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研究生:黃玫婷
研究生(外文):Mei-Ting Hunag
論文名稱:亮紅外星系NGC6090中分子氣體之研究
論文名稱(外文):Molecular Gas in Luminous Infrared Galaxy NGC 6090
指導教授:黃崇源
指導教授(外文):Chorng-Yuan Hwang
學位類別:碩士
校院名稱:國立中央大學
系所名稱:天文研究所
學門:自然科學學門
學類:天文及太空科學學類
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:37
中文關鍵詞:分子氣體亮紅外星系交互作用星系星遽增星系
外文關鍵詞:molecular gasluminous infrared galaxiesinteracting galaxiesstarburst galaxies
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在本篇論文中,我們利用多波段觀測來研究分析亮紅外星系NGC 6090。 NGC 6090星系的紅外亮度 (LIR=3×10^11 L⊙) 大約是Milky Way的三十倍。一般相信這麼強的紅外亮度的機制是由於兩星系交互作用,觸發星遽增現象,新生恆星加熱周圍的灰塵,因而發出許多紅外線的輻射。星遽增大多存在高密度的分子雲中,因此,我們利用BIMA毫米波陣列觀測CO J =1—0旋轉譜線,研究NGC 6090中的分子氣體。另外,我們利用UKIRT觀測的H2 ν=1—0 S(1)振轉譜線,研究 NGC 6090 中較溫暖的分子氣體。為了進一步討論 NGC 6090 中分子氣體與恆星形成區的關係,我們也分析了VLA 1.49 GHz無線電連續譜,以及HST 1.1 μm高解析度影像。
NGC 6090星系中的分子雲質量約為3.2×10^11 M⊙,和FCRAO單碟天線推得的值相當接近,表示NGC 6090中彌散的大結構分子雲極少,大多分子雲都集中在交互作用中心。此外,分子雲質量約為動力質量的2.9倍,我們推測這個不合理的現象應該是傾角效應與轉換係數所造成。而經過傾角效應與轉換係數修正後的surface filling factor仍然是Milky Way的4.5倍,表示NGC 6090中分子雲比Milky Way密集的多。
儘管1.49 GHz連續譜與高密度的分子雲在空間上沒有很好的相關性,但由(1)恆星形成區的位置,以及(2)星遽增的年齡,我們推測在交互作用剛開始時,分子雲會向星系中心集中,並觸發星遽增,兩星系進一步交互作用後,分子雲則開始向交互作用中心聚集。
NGC 6090中較溫暖的分子氣體質量約為1070 M⊙。空間分布上,除了東側星系北方類似旋臂構造之外,在東側星系靠近交互作用中心和兩星系之間都存在較冷與較溫暖的分子氣體,大多為溫度較冷的分子氣體。在論文中我們也討論到處在旋臂構造和交互作用中心不同的激發機制。


We analyze multiwavelength observations of the luminous infrared galaxy (LIRGs) NGC 6090.
The infrared luminosity of NGC 6090, LIR=3×10^11 11 L⊙, is about 30 times larger than
the Milky Way. Since the star formation is much related to molecular gas, we observed CO
J=1—0 line emission with the Berkeley Illinois Maryland Association (BIMA) array
to study the molecular gas in NGC 6090. We also analyze UKIRT H_2 ν=1-0 S(1) line emission
to find the distribution of warm molecular gas. For further analyses of the starburst regions,
we present VLA 1.49 GHz (20 cm) continuum and high resolution HST 1.1-μm image as well.

The cold molecular mass traced by CO is 3.2×10^11 M⊙, which is very close to the value
estimated by the single-dish observation (FCRAO, Young et al. 1995). It means that the molecular gas
in NGC 6090 is highly concentrated in the central region of the interacting system. Besides,
the molecular mass is ~ 2.9 times larger than the dynamical mass. Such a unphysical result
might be due to a combination of two effects, inclination and conversion factor. The surface
filling factor is still ~ 4.5 times larger than that of the Milky Way after corrected by
inclination and conversion factor.
Although the 20 cm radio continuum does not have fine correlation with high-density molecular gas,
we suggest the molecular gas might trigger the starburst in NGC 6090. During merging process,
the molecular gas is concentrated into the center of the two galaxies, trigger the starburst, and
then fall into the center of the interacting system. In proof of this suggestion, we argue the
time scale of the falling and the starburst age of NGC 6090.

The warm molecular mass traced by H2 is ~ 1070 M⊙. In addition to the starburst regions
of the east galaxy near the center of interacting system, the warm molecular gas is distributed
over almost the same regions with cold molecular gas. In NGC 6090 most molecular gas exist in the
form of cold H2 gas as compared with warm gas. We also discuss the different excitation mechanisms
of H2 in the central region and the east galaxy, respectively.


ABSTRACT
1 INTRODUCTION
2 OBSERVATIONS AND DATA REDUCTION
3 RESULTS AND DISCUSSION
4 CONCLUSIONS


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