论文标题
五个光学选择的2种类星体的高分辨率无线电观察结果
High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars
论文作者
论文摘要
许多低亮度活性银河核（AGN）都包含一个紧凑的无线电芯，可以使用非常长的基线干涉法（VLBI）观察到高角度分辨率。将ARCSEC规模的结构信息与Milliarcsec分辨率VLBI成像相结合是表征对象并在PARSEC尺度上找到紧凑核心的有用方法。当源显示具有平坦或倒无线电光谱的KPC尺度双对称结构时，VLBI成像也可以用于寻找双重AGN。我们在红移0.36 <z <0.58上观察到五个此类来源，从1.7和5 GHz的欧洲VLBI网络（EVN）的光学选择的2型类星体样品中取出。在这五个来源中，只有一个（SDSS J1026-0042）在两个频率下都表现出了一个确信被检测到的紧凑型VLBI核心。其他四个来源仅以1.7 GHz的速度检测到，表明已解决的无线电结构和陡峭的光谱。使用正在进行的Karl G. Jansky非常大的阵列Sky Sumple的第一期数据，我们确认确实，这四个来源在ARCSEC尺度上都具有陡峭的无线电光谱，这与文献早期报道的倒置光谱相反。但是，VLBI检测的源SDSS J1026-0042具有平坦的集成频谱。显示具有真正平坦或倒置光谱的KPC尺度对称结构的无线电AGN仍然可能是双重AGN的候选者，将来将以VLBI观察为目标。
Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts 0.36 < z < 0.58 taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026-0042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026-0042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future.
