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Dwarf galaxies are characterized by a very low luminosity and low mass. Because of significant accretion and ejection activity of massive black holes, some dwarf galaxies also host low-luminosity active galactic nuclei (AGNs). In a few dwarf AGNs, very long baseline interferometry (VLBI) observations have found faint non-thermal radio emission. SDSS J090613.77+561015.2 is a dwarf AGN owning an intermediate-mass black hole (IMBH) with a mass of |$M_\mathrm{BH} = 3.6^{+5.9}_{-2.3}\times 10^5 \mathrm{ M}_{\odot }$| and showing a rarely seen two-component radio structure in its radio nucleus. To further probe their nature, i.e. the IMBH jet activity, we performed additional deep observations with the European VLBI Network (EVN) at 1.66 and 4.99 GHz. We find the more diffuse emission regions and structure details. These new EVN imaging results allow us to reveal a two-sided jet morphology with a size up to about 150 mas (projected length ∼140 pc) and a radio luminosity of about 3 × 1038 erg s−1. The peak feature has an optically thin radio spectrum and thus more likely represents a relatively young ejecta instead of a jet base. The EVN study on SDSS J090613.77+561015.2 demonstrates the existence of episodic, relatively large-scale, and powerful IMBH jet activity in dwarf AGNs. Moreover, we collected a small sample of VLBI-detected dwarf AGNs and investigated their connections with normal AGNs. We notice that these radio sources in the dwarf AGNs tend to have steep spectra and small linear sizes, and possibly represent ejecta from scaled-down episodic jet activity. [ABSTRACT FROM AUTHOR]

AT 2019avd is a nuclear transient detected from infrared to soft X-rays, though its nature is yet unclear. The source has shown two consecutive flaring episodes in the optical and the infrared bands, and its second flare was covered by X-ray monitoring programs. During this flare, the UVOT/ Swift photometries revealed two plateaus: one observed after the peak and the other one appeared ∼240 d later. Meanwhile, our NICER and XRT / Swift campaigns show two declines in the X-ray emission, one during the first optical plateau and one 70–90 d after the optical/UV decline. The evidence suggests that the optical/UV could not have been primarily originated from X-ray reprocessing. Furthermore, we detected a timelag of ∼16–34 d between the optical and UV emission, which indicates the optical likely comes from UV reprocessing by a gas at a distance of 0.01–0.03 pc. We also report the first VLA and VLBA detection of this source at different frequencies and different stages of the second flare. The information obtained in the radio band – namely a steep and a late-time inverted radio spectrum, a high brightness temperature and a radio-loud state at late times – together with the multiwavelength properties of AT 2019avd suggests the launching and evolution of outflows such as disc winds or jets. In conclusion, we propose that after the ignition of black hole activity in the first flare, a super-Eddington flaring accretion disc formed and settled to a sub-Eddington state by the end of the second flare, associated with a compact radio outflow. [ABSTRACT FROM AUTHOR]

Tea domain transcription factor 4 (TEAD4) plays a pivotal role in tissue development and homeostasis by interacting with Yes-associated protein (YAP) in response to Hippo signaling inactivation. TEAD4 and YAP can also cooperate with transforming growth factor-β (TGF-β)-activated Smad proteins to regulate gene transcription. Yet, it remains unclear whether TEAD4 plays a YAP-independent role in TGF-β signaling. Here, we unveil a novel tumor suppressive function of TEAD4 in liver cancer via mitigating TGF-β signaling. Ectopic TEAD4 inhibited TGF-β-induced signal transduction, Smad transcriptional activity, and target gene transcription, consequently suppressing hepatocellular carcinoma cell proliferation and migration in vitro and xenograft tumor growth in mice. Consistently, depletion of endogenous TEAD4 by siRNAs enhanced TGF-β signaling in cancer cells. Mechanistically, TEAD4 associates with receptor-regulated Smads (Smad2/3) and Smad4 in the nucleus, thereby impairing the binding of Smad2/3 to the histone acetyltransferase p300. Intriguingly, these negative effects of TEAD4 on TGF-β/Smad signaling are independent of YAP, as impairing the TEAD4–YAP interaction through point mutagenesis or depletion of YAP and/or its paralog TAZ has little effect. Together, these results unravel a novel function of TEAD4 in fine tuning TGF-β signaling and liver cancer progression in a YAP-independent manner. [ABSTRACT FROM AUTHOR]

We conducted a Very Long Baseline Array (VLBA) observation of the low mass active galactic nucleus (AGN) in galaxy NGC 4293 (z  = 0.003). The object is associated with a low-ionization nuclear emission-line region (LINER). Its black hole mass is estimated as ∼105 or |${\sim}10^7 \, \mathrm{M}_\odot$|⁠. The VLBA 1.5 GHz image shows an inverse symmetric structure with two discrete radio blobs separated by an angular distance of ∼120 mas, corresponding to ∼7 parsec. Furthermore, its integrated radio spectrum has a turnover at the frequency of ∼0.44 GHz. Based on the compactness and spectrum, the nuclear radio source in NGC 4293 belongs to a sample of (megahertz) peaked spectrum (PS/MPS) radio sources with compact symmetric morphologies. NGC 4293 has 1.4 GHz radio power of only |${\sim}10^{20}\, \mathrm{W\, Hz^{-1}}$| with the VLBA observation, which is consistent with local AGNs but lower than the current PS samples. One of the two blobs has a steep radio spectrum α = −0.62 ± 0.08 (S ν ∝ ν+α), while the other one has an inverted spectrum α = 0.32 ± 0.10. The VLBA 1.5 GHz luminosity ratio of the two blobs is 3.23 and both blobs show lateral-flowing structures where the hotspots reside at the edge of each radio lobe. This can be explained as jet interactions with dense circumnuclear medium. We estimate the black hole mass of NGC 4293 through the Fundamental Plane of black hole activity, which constrains the black hole mass to be |${\lesssim}10^6\, \mathrm{M}_\odot$|⁠. It supports that the object is a low-mass AGN and a potential candidate for accreting and ejecting IMBHs. [ABSTRACT FROM AUTHOR]

NGC 4395 is a dwarf galaxy at a distance of about 4.3 Mpc (scale: ∼0.021 pc mas−1). It hosts an intermediate-mass black hole (IMBH) with a mass between ∼104 and ∼105 solar masses. The early radio observations of NGC 4395 with the very long baseline interferometry (VLBI) network, High Sensitivity Array (HSA), at 1.4 GHz in 2005 showed that its nucleus has a sub-mJy outflow-like feature (E) extending over 15 mas. To probe the possibility of the feature E as a continuous jet with a base physically coupled with the accretion disc, we performed deep VLBI observations with the European VLBI Network (EVN) at 5 GHz, and analysed the archival data obtained with the HSA at 1.4 GHz in 2008, NSF's Karl G. Jansky Very Large Array (VLA) at 12–18 GHz and the Atacama Large Millimetre/submillimetre Array (ALMA) at 237 GHz. The feature E displays more diffuse structure in the HSA image of 2008 and has no compact substructure detected in the EVN image. Together with the optically thin steep spectrum and the extremely large angular offset (about 220 mas) from the accurate optical Gaia position, we explain the feature E as nuclear shocks likely formed by the IMBH's episodic ejection or wide-angle outflow. The VLA and ALMA observations find a sub-mJy pc-scale diffuse feature, possibly tracing a thermal free–free emission region near the IMBH. There is no detection of a jet base at the IMBH position in the VLBI maps. The non-detections give an extremely low luminosity of ≤4.7 × 1033 erg s−1 at 5 GHz and indicate no evidence of a disc-jet coupling on sub-pc scales. [ABSTRACT FROM AUTHOR]

We report observations of a bright dumb-bell system of galaxies (z  = 0.162) with the upgraded Giant Metrewave Radio Telescope (u GMRT), which show that each member of this gravitationally bound pair of galaxies hosts bipolar radio jets extended on 100 kpc scales. Only two cases of such radio morphology have been reported previously, both being dumb-bell systems, as well. The famous first example, 3C 75, was discovered 4 decades ago, and the second case was discovered 3 decades ago. This implies that such 'Twin-Radio-Galaxies' (TRGs) are an exceedingly rare phenomenon. As in the case of its two senior cousins, the bipolar radio jets of the present TRG (J104454+354055) exhibit strong wiggles and are edge-darkened (Fanaroff–Riley class I). However, there are important differences, too. For instance, the jets in the present TRG do not merge and, moreover, show no signs of distortion due to an external crosswind. This makes the present TRG a much neater laboratory for studying the physics of (sideway) colliding jets of relativistic plasma. This TRG has a Wide-Angle-Tail neighbour hosted by another bright galaxy belonging to the same group, which appears to be moving towards the TRG. [ABSTRACT FROM AUTHOR]

In the time domain, the radio sky in particular along the Galactic plane direction may vary significantly because of various energetic activities associated with stars, stellar, and supermassive black holes. Multi-epoch Very Large Array surveys of the Galactic plane at 5.0 GHz enabled the finding of a catalogue of 39 variable radio sources in the flux density range 1–70 mJy. To probe their radio structures and spectra, we observed 17 sources with the very-long-baseline interferometric (VLBI) imaging technique and collected additional multifrequency data from the literature. We detected all of the sources at 5 GHz with the Westerbork Synthesis Radio Telescope, but only G23.6644–0.0372 with the European VLBI Network (EVN). Together with its decadal variability and multifrequency radio spectrum, we interpret it as an extragalactic peaked-spectrum source with a size of ≲10 pc. The remaining sources were resolved out by the long baselines of the EVN because of either strong scatter broadening at the Galactic latitude < 1° or intrinsically very extended structures on centi-arcsec scales. According to their spectral and structural properties, we find that the sample has a diverse nature. We notice two young H  ii regions and spot a radio star and a candidate planetary nebula. The rest of the sources are very likely associated with radio active galactic nuclei (AGNs). Two of them also display arcsec-scale faint jet activity. The sample study indicates that AGNs are common place even among variable radio sources in the Galactic plane. [ABSTRACT FROM AUTHOR]

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 analysing 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 ∼10 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 ∼13 yr, placing an upper limit of the separation speed as about 0.04 mas yr−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. [ABSTRACT FROM AUTHOR]

Broad Balmer emission lines in active galactic nuclei (AGN) may display dramatic changes in amplitude, even disappearance and re-appearance in some sources. As a nearby galaxy at a redshift of z = 0.0264, Mrk 590 suffered such a cycle of Seyfert type changes between 2006 and 2017. Over the last 50 yr, Mrk 590 also underwent a powerful continuum outburst and a slow fading from X-rays to radio wavelengths with a peak bolometric luminosity reaching about 10 per cent of the Eddington luminosity. To track its past accretion and ejection activity, we performed very long baseline interferometry (VLBI) observations with the European VLBI Network (EVN) at 1.6 GHz in 2015. The EVN observations reveal a faint (∼1.7 mJy) radio jet extending up to ∼2.8 mas (projected scale ∼1.4 pc) toward north, and probably resulting from the very intensive AGN activity. To date, such a parsec-scale jet is rarely seen in the known changing-look AGN. The finding of the faint jet provides further strong support for variable accretion as the origin of the type changes in Mrk 590. [ABSTRACT FROM AUTHOR]