Efstathiou, Andreas

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.

2000-08-21, Serjeant, Stephen B.G., Oliver, Sebastian James, Rowan-Robinson, Michael, Crockett, Hans, Missoulis, Vasilis, Sumner, Timothy J., Gruppioni, Carlotta, Robert Mann, Robert, Eaton, Nick, Elbaz, David, Clements, David L., Baker, Amanda C., Efstathiou, Andreas, Césarsky, Catherine J., Danese, Luigi, Franceschini, Alberto, Genzel, Reinhardt, Andy R. Lawrence, Andy, Lemke, Dietrich, McMahon, R. G., Miley, George K., Puget, Jean Loup, Rocca-Volmerange, Brigitte M.

We present preliminary source counts at 6.7 and 15 μm from the preliminary analysis of the European Large Area ISO Survey, with limiting flux densities of ∼2mJy at 15 μm and ∼1 mJy at 6.7 μm. We separate the stellar contribution from the extragalactic using identifications with automated plate measurement sources made with the likelihood ratio technique. We quantify the completeness and reliability of our source extraction using (a) repeated observations over small areas, (b) cross-identifications with stars of known spectral type, (c) detections of the point spread function wings around bright sources and (d) comparison with independent algorithms. Flux calibration at 15 μm was performed using stellar identifications; the calibration does not agree with the pre-flight estimates, probably due to effects of detector hysteresis and photometric aperture correction. The 6.7-μm extragalactic counts are broadly reproduced in the Pearson & Rowan-Robinson model, but the Franceschini et al. model underpredicts the observed source density by ∼0.5-1 dex, although the photometry at 6.7 μm is still preliminary. At 15 μm the extragalactic counts are in excellent agreement with the predictions of the Pearson & Rowan-Robinson. Franceschini et al., Guiderdoni et al. models and the evolving models of Xu et al., over seven orders of magnitude in 15-μm flux density. The counts agree with other estimates from the ISOCAM instrument at overlapping flux densities, provided a consistent flux calibration is used. Luminosity evolution at a rate of (1 + z)3, incorporating mid-infrared spectral features, provides a better fit to the 15-μm differential counts than (1 + z)4 density evolution. No-evolution models are excluded, implying that below around 10mJy at 15 μm the source counts become dominated by an evolving cosmological population of dust-shrouded starbursts and/or active galaxies.

2012-08-11, Hurley, Peter Donald, Oliver, Sebastian James, Farrah, Duncan G., Wang, Lingyu, Efstathiou, Andreas, Hurley, Peter Donald

The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain a variety of spectral features that can be used as diagnostics to characterize the spectra. However, such diagnostics are biased by our prior prejudices on the origin of the features. Moreover, by using only part of the spectrum they do not utilize the full information content of the spectra. Blind statistical techniques such as principal component analysis (PCA) consider the whole spectrum, find correlated features and separate them out into distinct components. We further investigate the principal components (PCs) of ULIRGs derived in Wang et al. We quantitatively show that five PCs are optimal for describing the Infrared Spectrograph spectra. These five components (PC1-PC5) and the mean spectrum provide a template basis set that reproduces spectra of all z < 0.35 ULIRGs within the noise. For comparison, the spectra are also modelled with a combination of radiative transfer models of both starbursts and the dusty torus surrounding active galactic nuclei (AGN). The five PCs typically provide better fits than the models. We argue that the radiative transfer models require a colder dust component and have difficulty in modelling strong polycyclic aromatic hydrocarbon features. Aided by the models we also interpret the physical processes that the PCs represent. The third PC is shown to indicate the nature of the dominant power source, while PC1 is related to the inclination of the AGN torus. Finally, we use the five PCs to define a new classification scheme using 5D Gaussian mixture modelling and trained on widely used optical classifications. The five PCs, average spectra for the four classifications and the code to classify objects are made available at: http://www.phys.susx.ac.uk/pdh21/PCA/.

2005-03-01, Rowan-Robinson, Michael, Babbedge, Tom S.R., Surace, Jason A., Shupe, David L., Fang, Fan, Lonsdale, Carol J., Smith, Gene P., Polletta, M., Siana, Brian D., González-Solares, Eduardo A., Kevin, Xu U., Owen, Frazer N., Domingue, Donovan L., Efstathiou, Andreas, Farrah, Duncan G., Fox, Matt J., Franceschini, Alberto, Frayer, David T., Hatziminaoglou, Evanthia, Masci, Frank J., Morrison, Glenn E., Nandra, Kirpaul P., Oliver, Sebastian James, Onyett, Natalie, Padgett, Deborah L., Pérez-Fournón, Ismaël, Serjeant, Stephen B.G., Stacey, Gordon J., Vaccari, Mattia, Rowan-Robinson, Michael

We discuss optical associations, spectral energy distributions (SEDs), and photometric redshifts for Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey sources in the European Large-Area ISO Survey (ELAIS) N1 area and the Lockman Validation Field (VF). The band-merged Infrared Array Camera (IRAC) (3.6,4.5,5.8, and 8.0 μm) and Multiband Imaging Photometer for Spitzer (24, 70, and 160 μm) data have been associated with optical UgriZ data from the Isaac Newton Telescope Wide Field Survey in ELAIS N1 and with our own optical Ugri data in Lockman-VF. Criteria for eliminating spurious infrared sources and for carrying out star-quasar-galaxy separation are discussed, and statistics of the identification rate are given. Thirty-two percent of sources in the ELAIS N1 field are found to be optically blank (to r = 23.5) and 16% in Lockman-VF (to r = 25). The SEDs of selected ELAIS sources in N1 detected by SWIRE, most with spectroscopic redshifts, are modeled in terms of a simple set of galaxy and quasar templates in the optical and near-infrared (NIR), and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and active galactic nucleus [AGN] dust torus) in the mid-infrared. The optical data, together with the IRAC 3.6 and 4.5 μm data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts, there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1 + z) to 7%. Although further spectroscopic data are needed to confirm this result, the prospect of determining good photometric redshifts for much of the SWIRE survey, expected to yield over 2 million extragalactic objects, is excellent. Some modifications to the optical templates were required in the previously uninvestigated wavelength region 2-5 μm. The photometric redshifts are used to derive the 3.6 and 24 μm redshift distribution and to compare this with the predictions of models. For those sources with a clear mid-infrared excess, relative to the galaxy starlight model used for the optical and NIR, the mid- and far-infrared data are modeled in terms of the same dust emission templates (cirrus, M82, Arp 220, and AGN dust torus). The proportions found of each template type are cirrus, 31%; M82, 29%; Arp 220,10%; and AGN dust tori, 29%. The distribution of the different infrared SED types in the L IR/L opt versus L IR plane, where L IR and L opt are the infrared and optical bolometric luminosities, respectively, is discussed. There is an interesting population of luminous cool cirrus galaxies with L IR > L opt, implying a substantial dust optical depth. Galaxies with Arp 220-like SEDs, of which there are a surprising preponderance compared with preexisting source count models, tend to have high ratios of infrared to optical bolometric luminosity, consistent with having very high extinction. There is also a high proportion of galaxies whose mid-infrared SEDs are fitted by an AGN dust torus template (29%). Of these only 8% of these are type 1 AGNs according to the optical-NIR template fitting, whereas 25% are fitted with galaxy templates in the optical-NIR and have L IR > L opt and so have to be type 2 AGN. The remainder have L IR < L opt and so can be Seyfert galaxies, in which the optical AGN fails to be detected against the light of the host galaxy. The implied dust covering factor, ≥75%, is much higher than that inferred for bright optically selected quasars.

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.

2016-02-10, Harris, Kathryn A., Farrah, Duncan G., Schulz, Bernhard, Hatziminaoglou, Evanthia, Viero, Marco P., Anderson, Nick, Béthermin, Matthieu, Chapman, Scott C., Clements, David L., Cooray, Asantha Roshan, Efstathiou, Andreas, Feltre, Anna, Hurley, Peter Donald, Ibar, Edo, Lacy, Mark D., Oliver, Sebastian James, Page, Mathew J., Pérez-Fournón, Ismaël, Petty, Sara M., Pitchford, Lura K., Rigopoulou, Dimitra, Scott, Douglas J., Symeonidis, Myrto, Vieira, Joaquin D., Wang, Lingyu

We investigate the relation between star formation rates (M˙s) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that M˙s remains approximately constant with redshift, at 300 ± 100M⊙ yr-1. Conversely, M˙s increases with AGN luminosity, up to a maximum of ~600M⊙ yr-1, and with CIV FWHM. In context with previous results, this is consistent with a relation between M˙s and black hole accretion rate (M˙bh) existing in only parts of the z - M˙s - M˙bh plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between M˙s and both AGN luminosity and C IV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing CIV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; Mi is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between M˙s and M˙bh. Finally, there is no strong relation between M˙s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects.

1/1/2001, Márquez, I., Masegosa, J., Morel, Thierry, Efstathiou, Andreas, Verma, Aprajita, Väisänen, Petri H., Alexander, David M., Héraudeau, Ph, Surace, Christian, Pérez-Fournón, Ismaël, Cabrera-Guerra, F., González-Serrano, José Ignacio, González-Solares, Eduardo A., Serjeant, Stephen B.G., Oliver, Sebastian James, Rowan-Robinson, Michael

We present the properties of all the galaxies detected by ISO at 7, 15 and 90μm in ELAIS northern fields. The spectral energy distribution (SED) of those 20 galaxies with IRAS detections can generally be well fitted by a predominant cirrus component plus a modest starburst contribution. Follow-up spectroscopy has shown that all the objects are emission-line galaxies but without a very intense star formation event. Most of the galaxies analyzed by means of optical R band photometry result to host an important exponential disk component, in good agreement with the SED IR modelling. We note that galaxies with morphological signs of perturbations seem to show slightly higher f15/f6.7 ratios, indicating that star formation could be more important in them. One of the objects is a broad-line, radio-quiet quasar at z=1.099; its spectral energy distribution indicates that it is a hyperluminous infrared galaxy (HLIG), the first HLIG detected in the ELAIS areas.

1997-01-01, Goldschmidt, Pippa, Oliver, Sebastian James, Serjeant, Stephen B.G., Baker, Amanda C., Eaton, Nick, Efstathiou, Andreas, Gruppioni, Carlotta, Robert Mann, Robert, Mobasher, Bahram, Rowan-Robinson, Michael, Sumner, Timothy J., Danese, Luigi, Elbaz, David, Franceschini, Alberto, Egami, Eiichi E., Kontizas, Maria, Andy R. Lawrence, Andy, McMahon, R. G., Nørgaard-Nielsen, Hans Ulrik, Pérez-Fournón, Ismaël, González-Serrano, José Ignacio, Goldschmidt, Pippa

We present positions and fluxes of point sources found in the Infrared Space Observatory (ISO) images of the Hubble Deep Field (HDF) at 6.7 and 15 μm. We have constructed algorithmically selected 'complete' flux-limited samples of 19 sources in the 15-μm image, and seven sources in the 6.7-μm image. The typical flux limit at 15 μm is ∼0.2 mJy and at 6.7 μm is ∼0.04 mJy. We have selected 'supplementary' samples of three sources at 15 μm and 20 sources at 6.7 μm by eye. We discuss the completeness and reliability of the connected pixel source detection algorithm used, by comparing the intrinsic and estimated properties of simulated data, and also by estimating the noise properties of the real data. The most pessimistic estimate of the number of spurious sources in the 'complete' samples is one at 15 μm and two at 6.7 μm, and in the 'supplementary' lists is one at 15 μm and five at 6.7 μm.

2013-12-01, Efstathiou, Andreas, Pearson, Chris P., Farrah, Duncan G., Rigopoulou, Dimitra, Graciá-Carpio, Javier, Verma, Aprajita, Spoon, Henrik W.W., Afonso, José M., Bernard-Salas, Jeronimo, Clements, David L., Cooray, Asantha Roshan, Cormier, Diane, Etxaluze, Mireya, Fischer, Jacqueline R., González-Alfonso, Eduardo, Hurley, Peter Donald, Lebouteiller, Vianney, Oliver, Sebastian James, Rowan-Robinson, Michael, Sturm, Eckhard

We 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.

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