NGC 300: An Extremely Faint, Outer Stellar Disk Observed to 10 Scale Lengths
NGC 300: An Extremely Faint, Outer Stellar Disk Observed to 10 Scale Lengths
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DOI：
10.1086/430512
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发表时间：
2005-03
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影响因子：
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通讯作者：
J. Bland-Hawthorn;M. Vlajić;K. Freeman;B. Draine
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作者：
J. Bland-Hawthorn;M. Vlajić;K. Freeman;B. Draine
我们利用Gemini南8米望远镜的Gemini多目标摄谱仪（GMOS）在特殊条件下（视宁度为0. 6 ″）对玉夫座星系NGC 300的外星盘进行了两个位置的观测。在我们的点源探测阈值r′ = 27.0（3 σ）等时，我们追踪恒星盘到半径为24 '，或2.2R25，其中R25是25等角秒-2等照度半径。这相当于这个低光度螺旋星系（MB = -18.6）的10个标度长度，或者在造父变星距离为2.0 ± 0.07 Mpc时约为14.4 kpc。背景星系数来自最外层的区域，这些都在哈勃深场平均调查数的10%以内。光度分布是很好地描述了一个核加上一个简单的指数分布到10个光学标度长度。在55%的完整性下，我们得到了μ = 30.5 mag arcsec-2（2 σ）的有效表面亮度，这是已知光盘径向范围的两倍。这些能级是非常微弱的，因为在B或V中的等效表面亮度约为32 mag arcsec-2。我们没有发现恒星盘被截断的证据。只有星星计数才能可靠地追踪到如此微弱的水平，因为表面测光最终受到非恒星辐射源的限制。在附录中，我们得到了一个这样的源的预期表面亮度：在外盘星光的尘埃散射。
We have used the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South 8 m telescope in exceptional conditions (0.″6 FWHM seeing) to observe the outer stellar disk of the Sculptor Group galaxy NGC 300 at two locations. At our point-source detection threshold of r′ = 27.0 (3 σ) mag, we trace the stellar disk out to a radius of 24', or 2.2R25, where R25 is the 25 mag arcsec-2 isophotal radius. This corresponds to about 10 scale lengths in this low-luminosity spiral galaxy (MB = -18.6), or about 14.4 kpc at a Cepheid distance of 2.0 ± 0.07 Mpc. The background galaxy counts are derived in the outermost field, and these are within 10% of the mean survey counts from both Hubble Deep Fields. The luminosity profile is well described by a nucleus plus a simple exponential profile out to 10 optical scale lengths. We reach an effective surface brightness of μ = 30.5 mag arcsec-2 (2 σ) at 55% completeness, which doubles the known radial extent of the optical disk. These levels are exceedingly faint in the sense that the equivalent surface brightness in B or V is about 32 mag arcsec-2. We find no evidence for truncation of the stellar disk. Only star counts can be used to reliably trace the disk to such faint levels, since surface photometry is ultimately limited by nonstellar sources of radiation. In the Appendix, we derive the expected surface brightness of one such source: dust scattering of starlight in the outer disk.