车轮星系与XMM-牛顿
The Cartwheel galaxy with XMM-Newton
摘要：
分析了车轮环提供的极端环境，以研究其X射线和光学紫外特性。我们比较车轮与其他成员的组和研究系统作为一个整体在X射线波段。我们分析了两个不同时期（2004年12月和2005年5月）的车轮星系的XMM-牛顿获得的数据。我们专注于系统的X射线特性，并使用OM数据来获得光学和紫外波段的额外信息。我们总共探测到8个与车轮星系有关的源，以及3个在其附近的源，包括G1和G2，都在L >= 10^39 erg/s，即超亮X射线（ULX）源范围。最亮的ULX光源已经在其他地方讨论过。接下来的三个最亮的ULX的光谱很好地拟合了幂律模型，平均光子指数为~2。我们比较了XMM-Newton和Chandra数据集，以研究源的长期变化。在两次XMM-牛顿观测之间的5个月内，至少有3个源发生变化，在钱德拉和XMM-牛顿观测之间的4年时间内，至少有4个源发生变化。一个钱德拉源消失了，一个新的钱德拉源被XMM-牛顿在环中检测到。车轮环的紫外光颜色与恒星形成的爆发相一致，接近达到最大值，得出平均恒星年龄约为4000万年。推断的变异性和年龄表明，高质量的X射线双星是对应的ULX源。这3个伴星系的光度范围在10^39-40 erg/s之间，与预期一致。车轮星系的热气体明亮且丰富（大约10^8兆索尔），并且在星系的外环和冲击波阵面后面的星系内部都有发现。在LX ~10^40 erg/s的组中也检测到气体。
英文摘要：
The extreme environment provided by the Cartwheel ring is analyzed to study its X-ray and optical-UV properties. We compare the Cartwheel with the other members of its group and study the system as a whole in the X-ray band. We analyze the data of the Cartwheel galaxy obtained with XMM-Newton in two different periods (December 2004 and May 2005). We focus on the X-ray properties of the system and use the OM data to obtain additional information in the optical and UV bands. We detect a total of 8 sources associated with the Cartwheel galaxy and three in its vicinity, including G1 and G2, all at L >= 10^39 erg/s, that is the Ultra Luminous X-ray (ULX) source range. The brightest ULX source has been already discussed elsewhere. The spectra of the next three brightest ULX are well fitted by a power-law model with a mean photon index of ~2. We compare the XMM-Newton and Chandra datasets to study the long-term variability of the sources. At least three sources vary in the 5 months between the two XMM-Newton observations and at least four in the 4-year timeframe between Chandra and XMM-Newton observations. One Chandra source disappears and a new one is detected by XMM-Newton in the ring. Optical-UV colors of the Cartwheel ring are consistent with a burst of star formation that is close to reaching its maximum, yielding a mean stellar age of about 40 Myr. The inferred variability and age suggest that high mass X-ray binaries are the counterparts to the ULX sources. The 3 companion galaxies have luminosities in the range 10^39-40 erg/s consistent with expectations. The hot gas of the Cartwheel galaxy is luminous and abundant (a few 10^8 Msol) and is found both in the outer ring, and in the inner part of the galaxy, behind the shock wave front. We also detect gas in the group with L_X ~10^40 erg/s.
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