arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1606.07809astro-ph.GA
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相互作用后:NGC5195中的高效成星分子盘

After the interaction: an efficiently star-forming molecular disk in NGC5195

Katherine Alatalo, Rebeca Aladro, Kristina Nyland, Susanne Aalto, Theodoros Bitsakis, John S. Gallagher, Lauranne Lanz

摘要:

我们从毫米波天文学研究组合阵列(CARMA)中展示了NGC 5195(也称为M51 b)的新分子气体图,包括12 CO(1-0),13 CO(1-0),CN(1-0)和CS(2-1)。NGC 5195也在3 mm连续谱中被检测到。NGC 5195的12 CO/13 CO比率与正常的恒星形成星系一致。CN(1-0)的强度比一般的恒星形成星系要高,可能是在扩散的光解离区域增强。NGC 5195核谱的恒星模板拟合显示了两个恒星星族:80%质量分数的老恒星(> 10 Gyr)和20%质量分数的中龄(~ 1 Gyr)恒星星族,这对NGC 5195在与M51 a相互作用期间经历增强恒星形成的时间尺度提供了限制。NGC 5195的平均分子气体耗尽时间尺度为:tdep=3.08Gyr,比附近恒星形成星系的耗尽时间尺度大2倍,但与CO探测到的早型星系的耗尽一致。虽然厘米和毫米波长的无线电连续辐射存在于NGC 5195的核心附近,但我们发现它最有可能与核恒星形成有关,而不是无线电响亮的AGN。因此,尽管在大约1/2 Gyr前与M51 a发生了实质性的相互作用,但NGC 5195中的分子气体已经重新定居,并且正在以与目前定居的早期类型星系一致的效率形成恒星。

英文摘要:

We present new molecular gas maps of NGC5195 (alternatively known as M51b) from the Combined Array for Research in Millimeter Astronomy (CARMA), including 12CO(1-0), 13CO(1-0), CN(1-0), and CS(2-1). NGC5195 has also been detected in 3mm continuum. NGC5195 has a 12CO/13CO ratio consistent with normal star-forming galaxies. The CN(1-0) intensity is higher than is seen in an average star-forming galaxy, possibly enhanced in the diffuse photo-dissociation regions. Stellar template fitting of the nuclear spectrum of NGC5195 shows two stellar populations: an 80% mass fraction of old (>10Gyr) and a 20% mass fraction of intermediate-aged (~1Gyr) stellar populations, providing a constraint on the timescale over which NGC5195 experienced enhanced star formation during its interaction with M51a. The average molecular gas depletion timescale in NGC5195 is: tdep=3.08Gyr, a factor of ~2 larger than the depletion timescales in nearby star-forming galaxies, but consistent with the depletion seen in CO-detected early-type galaxies. While the radio continuum emission at centimeter and millimeter wavelengths is present in the vicinity of the nucleus of NGC5195, we find it is most likely associated with nuclear star formation rather than a radio-loud AGN. Thus, despite having a substantial interaction with M51a ~1/2Gyr ago, the molecular gas in NGC5195 has resettled and is forming stars at an efficiency consistent with settled early-type galaxies at the present time.

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