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Efstathiou, Andreas
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Preferred name
Efstathiou, Andreas
Translated Name
Ευσταθίου, Ανδρέας
Position
Rector, Professor
Main Affiliation
School
Scopus Author ID
7005273826
Google Scholar ID
WxhQowAAAAJ
7 results
Now showing 1 - 7 of 7
- PublicationFar-infrared fine-structure line diagnostics of ultraluminous infrared galaxies(Institute of Physics Publishing, 2013-10-10)
; ;D. Farrah ;V. Lebouteiller ;H. W. W. Spoon ;J. Bernard-Salas ;C. Pearson ;D. Rigopoulou ;H. A. Smith ;E. González-Alfonso ;D. L. Clements ;D. Cormier ;J. Afonso ;S. M. Petty ;K. Harris ;P. Hurley ;C. Borys ;A. Verma ;A. CoorayV. SalvatelliWe present Herschel observations of 6 fine-structure lines in 25 ultraluminous infrared galaxies at z < 0.27. The lines, [O III]52 μm, [N III]57 μm, [O I]63 μm, [N II]122 μm, [O I]145 μm, and [C II]158 μm, are mostly single Gaussians with widths <600 km s-1 and luminosities of 107-109 LO. There are deficits in the [O I]63/L IR, [N II]/L IR, [O I]145/L IR, and [C II]/L IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from photodissociation regions or the interstellar medium (ISM). We derive relations between far-IR line luminosities and both the IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of the IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of the IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with the IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 101 < n < 102.5 and 102.2 < G 0 < 103.6, respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters: active galactic nucleus (AGN) activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity - PublicationHerschel observations and a model for IRAS 08572+3915: a candidate for the most luminous infrared galaxy in the local (z < 0.2) Universe(2013-12)
; ;C. Pearson ;D. Farrah ;D. Rigopoulou ;J. Gracia-Carpio ;A. Verma ;H. W. W. Spoon ;J. Afonso ;J. Bernard-Salas ;D. L. Clements ;A. Cooray ;D. Cormier ;M. Etxaluze ;J. Fischer ;E. Gonzalez-Alfonso ;P. Hurley ;V. Lebouteiller ;S. J. Oliver ;M. Rowan-RobinsonE. SturmWe present Herschel photometry and spectroscopy, carried out as part of the Herschel ultraluminous infrared galaxy (ULIRG) survey, and a model for the infrared to submillimetre emission of the ULIRG IRAS 08572+3915. This source shows one of the deepest known silicate absorption features and no polycyclic aromatic hydrocarbon emission. The model suggests that this object is powered by an active galactic nucleus (AGN) with a fairly smooth torus viewed almost edge-on and a very young starburst. According to our model, the AGN contributes about 90 per cent of the total luminosity of 1.1 × 1013 L⊙, which is about a factor of 5 higher than previous estimates. The large correction of the luminosity is due to theanisotropy of the emission of the best-fitting torus. Similar corrections may be necessary for other local and high-z analogues. This correction implies that IRAS 08572+3915 at a redshift of 0.058 35 may be the nearest hyperluminous infrared galaxy and probably the most luminous infrared galaxy in the local (z < 0.2) Universe. IRAS 08572+3915 shows a low ratio of [C II] to IR luminosity (log L[C II]/LIR < -3.8) and a [OI]63 μm to [CII]158 μm line ratio of about 1 that supports the model presented in this Letter - PublicationThe Galaxy Activity, Torus, and Outflow Survey (GATOS)(EDP Sciences, 2024-01-01)
; ;I. García-Bernete ;A. Alonso-Herrero ;D. Rigopoulou ;M. Pereira-Santaella ;T. Shimizu ;R. Davies ;F. R. Donnan ;P. F. Roche ;O. González-Martín ;C. Ramos Almeida ;E. Bellocchi ;P. Boorman ;F. Combes ;D. Esparza-Arredondo ;S. García-Burillo ;E. González-Alfonso ;E. K. S. Hicks ;S. Hönig ;A. Labiano ;N. A. Levenson ;E. López-Rodríguez ;C. Ricci ;C. Packham ;D. Rouan ;M. StalevskiM. J. WardWe use JWST/MIRI MRS spectroscopy of a sample of six local obscured type 1.9/2 active galactic nuclei (AGN) to compare their nuclear mid-IR absorption bands with the level of nuclear obscuration traced by X-rays. This study is the first to use subarcsecond angular resolution data of local obscured AGN to investigate the nuclear mid-IR absorption bands with a wide wavelength coverage (4.928.1 μm). All the nuclei show the 9.7 μm silicate band in absorption. We compare the strength of the 9.7 and 18 μm silicate features with torus model predictions. The observed silicate features are generally well explained by clumpy and smooth torus models. We report the detection of the 6 μm dirty water ice band (i.e., a mix of water and other molecules such as CO and CO2) at subarcsecond scales (0.26at 6 μm; inner 50 pc) in a sample of local AGN with different levels of nuclear obscuration in the range log NHX-Ray (cm2)2225. We find good correlation between the 6 μm water ice optical depths and NHX-Ray. This result indicates that the water ice absorption might be a reliable tracer of the nuclear intrinsic obscuration in AGN. The weak water ice absorption in less obscured AGN (log NHX-ray (cm2)23.0 m2) might be related to the hotter dust temperature (>TsubH110K) expected to be reached in the outer layers of the torus due to their more inhomogeneous medium. Our results suggest it might be necessary to include the molecular content, such as H2O, aliphatic hydrocarbons (CH), and more complex polycyclic aromatic hydrocarbon (PAH) molecules, in torus models to better constrain key parameters such as the torus covering factor (i.e., nuclear obscuration). - PublicationA technique to select the most obscured galaxy nuclei(EDP Sciences, 2022-07-01)
; ;I. García-Bernete ;D. Rigopoulou ;S. Aalto ;H.W.W. Spoon ;A. Hernán-Caballero ;P. F. RocheS. KönigCompact obscured nuclei (CONs) are mainly found in local luminous and ultraluminous infrared galaxies (U/LIRGs). In the local Universe, these sources are generally selected through the detection of the HCNa vib (3-2) emission line at submillimetre wavelengths. In this work, we present a diagnostic method to select deeply buried nuclei based on mid-infrared (mid-IR) polycyclic aromatic hydrocarbons (PAHs) and mid-IR continuum ratios. Using Spitzer InfraRed Spectrograph (IRS) spectra of a representative sample of local ULIRGs (za < a 0.27), we examine their PAH and underlying continuum emission ratios. For deeply embedded sources, we find that the 9.7 μm silicate absorption band has a particularly pronounced effect on the 11.3 μm PAH feature. The low flux level in the nuclear silicate absorption band enhances the 11.3 μm PAH feature contrast (high PAH equivalent width) compared to that of the other PAH features. The technique has been extended to include the use of the underlying 11.3/12.7 and 11.3/6.2 μm continuum ratios. However, the latter are affected by the extinction coming from both the host galaxy and the nuclear region, whereas the foreground (host-galaxy) extinction is cancelled out when using the PAH equivalent width ratios. We apply our method to local U/LIRGs from the HERUS and GOALS samples and classify 14 ULIRGs and 10 LIRGs as CON candidates, which corresponds to 30% of the ULIRGs and 7% of the LIRGs from these samples. We find that the observed continuum ratios of CON-dominated sources can be explained by assuming torus models with a tapered disc geometry and a smooth dust distribution. This suggests that the nuclear dusty structure of deeply obscured galaxy nuclei has an extremely high dust coverage. Finally, we demonstrate that the use of mid-IR coloura colour diagrams is an effective way to select CON-dominated sources at different redshifts. In particular, the combination of filters of the James Webb Space Telescope/Mid-Infrared Instrument will enable the selection of CONs out to za ∼ 1.5. This will allow the selection of CONs to be extended to high redshifts where U/LIRGs are more numerous. - PublicationHerMES: Spectral energy distributions of submillimeter galaxies at z > 4*(Institute of Physics Publishing, 2014-03-20)
; ;J.-S. Huang ;D. Rigopoulou ;G. Magdis ;M. Rowan-Robinson ;Y. Dai ;J. J. Bock ;D. Burgarella ;S. Chapman ;D. L. Clements ;A. Cooray ;D. Farrah ;J. Glenn ;S. Oliver ;A. J. Smith ;L. Wang ;M. Page ;D. Riechers ;I. Roseboom ;M. Symeonidis ;G. G. Fazio ;M. YunT. M. A. WebbWe present a study of the infrared properties for a sample of seven spectroscopically confirmed submillimeter galaxies (SMGs) at z > 4.0. By combining ground-based near-infrared, Spitzer IRAC and MIPS, Herschel SPIRE, and ground-based submillimeter/millimeter photometry, we construct their spectral energy distributions (SEDs) and a composite model to fit the SEDs. The model includes a stellar emission component at λrest < 3.5 μm, a hot dust component peaking at λrest ∼ 5 μm, and cold dust component which becomes significant for λrest > 50 μm. Six objects in the sample are detected at 250 and 350 μm. The dust temperatures for the sources in this sample are in the range of 40-80 K, and their LFIR ∼ 1013 L⊙ qualifies them as hyper-luminous infrared galaxies. The mean FIR-radio index for this sample is around 〈q〉 = 2.2 indicating no radio excess in their radio emission. Most sources in the sample have 24 μm detections corresponding to a rest-frame 4.5 μm luminosity of Log10(L4.5/L ⊙) = 11 ∼ 11.5. Their L4.5/LFIR ratios are very similar to those of starburst-dominated SMGs at z ∼ 2. The L CO-LFIR relation for this sample is consistent with that determined for local ULIRGs and SMGs at z ∼ 2. We conclude that SMGs at z > 4 are hotter and more luminous in the FIR but otherwise very similar to those at z ∼ 2. None of these sources show any sign of the strong QSO phase being triggered. - PublicationThe European Large-Area ISO Survey (ELAIS): The final band-merged catalogue(Oxford University Press, 2004)
; ;M. Rowan-Robinson ;C. Lari ;I. Perez-Fournon ;E. A. Gonzalez-Solares ;F. La Franca ;M. Vaccari ;S. Oliver ;C. Gruppioni ;P. Ciliegi ;P. Héraudeau ;S. Serjeant ;A. Efstathiou ;T. Babbedge ;I. Matute ;F. Pozzi ;A. Franceschini ;P. Vaisanen ;A. Afonso-Luis ;D. M. Alexander ;O. Almaini ;A. C. Baker ;S. Basilakos ;M. Barden ;C. del Burgo ;I. Bellas-Velidis ;F. Cabrera-Guerra ;R. Carballo ;C. J. Cesarsky ;D. L. Clements ;H. Crockett ;L. Danese ;A. Dapergolas ;B. Drolias ;N. Eaton ;E. Egami ;D. Elbaz ;D. Fadda ;M. Fox ;R. Genzel ;P. Goldschmidt ;J. I. Gonzalez-Serrano ;M. Graham ;G. L. Granato ;E. Hatziminaoglou ;U. Herbstmeier ;M. Joshi ;E. Kontizas ;M. Kontizas ;J. K. Kotilainen ;D. Kunze ;A. Lawrence ;D. Lemke ;M. J. D. Linden-Vørnle ;R. G. Mann ;I. Márquez ;J. Masegosa ;R. G. McMahon ;G. Miley ;V. Missoulis ;B. Mobasher ;T. Morel ;H. Nørgaard-Nielsen ;A. Omont ;P. Papadopoulos ;J.-L. Puget ;D. Rigopoulou ;B. Rocca-Volmerange ;N. Sedgwick ;L. Silva ;T. Sumner ;C. Surace ;B. Vila-Vilaro ;P. van der Werf ;A. Verma ;L. Vigroux ;M. Villar-Martin ;C. J. Willott ;A. CarramiñanaR. MujicaWe present the final band-merged European Large-Area ISO Survey (ELAIS) Catalogue at 6.7, 15, 90 and 175 μm, and the associated data at U, g′, r′, i′, Z, J, H, K and 20 cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed, and a summary of the area covered and the completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total Catalogue consists of 3762 sources. 23 per cent of the 15-μm sources and 75 per cent of the 6.7-μm sources are stars. For extragalactic sources observed in three or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions (SEDs) are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and active galactic nuclei (AGN) dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permits photometric redshifts to be estimated for galaxies and quasars. These agree well with the spectroscopic redshifts, within the uncertainty of the photometric method [∼ 10 per cent in (1 + z) for galaxies]. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies (log10 of 1-1000 μm luminosity Lir > 12.22) in the ELAIS Catalogue (14 per cent of 15-μm galaxies with known z), many with Arp220-like SEDs. 10 per cent of the 15-μm sources are genuine optically blank fields to r′ = 24: these must have very high infrared-to-optical ratios and probably have z > 0.6, so are high-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminous infrared galaxies (Lir > 13.22) and nine extremely red objects (EROs) (r - K > 6) are found in the survey. The latter are interpreted as ultraluminous dusty infrared galaxies at z ∼ 1. The large numbers of ultraluminous galaxies imply very strong evolution in the star formation rate between z = 0 and 1. There is also a surprisingly large population of luminous (Lir > 11.5), cool (cirrus-type SEDs) galaxies, with Lir - L opt > 0, implying Av > 1. - PublicationThe European Large‐AreaInfrared Space ObservatorySurvey V: ABeppoSAXHard X‐Ray Survey of the S1 Region(Institute of Physics Publishing, 2001-06-10)
; ;D. M. Alexander ;F. La Franca ;F. Fiore ;X. Barcons ;P. Ciliegi ;L. Danese ;R. Della Ceca ;A. Franceschini ;C. Gruppioni ;G. Matt ;I. Matute ;S. Oliver ;F. Pompilio ;A. Wolter ;P. Heraudeau ;G. C. Perola ;M. Perri ;D. Rigopoulou ;M. Rowan‐RobinsonS. SerjeantWe present BeppoSAX observations of the southern S1 region in the European Large-Area Infrared Space Observatory (ISO) Survey (ELAIS). These observations cover an area of ∼1.7 deg2 and reach an on-axis (∼0.7 deg2) 2-10 keV (hard X-ray, or HX) sensitivity of ∼10-13 ergs s-1 cm-2. This is the first HX analysis of an ISOCAM survey. We detect nine sources with a signal-to-noise ratio SNRHX > 3, four additional sources with a 1.3-10 keV (total X-ray, or T) SNRT > 3, and two additional sources that seem to be associated with QSOs having SNRT > 2.9. The number densities of the SNRHX > 3 sources are consistent with the ASCA and BeppoSAX log N-log S functions. Six BeppoSAX sources have reliable ISOCAM 15 μm counterparts within ∼60″. All these ISOCAM sources have optical counterparts of R < 20 mag. Five of these sources have been previously optically classified, four as QSOs and one as a broad absorption line (BAL) QSO at z = 2.2. The remaining unclassified source has X-ray and photometric properties consistent with those of a nearby Seyfert galaxy. One further HX source has a 2.6 σ ISOCAM counterpart associated with a galaxy at z = 0.325. If this ISOCAM source is real, the HX/MIR properties suggest either an unusual QSO or a cD cluster galaxy. We have constructed MIR and HX spectral energy distributions to compute the expected HX/MIR ratios for these classes of objects up to z = 3.2 and assess the HX/MIR survey depth. The BAL QSO has an observed X-ray softness ratio and HX/MIR flux ratio similar to those of QSOs but different from those found for low-redshift BAL QSOs. This difference can be explained in terms of absorption, and it suggests that high-redshift BAL QSOs should be comparatively easy to detect in the HX band, allowing their true fraction in the high-redshift QSO population to be determined. The QSOs cover a wide redshift range (0.4 < z < 2.6) and have HX/MIR flux ratios consistent with those found for nearby IRAS and optically selected Palomar-Green QSOs. This suggests that MIR-selected QSOs of R < 20 mag come from the same population as optically selected QSOs. We confirm this with a comparison of the B/MIR flux ratios of MIR and blue-band-selected QSOs.