分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ailing Wang
Tao An
Shaoguang Guo
Prashanth Mohan
Wara Chamani
Willem A. Baan
Talvikki Hovatta
Heino Falcke
Tim J. Galvin
Natasha Hurley-Walker
Sumit Jaiswal
Anne Lahteenmaki
Baoqiang Lao
Weijia Lv
Merja Tornikoski
Yingkang Zhang
摘要： Disk winds and jets are ubiquitous in active galactic nuclei (AGN), and how these two components interact remains an open question. We study the radio properties of a radio-intermediate quasar III Zw 2. We detect two jet knots J1 and J2 on parsec scales, which move at a mildly apparent superluminal speed of $1.35\,c$. Two $\gamma$-ray flares were detected in III Zw 2 in 2009--2010, corresponding to the primary radio flare in late 2009 and the secondary radio flare in early 2010. The primary 2009 flare was found to be associated with the ejection of J2. The secondary 2010 flare occurred at a distance of $\sim$0.3 parsec from the central engine, probably resulting from the collision of the jet with the accretion disk wind. The variability characteristics of III Zw 2 (periodic radio flares, unstable periodicity, multiple quasi-periodic signals and possible harmonic relations between them) can be explained by the global instabilities of the accretion disk. These instabilities originating from the outer part of the warped disk propagate inwards and can lead to modulation of the accretion rate and consequent jet ejection. At the same time, the wobbling of the outer disk may also lead to oscillations of the boundary between the disk wind and the jet tunnel, resulting in changes in the jet-wind collision site. III Zw 2 is one of the few cases observed with jet-wind interactions, and the study in this paper is of general interest for gaining insight into the dynamic processes in the nuclear regions of AGN.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ailing Wang
Tao An
Xiaopeng Cheng
Luis C. Ho
Kenneth I. Kellermann
Willem A. Baan
Jun Yang
Yingkang Zhang
摘要： We observed 20 Palomar-Green (PG) quasars at low redshift ($z 1 mJy, including 4 radio-loud quasars (RLQs) and 16 radio-quiet quasars (RQQs), using the Very Long Baseline Array (VLBA) at 5 GHz. Ten RQQs are clearly detected in the VLBA images, and a compact radio core is identified in eight of them, indicating the prevalence of active galactic nucleus (AGN)-related radio emission in this flux-density-limited RQQ sample. The RQQs and RLQs in our sample have a division at $\sim$30~mJy. The radio emission from RQQs appears to be the result of a combination of star formation and AGN-associated activities. All RQQs in our sample have a 5 GHz flux density ratio of Very Large Array (VLA) A-array to D-array $f_{\rm c} = S_{\rm A}^{\rm VLA}/S_{\rm D}^{\rm VLA}$ above 0.2. The RQQs with $f_a$ (VLBA and VLA flux density ratio $S^{\rm VLBA}/S_{\rm A}^{\rm VLA}) > 0.2$ versus $f_a < 0.2$ show significant differences in morphology, compactness and total flux density. $f_{\rm a}$ of RQQs is systematically lower than that of RLQs, probably due to the extended jets or relic jets of RQQs on 10s to 100s parsecs which are resolved out in VLBA images. Future larger samples, especially with the addition of milli-arcsec resolution radio images of RQQs with total flux densities below 1 mJy, can test the conclusions of this paper and contributes to the understanding of the radio emission mechanism of RQQs, and the dichotomy and physical connection between RQQs and RLQs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tao An
Ailing Wang
Yuanqi Liu
Yulia Sotnikova
Yingkang Zhang
J. N. H. S. Aditya
Sumit Jaiswal
George Khorunzhev
Baoqiang Lao
Ruqiu Lin
Alexander Mikhailov
Marat Mingaliev
Timur Mufakharov
Sergey Sazonov
摘要： Jets may have contributed to promoting the growth of seed black holes in the early Universe, and thus observations of radio-loud high-redshift quasars are crucial to understanding the growth and evolution of the early supermassive black holes. Here we report the radio properties of an X-ray bright $z=5.5$ quasar, SRGE J170245.3+130104 (J1702+1301). Our high-resolution radio images reveal the radio counterpart at the optical position of J1702+1301, while another radio component is also detected at $\sim$23.5\arcsec\ to the southwest. Our analysis suggests that this southwest component is associated with a foreground galaxy at $z\approx 0.677$, which is mixed with J1702+1301 in low-frequency low-resolution radio images. After removing the contamination from this foreground source, we recalculated the radio loudness of J1702+1301 to be $R>$1100, consistent with those of blazars. J1702+1301 exhibits a flat radio spectrum ($\alpha = -0.17 \pm 0.05$, $S \propto \nu^\alpha$) between 0.15 and 5 GHz; above 5 GHz, it shows a rising spectrum shape, and the spectral index $\alpha^{8.2}_{4.7}$ appears to be correlated with the variation of the flux density: in burst states, $\alpha^{8.2}_{4.7}$ becomes larger. J1702+1301 displays distinct radio variability on timescales from weeks to years in the source's rest frame. These radio properties, including high radio loudness, rising spectrum, and rapid variability, tend to support it as a blazar.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Krisztina Perger
Yingkang Zhang
Sándor Frey
Tao An
Krisztina É. Gabányi
Leonid I. Gurvits
Chorng-Yuan Hwang
Ekaterina Koptelova
Zsolt Paragi
Ailing Wang
摘要： There are approximately 250 quasars discovered at redshift $z\geq6$, of which only a handful were detected in radio bands, and even fewer were imaged with the highest resolution very long baseline interferometry (VLBI) technique. Here we report the results of our dual-frequency observations with the Very Long Baseline Array (VLBA) of two such recently discovered quasars, VIKING J231818.35$-$311346.3 at $z=6.44$ and FIRST J233153.20$+$112952.11 at $z=6.57$. Both extremely distant sources were imaged with VLBI for the first time. The radio properties of the former are consistent with those of quasars with young radio jets. The latter has an UV/optical spectrum characteristic of BL Lac objects, of which no others have been found beyond redshift 4 so far. Our VLBA observations revealed a flat-spectrum compact radio source.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We report the high-resolution radio observations of eight Fanaroff-Riley type 0 radio galaxies (FR 0s), selected from the published FR 0 sample. These observations were carried out with the Very Long Baseline Array (VLBA) and European VLBI Network (EVN) at frequencies of 5 and 8 GHz with a highest resolution of 0.6 mas. All eight sources show compact structures on projected physical sizes of 0.3-10 parsec. Six sources show a two-sided structure and two sources show a one-sided jet structure. J1025+1022 shows an X-shaped jet structure, which could result from a reorientation of the jet axis due to a restart of the central engine or a projection of a highly curved inner jet, but more studies are needed to examine these scenarios. Proper motions for 22 jet components of the eight sources are determined to be between -0.08 c and 0.51 c. Although most of the sources exhibit flat spectra, other observed characteristics, such as, low-amplitude flux density variations, low jet proper motion speeds, and symmetric two-sided jet structures, tend to support that the pc-scale FR 0 jets are mildly relativistic with lower bulk Lorentz factors and larger viewing angles.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Large surveys using modern telescopes are producing images that are increasing exponentially in size and quality. Identifying objects in the generated images by visual recognition is time-consuming and labor-intensive, while classifying the extracted radio sources is even more challenging. To address these challenges, we develop a deep learning-based radio source detector, named \textsc{HeTu}, which is capable of rapidly identifying and classifying radio sources in an automated manner for both compact and extended radio sources. \textsc{HeTu} is based on a combination of a residual network (ResNet) and feature pyramid network (FPN). We classify radio sources into four classes based on their morphology. The training images are manually labeled and data augmentation methods are applied to solve the data imbalance between the different classes. \textsc{HeTu} automatically locates the radio sources in the images and assigns them to one of the four classes. The experiment on the testing dataset shows an average operation time of 5.4 millisecond per image and a precision of 99.4\% for compact point-like sources and 98.1\% for double-lobe sources. We applied \textsc{HeTu} to the images obtained from the GaLactic and the Galactic Extragalactic All-Object Murchison Wide-field Array (GLEAM) survey project. More than 96.9\% of the \textsc{HeTu}-detected compact sources are matched compared to the source finding software used in the GLEAM. We also detected and classified 2,298 extended sources (including Fanaroff-Riley type I and II sources, and core-jet sources) above $5\sigma$. The cross-matching rates of extended sources are higher than 97\%, showing excellent performance of \textsc{HeTu} in identifying extended radio sources. \textsc{HeTu} provides an efficient tool for radio source finding and classification and can be applied to other scientific fields.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Studies of high redshift radio galaxies can shed light on the activity of active galactic nuclei (AGN) in massive elliptical galaxies, and on the assembly and evolution of galaxy clusters in the Universe. J1606+3124 has been tentatively identified as a radio galaxy at a redshift of 4.56, at an era of one-tenth of the current age of the Universe. Very long baseline interferometry (VLBI) images show a compact triple structure with a size of 68 parsecs. The radio properties of J1606+3124, including the edge-brightening morphology, peaked GHz radio spectrum, slow variability, and low jet speed, consistently indicate that it is a compact symmetric object (CSO). The radio source size and expansion rate of the hotspots suggest that J1606+3124 is a young (kinematic age of ~3600 years) radio source. Infrared observations reveal a gas- and dust-rich host galaxy environment, which may hinder the growth of the jet; however, the ultra-high jet power of J1606+3124 gives it an excellent chance to grow into a large-scale double-lobe radio galaxy. If its redshift and galaxy classification can be confirmed by further optical spectroscopic observations, J1606+3124 will be the highest redshift CSO galaxy known to date.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tao An
Ailing Wang
Yuanqi Liu
Yulia Sotnikova
Yingkang Zhang
J. N. H. S. Aditya
Sumit Jaiswal
George Khorunzhev
Baoqiang Lao
Ruqiu Lin
Alexander Mikhailov
Marat Mingaliev
Timur Mufakharov
Sergey Sazonov
摘要： Jets may have contributed to promoting the growth of seed black holes in the early Universe, and thus observations of radio-loud high-redshift quasars are crucial to understanding the growth and evolution of the early supermassive black holes. Here we report the radio properties of an X-ray bright $z=5.5$ quasar, SRGE J170245.3+130104 (J1702+1301). Our high-resolution radio images reveal the radio counterpart at the optical position of J1702+1301, while another radio component is also detected at $\sim$23.5\arcsec\ to the southwest. Our analysis suggests that this southwest component is associated with a foreground galaxy at $z\approx 0.677$, which is mixed with J1702+1301 in low-frequency low-resolution radio images. After removing the contamination from this foreground source, we recalculated the radio loudness of J1702+1301 to be $R>$1100, consistent with those of blazars. J1702+1301 exhibits a flat radio spectrum ($\alpha = -0.17 \pm 0.05$, $S \propto \nu^\alpha$) between 0.15 and 5 GHz; above 5 GHz, it shows a rising spectrum shape, and the spectral index $\alpha^{8.2}_{4.7}$ appears to be correlated with the variation of the flux density: in burst states, $\alpha^{8.2}_{4.7}$ becomes larger. J1702+1301 displays distinct radio variability on timescales from weeks to years in the source's rest frame. These radio properties, including high radio loudness, rising spectrum, and rapid variability, tend to support it as a blazar.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yingkang Zhang
Tao An
Sándor Frey
Xiaolong Yang
Máté Krezinger
Oleg Titov
Alexey Melnikov
Pablo de Vicente
Fengchun Shu
Ailing Wang
摘要： Jets of high-redshift active galactic nuclei (AGNs) can be used to directly probe the activity of the black holes in the early Universe. Radio sources with jets misaligned with respect to the line of sight are expected to dominate the high-redshift AGN population. In this paper, we present the high-resolution imaging results of a z=4.57 AGN J2102+6015 by analyzing its multi-epoch dual-frequency very long baseline interferometry (VLBI) data. The 8.4-GHz VLBI images reveal two major features along the east-west direction separated by $\sim$ 10 milli-arcsec (mas). From the spectral index map, both features show flat/inverted spectra. The separation between the two features remains almost unchanged over an observation period of $\sim$ 13 years, placing an upper limit of the separation speed as about 0.04 mas year$^{-1}$. Previous studies have classified the source as a GHz-peaked spectrum quasar. Our results indicate that J2102+6015 is most likely a young, compact symmetric object rather than a blazar-type core-jet source.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ailing Wang
Tao An
Xiaopeng Cheng
Luis C. Ho
Kenneth I. Kellermann
Willem A. Baan
Jun Yang
Yingkang Zhang
摘要： We observed 20 Palomar-Green (PG) quasars at low redshift ($z 1 mJy, including 4 radio-loud quasars (RLQs) and 16 radio-quiet quasars (RQQs), using the Very Long Baseline Array (VLBA) at 5 GHz. Ten RQQs are clearly detected in the VLBA images, and a compact radio core is identified in eight of them, indicating the prevalence of active galactic nucleus (AGN)-related radio emission in this flux-density-limited RQQ sample. The RQQs and RLQs in our sample have a division at $\sim$30~mJy. The radio emission from RQQs appears to be the result of a combination of star formation and AGN-associated activities. All RQQs in our sample have a 5 GHz flux density ratio of Very Large Array (VLA) A-array to D-array $f_{\rm c} = S_{\rm A}^{\rm VLA}/S_{\rm D}^{\rm VLA}$ above 0.2. The RQQs with $f_a$ (VLBA and VLA flux density ratio $S^{\rm VLBA}/S_{\rm A}^{\rm VLA}) > 0.2$ versus $f_a < 0.2$ show significant differences in morphology, compactness and total flux density. $f_{\rm a}$ of RQQs is systematically lower than that of RLQs, probably due to the extended jets or relic jets of RQQs on 10s to 100s parsecs which are resolved out in VLBA images. Future larger samples, especially with the addition of milli-arcsec resolution radio images of RQQs with total flux densities below 1 mJy, can test the conclusions of this paper and contributes to the understanding of the radio emission mechanism of RQQs, and the dichotomy and physical connection between RQQs and RLQs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ailing Wang
Tao An
Shaoguang Guo
Prashanth Mohan
Wara Chamani
Willem A. Baan
Talvikki Hovatta
Heino Falcke
Tim J. Galvin
Natasha Hurley-Walker
Sumit Jaiswal
Anne Lahteenmaki
Baoqiang Lao
Weijia Lv
Merja Tornikoski
Yingkang Zhang
摘要： Disk winds and jets are ubiquitous in active galactic nuclei (AGN), and how these two components interact remains an open question. We study the radio properties of a radio-intermediate quasar III Zw 2. We detect two jet knots J1 and J2 on parsec scales, which move at a mildly apparent superluminal speed of $1.35\,c$. Two $\gamma$-ray flares were detected in III Zw 2 in 2009--2010, corresponding to the primary radio flare in late 2009 and the secondary radio flare in early 2010. The primary 2009 flare was found to be associated with the ejection of J2. The secondary 2010 flare occurred at a distance of $\sim$0.3 parsec from the central engine, probably resulting from the collision of the jet with the accretion disk wind. The variability characteristics of III Zw 2 (periodic radio flares, unstable periodicity, multiple quasi-periodic signals and possible harmonic relations between them) can be explained by the global instabilities of the accretion disk. These instabilities originating from the outer part of the warped disk propagate inwards and can lead to modulation of the accretion rate and consequent jet ejection. At the same time, the wobbling of the outer disk may also lead to oscillations of the boundary between the disk wind and the jet tunnel, resulting in changes in the jet-wind collision site. III Zw 2 is one of the few cases observed with jet-wind interactions, and the study in this paper is of general interest for gaining insight into the dynamic processes in the nuclear regions of AGN.
点击量
待评议
点击量
下载量
评论
