Discovery of two Einstein crosses from massive post--blue nugget galaxies at z>1 in KiDS

N. R. Napolitano, R. Li, C. Spiniello, C. Tortora, A. Sergeyev, G. D'Ago, X. Guo, L. Xie, M. Radovich, N. Roy, L. V. E. Koopmans, K. Kuijken, M. Bilicki, T. Erben, F. Getman, C. Heymans, H. Hildebrandt, C. Moya, H. Y. Shan, G. VernardosA. H. Wright

Research output: Contribution to journalArticlepeer-review


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 MUSE@VLT, 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 RE=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 IMF); 3) the sources are ultra-compact galaxies, Re∼0.9 kpc (at redshift zs=1.59) and Re∼0.5 kpc (zs=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-NIR spectral energy distribution fitting, we argue that the two lensed sources in these ECs are blue nuggets migrating toward their quenching phase.
Original languageEnglish
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 3 Dec 2020


  • astro-ph.GA


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