The Evolution of AGN Host Galaxies: From Blue to Red and the Influence of Large-Scale Structures
J. D. Silverman, V. Mainieri, B. D. Lehmer, D. M. Alexander, F. E. Bauer, J. Bergeron, W. N. Brandt, R. Gilli, G. Hasinger, D. P. Schneider, P. Tozzi, C. Vignal… 展开作者
J. D. Silverman, V. Mainieri, B. D. Lehmer, D. M. Alexander, F. E. Bauer, J. Bergeron, W. N. Brandt, R. Gilli, G. Hasinger, D. P. Schneider, P. Tozzi, C. Vignali, A. M. Koekemoer, T. Miyaji, P. Popesso, P. Rosati, G. Szokoly
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Published in ApJ, 2008, 675, 1025; 17 pages, 14 figures
We present an analysis of 109 moderate-luminosity (41.9 < Log L{0.5-8.0 keV} < 43.7) AGN in the Extended Chandra Deep Field-South survey, which is drawn from 5,549 galaxies from the COMBO-17 and GEMS surveys having 0.4 < z < 1.1. These obscured or optically-weak AGN facilitate the study of their host galaxies since the AGN provide an insubstantial amount of contamination to the galaxy light. We find that the color distribution of AGN host galaxies is highly dependent upon (1) the strong color-evolution of luminous (M_V < -20.7) galaxies, and (2) the influence of ~10 Mpc scale structures. When excluding galaxies within the redshift range 0.63 < z < 0.76, a regime dominated by sources in large-scale structures at z=0.67 and z=0.73, we observe a bimodality in the host galaxy colors. Galaxies hosting AGN at z > 0.8 preferentially have bluer (rest-frame U-V < 0.7) colors than their z <~ 0.6 counterparts (many of which fall along the red sequence). The fraction of galaxies hosting AGN peaks in the ``green valley'' (0.5 < U-V < 1.0); this is primarily due to enhanced AGN activity in the redshift interval 0.63 < z < 0.76. The AGN fraction in this redshift and color interval is 12.8% (compared to its `field' value of 7.8%) and reaches a maximum of 14.8% at U-V~0.8. We further find that blue, bulge-dominated (Sersic index n>2.5) galaxies have the highest fraction of AGN (21%) in our sample. We explore the scenario that the evolution of AGN hosts is driven by galaxy mergers and illustrate that an accurate assessment requires a larger area survey since only three hosts may be undergoing a merger with timescales <1 Gyr following a starburst phase.
Environmental dependence of AGN activity in the supercluster A901/2
我们提供了超星系团A901/2的XMM数据，z ~ 0.17，结合深度成像和17波段光度红移（来自COMBO-17巡天），2dF光谱和斯皮策24 μ m数据，以确定超星系团中的活动星系核。90 ksec XMM图像包含139个点源，其中11个被确认为超星系团活动星系核，其LX（0.5-7.5keV）> 1.7 × 10^41 erg/cm ~ 2/s。宿主星系的M_R< -20 and only 2 of 8 sources with spectra could have been identified as AGN by the detected optical emission lines. Using a large sample of 795 supercluster galaxies we define control samples of massive galaxies with no detected AGN. The local environments of the AGN and control samples differ at >值为98%。活动星系核的宿主星系主要位于中等投影星系密度的区域，并且比对照样本有更多的蓝色星系，除了一个非常明亮的I型活动星系核非常靠近星系团中心。这些环境类似于但不限于集群郊区和蓝色组。尽管有大量潜在的宿主星系，但在星系密度最高…
