arXiv 0711.20712007-11-13astro-ph

关于银河系结构方程

Toward Equations of Galactic Structure

Dennis Zaritsky, Ann I. Zabludoff, Anthony H. Gonzalez

备注：: submitted to ApJ
DOI：: 10.1086/529577

摘要：

我们发现，从盘星系到球状体星系，从矮球状体星系到最亮的星系团星系，所有的星系都位于由半光半径r_e、r_e内的平均表面亮度I_e和内部速度V^2 =（1/2）v_c^2 + sigma^2的乘积定义的空间内的二维表面上，其中v_c是旋转速度，sigma是速度分散。如果这些量用kpc、L_solar/pc^2和km/s来表示，则log r_e - log V^2 + log I_e + log Upperdance_e + 0.8 = 0，其中我们提供Upperdance_e的拟合函数，Upperdance_e是r_e内的质光比，单位为M_solar/L_solar，它只取决于V和I_e。对于我们的1925个星系的异质样本，这个表面的散射很小（< 0.1 dex），可能低至~ 0.05 dex，或10%。这个小的散射有三个可能的含义，即星系的总体结构如何受到内部因素（如恒星轨道结构）和外部因素（如环境）的影响。这些因素要么1）除了产生一些观察到的散射外没有任何作用，2）沿着表面移动星系，或者3）相互平衡以保持这个表面作为星系结构平衡的轨迹。我们用重子转化为恒星的比例eta和暗物质晕中这些恒星的浓度xi = R_{200} /r_e来描述Uppermum_e的行为。我们推导出eta = 1.9 × 10^{-5}（L/L^*）UppermeV ^{-3}和xi = 1.4 V/r_e。最后，我们提出并讨论了整个星系的eta和xi的分布。对于内部速度与银河系相当的系统（149 < V < 163 km/s），eta = 0.14 +- 0.05，平均而言，球状体的xi比圆盘大5倍。（节录）

英文摘要：

We find that all classes of galaxies, ranging from disks to spheroids and from dwarf spheroidals to brightest cluster galaxies, lie on a two dimensional surface within the space defined by the logarithms of the half-light radius, r_e, mean surface brightness within r_e, I_e, and internal velocity, V^2 = (1/2)v_c^2 + sigma^2, where v_c is the rotational velocity and sigma is the velocity dispersion. If these quantities are expressed in terms of kpc, L_solar/pc^2, and km/s, then log r_e - log V^2 + log I_e + log Upsilon_e + 0.8 = 0, where we provide a fitting function for Upsilon_e, the mass-to-light ratio within r_e in units of M_solar/L_solar, that depends only on V and I_e. The scatter about this surface for our heterogeneous sample of 1925 galaxies is small (< 0.1 dex) and could be as low as ~ 0.05 dex, or 10%. This small scatter has three possible implications for how gross galactic structure is affected by internal factors, such as stellar orbital structure, and by external factors, such as environment. These factors either 1) play no role beyond generating some of the observed scatter, 2) move galaxies along the surface, or 3) balance each other to maintain this surface as the locus of galactic structure equilibria. We cast the behavior of Upsilon_e in terms of the fraction of baryons converted to stars, eta, and the concentration of those stars within the dark matter halo, xi = R_{200}/r_e. We derive eta = 1.9 x 10^{-5} (L/L^*) Upsilon_* V^{-3} and xi = 1.4 V/r_e. Finally, we present and discuss the distributions of eta and xi for the full range of galaxies. For systems with internal velocities comparable to that of the Milky Way (149 < V < 163 km/s), eta = 0.14 +- 0.05, and xi is, on average, ~ 5 times greater for spheroids than for disks. (Abridged)

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英文摘要：

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