The VMC survey

Abstract

We derive the star formation history (SFH) for several regions of the Large Magellanic Cloud (LMC), using deep near-infrared data from the VISTA near-infrared Y JK s survey of the Magellanic system (VMC). The regions include three almost-complete 1.4 deg 2 tiles located ∼3.5• away from the LMC centre in distinct directions. They are split into 21.0 × 21.5 (0.12 deg 2 ) subregions, and each of these is analysed independently. To this dataset, we add two 11.3 × 11.3 (0.036 deg 2 ) subregions selected based on their small and uniform extinction inside the 30 Doradus tile. The SFH is derived from the simultaneous reconstruction of two different colour-magnitude diagrams (CMDs), using the minimization code StarFISH together with a database of "partial models" representing the CMDs of LMC populations of various ages and metallicities, plus a partial model for the CMD of the Milky Way foreground. The distance modulus (m− M) 0 and extinction A V is varied within intervals ∼0.2 and ∼0.5 mag wide, respectively, within which we identify the best-fitting star formation rate SFR(t) as a function of lookback time t, age-metallicity relation (AMR), (m− M) 0 and A V . Our results demonstrate that VMC data, due to the combination of depth and little sensitivity to differential reddening, allow the derivation of the space-resolved SFH of the LMC with unprecedented quality compared to previous wide-area surveys. In particular, the data clearly reveal the presence of peaks in the SFR(t) at ages log(t/yr) 9.3 and 9.7, which appear in most of the subregions. The most recent SFR(t) is found to vary greatly from subregion to subregion, with the general trend of being more intense in the innermost LMC, except for the tile next to the N11 complex. In the bar region, the SFR(t) seems remarkably constant over the time interval from log(t/yr) 8.4 to 9.7. The AMRs, instead, turn out to be remarkably similar across the LMC. Thanks to the accuracy in determining the distance modulus for every subregion -with typical errors of just ∼0.03 mag -we make a first attempt to derive a spatial model of the LMC disk. The fields studied so far are fit extremely well by a single disk of inclination i = 26.2 ± 2.0• , position angle of the line of nodes θ 0 = 129.1 ± 13.0• , and distance modulus of (m− M) 0 = 18.470 ± 0.006 mag (random errors only) up to the LMC centre. We show that once the (m− M) 0 values or each subregion are assumed to be identical to those derived from this best-fitting plane, systematic errors in the SFR(t) and AMR are reduced by a factor of about two.

The VMC Survey – XIII. Type II Cepheids in the Large Magellanic Cloud★

“…larger dispersion in the various relationships mentioned above. To verify if different choices about the inclined disc parameters could improve the results, we have carried out the de-projection using several results present in the literature (see Haschke et al 2012;Rubele et al 2012;Subramanian & Subramaniam 2013, and references therein). Under no circumstances the dispersion of the P W s decreased (we used P W s as reference because they are reddening-free).…”

The VMC survey – XVI. Spatial variation of the cluster formation activity in the innermost regions of the Large Magellanic Cloud

“…We repeated these steps for each epoch separately. Finally, all homogenized paw-print images were combined using the SWARP tool (Bertin et al 2002), as described in Rubele et al (2012), thus generating deep tile images with homogeneous PSFs.…”

“…We ran a large number of artificial-star tests to estimate the incompleteness and error distribution of our photometric catalogues for each tile and in every part of the colourmagnitude diagram (CMD), as described in Rubele et al (2012), where the photometry for two small subregions in tile LMC 6 6 is presented. Photometric errors of 0.10 mag were derived for stars with Y = 20.8 mag, J = 20.6 mag and Ks = 19.7 mag in tile LMC 6 4 and for Y = 21.2 mag, J = 20.9 mag, and Ks = 19.9 mag in tile LMC 6 6.…”

“…We estimated reddening values and ages for our 313 sample clusters using the theoretical isochrones of Bressan et al (2012) in the Vegamag system (where, by definition, Vega has a magnitude of zero in all filters), corrected by −0.074 mag in Y and −0.003 mag in Ks to put them on the VMC system (Rubele et al 2015), to match the cleaned cluster CMDs. We adopted the same distance modulus for all clusters (m − M )0 = 18.49 ± 0.09 mag (de Grijs, Wicker & Bono 2014) and Ks − MK s = (m − M )0 + 0.372E(B − V ), for RV = 3.1 (Cardelli, Clayton & Mathis 1989;Gao et al 2013), since by considering an average depth for the LMC disc of (3.44±1.16) kpc ), we derived a smaller age difference than that resulting from the isochrones (characterized by the same metallicity) bracketing the observed cluster features in the CMD.…”

The VMC survey

“…Walker 2011; Ripepi et al 2012). It has a rotating disc of gas and young and intermediate-age stellar populations, seen under an inclination angle of i = 26 ± 2 • (Rubele et al 2012) 1 . This structure extends ∼10 • on the sky, and has a depth along the lineof-sight of ∼4 kpc ).…”