Efstathiou, Andreas

2012-07-05, Romero-Cañizales, Cristina, Pérez-Torres, M. A., Alberdi, A., Argo, Megan K., Beswick, Robert J., Kankare, Erkki, Batejat, Fabien, Efstathiou, Andreas, Mattila, Seppo S., Conway, John E., Garrington, Simon T., Muxlow, Thomas W.B., Ryder, Stuart D., Väisänen, Petri H.

Context. The high star formation rates of luminous infrared galaxies (LIRGs) make them ideal places for core-collapse supernova (CCSN) searches. Massive star formation can often be found in coexistence with an active galactic nucleus (AGN), contributing jointly to the energy source of LIRGs. At radio frequencies, where light is unaffected by dust extinction, it is possible to detect compact components within the innermost LIRG nuclear regions, such as SNe and SN remnants, as well as AGN buried deep in the LIRG nuclei. Aims. Our study of the LIRG IC 883 aims at: (i) investigating the parsec-scale radio structure of the (circum-)nuclear regions of IC 883; (ii) detecting at radio frequencies the two recently reported circumnuclear SNe 2010cu and 2011hi, which were discovered by near-IR (NIR) adaptive optics observations of IC 883; and (iii) further investigating the nature of SN 2011hi at NIR wavelengths. Methods. We used the electronic European very long baseline interferometry (VLBI) Network (e-EVN) at 5 GHz, and the electronic Multi-Element Remotely Linked Interferometer Network (e-MERLIN) at 6.9 GHz, to observe contemporaneously the LIRG IC 883 at high angular-resolution (from tens to hundreds of milliarcsec) and with high sensitivity (<70 μJy), complemented by archival VLBI data at 5 GHz and 8.4 GHz. We also used the Gemini North telescope to obtain late-time JHK photometry for SN 2011hi. Results. The circumnuclear regions traced by e-MERLIN at 6.9 GHz have an extension of ∼ 1 kpc, at a position angle of 130°, and show a striking double-sided structure, which very likely corresponds to a warped rotating ring, in agreement with previous studies. Our e-EVN observations at 5 GHz and complementary archival VLBI data at 5 GHz and 8.4 GHz, reveal various milliarcsec compact components in the nucleus of IC 883. A single compact source, an AGN candidate, dominates the emission at both nuclear and circumnuclear scales, as imaged with the e-EVN and e-MERLIN, respectively. The other milliarcsec components are strongly indicative of ongoing nuclear CCSN activity. Our e-EVN observations also provided upper limits to the radio luminosity of the two SNe in IC 883 recently discovered at NIR wavelengths. We refine the classification of SN 2011hi as a Type IIP SN according to our latest epoch of Gemini North observations acquired in 2012, in agreement with a low-luminosity radio SN nature. We estimate a CCSN rate lower limit of 1.1 -0.6 +1.3 yr -1 for the entire galaxy, based on three nuclear radio SNe and the circumnuclear SNe 2010cu and 2011hi.

2022, Efstathiou, Andreas, Boukas, Nikolaos, Maik Arnold, Stefan Jung, Helge Fischer, Stéphanie Philippe, Valerie Radelet, Pierre-Charles Chevallier, Christakis Sourouklis

Both the European Union and the OECD highlight, amongst others, collaboration, virtual communication and problem-solving, as well as social and digital skills as key competences for the 21st century. As such, the Hotel Academy project aims at the development of a joint curriculum that allows for virtual interdisciplinary, international, and intercultural collaboration and exchange between three European universities in the field of hospitality management. In the implementation of the curriculum, immersive technologies are applied to role plays as the primary didactic method. In this paper, we present research on the piloting of an industry-specific desktop/VR-based role play after a detailed description of the project and the VR learning environment. The evaluation of participants’ user experiences follows a mixed methods approach and helps not only to draw attention to learners’ experiences of presence and immersion, but also to the reflection on the role play design and didactical approach, as well as the teaching and learning environment. Our results imply that students were willing to draw their full attention to the underlying learning task when working in the desktop VR environment.

2002-01-21, Aitken, David K., Efstathiou, Andreas, McCall, Alan, James H. Hough, James, Aitken, David K.

Polarimetric imaging in the infrared and submm offers the possibility of identifying magnetic field configurations in astronomical objects. To test this conjecture a set of field geometries within internally heated discs has been modelled and polarization transfer followed for a range of view angles with respect to the disc axis. The wavelength range considered is from the mid-infrared to submm, the dominant polarization processes then being only dichroic emission and absorption by aligned grains. A sample of the resulting polarization images is presented and their salient features discussed. There are obvious, and some not so obvious, associations of polarization structure with the parent model field and, while these are not always unique, they will usually lead to strong constraints on the field configuration. For star formation regions the polarization structure is likely to be on a small spatial scale and then the full potential of this technique must await the advent of millimetre synthesis systems.

2006-05-01, Livanou, E., Kontizas, Maria, Gonidakis, Ioannis, Kontizas, Evanghelos, Maragoudaki, F., Oliver, Sebastian James, Efstathiou, Andreas, Klein, Ulrich

Aims. Filamentary structures of early type stars are found to be a common feature of the Magellanic Clouds formed at an age of about 0.9-2 × 10 8 yr. As we go to younger ages these large structures appear fragmented and sooner or later form young clusters and associations. In the optical domain we have detected 56 such large structures of young objects, known as stellar complexes in the LMC for which we give coordinates and dimensions. We also investigate star formation activity and evolution of these stellar complexes and define the term "starburst region". Methods. IR properties of these regions have been investigated using IRAS data. A colour-magnitude diagram (CMD) and a two-colour diagram from IRAS data of these regions ware compared with observations of starburst galaxies and cross-matching with HII regions and SNRs was made. Radio emission maps at 8.6-GHz and the CO (1 → 0) line were also cross correlated with the map of the stellar complexes. Results. It has been found that nearly 1/3 of the stellar complexes are extremely active resembling the IR behaviour of starburst galaxies and HII regions. These stellar complexes illustrating such properties are called here "starburst regions". They host an increased number of HII regions and SNRs. The main starburst tracers are their IR luminosity (F60 well above 5.4 Jy) and the 8.6-GHz radio emission. Finally the evolution of all stellar complexes is discussed based on the CO emission.

2017-11-10, González-Alfonso, Eduardo, Armus, Lee, Carrera, Francisco J., Charmandaris, Vassilis, Efstathiou, Andreas, Egami, Eiichi E., Fernández-Ontiveros, Juan Antonio, Fischer, Jacqueline R., Granato, Gianluigi, Gruppioni, Carlotta, Hatziminaoglou, Evanthia, Imanishi, Masatoshi, Isobe, Naoki, Kaneda, Hidehiro, Kozieł-Wierzbowska, Dorota, Malkan, Matthew A., Martín-Pintado, Jesús M., Mateos, Silvia, Matsuhara, Hideo, Miniutti, Giovanni, Nakagawa, Takao, Pozzi, Francesca, Rico-Villas, F., Rodighiero, Giulia, Roelfsema, Peter R., Spinoglio, L., Spoon, Henrik W.W., Sturm, Eckhard, Van Der Tak, Floris F.S., Vignali, Cristian, Wang, Lingyu, González-Alfonso, Eduardo

A far-infrared observatory such as the SPace Infrared telescope for Cosmology and Astrophysics, with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last ~10 Gyr of the Universe (z = 1.5–2), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionised gas. We quantify the detectability of galaxy-scale massive molecular and ionised outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths.

1/1/2014, Herrero-Illana, Rubén, Pérez-Torres, M. A., Alberdi, A., Alonso-Herrero, Almudena, Colina, Luis, Efstathiou, Andreas, Hernández-García, Lorena, Miralles-Caballero, Daniel, Väisänen, Petri H., Packham, Christopher C., Rajpaul, Vinesh M., Albert A. Zijlstra, Albert, Herrero-Illana, Rubén

The Luminous Infrared Galaxy NGC1614 hosts a prominent circumnuclear ring of star formation[1]. However, the nature of the dominant emitting mechanism in its central ∼ 100 pc is still under debate. We present sub-arcsecond angular resolution radio, mid-infrared, Paα, optical, and X-ray observations of NGC 1614, aimed at studying in detail both the circumnuclear ring and the nuclear region. We conclude that there is no need to invoke an AGN to explain the observed bolometric properties of the galaxy. This study is detailed in Herrero-Illana et al.

2002-04-21, Fox, Matt J., Efstathiou, Andreas, Rowan-Robinson, Michael, James S. Dunlop, James, Scott, Susan E., Serjeant, Stephen B.G., Robert Mann, Robert, Oliver, Sebastian James, Ivison, Robert J., Blain, Andrew W., Almaini, Omar, Hughes, David Handel, Willott, Chris J., Longair, Malcolm S., Andy R. Lawrence, Andy, Peacock, John A., Fox, Matt J.

We present the results of a multiwavelength study of the 19 most significant submillimetre (submm) sources detected in the SCUBA 8-mJy survey. As described in Scott et al., this survey covers ≃ 260 arcmin2 using the submillimetre camera SCUBA, to a limiting source detection limit S850 μm 8 mJy. One advantage of this relatively bright flux-density limit is that accurate astrometric positions are potentially achievable for every source using existing radio and/or millimetre-wave interferometers. However, an associated advantage is that spectral energy distribution (SED) based redshift constraints should be more powerful than in fainter submm surveys. Here we therefore exploit the parallel SCUBA 450-μm data, in combination with existing radio and Infrared Space Observatory (ISO) data at longer and shorter wavelengths to set constraints on the redshift of each source. We also analyse new and existing optical and near-infrared imaging of our SCUBA survey fields to select potential identifications consistent with these constraints. Our derived SED-based redshift constraints, and the lack of statistically significant associations with even moderately bright galaxies allow us to conclude that all 19 sources lie at z > 1, and at least half of them apparently lie at z > 2.

2022-10-14, Pavlou, Orestis, Efstathiou, Andreas, Papadopoulou Lesta, Vicky, Andreas A. Ioannides, Constantinos Kourouyiannis, Christodoulos Karittevlis, Lichan Liu, Ioannis Michos, Michalis Papadopoulos, Evangelos Papaefthymiou

In this article, we present a unified framework for the analysis and characterization of a complex system and demonstrate its application in two diverse fields: neuroscience and astrophysics. The framework brings together techniques from graph theory, applied mathematics, and dimensionality reduction through principal component analysis (PCA), separating linear PCA and its extensions. The implementation of the framework maps an abstract multidimensional set of data into reduced representations, which enable the extraction of its most important properties (features) characterizing its complexity. These reduced representations can be sign-posted by known examples to provide meaningful descriptions of the results that can spur explanations of phenomena and support or negate proposed mechanisms in each application. In this work, we focus on the clustering aspects, highlighting relatively fixed stable properties of the system under study. We include examples where clustering leads to semantic maps and representations of dynamic processes within the same display. Although the framework is composed of existing theories and methods, its usefulness is exactly that it brings together seemingly different approaches, into a common framework, revealing their differences/commonalities, advantages/disadvantages, and suitability for a given application. The framework provides a number of different computational paths and techniques to choose from, based on the dimension reduction method to apply, the clustering approaches to be used, as well as the representations (embeddings) of the data in the reduced space. Although here it is applied to just two scientific domains, neuroscience and astrophysics, it can potentially be applied in several other branches of sciences, since it is not based on any specific domain knowledge. Copyright

2003-02, Efstathiou, Andreas, Verma, Aprajita, Michael Rowan, Richard Mcmahon

We present 7-180μm photometry of a sample of hyperluminous infrared galaxies (HyLIGs) obtained with the photometer and camera mounted on the Infrared Space Observatory (ISO). We have used state-of-the-art' radiative transfer models of obscured starbursts and dusty tori to model their broadband spectral energy distributions (SEDs). We find that IRAS F00235+1024, IRAS F14218+3845 and IRAS F15307+3252 require a combination of starburst and AGN components to explain their mid to far-infrared emission, while for TXS0052+471 a dust torus model alone is sufficient. For IRAS F00235+1024 and IRAS F14218+3845 the starburst component is the predominant contributor whereas for IRAS F15307+3252 the dust torus component dominates. The implied star formation rates (SFR) estimated from the starburst infrared luminosities are dM*,all/dt > 1000M⊙yr-1h50-2 and are amongst the highest SFRs estimated to date. We also demonstrate that the well-known radio-FIR correlation observed for extragalactic sources extends into both higher radio and infrared power than previously investigated. The relation for HyLIGs has a mean q value of 1.94. The results of this study imply that better sampling of the IR SEDs of HyLIGs may reveal that both AGN and starburst components are required to explain their emission from the NIR to the sub-millimetre.

2012-01-10, Kankare, Erkki, Mattila, Seppo S., Ryder, Stuart D., Väisänen, Petri H., Alberdi, A., Alonso-Herrero, Almudena, Colina, Luis, Efstathiou, Andreas, Kotilainen, Jari K., Melinder, Jens, Pérez-Torres, M. A., Romero-Cañizales, Cristina, Takalo, A., Kankare, Erkki

We report the discovery of two consecutive supernovae (SNe), 2010cu and 2011hi, located at 037 (180pc) and 079 (380pc) projected distance, respectively, from the center of the K-band nucleus of the luminous infrared galaxy (LIRG) IC 883. The SNe were discovered in an ongoing near-infrared K-band search for core-collapse SNe in such galaxies using the ALTAIR/NIRI adaptive optics system with laser guide star at the Gemini-North Telescope. These are thus the closest SNe yet discovered to an LIRG nucleus in optical or near-infrared wavelengths. The near-infrared light curves and colors of both SNe are consistent with core-collapse events. Both SNe seem to suffer from relatively low host galaxy extinction suggesting that regardless of their low projected galactocentric distances, they are not deeply buried in the nuclear regions of the host galaxy.