作者:R. J. Wilman、R. M. Johnstone、C. S. Crawford
DOI:10.1046/j.1365-8711.2000.03453.x
日期:2000.9
We present near-infrared spectra of seven radio-loud quasars with a median redshift of 2.1, five of which were previously known to have Lyα nebulae. Extended [O iii] λ5007 and Hα emission are evident around six objects, at the level of a few times 10−16 erg cm−2 arcsec−2 s−1 within ≃2 arcsec of the nucleus (≡16 kpc in the adopted cosmology). Nuclear [O ii] λ3727 is detected in three of the five quasars studied at this wavelength and clearly extended in one of them.The extended [O iii] tends to be brighter on the side of the nucleus with the stronger, jet-like radio emission, indicating at least that the extranuclear gas is distributed anisotropically. It is also typically redshifted by several hundred km s−1 from the nuclear [O iii], perhaps because of the latter being blueshifted from the host galaxy's systemic velocity. Alternatively, the velocity shifts could be due to infall (which is suggested by linewidths ∼1000 km s−1 FWHM) in combination with a suitable dust geometry. Lyα/Hα ratios well below the case B value suggest that some dust is present.Photoionization modelling of the [O iii]/[O ii] ratios in the extended gas suggests that its pressure is around or less than a few times 107 cm−3 K; any confining intracluster medium is thus likely to host a strong cooling flow. A comparison with lower redshift work suggests that there has been little evolution in the nuclear emission-line properties of radio-loud quasars between redshifts 1 and 2.
我们展示了七个射电强类星体(具有2.1的中值红移)的近红外光谱,其中五个已知具有Lyα星云。六个天体周围显示出延展的[O iii] λ5007和Hα发射,位于核区≃2角秒(采用的宇宙学中的16千秒差距)内,亮度水平为每平方角秒每秒几乘以10^-16 尔格/平方厘米。在研究的五个类星体中,有三个在其波长上探测到了核区的[O ii] λ3727,其中一个明显延展。延展的[O iii]在具有较强类喷流射电发射的核区一侧更亮,表明至少非核区气体呈各向异性分布。它通常相对于核区[O iii]有数百公里每秒的红移,可能是由于后者相对于宿主星系的系统速度发生蓝移。或者,速度偏移可能是由于合并(由线宽≈1000公里每秒 FWHM 提示)结合适当的尘埃几何结构所致。远低于B值情况的Lyα/Hα比率表明存在一些尘埃。对延展气体中[O iii]/[O ii]比率的 photoionization 建模表明其压力约为或小于几乘以10^7 厘米^-3 K;因此,任何限制的星系团介质都可能伴随强烈的冷却流。与低红移工作的比较表明,在红移1到2之间,射电强类星体的核区发射线特性几乎没有演化。