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1. Building LOFAR as a Service

Author

Mechev, A.P., Oonk, J.B.R., Plaat, A., Danezi, A., Shimwell, T.W., Teuben, P.J., Pound, M.W., Thomas, B.A., and Warner, E.M.

Subjects
ComputerApplications_COMPUTERSINOTHERSYSTEMS
Abstract

The LOFAR radio telescope is a low-frequency aperture synthesis radio telescope with headquarters in the Netherlands and stations across Europe. As a general purpose telescope, LOFAR produces petabytes of data each year serving a wide range of science cases. The data volumes produced are difficult or impossible to process on a single machine or even a small cluster at a scientific institute. We provide a layout for serving LOFAR processing to the astronomical community by providing access to LOFAR pipelines accelerated on a high throughput platform. We build this on our previous success with parallelizing the LOFAR Surveys pipeline and with creating automated LOFAR workflows on a distributed architecture. The LOFAR As A Service platform will serve the LOFAR Key Science Projects (KSPs), specifically the LOFAR Surveys KSP, which aims to provide science ready products to the scientific community. Additionally, this system will provide a robust method to re-process LOFAR data with a single click.

Published
2019

2. LOFAR 144-MHz follow-up observations of GW170817

Author

Broderick, J.W., Shimwell, T.W., Gourdji, K., Rowlinson, A., Nissanke, S., Hotokezaka, K., Jonker, P.G., Tasse, C., Hardcastle, M.J., Oonk, J.B.R., Fender, R.P., Wijers, R.A.M.J., Shulevski, A., Stewart, A.J., ter Veen, S., Moss, V.A., van der Wiel, M.H.D., Nichols, D., Piette, A., Bell, M.E., Carbone, D., Corbel, S., Eislöffel, J., Grießmeier, J.-M., Keane, E.F., Law, C.J., Muñoz-Darias, T., Pietka, M., Serylak, M, van der Horst, A.J., van Leeuwen, J., Wijnands, R., Zarka, P., Anderson, J.M., Bentum, M.J., Blaauw, R., Brouw, W.N., Brüggen, M., Ciardi, B., de Vos, M., Duscha, S., Fallows, R.A., Franzen, T.M.O., Garrett, M.A., Gunst, A.W., Hoeft, M., Hörandel, J.R., Iacobelli, M., Jütte, E., Koopmans, L.V.E., Krankowski, A., Maat, P., Mann, G., Mulder, H., Paas, H., Pandey-Pommier, M., Pekal, R., Reich, W., Röttgering, H.J.A., Schwarz, D.J., Smirnov, O., Soida, M., Toribio, M.C., van Haarlem, M.P., van Weeren, R.J., Vocks, C., Wucknitz, O., Zucca, P., Broderick, J.W., Shimwell, T.W., Gourdji, K., Rowlinson, A., Nissanke, S., Hotokezaka, K., Jonker, P.G., Tasse, C., Hardcastle, M.J., Oonk, J.B.R., Fender, R.P., Wijers, R.A.M.J., Shulevski, A., Stewart, A.J., ter Veen, S., Moss, V.A., van der Wiel, M.H.D., Nichols, D., Piette, A., Bell, M.E., Carbone, D., Corbel, S., Eislöffel, J., Grießmeier, J.-M., Keane, E.F., Law, C.J., Muñoz-Darias, T., Pietka, M., Serylak, M, van der Horst, A.J., van Leeuwen, J., Wijnands, R., Zarka, P., Anderson, J.M., Bentum, M.J., Blaauw, R., Brouw, W.N., Brüggen, M., Ciardi, B., de Vos, M., Duscha, S., Fallows, R.A., Franzen, T.M.O., Garrett, M.A., Gunst, A.W., Hoeft, M., Hörandel, J.R., Iacobelli, M., Jütte, E., Koopmans, L.V.E., Krankowski, A., Maat, P., Mann, G., Mulder, H., Paas, H., Pandey-Pommier, M., Pekal, R., Reich, W., Röttgering, H.J.A., Schwarz, D.J., Smirnov, O., Soida, M., Toribio, M.C., van Haarlem, M.P., van Weeren, R.J., Vocks, C., Wucknitz, O., and Zucca, P.

Abstract

Contains fulltext : 219289.pdf (publisher's version ) (Open Access)

Published
2020

3. The LOFAR Two-metre Sky Survey: II. First data release

Author

Shimwell, T.W., Tasse, C., Hardcastle, M.J., Mechev, A.P., Williams, W.L., Best, P.N., Röttgering, H.J.A., Callingham, J.R., Dijkema, T.J., De Gasperin, F., Hoang, D.N., Hugo, B., Mirmont, M., Oonk, J.B.R., Prandoni, I., Rafferty, D., Sabater, J., Smirnov, O., Van Weeren, R.J., White, G.J., Atemkeng, M., Bester, L., Bonnassieux, E., Brüggen, M., Brunetti, G., Chy, K.T., Cochrane, R., Conway, J.E., Croston, J.H., Danezi, A., Duncan, K., Haverkorn, M., Heald, G.H., Iacobelli, M., Intema, Huib, Jackson, N., Jamrozy, M., Jarvis, M.J., Lakhoo, R., Mevius, M., Miley, G.K., Morabito, L., Morganti, R., Nisbet, D., Orrú, E., Perkins, S., Pizzo, R.F., Schrijvers, C., Smith, D.J.B., Vermeulen, R., Wise, M.W., Alegre, L., Bacon, D.J., Van Bemmel, I.M., Beswick, R.J., Bonafede, A., Botteon, A., Bourke, S., Brienza, M., Calistro Rivera, G., Cassano, R., Clarke, A.O., Conselice, C.J., Dettmar, R.J., Drabent, A., Dumba, C., Emig, K.L., Enßlin, T.A., Ferrari, C., Garrett, M.A., Génova-Santos, R.T., Goyal, A., Gürkan, G., Hale, C., Harwood, J.J., Heesen, V., Hoeft, M., Horellou, C., Jackson, Carole, Kokotanekov, G., Kondapally, R., Kunert-Bajraszewska, M., Mahatma, V., Mahony, E.K., Mandal, S., McKean, J.P., Merloni, A., Mingo, B., Miskolczi, A., Mooney, S., Nikiel-Wroczyński, B., O'Sullivan, S.P., Quinn, J., Reich, W., Roskowiński, C., Rowlinson, A., Savini, F., Saxena, A., Schwarz, D.J., Shulevski, A., Shimwell, T.W., Tasse, C., Hardcastle, M.J., Mechev, A.P., Williams, W.L., Best, P.N., Röttgering, H.J.A., Callingham, J.R., Dijkema, T.J., De Gasperin, F., Hoang, D.N., Hugo, B., Mirmont, M., Oonk, J.B.R., Prandoni, I., Rafferty, D., Sabater, J., Smirnov, O., Van Weeren, R.J., White, G.J., Atemkeng, M., Bester, L., Bonnassieux, E., Brüggen, M., Brunetti, G., Chy, K.T., Cochrane, R., Conway, J.E., Croston, J.H., Danezi, A., Duncan, K., Haverkorn, M., Heald, G.H., Iacobelli, M., Intema, Huib, Jackson, N., Jamrozy, M., Jarvis, M.J., Lakhoo, R., Mevius, M., Miley, G.K., Morabito, L., Morganti, R., Nisbet, D., Orrú, E., Perkins, S., Pizzo, R.F., Schrijvers, C., Smith, D.J.B., Vermeulen, R., Wise, M.W., Alegre, L., Bacon, D.J., Van Bemmel, I.M., Beswick, R.J., Bonafede, A., Botteon, A., Bourke, S., Brienza, M., Calistro Rivera, G., Cassano, R., Clarke, A.O., Conselice, C.J., Dettmar, R.J., Drabent, A., Dumba, C., Emig, K.L., Enßlin, T.A., Ferrari, C., Garrett, M.A., Génova-Santos, R.T., Goyal, A., Gürkan, G., Hale, C., Harwood, J.J., Heesen, V., Hoeft, M., Horellou, C., Jackson, Carole, Kokotanekov, G., Kondapally, R., Kunert-Bajraszewska, M., Mahatma, V., Mahony, E.K., Mandal, S., McKean, J.P., Merloni, A., Mingo, B., Miskolczi, A., Mooney, S., Nikiel-Wroczyński, B., O'Sullivan, S.P., Quinn, J., Reich, W., Roskowiński, C., Rowlinson, A., Savini, F., Saxena, A., Schwarz, D.J., and Shulevski, A.

Published
2019

6. Low-frequency radio absorption in Cassiopeia A

Author

Arias, M., Vink, J., Gasperin, F. de, Salas, P., Oonk, J.B.R., Weeren, R.J. van, Horandel, J., Zarka, P., Zucca, P., Arias, M., Vink, J., Gasperin, F. de, Salas, P., Oonk, J.B.R., Weeren, R.J. van, Horandel, J., Zarka, P., and Zucca, P.

Abstract

Contains fulltext : 191392.pdf (preprint version ) (Open Access)

Published
2018

7. ALMA reveals optically thin, highly excited CO gas in the jet-driven winds of the galaxy IC 5063

Author

Dasyra, K.M. Combes, F. Oosterloo, T. Oonk, J.B.R. Morganti, R. Salomé, P. Vlahakis, N.

Abstract

Using CO (4-3) and (2-1) Atacama Large Millimeter Array (ALMA) data, we prove that the molecular gas in the jet-driven winds of the galaxy IC 5063 is more highly excited than the rest of the molecular gas in the disk of the same galaxy. On average, the CO(4 - 3) /CO(2 - 1) flux ratio is 1 for the disk and 5 for the jet accelerated or impacted gas. Spatially-resolved maps reveal that in regions associated with winds, the CO(4 - 3) /CO(2 - 1) flux ratio significantly exceeds the upper limit of 4 for optically thick gas. It frequently takes values between 5 and 11, and it occasionally further approaches the upper limit of 16 for optically thin gas. Excitation temperatures of 30-100 K are common for the molecules in these regions. If all of the outflowing molecular gas is optically thin, at 30-50 K, then its mass is 2 × 106 M. This lower mass limit is an order of magnitude below the mass derived from the CO(2 - 1) flux in the case of optically thick gas. Molecular winds can thus be less massive, but more easily detectable at high z than they were previously thought to be. © ESO, 2016.

Published
2016

8. Preparing for science run 1 of MiniGrail

Author

de Waard, A., Bassan, M., Benzaim, Y., Fafone, V., Flokstra, Jakob, Frossati, G., Gottardi, L., Herbschleb, C.T., Karbalai-Sadegh, A., Kuit, K.H., van der Mark, H., Minenkov, Y., Oonk, J.B.R., Pallottino, G.V., Pleikies, J., Rocchi, A., Usenko, O., Visco, M., and Faculty of Science and Technology

Subjects
Physics, Millisecond, IR-61503, Physics and Astronomy (miscellaneous), business.industry, Matched filter, Amplifier, Detector, Settore FIS/01 - Fisica Sperimentale, Electrical engineering, Cosmic ray, law.invention, Data acquisition, Transducer, Settore FIS/05 - Astronomia e Astrofisica, law, METIS-234890, business, Transformer
Abstract

We report on the eighth cryogenic run of MiniGRAIL, which is planned to be the first science run. Three new capacitive transducers were mounted on the sphere, all coupled to superconducting transformers and a double-stage SQUID amplifier. All SQUID modules had a noise level between 1 and 2 μΦ0 Hz−1/2 at 4 K in separate test runs. The detector was upgraded with a complete data acquisition and data storage system, and a data analysis program for millisecond burst signals was written using a matched filter. Two cosmic-ray detectors were built and installed on the roof above MiniGRAIL as a veto for cosmic rays. A test run was done, but failed because of bad electrical isolation of the transducer electrode at low temperatures. A new cool-down is currently going on. With an already obtained sphere temperature of 65 mK and a SQUID noise of 100, the expected sensitivity should be 4 × 10−22 Hz−1/2.

Published
2006
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9. Cool gas in brightest cluster galaxies

Author

Oonk, J.B.R., Jaffe, W., and Leiden University

Subjects
Infrared ISM, Galaxy Clusters, Astrophysics::High Energy Astrophysical Phenomena, Cooling Flows, Astrophysics::Cosmology and Extragalactic Astrophysics, Ultraviolet ISM, Astrophysics::Galaxy Astrophysics
Abstract

This thesis deals with the cool gas, i.e. less than 10000 degrees Kelvin, at the centres of relaxed, rich galaxy clusters. We find that a significant amount of this gas exists within a 50 kiloparsec nebula centered on the Brightest Cluster Galaxy. The cool gas is locked up in long, thin filaments and exists in three phases, i.e. ionised, atomic and molecular, that share the same extent and dynamics. The bright line emission of this gas implies rapid cooling. However, the inferred cooling rates are not in line with observations and therefore this gas requires continues reheating. The total reheating necessary rivals that of the hot X-ray emitting phase. Several sources of reheating are investigated with heating by X-rays or Cosmic rays being the most promising candidates

Published
2011

12. The Herschel view of clusters of galaxies.

Author

Edge, A.C., Oonk, J.B.R., and Mittal, R.

Abstract

Clusters of galaxies provide a rich variety of phenomena in the far-infrared and the Herschel Space Observatory has performed a number of comprehensive imaging and spectroscopic observations of clusters over a wide redshift range. This talk gives an overview of the results available to date and the prospects for the observations yet to come. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Published
2013
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13. Orchestration of Distributed LOFAR Workflows

Author

Mechev, A.P., Röttgering, H.J.A., Plaat, A., Oonk, J.B.R., Portegies Zwart, S.F., Wijshoff, H.A.G., Nieuwpoort, R. van, Hardcastle, M., Varbanescu, A.L., Intema, H.T., Shimwell, T.W., and Leiden

Subjects
Astrophysics::Instrumentation and Methods for Astrophysics, Performance Analysis, ComputerApplications_COMPUTERSINOTHERSYSTEMS, Radio Astronomy, Astrophysics::Cosmology and Extragalactic Astrophysics, Distributed Computing, Workflow Orchestration
Abstract

The LOFAR radio telescope produces petabytes of data every year. Radio Astronomers use complex multi-step pipelines to process this data and produce scientific images. In this thesis, we describe methods for astronomers to efficiently process massive amounts of data on high-throughput clusters. We gain insights into efficient acceleration of complex scientific pipelines, as well as understanding of the scalability of the underlying software. These insights ensure the scientific output of LOFAR keeps up with the pace of the data the telescope produces. Moreover, our results can be applied to arbitrary scientific studies, greatly increasing the potential of the LOFAR telescope. Finally, our discoveries can be applied to current and future telescopes. These lessons will help astronomers efficiently producing science in the big data era.

Published
2019

14. A fresh view on carbon radio recombination lines powered by LOFAR

Author

Salas Munoz, P.A., Tielens, A.G.G.M., Röttgering, H.J.A., Oonk, J.B.R., Heiles, C., Menten, K., White, G., Langeveld, H.J. van, Werft, P.P. van der, and Leiden University

Subjects
Interstellar medium, Radio lines
Abstract

The Low Frequency Array enables studies of low-frequency carbon radio recombination lines with unprecedented sensitivity, spectral and spatial resolution. In this thesis we benefit from the capabilities of LOFAR to study the cold interstellar medium through carbon radio recombination lines. We find that at low-frequencies these lines trace cold gas, associated with the C+/CI/CO interface of photo-dissociation regions. This opens up the possibility to study these interfaces over large regions of the Milky Way.

Published
2019

15. The LOFAR Two-metre Sky Survey. II. First data release

Author

Eskil Varenius, Huub Röttgering, Magdalena Kunert-Bajraszewska, Ricardo Genova-Santos, Judith H. Croston, D. Nisbet, R. Lakhoo, R. Kondapally, F. Savini, Joseph R. Callingham, A. O. Clarke, H. R. Stacey, M. H. D. van der Wiel, Isabella Prandoni, Antonia Rowlinson, R. Pizzo, Gianfranco Brunetti, David Bacon, George K. Miley, Marcus Brüggen, L. Alegre, R.-J. Dettmar, C. Dumba, R. J. van Weeren, Volker Heesen, Stephen Bourke, G. Calistro Rivera, A. Botteon, J. Sabater, M. Mirmont, G. Gürkan, Andrea Merloni, Torsten A. Enßlin, Marek Jamrozy, Philip Best, A. Drabent, Marcellin Atemkeng, Glenn J. White, R. C. Vermeulen, Wolfgang Reich, Neal Jackson, Chiara Ferrari, Marco Iacobelli, Huib Intema, J. B. R. Oonk, D. N. Hoang, John Conway, A. Wilber, Marisa Brienza, T. J. Dijkema, B. Webster, M. A. Garrett, Simon Perkins, A. P. Mechev, Shane O'Sullivan, Christopher J. Conselice, I. van Bemmel, Annalisa Bonafede, Oleg Smirnov, John L. Quinn, John McKean, G. Kokotanekov, Subhash C. Mandal, Daniel J. Smith, C. L. Hale, Arti Goyal, Błażej Nikiel-Wroczyński, K. L. Emig, S. Urquhart, Marijke Haverkorn, Timothy W. Shimwell, R. Morganti, Michael W. Wise, Elizabeth K. Mahony, Beatriz Mingo, Arpad Miskolczi, C. A. Jackson, Leah K. Morabito, D. A. Rafferty, A. Saxena, C. Roskowinski, Rachel Cochrane, C. Schrijvers, M. Mevius, Wendy L. Williams, E. Bonnassieux, Rossella Cassano, Matthias Hoeft, Krzysztof T. Chyzy, Dominik J. Schwarz, B. Hugo, Robert Beswick, George Heald, C. Tasse, S. Mooney, Jeremy J. Harwood, Emanuela Orru, Martin J. Hardcastle, Kenneth Duncan, S. S. Sridhar, Cathy Horellou, Matt J. Jarvis, L. Bester, F. de Gasperin, Aleksandar Shulevski, A. Danezi, V. H. Mahatma, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Astronomy, Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Shimwell T.W., Tasse C., Hardcastle M.J., Mechev A.P., Williams W.L., Best P.N., Rottgering H.J.A., Callingham J.R., Dijkema T.J., De Gasperin F., Hoang D.N., Hugo B., Mirmont M., Oonk J.B.R., Prandoni I., Rafferty D., Sabater J., Smirnov O., Van Weeren R.J., White G.J., Atemkeng M., Bester L., Bonnassieux E., Bruggen M., Brunetti G., Chy K.T., Cochrane R., Conway J.E., Croston J.H., Danezi A., Duncan K., Haverkorn M., Heald G.H., Iacobelli M., Intema H.T., Jackson N., Jamrozy M., Jarvis M.J., Lakhoo R., Mevius M., Miley G.K., Morabito L., Morganti R., Nisbet D., Orru E., Perkins S., Pizzo R.F., Schrijvers C., Smith D.J.B., Vermeulen R., Wise M.W., Alegre L., Bacon D.J., Van Bemmel I.M., Beswick R.J., Bonafede A., Botteon A., Bourke S., Brienza M., Calistro Rivera G., Cassano R., Clarke A.O., Conselice C.J., Dettmar R.J., Drabent A., Dumba C., Emig K.L., Ensslin T.A., Ferrari C., Garrett M.A., Genova-Santos R.T., Goyal A., Gurkan G., Hale C., Harwood J.J., Heesen V., Hoeft M., Horellou C., Jackson C., Kokotanekov G., Kondapally R., Kunert-Bajraszewska M., Mahatma V., Mahony E.K., Mandal S., McKean J.P., Merloni A., Mingo B., Miskolczi A., Mooney S., Nikiel-Wroczynski B., O'Sullivan S.P., Quinn J., Reich W., Roskowinski C., Rowlinson A., Savini F., Saxena A., Schwarz D.J., Shulevski A., Sridhar S.S., Stacey H.R., Urquhart S., Van Der Wiel M.H.D., Varenius E., Webster B., and Wilber A.

Subjects
Astronomy, radio continuum: general, Flux, techniques: image processing, Astrophysics, 01 natural sciences, CLUSTER ENVIRONMENTS, ST/M001229/1, Survey, 010303 astronomy & astrophysics, SOUTHERN SKY, media_common, astro-ph.HE, Physics, CALIBRATION, High Energy Astrophysical Phenomena (astro-ph.HE), image processing [techniques], UNDERSTANDING RADIO POLARIMETRY, ST/R00109X/1, ST/P000096/1, astro-ph.CO, general [radio continuum], Catalog, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Noise (radio), Astrophysics - Cosmology and Nongalactic Astrophysics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), astro-ph.GA, media_common.quotation_subject, FOS: Physical sciences, Declination, surveys, 0103 physical sciences, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], AGN, Instrumentation and Methods for Astrophysics (astro-ph.IM), STFC, ST/M001326/1, 010308 nuclear & particles physics, RCUK, Astronomy and Astrophysics, LOFAR, Astrophysics - Astrophysics of Galaxies, Galaxy, Redshift, GALAXY, ST/M001008/1, Space and Planetary Science, Sky, IMAGING SURVEY, DISCOVERY, Astrophysics of Galaxies (astro-ph.GA), FLUX-DENSITY SCALE, Right ascension, EMISSION, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], catalogs, astro-ph.IM
Abstract

The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45$^\circ$00$'$00$''$ to 57$^\circ$00$'$00$''$) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325,694 sources are detected with a signal of at least five times the noise, and the source density is a factor of $\sim 10$ higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S$_{\rm 144 MHz} = 71\,\mu$Jy beam$^{-1}$ and the point-source completeness is 90% at an integrated flux density of 0.45mJy. The resolution of the images is 6$''$ and the positional accuracy is within 0.2$''$. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further $\sim$20 articles that highlight the scientific potential of LoTSS., Comment: 16 figures, 1 table and 22 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal

Published
2019
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16. Studies of dust and gas in the interstellar medium of the Milky Way

Author

Salgado Cambiazo, F.J., Tielens, A.G.G.M., Oonk, J.B.R., Röttgering, H.J.A., Brandl, B.R., Walmsley, C.M., Abergel, A., White, G.J., and Leiden University

Subjects
Atoms, Galaxy, Radio lines, Dust, Extinction, Photon-dominated regions, ISM, HII-regions
Abstract

This thesis focus on the study of the Interstellar Medium (ISM) of the Milky Way and consists of two parts: in the first one we present a study of the dust properties in HII regions and their surrounding PDRs. We focus our studies on two compact HII regions: W3(A) and the Orion Nebula (Chapters 2 and 3, respsectively). Using SOFIA/FORCAST observations, we determine the properties of dust in the ionized gas, their surrounding PhotoDissociation Regions and their parent molecular clouds. One of the most important conclusions of this thesis is that the grain growth can affect the dust size distribution in regions of massive star formation. The large amount of archival data available for Orion allow us to study other important phenomena related to dust in this region, such as the photoelectric heating effect and Lyman alpha heating. The second part of this thesis presents theoretical studies of the properties of the cold neutral medium (CNM) using carbon radio recombination lines (CRRL). Chapters 4 and 5 consists on the complete theory of CRRLs from the level population equation to the radiative transfer equation. Using these models and observations of CRRLs the physical parameters of the CNM can be determined.

Published
2015

17. Discovery of carbon radio recombination lines in absorption towards Cygnus A

Author

J. van Enst, D. Engels, J. B. R. Oonk, S. ter Veen, Tim Hassall, Leah K. Morabito, M. A. Garrett, Alexander G. G. M. Tielens, Ashish Asgekar, J. M. Anderson, Rainer Beck, D. D. Mulcahy, Neal Jackson, Frank Breitling, Vishambhar Pandey, Harvey Butcher, Rob Fender, James Miller-Jones, M. Pandey-Pommier, Sarod Yatawatta, Giulia Macario, Michel Tagger, J. Kohler, Anton Zensus, John Conway, H. J. A. Röttgering, Heino Falcke, H. Munk, Marcus Brüggen, A. Horneffer, Richard Fallows, Jochen Eislöffel, E. Juette, Olaf Wucknitz, P. Maat, M. J. Norden, A. Alexov, C. Vogt, Aris Karastergiou, Maaijke Mevius, G. Kuper, S. Duscha, V. I. Kondratiev, Michael W. Wise, Gianni Bernardi, Philip Best, Benjamin Stappers, Dominik J. Schwarz, Wilfred Frieswijk, Y. Tang, A. Shulevski, Anna M. M. Scaife, Chiara Ferrari, Glenn J. White, B. Ciardi, Marco Iacobelli, M. de Vos, Jean-Mathias Grießmeier, A. G. Polatidis, Arthur Corstanje, Matthias Hoeft, J. Sluman, John McKean, C. Tasse, John D. Swinbank, Francisco Salgado, J. W. Broderick, Roberto Pizzo, E. de Geus, Satyendra Thoudam, Ralph A. M. J. Wijers, Christian Vocks, Sera Markoff, C. Toribio, J. D. Mol, M. Kuniyoshi, Annalisa Bonafede, Jason W. T. Hessels, Michiel A. Brentjens, Mark J. Bentum, George Heald, Michael Kramer, J. van Leeuwen, Philippe Zarka, R. van Nieuwpoort, J. P. Hamaker, Charlotte Sobey, Emanuela Orrú, H. Paas, F. Batejat, W. Reich, Oleg Smirnov, F. de Gasperin, I. van Bemmel, Martin Bell, Gottfried Mann, Matthias Steinmetz, I. M. Avruch, R. J. van Weeren, Rene C. Vermeulen, Wouter Klijn, A. J. van der Horst, A. P. Schoenmakers, Netherlands Institute for Radio Astronomy (ASTRON), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Leiden Observatory [Leiden], Universiteit Leiden, Department of Physics and Astronomy [Milton Keynes], The Open University [Milton Keynes] (OU), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, SRON Netherlands Institute for Space Research (SRON), Max-Planck-Institut für Radioastronomie (MPIFR), Sydney Institute for Astronomy (SIfA), The University of Sydney, Department of Physics-Electronics, Rhodes University, Grahamstown, University of Edinburgh, Universität Hamburg (UHH), Leibniz-Institut für Astrophysik Potsdam (AIP), School of Physics and Astronomy [Southampton], University of Southampton, Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], Radboud University [Nijmegen], Medstar Research Institute, Thüringer Landessternwarte Tautenburg (TLS), Hamburger Sternwarte/Hamburg Observatory, Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], University of Amsterdam [Amsterdam] (UvA), Ruhr-Universität Bochum [Bochum], Oxford Astrophysics, University of Oxford, Karlsruhe Institute of Technology (KIT), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Universität Bielefeld, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Observatoire de Paris - Site de Paris (OP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Oonk, J.B.R., van Weeren, R.J., salgado, F., Morabito, L.K., Tielens, A.G.G.M., Rottgering, H.J.A., Asgekar, A., White, G.J., Alexov, A., Anderson, J., Avruch, I.M., Batejat, F., Beck, R., Be, M.E., van Bemmel, I., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Brentjens, M., Broderick, J., Brüggen, M., Butcher, H.R., Ciardi, B., Conway, J.E., Corstanje, A., de Gasperin, F., de Geus, E., de Vos, M., Duscha, S., Eislöffel, J., Engels, D., van Enst, J., Falcke, H., Fallows, R.A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., Griemeier, J., Hamaker, J.P., Hassa, T.E., Heald, G., Hessels, J.W.T., Hoeft, M., Horneffer, A., van der Horst, A., Iacobelli, M., Jackson, N.J., Juette, E., Karastergiou, A., Klijn, W., Kohler, J., Kondratiev, V.I., Kramer, M., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Macario, G., Mann, G., Markoff, S., McKean, J.P., Mevius, M., Miller-Jones, J.C.A., Mol, J.D., Mulcahy, D.D., Munk, H., Norden, M.J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A.G., Reich, W., scaife, A.M.M., schoenmakers, A., schwarz, D., shulevski, A., sluman, J., smirnov, O., Sobey, C., Stappers, B.W., steinmetz, M., swinbank, J., Tagger, M., Tang, Y., Tasse, C., ter Veen, S., Thoudam, S., Toribio, C., van Nieuwpoort, R., Vermeulen, R., Vocks, C., Vogt, C., Wijers, R.A.M.J., Wise, M.W., Wucknitz, O., Yatawatta, S., Zarka, P., Zensus, A., Harvard University [Cambridge]-Smithsonian Institution, Universiteit Leiden [Leiden], Radboud university [Nijmegen], Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), University of Oxford [Oxford], École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Astronomy, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
[SDU.ASTR.CO]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO], Astronomy, ISM: structure, Interstellar cloud, EWI-24499, FOS: Physical sciences, Astrophysics, structure-local interstellar matter-radio line, ISM [radio lines], Cygnus A, Absorption (electromagnetic radiation), Optical depth, Astrophysics::Galaxy Astrophysics, ISM, Line (formation), ISM: general, Physics, IsM, radio lines, radio lines: ISM, general [ISM], local interstellar matter, Local standard of rest, Astronomy and Astrophysics, METIS-302715, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Galaxy, Cassiopeia A, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, General-IsM, structure [ISM], IR-89519, ISM: general ISM: structure local interstellar matter radio lines: ISM
Abstract

We present the first detection of carbon radio recombination line absorption along the line of sight to Cygnus A. The observations were carried out with the LOw Frequency ARray in the 33 to 57 MHz range. These low frequency radio observations provide us with a new line of sight to study the diffuse, neutral gas in our Galaxy. To our knowledge this is the first time that foreground Milky Way recombination line absorption has been observed against a bright extragalactic background source. By stacking 48 carbon $\alpha$ lines in the observed frequency range we detect carbon absorption with a signal-to-noise ratio of about 5. The average carbon absorption has a peak optical depth of 2$\times$10$^{-4}$, a line width of 10 km s$^{-1}$ and a velocity of +4 km s$^{-1}$ with respect to the local standard of rest. The associated gas is found to have an electron temperature $T_{e}\sim$ 110 K and density $n_{e}\sim$ 0.06 cm$^{-3}$. These properties imply that the observed carbon $\alpha$ absorption likely arises in the cold neutral medium of the Orion arm of the Milky Way. Hydrogen and helium lines were not detected to a 3$\sigma$ peak optical depth limit of 1.5$\times$10$^{-4}$ for a 4 km s$^{-1}$ channel width. Radio recombination lines associated with Cygnus A itself were also searched for, but are not detected. We set a 3$\sigma$ upper limit of 1.5$\times$10$^{-4}$ for the peak optical depth of these lines for a 4 km s$^{-1}$ channel width., Comment: In press

Published
2014
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18. LOFAR Low-band Antenna Observations of the 3C 295 and Boötes Fields: Source Counts and Ultra-steep Spectrum Sources

Author

Stappers, Benjamin, {van Weeren}, R J, {Williams}, W L, {Tasse}, C, {Röttgering}, H J A, {Rafferty}, D A, {van der Tol}, S, {Heald}, G, {White}, G J, {Shulevski}, A, {Best}, P, {Intema}, H T, {Bhatnagar}, S, {Reich}, W, {Steinmetz}, M, {van Velzen}, S, {En{\ss}lin}, T A, {Prandoni}, I, {de Gasperin}, F, {Jamrozy}, M, {Brunetti}, G, {Jarvis}, M J, {McKean}, J P, {Wise}, M W, {Ferrari}, C, {Harwood}, J, {Oonk}, J B R, {Hoeft}, M, {Kunert-Bajraszewska}, M, {Horellou}, C, {Wucknitz}, O, {Bonafede}, A, {Mohan}, N R, {Scaife}, A M M, {Klöckner}, H-R, {van Bemmel}, I M, {Merloni}, A, {Chyzy}, K T, {Engels}, D, {Falcke}, H, {Pandey-Pommier}, M, {Alexov}, A, {Anderson}, J, {Avruch}, I M, {Beck}, R, {Bell}, M E, {Bentum}, M J, {Bernardi}, G, {Breitling}, F, {Broderick}, J, {Brouw}, W N, {Brüggen}, M, {Butcher}, H R, {Ciardi}, B, {de Geus}, E, {de Vos}, M, {Deller}, A, {Duscha}, S, {Eislöffel}, J, {Fallows}, R A, {Frieswijk}, W, Garrett, Michael, {Grie{\ss}meier}, J, {Gunst}, A W, {Hamaker}, J P, {Hassall}, T E, {Hörandel}, J, {van der Horst}, A, {Iacobelli}, M, {Jackson}, N J, {Juette}, E, {Kondratiev}, V I, {Kuniyoshi}, M, {Maat}, P, {Mann}, G, {McKay-Bukowski}, D, {Mevius}, M, {Morganti}, R, {Munk}, H, {Offringa}, A R, {Orrù}, E, {Paas}, H, {Pandey}, V N, {Pietka}, G, {Pizzo}, R, {Polatidis}, A G, {Renting}, A, {Rowlinson}, A, {Schwarz}, D, {Serylak}, M, {Sluman}, J, {Smirnov}, O, {Stappers}, B W, {Stewart}, A, {Swinbank}, J, {Tagger}, M, {Tang}, Y, {Thoudam}, S, {Toribio}, C, {Vermeulen}, R, {Vocks}, C, {Zarka}, P, Astronomy, Netherlands Institute for Radio Astronomy (ASTRON), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Leiden Observatory [Leiden], Universiteit Leiden [Leiden], SKA South Africa, Ska South Africa, Rhodes University, Grahamstown, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Department of Astronomy and Astrophysics [PennState], Pennsylvania State University (Penn State), Penn State System-Penn State System, SLAC National Accelerator Laboratory (SLAC), Stanford University, University of Edinburgh, Department of Computer Science and Automation [Bangalore] (CSA), Indian Institute of Science [Bangalore] (IISc Bangalore), Max-Planck-Institut für Radioastronomie (MPIFR), Charles Darwin University, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Laboratoire Réactions et Génie des Procédés (LRGP), Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Thüringer Landessternwarte Tautenburg (TLS), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Jacobs University [Bremen], School of Physics and Astronomy [Southampton], University of Southampton, Radboud university [Nijmegen], Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Leibniz-Institut für Astrophysik Potsdam (AIP), SRON Netherlands Institute for Space Research (SRON), Laboratoire de Chimie Physique Moléculaire (LCPM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Medstar Research Institute, Institute of Mathematical and Physical Sciences, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Dipartimento di Matematica 'Guido Castelnuovo' [Roma I] (Sapienza University of Rome), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome], Centre de Mathématiques Laurent Schwartz (CMLS), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Ruhr-Universität Bochum [Bochum], University of Oulu, Applied Stochastics (IMAPP), Oxford Astrophysics, University of Oxford [Oxford], Interactions Son Musique Mouvement, Sciences et Technologies de la Musique et du Son (STMS), Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, ANR-09-JCJC-0001,OPALES(2009), High Energy Astrophys. & Astropart. Phys (API, FNWI), Van Weeren, R.J., Williams, W.L., Tasse, C., Röttgering, H.J.A., Rafferty, D.A., Van Der Tol, S., Heald, G., White, G.J., Shulevski, A., Best, P., Intema, H.T., Bhatnagar, S., Reich, W., Steinmetz, M., Van Velzen, S., Enßlin, T.A., Prandoni, I., De Gasperin, F., Jamrozy, M., Brunetti, G., Jarvis, M.J., McKean, J.P., Wise, M.W., Ferrari, C., Harwood, J., Oonk, J.B.R., Hoeft, M., Kunert-Bajraszewska, M., Horellou, C., Wucknitz, O., Bonafede, A., Mohan, N.R., Scaife, A.M.M., Klöckner, H.-R., Van Bemmel, I.M., Merloni, A., Chyzy, K.T., Engels, D., Falcke, H., Pandey-Pommier, M., Alexov, A., Anderson, J., Avruch, I.M., Beck, R., Bell, M.E., Bentum, M.J., Bernardi, G., Breitling, F., Broderick, J., Brouw, W.N., Brüggen, M., Butcher, H.R., Ciardi, B., De Geus, E., De Vos, M., Deller, A., Duscha, S., Eislöffel, J., Fallows, R.A., Frieswijk, W., Garrett, M.A., Grießmeier, J., Gunst, A.W., Hamaker, J.P., Hassall, T.E., Hörandel, J., Van Der Horst, A., Iacobelli, M., Jackson, N.J., Juette, E., Kondratiev, V.I., Kuniyoshi, M., Maat, P., Mann, G., McKay-Bukowski, D., Mevius, M., Morganti, R., Munk, H., Offringa, A.R., Orrù, E., Paas, H., Pandey, V.N., Pietka, G., Pizzo, R., Polatidis, A.G., Renting, A., Rowlinson, A., Schwarz, D., Serylak, M., Sluman, J., Smirnov, O., Stappers, B.W., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Thoudam, S., Toribio, C., Vermeulen, R., Vocks, C., Zarka, P., Harvard University-Smithsonian Institution, Universiteit Leiden, Radboud University [Nijmegen], École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome] (UNIROMA), École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), and University of Oxford

Subjects
Cosmology and Nongalactic Astrophysics (astro-ph.CO), general, surveys [radio continuum], EWI-25425, Radio galaxy, Astronomy, techniques, galaxies: active, radio continuum: general, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, METIS-309728, surveys, survey, Source counts, Astrophysics::Galaxy Astrophysics, Physics, Spectral index, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astronomy and Astrophysics, BOOTES, LOFAR, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Redshift, interferometric [techniques], IR-93230, Space and Planetary Science, [SDU]Sciences of the Universe [physics], techniques: interferometric, Astrophysics of Galaxies (astro-ph.GA), interferometric, active [galaxies], ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Spectral energy distribution, general [radio continuum], Noise (radio), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

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 ($\alpha < -1.1$) 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 Bo\"otes 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., Comment: 26 pages, 20 figures, ApJ in press

Published
2014
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19. LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A

Author

Jochen Eislöffel, Maaijke Mevius, R. J. van Weeren, Ralph A. M. J. Wijers, A. G. Polatidis, D. McKay-Bukowski, Chiara Ferrari, John Conway, Wilfred Frieswijk, Y. Tang, Glenn J. White, Robert Braun, Michael R. Bell, J. Sluman, W. A. van Cappellen, V. N. Pandey, Richard Fallows, Raffaella Morganti, H. J. A. Röttgering, Philip Best, M. A. Garrett, T. Grit, Charlotte Sobey, Emanuela Orrú, I. M. Avruch, P. Maat, M. J. Norden, Rainer Beck, D. D. Mulcahy, Michel Tagger, Annalisa Bonafede, James Miller-Jones, Aris Karastergiou, Sarod Yatawatta, J.-M. Grießmeier, J. B. R. Oonk, H. Paas, B. Ciardi, C. Tasse, Michael W. Wise, Heino Falcke, Gianni Bernardi, Ashish Asgekar, M. Kuniyoshi, Oleg Smirnov, Matthias Steinmetz, J. Kohler, Marco Iacobelli, E. Juette, John McKean, H. Munk, Marcus Brüggen, Harvey Butcher, G. Kuper, J. M. Anderson, V. I. Kondratiev, Christian Vocks, T. E. Hassall, M. Pandey-Pommier, Casey J. Law, F. Breitling, M. de Vos, A. W. Gunst, S. Duscha, Neal Jackson, Olaf Wucknitz, Sera Markoff, A. de Jong, Laura Birzan, Giulia Macario, A. Schoenmakers, Wolfgang Reich, Huib Intema, J. W. Broderick, J. D. Mol, E. de Geus, Jason W. T. Hessels, R. Pizzo, P. Zarka, George Heald, Mark J. Bentum, W. N. Brouw, Gottfried Mann, R. Vermeulen, Matthias Hoeft, F. Batejat, Bart Scheers, I. van Bemmel, Martin Bell, F. de Gasperin, J. van Leeuwen, R. H. van de Brink, Netherlands Institute for Radio Astronomy (ASTRON), Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Harvard-Smithsonian Center for Astrophysics (CfA), Smithsonian Institution-Harvard University [Cambridge], SLAC National Accelerator Laboratory (SLAC), Stanford University, Jodrell Bank Cent. for Astrophysics, University of Manchester [Manchester], Max-Planck-Institut für Radioastronomie (MPIFR), SRON Netherlands Institute for Space Research (SRON), Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], Laboratoire de Chimie Physique Moléculaire (LCPM), Ecole Polytechnique Fédérale de Lausanne (EPFL), University of Southampton, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Jacobs University [Bremen], Technische Universität Dresden = Dresden University of Technology (TU Dresden), Leibniz-Institut für Astrophysik Potsdam (AIP), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Medstar Research Institute, Thüringer Landessternwarte Tautenburg (TLS), Radboud university [Nijmegen], Institute of Mathematical and Physical Sciences, Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), Jodrell Bank Centre for Astrophysics, University of Amsterdam [Amsterdam] (UvA), Dipartimento di Matematica 'Guido Castelnuovo' [Roma I] (Sapienza University of Rome), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome], Centre de Mathématiques Laurent Schwartz (CMLS), Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), Ruhr-Universität Bochum [Bochum], Oxford Astrophysics, University of Oxford [Oxford], Karlsruhe Institute of Technology (KIT), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Oulu, Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), National Radio Astronomy Observatory [Charlottesville] (NRAO), National Radio Astronomy Observatory (NRAO), Rhodes University, Grahamstown, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, ANR-09-JCJC-0001,OPALES(2009), Harvard University-Smithsonian Institution, Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Universiteit Leiden, Radboud University [Nijmegen], Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Università degli Studi di Roma 'La Sapienza' = Sapienza University [Rome] (UNIROMA), École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), University of Oxford, École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Asgekar, A., Oonk, J.B.R., Yatawatta, S., Van Weeren, R.J., McKean, J.P., White, G., Jackson, N., Anderson, J., Avruch, I.M., Batejat, F., Beck, R., Bell, M.E., Bell, M.R., Van Bemmel, I., Bentum, M.J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Braun, R., Breitling, F., Van De Brink, R.H., Broderick, J., Brouw, W.N., Brüggen, M., Butcher, H.R., Van Cappellen, W., Ciardi, B., Conway, J.E., De Gasperin, F., De Geus, E., De Jong, A., De Vos, M., Duscha, S., Eislöffel, J., Falcke, H., Fallows, R.A., Ferrari, C., Frieswijk, W., Garrett, M.A., Grießmeier, J.-M., Grit, T., Gunst, A.W., Hassall, T.E., Heald, G., Hessels, J.W.T., Hoeft, M., Iacobelli, M., Intema, H., Juette, E., Karastergiou, A., Kohler, J., Kondratiev, V.I., Kuniyoshi, M., Kuper, G., Law, C., Van Leeuwen, J., Maat, P., MacArio, G., Mann, G., Markoff, S., McKay-Bukowski, D., Mevius, M., Miller-Jones, J.C.A., Mol, J.D., Morganti, R., Mulcahy, D.D., Munk, H., Norden, M.J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A.G., Reich, W., Röttgering, H., Scheers, B., Schoenmakers, A., Sluman, J., Smirnov, O., Sobey, C., Steinmetz, M., Tagger, M., Tang, Y., Tasse, C., Vermeulen, R., Vocks, C., Wijers, R.A.M.J., Wise, M.W., Wucknitz, O., Zarka, P., High Energy Astrophys. & Astropart. Phys (API, FNWI), Astronomy, and Kapteyn Astronomical Institute

Subjects
Astronomy, chemistry.chemical_element, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, ISM: individual objects: Cassiopeia A, IR-89496, Astronomy & Astrophysics, Low frequency, ISM: individual objects: Cas siopeia A, 01 natural sciences, ISM: clouds, Spectral line, CARBON, MHZ, ISM: cloud, 0103 physical sciences, EWI-24495, Spectral resolution, Supernova remnant, 010303 astronomy & astrophysics, Helium, Radio lines: ISM, Astrophysics::Galaxy Astrophysics, Line (formation), Physics, radio lines : ISM, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, REGIONS, Astrophysics - Astrophysics of Galaxies, METIS-302711, Cassiopeia A, chemistry, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, ISM: clouds / radio lines: ISM / ISM: individual objects: Cassiopeia A, [SDU.ASTR.GA]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Galactic Astrophysics [astro-ph.GA]
Abstract

Cassiopeia A was observed using the Low-Band Antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon-alpha RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of > 5 from two independent LOFAR datasets. The derived line velocities (v_LSR ~ -50 km/s) and integrated optical depths (~ 13 s^-1) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR dataset and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 %) integrated optical depths, indicating that there is small-scale angular structure on the order of ~1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 x 10^-4 on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band., Accepted for publication in A&A Letters; 5 pages, 4 colour figures

Published
2013
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20. Discovery of Carbon Radio Recombination Lines in M82

Author

D. D. Mulcahy, Matt J. Jarvis, Leah K. Morabito, Ivan Marti-Vidal, Marco Iacobelli, Gianfranco Brunetti, M. Carmen Toribio, Francisco Salgado, Rainer Beck, Emanuela Orru, J. B. R. Oonk, Roberto Pizzo, H. J. A. Röttgering, George Heald, B. Adebahr, Philip Best, Michael W. Wise, Krzysztof T. Chyzy, Alexander G. G. M. Tielens, J. Gregson, John Conway, Anna M. M. Scaife, Glenn J. White, Wim van Driel, Cathy Horellou, Robert Beswick, Reinout J. van Weeren, George K. Miley, Marcus Brüggen, A. Horneffer, Marijke Haverkorn, Annalisa Bonafede, Eskil Varenius, Morabito, Leah K., Oonk, J.B.R., Salgado, Francisco, Toribio, M. Carmen, Röttgering, H.J.A., Tielens, A.G.G.M., Beck, Rainer, Adebahr, Björn, Best, Philip, Beswick, Robert, Bonafede, Annalisa, Brunetti, Gianfranco, Brüggen, Marcu, Chyzy, Krzysztof T., Conway, J.E., Van Driel, Wim, Gregson, Jonathan, Haverkorn, Marijke, Heald, George, Horellou, Cathy, Horneffer, Andrea, Iacobelli, Marco, Jarvis, Matt J., Marti-Vidal, Ivan, Miley, George, Mulcahy, D.D., Orrú, Emanuela, Pizzo, Roberto, Scaife, A.M.M., Varenius, Eskil, Van Weeren, Reinout J., White, Glenn J., Wise, Michael W., Leiden Observatory [Leiden], Universiteit Leiden [Leiden], MRI Whale Unit, South African Museum, Onsala Space Observatory, Dept. of Radio and Space Science, Chalmers University of Technology, Chalmers University of Technology [Göteborg], Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud university [Nijmegen], Onsala Space Observatory (OSO), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], School of Physics and Astronomy [Southampton], University of Southampton, SLAC National Accelerator Laboratory (SLAC), Stanford University, Department of Astrophysical Sciences [Princeton], Princeton University, Kapteyn Astronomical Institute, and Astronomy

Subjects
Astronomy, FOS: Physical sciences, Starburst region, Astrophysics, Spectral line, galaxies: individual: M82, ISM [radio lines], galaxies: individual (M82), Optical depth (astrophysics), Absorption (electromagnetic radiation), ComputingMilieux_MISCELLANEOUS, Line (formation), ISM: general, radio lines: galaxies, Physics, [PHYS]Physics [physics], radio lines: ISM, ISM [galaxies], general [ISM], Astronomy and Astrophysics, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, galaxies [radio lines], Interstellar medium, Radial velocity, Supernova, radio lines: galaxie, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), individual (M82) [galaxies], ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], galaxies: ISM
Abstract

Carbon radio recombination lines (RRLs) at low frequencies (, Comment: 6 pages, 5 figures, accepted for publication in ApJL

Published
2014
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