RSAA Colloquia / Seminars / Feast-of-Facts: Friday, 04 March 2016, 14:00-14:20; Duffield Lecture Theatre

Anshu Gupta

"Radial Distribution of gas-phase metallicities of galaxies in two CLASH clusters at z ~ 0.35"

The radial distribution of metallicity of star-forming galaxies in a galaxy cluster can inform us about the mass assembly and enrichment history of the galaxy cluster. This paper presents observation of radial distribution of global metallicity of star-forming galaxies in two CLASH clusters. We present the first observation of ra- dial distribution of cluster member metallicity in galaxy clusters. The two CLASH clusters, MACS1115+01 and RXJ1532+30, were observed with DEIMOS spectro- graph at Keck-II telescope. Both galaxy clusters are cool-core clusters at redshift z ≃ 0.35. We identified 22 (14 - emission line galaxies) and 36 (21 - emission line galaxies) cluster members for MACS1115+01 and RXJ1532+30 respectively. ISM properties such as metallicity and ionization parameter, were estimated using emission line ratios [NII]/Hα, [NII]/[SII] and [OIII]/Hβ. The gas-phase metallicity of star- forming galaxies in MACS1115+01 exhibit anti-correlation with projected distance −0.15 ± 0.08 dex/Mpc, whereas the radial metallicity distribution of RXJ1532+30 is statistically flat (−0.09 ± 0.12 dex/Mpc). In addition, the mass-metallicity relation of MACS1115+01 has 0.2 dex offset metallicity than the local comparison sample, but the RXJ1532+30 mass-metallicity relation is statistically similar to the local comparison sample. The negative radial abundance gradient of MACS1115+01 suggests the impact of cluster environment via ram pressure stripping, strangulation on galaxy evolution. Our observations suggests towards the un-relaxed dynamical state of RXJ1532+30, which in turn explains the observed flat metallicity gradient of RXJ1532+30. We compare our metallicity gradient observations with the metallicity gradient in galaxy cluster simulations (Rhapsody-G) after matching with the concentration parameter. The star-forming galaxies in simulated cluster also exhibit a slight negative abundance gradient of −0.04 ± 0.03 dex/Mpc, however the slope is significantly smaller than the observations.