ACS天炉座星团巡天。五.测量和重新校准表面亮度波动和天炉座-室女座相对距离的精确值
The ACS Fornax Cluster Survey. V. Measurement and Recalibration of Surface Brightness Fluctuations and a Precise Value of the Fornax--Virgo Relative Distance
摘要：
利用HST/ACS对天炉座星系团中43个早型星系进行了g-z色和z波段表面亮度起伏（SBF）测量。结合对室女星系团星系的观测，得到了一个修正的、非线性的z波段SBF绝对星等定标。总之，我们列出了重新校准的SBF距离在室女座，天炉座，室女座W'组，和NGC 4697在室女座南延的134个星系。校准过程产生了一个精确的相对距离模天炉座相对室女座0.42+/-0.03等，或距离比1.214 +/-0.017。由此得到的天炉座距离模数为31.51 +/-0.03 +/-0.15 mag，20.0 +/-0.3 +/-1.4 Mpc，其中第二组误差条反映了我们假设的室女座距离16.5 Mpc的系统不确定性。早期型天炉座星系的均方根距离散射为0.49^{+0.11}-0.15} Mpc，与其在天空中的紧凑外观相一致。这转化为小于SBF校准中的内在或“宇宙”散射sigma_cosmic的深度散射，与Virgo不同。因此，我们能够对sigma_cosmic的值进行第一次严格的限制，发现0.06 +/- 0.01等，至少对于g-z>1.02的星系来说，sigma_cosmic的上限是<0.08等。我们还提出了一种替代的SBF校准的基础上的“波动计数”参数Nbar，代理星系质量，这给出了一个一致的相对距离。最后，我们没有发现星系距离随位置或速度的系统趋势的证据（例如，天炉座星系团看起来既紧凑又很有活力。[删节]
英文摘要：
We present g-z color and z-band surface brightness fluctuations (SBF) measurements for 43 early-type galaxies in the Fornax cluster imaged with HST/ACS. These are combined with measurements for Virgo cluster galaxies to derive a revised, nonlinear calibration of the z-band SBF absolute magnitude as a function of g-z. In all, we tabulate recalibrated SBF distances for 134 galaxies in Virgo, Fornax, the Virgo W' group, and NGC4697 in the Virgo Southern Extension. The calibration procedure yields a precise relative distance modulus for Fornax with respect to Virgo of 0.42+/-0.03 mag, or a distance ratio 1.214 +/- 0.017. The resulting Fornax distance modulus is 31.51 +/-0.03 +/-0.15 mag, 20.0 +/-0.3 +/-1.4 Mpc, where the second set of error bars reflects systematic uncertainty from our assumed Virgo distance of 16.5 Mpc. The rms distance scatter for the early-type Fornax galaxies is 0.49^{+0.11}_{-0.15} Mpc, consistent with its compact appearance on the sky. This translates to a depth scatter smaller than the intrinsic, or "cosmic", scatter sigma_cosmic in the SBF calibration, unlike in Virgo. As a result, we are able to place the first tight constraints on the value of sigma_cosmic, finding 0.06 +/- 0.01 mag, with a firm upper limit of sigma_cosmic<0.08 mag, at least for galaxies with g-z>1.02. We also present an alternative SBF calibration based on the `fluctuation count' parameter Nbar, a proxy for galaxy mass, which gives a consistent relative distance. Finally, we find no evidence for systematic trends of the galaxy distances with position or velocity (e.g., no current infall); the Fornax cluster appears both compact and well virialized.[abridged]
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