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arXiv 1107.2397astro-ph.CO
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z~4亮类星体的宿主星系和黑洞:星系质量比

The host galaxies and black-hole:galaxy mass ratios of luminous quasars at z~4

Thomas A. Targett, James S. Dunlop, Ross J. McLure

摘要:

我们展示并分析了迄今为止所获得的z~4的明亮类星体的最深、高质量的KS波段图像,试图确定它们的宿主星系在首次记录到的Mbh > 10^9 Msol的黑洞出现后小于1 Gyr的基本性质。为了最大限度地提高我们的结果的鲁棒性,我们仔细选择了两个SDSS类星体在z~4。这些类星体是这个时期已知的最明亮的类星体的代表,但它们也是至关重要的,位于相对明亮的前景恒星的40弧秒内(精确的PSF定义所需的),并且具有确保无线KS波段成像的红移。在ESO VLT上获得的数据具有极好的视宁度(<0.4角秒),每个源的积分时间约为5.5小时。通过仔细控制分离的主星系和核光,我们估计的光度和恒星质量的主星系,并设置其半光半径的限制。类星体宿主星系的K波段光度类似于射电星系,红移相当,这表明这些类星体宿主星系也是这个时代存在的最大的星系之一。然而,类星体的宿主比发光的低红移类星体的宿主星系小5倍。我们估计z~4宿主星系的恒星质量在2- 10 × 10^11 Msol之间,并利用斯隆光谱中的CIV发射线估计其黑洞的质量。结果表明,黑洞与主星系的质量比Mbh:Mgal约为0.01-0.05。这比通常在低红移宇宙中看到的要高出一个数量级,并且与现有的证据相一致,即随着红移的增加,这种质量比会系统性地增长,至少对于被选为强大AGN的天体来说是这样。

英文摘要:

We present and analyse the deepest, high-quality Ks-band images ever obtained of luminous quasars at z~4, in an attempt to determine the basic properties of their host galaxies less than 1 Gyr after the first recorded appearance of black holes with Mbh > 10^9 Msol. To maximise the robustness of our results we have carefully selected two SDSS quasars at z~4. These quasars are representative of the most luminous quasars known at this epoch but they also, crucially, lie within 40 arcsec of comparably-bright foreground stars (required for accurate PSF definition), and have redshifts which ensure line-free Ks-band imaging. The data were obtained in excellent seeing (<0.4-arcsec) at the ESO VLT with integration times of ~5.5 hours per source. Via carefully-controlled separation of host-galaxy and nuclear light, we estimate the luminosities and stellar masses of the host galaxies, and set constraints on their half-light radii. The quasar host galaxies have K-band luminosities similar to radio galaxies at comparable redshifts, suggesting that these quasar hosts are also among the most massive galaxies in existence at this epoch. However, the quasar hosts are a factor ~5 smaller than the host galaxies of luminous low-redshift quasars. We estimate the stellar masses of the z~4 host galaxies to lie in the range 2-10x10^11 Msol, and use the CIV emission line in the Sloan spectra to estimate the masses of their black holes. The results imply a black-hole:host-galaxy mass ratio Mbh:Mgal~0.01-0.05. This is an order of magnitude higher than typically seen in the low-redshift Universe, and is consistent with existing evidence for a systematic growth in this mass ratio with increasing redshift, at least for objects selected as powerful AGN.

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