The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow ...relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli-arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.
Abstract
We present the first data release of high-resolution (≤0.2 arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the ...LeMMINGs survey. This sample includes galaxies which are active (low-ionization nuclear emission-line regions LINER and Seyfert) and quiescent (H ii galaxies and absorption line galaxies, ALGs), which are reclassified based upon revised emission-line diagrams. We detect radio emission ≳0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for H ii galaxies, and 5/14 for ALGs) with radio sizes typically of ≲100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 1032 to 1040 erg s−1: LINERs and H ii galaxies show the highest and lowest radio powers, respectively, while ALGs and Seyferts have intermediate luminosities. We find that radio core luminosities correlate with black hole (BH) mass down to ∼107 M⊙, but a break emerges at lower masses. Using O iii line luminosity as a proxy for the accretion luminosity, active nuclei and jetted H ii galaxies follow an optical Fundamental Plane of BH activity, suggesting a common disc–jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; H ii galaxies may host weak active BHs and/or nuclear star-forming cores; and recurrent BH activity may account for ALG properties.
Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the ...western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 10
erg at infrared and radio wavelengths but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.
Radio jets in NGC 4151: where eMERLIN meets HST Williams, D. R. A; McHardy, I. M; Baldi, R. D ...
Monthly notices of the Royal Astronomical Society,
12/2017, Volume:
472, Issue:
4
Journal Article
Peer reviewed
Open access
Abstract
We present high-sensitivity eMERLIN radio images of the Seyfert galaxy NGC 4151 at 1.51 GHz. We compare the new eMERLIN images to those from archival MERLIN observations in 1993 to determine ...the change in jet morphology in the 22 yr between observations. We report an increase by almost a factor of 2 in the peak flux density of the central core component, C4, thought to host the black hole, but a probable decrease in some other components, possibly due to adiabatic expansion. The core flux increase indicates an active galactic nucleus (AGN) that is currently active and feeding the jet. We detect no significant motion in 22 yr between C4 and the component C3, which is unresolved in the eMERLIN image. We present a spectral index image made within the 512 MHz band of the 1.51 GHz observations. The spectrum of the core, C4, is flatter than that of other components further out in the jet. We use HST emission-line images (H α, O iii and O ii) to study the connection between the jet and the emission-line region. Based on the changing emission-line ratios away from the core and comparison with the eMERLIN radio jet, we conclude that photoionization from the central AGN is responsible for the observed emission-line properties further than 4 arcsec (360 pc) from the core, C4. Within this region, a body of evidence (radio-line co-spatiality, low O iii/H α and estimated fast shocks) suggests additional ionization from the jet.
Context.
For nearly seven decades, astronomers have been studying active galaxies, that is to say, galaxies with actively accreting central supermassive black holes: active galactic nuclei (AGN). A ...small fraction are characterized by luminous, powerful radio emission: This class is known as radio-loud AGN. A substantial fraction, the so-called radio-quiet AGN population, display intermediate or weak radio emission. However, an appreciable fraction of strong X-ray-emitting AGN are characterized by the absence of radio emission, down to an upper limit of about 10
−7
times the luminosity of the most powerful radio-loud AGN.
Aims.
We wish to address the nature of these – seemingly radio-silent – X-ray-luminous AGN and their host galaxies to determine if there is any radio emission, and, if so, where it originates.
Methods.
Focusing on the GOODS-N field, we examine the nature of these objects, employing stacking techniques on ultra-deep radio data obtained with the JVLA. We combine these radio data with
Spitzer
far-infrared data.
Results.
We establish the absence, or totally insignificant contribution, of jet-driven radio emission in roughly half of the otherwise normal population of X-ray-luminous AGN, which appear to reside in normal star-forming galaxies.
Conclusions.
AGN- or jet-driven radio emission is simply a mechanism that may be at work or may be dormant in galaxies with actively accreting black holes. The latter cases can be classified as radio-silent AGN.
ABSTRACT
We present the second data release of high-resolution (≤0.2 arcsec) 1.5-GHz radio images of 177 nearby galaxies from the Palomar sample, observed with the e-MERLIN array, as part of the ...Legacy e-MERLIN Multi-band Imaging of Nearby Galaxies Sample (LeMMINGs) survey. Together with the 103 targets of the first LeMMINGs data release, this represents a complete sample of 280 local active (LINER and Seyfert) and inactive galaxies (H ii galaxies and absorption line galaxies, ALG). This large program is the deepest radio survey of the local Universe, ≳1017.6 W Hz−1, regardless of the host and nuclear type: we detect radio emission ≳0.25 mJy beam−1 for 125/280 galaxies (44.6 per cent) with sizes of typically ≲100 pc. Of those 125, 106 targets show a core which coincides within 1.2 arcsec with the optical nucleus. Although we observed mostly cores, around one third of the detected galaxies features jetted morphologies. The detected radio core luminosities of the sample range between ∼1034 and 1040 erg s−1. LINERs and Seyferts are the most luminous sources, whereas H ii galaxies are the least. LINERs show FR I-like core-brightened radio structures while Seyferts reveal the highest fraction of symmetric morphologies. The majority of H ii galaxies have single radio core or complex extended structures, which probably conceal a nuclear starburst and/or a weak active nucleus (seven of them show clear jets). ALGs, which are typically found in evolved ellipticals, although the least numerous, exhibit on average the most luminous radio structures, similar to LINERs.
•Green hydrogen is uniquely equipped to decarbonize sectors which do not have green alternatives.•A ‘hydrogen economy’ is an essential secondary energy economy to realizing a majority renewable ...energy society.•Early implementation of green hydrogen will be in the current chemical synthesis market.•Hydrogen will penetrate the transportation and buildings and heating sectors in the midterm transition toward 100% renewables.•Hydrogen will be a necessary seasonal storage technology in the long term.
A hydrogen economy has long been promoted as a ground-breaking aspect of a low-carbon future. However, there is little consensus on what this future entails, with some overly concerned about lack of demand and others disregarding hydrogen’s limitations. Here, we fill the need for a comprehensive definition of the ‘hydrogen economy’ and illustrate a vision in which hydrogen will primarily be used for decarbonization where no alternative exists. We propose a three-phase implementation plan for hydrogen into the industrial sector as a chemical feedstock, the transportation sector for long-range, heavy-duty vehicles, the buildings sector for heat, and the power sector for seasonal storage. We find that hydrogen will not be the largest energy economy, but with a projected need of 2.3 Gt H2 annually, it can decarbonize around 18% of energy-related sectors. In the long-term, hydrogen can complement renewable electricity and be the keystone to a 100% renewable future.
ABSTRACT
We present high spatial resolution (0.4 arcsec, kpc) Plateau de Bure Interferometer interferometric data on three ultraluminous infrared galaxies (ULIRGs) at : two submillimetre galaxies ...(SMGs) and one submillimetre faint star‐forming radio galaxy. The three galaxies have been robustly detected in CO rotational transitions, either 12CO (J= 43) or 12CO (J= 32), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of 2) for intermediate‐excitation CO emission in ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High‐resolution (0.3 arcsec) combined Multi‐Element Radio‐Linked Interferometer Network‐Very Large Array observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to those of the CO observations. This ‘matched beam’ approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt–Schmidt (KS)‐style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high‐z star‐forming galaxies.
We present Atacama Large Millimeter/submillimeter Array observations of 99.02 GHz free–free and H40α emission from the centre of the nearby starburst galaxy NGC 253. We calculate electron ...temperatures of 3700–4500 K for the photoionized gas, which agrees with previous measurements. We measure a photoionizing photon production rate of (3.2 ± 0.2) × 1053 s−1 and a star formation rate of 1.73 ± 0.12 M⊙ yr−1 within the central 20 × 10 arcsec, which fall within the broad range of measurements from previous millimetre and radio observations but which are better constrained. We also demonstrate that the dust opacities are ∼3 dex higher than inferred from previous near-infrared data, which illustrates the benefits of using millimetre star formation tracers in very dusty sources.
Abstract
We present a radio light curve of supernova (SN) 2014C taken with the Arcminute Microkelvin Imager (AMI) Large Array at 15.7 GHz. Optical observations presented by Milisavljevic et al. ...demonstrated that SN 2014C metamorphosed from a stripped-envelope Type Ib SN into a strongly interacting Type IIn SN within 1 yr. The AMI light curve clearly shows two distinct radio peaks, the second being a factor of 4 times more luminous than the first peak. This double bump morphology indicates two distinct phases of mass-loss from the progenitor star with the transition between density regimes occurring at 100–200 d. This reinforces the interpretation that SN 2014C exploded in a low-density region before encountering a dense hydrogen-rich shell of circumstellar material that was likely ejected by the progenitor prior to the explosion. The AMI flux measurements of the first light-curve bump are the only reported observations taken within ∼50 to ∼125 d post-explosion, before the blast-wave encountered the hydrogen shell. Simplistic synchrotron self-absorption and free–free absorption modelling suggest that some physical properties of SN 2014C are consistent with the properties of other Type Ibc and IIn SNe. However, our single frequency data does not allow us to distinguish between these two models, which implies that they are likely too simplistic to describe the complex environment surrounding this event. Lastly, we present the precise radio location of SN 2014C obtained with the electronic Multi-Element Remotely Linked Interferometer Network, which will be useful for future very long baseline interferometry observations of the SN.
PDF
