标题： 显而易见的隐藏：UVIT和MUSE发现一个大而弥散的恒星形成星系 显示英文标题

标题： Hidden in Plain Sight: UVIT and MUSE Discovery of a Large, Diffuse Star-Forming Galaxy

摘要： 我们报告发现了一个附近的大型、弥散的星系，该星系显示出恒星形成，使用了远紫外成像望远镜（UVIT）的紫外观测数据，多单元光谱巡天探测器（MUSE）和暗能量相机遗产调查（DECaLS）的存档光学数据，以及红外巡天设施（IRSF）的近红外观测数据。由于该星系与背景星系NGC 6902A重叠，之前未被检测到。它们被错误地分类为一个相互作用系统。NGC 6902A的红移为0.05554，但MUSE观测表明相互作用的尾部是一个单独的恒星形成前景星系，其红移为0.00980。我们将新发现的星系称为UVIT J202258.73-441623.8（UVIT J2022）。近红外观测显示，UVIT J2022的恒星质量为8.7$\times$10$^{8}$M$_{\odot}$。其内部盘（R$<$4 kpc）显示出正在进行的大质量恒星形成的紫外和H$\alpha$发射。盘的其余部分亮度极低，恒星表面密度低，并延伸到半径为R$\sim$9 kpc。速度和金属丰度分布图以及恒星形成历史表明，UVIT J2022经历了三次恒星形成爆发。最近一次爆发仍在持续，这由其内部盘中广泛存在的H$\alpha$和紫外发射所支持。该星系在远紫外中显示出斑块状的旋臂，并且沿着类似棒状特征的区域存在金属丰度增强。因此，UVIT J2022是弥散星系中触发恒星形成的独特例子，导致了其内部恒星盘的增长。 我们的研究提出了一个引人深思的可能性，即(i)可能存在类似的弥散星系，由于它们的叠加而被错误地解释为相互作用的星系，以及(ii)紫外线或H$\alpha$可能是检测我们本地宇宙中此类弥散星系的一种方法。 显示英文摘要

摘要： We report the discovery of a nearby large, diffuse galaxy that shows star formation, using Ultra Violet Imaging Telescope (UVIT) far-UV observations, archival optical data from Multi-Unit Spectroscopic Explorer (MUSE) and Dark Energy Camera Legacy Survey (DECaLS), and InfraRed Survey Facility (IRSF) near-infrared observations. The galaxy was not detected earlier due to its superposition with the background galaxy, NGC 6902A. They were together mistakenly classified as an interacting system. NGC 6902A is at a redshift of 0.05554, but MUSE observations indicate that the interacting tail is a separate star-forming, foreground galaxy at a redshift of 0.00980. We refer to the new galaxy as UVIT J202258.73-441623.8 (UVIT J2022). The near-infrared observations show that UVIT J2022 has a stellar mass of 8.7$\times$10$^{8}$M$_{\odot}$. Its inner disk (R$<$4 kpc) shows UV and H$\alpha$ emission from ongoing massive star formation. The rest of the disk is extremely low luminosity, has a low stellar surface density, and extends out to a radius of R$\sim$9 kpc. The velocity and metallicity distribution maps and the star formation history indicate that UVIT J2022 has undergone three bursts of star formation. The latest episode is ongoing, which is supported by the presence of widespread H$\alpha$ and UV emission in its inner disk. The galaxy also shows patchy spiral arms in far-UV, and there is a metallicity enhancement along a bar-like feature. UVIT J2022 is thus a unique example of triggered star formation in a diffuse galaxy, resulting in the growth of its inner stellar disk. Our study raises the intriguing possibility that (i) there could be similar diffuse galaxies that have been mistakenly interpreted as interacting galaxies due to their superposition, and (ii) UV or H$\alpha$ could be a way to detect such diffuse galaxies in our local universe.