Public Seminar of RPg Student:- The Properties and Star-forming Potential of Cooled Intracluster Gas
Elliptical galaxies lying at the center of cool-core groups and clusters display a puzzling set of characteristics, including sprawling lamentary nebulae showing strong H and H2 emission lines. The physics of these nebulae(temperature, mass, origin, excitation and potential for star formation) are poorly understood. In this seminar, the speaker presents the first detailed comparison of the molecular and atomic hydrogen emission(H2 1-0 S(1) ro-vibrational and H lines, respectively) from a cool-core central elliptical galaxy(NGC 5044), using data from the ISAAC and MUSE instruments mounted on the VLT. Comparing the kinematics of the H and H2 lines, the speaker finds that the spectral proles are consistent with molecular and atomic emission from common gas clouds. In addition, he shows that the ratio of H2 to H surface brightness is 0.061, close to the value found in NGC1275(the central elliptical galaxy in the Perseus cluster) by Lim et al. (2011). He thus concludes that the similarity of the line ratios in NCG5044 and NGC1275 is consistent with the excitation model presented by Ferland et al. (2009) and Fabian et al. (2011) in which electrons from the surrounding X-ray emitting intracluster medium penetrate the nebula and excite the gas. He also reports the first detection of a radial color gradient in the near-infrared continuum of NGC5044, and discuss the implications for the stellar population. Current work focuses on analysis of the HI 21-cm line of neutral hydrogen from NGC5044 and NGC1275, among other cool-core central elliptical galaxies, to constrain the mass of atomic hydrogen in the nebula. This can then be used as a check on the H2 mass inferred by Lim et al. (2015) in their analysis of the radio CO line emission from NGC5044, thus giving us a constraint on the gas reservoir available for star formation. Future research will focus on imaging the nebula in NGC1275 in the [OIII]5007A line with the MegaCam instrument mounted on the CFHT, thus identifying which regions of the nebula are actively forming stars for the first time. These results will then be compared to the distribution of young globular clusters reported by Lim et al. (2019), thus helping to shed light on the formation of globular clusters and the super star clusters around NGC1275.
地點：香港大學 莊月明物理樓522室 (網上講授)經ZoomID: 985-7580-6360
講者：James Michael George NIANIAS(香港大學)