论文标题
Nustar观察了两个无块状星系：在NGC 4178或J0851+3926中未检测到硬X射线AGN
NuSTAR Observes Two Bulgeless Galaxies: No Hard X-ray AGN Detected in NGC 4178 or J0851+3926
论文作者
论文摘要
在过去的几十年中，在磁盘为主的星系中的中等光度AGN的发现（没有显示“经典”凸起）表明，世俗机制代表了这些系统中超级质量黑洞的重要生长途径。我们介绍了两个无块状星系中光学难以捉摸的AGN的新随访，NGC 4178和J0851+3926。 NGC 4178最初是基于Spitzer检测到的[NE V]中红外发射的检测，并基于Chandra X射线成像，其主张托管了它，因此它被认为是托管严重掩盖的AGN或超新星残留物。 J0851+3926最初是根据其明智的中红色颜色确定为AGN的，然后随访的近红外光谱验证了先前揭示了一个隐藏的宽线区域，提供了令人信服的证据，证明了光学无用的AGN。在新的nustar成像中都没有检测到AGN，我们在硬X射线上的上限10-24 keV通量$ <7.41 \ 7.41 \ times10^{ - 14} $ erg cm $^{ - 2} $ s $ s $ s $^{ - 1} NGC 4178和J0851+3926中的AGNS的S $^{ - 1} $。如果这些非检测是由于沿视线沿线吸收柱引起的，则可以用log的列密度（$ n _ {\ rm {h}}/\ rm {cmm}^2）和24.2 $ 24.2 $ 24.2 $ 24.2 $ {\ rm {h}}/\ rm {\ rm {h}}/\ rm {\ rm {h}} log（$ n _ {\ rm {h}}/\ rm {cm}^2）> 24.1 $。 NGC 4178中核活动的性质尚无定论； [ne v]在过去的一个较高活性时期追溯，但现在的AGN现在相对静止。 J0851+3926中的非检测和多波长特性与AGN的严重遮盖一致。
The discovery over the last several decades of moderate luminosity AGNs in disk-dominated galaxies - which show no "classical" bulges - suggests that secular mechanisms represent an important growth pathway for supermassive black holes in these systems. We present new follow-up NuSTAR observations of the optically-elusive AGNs in two bulgeless galaxies, NGC 4178 and J0851+3926. NGC 4178 was originally reported as hosting an AGN based on the detection of [Ne V] mid-infrared emission detected by Spitzer, and based on Chandra X-ray imaging it has since been argued to host either a heavily obscured AGN or a supernova remnant. J0851+3926 was originally identified as an AGN based on its WISE mid-IR colors, and follow-up near-infrared spectroscopy previously revealed a hidden broad line region, offering compelling evidence for an optically-elusive AGN. Neither AGN is detected within the new NuSTAR imaging, and we derive upper limits on the hard X-ray 10-24 keV fluxes of $<7.41\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ and $<9.40\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ for the AGNs in NGC 4178 and J0851+3926, respectively. If these non-detections are due to large absorbing columns along the line of sight, the non-detections in NGC 4178 and J0851+3926 could be explained with column densities of log($N_{\rm{H}}/\rm{cm}^2)>24.2$ and log($N_{\rm{H}}/\rm{cm}^2)>24.1$, respectively. The nature of the nuclear activity in NGC 4178 remains inconclusive; it is plausible that the [Ne V] traces a period of higher activity in the past, but that the AGN is relatively quiescent now. The non-detection in J0851+3926 and multiwavelength properties are consistent with the AGN being heavily obscured.
