A galaxy classification grid that better recognises early-type galaxy morphology

Abstract

A modified galaxy classification scheme for local galaxies is presented. It builds upon the Aitken-Jeans nebula sequence, by expanding the Jeans-Hubble tuning fork diagram, which itself contained key ingredients from Curtis and Reynolds. The two-dimensional grid of galaxy morphological types presented here, with elements from de Vaucouleurs' three-dimensional classification volume, has an increased emphasis on the often overlooked bars and continua of disc sizes in early-type galaxies - features not fully captured by past tuning forks, tridents, or combs. The grid encompasses nuclear discs in elliptical (E) galaxies, intermediate-scale discs in ellicular (ES) galaxies, and large-scale discs in lenticular (S0) galaxies, while the E4-E7 class is made redundant given that these galaxies are lenticular galaxies. Today, these disc structures continue to be neglected, or surprise researchers, perhaps partly due to our indoctrination to galaxy morphology through the tuning fork diagram. To better understand the past and present classification schemes - whose origins reside in solar/planetary formation models - a holistic overview is given. This provides due credit to some of the lesser known pioneers, presents some rationale for the grid, and reveals the incremental nature of, and some of the lesser known connections in, the field of galaxy morphology.

11 pages (incl. 2 figures) plus an extensive reference list

References in corpus (17)

• The SAURON project -- IX. A kinematic classification for early-type galaxies
• The SAURON project -- X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/sigma,epsilon) diagram with integral-field stellar kinematics
• The Fundamental Properties of Galaxies and a New Galaxy Classification System
• The SAURON project - XII. Kinematic substructures in early-type galaxies: evidence for disks in fast rotators
• The SAMI Galaxy Survey: Revisiting Galaxy Classification Through High-Order Stellar Kinematics
• Stellar Population and Kinematic Profiles in Spiral Bulges & Disks: Population Synthesis of Integrated Spectra
• The Atlas3D project - XXIV. The intrinsic shape distribution of early-type galaxies
• Clusters at Half Hubble Time: Galaxy Structure and Colors in RXJ0152.7-1357 and MS1054-03
• Hiding in plain sight: An abundance of compact massive spheroids in the local Universe
• Distribution of Slow and Fast Rotators in the Fornax Cluster
• The Argo Simulation: II. The Early Build-up of the Hubble Sequence
• Galactic Rings Revisited. I. CVRHS Classifications of 3962 Ringed Galaxies from the Galaxy Zoo 2 Database
• Spectral classification and composites of galaxies in LAMOST DR4
• Kinematic classifications of local interacting galaxies: implications for the merger/disk classifications at high-z
• Galaxy And Mass Assembly (GAMA): Blue spheroids within 87 Mpc
• Galaxy And Mass Assembly: Automatic Morphological Classification of Galaxies Using Statistical Learning
• The SLUGGS Survey: Trails of SLUGGS galaxies in a modified spin-ellipticity diagram