.1R_{200\mathrm{c}}$. These results demonstrate the capability of Euclid to characterise the ICL morphology with high statistical precision, allowing new constraints on cluster halo structure and its evolution with redshift.

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Euclid Collaboration, T. Kolcu, N. A. Hatch, A. Fernandez, S. P. Bamford, H. Gao, J. B. Golden-Marx, G. Martin, Y. M. Bahé, S. L. Ahad, C. Bellhouse, J. Butler, S. de Nicola, F. Durret, A. Ellien, A. H. Gonzalez, H. Gully, M. Kluge, M. Maturi, M. Montes, L. Moscardini, R. Ragusa, A. Saro, M. Urbano, N. Aghanim, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, R. Bender, A. Biviano, M. Bolzonella, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, J. -C. Cuillandre, A. Da Silva, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, F. Dubath, X. Dupac, S. Escoffier, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, S. Hemmati, H. Hoekstra, W. Holmes, F. Hormuth, A. Hornstrup, M. Huertas-Company, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, R. Laureijs. 2026-10-21. Euclid Quick Data Release (Q1). The shape of cluster haloes revealed by intracluster light. https://arxiv.org/abs/2610.29683

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