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

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！）

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.

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

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

M31)

The field containing M81 and M82

Difference caused by integration time

Optical image compared with radio observation (HI)

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 105 lys.

Properties of M87

mV = 8.6, MV = -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

Virgo Cluster containing M84, M86, and M87

Long exposure of M87 – Halo component found

Inverted contrast of M87 Image

The Optical Jet of M87

One Challenging Topic: The Irregular Extension of Nearby Galaxies — M31

A Stellar (?) Component has been observed along one side of M31 galaxy.

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

Motivation of Observing Galaxy Extension

Sagittarius dwarf galaxy and Gould BeltMerger, Cannibalism, tidal distortion, lead

ing 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

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 t

he extension component.

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

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 fibersForeground and background star

contaminationVery long exposure !Heritage: Spectral Study of QSO Host

Galaxies; BATC M33 SED DistributionEx. Observing M31 from the center outward