Star formation in far-IR AGN and non-AGN galaxies in the green valley – II. Morphological analysis

Abstract

This paper studies morphological properties of 103 green valley FIR active and 2609 non-active galaxies presented in Mahoro et al. (2017). The photometric data from the COSMOS survey were used, and the morphological parameters, such as Abraham and Conselice-Bershady concentration indices, Gini, M20 moment of light, and asymmetry, were analysed taking into account public catalogues. Furthermore, a visual classification of galaxies was performed. We found that the fraction of peculiar galaxies with clear signs of interactions and mergers is significantly higher in AGN (38%) than non-AGN (19%) green valley galaxies, while non-AGN galaxies from our sample are predominantly spirals (46%). We found that the largest fraction of our green valley galaxies is located on the main-sequence (MS) of star formation, independently on morphology, which is in contrast with most of previous studies carried out in optical. We also found that FIR AGN green valley galaxies have significantly higher star formation rates in all analysed morphological types. Therefore, our results suggest that interactions and mergers obtained in the high fraction of FIR AGN contribute significantly to high star formation rates observed in the selected sample, but are not the only mechanism responsible for enhancing star formation, and others such as AGN positive feedback could contribute as well. In future we will study in more details the possibility of AGN positive feedback through the spectroscopic analysis of public and our SALT data.

Properties of X-ray detected far-IR AGN in the green valley

“…We compared our visual classifications with available nonparametric classifications in COSMOS, and we did more analysis of the distributions of different morphological parameters by comparing FIR AGN and FIR non-AGN green valley galaxies. We found the standard behaviour of morphological parameters, as explained in Mahoro et al (2019).…”

“…3 shows the comparison of SFRs of AGN and non-AGN samples for the same stellar mass ranges taking into account morphology. In all cases the AGN sample shows higher SFRs in comparison to non-AGN galaxies, independently of morphology (Mahoro et al 2019). In case of class 4, interactions and mergers could explain higher values of SFRs observed in AGN.…”

“…In case of class 4, interactions and mergers could explain higher values of SFRs observed in AGN. However, taking into account higher SFRs in the rest of AGN green valley sample (e.g., in 26% and 25% of class 1 and class 2 galaxies, respectively), we suggested that interactions and mergers alone cannot explain the results of Mahoro et al (2019). Therefore, if there is an impact of AGN feedback on star formation in case of selected FIR emitters it looks to be rather positive than negative.…”

The OTELO survey as a morphological probe. Last ten Gyr of galaxy evolution

“…Galaxy morphology is related to other physical properties such as star formation, dynamical histories, stellar mass, colours, luminosities, and different morphological parameters (Kauffmann et al 2003;Baldry et al 2004;Salim et al 2007;Pović et al 2013Pović et al , 2012Schawinski et al 2014;Mahoro et al 2019). Since Hubble (1925) discovered the extragalactic nature of some 'nebulae', the first step for tackling their systematic study was to establish a morphological classification.…”

Properties of green valley galaxies in relation to their selection criteria

“…Between the red sequence and the blue cloud there is a sparsely populated green valley region that has been viewed as the crossroads of galaxy evolution where the galaxies in it are thought to represent the transition population between the blue cloud of star-forming galaxies and the red sequence of quenched and passively evolving galaxies (Schiminovich et al 2007;Pović et al 2012;Salim 2014;Lin et al 2017;Coenda et al 2018;Bryukhareva & Moiseev 2019;Phillipps et al 2019). Several selection criteria have been used to define green valley in order to study the properties of the green galaxy population, using colours such as U -V (Brammer et al 2009), U -B (Mendez et al 2011;Mahoro et al 2017Mahoro et al , 2019, NUV -r (Wyder et al 2007;Lee et al 2015;Coenda et al 2018), g -r (Trayford et al 2015(Trayford et al , 2017Walker et al 2013, Eales et al 2018, u -r (Bremer et al 2018;Eales et al 2018;Kelvin et al 2018;Ge et al 2019;Phillipps et al 2019), specific SFR (sSFR) (Schiminovich et al 2007;Salim et al 2009;Salim 2014;Phillipps et al 2019;Starkenburg et al 2019), and the SFR-stellar mass (M * ) diagram (Noeske et al 2007;Chang et al 2015). Therefore, the study of green valley galaxies provides us crucial clues to connect the red sequence and blue cloud galaxies in terms of their star formation quenching and evolution.…”