LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources
R. J. van Weeren, W. L. Williams, C. Tasse, H. J. A. Rottgering, D. A. Rafferty, S. van der Tol, G. Heald, G. J. White, A. Shulevski, P. Best, H. T. Intema, S. … 展开作者
R. J. van Weeren, W. L. Williams, C. Tasse, H. J. A. Rottgering, D. A. Rafferty, S. van der Tol, G. Heald, G. J. White, A. Shulevski, P. Best, H. T. Intema, S. Bhatnagar, W. Reich, M. Steinmetz, S. van Velzen, T. A. Ensslin, I. Prandoni, F. de Gasperin, M. Jamrozy, G. Brunetti, M. J. Jarvis, J. P. McKean, M. W. Wise, C. Ferrari, J. Harwood, J. B. R. Oonk, M. Hoeft, M. Kunert-Bajraszewska, C. Horellou, O. Wucknitz, A. Bonafede, N. R. Mohan, A. M. M. Scaife, H. -R. Klockner, I. M. van Bemmel, A. Merloni, K. T. Chyzy, D. Engels, H. Falcke, M. Pandey-Pommier, A. Alexov, J. Anderson, I. M. Avruch, R. Beck, M. E. Bell, M. J. Bentum, G. Bernardi, F. Breitling, J. Broderick, W. N. Brouw, M. Bruggen, H. R. Butcher, B. Ciardi, E. de Geus, M. de Vos, A. Deller, S. Duscha, J. Eisloffel, R. A. Fallows, W. Frieswijk, M. A. Garrett, J. Griessmeier, A. W. Gunst, J. P. Hamaker, T. E. Hassall, J. Horandel, A. van der Horst, M. Iacobelli, N. J. Jackson, E. Juette, V. I. Kondratiev, M. Kuniyoshi, P. Maat, G. Mann, D. McKay-Bukowski, M. Mevius, R. Morganti, H. Munk, A. R. Offringa, E. Orru, H. Paas, V. N. Pandey, G. Pietka, R. Pizzo, A. G. Polatidis, A. Renting, A. Rowlinson, D. Schwarz, M. Serylak, J. Sluman, O. Smirnov, B. W. Stappers, A. Stewart, J. Swinbank, M. Tagger, Y. Tang, S. Thoudam, C. Toribio, R. Vermeulen, C. Vocks, P. Zarka
We present LOFAR Low Band observations of the Bootes and 3C295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam$^{-1}$, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17 to 52 deg$^{2}$. From the observations we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and VLA 74 MHz differential source counts, scaling with a spectral index of $-0.7$. We find that a spectral index scaling of $-0.5$ is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens towards lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum ($α< -1.1$) radio sources, that could be associated with massive high redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogues and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the $ 0.7 \lesssim z \lesssim 2.5$ range.
We present an estimate of the optical luminosity function (OLF) of LOFAR radio-selected quasars (RSQs) at $1.4<z<5.0$ in the $9.3\:\textrm{deg}^{2}$ NOAO Deep Wide-field survey (NDWFS) of the Boötes field. The selection was based on optical/mid-ir photometry used to train three different machine learning (ML) algorithms. Objects taken as quasars by the ML algorithms are required to be detected at $5σ$ significance in deep radio maps to be classified as candidate quasars. The optical imaging came from the SDSS and the PS1 $3π$ survey; mid-ir photometry was taken from the SDWFS survey; and radio…
We present the first sub-mJy ($\approx0.7$ mJy beam$^{-1}$) survey to be completed below 100 MHz, which is over an order of magnitude deeper than previously achieved for widefield imaging of any field at these low frequencies. The high resolution ($15 \times 15$ arcsec) image of the Boötes field at 34-75 MHz is made from 56 hours of observation with the LOw Frequency ARray (LOFAR) Low Band Antenna (LBA) system. The observations and data reduction, including direction-dependent calibration, are described here. We present a radio source catalogue containing 1,948 sources detected over an area of…
Giant radio galaxies (GRGs) are radio galaxies that have projected linear extents of more than 700 kpc or 1 Mpc, depending on definition. We have carried out a careful visual inspection in search of GRGs of the Bootes LOFAR Deep Field (BLDF) image at 150 MHz. We identified 74 GRGs with a projected size larger than 0.7 Mpc of which 38 are larger than 1 Mpc. The resulting GRG sky density is about 2.8 (1.43) GRGs per square degree for GRGs with linear size larger than 0.7 (1) Mpc. We studied their radio properties and the accretion state of the host galaxies using deep optical and infrared survey…
Context. Radio halos are megaparsec-scale diffuse radio sources{ mostly} located at the centres of merging galaxy clusters. The common mechanism invoked to explain their origin is the re-acceleration of relativistic particles caused by large-scale turbulence. Aims. Current re-acceleration models predict that a significant number of halos at high redshift should be characterised by very steep spectra ($α<-1.5$) because of increasing inverse Compton energy losses. In this paper, we investigate the spectral index properties of a sample of nine clusters selected from the second Planck Sunyaev-Zel'…
Diffuse radio emission at the centre of galaxy clusters has been observed both in merging clusters on scales of Mpc, called giant radio haloes, and in relaxed systems with a cool-core on smaller scales, named mini haloes. Giant radio haloes and mini haloes are thought to be distinct classes of sources. However, recent observations have revealed the presence of diffuse radio emission on Mpc scales in clusters that do not show strong dynamical activity. RX J1720.1+2638 is a cool-core cluster, presenting both a bright central mini halo and a fainter diffuse, steep-spectrum emission extending beyo…
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…
In this Letter, we report the discovery of a radio halo in the high-redshift galaxy cluster PSZ2 G099.86+58.45 ($z=0.616$) with the LOw Frequency ARray (LOFAR) at 120-168 MHz. This is one of the most distant radio halos discovered so far. The diffuse emission extends over $\sim$ 1 Mpc and has a morphology similar to that of the X-ray emission as revealed by XMM-Newton data. The halo is very faint at higher frequencies and is barely detected by follow-up 1-2 GHz Karl G.~Jansky Very Large Array (JVLA) observations, which enable us to constrain the radio spectral index to be $α\leq 1.5-1.6$, i.e.…
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…
Centrally located diffuse radio emission has been observed in both merging and non-merging galaxy clusters. Depending on their morphology and size, we distinguish between giant radio haloes, which occur predominantly in merging clusters, and mini haloes, which are found in non-merging, cool-core clusters. Low-frequency sensitive observations are required to assess whether the emission discovered in these few cases is common in galaxy clusters or not. With this aim, we carried out a campaign of observations with the LOw Frequency ARay (LOFAR) in the frequency range 120 - 168 MHz of nine massive…
The sub-arcsecond ILT view of the Boötes Deep Field: A link between low-frequency kiloparsec radio morphology and AGN driven ionised outflows
Durham University（杜伦大学）；CSIRO（澳大利亚联邦科学与工业研究组织）；Newcastle University（纽卡斯尔大学）；Leiden University（莱顿大学）；ASTRON, The Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；University of Bristol（布里斯托大学）；INAF-IRA（意大利国家天体物理研究所罗马分所）
We present LOFAR data from 110--180~MHz of the merging galaxy cluster Abell 1682, alongside archival optical, radio and X-ray data. Our 6 arc-second resolution images at low frequencies reveal new structures associated with numerous radio galaxies in the cluster. At 20 arc-second resolution we see diffuse emission throughout the cluster over hundreds of kpc, indicating particle acceleration mechanisms are in play as a result of the cluster merger event and powerful active galactic nuclei. We show that a significant part of the cluster emission is from an old radio galaxy with very steep spectr…
Investigating the radio emission in the Perseus cluster with LOFAR sub-80 MHz LBA
INAF – Istituto di Radioastromia（意大利国家天体物理研究所射电天文学研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Université Laval（拉瓦尔大学）；Dunlap Institute for Astronomy and Astrophysics, University of Toronto（多伦多大学邓普天文学与天体物理学研究所）；Università di Bologna（博洛尼亚大学）
We study for the first time the low-frequency ($\sim$150 MHz) radio brightness distribution of Arp~299 at subarcsecond resolution, tracing in both compact and extended emission regions the local spectral energy distribution (SED) in order to characterize the dominant emission and absorption processes. We analysed the spatially resolved emission of Arp 299 revealed by 150 MHz international baseline Low-Frequency Array (LOFAR) and 1.4, 5.0, and 8.4 GHz Very Large Array (VLA) observations. We present the first subarcsecond (0.4"$\sim$100~pc) image of the whole Arp~299 system at 150~MHz. The high …
The radio source at the center of the galaxy cluster Abell 2626, also known as the Kite, stands out for its unique morphology composed of four, symmetric arcs. Previous studies have probed the properties of this source at different frequencies and its interplay with the surrounding thermal plasma, but the puzzle of its origin is still unsolved. We use new LOw Frequency ARray (LOFAR) observation from the LOFAR Two-meter Sky Survey at 144 MHz to investigate the origin of the Kite.} We present a detailed analysis of the new radio data which we combined with archival radio and X-ray observations. …
Winged radio sources are a small sub-class of extragalactic radio sources which display a pair of low surface brightness radio lobes, known as `wings' aligned at a certain angle with the primary jets. Depending on the location of wings, these galaxies look like X or Z and are known as X-shaped Radio Galaxy (XRG) or Z-shaped Radio Galaxy (ZRG). We report the identification of 33 winged radio sources from the LOFAR Two-metre Sky Survey First Data Release (LoTSS DR1) out of which 21 sources are identified as X-shaped radio galaxies and 12 as Z-shaped radio galaxies. Optical counterparts are ident…
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 …
Single- and double-headed odd radio circles in the LOFAR surveys
Hamburger Sternwarte, Universität Hamburg（汉堡天文台，汉堡大学）；Thüringer Landessternwarte（图林根州立天文台）；Universidad de Guanajuato（瓜纳华托大学）；Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München（慕尼黑大学物理学院大学天文台）；Department of Astronomy and Astrophysics, The University of Chicago（芝加哥大学天体物理学系）；ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所 ASTRON）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内克天文研究所）；Department of Physics, Astronomy and Mathematics, University of Hertfordshire（赫特福德郡大学物理、天文与数学系）；INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）
We have examined the giant radio galaxy 3C~236 using LOFAR at 143 MHz down to an angular resolution of 7", in combination with observations at higher frequencies. We have used the low frequency data to derive spectral index maps with the highest resolution yet at these low frequencies. We confirm a previous detection of an inner hotspot in the north-west lobe and for the first time observe that the south-east lobe hotspot is in fact a triple hotspot, which may point to an intermittent source activity. Also, the spectral index map of 3C 236 shows that the spectral steepening at the inner region…
MS 0735.6+7421 is a galaxy cluster which hosts a central radio galaxy with a very steep spectrum, produced by one of the most powerful known jetted active galactic nuclei (AGN). The radio plasma, ejected at nearly light speed from the central AGN, have displaced the intra-cluster medium, leaving two pairs of cavities observable in the X-ray, associated to two different outbursts, and have distributed energy to the surrounding medium. In this work we have performed for the first time a detailed, high-resolution spectral study of the source at radio frequencies and investigated its duty cycle to…
Radio halos are extended ($\sim{\rm Mpc}$), steep-spectrum sources found in the central region of dynamically disturbed clusters of galaxies. Only a handful of radio halos have been reported to reside in galaxy clusters with a mass $M_{500}\lesssim5\times10^{14}\,M_\odot$. In this paper we present a LOFAR 144 MHz detection of a radio halo in the galaxy cluster Abell 990 with a mass of $M_{500}=(4.9\pm0.3)\times10^{14}\,M_\odot$. The halo has a projected size of $\sim$700$\,{\rm kpc}$ and a flux density of $20.2\pm2.2\,{\rm mJy}$ or a radio power of $1.2\pm0.1\times10^{24}\,{\rm W\,Hz}^{-1}$ at…
We report new observations of "Hanny's Voorwerp" (hereafter HV) taken from the second data release of the LOFAR Two-metre Sky Survey (LoTSS). HV is a highly-ionised region in the environs of the galaxy IC2497, first discovered by the Galaxy Zoo project. The new 150MHz observations are considered in the context of existing multi-frequency radio data and archival narrow-band imaging from the Hubble Space Telescope, centred on the [Oiii] emission line. The combined sensitivity and spatial resolution of the LoTSS data -- which far exceed what was previously available at radio frequencies -- reveal…
Context. Magnetic fields are key to understand galaxy evolution, regulating stellar feedback and star formation in galaxies. Aims. We probe the origin of magnetic fields in late-type galaxies, measuring magnetic field strengths, exploring whether magnetic fields are only passive constituents of the interstellar medium, or whether they are active constituents being part of the local energy equilibrium. Methods. We measure equipartition magnetic field strengths in 39 galaxies from LoTSS-DR2 using LOFAR observations at 144 MHz with 6 arcsec angular resolution which (0.1-0.7 kpc). For a subset of …
In recent years, the level of the extragalactic radio background has become a point of considerable interest, with some lines of argument pointing to an entirely new cosmological synchrotron background. The contribution of the known discrete source population to the sky temperature is key to this discussion. Because of the steep spectral index of the excess over the cosmic microwave background, it is best studied at low frequencies where the signal is strongest. The Low-Frequency Array (LOFAR) wide and deep sky surveys give us the best constraints yet on the contribution of discrete extragalac…
Our goal is to study the termination of an AGN jet in the young universe and to deduce physical parameters of the jet and the intergalactic medium. We use LOFAR to image the long-wavelength radio emission of the high-redshift blazar S5 0836+710 on arcsecond scales between 120 MHz and 160 MHz. The LOFAR image shows a compact unresolved core and a resolved emission region about 1.5 arcsec to the southwest of the radio core. This structure is in general agreement with previous higher-frequency radio observations with MERLIN and the VLA. The southern component shows a moderately steep spectrum wit…
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…
3C295 is a bright, compact steep spectrum source with a well-studied integrated radio spectral energy distribution (SED) from 132 MHz to 15 GHz. However, spatially resolved spectral studies have been limited due to a lack of high resolution images at low radio frequencies. These frequencies are crucial for measuring absorption processes, and anchoring the overall spectral modelling of the radio SED. In this paper, we use International LOFAR (LOw-Frequency ARray) Telescope (ILT) observations of 3C295 to study its spatially resolved spectral properties with sub-arcsecond resolution at 132 MHz. C…
Radio emission in the brightest radio quasars can be attributed to processes inherent to SMBHs, while the origins of the radio fluxes in quasars without radio detections is still uncertain. We investigate the radio-infrared continuum of LOFAR radio-detected quasars (RDQs) and LOFAR radio-undetected quasars (RUQs) in the $9.3\:\textrm{deg}^{2}$ NDWFS-Boötes field; RUQs are quasars that are individually undetected at $\geq5σ$ by LOFAR. We used a median image stacking procedure. This was done in the frequencies of 150 MHz, 325 MHz, 1.4 GHz and 3.0 GHz, and in nine infrared (ir) bands between $8$ …
Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. II. Properties of filaments using multi-frequency radio data
Università di Bologna（博洛尼亚大学）；INAF - Istituto di Radioastronomia di Bologna（意大利国家天体物理研究所波洛尼亚射电天文台）；Leiden University（莱顿大学）；ASTRON, The Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；University of Minnesota（明尼苏达大学）；Universität Hamburg（汉堡大学）；Durham University（杜伦大学）
