2019年8月8日 (四) 09:44 Quan787

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==英文题目==
'''(T8) A Possible Dark Matter Deficient Galaxy (25 points)'''

Earlier this year, a team of astronomers reported their discovery of a galaxy with much less dark matter than the galaxy evolution model predicted (van Dokkum et al. 2018, Nature). This galaxy, named NGC 1052-DF2, is located close to the elliptical galaxy NGC 1052 (D=20Mpc from the Sun) in the sky. The shape of NGC 1052-DF2 resembles an ellipse with semi major axis (a) of 22.6" and $$\frac{b}{a}=0.85$$. Half of the total light from the galaxy comes from within this ellipse and the mean surface brightness within the ellipse is about 24.7 mag arcsec<sup>-2</sup> .

(a) Calculate the total apparent magnitude of this galaxy.

(b) The team suggested the galaxy is a companion of NGC 1052. Determine the total mass of stars in NGC 1052-DF2, assuming it has a mass to light ratio $$(\frac{M/M_⊙}{L/L_⊙})$$ of 2.0.

(c) The team identified 10 globular clusters in NGC 1052-DF2 with a mean galactocentric distance of 78.4". They also measured the velocity dispersion of these clusters to be not more than 8.4 km/s. Estimate the dynamical mass of this galaxy. For simplicity, assume the mass distribution in the galaxies is uniform and is spherically symmetric.

(d) This discovery was challenged by other groups (Kroupa et al., Nature, 2018, Truijlo et al., MNRAS, 2018), who claimed that NGC 1052-DF2 is not a satellite of NGC 1052, and it is located at a much smaller distance to us. Show why a smaller distance would weaken the assertion of the dark matter deficiency in NGC 1052-DF2.

==中文翻译==
'''(T8)一个可能的贫暗物质星系(25分)'''

今年早些时候，一个科学家团队报道他们发现了一个星系的暗物质远低于星系演化模型的预计（van Dokkum et al. 2018, Nature）。这个星系编号是NGC 1052-DF2，位于椭圆星系NGC 1052 (距离太阳D=20Mpc)附近。NGC
1052-DF2的形状像一个椭圆形，半长轴（a）22.6"，$$\frac{b}{a}=0.85$$。这个星系一般的光来自于这个椭圆内，椭圆内的平均面亮度是24.7星等每平方角秒。

(a)计算这个星系的总视星等。

(b)这个团队认为这个星系是NGC 1052的伴星系。假设NGC 1052-DF2的质光关系为$$(\frac{M/M_⊙}{L/L_⊙})$$，计算这个星系中恒星的总质量。

(c)这个团队证认出NGC 1052-DF2中的10个球状星团，它们与星系中心的平均角距离是78.4"。他们同时测量出球状星团的速度弥散度不超过8.4km/s。估计这个星系的动力学质量，假设这个星系的质量分布是均匀且球对称的。

(d)其他团队对这个发现表示质疑 (Kroupa et al., Nature, 2018, Truijlo et al., MNRAS, 2018)，他们认为NGC 1052-DF2并不是NGC 1052的伴星系，距离我们比NGC 1052近得多。解释为何更近的距离会弱化NGC 1052-DF2缺乏暗物质的论证。

[[分类:天体力学]]

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 (a)计算这个星系的总视星等。
-(b)这个团队认为这个星系是NGC 1052的伴星系。假设NGC 1052-DF2的质光关系为$$(\frac{M/M_⊙}{L/L_⊙})$$，计算这个星系中恒星的总质量。
+(b)这个团队认为这个星系是NGC 1052的伴星系。假设NGC 1052-DF2的质光关系$$(\frac{M/M_⊙}{L/L_⊙})$$为2.0，计算这个星系中恒星的总质量。
 (c)这个团队证认出NGC 1052-DF2中的10个球状星团，它们与星系中心的平均角距离是78.4"。他们同时测量出球状星团的速度弥散度不超过8.4km/s。估计这个星系的动力学质量，假设这个星系的质量分布是均匀且球对称的。

2018年IOAA理论第8题-贫暗物质星系 - 版本历史

2019年8月8日 (四) 09:44 Quan787

Quan787：创建页面，内容为“{{需要解答}} ==英文题目== '''(T8) A Possible Dark Matter Deficient Galaxy (25 points)''' Earlier this year, a team of astronomers reported their discovery o…”