标题： 白矮星银河晕的启示 显示英文标题

标题： Implications of White Dwarf Galactic Halos

摘要： 受最近测量结果的启发，这些测量表明大约一半的星系晕质量可能以白矮星的形式存在，我们研究了这种晕结构的含义。 首先，我们使用当前对红外背景光和星系金属丰度的限制来约束产生白矮星的恒星群体的初始质量函数（IMF）。 IMF 必须在一个特征质量尺度$M_C \approx 2.3 M_\odot$附近急剧峰值。 由于恒星的初始质量只有部分被纳入残余的白矮星中，我们论证说晕中白矮星的质量分数很可能为 25% 或更少，而 50% 是一个极端上限。 我们利用 IMF 的结果对恒星形成原始初始条件施加相应的限制。 初始条件必须比导致目前 IMF 的条件更加均匀，并且倾向于更高的温度（$T_{\rm gas} \sim$ 200 K）。 接下来我们确定白矮星的亮度函数。 通过将此结果与观测到的亮度函数进行比较，我们发现晕群体的年龄必须大于$\sim 16$Gyr。 最后，我们计算白矮星晕的辐射特征。 这种红外背景非常微弱，但未来观测有可能探测到它。 显示英文摘要

摘要： Motivated by recent measurements which suggest that roughly half the mass of the galactic halo may be in the form of white dwarfs, we study the implications of such a halo. We first use current limits on the infrared background light and the galactic metallicity to constrain the allowed initial mass function (IMF) of the stellar population that produced the white dwarfs. The IMF must be sharply peaked about a characteristic mass scale $M_C \approx 2.3 M_\odot$. Since only a fraction of the initial mass of a star is incorporated into the remnant white dwarf, we argue that the mass fraction of white dwarfs in the halo is likely to be 25\% or less, and that 50\% is an extreme upper limit. We use the IMF results to place corresponding constraints on the primordial initial conditions for star formation. The initial conditions must be much more homogeneous and skewed toward higher temperatures ($T_{\rm gas} \sim$ 200 K) than the conditions which lead to the present day IMF. Next we determine the luminosity function of white dwarfs. By comparing this result with the observed luminosity function, we find that the age of the halo population must be greater than $\sim 16$ Gyr. Finally, we calculate the radiative signature of a white dwarf halo. This infrared background is very faint, but is potentially detectable with future observations.