Quantifying correlations between galaxy emission lines and stellar continua

Abstract

We analyse the correlations between continuum properties and emission line equivalent widths of star-forming and active galaxies from the Sloan Digital Sky Survey. Since upcoming large sky surveys will make broad-band observations only, including strong emission lines into theoretical modelling of spectra will be essential to estimate physical properties of photometric galaxies. We show that emission line equivalent widths can be fairly well reconstructed from the stellar continuum using local multiple linear regression in the continuum principal component analysis (PCA) space. Line reconstruction is good for star-forming galaxies and reasonable for galaxies with active nuclei. We propose a practical method to combine stellar population synthesis models with empirical modelling of emission lines. The technique will help generate more accurate model spectra and mock catalogues of galaxies to fit observations of the new surveys. More accurate modelling of emission lines is also expected to improve template-based photometric redshift estimation methods. We also show that, by combining PCA coefficients from the pure continuum and the emission lines, automatic distinction between hosts of weak active galactic nuclei (AGNs) and quiescent star-forming galaxies can be made. The classification method is based on a training set consisting of high-confidence starburst galaxies and AGNs, and allows for the similar separation of active and star-forming galaxies as the empirical curve found by Kauffmann et al. We demonstrate the use of three important machine learning algorithms in the paper: k-nearest neighbour finding, k-means clustering and support vector machines.

14 pages, 14 figures. Accepted by MNRAS on 2015 December 22. The paper's website with data and code is at http://www.vo.elte.hu/papers/2015/emissionlines/

References in corpus (9)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE
• The 2013 Release of Cloudy
• The Effects of Stellar Rotation. II. A Comprehensive Set of Starburst99 Models
• Modeling the color evolution of luminous red galaxies - improvements with empirical stellar spectra
• The Efficiency of Stellar Reionization: Effects of Rotation, Metallicity, and Initial Mass Function
• Machine learning for transient discovery in Pan-STARRS1 difference imaging
• Star-galaxy separation strategies for WISE-2MASS all-sky infrared galaxy catalogs
• Interpreting high [O III]/Hbeta ratios with maturing starbursts

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• UV bright red-sequence galaxies: how do UV upturn systems evolve in redshift and stellar mass?
• Impact of stellar population synthesis choices on forward modelling-based redshift distribution estimates
• Emission Line Predictions for Mock Galaxy Catalogues: a New Differentiable and Empirical Mapping from DESI
• The effect of emission lines on the performance of photometric redshift estimation algorithms
• UV bright red-sequence galaxies: a comparative study between UV upturn and UV weak systems