Modelling the impact of quasar redshift errors on the full-shape analysis of correlations in the Lyman-$α$ forest
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| Format: | Preprint |
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2025
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| author | Gordon, Calum Cuceu, Andrei Font-Ribera, Andreu Herrera-Alcantar, Hiram K. Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd Cole, Shaun de la Macorra, Axel Dey, Biprateep Doel, Peter Forero-Romero, Jaime E. Gaztañaga, Enrique Gontcho, Satya Gontcho A Gutierrez, Gaston Guy, Julien Honscheid, Klaus Ishak, Mustapha Kehoe, Robert Kirkby, David Kisner, Theodore Kremin, Anthony Landriau, Martin Guillou, Laurent Le Levi, Michael Manera, Marc Martini, Paul Miquel, Ramon Moustakas, John Nadathur, Seshadri Niz, Gustavo Palanque-Delabrouille, Nathalie Percival, Will Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schlegel, David Schubnell, Michael Seo, Hee-Jong Silber, Joseph Harry Sprayberry, David Tarlé, Gregory Weaver, Benjamin Alan Zhou, Rongpu Zou, Hu |
| author_facet | Gordon, Calum Cuceu, Andrei Font-Ribera, Andreu Herrera-Alcantar, Hiram K. Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd Cole, Shaun de la Macorra, Axel Dey, Biprateep Doel, Peter Forero-Romero, Jaime E. Gaztañaga, Enrique Gontcho, Satya Gontcho A Gutierrez, Gaston Guy, Julien Honscheid, Klaus Ishak, Mustapha Kehoe, Robert Kirkby, David Kisner, Theodore Kremin, Anthony Landriau, Martin Guillou, Laurent Le Levi, Michael Manera, Marc Martini, Paul Miquel, Ramon Moustakas, John Nadathur, Seshadri Niz, Gustavo Palanque-Delabrouille, Nathalie Percival, Will Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schlegel, David Schubnell, Michael Seo, Hee-Jong Silber, Joseph Harry Sprayberry, David Tarlé, Gregory Weaver, Benjamin Alan Zhou, Rongpu Zou, Hu |
| contents | In preparation for the first cosmological measurements from the full-shape of the Lyman-$α$ (Ly$α$) forest from DESI, we must carefully model all relevant systematics that might bias our analysis. It was shown in Youles et al. (2022) that random quasar redshift errors produce a smoothing effect on the mean quasar continuum in the Ly$α$ forest region. This in turn gives rise to spurious features in the Ly$α$ auto-correlation, and its cross-correlation with quasars. Using synthetic data sets based on the DESI survey, we confirm that the impact on BAO measurements is small, but that a bias is introduced to parameters which depend on the full-shape of our correlations. We combine a model of this contamination in the cross-correlation (Youles et al. 2022) with a new model we introduce here for the auto-correlation. These are parametrised by 3 parameters, which when included in a joint fit to both correlation functions, successfully eliminate any impact of redshift errors on our full-shape constraints. We also present a strategy for removing this contamination from real data, by removing $\sim$0.3% of correlating pairs. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_08789 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Modelling the impact of quasar redshift errors on the full-shape analysis of correlations in the Lyman-$α$ forest Gordon, Calum Cuceu, Andrei Font-Ribera, Andreu Herrera-Alcantar, Hiram K. Aguilar, Jessica Nicole Ahlen, Steven Bianchi, Davide Brooks, David Claybaugh, Todd Cole, Shaun de la Macorra, Axel Dey, Biprateep Doel, Peter Forero-Romero, Jaime E. Gaztañaga, Enrique Gontcho, Satya Gontcho A Gutierrez, Gaston Guy, Julien Honscheid, Klaus Ishak, Mustapha Kehoe, Robert Kirkby, David Kisner, Theodore Kremin, Anthony Landriau, Martin Guillou, Laurent Le Levi, Michael Manera, Marc Martini, Paul Miquel, Ramon Moustakas, John Nadathur, Seshadri Niz, Gustavo Palanque-Delabrouille, Nathalie Percival, Will Prada, Francisco Pérez-Ràfols, Ignasi Rossi, Graziano Sanchez, Eusebio Schlegel, David Schubnell, Michael Seo, Hee-Jong Silber, Joseph Harry Sprayberry, David Tarlé, Gregory Weaver, Benjamin Alan Zhou, Rongpu Zou, Hu Cosmology and Nongalactic Astrophysics In preparation for the first cosmological measurements from the full-shape of the Lyman-$α$ (Ly$α$) forest from DESI, we must carefully model all relevant systematics that might bias our analysis. It was shown in Youles et al. (2022) that random quasar redshift errors produce a smoothing effect on the mean quasar continuum in the Ly$α$ forest region. This in turn gives rise to spurious features in the Ly$α$ auto-correlation, and its cross-correlation with quasars. Using synthetic data sets based on the DESI survey, we confirm that the impact on BAO measurements is small, but that a bias is introduced to parameters which depend on the full-shape of our correlations. We combine a model of this contamination in the cross-correlation (Youles et al. 2022) with a new model we introduce here for the auto-correlation. These are parametrised by 3 parameters, which when included in a joint fit to both correlation functions, successfully eliminate any impact of redshift errors on our full-shape constraints. We also present a strategy for removing this contamination from real data, by removing $\sim$0.3% of correlating pairs. |
| title | Modelling the impact of quasar redshift errors on the full-shape analysis of correlations in the Lyman-$α$ forest |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2505.08789 |