1. New Measurements of the Lyα Forest Continuum and Effective Optical Depth with LyCAN and DESI Y1 Data
- Author
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Wynne Turner, Paul Martini, Naim Göksel Karaçaylı, J. Aguilar, S. Ahlen, D. Brooks, T. Claybaugh, A. de la Macorra, A. Dey, P. Doel, K. Fanning, J . E. Forero-Romero, S. Gontcho A Gontcho, A. X. Gonzalez-Morales, G. Gutierrez, J. Guy, H. K. Herrera-Alcantar, K. Honscheid, S. Juneau, T. Kisner, A. Kremin, A. Lambert, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, J. Moustakas, E. Mueller, A. Muñoz-Gutiérrez, A. D. Myers, J. Nie, G. Niz, C. Poppett, F. Prada, M. Rezaie, G. Rossi, E. Sanchez, E. F. Schlafly, D. Schlegel, Michael F. Schubnell, H. Seo, D. Sprayberry, G. Tarlé, B. A. Weaver, and H. Zou
- Subjects
Convolutional neural networks ,Cosmology ,Dark energy ,Intergalactic medium ,Large-scale structure of the universe ,Lyman alpha forest ,Astrophysics ,QB460-466 - Abstract
We present the Ly α Continuum Analysis Network (LyCAN), a convolutional neural network that predicts the unabsorbed quasar continuum within the rest-frame wavelength range of 1040–1600 Å based on the red side of the Ly α emission line (1216–1600 Å). 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 (COS) 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 ≤ z ≤ 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 $\tau {(z)={\tau }_{0}(1+z)}^{\gamma }$ to our measurements and find τ _0 = (2.46 ± 0.14) × 10 ^−3 and γ = 3.62 ± 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.
- Published
- 2024
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