| 1. |
- Morganti, R., et al.
(författare)
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Continuum surveys with LOFAR and synergy with future large surveys in the 1 – 2 GHz band
- 2009
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Ingår i: Proceedings of Science. - 1824-8039. ; 89
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Konferensbidrag (refereegranskat)abstract
- Radio astronomy is entering the era of large surveys. This paper describes the plans for wide surveys with the LOw Frequency ARray (LOFAR) and their synergy with large surveys at higher frequencies (in particular in the 1 – 2 GHz band) that will be possible using future facilities like Apertif or ASKAP. The LOFAR Survey Key Science Project aims at conducting large-sky surveys at 15, 30, 60, 120 and 200 MHz taking advantage of the wide instantaneous field of view and of the unprecedented sensitivity of this instrument.
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| 2. |
- Rottgering, H., et al.
(författare)
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LOFAR and APERTIF Surveys of the Radio Sky: Probing Shocks and Magnetic Fields in Galaxy Clusters
- 2011
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Ingår i: Journal of Astrophysics and Astronomy. - : Springer Science and Business Media LLC. - 0250-6335 .- 0973-7758. ; 32:4, s. 557-566
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Tidskriftsartikel (refereegranskat)abstract
- At very low frequencies, the new pan-European radio telescope LOFAR is opening the last unexplored window of the electromagnetic spectrum for astrophysical studies. The revolutionary APERTIF-phased arrays that are about to be installed on the Westerbork radio telescope (WSRT) will dramatically increase the survey speed for the WSRT. Combined surveys with these two facilities will deeply chart the northern sky over almost two decades in radio frequency from similar to 15 up to 1400 MHz. Here we briefly describe some of the capabilities of these new facilities and what radio surveys are planned to study fun-damental issues related to the formation and evolution of galaxies and clusters of galaxies. In the second part we briefly review some recent observational results directly showing that diffuse radio emission in clusters traces shocks due to cluster mergers. As these diffuse radio sources are relatively bright at low frequencies, LOFAR should be able to detect thousands of such sources up to the epoch of cluster formation. This will allow addressing many question about the origin and evolution of shocks and magnetic fields in clusters. At the end we briefly review some of the first and very preliminary LOFAR results on clusters.
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| 3. |
- Rottgering, H., et al.
(författare)
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The "Sausage" and "Toothbrush" clusters of galaxies and the prospects of LOFAR observations of clusters of galaxies
- 2013
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Ingår i: Astronomische Nachrichten. - : Wiley. - 0004-6337 .- 1521-3994. ; 334:4-5, s. 333-337
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Tidskriftsartikel (refereegranskat)abstract
- LOFAR, the Low Frequency Radio Array, is a new pan-European radio telescope that is almost fully operational. One of its main drivers is to make deep images of the low frequency radio sky. To be able to do this a number of challenges need to be addressed. These include the high data rates, removal of radio frequency interference, calibration of the beams and correcting for the corrupting influence of the ionosphere. One of the key science goals is to study merger shocks, particle acceleration mechanisms and the structure of magnetic fields in nearby and distant merging clusters. Recent studies with the GMRT and WSRT radio telescopes of the "Sausage" and the "Toothbrush" clusters have given a very good demonstration of the power of radio observations to study merging clusters. Recently we discovered that both clusters contain relic and halo sources, large diffuse regions of radio emission not associated with individual galaxies. The 2 Mpc northern relic in the Sausage cluster displays highly aligned magnetic fields and and exhibits a strong spectral index gradient that is a consequence of cooling of the synchrotron emitting particles in the post-shock region. We have argued that these observations provide strong evidence that shocks in merging clusters are capable of accelerating particles. For the Toothbrush cluster we observe a puzzling linear relic that extends over 2 Mpc. The proposed scenario is that a triple-merger can lead to such a structure. With LOFAR's sensitivity it will not only be possible to trace much weaker shocks, but also to study those shocks due to merging clusters up to redshifts of at least one. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 4. |
- Snellen, I., et al.
(författare)
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Future investigations of GPS and CSS radio sources with LOFAR
- 2009
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Ingår i: Astronomische Nachrichten. - : Wiley. - 0004-6337 .- 1521-3994. ; 330:2-3, s. 297-300
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Tidskriftsartikel (refereegranskat)abstract
- In the next few years, the Low Frequency Array (LOFAR) will open up one of the last astronomically unexplored wavelength regimes. While the LOFAR core is currently being erected in the Netherlands, its outer stations will cover a large part of Europe, resulting in an unprecedented angular resolution at > meter wavelengths. Next to many other exciting scientific endeavours, LOFAR will be the first instrument to probe the low frequency spectra of Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources. It will give new insights into their absorption processes, and probe associated extended emission (possibly linked to earlier epochs of activity) in these enigmatic class of young active galactic nuclei. Furthermore, LOFAR will be sensitive to possibly the most distant GPS and CSS sources, of which their spectral turnovers have redshifted down to the lowest observable radio frequencies.
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| 5. |
- Drouart, Guillaume, 1987, et al.
(författare)
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Rapidly growing black holes and host galaxies in the distant Universe from the Herschel Radio Galaxy Evolution Project
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
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Tidskriftsartikel (refereegranskat)abstract
- We present results from a comprehensive survey of 70 radio galaxies at redshifts 1 10(12) L-circle dot) or hyper-luminous (L-tot(IR) > 10(13) L-circle dot) infrared galaxies. We fit the infrared SEDs with a set of empirical templates which represent dust heated by a variety of starbursts (SB) and by an active galactic nucleus (AGN). We find that the SEDs of radio galaxies require the dust to be heated by both AGN and SB, but the luminosities of these two components are not strongly correlated. Assuming empirical relations and simple physical assumptions, we calculate the star formation rate (SFR), the black hole mass accretion rate ((M) over dot(BH)), and the black hole mass (M-BH) for each radio galaxy. We find that the host galaxies and their black holes are growing extremely rapidly, having SFR approximate to 100-5000 M-circle dot yr(-1) and. (M) over dot(BH) approximate to 1-100 M(circle dot)yr(-1). The mean specific SFRs (sSFR) of radio galaxies at z > 2 : 5 are higher than the sSFR of typical star forming galaxies over the same redshift range, but are similar or perhaps lower than the galaxy population for radio galaxies at z
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| 6. |
- Emonts, B., et al.
(författare)
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The Dragonfly Galaxy: II. ALMA unveils a triple merger and gas exchange in a hyper-luminous radio galaxy at z = 2
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 584
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Tidskriftsartikel (refereegranskat)abstract
- The Dragonfly Galaxy (MRC 0152-209), at redshift z similar to 2, is one of the most vigorously star-forming radio galaxies in the Universe. What triggered its activity? We present ALMA Cycle 2 observations of cold molecular CO(6 5) gas and dust, which reveal that this is likely a gas-rich triple merger. It consists of a close double nucleus (separation similar to 4 kpc) and a weak CO-emitter at similar to 10 kpc distance, all of which have counterparts in HST/NICMOS imagery. The hyper-luminous starburst and powerful radio-AGN were triggered at this precoalescent stage of the merger. The CO(6-5) traces dense molecular gas in the central region, and complements existing CO(1-0) data, which reveal more widespread tidal debris of cold gas. We also find similar to 10(10) M-circle dot of molecular gas with enhanced excitation at the highest velocities. At least 20-50% of this high-excitation, high-velocity gas shows kinematics that suggests it is being displaced and redistributed within the merger, although with line-of-sight velocities of vertical bar v vertical bar < 500 km s(-1), this gas will probably not escape the system. The processes that drive the redistribution of cold gas are likely related to either the gravitational interaction between two kpc-scale discs, or starburst/AGN-driven outflows. We estimate that the rate at which the molecular gas is redistributed is at least. M similar to 1200 +/- 500 M-circle dot yr(-1), and could perhaps even approach the star formation rate of similar to 3000 +/- 800 M-circle dot yr(-1). The fact that the gas depletion and gas redistribution timescales are similar implies that dynamical processes can be important in the evolution of massive high-z galaxies.
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