內容: Discovery of the closest collisional ring galaxy to the Milky Way
時間：2015年12月11日（星期五）13:30-15:30
地點：玉泉校區第五教學樓326
報告人: Prof.Parker, Quentin A
Abstract: We report the discovery of the closest collisional ring galaxy to the Milky Way. Such rare systems occur due to ‘bulls-eye’ encounters between two reasonably matched galaxies. The recessional velocity of about 840 km s−1 is low enough that it was detected in the Anglo- Australian Observatory/UK Schmidt Telescope Survey for Galactic H α emission. The distance is only ∼10 Mpc and the main galaxy shows a full ring of star-forming knots, 6.1 kpc in diameter surrounding a quiescent disc. The smaller assumed ‘bullet’ galaxy also shows vigorous star formation. The spectacular nature of the object had been overlooked because of its location in the Galactic plane and proximity to a bright star and even though it is the 60th brightest galaxy in the HI Parkes All Sky Survey (HIPASS) H I survey. The overall system has a physical size of ∼15 kpc, a total mass of M∗ = 6.6 × 109 M⊙ (stars + H I), a metallicity of [O/H]∼ −0.4, and a star formation rate of 0.2–0.5 M⊙ yr−1, making it a Magellanic-type system. Collisional ring galaxies therefore extend to much lower galaxy masses than commonly assumed. We derive a space density for such systems of 7 × 10−5 Mpc−3, an order of magnitude higher than previously estimated. This space density suggests Kathryn’s Wheel is the nearest such system. We present discovery images, CTIO 4-m telescope narrow-band follow-up images and spectroscopy for selected emission components. Given its proximity and modest extinction along the line of sight, this spectacular system provides an ideal target for future high spatial resolution studies of such systems and for direct detection of its stellar populations.
Speaker Introduction: Quentin Parker obtained a BSc(Hons) in 1982 and a PhD (1986) from the University of St.Andrews. He joined the department of Physics at Hong Kong University in March 2014. Prior to that he was the joint AAO/Macquarie lecturer in astronomy (2002-2015) and director of the research centre for Astronomy, Astrophysics and Astrophotonics (2010-2014). Quentin also worked at the Royal Observatory Edinburgh (1986-1992), Anglo-Australian observatory (1992-1999) and as a senior research fellow at the Institute for Astronomy in Edinburgh (1999-2002). Quentin was responsible for helping to develop the FLAIR-II and 6DF fibre-spectroscopy systems at the UKST and supported the 2dF and AAOmega multi-object fibre spectroscopy systems on the AAT.
Quentin was also P.I. for the UKST H-alpha survey of the Southern Galactic Plane. Research activities are mainly but not exclusively associated with Wide Field Astronomy, including large-scale redshift surveys, low-surface brightness galaxies, supernova remnants and especially Planetary Nebulae. He has supervised and co-supervised a significant number of PhD, MSc and honours students to successful completion and is always keen to attract students. Quentin is currently on the IAU working group on planetary nebulae. He also heads both the H-alpha international survey consortium and the associated 'MASH' Planetary nebulae team. He also has a life-long interest in antiquities and a strong interest in Chinese Bronze artefacts.
