利用ALMA CO 光譜搜尋來學習在紅移z>7時最遙遠的類星體;Search for Z~7 Quasars Using Alma Co Spectral Scans and Near-Infrared Spectroscopy

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/84821

Title:	利用ALMA CO 光譜搜尋來學習在紅移z>7時最遙遠的類星體;Search for Z~7 Quasars Using Alma Co Spectral Scans and Near-Infrared Spectroscopy
Authors:	柯伊娜
Contributors:	天文研究所
Keywords:	關鍵字：系外天體 / 類星體;星系;超巨質量黑洞;高紅移;巡天;分子雲;發射線;Extragalactic / Quasars;Galaxies;Supermassive Black Holes;High-redshift;Survey;Molecular gas;Emission lines
Date:	2020-12-08
Issue Date:	2020-12-09 14:14:30 (UTC+8)
Publisher:	科技部
Abstract:	高紅移的類星體 (quasar) 是獨特的星體，對於宇宙早期階段的研究有非常重要的影響。這些類星體的光學/近紅外光譜提供了重要的證據，協助我們釐清在再電離 (reionization) 過程中的星際介質離子化程度以及宇宙中第一個超巨質量黑洞的質量。對高紅移類星體宿主星系的次毫米波觀測幫助了解在宇宙中超巨質量黑洞及宿主星系的形成。近期大型的光學及近紅外波段望遠鏡以及先進的儀器讓紅移在 6.5 < z < 7.5 的類星體觀測變得可能。然而，只有兩個類星體在紅移 z > 7 的地方被發現。利用 ALMA 望遠鏡的次毫米波光譜觀測，我們提出並測試一個對於 z > 6.5 類星體的新的觀測策略。這方法是基於利用一氧化碳 (CO) 發射線的高旋轉能階，這些能階被認為是高紅移類星體的宿主星系中的強烈恆星形成作用所造成。從PanSTARRS觀測中，我們成功地偵測一氧化碳的發射光譜從約數十個我們所挑選在紅移範圍6.5 < z < 7.5的類星體。更甚至，在紅移z > 7時我們已經發現了三個最新的遙遠類星體，幾乎翻倍了所有已知紅移在z > 7的類星體。已發現類星體的一氧化碳氣體分佈表示宿主星系有一個靠近的絆生原星系處於由大部份是分子雲所組成不同階段的交互作用。這些絆生原星系的發現提供了對原生分子雲環繞超巨質量黑洞的第一個直接的證據。我們也首次從一些新發現的類星體中偵測到水蒸氣的放射譜線。已偵測到水的放射譜線建議年輕宇宙在銀河的恆星生成區域有非常高的密度和溫度，這在低紅移的星系中並不典型被觀測到。在這份計劃中，我們提出對於我們所發現的高紅移類星體的詳細學習。我們的學習將包含1)分子雲氣體質量的測量2)恆星形成率的估算3)附近環境的學習4)最新發現紅移z > 7的類星體中的黑洞質量測量。藉由這些類星體的學習，我們將首次得到年輕宇宙中宿主星系裡超巨質量黑洞在非常早期階段恆星形成的珍貴資訊。 ;High-redshift quasars are unique objects for studies of the early epochs of our Universe. Their optical/near-infrared spectra provide important constraints on the ionization state of the intergalactic medium at the epoch of reionization and on the masses of the first supermassive black holes formed in the Universe. The submillimeter observations of the host galaxies of high-redshift quasars help to understand how supermassive black holes and their host galaxies formed in the Universe. Recent big optical and near-infrared surveys and developments in instrumentation made it possible to observe quasars at redshifts 6.5<z<7.5, well before the end of the epoch of reionization. However, only two quasars have been found at z > 7. We proposed and tested a new method for the redshift survey of quasars at z>6.5 using submillimeter spectroscopy with ALMA. The method is based on the observations of the emission lines of carbon monoxide at high rotational transitions expected from the host galaxies of high-redshift quasars with active star formation. We successfully detected emission lines of carbon monoxide from about a dozen quasar candidates at redshifts 6.5<z<7.5 selected by us from the Pan-STARRs survey. Moreover, we have discovered three new quasars at z>7 and almost doubled the number of the quasars known at z>7. The spatial distribution of the carbon monoxide gas around the discovered quasars indicates that their host galaxies have close companion protogalaxies at different stages of interaction composed mostly of molecular gas. The discovery of these companion protogalaxies provides first direct evidence for enormous amounts of raw molecular gas surrounding supermassive black holes at early epochs. We also detected, for the first time, the emission lines of water vapour from some of the newly discovered quasars. The detected water emission suggests very high densities and temperatures in the star-forming regions of the galaxies in the young Universe which are not typically observed in galaxies at low redshifts. In the current project we propose detailed study of the high-redshift quasars discovered by us. Our study will include 1) measurements of the molecular gas mass; 2) estimation of the star-formation rates; 3) study of the nearest environment and 4) measurements of the black hole masses of newly discovered z>7 quasars. By studying these quasars, we, for the first time, will obtain valuable information on the very early stages of star formation in the galaxies hosting growing supermassive black holes at the early epochs of our Universe.
Relation:	財團法人國家實驗研究院科技政策研究與資訊中心
Appears in Collections:	[Graduate Institute of Astronomy] Research Project

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