101. New measurements of the Lyman-$\alpha$ forest continuum and effective optical depth with LyCAN and DESI Y1 data
- Author
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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., and Zou, H.
- Subjects
Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
We present the Lyman-$\alpha$ 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-$\alpha$ 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 a factor of two 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 $\tau(z) = \tau_0 (1+z)^\gamma$ to our measurements and find $\tau_0 = (2.46 \pm 0.14)\times10^{-3}$ and $\gamma = 3.62 \pm 0.04$. 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., Comment: 23 pages, 15 figures, 3 tables; submitted to ApJ
- Published
- 2024