Browsing by Author "Erben, T."

Now showing 1 - 6 of 6
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    Discovery of Two Einstein Crosses from Massive Post-blue Nugget Galaxies at z > 1 in KiDS*
    (2020) Napolitano, N. R.; Li, R.; Spiniello, C.; Tortora, C.; Sergeyev, A.; D'Ago, G.; Guo, X.; Xie, L.; Radovich, M.; Roy, N.; Koopmans, L. V. E.; Kuijken, K.; Bilicki, M.; Erben, T.; Getman, F.; Heymans, C.; Hildebrandt, H.; Moya, C.; Shan, H. Y.; Vernardos, G.; Wright, A. H.
    We report the discovery of two Einstein Crosses (ECs) in the footprint of the Kilo-Degree Survey (KiDS): KIDS J232940-340922 and KIDS J122456+005048. Using integral field spectroscopy from the Multi Unit Spectroscopic Explorer at the Very Large Telescope, we confirm their gravitational-lens nature. In both cases, the four spectra of the source clearly show a prominence of absorption features, hence revealing an evolved stellar population with little star formation. The lensing model of the two systems, assuming a singular isothermal ellipsoid (SIE) with external shear, shows that: (1) the two crosses, located at redshift z = 0.38 and 0.24, have Einstein radius R-E = 5.2 kpc and 5.4 kpc, respectively; (2) their projected dark matter fractions inside the half effective radius are 0.60 and 0.56 (Chabrier initial mass function); (3) the sources are ultra-compact galaxies, R-e similar to 0.9 kpc (at redshift, z(s) = 1.59) and R-e similar to 0.5 kpc (z(s) = 1.10), respectively. These results are unaffected by the underlying mass density assumption. Due to size, blue color, and absorption-dominated spectra, corroborated by low specific star formation rates derived from optical-near-infrared spectral energy distribution fitting, we argue that the two lensed sources in these ECs are blue nuggets migrating toward their quenching phase.
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    Dramatic X-ray spectral variability of a Compton-thick type-1 QSO at z ∼ 1
    (2018) Simm, T.; Buchner, J.; Merloni, A.; Nandra, K.; Shen, Y.; Erben, T.; Coil, A. L.; Willmer, C. N. A.; Schneider, D. P.
    We report on the discovery of a dramatic X-ray spectral variability event observed in a z similar to 1 broad line type-1 QSO. The XMM Newton spectrum from the year 2000 is characterized by an unobscured power-law spectrum with photon index of Gamma similar to 2, a column density of N-H similar to 5 x 10(20) cm(-2), and no prominent reflection component. Five years later, Chandra captured the source in a heavily-obscured, reflection-dominated state. The observed X-ray spectral variability could be caused by a Compton-thick cloud with N-H similar to 2 x 10(24) cm(-2) eclipsing the direct emission of the hot corona, implying an extreme N-H variation never before observed in a type-1 QSO. An alternative scenario is a corona that switched off in between the observations. In addition, both explanations require a significant change of the X-ray luminosity prior to the obscuration or fading of the corona and/or a change of the relative geometry of the source/reflector system. Dramatic X-ray spectral variability of this kind could be quite common in type-1 QSOs, considering the relatively few data sets in which such an event could have been identified. Our analysis implies that there may be a population of type-1 QSOs which are Compton-thick in the X-rays when observed at any given time.
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    Next Generation Virgo Cluster Survey. XXI. The Weak Lensing Masses of the CFHTLS and NGVS RedGOLD Galaxy Clusters and Calibration of the Optical Richness
    (2017) Parroni, C.; Mei, S.; Erben, T.; Van Waerbeke, L.; Raichoor, A.; Ford, J.; Licitra, R.; Meneghetti, M.; Hildebrandt, H.; Puzia, Thomas H.; Miller, L.; Cote, P.; Covone, G.; Cuillandre, J.; Duc, P.; Ferrarese, L.; Gwyn, S.
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    The Next Generation Virgo Cluster Survey (NGVS). XIV. The Discovery of Low-mass Galaxies and a New Galaxy Catalog in the Core of the Virgo Cluster
    (2020) Ferrarese, L.; Côté, P.; Macarthur, L. A.; Durrell, P. R.; Gwyn, S. D. J.; Duc, P. A.; Sánchez Janssen, R.; Jordán Colzani, Andrés Cristóbal; Puzia, Thomas H.; Santos, M.; Blakeslee, J. P.; Boselli, A.; Boyer, F.; Cantiello, M.; Courteau, S.; Cuillandre, J. C.; Emsellem, E.; Erben, T.; Gavazzi, G.; Guhathakurta, P.; Huertas Company, M.; Lançon, A.; Liu, C.; Mei, S.; Mihos, J. C.; Peng, E. W.; Roediger, J.; Schade, D.; Taylor, J. E.; Toloba, E.; Zhang, H.
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    The next generation virgo cluster survey. XV. The photometric redshift estimation for background sources
    (2014) Raichoor, A.; Mei, S.; Erben, T.; Hildebrandt, H.; Huertas Company, M.; Ilbert, O.; Licitra, R.; Ball, N.M.; Muñoz Soria, Roberto; Puzia, Thomas H.
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    Weak-lensing mass calibration of the Atacama Cosmology Telescope equatorial Sunyaev-Zeldovich cluster sample with the Canada-France-Hawaii telescope stripe 82 survey
    (2016) Battaglia, N.; Leauthaud, A.; Miyatake, H.; Hasselfield, M.; Grallad, M.; Allison, R.; Calabrese, E.; Devlin, M.; Erben, T.; Dünner Planella, Rolando; Ferrara, S.; Halpern, M.; Hilton, M.; Hill, J.; Hincks, A.; Hlozek, R.