NOAO >   Observing Info >   Approved Programs >   2011B-0435

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Proposal Information for 2011B-0435


PI: Narae Hwang, National Astronomical Observatory of Japan, narae.hwang@nao.ac.jp
Address: Optical and Infrared Astronomy Division, 2-21-1 Osawa Mitaka, Tokyo 181-8588, Japan

CoI: Myung Gyoon Lee, Seoul National University, Korea
CoI: Hong Soo Park, Seoul National University, Korea
CoI: Sungsoon Lim, Seoul National University, Korea
CoI: Bryan Miller, Gemini Observatory, Southern Operations
CoI: Sang Chul Kim, Korea Astronomy and Space Science Institute, Korea
CoI: Paul W. Hodge, University of Washington, USA
CoI: Daniel R. Weisz, University of Washington, USA
CoI: Matthew G. Walker, Harvard University, USA
CoI: Cliff L. Johnson, University of Washington, USA

Title: Spectroscopic Study of New Extended Star Clusters in NGC 6822

Abstract: We propose to get spectra of four new `extended star clusters (ESCs)' in NGC 6822 using GMOS at Gemini South in long-slit mode to determine their ages and metallicites, and then to understand the nature of ESCs. NGC 6822 is a nearby dwarf irregular galaxy with intriguing structures of HI cloud and large stellar halo. From the recent imaging surveys, we have discovered four ESCs widely distributed in the halo of NGC 6822, reaching out to about 77 arcmin or 11 kpc. ESCs are globular- like clusters with their sizes larger than typical globular clusters (GCs) and the origin and nature of these objects are not clearly understood yet. From this spectroscopic observation, (1) we are going to measure the radial velocities to confirm whether these ESCs are bound to NGC 6822, and then to estimate the dynamical mass and dark matter content of NGC 6822. Any ESCs that are not bound to NGC 6822 could be intragroup star clusters in the Local Group. (2) We aim to determine the ages, metallicities, and [(alpha)/Fe] of the ESCs, which would be a chemical property indicator of the old stellar halo in NGC 6822. By increasing the number of ESC samples with their spectra by four times, this spectroscopic campaign will also be an invaluable asset for the understanding of the nature and the formation condition of ESCs themselves.


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