New quasars behind the Magellanic Clouds. Spectroscopic confirmation of near-infrared selected candidates

¹ European Southern Observatory, Ave. Alonso de Córdova 3107, Vitacura, Santiago, Chile
e-mail: vivanov@eso.org
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Universität Potsdam, Institut für Physik und Astronomie, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
⁴ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁵ University of Hertfordshire, Physics Astronomy and Mathematics, College Lane, Hatfield AL10 9AB, UK
⁶ ICRAR, M468, The University of Western Australia, 35 Stirling Hwy, 6009 Crawley, Western Australia, Australia
⁷ Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, 100871 Beijing, PR China
⁸ Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, 100871 Beijing, PR China
⁹ International Space Science Institute-Beijing, 1 Nanertiao, Hai Dian District, 100190 Beijing, PR China
¹⁰ School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, UK
¹¹ E.A. Milne Centre for Astrophysics, Department of Physics & Mathematics, University of Hull, Hull HU6 7RX, UK
¹² Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D bus 2401, 3001 Leuven, Belgium
¹³ Lennard-Jones Laboratories, Keele University, ST5 5BG, UK
¹⁴ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina
¹⁵ Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917, C1033AAJ, Buenos Aires, Argentina

Received: 18 September 2015
Accepted: 19 October 2015

Abstract

Context. Quasi-stellar objects (quasars) located behind nearby galaxies provide an excellent absolute reference system for astrometric studies, but they are difficult to identify because of fore- and background contamination. Deep wide-field, high angular resolution surveys spanning the entire area of nearby galaxies are needed to obtain a complete census of such quasars.

Aims. We embarked on a program to expand the quasar reference system behind the Large and the Small Magellanic Clouds, the Magellanic Bridge, and the Magellanic Stream that connects the Clouds with the Milky Way.

Methods. Hundreds of quasar candidates were selected based on their near-infrared colors and variability properties from the ongoing public ESO VISTA Magellanic Clouds survey. A subset of 49 objects was followed up with optical spectroscopy.

Results. We confirmed the quasar nature of 37 objects (34 new identifications): four are low redshift objects, three are probably stars, and the remaining three lack prominent spectral features for a secure classification. The bona fide quasars, identified from their broad emisison lines, are located as follows: 10 behind the LMC, 13 behind the SMC, and 14 behind the Bridge. The quasars span a redshift range from z ~ 0.5 to z ~ 4.1.

Conclusions. Upon completion the VMC survey is expected to yield a total of ~1500 quasars with Y< 19.32 mag, J< 19.09 mag, and K_s< 18.04 mag.