1. The Stellar Study of the Low Surface Brightness Extension of Nearby Galaxies Wei-Hsin Sun ( 孫維新 ) National Central University ( 中央大學天文研究所 ) Beijing, 2003.2.28

2. Having an Advanced Telescope:  Usually people know what they will get when they write proposals and carry out observations!  Selecting a few challenging topics which will push the telescope to its limits. It may not be practical, nor reliable, nor fruitful, but it may be rewarding at the end. （不是實用而可靠的方案, 而是具有挑 戰性的未知課題, 可能沒有結果, 但也可能有大突 破！）

3. Good Examples: International Ultraviolet Explorer and BeppoSAX satellites  The IUE satellite, originally designed for stellar work, has contributed significantly to extragalactic studies – such as active galactic nuclei and quasar studies, using low dispersion grating and large aperture.  Similarly, BeppoSAX has made the milestone observations leading to the important discoveries of GRB’s optical counterparts, while it’s original goal is not on GRB’s at all.

4. One Challenging Topic: The Irregular Extension of Nearby Galaxies — M81/M82/NGC3077  M81/82/NGC3077 Association showing interaction among 3 galaxies  The interacting group is being studied with BATC data

5. Gaseous or Stellar components in the Nearby Galaxies? (M81/82, M87, and M31)

6. The field containing M81 and M82

7. Difference caused by integration time

8. Optical image compared with radio observation (HI)

9. One Challenging Topic: The Irregular Extension of Nearby Galaxies — M87  Deep Exposure of M87 by David Malin using AAT 3.9 m Telescope;  The Low-Surface Brightness Extension (LSBE), or the Irregular Halo Component, is well over 30 arc-minutes in dimension, corresponding to a linear scale of 5 x 10 5 lys.

10. Properties of M87  m V = 8.6, M V = -22  Estimated 2.7 trillion stars  Dis: 60 million lys  Dia: 120,000 lys  Ang. Dia.:7 arc-minutes  Huge GC system: ~ 13,000-15,000 GCs  Linear Scale of the Optical jet: 7,000-8,000 lys

11. Virgo Cluster containing M84, M86, and M87

12. Long exposure of M87 – Halo component found

13. Inverted contrast of M87 Image

14. The Optical Jet of M87

15. One Challenging Topic: The Irregular Extension of Nearby Galaxies — M31  A Stellar (?) Component has been observed along one side of M31 galaxy.

20. LELIS wide-field image of M31  Lu-Lin Emission Line Imaging Survey, with a field of view of 7.2 deg  R-band, a total of 900 sec exposure, limited by the background so the obs efficiency is fairly low  Too big for BATC 1- deg field

21. Motivation of Observing Galaxy Extension  Sagittarius dwarf galaxy and Gould Belt  Merger, Cannibalism, tidal distortion, leading to the understanding of galactic history.  Motion and chemical abundance to tell the nature of the halo component.  Moreover, the PNe, HIIs and GCs in galaxies

22. Forming a Scientific Question:  What is the nature of the low surface brightness extension (the faint halo) of galaxies (either spiral or elliptical)? — Remainder of cannibalized galaxy? — Distortion by neighboring galaxies? — Tidal tail of warped galaxy?  Temperature and State of Evolution of the extension component.

23. Observing the Halo Component of nearby Galaxies (I)  The Challenge: Observing faint, extended structures  Low dispersion spectra of the stellar component of nearby galaxies, 3700- 6200A, 6000-9000A, 5A/pixel, R=1000, from the center outward  Difficulties: Threshold of sensitivity, highly binned to increase S/N

24. Observing the Halo Component of nearby Galaxies (II)  Spatial resolution (ex. M87, 30 arc-minutes vs. the field of view of 5 deg of LAMOST)  The Spacing between optical fibers  Foreground and background star contamination  Very long exposure !  Heritage: Spectral Study of QSO Host Galaxies; BATC M33 SED Distribution  Ex. Observing M31 from the center outward