New measurements of the Lyman-$α$ forest continuum and effective optical depth with LyCAN and DESI Y1 data
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| Natura: | Preprint |
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2024
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| author | Turner, Wynne Martini, Paul Karaçaylı, Naim Göksel Aguilar, J. Ahlen, S. Brooks, D. Claybaugh, T. de la Macorra, A. Dey, A. Doel, P. Fanning, K. Forero-Romero, J. E. Gontcho, S. Gontcho A Gonzalez-Morales, A. X. Gutierrez, G. Guy, J. Herrera-Alcantar, H. K. Honscheid, K. Juneau, S. Kisner, T. Kremin, A. Lambert, A. Landriau, M. Guillou, L. Le Meisner, A. Miquel, R. Moustakas, J. Mueller, E. Muñoz-Gutiérrez, A. Myers, A. D. Nie, J. Niz, G. Poppett, C. Prada, F. Rezaie, M. Rossi, G. Sanchez, E. Schlafly, E. F. Schlegel, D. Schubnell, M. Seo, H. Sprayberry, D. Tarlé, G. Weaver, B. A. Zou, H. |
| author_facet | Turner, Wynne Martini, Paul Karaçaylı, Naim Göksel Aguilar, J. Ahlen, S. Brooks, D. Claybaugh, T. de la Macorra, A. Dey, A. Doel, P. Fanning, K. Forero-Romero, J. E. Gontcho, S. Gontcho A Gonzalez-Morales, A. X. Gutierrez, G. Guy, J. Herrera-Alcantar, H. K. Honscheid, K. Juneau, S. Kisner, T. Kremin, A. Lambert, A. Landriau, M. Guillou, L. Le Meisner, A. Miquel, R. Moustakas, J. Mueller, E. Muñoz-Gutiérrez, A. Myers, A. D. Nie, J. Niz, G. Poppett, C. Prada, F. Rezaie, M. Rossi, G. Sanchez, E. Schlafly, E. F. Schlegel, D. Schubnell, M. Seo, H. Sprayberry, D. Tarlé, G. Weaver, B. A. Zou, H. |
| contents | We present the Lyman-$α$ Continuum Analysis Network (LyCAN), a Convolutional Neural Network that predicts the unabsorbed quasar continuum within the rest-frame wavelength range of $1040-1600$ Angstroms based on the red side of the Lyman-$α$ emission line ($1216-1600$ Angstroms). We developed synthetic spectra based on a Gaussian Mixture Model representation of Nonnegative Matrix Factorization (NMF) coefficients. These coefficients were derived from high-resolution, low-redshift ($z<0.2$) Hubble Space Telescope/Cosmic Origins Spectrograph quasar spectra. We supplemented this COS-based synthetic sample with an equal number of DESI Year 5 mock spectra. LyCAN performs extremely well on testing sets, achieving a median error in the forest region of 1.5% on the DESI mock sample, 2.0% on the COS-based synthetic sample, and 4.1% on the original COS spectra. LyCAN outperforms Principal Component Analysis (PCA)- and NMF-based prediction methods using the same training set by 40% or more. We predict the intrinsic continua of 83,635 DESI Year 1 spectra in the redshift range of $2.1 \leq z \leq 4.2$ and perform an absolute measurement of the evolution of the effective optical depth. This is the largest sample employed to measure the optical depth evolution to date. We fit a power-law of the form $τ(z) = τ_0 (1+z)^γ$ to our measurements and find $τ_0 = (2.46 \pm 0.14)\times10^{-3}$ and $γ= 3.62 \pm 0.04$. Our results show particular agreement with high-resolution, ground-based observations around $z = 2$, indicating that LyCAN is able to predict the quasar continuum in the forest region with only spectral information outside the forest. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2405_06743 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | New measurements of the Lyman-$α$ forest continuum and effective optical depth with LyCAN and DESI Y1 data Turner, Wynne Martini, Paul Karaçaylı, Naim Göksel Aguilar, J. Ahlen, S. Brooks, D. Claybaugh, T. de la Macorra, A. Dey, A. Doel, P. Fanning, K. Forero-Romero, J. E. Gontcho, S. Gontcho A Gonzalez-Morales, A. X. Gutierrez, G. Guy, J. Herrera-Alcantar, H. K. Honscheid, K. Juneau, S. Kisner, T. Kremin, A. Lambert, A. Landriau, M. Guillou, L. Le Meisner, A. Miquel, R. Moustakas, J. Mueller, E. Muñoz-Gutiérrez, A. Myers, A. D. Nie, J. Niz, G. Poppett, C. Prada, F. Rezaie, M. Rossi, G. Sanchez, E. Schlafly, E. F. Schlegel, D. Schubnell, M. Seo, H. Sprayberry, D. Tarlé, G. Weaver, B. A. Zou, H. Cosmology and Nongalactic Astrophysics We present the Lyman-$α$ Continuum Analysis Network (LyCAN), a Convolutional Neural Network that predicts the unabsorbed quasar continuum within the rest-frame wavelength range of $1040-1600$ Angstroms based on the red side of the Lyman-$α$ emission line ($1216-1600$ Angstroms). We developed synthetic spectra based on a Gaussian Mixture Model representation of Nonnegative Matrix Factorization (NMF) coefficients. These coefficients were derived from high-resolution, low-redshift ($z<0.2$) Hubble Space Telescope/Cosmic Origins Spectrograph quasar spectra. We supplemented this COS-based synthetic sample with an equal number of DESI Year 5 mock spectra. LyCAN performs extremely well on testing sets, achieving a median error in the forest region of 1.5% on the DESI mock sample, 2.0% on the COS-based synthetic sample, and 4.1% on the original COS spectra. LyCAN outperforms Principal Component Analysis (PCA)- and NMF-based prediction methods using the same training set by 40% or more. We predict the intrinsic continua of 83,635 DESI Year 1 spectra in the redshift range of $2.1 \leq z \leq 4.2$ and perform an absolute measurement of the evolution of the effective optical depth. This is the largest sample employed to measure the optical depth evolution to date. We fit a power-law of the form $τ(z) = τ_0 (1+z)^γ$ to our measurements and find $τ_0 = (2.46 \pm 0.14)\times10^{-3}$ and $γ= 3.62 \pm 0.04$. Our results show particular agreement with high-resolution, ground-based observations around $z = 2$, indicating that LyCAN is able to predict the quasar continuum in the forest region with only spectral information outside the forest. |
| title | New measurements of the Lyman-$α$ forest continuum and effective optical depth with LyCAN and DESI Y1 data |
| topic | Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2405.06743 |