Detection of the Tip of the Red Giant Branch in NGC 5128
Detection of the Tip of the Red Giant Branch in NGC 5128
复制标题
NGC 5128 中红巨星分支尖端的探测
DOI：
--
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
J. Westphal
中科院分区：
文献类型：
--
作者：
R. Soria;J. Mould;A. Watson;J. Gallagher;G. Ballester;C. Burrows;S. Casertano;J. Clarke;D. Crisp;R. Griffiths;J. Hester;J. Hoessel;J. Holtzman;P. Scowen;K. Stapelfeldt;J. Trauger;J. Westphal
我们给出了一张NGC5128(半人马座A)星系晕中超过10,000颗恒星的彩色星等图，该图基于WFPC2图像，通过V波段和I波段滤光片。比较了6个球状星团和矮小椭圆星系NGC185中红巨星分支的位置和红巨星分支的轨迹；红巨星分支的尖端是由观测到的光度函数在I≃24.1±0.1mag处的转向来表示的；这给出了NGC5128的距离模数(m-M)_0=27.8±0.2(即，距离3.6±0.2Mpc)，这与以前基于行星状星云光度函数和表面亮度起伏技术的测定一致。渐近巨星分支星的光度函数表明存在中年恒星群(~5Gyr)，其扩展到I=22.6mag(对于V-i>；2)和M_(Bot)~-5mag，然而，这些恒星的数量限制了NGC5128晕中的中年恒星群不到总数的10%。恒定I等的颜色分布，尽管受到我们样品的完整性水平的影响，但强烈地表明[Fe/H]>；-0.9Dex的平均值，可能与M31中的值相似，而高于NGC185中观察到的值。与M31晕一样，NGC5128的晕显示出广泛的化学富集度。
We present a color-magnitude diagram of more than 10,000 stars in the halo of the galaxy NGC 5128 (Centaurus A), based on WFPC2 images through V-band and I-band filters. The position of the red giant branch (RGB) stars is compared with the loci of the red giant branch in six well-studied globular clusters and in the dwarf elliptical galaxy NGC 185; the tip of the RGB is signalled by an observed turn-up in the luminosity function at I≃24.1 ± 0.1 mag; this yields a distance modulus (m - M)_0 = 27.8 ± 0.2 for NGC 5128 (i.e., a distance of 3.6 ± 0.2 Mpc), in agreement with previous determinations based on the planetary nebulae luminosity function and on the surface brightness fluctuations technique. The presence of an intermediate-age stellar population (~5 Gyr) is suggested by the luminosity function of the asymptotic giant branch stars, extending up to I= 22.6 mag (for V - I > 2) and M_(bot) ~ -5 mag; however, the number of these stars constrains the intermediate-age stellar population in the halo of NGC 5128 to be less than ~ 10% of the total. The color distribution at constant I magnitude, albeit affected by the completeness level of our sample, strongly suggests a mean value of [Fe/H] > -0.9 dex, possibly similar to the value found in M31 and higher than that observed in NGC 185. Like the M31 halo, the halo of NGC 5128 exhibits a broad range of levels of chemical enrichment.