The PCA Filtering method for an unbiased spectral survey of Complex Organic Molecules (COMs)

Abstract: A variety of interstellar complex organic molecules (COMs) have been detected in various physical conditions. However, in the protostellar and protoplanetary environments, their complex kinematics make line profiles blend each other and the line strength of weak lines weaker. In this paper, we utilize the principal component analysis (PCA) technique to develop a filtering method which can extract COM spectra from the main kinematic component associated with COM emission and increase the signal-to-noise ratio (SNR) of spectra. This filtering method corrects non-Gaussian line profiles caused by the kinematics. For this development, we adopt the ALMA BAND 6 spectral survey data of V883 Ori, an eruptive young star with a Keplerian disk. A filter was, first, created using 34 strong and well-isolated COM lines and then applied to the entire spectral range of the dataset. The first principal component (PC1) describes the most common emission structure of the selected lines, which is confined within the water sublimation radius ($\sim$ 0.3 arcsec) in the Keplerian disk of V883 Ori. Using this PC1 filter, we extracted high-SNR kinematics-corrected spectra of V883 Ori over the entire spectral coverage of $\sim$50 GHz. The PC1-filtering method reduces the noise by a factor of $\sim$ 2 compared to the average spectra over the COM emission region. One important advantage of this PC1-filtering method over the previously developed matched filtering method is to preserve the original integrated intensities of COM lines.