Photometry and Spectroscopy: A Combined Approach to Galaxy Morphology and Its Intrinsic Shapes

Abstract: The study of galaxy morphology plays an important role in understanding galaxy formation and evolution. Photometry and spectroscopy are two of the most fundamental observational techniques that provide essential information about galaxy structures, kinematics and stellar populations. This review explores the combined approach of photometric and spectroscopic methods in analysing galaxy morphology, with a focus on elliptical galaxies. Galaxy morphology remains a cornerstone of extragalactic astronomy, offering crucial insights into the formation, evolution and dynamical states of galaxies. Photometry and spectroscopy have traditionally served as the primary tools for investigating structural properties, stellar populations and kinematics. Photometric analyses, through surface brightness profiles, axial ratios and colour–magnitude relations, reveal information about stellar distributions and intrinsic shapes, while spectroscopy complements these by uncovering velocity dispersions, stellar dynamics and chemical compositions. Elliptical galaxies, in particular, present unique challenges due to projection effects and degeneracies in shape determination. While once assumed to be simple oblate spheroids, combined photometric–spectroscopic surveys such as SAURON and ATLAS3D have reshaped this view. The integration of large-scale surveys—SDSS, CALIFA and MaNGA—alongside automated tools such as GALFIT, Imfit and MORPHOFIT, has greatly enhanced parameter estimation for stellar populations, metallicity, and mass-to-light ratios. High-redshift observations with HST and JWST reveal that compact and peculiar morphologies dominated the early universe, shaped by mergers and secular processes.