Radio Galaxy Zoo: The Distortion of Radio Galaxies by Galaxy Clusters

We study the impact of cluster environment on the morphology of a sample of 4304 extended radio galaxies from Radio Galaxy Zoo. A total of 87% of the sample lies within a projected 15 Mpc of an optically identified cluster. Brightest cluster galaxies (BCGs) are more likely than other cluster members to be radio sources, and are also moderately bent. The surface density as a function of separation from cluster center of non-BCG radio galaxies follows a power law with index $-1.10\pm 0.03$ out to $10~r_{500}$ ($\sim 7~$Mpc), which is steeper than the corresponding distribution for optically selected galaxies. Non-BCG radio galaxies are statistically more bent the closer they are to the cluster center. Within the inner $1.5~r_{500}$ ($\sim 1~$Mpc) of a cluster, non-BCG radio galaxies are statistically more bent in high-mass clusters than in low-mass clusters. Together, we find that non-BCG sources are statistically more bent in environments that exert greater ram pressure. We use the orientation of bent radio galaxies as an indicator of galaxy orbits and find that they are preferentially in radial orbits. Away from clusters, there is a large population of bent radio galaxies, limiting their use as cluster locators; however, they are still located within statistically overdense regions. We investigate the asymmetry in the tail length of sources that have their tails aligned along the radius vector from the cluster center, and find that the length of the inward-pointing tail is weakly suppressed for sources close to the center of the cluster.Comment: 23 pages, 17 figures, 2 tables. Supplemental data files available in The Astronomical Journal or contact autho

The GLEAMing of the first supermassive black holes

International audienceWe present the results of a new selection technique to identify powerful ($L_500 MHz 10^{27} WHz^{-1}$) radio galaxies towards the end of the Epoch of Reionisation. Our method is based on the selection of bright radio sources showing radio spectral curvature at the lowest frequency (${∼}100 MHz$) combined with the traditional faintness in K-band for high-redshift galaxies. This technique is only possible, thanks to the Galactic and Extra-galactic All-sky Murchison Wide-field Array survey which provides us with 20 flux measurements across the 70-$230 MHz$ range. For this pilot project, we focus on the GAMA 09 field to demonstrate our technique. We present the results of our follow-up campaign with the Very Large Telescope, Australian Telescope Compact Array, and the Atacama Large Millimetre Array to locate the host galaxy and to determine its redshift. Of our four candidate high-redshift sources, we find two powerful radio galaxies in the $15.5$ has a high 25-50% success rate

Remnant radio galaxies discovered in a multi-frequency survey

The remnant phase of a radio galaxy begins when the jets launched from an active galactic nucleus are switched off. To study the fraction of radio galaxies in a remnant phase, we take advantage of a 8.31 deg2 subregion of the GAMA 23 field which comprises of surveys covering the frequency range 0.1-9 GHz. We present a sample of 104 radio galaxies compiled from observations conducted by the MurchisonWidefield Array (216 MHz), the Australia Square Kilometer Array Pathfinder (887 MHz), and the Australia Telescope Compact Array (5.5 GHz). We adopt an ‘absent radio core’ criterion to identify 10 radio galaxies showing no evidence for an active nucleus. We classify these as new candidate remnant radio galaxies. Seven of these objects still display compact emitting regions within the lobes at 5.5 GHz; at this frequency the emission is short-lived, implying a recent jet switch off. On the other hand, only three show evidence of aged lobe plasma by the presence of an ultra-steep-spectrum (α <-1.2) and a diffuse, low surface brightness radio morphology. The predominant fraction of young remnants is consistent with a rapid fading during the remnant phase.Within our sample of radio galaxies, our observations constrain the remnant fraction to 4% ≤ frem ≤ 10%; the lower limit comes from the limiting case in which all remnant candidates with hotspots are simply active radio galaxies with faint, undetected radio cores. Finally, we model the synchrotron spectrum arising from a hotspot to show they can persist for 5-10 Myr at 5.5 GHz after the jets switch of - radio emission arising from such hotspots can therefore be expected in an appreciable fraction of genuine remnants

The Impact of Historical Geography and Agricultural Land Development Processes on Wetland Restoration Methods Used to Create Ecological Networks: A Comparison of Japan and the Netherlands

In the Osaka area in the 1880s, rice was grown mostly in dry fields in upland areas, and a few paddy fields were situated on the natural wet landforms along the major rivers and streams on the Osaka Plain. As the area developed, dry fields became irrigated, and the lowland fields were filled and converted to urban land uses. For the Osaka city region, developed in this historical context, an ecological network has been proposed by the national government in 2006. The proposal was partially influenced by ecological network planning in the Netherlands, and it focuses on spatial patterns and wetland restoration measures at a limited number of sites. However, its historical geography is not taken into consideration. Therefore we examined historical land-use changes in the Osaka area and then compared restoration projects in both countries. On the one hand, we found some similarities in wetland restoration processes and measures at unused industrial sites in reclaimed coastal areas in Japan (the Osaka Nankou Bird Sanctuary) and the Netherlands (the Oostvaardersplassen). There are, on the other hand, notable differences in appropriate wetland restoration measures in farmland areas. Some potential wetland restoration candidates in Japan require either winter flooding or the resumption of labor-intensive agricultural practices in abandoned paddy fields, because many of these sites were naturally dry before the introduction of irrigation. In the Netherlands (e.g., at Tiengemeten), however, this was not a problem because areas are being converted from drained fields to natural wetlands. To conclude, regional considerations are therefore important when ecological networks are planned, and the perspective of historical geography is essential when networks are planned with wetland restoration as a core element.UrbanismArchitecture and The Built Environmen