X‐ray bright optically inactive galaxies in XMM–Newton/Sloan Digital Sky Survey fields: more diluted than absorbed?
X‐ray bright optically inactive galaxies in XMM–Newton/Sloan Digital Sky Survey fields: more diluted than absorbed?
复制标题
XMM-牛顿/斯隆数字巡天场中的 X 射线明亮光学不活跃星系：稀释程度大于吸收程度？
DOI：
--
复制
发表时间：
2004
期刊：
影响因子：
--
通讯作者：
A. Georgakakis
中科院分区：
文献类型：
--
作者：
I. Georgantopoulos;A. Georgakakis
我们探索了在与斯隆数字巡天(SDSS)重叠的20个公共XMM-牛顿场中在0.5-8keV光谱带内探测到的X射线明亮光学不活动星系(XBONG)的性质。我们将我们的样本限制在具有logf X/f opt>；的光学扩展系统，这些系统具有可从SDSS(R<；19.2 MAG)获得的光谱标识。得到的样品包含12个样品，L X(0.58keV)=5x1041-2x1044erg S-1，红移范围为0.06<；z<；0.45。有四个案例的X射线发射被延长，这表明存在与一个星系团或一组星系相关的热气体。X射线能谱拟合表明，两个额外的源最适合一个热组分发射(KT∼1keV)。有三个源最有可能与活动星系核(AGN)有关：它们的X射线光谱由陡峭的光子指数r∼1.9描述，而它们在X射线中非常明亮[L X(0.5-8keV)10 43-10 44erg S-1]。最后，另外三个源可能与正常星系或未遮挡的低亮度活动星系核有关(L X<；1042erg S-1)。我们在我们的任何XBONG中都没有发现明显的X射线吸收柱的证据。上述结果表明，XBONGs被选在0.5-8keV的总频带内，由一个主要包括正常椭圆星系和第一类活动星系核的混合袋组成，它们的光学核光谱可能被强烈的恒星连续体稀释了。然而，由于我们的样本在统计上并不完整，我们不能排除一小部分光学较弱的XBONG可能与严重遮挡的活动星系核有关。
We explore the properties of X-ray bright optically inactive galaxies (XBONGs) detected in the 0.5-8 keV spectral band in 20 public XMM-Newton fields overlapping with the Sloan Digital Sky Survey (SDSS). We constrain our sample to optically extended systems with log f X /f opt > -2 that have spectroscopic identifications available from the SDSS (r < 19.2 mag). The resulting sample contains 12 objects with L X (0.5-8 keV) = 5 x 10 41 -2 x 10 44 erg s -1 in the redshift range 0.06 < z < 0.45. The X-ray emission in four cases is extended, suggesting the presence of hot gas associated with a cluster or group of galaxies. The X-ray spectral fits show that two additional sources are best fit with a thermal component emission (kT ∼ 1 keV). Three sources are most likely associated with active galactic nuclei (AGNs): their X-ray spectrum is described by a steep photon index r ∼ 1.9 typical of unobscured AGNs, while they are very luminous in X-rays [L X (0.5-8 keV) 10 43 -10 44 erg s -1 ]. Finally, three more sources could be associated with either normal galaxies or unobscured low-luminosity AGNs (L X < 10 42 erg s -1 ). We find no evidence for significant X-ray absorbing columns in any of our XBONGs. The above suggest that XBONGs, selected in the total 0.5-8 keV band, comprise a mixed bag of objects primarily including normal elliptical galaxies and type 1 AGNs whose optical nuclear spectrum is probably diluted by the strong stellar continuum. Nevertheless, as our sample is not statistically complete we cannot exclude the possibility that a fraction of optically fainter XBONGs may be associated with heavily obscured AGNs.