ENHANCED NITROGEN IN MORPHOLOGICALLY DISTURBED BLUE COMPACT GALAXIES AT 0.20 < z < 0.35: PROBING GALAXY MERGING FEATURES

Abstract

We present a study of correlations between the elemental abundances and galaxy morphologies of 91 blue compact galaxies (BCGs) at z = 0.20-0.35 with Sloan Digital Sky Survey (SDSS) DR7 data. We classify the morphologies of the galaxies as either "disturbed" or "undisturbed" by visual inspection of the SDSS images, and using the Gini coefficient and M 20 . We derive oxygen and nitrogen abundances using the T e method. We find that a substantial fraction of BCGs with disturbed morphologies, indicative of merger remnants, show relatively high N/O and low O/H abundance ratios. The majority of the disturbed BCGs exhibit higher N/O values at a given O/H value compared to the morphologically undisturbed galaxies, implying more efficient nitrogen enrichment in disturbed BCGs. We detect Wolf-Rayet (WR) features in only a handful of the disturbed BCGs, which appears to contradict the idea that WR stars are responsible for high nitrogen abundance. Combining these results with Galaxy Evolution Explorer GR6 ultraviolet (UV) data, we find that the majority of the disturbed BCGs show systematically lower values of the Hα to near-UV star formation rate ratio. The equivalent width of the Hβ emission line is also systematically lower in the disturbed BCGs. Based on these results, we infer that disturbed BCGs have undergone star formation over relatively longer timescales, resulting in a more continuous enrichment of nitrogen. We suggest that this correlation between morphology and chemical abundances in BCGs is due to a difference in their recent star formation histories.

The impact from survey depth and resolution on the morphological classification of galaxies

“…Lotz et al 2004;Pierce et al 2007;Lotz et al 2008;Conselice et al 2008;Mendez et al 2011;Chen et al 2009;Stott et al 2013;Petty et al 2014;Hung et al 2014); often it was used in the analysis where different types of galaxies, e.g. ULIRGs, dust obscured galaxies, star-forming galaxies, or quiescent galaxies, were compared with control samples (Bussmann et al 2009;Pentericci et al 2010;Lanyon-Foster et al 2012;Wang et al 2012;Chung et al 2013;Böhm et al 2014); or for selecting ET and LT galaxies (Lotz et al 2004(Lotz et al , 2008.…”

“…Finally, different combinations of 2 -3 parameters analysed in the previous sections, were used in many studies to distinguish between the ET and LT galaxies, and also to study the structure of galaxies with other properties, like SFR, mass, environment, nuclear activity, etc (e.g. Pierce et al 2007;Cassata et al 2007;Bussmann et al 2009;Pović et al 2009a,b;Pentericci et al 2010;Chung et al 2013;Böhm et al 2014). The combination between the concentration parameters (CABR and/or CCON) and ASYM was also used for selecting ET and LT sources (Abraham et al 1994(Abraham et al , 1996Conselice et al 2006;Huertas-Company et al 2007;Pović et al 2009a), while in some cases the combination between the GINI and CCON was used to study the host properties of AGN and quasars (e.g.…”

O vi EMISSION IMAGING OF A GALAXY WITH THE HUBBLE SPACE TELESCOPE: A WARM GAS HALO SURROUNDING THE INTENSE STARBURST SDSS J115630.63+500822.1∗

“…As we present only one single galaxy, this stage of the project can be regarded as a pilot study, although it will be expanded in the current observing cycle of HST. We have selected an intense local starburst that hitherto has not been studied in much detail, although it does enter the sample of highly excited blue compact galaxies studied by Chung et al (2013). We present the motivation for selecting this target in Section 2 and derive a number of common physical properties from the optical spectrum and spectral energy distribution.…”

The Evolution of the Mass-Metallicity Relation at 0.20 < z < 0.35

“…Furthermore, disturbed BCGs might have undergone active star formation http://janss.kr Jiwon Chung et al Evolution of the Mass-Metallicity Relation through mergers and/or interactions between two galaxies, and star formation is continuously enhanced by newly formed massive stars (e.g., Bekki 2008). Most recently, Chung et al (2013) infer that disturbed BCGs show different recent star formation histories to those of undisturbed ones in which disturbed BCGs have undergone star formation over relatively longer timescales. Consequently, we confirm that the gas metallicity and SFR of BCGs are closely related with galaxy morphology and dynamical event would play an important role in the chemical evolution and star formation histories of BCGs.…”