Feedback from radio jets associated with Active Galactic Nuclei (AGN) plays a profound role in the evolution of galaxies. Kinetic power of these radio jets appears to show temporal variation, but the mechanism(s) responsible for this process are not yet clear. Recently, the LOw Frequency ARray (LOFAR) has uncovered large populations of active, remnant and restarted radio jet populations. By focusing on LOFAR data in the Lockman Hole, in this work we use the Radio AGN in Semi-Analytic Environments (RAiSE) dynamical model to present the first self-consistent modelling analysis of active, remnant and restarted radio source populations. Consistent with other recent work, our models predict that remnant radio lobes fade quickly. Any high (>10 percent) observed fraction of remnant and restarted sources therefore requires a dominant population of short-lived jets. We speculate that this could plausibly be provided by feedback-regulated accretion.
The Lockman Hole Project is a wide international collaboration aimed at exploiting the multi-band extensive and deep information available for the Lockman Hole region, with the aim of better characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields. Recent observations with the LOw-Frequency ARray (LOFAR) extends the multi-frequency radio information currently available for the Lockman Hole (from 350 MHz up to 15 GHz) down to 150 MHz, allowing us to explore a new radio spectral window for the faint radio source population. These LOF…
After the jets have switched off, radio galaxies undergo a fading phase which is often named the dying phase. The luminosity evolution of the remnant plasma during this period is still poorly constrained because of the paucity of objects detected. Using the new 150-MHz deep LOFAR observations of the well-known extragalactic field the Lockman Hole, we performed a systematic search of dying radio sources aiming to provide good statistics on their detection and properties. To avoid selection biases towards any specific class of dying sources we used both morphological and spectral selection crite…
Radio galaxies are known to go through cycles of activity, where phases of apparent quiescence can be followed by repeated activity of the central supermassive black hole. A better understanding of this cycle is crucial for ascertaining the energetic impact that the jets have on the host galaxy, but little is known about it. We used deep LOFAR images at 150 MHz of the Lockman Hole extragalactic field to select a sample of 158 radio sources with sizes $> 60^{\prime\prime}$ in different phases of their jet life cycle. Using a variety of criteria (e.g. core prominence combined with low-surface br…
The phase of radio galaxy evolution after the jets have switched off, often referred to as the remnant phase, is poorly understood and very few sources in this phase are known. In this work we present an extensive search for remnant radio galaxies in the Lockman Hole, a well-studied extragalactic field. We create mock catalogues of low-power radio galaxies based on Monte Carlo simulations to derive first-order predictions of the fraction of remnants in radio flux limited samples for comparison with our Lockman-Hole sample. We have combined LOFAR observations at 150 MHz with public surveys at h…
The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterising the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper we present new 150-MHz observations carried out with the LOw Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6$\times$14.7 arcsec and rea…
We have exploited LOFAR deep observations of the Lockman Hole field at 150 MHz to investigate the relation between the radio luminosity of star-forming galaxies (SFGs) and their star formation rates (SFRs), as well as its dependence on stellar mass and redshift. The adopted source classification, SFRs and stellar masses are consensus estimates based on a combination of four different SED fitting methods. We note a flattening of radio spectra of a substantial minority of sources below $\sim 1.4 $ GHz. Such sources have thus a lower "radio-loudness" level at 150 MHz than expected from extrapolat…
The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in AGN, as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy feedback, and accretion mechanisms. Large catalogues of radio sources provide statistical information about the evolution of the radio-loud AGN population out to high redshifts. Using wide-field imaging with the LOFAR telescope, we study both a well-known DDRG as well as a large number of radio sources in the field of view. We present a hi…
Active galactic nuclei (AGNs) show episodic activity, evident in galaxies that exhibit restarted radio jets. These restarted jets can interact with their environment, leaving signatures on the radio spectral energy distribution. Tracing these signatures requires resolved spectral index measurements over a broad frequency range including low frequencies. We present such a study for the radio galaxy 3C 293. Using the International LOFAR telescope (ILT) we probed spatial scales as fine as ~0.2" at 144 MHz, and to constrain the spectrum we combined these data with Multi-Element Radio Linked Interf…
Active galactic nuclei (AGN) at the centres of galaxies can cycle between periods of activity and of quiescence. Characterising the duty-cycle of AGN is crucial for understanding their impact on the evolution of the host galaxy. For radio AGN, their evolutionary stage can be identified from a combination of morphological and spectral properties. We summarise the results we have obtained in the last few years by studying radio galaxies in various crucial phases of their lives, such as remnant and restarted sources. We used morphological information derived from LOw Frequency ARray (LOFAR) image…
Supermassive black holes at the centres of galaxies can cycle through periods of activity and quiescence. Characterising the duty cycle of active galactic nuclei is crucial for understanding the impact of the energy they release on the host galaxy. For radio AGN, this can be done by identifying dying (remnant) and restarted radio galaxies from their radio spectral properties. Using the combination of images at 1400 MHz produced by Apertif, the new phased-array feed receiver installed on the Westerbork Synthesis Radio Telescope, and images at 150 MHz provided by LOFAR, we have derived resolved …
Remnant radio galaxies represent an important phase in the life-cycle of radio active galactic nuclei. It is suggested that in this phase, the jets have switched off and the extended emission is fading rapidly. This phase is not well-studied due to the lack of statistical samples observed at both low and high frequencies. In this work, we study a sample of 23 candidate remnant radio galaxies previously selected using the Low Frequency Array at 150 MHz in the Lockman Hole field. We examine their morphologies and study their spectral properties to confirm their remnant nature and revise the morp…
We provide the most accurate estimate yet of the bright end of the infrared (IR) luminosity functions (LFs) and the abundance of hyperluminous IR galaxies (HLIRGs) with IR luminosities > 10^13 L_solar, thanks to the combination of the high sensitivity, angular resolution, and large area of the LOFAR Deep Fields, which probes an unprecedented dynamic range of luminosity and volume. We cross-match Herschel sources and LOFAR sources in Bootes (8.63 deg^2), Lockman Hole (10.28 deg^2), and ELAIS-N1 (6.74 deg^2) with rms sensitivities of around 32, 22, and 20 mJy per beam, respectively. We divide th…
We present the source associations, cross-identifications, and multi-wavelength properties of the faint radio source population detected in the deep tier of the LOFAR Two Metre Sky Survey (LoTSS): the LoTSS Deep Fields. The first LoTSS Deep Fields data release consists of deep radio imaging at 150~MHz of the ELAIS-N1, Lockman Hole, and Boötes fields, down to RMS sensitives of around 20, 22, and 32$~μ$Jy\,beam$^{-1}$, respectively. These fields are some of the best studied extra-galactic fields in the northern sky, with existing deep, wide-area panchromatic photometry from X-ray to infrared wav…
Identifying active galactic nuclei (AGN) and isolating their contribution to a galaxy's energy budget is crucial for studying the co-evolution of AGN and their host galaxies. Brightness temperature ($T_b$) measurements from high-resolution radio observations at GHz frequencies are widely used to identify AGN. Here we investigate using new sub-arcsecond imaging at 144 MHz with the International LOFAR Telescope to identify AGN using $T_b$ in the Lockman Hole field. We use ancillary data to validate the 940 AGN identifications, finding 83 percent of sources have AGN classifications from SED fitti…
Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of what causes the jets to switch off and restart is crucial to our understanding of galaxy evolution, while it is important to know if DDRGs form a host galaxy dichotomy relative to RLAGN. We utilised the…
Restarted radio galaxies represent a unique tool to investigate the duty cycle of the jet activity in Active Galactic Nuclei. Due to a sharp discontinuity of the GHz spectral index distribution within its lobes, the radio galaxy 3C388 has for long being claimed to be a peculiar example of AGN with multi-epoch activity. In this work we have performed, for the first time, a spatially resolved study of the radio spectrum of this source down to MHz-frequencies, aimed at investigating its radiative age and duty cycle. We have used new low frequency observations at 144 MHz performed with LOFAR and a…
We study the properties and the origin of the radio emission in the most luminous early-type galaxies (ETGs) in the nearby Universe (MK<-25, recession velocity < 7,500 km/s) as seen by the 150 MHz Low-Frequency ARray (LOFAR) observations. LOFAR images are available for 188 of these giant ETGs (gETGs) and 146 (78%) of them are detected above a typical luminosity of ~10E21 W/Hz. They show a large spread in power, reaching up to ~10E26 W/Hz. We confirm a positive link between the stellar luminosity of gETGs and their median radio power, the detection rate, and the fraction of extended sources. Ab…
Radio emission in star-forming galaxies: connection to restarted or relic AGN activity
Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut（海德堡大学天文学中心，天文计算研究所）；Departamento de Física, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria（圣卡塔琳娜联邦大学自然科学与精确科学中心物理系）；Departamento de Astronomia, Instituto de Física, Universidade Federal do Rio Grande do Sul（南里奥格兰德联邦大学物理系天文学系）
High quality low-frequency radio surveys have the promise of advancing our understanding of many important topics in astrophysics, including the life cycle of active galactic nuclei (AGN), particle acceleration processes in jets, the history of star formation, and exoplanet magnetospheres. Currently leading low-frequency surveys reach an angular resolution of a few arcseconds. However, this resolution is not yet sufficient to study the more compact and distant sources in detail. Sub-arcsecond resolution is therefore the next milestone in advancing these fields. The biggest challenge at low rad…
The Low Frequency Array (LOFAR) Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168 MHz survey split across multiple tiers over the northern sky. The first LoTSS Deep Fields data release consists of deep radio continuum imaging at 150 MHz of the Boötes, European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1), and Lockman Hole fields, down to rms sensitivities of $\sim$32, 20, and 22 $μ$Jy beam$^{-1}$, respectively. In this paper we present consistent photometric redshift (photo-$z$) estimates for the optical source catalogues in all three fields - totalling ov…
Challenging the archetypal intermittent radio galaxy J0111+3906. New insights from optical GTC/OSIRIS and radio VLA and LOFAR observations
INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉古纳大学）；Hamburger Sternwarte, Universität Hamburg（汉堡天文台，汉堡大学）；European Southern Observatory（欧洲南方天文台）
With the advent of new generation low-frequency telescopes, such as the LOw Frequency ARray (LOFAR), and improved calibration techniques, we have now started to unveil the sub GHz radio sky with unprecedented depth and sensitivity. The LOFAR Two Meter Sky Survey (LoTSS) is an ongoing project in which the whole northern radio sky will be observed at 150 MHz with a sensitivity better than 100 $μ$Jy beam$^{-1}$ at a resolution of \asec{6}. Additionally, deeper observations are planned to cover smaller areas with higher sensitivity. The Lockman Hole, the Boötes and the Elais-N1 regions are among t…
Radio loud Active Galactic Nuclei are episodic in nature, cycling through periods of activity and quiescence. In this work we investigate the duty cycle of the radio galaxy B2~0258+35, which was previously suggested to be a restarted radio galaxy based on its morphology. The radio source consists of a pair of kpc-scale jets embedded in two large-scale lobes (~240 kpc) with relaxed shape and very low surface brightness, which resemble remnants of a past AGN activity. We have combined new LOFAR data at 145 MHz and new SRT data at 6600 MHz with available WSRT data at 1400 MHz to investigate the s…
