A Complete 16 $μ$m selected Galaxy Sample at $z \sim 1$. II: Morphological Analysis

Abstract

We present morphological analysis of the 16$μ$m flux-density-limited galaxy sample at 0.8$<z<$1.3 from arXiv:2103.04585. At the targeted redshift, the 16$μ$m emission corresponds to the Polycyclic aromatic hydrocarbon (PAH) feature from intense star formation, or dust heated by AGN (Active galactic nuclei). Our sample of 479 galaxies are dominated by Luminous Infrared Galaxies (LIRGs, 67\%) in three CANDLES fields (EGS, GOODS-N, and GOODS-S), and are further divided into AGN dominated, star-forming dominated, composite, and blue compact galaxies by their spectral energy distribution (SED) types. The majority of our sample (71\%) have disky morphologies, with the few AGN dominated galaxies being more bulge-dominanted than the star-forming dominated and composite galaxies. The distribution of our sample on the Gini vs. M$_{\text{20}}$ plane is consistent with previous studies, where the Sérsic index $n$ shows an increasing trend towards the smaller M$_{\text{20}}$ and higher Gini region below the dividing line for mergers. The subsample of ULIRGs follow a steep size-mass relation that is closer to the early-type galaxies. In addition, as the 4.5 $μ$m luminosity excess ($L_{4.5}^{Exc}$, proxy for AGN strength) increases, our sample appear to be more bulge-dominated (i.e. higher $n$). Based on the sSFR and compactness ($log_{10}Σ_{1.5}, Σ_{1.5}=M_*/R_e^{1.5}$) diagram, the majority of our LIRG-dominated galaxy sample follow a secular evolution track, and their distribution can be explained without involving any merging activities. Out of the 16 ULIRGs in our sample, six are compact with strong AGN contributions, likely evolving along the fast-track from more violent activities.