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arXiv 1107.5587astro-ph.CO
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矮不规则星系的外星系

The Outer Disks of Dwarf Irregular Galaxies

Deidre A. Hunter, Bruce G. Elmegreen, Se-Heon Oh, Ed Anderson, Tyler E. Nordgren, Philip Massey, Nick Wilsey, Malanka Riabokin

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摘要：

为了探索极端外星盘的性质，我们获得了4个矮不规则星系和1个蓝色致密矮星系的超深V和GALEX UV图像，以及其中3个星系的超深B图像。我们的V波段地表测光扩展到29.5等角秒^-2。我们将FUV和V波段测光，随着Halpha测光，径向恒星形成率的配置文件，是敏感的时间尺度从10百万年的银河系的寿命。我们还比较了恒星分布，表面亮度剖面，恒星形成率剖面HI线发射图，气体表面密度剖面和气体运动学。我们的数据使我们得到两个普遍的观察结果：第一，这些不规则星系中的指数盘是非常规则的。就我们的测量范围而言，恒星盘继续呈指数级下降。尽管年轻恒星的分布和HI分布和运动学有显着的无序运动，零星的过程，建立了磁盘-恒星形成，恒星的径向运动，甚至可能是来自外部的扰动-有块状，然而，合谋产生标准的磁盘配置文件。第二，随着时间的推移，在这些盘中有一个显着的恒星形成的连续性。在我们五个星系中的四个中，从V波段确定的FUV轨道测量的外盘中的恒星形成率在5倍以内，需要在星系的一生中以相当稳定的速度形成恒星。然而，HI的表面密度分布通常比恒星光更浅地随半径下降，并且气体在重力作用下是边缘稳定的，不会塌缩成云。外部恒星盘正在挑战我们的恒星形成和盘生长的概念，并提供了一个关键的环境，以了解塑造星系盘的过程。

英文摘要：

To explore the properties of extreme outer stellar disks, we obtained ultra-deep V and GALEX UV images of 4 dwarf irregular galaxies and one Blue Compact Dwarf galaxy and ultra-deep B images of 3 of these. Our V-band surface photometry extends to 29.5 magnitudes arcsec^-2. We convert the FUV and V-band photometry, along with Halpha photometry, into radial star formation rate profiles that are sensitive to timescales from 10 Myrs to the lifetime of the galaxy. We also compare the stellar distributions, surface brightness profiles, and star formation rate profiles to HI-line emission maps, gas surface density profiles, and gas kinematics. Our data lead us to two general observations: First, the exponential disks in these irregular galaxies are extraordinarily regular. The stellar disks continue to decline exponentially as far as our measurements extend. In spite of lumpiness in the distribution of young stars and HI distributions and kinematics that have significant unordered motions, sporadic processes that have built the disks-star formation, radial movement of stars, and perhaps even perturbations from the outside-have, nevertheless, conspired to produce standard disk profiles. Second, there is a remarkable continuity of star formation throughout these disks over time. In four out of five of our galaxies the star formation rate in the outer disk measured from the FUV tracks that determined from the V-band, to within factors of 5, requiring star formation at a fairly steady rate over the galaxy's lifetime. Yet, the HI surface density profiles generally decline with radius more shallowly than the stellar light, and the gas is marginally gravitationally stable against collapse into clouds. Outer stellar disks are challenging our concepts of star formation and disk growth and provide a critical environment in which to understand processes that mold galaxy disks.

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