THE OUTER DISKS OF EARLY-TYPE GALAXIES. II. SURFACE-BRIGHTNESS PROFILES OF UNBARRED GALAXIES AND TRENDS WITH HUBBLE TYPE
THE OUTER DISKS OF EARLY-TYPE GALAXIES. II. SURFACE-BRIGHTNESS PROFILES OF UNBARRED GALAXIES AND TRENDS WITH HUBBLE TYPE
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DOI：
10.1088/0004-6256/142/5/145
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发表时间：
2011-08
期刊：
影响因子：
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通讯作者：
L. Gutiérrez;P. Erwin;R. Aladro;J. Beckman
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文献类型：
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作者：
L. Gutiérrez;P. Erwin;R. Aladro;J. Beckman
我们提出了一个完整的样本47早型，unbarred星系的R-波段表面亮度的方位角平均径向配置文件，作为我们以前的研究早型棒星系的补充。在非常仔细的天空相减之后，轮廓通常可以确定到远低于27 mag arcsec-2的亮度水平，最好的情况下低于28 mag arcsec-2。我们根据先前用于条形样品的方案对轮廓进行了分类：I型轮廓是亮度的单一连续指数径向下降; II型轮廓是亮度的单一连续指数径向下降。（“截断”）有一个内部浅坡（通常是指数的），其在明确定义的断裂半径处变化为更陡的指数;和III型分布（“反截短”）具有更陡的内部指数，让位于更浅的外部（通常为指数）下降。通过将这些轮廓与以前的研究相结合，我们可以对沿着哈勃序列的外盘轮廓类型的趋势（包括棒星系和非棒星系）及其全球频率做出第一个明确的陈述。我们发现，I型配置文件是最常见的早期型磁盘，从三分之一的所有S 0-Sa磁盘的最新类型的螺旋下降到10%。相反，II型轮廓（截断）的频率随着哈勃类型的增加而增加，从S 0星系的25%增加到Sd-Sm螺旋星系的80%。总的来说，所有盘状星系（哈勃型S 0-Sm）的I、II和III型轮廓的比例分别为21%、50%和38%;这包括具有复合II+III型轮廓（计数两次）的星系（占总数的1.8%）。最后，我们注意到之前（光学上）被归类为“无棒”的10个星系中存在棒。这意味着大约20%的光学无棒星系实际上是有棒的;在这种情况下，棒可能很弱，被尘埃掩盖，或者太大以至于被误认为是星系的主盘。
We present azimuthally averaged radial profiles of R-band surface brightness for a complete sample of 47 early-type, unbarred galaxies, as a complement to our previous study of early-type barred galaxies. Following very careful sky subtraction, the profiles can typically be determined down to brightness levels well below 27 mag arcsec−2 and in the best cases below 28 mag arcsec−2. We classified the profiles according to the scheme used previously for the barred sample: Type I profiles are single unbroken exponential radial declines in brightness; Type II profiles (“truncations”) have an inner shallow slope (usually exponential) which changes at a well-defined break radius to a steeper exponential; and Type III profiles (“antitruncations”) have an inner exponential that is steeper, giving way to a shallower outer (usually exponential) decline. By combining these profiles with previous studies, we can make the first clear statements about the trends of outer-disk-profile types along the Hubble sequence (including both barred and unbarred galaxies), and their global frequencies. We find that Type I profiles are most frequent in early-type disks, decreasing from one-third of all S0–Sa disks to barely 10% of the latest-type spirals. Conversely, Type II profiles (truncations) increase in frequency with Hubble type, from only ∼25% of S0 galaxies to ∼80% of Sd–Sm spirals. Overall, the fractions of Type I, II, and III profiles for all disk galaxies (Hubble types S0–Sm) are 21%, 50%, and 38%, respectively; this includes galaxies (∼8% of the total) with composite Type II+III profiles (counted twice). Finally, we note the presence of bars in 10 galaxies previously classified (optically) as “unbarred.” This suggests that ∼20% of optically unbarred galaxies are actually barred; the bars in such cases can be weak, obscured by dust, or so large as to be mistaken for the main disk of the galaxy.