论文标题
Leoncino矮人银河系：探索亮度金属性和质量金属关系的低金属端
The Leoncino Dwarf Galaxy: Exploring the Low-Metallicity End of the Luminosity-Metallicity and Mass-Metallcity Relations
论文作者
论文摘要
极为金属贫困（XMP）星系是低质量的，恒星形成的星系，气相氧的丰度低于12+log（O/H）= 7.35（〜1/20 Zsun）。星系演化方案提出了形成XMP的三个途径：（1）在低星系质量下的世俗进化，（2）空隙中的缓慢演变，或（3）（3）原始气体插入中测量的丰度稀释。最近发现的XMP Galaxy Leoncino，氧气丰度低于3％Zsun，提供了探索这些不同情况的机会。使用Leoncino分辨出的恒星种群的Hubble空间望远镜成像，我们测量到星系的距离为d = 12.1（+1.7/-3.4）MPC，并发现Leoncino位于低强度的环境中。 Leoncino具有紧凑的形态，容纳了一群年轻，大型的恒星，具有高气压比率，并且显示出与附近的星空的互动迹象，UGC 5186，类似于几乎所有XMP星系，在附近的环球中已知，Leoncino在Leoncino中均来自LuminSolusity-Metallicity-Metallic-Metallic-Metallicity（lz）的关系。然而，Leoncino与局部体积星系定义的恒星质量金属关系（MZ）关系一致。因此，我们的结果表明，与LZ关系的偏移是由于最近的恒星形成较高，这可能是由较小的相互作用触发的，而低氧丰度则与预期低质量星系的期望一致，即低质量的星系会经历效率不佳的星体进化，这是由恒星形成不足的恒星形成和金属损伤，而金属则通过银河系风。这与LZ和MZ关系中的异常值的XMP星系相反。在这种情况下，由于原始气体的灌注，稀释度可以很好地解释低氧丰度。我们还讨论了为什么在当前的调查中静态XMP星系的代表性不足。
Extremely metal-poor (XMP) galaxies are low-mass, star-forming galaxies with gas-phase oxygen abundances below 12+log(O/H) = 7.35 (~1/20 Zsun). Galaxy evolution scenarios suggest three pathways to form an XMP: (1) secular evolution at low galaxy masses, (2) slow evolution in voids, or (3) dilution of measured abundances from infall of pristine gas. The recently discovered XMP galaxy Leoncino, with an oxygen abundance below 3% Zsun, provides an opportunity to explore these different scenarios. Using Hubble Space Telescope imaging of the resolved stellar populations of Leoncino, we measure the distance to the galaxy to be D=12.1 (+1.7/-3.4) Mpc and find that Leoncino is located in an under-dense environment. Leoncino has a compact morphology, hosts a population of young, massive stars, has a high gas-to-star mass ratio, and shows signs of interaction with a galaxy nearby on the sky, UGC 5186. Similar to nearly all XMP galaxies known in the nearby universe, Leoncino is offset from the Luminosity-Metallicity (LZ) relation. Yet, Leoncino is consistent with the stellar Mass-Metallicity (MZ) relation defined by Local Volume galaxies. Thus, our results suggest that the offset from the LZ relation is due to higher recent star formation, likely triggered by a minor interaction, while the low oxygen abundance is consistent with the expectation that low-mass galaxies will undergo secular evolution marked by inefficient star formation and metal-loss via galactic winds. This is in contrast to XMP galaxies that are outliers in both the LZ and MZ relations; in such cases, the low oxygen abundances are best explained by dilution due to the infall of pristine gas. We also discuss why quiescent XMP galaxies are underrepresented in current surveys.
