Spectral classification and composites of galaxies in LAMOST DR4

TL;DR

This paper classifies 40,182 galaxy spectra from LAMOST DR4 into six categories, analyzes their composite spectra, and explores correlations with morphological parameters, providing a valuable galaxy catalog and spectral features for future research.

Contribution

The study introduces a new classification of LAMOST DR4 galaxy spectra into six types and provides composite spectra and morphological correlations, enhancing galaxy spectral analysis tools.

Findings

Six spectral classes identified and classified.

Composite spectra reveal key features differentiating classes.

Correlation between spectral types and morphological parameters established.

Abstract

We study the classification and composite spectra of galaxy in the fourth data release (DR4) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). We select 40,182 spectra of galaxies from LAMOST DR4, which have photometric in- formation but no spectroscopic observations in the Sloan Digital Sky Survey(SDSS). These newly observed spectra are re-calibrated and classified into six classes, i.e. pas- sive, H{\alpha}-weak, star-forming, composite, LINER and Seyfert using the line intensity (H\b{eta}, [OIII]{\lambda}5007, H{\alpha} and [NII]{\lambda}6585). We also study the correlation between spectral classes and morphological types through three parameters: concentration index, (u - r) color, and D4000n index. We calculate composite spectra of high signal-to-noise ra- tio(S/N) for six spectral classes, and using these composites we pick out some features that can differentiate the classes effectively, including H\b{eta}, Fe5015, H{\gamma}A, HK, and Mg2 band etc. In addition, we compare our composite spectra with the SDSS ones and analyse their difference. A galaxy catalogue of 40,182 newly observed spectra (36,601 targets) and the composite spectra of the six classes are available online.