Molecular gas and star formation in early-type galaxies
Molecular gas and star formation in early-type galaxies
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DOI：
10.1111/j.1365-2966.2010.17537.x
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发表时间：
2005-06
影响因子：
4.8
通讯作者：
A. Crocker;M. Bureau;L. Young;F. Combes
中科院分区：
文献类型：
--
作者：
A. Crocker;M. Bureau;L. Young;F. Combes
我们提出了新的MM干涉测量和光学积分场单位(IFU)观测，并构造了一个含有分子气体的12个椭圆(E)和透镜(S0)星系的样本，这些星系同时具有CO和光学地图。星系包含2×107到5×109M⊙的分子气体，主要分布在中心盘或环(半径0.5-4kpc)。分子气体的分布总是与光学遮蔽尘埃的分布一致，在许多情况下，这些尘埃显示出紧密缠绕的螺旋结构。电离气体总是与分子气体近似共转，这证明了这两种气体成分之间的联系，然而恒星形成并不总是主要的电离源。分子气体较少的星系往往有[Om]/Hβ发射线比在高值时不适合恒星形成。大多数带有分子气体的E/SOS具有基于光学颜色、紫外线颜色和吸收谱线强度的年轻或中年恒星群。少数几颗看起来纯粹是年老的恒星，根据预期的年轻恒星到观测到的年老恒星的质量比例，接近无法检测到这样的数量的极限。8μm多环芳烃和24μm辐射得到的E/SOS恒星形成率相近，但总红外数据高估了E/SOS的恒星形成率，这是由于来自较老恒星的尘埃加热所致。射电-远红外关系也比其他恒星形成星系有更多的散射。然而，尽管有这些偏差和额外的散射，导出的恒星形成率位于施密特-肯尼库特和恒效率恒星形成定律的大范围内。因此，E/SOS中的恒星形成过程与其他恒星形成星系中的恒星形成过程并没有压倒性的不同，尽管其中一个更可靠的示踪剂(24μm)指出，在给定的气体表面密度下，恒星形成效率可能较低。
We present new mm interferometric and optical integral-field unit (IFU) observations and construct a sample of 12 elliptical (E) and lenticular (S0) galaxies with molecular gas which have both CO and optical maps. The galaxies contain 2 x 10 7 to 5 × 10 9 M ⊙ of molecular gas distributed primarily in central discs or rings (radii 0.5-4 kpc). The molecular gas distributions are always coincident with distributions of optically obscuring dust that reveal tightly wound spiral structures in many cases. The ionized gas always approximately corotates with the molecular gas, evidencing a link between these two gas components, yet star formation is not always the dominant ionization source. The galaxies with less molecular gas tend to have [O m]/Hβ emission-line ratios at high values not expected for star formation. Most E/S0s with molecular gas have young or intermediate-age stellar populations based on optical colours, ultraviolet colours and absorption linestrengths. The few that appear purely old lie close to the limit where such populations would be undetectable based on the mass fractions of expected young to observed old stars. The 8 μm polycyclic aromatic hydrocarbon (PAH) and 24 μm emission yield similar star formation rate (SFR) estimates of E/S0s, but the total infrared overpredicts the rate due to a contribution to dust heating from older stars. The radio-far-infrared relation also has much more scatter than for other star-forming galaxies. However, despite these biases and additional scatter, the derived star formation rates locate the E/S0 galaxies within the large range of the Schmidt-Kennicutt and constant efficiency star formation laws. Thus, the star formation process in E/S0s is not overwhelmingly different than in other star-forming galaxies, although one of the more reliable tracers (24 μm) points to a possible lower star formation efficiency at a given gas surface density.