Influence of Stellar Mass and Redshift on Galaxy Morphological Classification Using the Concentration Index

Abstract

Morphological classification of galaxies has for a long
time relied on visual inspection since the pioneering
morphological scheme introduced by Hubble (1926).
This approach is labour-intensive and time-consuming,
particularly for current large surveys. An effective
alternative is to use the central concentration index,
computed from the central light profiles, a quantitative
parameter that reliably separates late-type from earlytype galaxies based on the central light profile of galaxies,
offering a more efficient classification method for extensive
galaxy surveys. Understanding how stellar mass and redshift
affect concentration index as quantitative morphological
galaxy classifier is important because both parameters trace
key stages of galaxy evolution, and their influence may
affect the reliability of morphological classifications across
different galaxy populations. This work explores how
fundamental galaxy parameters; stellar mass and redshift
influence the application of the concentration index as a
classification tool. The archival dataset for this work was
obtained from the Sloan Digital Sky Survey-Data Release
16 (SDSS-DR16) of the AMIGA catalog. The lowdensity galaxy sample was selected within a redshift range
of 0.005 ≤ z ≤ 0.080 and r-band magnitudes between 11
≤ Mr
≤ 15.7. To investigate the influence of redshift on
the concentration index (Cr
), we analyzed a low-density
galaxy sample that is Singly Isolated Galaxies (SIG) with
stellar masses in the range of 10 ≤ logM☉ ≤ 12, comprising
3148 galaxies. A regression analysis of the derived Cr
values revealed a positive correlation with redshift, given
by Cr
=2.60+2.06 z, indicating that Cr
increases at higher
redshifts. Similarly, to assess the effect of stellar mass, we
focused on the SIG population within a redshift range
of 0.02 ≤ z ≤ 0.04. Analysis of the relationship between
the Cr and stellar mass also revealed that Cr increases with
increase in stellar masses