Magnitude and size evolution of bulgeless galaxies

TL;DR

This study investigates how bulgeless galaxies evolve in brightness and size up to redshift 0.9, revealing that they dim and grow slightly over time, with some transforming into normal-disc galaxies.

Contribution

It provides the first detailed comparison of the magnitude and size evolution of bulgeless versus normal-disc galaxies up to z~0.9, highlighting morphological transitions over cosmic time.

Findings

Bulgeless galaxies dim by 0.79 mag from z~0.9 to 0.04.

Normal-discs dim by 1.16 mag over the same period.

The proportion of bulgeless galaxies declines with decreasing redshift.

Abstract

We examine the magnitude and size evolution of bulgeless (discs with no-bulge or pseudo-bulge) galaxies up to z~0.9 in rest-frame B-band. Their evolution is compared to that of normal-discs (discs with classical-bulge). The study is done for luminous sources (M_B<=-20) in two equal-volume redshift-bins (0.4<=z<0.77 and 0.77<=z<1.0) and a local range (0.02<=z<0.05). The mean surface-brightness, from z_{mean}=0.89 to z_{mean}=0.04, shows a dimming of 0.79 mag for bulgeless galaxies and 1.16 mag for normal-discs. The characteristic magnitude, M_B^*, shows an increase of 0.55-mag for bulgeless galaxies and 0.95-mag for normal-discs. Both dimming and faintness observed since z~0.9 are more pronounced for the normal-discs by ~0.4-mag. The size-distribution is log-normal and both bulgeless and normal-discs show a slight increase in the mean value from z_{mean}=0.89 to z_{mean}=0.04. The proportion of bulgeless galaxies in the full disc sample undergoes a considerable decline with decrease in redshift. This along with the larger dimming and faintness seen for normal-discs suggests that some fraction of the bulgeless sources switch to the normal-disc morphology with time. To ascertain the validity of studying morphology in the optical, the properties of the galaxies observed in both rest-frame B and I-band are compared. The common sample is more luminous in the I-band but the sizes are larger in the B-band for more than 74 % of the sources. The variation in the sersic-index values of the galaxies in the two rest-bands is minor enough to have any affect on the morphological classification.