星系动物园：具有突出尘埃带的早期型星系中的尘埃和分子气体
Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes
摘要：
我们研究了352个附近的早型星系（ETG）的尘埃和相关的分子气体与突出的尘埃带。65%的这些“尘埃ETG”（D-ETG）的形态干扰，这表明合并的起源。这与与从一般ETG群体抽取的对照相比，D-ETG驻留在较低密度环境中一致。80%的D-ETG存在于视野中（与60%的对照相比），<2%存在于簇中（与10%的对照相比）。与对照组相比，D-ETG表现出更蓝的紫外光颜色（表明增强的恒星形成）和一个超过一个数量级的AGN部分（表明更高的核活动发生率）。利用SDSS r波段图像估计，大尺度特征中的尘埃质量为10^{4.5}-10 ^{6.5} MSun。与总尘埃质量（云团+弥散）的比较-使用IRAS探测到的15% D-ETG的远红外通量计算-表明只有约20%的尘埃存在于这些大尺度特征中。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。没有发现与最近的星爆年龄的相关性，这表明尘埃是直接在合并中吸积的，而不是由触发的恒星形成原位产生的。利用文献中ETG的分子气尘比，我们估计中值电流和初始分子气分数分别为~1.3%和~ 4%。最近的研究表明，附近ETG的合并活动主要涉及较小的合并（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分数为20%-44%。[删节]
英文摘要：
We study dust and associated molecular gas in 352 nearby early-type galaxies (ETGs) with prominent dust lanes. 65% of these `dusty ETGs' (D-ETGs) are morphologically disturbed, suggesting a merger origin. This is consistent with the D-ETGs residing in lower density environments compared to the controls drawn from the general ETG population. 80% of D-ETGs inhabit the field (compared to 60% of the controls) and <2% inhabit clusters (compared to 10% of the controls). Compared to the controls, D-ETGs exhibit bluer UV-optical colours (indicating enhanced star formation) and an AGN fraction that is more than an order of magnitude greater (indicating higher incidence of nuclear activity). The clumpy dust mass residing in large-scale features is estimated, using the SDSS r-band images, to be 10^{4.5}-10^{6.5} MSun. A comparison to the total (clumpy + diffuse) dust masses- calculated using the far-IR fluxes of 15% of the D-ETGs that are detected by the IRAS- indicates that only ~20% of the dust resides in these large-scale 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. 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 and initial molecular gas fraction are ~1.3% and ~4%, respectively. Recent work suggests that the merger activity in nearby ETGs largely involves minor mergers (mass ratios between 1:10 and 1:4). If the IRAS-detected D-ETGs form via this channel, then the original gas fractions of the accreted satellites are 20%-44%. [Abridged]
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