Galvanic在哪里结束？
Where Do Galaxies End?
摘要：
我们目前对星系的看法认为它们是恒星和气体的系统，嵌入在暗物质的扩展晕中，其中大部分是由早期较小系统的坠落形成的。一个星系的真实范围仍然很难确定，维里半径（R_vir）提供了一个典型的分离动力学平衡中的坍缩结构和外部坠落物质。引力影响程度的其他物理估计包括引力半径、气体吸积半径和在流出参数和封闭气体压力范围内在100-200 kpc失速的流出所产生的“银河层顶”。提出了定义束缚结构的物理判据，包括对恒星质量M* 和晕质量M_h的R_vir（M*，M_h，z_a）的更现实的定义，其中一半在“组装红移”z_a = 0.7-1.3处形成。我们估计L* 星系周围的束缚气体和暗物质的范围约为200 kpc。新的维里半径平均R_vir ~ 200 kpc，比最近HST/COS探测到的星系周围H_I和O_VI吸收体的估计值小40-50%。在新的形式中，银河系恒星质量log M* = 10.7 +/- 0.1，对应于Z_a = 1.06 +/- 0.03的半质量晕集合体的R_vir = 153（+25，-16）kpc。类星体光谱中低红移O-VI吸收线的单位红移频率表明，当与0.1L* 星系相关时，吸收体的大小约为150 kpc。这种形式主义的目的是澄清语义上的差异所产生的观测扩展气体在星系晕，环星系介质（CGM），星系际介质（IGM）的细丝。天文学家应该参考星系晕或CGM中的束缚气体，以及CGM-IGM界面处的非束缚气体，这些气体正在进入IGM。
英文摘要：
Our current view of galaxies considers them as systems of stars and gas embedded in extended halos of dark matter, much of it formed by the infall of smaller systems at earlier times. The true extent of a galaxy remains poorly determined, with the virial radius (R_vir) providing a characteristic separation between collapsed structures in dynamical equilibrium and external infalling matter. Other physical estimates of the extent of gravitational influence include the gravitational radius, gas accretion radius, and "galactopause" arising from outflows that stall at 100-200 kpc over a range of outflow parameters and confining gas pressures. Physical criteria are proposed to define bound structures, including a more realistic definition of R_vir (M*, M_h, z_a) for stellar mass M* and halo mass M_h, half of which formed at "assembly redshifts" z_a = 0.7-1.3. We estimate the extent of bound gas and dark matter around L* galaxies to be ~200 kpc. The new virial radii, with mean R_vir ~ 200 kpc, are 40-50% smaller than values estimated in recent HST/COS detections of H I and O VI absorbers around galaxies. In the new formalism, the Milky Way stellar mass, log M* = 10.7 +/- 0.1, would correspond to R_vir = 153 (+25,-16) kpc for half-mass halo assembly at z_a = 1.06 +/- 0.03. The frequency per unit redshift of low-redshift O VI absorption lines in QSO spectra suggests absorber sizes ~150 kpc when related to intervening 0.1L* galaxies. This formalism is intended to clarify semantic differences arising from observations of extended gas in galactic halos, circumgalactic medium (CGM), and filaments of the intergalactic medium (IGM). Astronomers should refer to bound gas in the galactic halo or CGM, and unbound gas at the CGM-IGM interface, on its way into the IGM.
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