MAPPING THE DARK MATTER IN THE NGC 5044 GROUP WITH ROSAT : EVIDENCE FOR A NEARLY HOMOGENEOUS COOLING FLOW WITH A COOLING WAKE
MAPPING THE DARK MATTER IN THE NGC 5044 GROUP WITH ROSAT : EVIDENCE FOR A NEARLY HOMOGENEOUS COOLING FLOW WITH A COOLING WAKE
复制标题
使用 ROSAT 绘制 NGC 5044 群中的暗物质：具有冷却尾流的几乎均匀冷却流的证据
DOI：
10.1086/174264
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
S. Daines
中科院分区：
文献类型：
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作者：
L. David;C. Jones;W. Forman;S. Daines
NGC5044星系团是用ROSAT位置灵敏正比计数器(PSPC)在其缩短点阶段(1991年7月)观测了30k。由于该星系群中的气体温度相对较低(KT=0.98+/-0.02keV)和出色的光子统计数据(净计数为65,000个)，我们能够在中心星系的250kpc范围内精确地确定该星系群的一些基本性质。特别是，我们给出了总引力质量、气体温度和丰度分布以及质量吸积率的独立于模型的测量结果。在60-250kpc之间，气体几乎等温，T随r变化(exp(-0.13+/-0.03))。根据观测到的气体密度和温度分布，利用流体静力平衡方程，可以明确地确定该群的总引力质量。在250kpc范围内，引力质量是1.6x10(Exp 13)太阳质量，产生130太阳质量/太阳光度的质光比。重子(气体和恒星)占该半径内总质量的12%。在小半径下，温度明显向外升高，并在60kpc时达到最大值。群中心的正温度梯度证实了冷却流的存在。冷却流动区域远远超出最高温度，冷却半径在100到150 kpc之间。冷却流中有两个明显的区域，由最高温度隔开。在外层，气体是近等温的，m-Fe丰度约为80%太阳，流动接近均匀，Dot-M=20~25太阳质量/年，X射线等高线为球对称，Rho(亚气体)随r(exp-1.6)变化。在内部区域，温度分布具有正的梯度，质量吸积率向内快速下降，气体密度分布较陡，X射线图像显示出一些亚结构。NGC5044偏离外部X射线等高线的质心，表明中心星系可能具有相对于群势中心的剩余速度。还有一个线性X射线特征，其范围约为30kpc，一端与NGC 5044重合。这一特征发出的X射线比周围的气体要软。我们将这一特征解释为吸积气体在引力聚焦到NGC 5044尾迹时形成的“冷却尾迹”。我们PSPC观测的最令人惊讶的结果之一是发现了几乎均匀的冷却流。以往关于冷却流中质量吸积分布的结果表明，点M随r变化。这一关系表明，在大半径处发生了显著的质量沉积，从而产生了不均匀的流动。NGC 5044群中的质量吸积率基本上是一个超过40kpc(完全在冷却半径内)的常量。大量的质量沉积(下降的点-M)直到气体聚集到群中心的40kpc以内才开始，那里的辐射冷却时间大约等于10(Exp 9)年。这一半径也对应于最高温度、气体密度分布的破裂以及X射线图像中结构的开始。哈勃常数H(小于0)=50公里/秒/MPC贯穿全文。
The NGC 5044 group of galaxies was observed by the ROSAT Position Sensitive Proportional Counter (PSPC) for 30 ks during its reduced pointed phase (1991 July). Due to the relatively cool gas temperature in the group (kT = 0.98 +/- 0.02 keV) and the excellent photon statistics (65,000 net counts), we are able to determine precisely a number of fundamental properties of the group within 250 kpc of the central galaxy. In particular, we present model-independent measurements of the total gravitating mass, the temperature and abundance profiles of the gas, and the mass accretion rate. Between 60 and 250 kpc, the gas is nearly isothermal with T varies as r(exp (-0.13 +/- 0.03)). The total gravitating mass of the group can be unambiguously determined from the observed density and temperature profiles of the gas using the equation of hydrostatic equilibrium. Within 250 kpc, the gravitating mass is 1.6 x 10(exp 13) solar mass, yielding a mass-to-light ratio of 130 solar mass/solar luminosity. The baryons (gas and stars) comprise 12% of the total mass within this radius. At small radii, the temperature clearly increases outward and attains a maximum value at 60 kpc. The positive temperature gradient in the center of the group confirms the existence of a cooling flow. The cooling flow region extends well beyond the temperature maximum with a cooling radius between 100 and 150 kpc. There are two distinct regions in the cooling flow separated by the temperature maximum. In the outer region, the gas is nearly isothermal with a unifor m Fe abundance of approximately 80% solar, the flow is nearly homogeneous with dot-M= 20 to 25 solar mass/year, the X-ray contours are spherically symmetric, and rho(sub gas) varies as r(exp -1.6). In the inner region, the temperature profile has a positive gradient, the mass accretion rate decreases rapidly inward, the gas density profile is steeper, and the X-ray image shows some substrucutre. NGC 5044 is offset from the centroid of the outer X-ray contours indicating that the central galaxy may have a residual velocity with respect to the center of the group potential. There is also a linear X-ray feature with an extent of approximately 30 kpc with one end coincident with NGC 5044. The X-ray emission from this feature is softer than the ambient gas. We interpret this feature as a 'cooling wake' formed by the accreting gas as it is gravitationally focused into the wake of NGC 5044. One of the most surprising results of our PSPC observation is the discovery of a nearly homogeneous cooling flow. Prior results concerning the mass accretion profile in cooling flows indicate that dot-M varies as r. This relation implies that significant mass deposition occurs at large radii which generates an inhomogeneous flow. The mass accretion rate in the NGC 5044 group is essentially a constant beyond 40 kpc (well within the cooling radius). Significant mass deposition (a declining dot-M) does not commence until the gas accretes to within 40 kpc of the group center where the radiative cooling time is approximately equals 10(exp 9) year. Th is radius also corresponds to the temperature maximum, the break in gas density profile, and the onset of structure in the X-ray image. A Hubble constant of H(sub 0) = 50 km/sec/Mpc is used throughout the paper.