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Owing to their quiet evolutionary histories, nearby dwarf galaxies (stellar masses |$M_\star \lesssim 3 \times 10^9 \, \mathrm{M}_\odot$|⁠) have the potential to teach us about the mechanism(s) that 'seeded' the growth of supermassive black holes, and also how the first stellar mass black holes formed and interacted with their environments. Here, we present high spatial resolution observations of three dwarf galaxies in the X-ray (Chandra), the optical/near-infrared (Hubble Space Telescope), and the radio (Karl G. Jansky Very Large Array). These three galaxies were previously identified as hosting candidate active galactic nuclei on the basis of lower resolution X-ray imaging. With our new observations, we find that X-ray sources in two galaxies (SDSS J121326.01+543631.6 and SDSS J122111.29+173819.1) are off-nuclear and lack corresponding radio emission, implying they are likely luminous X-ray binaries. The third galaxy (Mrk 1434) contains two X-ray sources (each with L X ≈ 1040 erg s−1) separated by 2.8 arcsec, has a low metallicity [12 + log(O/H)  = 7.8], and emits nebular He  ii λ4686 line emission. The northern source has spatially coincident point-like radio emission at 9.0 GHz and extended radio emission at 5.5 GHz. We discuss X-ray binary interpretations (where an ultraluminous X-ray source blows a 'radio bubble') and active galactic nucleus interpretations (where an |$\approx 4\times 10^5 \, \mathrm{M}_\odot$| black hole launches a jet). In either case, we find that the He  ii emission cannot be photoionized by the X-ray source, unless the source was ≈30–90 times more luminous several hundred years ago. [ABSTRACT FROM AUTHOR]

We present the results of a high-cadence spectroscopic and imaging monitoring campaign of the active galactic nucleus (AGN) of NGC 4395. High signal-to-noise-ratio spectra were obtained at the Gemini-N 8 m telescope using the GMOS integral field spectrograph (IFS) on 2019 March 7 and at the Keck I 10 m telescope using the Low-Resolution Imaging Spectrometer with slit masks on 2019 March 3 and April 2. Photometric data were obtained with a number of 1 m-class telescopes during the same nights. The narrow-line region (NLR) is spatially resolved; therefore, its variable contributions to the slit spectra make the standard procedure of relative flux calibration impractical. We demonstrate that spatially resolved data from the IFS can be effectively used to correct the slit-mask spectral light curves. While we obtained no reliable lag owing to the lack of a strong variability pattern in the light curves, we constrain the broad-line time lag to be less than 3 hr, consistent with the photometric lag of ∼80 minutes reported by Woo et al. By exploiting the high-quality spectra, we measure the second moment of the broad component of the H α emission line to be 586 ± 19 km sâˆ'1, superseding the lower value reported by Woo et al. Combining the revised line dispersion and the photometric time lag, we update the black hole mass to (1.7 ± 0.3) Ă— 104 M ⊙. [ABSTRACT FROM AUTHOR]

We present a definitive assessment of the role of inverse Compton scattering of cosmic microwave background photons (IC/CMB) in the context of radio galaxies. Owing to the steep increase of the CMB radiation energy density, IC/CMB is supposed to become progressively more important with respect to radio synchrotron cooling as the redshift increases. For typical energies at play, this process will up-scatter the CMB photons into the X-ray band, and is thus expected to yield a redshift-dependent, concurrent X-ray brightening and radio dimming of the jet-powered structures. Here, we show how a conclusive proof of this effect hinges on high-resolution imaging data in which the extended lobes can be distinguished from the compact hotspots where synchrotron self-Compton dominates the X-ray emission regardless of redshift. We analyse Chandra and Very Large Array data of 11 radio galaxies between |$1.3 \lesssim z \lesssim 4.3$|⁠ , and demonstrate that the emission from their lobes is fully consistent with the expectations from IC/CMB in equipartition. Once the dependence on size and radio luminosity are properly accounted for, the measured lobe X-ray luminosities bear the characteristic ∝(1 + z)4 proportionality expected of a CMB seed radiation field. Whereas this effect can effectively quench the (rest-frame) GHz radio emission from |$z \gtrsim 3$| radio galaxies below |${\lesssim}$| 1 mJy, IC/CMB alone cannot be responsible for a deficit in high- z , radio-loud active galactic nuclei (AGNs) if – as we argue – such AGNs typically have bright, compact hotspots. [ABSTRACT FROM AUTHOR]

In an effort to understand the cause of the apparent depletion in the number density of radio-loud active galactic nuclei (AGNs) at z > 3, this work investigates the viability of the so-called cosmic microwave background (CMB) quenching mechanism of intrinsically jetted, high-z AGNs, whereby inverse Compton scattering of CMB photons off electrons within the extended lobes results in a substantial dimming of the lobe synchrotron emission at GHz frequencies, while simultaneously boosting their diffuse X-ray signal. We focus on five z > 3.5 radio galaxies that have sufficiently deep Chandra exposure (>50 ks) to warrant a meaningful investigation of any extended X-ray emission. For those objects with evidence for statistically significant extended X-ray lobes (4C 41.17 and 4C 03.24), we combine the Chandra measurements with literature data at lower frequencies to assemble the systems' spectral energy distributions (SEDs), and utilize state-of-the-art SED modelling - including emission from the disc, torus, jet, hotspots and lobes - to infer their physical parameters. For both radio galaxies, the magnetic energy density in the hotspots is found to exceed the energy density in CMB photons, whereas the opposite is true for the lobes. This implies that any extended synchrotron emission likely originates from the hotspots themselves, rather than the lobes. Conversely, inverse Compton scattering of CMB photons dominates the extended X-ray emission from the lobes, which are effectively 'radio-quenched'. As a result, CMB quenching is effective in these systems in spite of the fact that the observed X-ray to radio luminosity ratio does not bear the signature (1 + z)4 dependence of the CMB energy density. [ABSTRACT FROM AUTHOR]

We have recently put forward a ‘unified’ semi-empirical model for the coupling between accretion and jet production in galactic black hole X-ray binaries. In this paper, we summarise this model and briefly discuss relevant considerations that have arisen since its publication. [ABSTRACT FROM AUTHOR]

A large sample of active galactic nuclei (AGN) studied here shows a ‘quenching’ of the radio emission that occurs when the luminosity is from a few per cent to about 10 per cent of the Eddington rate, just as is seen in the high/soft state of X-ray binaries. The result holds even when the sample of AGN includes no narrow line Seyfert 1 galaxies (the systems most commonly suggested to be the analogue of the high/soft state). This adds substantially to the body of evidence that AGN show the same spectral state phenomenology and related disc–jet coupling as the stellar mass accreting black holes. That the power-law correlation between X-ray and radio luminosity is the same in both AGN and X-ray binaries and extends below 10−7 LEDD strengthens the argument that there is no fundamental difference between the low/hard state and the so-called quiescent state in X-ray binaries. We also discuss possible reasons for the scatter in the radio to X-ray luminosity correlation in the AGN. [ABSTRACT FROM AUTHOR]