Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes
Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes
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星系动物园：具有突出尘埃带的早期星系中的尘埃和分子气体
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发表时间：
2011
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通讯作者：
S. Bamford
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作者：
S. Kaviraj;S. Kaviraj;Y. Ting;Y. Ting;M. Bureau;S. Shabala;S. Shabala;R. M. Crockett;J. Silk;C. Lintott;Arfon M. Smith;W. Keel;K. Masters;K. Schawinski;S. Bamford
我们研究了来自斯隆数字巡天（SDSS）的352个附近（0.01 < z < 0.07）具有显著尘埃带的早型星系（ETG）中尘埃和相关分子气体的性质。这些“尘埃ETG”（D-ETG）中有三分之二在形态上受到干扰，这表明合并起源，使这些星系成为研究低红移合并过程的理想试验床。与从一般ETG群体中抽取的对照样品相比，D-ETG优先驻留在较低密度环境中。大约80%的D-ETG居住在田间（对照ETG为60%），不到2%居住在集群（对照ETG为10%）。与对照样品相比，D-ETG显示出更蓝的紫外光颜色（表明星星形成的水平提高）和一个活跃的星系核分数，这是一个数量级以上（表明核活动的发生率显着更高）。使用SDSS的r波段图像，估计大尺度尘埃特征中的cluerous尘埃质量在104.5-106.5 M之间。与总的（云尘+弥散）尘埃质量-使用红外天文卫星探测到的15%的D-ETG的远红外通量计算-的比较表明，只有20%的尘埃通常包含在这些大尺度尘埃特征中。尘埃质量比预期的恒星质量损失最大值大好几倍，排除了内部起源。尘埃含量与蓝色光度没有相关性，表明它与银河系尺度的冷却流无关。此外，没有发现与最近的恒星爆发的年龄相关，这表明尘埃是直接在合并中吸积的，而不是由触发的星星形成原位产生的。利用文献中ETG的分子气尘比，我们估计IRAS探测到的ETG中分子气体的中位含量为1.3%。在这些D-ETG中，初始气体含量的中位数为0.4%，最近的研究表明，附近ETG中的合并活动主要涉及小型合并（干ETG +富气矮星），质量比在1：10和1：4之间。如果IRAS探测到的D-ETG是通过这个通道形成的，那么吸积卫星的原始气体比例在20%到44%之间。
We explore the properties of dust and associated molecular gas in 352 nearby (0.01 < z < 0.07) early-type galaxies (ETGs) with prominent dust lanes, drawn from the Sloan Digital Sky Survey (SDSS). Two-thirds of these ‘dusty ETGs’ (D-ETGs) are morphologically disturbed, which suggests a merger origin, making these galaxies ideal test beds for studying the merger process at low redshift. The D-ETGs preferentially reside in lower density environments, compared to a control sample drawn from the general ETG population. Around 80 per cent of D-ETGs inhabit the field (compared to 60 per cent of the control ETGs) and less than 2 per cent inhabit clusters (compared to 10 per cent of the control ETGs). Compared to their control-sample counterparts, D-ETGs exhibit bluer ultraviolet–optical colours (indicating enhanced levels of star formation) and an active galactic nucleus fraction that is more than an order of magnitude greater (indicating a strikingly higher incidence of nuclear activity). The mass of clumpy dust residing in large-scale dust features is estimated, using the SDSS r-band images, to be in the range 104.5–106.5 M⊙. A comparison to the total (clumpy + diffuse) dust masses – calculated using the far-infrared fluxes of 15 per cent of the D-ETGs that are detected by the Infrared Astronomical Satellite (IRAS) – indicates that only 20 per cent of the dust is typically contained in these large-scale dust features. The dust masses are several times larger than the maximum value expected from stellar mass loss, ruling out an internal origin. The dust content shows no correlation with the blue luminosity, indicating that it is not related to a galactic scale cooling flow. Furthermore, no correlation is found with the age of the recent starburst, suggesting that the dust is accreted directly in the merger rather than being produced in situ by the triggered star formation. Using molecular gas-to-dust ratios of ETGs in the literature, we estimate that the median current molecular gas fraction in the IRAS-detected ETGs is ∼1.3 per cent. Adopting reasonable values for gas depletion time-scales and starburst ages, the median initial gas fraction in these D-ETGs is ∼4 per cent. Recent work has suggested that the merger activity in nearby ETGs largely involves minor mergers (dry ETG + gas-rich dwarf), with mass ratios between 1:10 and 1:4. If the IRAS-detected D-ETGs have formed via this channel, then the original gas fractions of the accreted satellites are between 20 and 44 per cent.