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arXiv 1601.04715astro-ph.GAastro-ph.CO
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SDSS恒星形成星系的外流和复杂的恒星运动学

Outflows and complex stellar kinematics in SDSS star forming galaxies

Claudia Cicone, Roberto Maiolino, Alessandro Marconi

摘要:

我们研究了恒星形成驱动的外流的性质,通过使用一个大型光谱样本的~160,000本地“正常”恒星形成星系,从SDSS,跨越广泛的恒星形成率和恒星质量。在M_*-SFR参数空间中,将星系样本划分为一个细网格,对每个细网格,我们将包含在该网格中的星系的SDSS谱叠加在一起,生成一个合成谱。我们利用堆叠光谱的高信噪比来研究光学发射线的微弱特征的出现,这些光学发射线可能会追踪星系外流,否则在单个星系光谱中会太微弱而无法检测到。我们采用了一种新的方法,该方法依赖于电离气体的视线速度分布(LoSVD)(由[OIII]5007和Halpha+[NII] 6548,6583发射线跟踪)和恒星的LoSVD之间的比较,这些恒星被用作跟踪维里运动的参考。从恒星运动学的气体运动学在高速尾部的LoSVDs的显着偏差被解释为外流的签名。我们的研究结果表明,电离外流的发生率增加与SFR和sSFR。当SFR>1 M_Sun/yr时,外流速度(v_out)与SFR密切相关,而在较低的SFR时,v_out对SFR的依赖性几乎是平坦的。流出速度虽然有较大的散射,但也随恒星速度色散的增加而增加,我们推断流出速度高达v_out~(6-8)*sigma_stars。引人注目的是,我们只在M_*-SFR图中位于恒星形成星系主序(MS)之上的星系中检测到了电离外流的特征,并且这种外流的发生率随着偏离MS而急剧增加。我们对恒星运动学的补充分析揭示了恒星LoSVDs中存在几个10 km/s的蓝色不对称。[删节]

英文摘要:

We investigate the properties of star formation-driven outflows by using a large spectroscopic sample of ~160,000 local "normal" star forming galaxies, drawn from the SDSS, spanning a wide range of star formation rates and stellar masses. The galaxy sample is divided into a fine grid of bins in the M_*-SFR parameter space, for each of which we produce a composite spectrum by stacking together the SDSS spectra of the galaxies contained in that bin. We exploit the high signal-to-noise of the stacked spectra to study the emergence of faint features of optical emission lines that may trace galactic outflows and would otherwise be too faint to detect in individual galaxy spectra. We adopt a novel approach that relies on the comparison between the line-of-sight velocity distribution (LoSVD) of the ionised gas (as traced by the [OIII]5007 and Halpha+[NII]6548,6583 emission lines) and the LoSVD of the stars, which are used as a reference tracing virial motions. Significant deviations of the gas kinematics from the stellar kinematics in the high velocity tail of the LoSVDs are interpreted as a signature of outflows. Our results suggest that the incidence of ionised outflows increases with SFR and sSFR. The outflow velocity (v_out) correlates tightly with the SFR for SFR>1 M_Sun/yr, whereas at lower SFRs the dependence of v_out on SFR is nearly flat. The outflow velocity, although with a much larger scatter, increases also with the stellar velocity dispersion, and we infer velocities as high as v_out~(6-8)*sigma_stars. Strikingly, we detect the signature of ionised outflows only in galaxies located above the main sequence (MS) of star forming galaxies in the M_*-SFR diagram, and the incidence of such outflows increases sharply with the offset from the MS. Our complementary analysis of the stellar kinematics reveals the presence of blue asymmetries of a few 10 km/s in the stellar LoSVDs. [abridged]

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