SNIa宿主星系的灭绝：ISM结构和灭绝规律与恒星形成的协同演化
Host Galaxy Extinction of SNIa: Co-evolution of ISM Structure and Extinction Law with Star-Formation
摘要：
本文提出了一种机制，可能会修改消光定律SNIa观察到更高的红移。从观察到（1）SNIa主要发生在螺旋星系中，（2）恒星形成的Esclanism出螺旋平面，（3）恒星形成改变了ISM中尘埃的消光性质，（4）在更高的红移有更多的恒星形成，我认为螺旋星系在过去比现在有一个更大的尘埃晕。喷射出的物质的$R_V$值较低，这将导致在较高红移下观测到的SNIa的平均值（$\bar{R}_V$）较低。SNIa观测中的两种关系表明了平均$R_V$的演化：低红移时观测到的$R_V$与宿主星系倾角的关系和不同红移区间SNIa消光值（$A_V$）分布的匹配。倾角效应确实指向具有较低$R_V$值的光晕。相比之下，$A_V$值的分布最适合于$\bar{R}_V(z)$演化，该演化模拟了SNIa变暗与归因于宇宙学常数的红移的关系。然而，即使在最坏的情况下，演化$\bar{R}_V$不能完全解释SNIa的变暗：宿主星系消光定律演化不是解释SNIa变暗的可行替代方案。SNIa的未来观测--多色光变曲线和光谱--将分别求解每个SNIa的$A_V$和$R_V$值。解决带有红移的$\bar{R}_V$（和$A_V$）的演化对于下一代宇宙学SNIa测量将是重要的，并且具有洞察遥远过去宿主星系中富含尘埃的ISM分布的额外科学。
英文摘要：
This paper presents a mechanism that may modify the extinction law for SNIa observed at higher redshift. Starting from the observations that (1) SNIa occur predominantly in spiral galaxies, (2) star-formation ejects ISM out of the plane of spirals, (3) star-formation alters the extinction properties of the dust in the ISM, and (4) there is substantially more star-formation at higher redshift, I propose that spiral galaxies have a dustier halo in the past than they do now. The ejected material's lower value of $R_V$ will lead to a lower average value ($\bar{R}_V$) for SNIa observed at higher redshift. Two relations in SNIa observations indicate evolution of the average $R_V$: the relation of observed $R_V$ with inclination of the host galaxy at low redshift and the matching of the distribution of extinction values ($A_V$) for SNIa in different redshift intervals. The inclination effect does point to a halo with lower $R_V$ values. In contrast, the distributions of $A_V$ values match best for a $\bar{R}_V(z)$ evolution that mimics the relation of SNIa dimming with redshift attributed to the cosmological constant. However, even in the worse case scenario, the evolution $\bar{R}_V$ can not fully explain the dimming of SNIa: host galaxy extinction law evolution is not a viable alternative to account for the dimming of SNIa. Future observations of SNIa --multi-color lightcurves and spectra-- will solve separately for values of $A_V$ and $R_V$ for each SNIa . Solving for evolution of $\bar{R}_V$ (and $A_V$) with redshift will be important for the coming generation of cosmological SNIa measurements and has the bonus science of insight into the distribution of dust-rich ISM in the host galaxies in the distant past.
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