Exploring a new definition of the green valley and its implications
Exploring a new definition of the green valley and its implications
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DOI：
10.1093/mnrasl/slz106
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发表时间：
2019-07
影响因子：
--
通讯作者：
J. Angthopo;I. Ferreras;J. Silk
中科院分区：
文献类型：
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作者：
J. Angthopo;I. Ferreras;J. Silk
星系在颜色星等图上的分布显示出双峰性，具有被动演化的红色序列和恒星形成的蓝色云。这两个之间的区域，绿色谷（GV），代表了一个基本的转变，淬火过程的运作。我们利用了GV的另一种定义，使用4000 μ m的断裂强度，这是一个比颜色更能适应灰尘衰减的指标。我们比较和对比我们的GV定义与传统的，基于灰尘校正的颜色，利用数据从斯隆数字巡天。我们的GV选择--不需要尘埃校正，因此不携带固有的系统学--揭示了与标准尘埃校正的0.1（g-r）非常相似的星云活动趋势（星星形成，AGN，静止）。利用静止GV子样本的高信噪比叠加光谱，我们得到了GV上简单星族年龄差，这是猝灭时间尺度（Δt）的一个粗略替代。我们得到了随速度色散（σ）的增加趋势，从σ = 100 km s−1时的Δt = 1.5 Gyr，上升到σ = 200 km s−1时的3.5 Gyr，然后在最大质量的GV星系中迅速减小（σ = 250 km s−1时的Δt = 1 Gyr），这表明存在两种不同的猝灭模式，或者存在额外的通道（复兴）。
The distribution of galaxies on a colour–magnitude diagram reveals a bimodality, featuring a passively evolving red sequence and a star-forming blue cloud. The region between these two, the green valley (GV), represents a fundamental transition where quenching processes operate. We exploit an alternative definition of the GV using the 4000 Å break strength, an indicator that is more resilient than colour to dust attenuation. We compare and contrast our GV definition with the traditional one, based on dust-corrected colour, making use of data from the Sloan Digital Sky Survey. Our GV selection – that does not need a dust correction and thus does not carry the inherent systematics – reveals very similar trends regarding nebular activity (star formation, AGN, quiescence) to the standard dust-corrected 0.1(g − r). By use of high-SNR stacked spectra of the quiescent GV subsample, we derive the simple stellar population (SSP) age difference across the GV, a rough proxy of the quenching time-scale (Δt). We obtain an increasing trend with velocity dispersion (σ), from Δt ∼ 1.5 Gyr at σ = 100 km s−1, up to 3.5 Gyr at σ = 200 km s−1, followed by a rapid decrease in the most massive GV galaxies (Δt ∼ 1 Gyr at σ = 250 km s−1), suggesting two different modes of quenching, or the presence of an additional channel (rejuvenation).