合併中之明亮紅外線星系的次毫米波段觀測; Sub-millimeter Observations of Luminous Infrared Galaxies in a Merging Sequence

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題名:	合併中之明亮紅外線星系的次毫米波段觀測;Sub-millimeter Observations of Luminous Infrared Galaxies in a Merging Sequence
作者:	蔡肇偉;Chao-Wei Tsai
貢獻者:	天文研究所
關鍵詞:	星系;星系:交互作用;星系:星遽增;星遽增:星系;次毫米波段;galaxies;galaxies: interactions;galaxies: starburst;starburst: galaxies;sub-millimeter
日期:	2000-07-13
上傳時間:	2009-09-22 10:10:52 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	明亮紅外線星系因其在紅外線能譜區間發射出極高比例的能量而得名。由定義上來說，他們在紅外線區間可以達到十的十一次方倍以上的太陽光度。許多明亮紅外線星系存在於交互作用星系系統之中，並且具有大量的分子氣體。一般認為，這些系統所擁有的大量紅外線輻射，乃導因於交互作用所觸發的星遽增現象。然而，由交互作用而引發星遽增現象的細部過程，至今尚未清楚。由數值模擬所預測的交互作用系統之星系合併序列，也尚未有很好的觀測結果佐證。在本篇論文中，利用裝置於【詹姆士?克力克?馬克斯威爾望遠鏡】上之【次毫米輻射熱測定器陣列】的次毫米觀測來研究十個正在交互作用的明亮紅外線星系。使用該陣列的好處，是因為此陣列擁有高量測敏感度以及高度空間解析力，十分適合用以觀測冷塵埃（溫度約為凱氏溫標十度左右）在明亮紅外線星系中的空間分佈及光譜能量分佈。我的研究樣本包括了在合併初期（推測為先星遽增階段）、合併過渡期、以及合併晚期的星系系統。這個序列以交互作用星系的核心投影分離距作為指標，用以探討在不同交互作用強度下，明亮紅外線星系中塵埃的連續譜在不同波段之通量密度比、溫度、質量、和恆星形成效率與星系合併過程的關係。在本文中，我也討論了明亮紅外線星系中的冷塵埃、分子氣體與塵埃之質量比、以及一氧化碳分子由第三到第二級（落在【次毫米輻射熱測定器陣列】之八百五十微米濾光鏡的透射波段中）與第一到第零級轉動躍遷譜線的通量密度比。如果當一氧化碳譜線強度比很小時，也就是第三到第二級轉動躍遷譜線很弱時，那麼分子氣體與塵埃的質量比就會與本銀河系所得到的比值相近。這樣的結果可以解決以往使用【紅外線天文衛星】（其觀測波段對較高溫之塵埃較為敏感）所做的研究中，發現分子氣體與塵埃之質量比約為本銀河系所得到比值的十倍的問題。另一方面，如果一氧化碳由第三到第二級轉動躍遷譜線在【次毫米輻射熱測定器陣列】之八百五十微米的量測中佔有很高的比例，那麼冷塵埃在星系系統中的質量就不會如其他以【次毫米輻射熱測定器陣列】所得之研究成果所預期。利用手中的數據，我也給定第三到第二級與第一到第零級躍遷譜線之通量密度比的上限。在大部分的樣本中，其質約為〝一〞，這表示了這兩條一氧化碳的譜線都為光學厚。這些研究有助於目前對星遽增星系及合併星系中星際介質的瞭解；對於日後使用【次毫米輻射熱測定器陣列】的研究，也有一定的參考價值。 Luminous infrared galaxies (LIRGs) are galaxies which emit a large fraction of their bolometric luminosity in the infrared. They typically have total infrared luminosities, $L_{IR}>10^{11}$ solar luminosity. Many LIRGs are interacting systems and contain a large amount of molecular gas. A common interpretation of the exceedingly high infrared luminosity in interacting LIRGs is that these galaxies are currently experiencing starburst phenomena triggered by the interactions. The detailed processes of how and when during an interaction starbursts begin are, however, unclear. Merging sequence predicted by numerical simulations has not been well proven by observations. In this work, my collaborators and I use sub-millimeter observations carried out with the QTR{it}{Sub-millimeter Common User Bolometre Array} (QTR{it}{SCUBA}) on QTR{it}{James Clerk Maxwell Telescope} (QTR{it}{JCMT}) to study a sample of 10 interacting LIRGs. The benefit of QTR{it}{SCUBA} observation is that QTR{it}{SCUBA} is a camera with high sensitivity and spacial resolutions. It can achieve the detail study in both morphology and spectral energy distribution of colder dust components in our samples. Like previous works with mid-infrared and CO line emission, our samples include galaxy pairs at the early (presumably pre-starburst), intermediate and late stages of interaction. This sequence is essential for locating the onset of starbursts and developing mergers, and allowing quantitative measurements of such parameters as flux ratios $S_{450mu m}/S_{850mu m}$, dust temperatures, dust mass, and the star formation efficiencies as a function of merger stage. I also discuss the constraints imposed by cold dust components ($T_{dust}sim 10$ K), molecular gas-to-dust mass ratios and flux ratios of CO (J=3-2) line emission, which lies in the transmission band of QTR{it}{SCUBA} 850 $mu m$ filter, to CO (J=1-0). If the flux ratio is small ($ll 1$), which means that CO (J=3-2) is weak in 850 $mu m$ waveband, the cold dust contributes a large fraction of total dust content. It suggests that molecular gas-to-dust ratio in these galaxies is not very different from the Galactic value. This result can solve the problem that the molecular gas-to-dust mass ratios in LIRGs are about 10 times higher than that ratio in our Galaxy, which are estimated from the CO and far-infrared observations. On the other hand, if CO (J=3-2) contributes a significant fraction of 850 $mu m$ measurements, the cold dust would have less mass than other QTR{it}{SCUBA} results suggested. I also get that the upper limit of CO (J=3-2) / CO (J=1-0) emission. The value in my cases is close to 1 which shows that the two CO transition lines are both optically thick. Such investigation is important for the understanding of the actual physical conditions of ISM in starburst galaxies and mergers.
顯示於類別:	[天文研究所] 博碩士論文

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