论文标题
星系凸起中的恒星年龄梯度和内而外的星形淬火
Stellar age gradients and inside-out star formation quenching in galaxy bulges
论文作者
论文摘要
径向年龄段梯度保持着众多的物理过程的累积记录，推动了星系凸起的恒星群体和随之而来的恒星形成（SF）淬火过程，因此在凸起形成和进化方面具有竞争性理论概念之间有潜在敏感的歧视因子。基于CALICA调查的整体现场光谱数据的光谱建模，我们在光度确定的凸起半径（RB）中得出了质量和轻度加权的恒星年龄梯度（$ \ nabla $（t，b）L，M），用于当地型面向后期的近期型号的当地面部面部型号2.6 Dex 2.6 Dex in 2.6 spanlar in spanlar s in spellar s instellar in stallar in stallar in stallar s intellar intellar。我们的分析记录了减少$ \ nabla $（t，b）L，M的趋势，其中M，T增加，高质量凸起主要显示出负年龄段，反之亦然。从正向$ \ nabla $（t，b）l，m发生的反转发生在logm，t〜10，这与从下部质量凸起的过渡大致相吻合，从低质量凸起的过渡，其气体激发由SF驱动到分类为复合，衬里或seyfert的凸起。我们讨论了大量LTG凸起中径向年龄梯度起源的两个限制案例。第一个假设凸起的恒星年龄最初是空间均匀的，因此观察到的年龄梯度是由内而外的SF淬灭（IOSFQ）前部产生的，该前部正以平均速度VQ径向扩展。在这种情况下，年龄梯度转化为慢速iosFQ，持续到Z〜2，表明SF或AGN的轻度负反馈。 If negative age gradients in massive bulges are not due to ioSFQ but primarily due to their inside-out formation process, then the standard hypothesis of quasi-monolithic bulge formation has to be discarded in favor of a scenario that involves gradual buildup of stellar mass over 2-3 Gyr through, e.g., inside-out SF and inward migration of SF clumps from the disk.在这种情况下，不能排除以AGN驱动的快速驱动的IOSFQ。
Radial age gradients hold the cumulative record of the multitude of physical processes driving the build-up of stellar populations and the ensuing star formation (SF) quenching process in galaxy bulges, therefore potentially sensitive discriminators between competing theoretical concepts on bulge formation and evolution. Based on spectral modeling of integral field spectroscopy data from the CALIFA survey, we derive mass- and light-weighted stellar age gradients ($\nabla$(t,B)L,M) within the photometrically determined bulge radius (RB) of a representative sample of local face-on late-type galaxies that span 2.6 dex in stellar mass. Our analysis documents a trend for decreasing $\nabla$(t,B)L,M with increasing M,T, with high-mass bulges predominantly showing negative age gradients and vice versa. The inversion from positive to negative $\nabla$(t,B)L,M occurs at logM,T ~ 10, which roughly coincides with the transition from lower-mass bulges whose gas excitation is powered by SF to bulges classified as Composite, LINER or Seyfert. We discuss two limiting cases for the origin of radial age gradients in massive LTG bulges. The first assumes that the stellar age in the bulge is initially spatially uniform, thus the observed age gradients arise from an inside-out SF quenching (ioSFQ) front that is radially expanding with a mean velocity vq. In this case, the age gradients translate into a slow ioSFQ that lasts until z~2, suggesting mild negative feedback by SF or an AGN. If negative age gradients in massive bulges are not due to ioSFQ but primarily due to their inside-out formation process, then the standard hypothesis of quasi-monolithic bulge formation has to be discarded in favor of a scenario that involves gradual buildup of stellar mass over 2-3 Gyr through, e.g., inside-out SF and inward migration of SF clumps from the disk. In this case, rapid AGN-driven ioSFQ cannot be ruled out.
