Abstract This talk describes a proposed transformation of LOFAR, the world’s largest, most sensitive high-resolution radio telescope that operates at low frequencies (<300 MHz), into a ...multidisciplinary intercontinental facility that will be a unique engine for capacity building and development throughout Europe, North Africa, the Middle East and West Asia. As an astronomical array, GLORAY would be the “Hubble Space Telescope” of low-frequency radio astronomy, having a resolution more than 50 times better than any other presently planned low-frequency facility, including SKA-LOW. The mutually interdependent network of LOFAR antenna stations that presently stretch from Ireland to Latvia would be extended to cover North Africa, the Middle East and West Asia and converted into “innovation hubs”. These would form an intercontinental network for pure research, applied research, capacity building, education and science diplomacy within and between the participating countries.
Abstract Using the Karl G. Jansky Very Large Array, we have detected absorption lines due to carbon monoxide, CO( J = 0 → 1), and the cyano radical, CN( N = 0 → 1), associated with radio galaxy B2 ...0902+34 at redshift z = 3.4. The detection of millimeter-band absorption observed 1.5 Gyr after the Big Bang facilitates studying molecular clouds down to gas masses inaccessible to emission-line observations. The CO absorption in B2 0902+34 has a peak optical depth of τ ≥ 8.6% and consists of two components, one of which has the same redshift as previously detected 21 cm absorption of neutral hydrogen (H i ) gas. Each CO component traces an integrated H 2 column density of N H 2 ≳ 3 × 10 20 cm −2 . CN absorption is detected for both CO components, as well as for a blueshifted component not detected in CO, with CO/CN line ratios ranging from ≲0.4 to 2.4. We discuss the scenario that the absorption components originate from collections of small and dense molecular clouds that are embedded in a region with more diffuse gas and high turbulence, possibly within the influence of the central active galactic nucleus or a starburst region. The degree of reddening in B2 0902+34, with rest-frame color B − K ∼ 4.2, is lower than the very red colors ( B − K > 6) found among other known redshifted CO absorption systems at z < 1. Nevertheless, when including the many nondetections from the literature, a potential correlation between the absorption-line strength and B − K color is evident, giving weight to the argument that the red colors of CO absorbers are due to a high dust content.
Abstract
Powerful radio sources associated with supermassive black holes are among the most luminous objects in the universe, and are frequently recognized both as cosmological probes and active ...constituents in the evolution of galaxies. We present alignments between radio jets and cold molecular gas in the environment of distant radio galaxies, and show that the brightness of the radio synchrotron source can be enhanced by its interplay with the molecular gas. Our work is based on CO
J
> 1 observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of three radio galaxies with redshifts in the range 1.4 <
z
< 2.1, namely MRC 0114-211 (
z
= 1.41), MRC 0156-252 (
z
= 2.02), and MRC 2048-272 (
z
= 2.05). These ALMA observations support previous work that found molecular gas out to 50 kpc in the circumgalactic environment, based on a CO(1–0) survey performed with the Australia Telescope Compact Array. The CO emission is found along the radio axes but beyond the main radio lobes. When compared to a large sample of high-
z
radio galaxies from the literature, we find that the presence of this cold molecular medium correlates with an increased flux-density ratio of the main versus counter-lobe. This suggest that the radio lobe brightens when encountering cold molecular gas in the environment. While part of the molecular gas is likely related to the interstellar medium from either the host or a companion galaxy, a significant fraction of the molecular gas in these systems shows very low excitation, with
r
2−1/1−0
and
r
3−2/1−0
values ≲0.2. This could be part of the circumgalactic medium.
ABSTRACT
Feedback from low-excitation radio galaxies (LERGs) plays a key role in the lifecycle of massive galaxies in the local Universe; their evolution, and the impact of these active galactic ...nuclei on early galaxy evolution, however, remain poorly understood. We use a sample of 10 481 LERGs from the first data release of the LOFAR two-metre Sky Survey Deep Fields, covering ∼25 deg2, to present the first measurement of the evolution of the radio luminosity function (LF) of LERGs out to z ∼ 2.5; this shows relatively mild evolution. We split the LERGs into those hosted by quiescent and star-forming galaxies, finding a new dominant population of LERGs hosted by star-forming galaxies at high redshifts. The incidence of LERGs in quiescent galaxies shows a steep dependence on stellar mass out to z ∼ 1.5, consistent with local Universe measurements of accretion occurring from cooling of hot gas haloes. The quiescent-LERGs dominate the LFs at z < 1, showing a strong decline in space density with redshift, tracing that of the available host galaxies, while there is an increase in the characteristic luminosity. The star-forming LERG LF increases with redshift, such that this population dominates the space densities at most radio-luminosities by z ∼ 1. The incidence of LERGs in star-forming galaxies shows a much weaker stellar-mass dependence, and increases with redshift, suggesting a different fuelling mechanism compared to their quiescent counterparts, potentially associated with the cold gas supply present in the star-forming galaxies.
Active galactic nuclei show episodic activity, which can be 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 is a powerful way to explore the life of radio galaxies. This requires resolved spectral index measurements over a broad frequency range including low frequencies. We present such a study for the radio galaxy 3C 293, which has long been thought to be a restarted galaxy on the basis of its radio morphology. 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 Interferometer Network and Very Large Array archival data at frequencies up to 8.4 GHz that have a comparable resolution. In the inner lobes (~2 kpc), we detect the presence of a spectral turnover that peaks at ~225 MHz and is most likely caused by free-free absorption from the rich surrounding medium. We confirm that these inner lobes are part of a jet-dominated young radio source (spectral age ≲0.17 Myr), which is strongly interacting with the rich interstellar medium of the host galaxy. The diffuse emission surrounding these lobes on scales of up to ~4.5 kpc shows steeper spectral indices (Δ
α
~ 0.2–0.5, S ∝
ν
−
α
) and a spectral age of ≲0.27 Myr. The outer lobes (extending up to ~100 kpc) have a spectral index of
α
~ 0.6–0.8 from 144–4850 MHz with a remarkably uniform spatial distribution and only mild spectral curvature (Δ
α
≲ 0.2). We propose that intermittent fuelling and jet flow disruptions are powering the mechanisms that keep the spectral index in the outer lobes from steepening and maintain the spatial uniformity of the spectral index. Overall, it appears that 3C 293 has gone through multiple (two to three) epochs of activity. This study adds 3C 293 to the new sub-group of restarted galaxies with short interruption time periods. This is the first time a spatially resolved study has been performed that simultaneously studies a young source as well as the older outer lobes at such low frequencies. This illustrates the potential of the International LOFAR telescope to expand such studies to a larger sample of radio galaxies.
The growth of galaxies in the early Universe is driven by accretion of circum- and intergalactic gas. Simulations have predicted that steady streams of cold gas penetrate the dark matter halos of ...galaxies and provide the raw material necessary to sustain star formation. We report a filamentary stream of gas that extends for 100 kiloparsecs and connects to the massive radio galaxy 4C 41.17. We detected the stream using submillimeter observations of the
to
emission from the C i line of atomic carbon, a tracer of neutral atomic or molecular hydrogen gas. The galaxy contains a central gas reservoir that is fueling a vigorous starburst. Our results show that the raw material for star formation can be present in cosmic streams outside galaxies.
Active galactic nuclei show episodic activity, which can be evident in galaxies that exhibit restarted radio jets. These restarted jets can interact with their environment, leaving signatures in the ...radio spectral energy distribution. Tracing these signatures requires resolved spectral index measurements over a broad frequency range. We present such a study for the radio galaxy 3C 293. Using the International Low Frequency Array Telescope (ILT), we probe spatial scales as fine as ∼0.2″ at 144 MHz and to constrain the spectrum, we combine these data with Multi‐Element Radio Linked Interferometer Network and Very Large Array archival data at frequencies up to 8.4 GHz. In the inner lobes (∼2 kpc), we detect the presence of a compact steep spectrum (CSS) source with a spectral turnover at ∼225 MHz, caused by free‐free absorption from the rich surrounding medium. We find evidence of interaction of the lobes with the rich interstellar medium of the host galaxy. The outer lobes (extending up to ∼100 kpc) have a remarkably uniform spatial distribution of spectral index and only mild spectral curvature (of ∼0.2). Overall, it appears that 3C 293 has gone through multiple (two to three) epochs of activity. This study adds 3C 293 to the new sub‐group of restarted galaxies with short interruption time periods (≲1 Myr). This is the first time a spatially resolved study has been performed that simultaneously studies a young CSS source as well as the older outer lobes at such low frequencies.
We present newly acquired images of the near-infrared counterpart of 3CR radio sources. All the sources were selected to have a redshift of less than 0.3 to allow us to obtain the highest spatial ...resolution. The observations were carried out as a snapshot program using the Near-Infrared Camera and Multiobject Spectrograph (NICMOS) on-board the Hubble Space Telescope (HST). In this paper we describe 69 radio galaxies observed for the first time with NICMOS during HST cycle 13. All the objects presented here are elliptical galaxies. However, each of them has unique characteristics such as close companions, dust lanes, unresolved nuclei, arclike features, globular clusters, and jets clearly visible from the images or with basic galaxy subtraction.
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