The morphology of the Magellanic Clouds revealed by stars of different age: results from the DENIS survey

The spatial distribution of sources populating different regions of the colour-magnitude diagram (I-J, I) extracted from the DENIS catalogue towards the Magellanic Clouds (DCMC -- Cioni et al. 2000) reveal significantly different morphologies. Each region is associated to a different age group. The Large Magellanic Cloud (LMC) shows an extended circular shape with a prominent, off center bar, a nucleus and irregular spiral arms. The Small Magellanic Cloud shows a perturbated structure with a prominent central concentration of stars. Old and young populations are offset from one another.Comment: 4 pages and 7 figures, accepted for publication in A&A Journal Letter

The Tip of the Red Giant Branch and Distance of the Magellanic Clouds: results from the DENIS survey

We present a precise determination of the apparent magnitude of the tip of the red giant branch (TRGB) in the I (0.8 micron), J (1.25 micron), and K_S (2.15 micron) bands from the luminosity function of a sample of data extracted from the DENIS catalogue towards the Magellanic Clouds (Cioni et al. 2000). From the J and Ks magnitudes we derive bolometric magnitudes m_bol. We present a new algorithm for the determination of the TRGB magnitude, which we describe in detail and test extensively using Monte-Carlo simulations. We note that any method that searches for a peak in the first derivative (used by most authors) or the second derivative (used by us) of the observed luminosity function does not yield an unbiased estimate for the actual magnitude of the TRGB discontinuity. We stress the importance of correcting for this bias, which is not generally done. We combine the results of our algorithm with theoretical predictions to derive the distance modulus of the Magellanic Clouds. We obtain m-M = 18.55 (0.04 formal, 0.08 systematic) for the Large Magellanic Cloud (LMC), and m-M = 18.99 (0.03 formal, 0.08 systematic) for the Small Magellanic Cloud (SMC). These are among the most accurate determinations of these quantities currently available, which is a direct consequence of the large size of our sample and the insensitivity of near infrared observations to dust extinction.Comment: 16 pages, 8 figures, revised version, accepted for publication in A&

Pulsating stars in the VMC survey

The VISTA survey of the Magellanic Clouds system (VMC) began observations in 2009 and since then, it has collected multi-epoch data at Ks and in addition multi-band data in Y and J for a wide range of stellar populations across the Magellanic system. Among them are pulsating variable stars: Cepheids, RR Lyrae, and asymptotic giant branch stars that represent useful tracers of the host system geometry.Comment: 8 pages, 7 figures, proceeding contribution of invited presentation at "Wide-field variability surveys: a 21st-century perspective", San Pedro de Atacama (Chile

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

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 Ks< 18.04 mag