活动星系核(active galactic nucleus,AGN)的反馈作用(包括喷流、外流以及风等形式)是理解星系与其中心超大质量黑洞(supermassive black hole,SMBH)共同演化的关键.然而,对于快速吸积的SMBH(例如超爱丁顿吸积的SMBH),其产生喷流的机制目前仍不清楚.大量观测样本研究表明AGN射电噪度随爱丁顿比的增加而降低,这可能是喷流过程与吸积过程的耦合结果.最近陆续有研究发现超爱丁顿吸积的AGN也可能存在喷流.对超爱丁顿AGN的喷流开展高分辨率成像研究,有助于理解快速吸积情形下喷流与吸积之间的联系.J1034+3938是一个射电宁静的窄线I型塞弗特星系(narrow-line Seyfert 1,NLS1),其中心很可能存在一个超爱丁顿吸积的SMBH.我们利用甚长基线干涉阵(Very Long Baseline Array,VLBA)对J1034+3938在2022年10月21日进行L波段的观测,发现其射电辐射形态展示出一个向西约20 mas(17pc)的细长准直喷流结构,其峰值流量密度为3.16±0.48 mJy/beam,射电亮温度高达5.7×107 K.我们的观测结果有力地证明了射电宁静且超爱丁顿吸积的AGN具备产生秒差距尺度的喷流的可能性.
VLBI observations of the super-Eddington accretion active galactic nucleus J1034+3938
Active galactic nuclei(AGNs)are known to influence the co-evolution of central supermassive black holes(SMBHs)and their host galaxies,with AGN jets playing a pivotal role in this feedback process.This study presents new insights into the radio-quiet(RQ)narrow-line Seyfert 1(NLS1)galaxy J1034+3938,which features a SMBH with a mass of 2.38× 107 M☉and an Eddington ratio of 3.15,indicative of super Eddington accretion.Despite previous observations with the Very Large Array(VLA)and the Jansky VLA(JVLA)revealing only compact,unresolved radio sources,our high-resolution radio imaging observations using the Very Long Baseline Array(VLBA)at 1.5 GHz have uncovered a parsec-scale jet extending approximately 20 mas(17 pc)to the west,with a significant brightness temperature of 5.65 × 107 K.The detection of this jet in J1034+3938,a galaxy historically classified as radio-quiet,challenges existing paradigms and provides a unique opportunity to study jet formation and its relation to SMBH accretion processes at high Eddington ratios.Our VLBA observations,conducted on October 21,2022,as part of project BY 175,utilized a dual circular polarization mode with four intermediate frequencies,each with a bandwidth of 64 MHz,to achieve a data recording rate of 2048 Mb/s.The observations were carried out using a phase-referencing technique with a nearby source J1033+3935,allowing for the mitigation of atmospheric and instrumental effects.The data processing involved several steps,including calibration for atmospheric errors using total electron content(TEC)from Global Positioning System(GPS)satellites,correction for reference frame errors such as parallax and earth orientation parameters(EOP),and instrumental errors through amplitude and phase calibration using antenna gain curves and system temperature information.The visibility data were then imaged using the DIFMAP software package,revealing a complex radio morphology that was further analyzed using a circular Gaussian model fitting approach.Our findings indicate that the radio emission from J1034+3938 not only is compact but also exhibits an extended structure,which is indicative of a jet.The extended nature of the radio emission,with a Speak/Stot ratio of 0.48,classifies J1034+393 8 as an extended source,contrasting with previous observations that suggested a compact morphology.The high brightness temperature of the jet component suggests that the radio emission is likely due to non-thermal processes associated with relativistic electrons within the jet,supporting the idea that the emission is jet-driven.The comparison of our VLBA observations with historical data from the VLA and JVLA shows a decline in the total flux density of J1034+3938 overtime,from 25.9 mJy in 1990 to 6.55 mJy in 2022.J1034+3938 is well classified as a RQ AGN under the double standard of combining radio luminosity and radio loudness.The variability in radio emission and the presence of a jet in a RQ NLS1 galaxy like J1034+3938 provide valuable insights into the accretion-jet coupling mechanism,particularly in the context of high Eddington ratios.In conclusion,our study of the RQ NLS1 galaxy J1034+3938 has revealed the presence of a parsec-scale jet,a finding that expands our understanding of AGN feedback mechanisms and the role of jets in the evolution of galaxies.The detection of this jet in a high-accretion rate environment offers a new perspective on the conditions under which jets form and evolve.Future multi-frequency and multi-scale observations will be crucial for unraveling the complex interplay between accretion processes and jet formation in AGNs,particularly in the context of high Eddington ratios.
supermassive black holeactive galactic nucleijetnarrow-line SeyfertVery Long Baseline Interferometry
万方数据
维普
