Unravelling the morphologies of Luminous Compact Galaxies using the HST/ACS GOODS survey

Abstract

(Abridged) Luminous Compact Galaxies (LCGs) (M_B < -20, R_{1/2} < 4.5kpc and EW_{0}(OII) >15Å) constitute one of the most rapidly evolving galaxy populations over the last ~8 Gyr history of the universe. Due to their inherently compact sizes, any detailed quantitative analysis of their morphologies has proved to be difficult in the past. In this work we use the high angular resolution imaging data, from the HST/ACS GOODS survey, to study the quantitative morphology of a complete sample of LCGs in the redshift range 0.5 < z < 1.2. We have derived structural parameters for a representative sample of 39 LCGs selected from the GOODS-S field, using full 2-dimensional surface brightness profile fitting of the galaxy images in each of the four filters available. B-z color maps are used as an aid in the morphological classification. We then use the rest frame B band bulge flux fraction (B/T) to determine the morphological class of the galaxies. Mergers were essentially identified visually by the presence of multiple maxima of comparable intensity in the rest frame B band images, aided by the color maps to distinguish them from HII regions. We derive the following morphological mix for our sample of intermediate redshift LCGs: Mergers: ~36%, Disk dominated: ~22%, S0: ~20%, Early types: ~7%, Irr/tadpole: ~15%. We establish that our sample LCGs are intermediate mass objects with a median stellar mass of Log(M/M_{\odot})=10.32. We also derive dust enshrouded SFR values ranging from a few to ~65 $M_{\odot}$/year using Spitzer 24$μm$ data. We estimate a factor ~11 fall in the comoving number density of blue LCGs from redshifts 0.5 < z < 1.2 to the current epoch. We finally discuss the evolutionary scenario of these LCGs which might give us some clues regarding their descendants in the local universe.