论文标题
银河系中的中间和高速云I：覆盖因子和垂直高度
Intermediate- and high-velocity clouds in the Milky Way I: covering factors and vertical heights
论文作者
论文摘要
中间和高速云（IVC，HVCS）是以银河系形成恒星形成的潜在燃料来源（MW），但它们的起源和命运敏感地取决于它们的距离。我们在HST的高分辨率紫外光谱中搜索IVC和HVC，该光谱在垂直高度为55个光晕星$ | z | \ gtrsim 1 $ kpc。 We show that IVCs ($40 \leq |v_{\rm LSR}| <90$ km/s) have a high detection rate - the covering factor, $f_c$ - that is about constant ($f_c =0.90\pm 0.04$) from $z=1.5$ to $14$ kpc, implying IVCs are essentially confined to $|z|\lesssim 1.5$ KPC。对于HVC（$ 90 \ leq | v _ {\ rm lsr} | \ Lessim 170 $ km/s），我们发现$ f_c $从$ f_c \ simeq 0.14 \ simeq 0.14 \ pm 0.10 $ pm 0.10 $ pm | z | z | | | z | \ Lessim 14 $ kpc，后一个值类似于QSOS的值。相反，非常高速云的覆盖率（VHVC，$ | v _ {\ rm lsr} | \ gtrsim 170 $ km/s）是$ f_c <4 \％\％\％\％$在恒星样本中，与这些云中的20 \％相比，这些云中必须是$ d \ kp， （$ | z | \ gtrsim 10 $ kpc）。 $ | v _ {\ rm lsr} |> 40 $ km/s的气云处为$ | b | \ gtrsim 15^\ circ $，因此$ | v _ {\ rm lsr} | $随着$ | z | $的减少而减小。假设每个功能源自单个云，我们将分别用于IVCS和HVC的比例高度为$ 1.0 \ pm 0.3 $和$ 2.8 \ pm 0.3 $ kpc。我们的发现为“雨”和银河喷泉型号提供了支持。在后一种情况下，VHVC可能主要用作MW Halo的燃料。鉴于其位置和高覆盖因素，IVC和HVC是维持MW中星形形成的好候选者。
Intermediate- and high-velocity clouds (IVCs, HVCs) are a potential source of fuel for star formation in the Milky Way (MW), but their origins and fates depend sensitively on their distances. We search for IVC and HVC in HST high-resolution ultraviolet spectra of 55 halo stars at vertical heights $|z| \gtrsim 1$ kpc. We show that IVCs ($40 \leq |v_{\rm LSR}| <90$ km/s) have a high detection rate - the covering factor, $f_c$ - that is about constant ($f_c =0.90\pm 0.04$) from $z=1.5$ to $14$ kpc, implying IVCs are essentially confined to $|z|\lesssim 1.5$ kpc. For the HVCs ($90 \leq |v_{\rm LSR}| \lesssim 170$ km/s), we find $f_c$ increases from $f_c \simeq 0.14\pm 0.10$ at $|z|\lesssim 2-3$ kpc to $f_c =0.60\pm 0.15$ at $5\lesssim |z|\lesssim 14$ kpc, the latter value being similar to that found towards QSOs. In contrast, the covering factor of very high-velocity clouds (VHVCs, $|v_{\rm LSR}|\gtrsim 170$ km/s) is $f_c<4\%$ in the stellar sample compared to 20\% in a QSO sample, implying these clouds must be at $d\gtrsim 10-15$ kpc ($|z|\gtrsim 10$ kpc). Gas clouds with $|v_{\rm LSR}|>40$ km/s at $|b|\gtrsim 15^\circ$ have therefore $|v_{\rm LSR}|$ decreasing with decreasing $|z|$. Assuming each feature originates from a single cloud, we derive scale-heights of $1.0 \pm 0.3$ and $2.8 \pm 0.3$ kpc for the IVCs and HVCs, respectively. Our findings provide support to the "rain" and galactic fountain models. In the latter scenario, VHVCs may mostly serve as fuel for the MW halo. In view of their locations and high covering factors, IVCs and HVCs are good candidates to sustain star formation in the MW.
