论文标题
TXS226-184中H2O Gigamaser的VLBI观察
VLBI observations of the H2O gigamaser in TXS2226-184
论文作者
论文摘要
在银河系之外，由于在活性银河核中，主要检测到与星际式和恒星形成相关的银河系和乳突外H2O酶的极端亮度，因此在22 GHz的最具光泽的H2O masers被称为“ Megamasers”。对于在Galaxy TXS2226-184的核区域中检测到的H2O Maser，首次使用“ Gigamaser”一词。但是，这种非常发光的H2O MASER排放的起源从未被研究过细节。我们通过比较大约20年后在VLBI尺度上比较了Maser发射的形态和特征，并试图检测其极性发射，从而研究了TXS2226-184中H2O Gigamaser在MAS分辨率下的绝对位置，从而研究了H2O Gigamaser的性质。我们观察到Maser对TXS2226-184的发射三次：第一个具有VLBA（Epoch 2017.45），接下来的两次与EVN（Epochs 2017.83和2018.44）。在相文引用模式下观察到前两个时期，而最后两个时期是在完整的时期模式下观察到的，但在相文引用模式下观察到以增加源代码积分时间。我们还检索并分析了1998.40观察到的TXS2226-184的22 GHz的VLBA档案数据。我们在Epoch 2017.45（VLBA）中检测到6个H2O MASER功能，一项在Epoch 2017.83（EVN）中，而Epoch 2018.44（EVN）中有两个。除了一个人，除了一个txs2226-184的系统性速度时，所有这些都被红移了，我们仅检测到一个蓝色变速的maser特征，这是最弱的特征。我们第一次能够以低于1 MAS的错误来测量H2O MASER特征的绝对位置。未检测到线性和圆极化。我们能够将TXS2226-184中的H2O MASER特征与文献中报道的最发光的无线电连续性团块相关联。
Outside the Milky Way, the most luminous H2O masers at 22 GHz, called 'megamasers' because of their extreme luminosity with respect to the Galactic and extragalactic H2O masers associated with star formation, are mainly detected in active galactic nuclei. In the case of the H2O maser detected in the nuclear region of the galaxy TXS2226-184 for the first time the term 'gigamaser' was used. However, the origin of this very luminous H2O maser emission has never been investigated into details. We study the nature of the H2O gigamaser in TXS2226-184 by measuring for the first time its absolute position at mas resolution, by comparing the morphology and characteristics of the maser emission at the VLBI scales after about 20 years, and by trying to detect its polarized emission. We observed the maser emission towards TXS2226-184 three times: the very first one with the VLBA (epoch 2017.45) and the next two times with the EVN (epochs 2017.83 and 2018.44). The first two epochs were observed in phase-reference mode, while the last epoch was observed in full-polarization mode but not in phase-reference mode to increase the on-source integration time. We also retrieved and analyzed the VLBA archival data at 22 GHz of TXS2226-184 observed in 1998.40. We detected 6 H2O maser features in epoch 2017.45 (VLBA), one in epoch 2017.83 (EVN), and two in epoch 2018.44 (EVN). All of them but one are red-shifted with respect to the systemic velocity of TXS2226-184, we detected only one blue-shifted maser feature and it is the weakest one. For the first time, we were able to measure the absolute position of the H2O maser features with errors below 1 mas. No linear and circular polarization was detected. We were able to associate the H2O maser features in TXS2226-184 with the most luminous radio continuum clump reported in the literature.
