We estimated the galactic model parameters for a set of 20 intermediate-latitude fields with galactic longitudes 0<l<100 and 160<l<240, included in the currently available Data Release 6 (DR6) of SDSS, to explore their possible variation with galactic longitude. The local space densities of the thick disc and halo are almost the same for all fields, <(n_{2}/n_{1})>=6.52% and <(n_{3}/n_{1})>=0.35%, respectively, a result different than the one cited for high-latitude fields. The thin disc's scaleheight is 325 pc in the galactic centre changes to 369 pc in the third quadrant, which confirms the existence of disc flare, whereas the thick disc scaleheight is as large as 952 pc at galactic longitude l=20 and 10% lower at l=160, which confirms the existence of the disc long bar in the direction l=27. Finally, the variation of the axis ratio of the halo with galactic longitude is almost flat, <(c/a)>=0.56, except a slight minimum and a small maximum in the second and third quadrants, respectively, indicating an effect of the long bar which seems plausible for a shallow halo. We estimated the metallicities of unevolved G-type stars and discussed the metallicity gradient for different vertical distances. The metallicity gradient is d[M/H]/dz=-0.30 dex kpc$^{-1}$ for short distances, confirming the formation of this region of the Galaxy by dissipational collapse. However, its change is steeper in the transition regions of different galactic components. The metallicity gradient is almost zero for inner halo (5<z<10 kpc), indicating a formation of merger or accretion of numerous fragments such as dwarf galaxies.
Small-Scale HI Channel Map Structure is Cold: Evidence from Na I Absorption at High Galactic Latitudes
中性氢辐射的空间分布是研究星际介质物理的重要手段。在H I通道图中的小尺度结构通常被假定为探测速度场而不是真实的密度结构。在这项工作中，我们使用高分辨率的GALFA-H I观测和SDSS的50，985个类星体光谱直接测试了这一假设。我们测量了星际Na I D $_1$和Na I D $_2$吸收的等效宽度，并有力地得出结论：它们对H I中小尺度结构的柱密度的依赖性比对大尺度H I结构或总H I柱的依赖性更强。这与小尺度通道图结构由速度拥挤驱动的假设不一致。相反，这些数据支持这样的解释，即这种发射结构主要起源于寒冷、致密的星际物质，与寒冷的中性介质一致。
The fall of the Northern Unicorn: Tangential motions in the Galactic Anti-centre with SDSS and Gaia
我们提出了第一个详细的研究行为的恒星自行在整个银河系反中心地区可见的斯隆数字巡天数据。我们使用重新校准的SDSS天体测量结合位置从{ \it盖亚} DR 1提供切向运动测量与系统的不确定性$<$ 5公里$^{-1}$的距离的麒麟座环的主序星。我们证明麒麟座成员围绕银河系旋转的方位角速度约为230公里$^{-1}$，仅略低于太阳。此外，垂直和方位角分量的运动显示出变化很大，但逐渐作为银河系经度和纬度的函数。反中心区的恒星过密度可以分为两个部分，即狭窄的流线型ACS和光滑的环。根据我们的分析，这两个结构显示出非常相似但明显不同的运动学趋势，可以总结如下：与环相比，ACS中$v_ϕ$和$v_z$的速度变化幅度更高，环的速度梯度似乎更平坦。目前，没有可用的模型可以解释这一天空区域的全部数据。然而，这里介绍的新的精确的运动学地图应该提供强大的制约麒麟环的成因和相关的子结构。
