The VMC Survey

XXXII. Pre-main-sequence populations in the Large Magellanic Cloud

¹ Lennard-Jones Laboratories, School of Chemical and Physical Sciences, Keele University, ST5 5BG, UK
e-mail: v.zivkov@keele.ac.uk
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Dipartimento di Fisica e Astronomia, Universitá di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
⁵ Osservatorio Astronomico di Padova – INAF, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁶ ICRAR, M468, University of Western Australia, 35 Stirling Hwy, 6009 Crawley, Western Australia, Australia
⁷ INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy
⁸ Department of Physics and Astronomy, Macquarie University, Balaclava Road, Sydney, NSW 2109, Australia
⁹ Research Centre for Astronomy, Astrophysics and Astrophotonics, Macquarie University, Balaclava Road, Sydney, NSW 2109, Australia
¹⁰ International Space Science Institute–Beijing, 1 Nanertiao, Zhongguancun, Hai Dian District, Beijing 100190, PR China
¹¹ INAF-Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy
¹² Kavli Institute for Astronomy & Astrophysics and Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871, PR China

Received: 25 July 2018
Accepted: 8 October 2018

Abstract

Context. Detailed studies of intermediate- and low-mass pre-main-sequence (PMS) stars outside the Galaxy have so far been conducted only for small targeted regions harbouring known star formation complexes. The VISTA Survey of the Magellanic Clouds (VMC) provides an opportunity to study PMS populations down to solar masses on a galaxy-wide scale.

Aims. Our goal is to use near-infrared data from the VMC survey to identify and characterise PMS populations down to ∼1 M_⊙ across the Magellanic Clouds. We present our colour–magnitude diagram method, and apply it to a ∼1.5 deg² pilot field located in the Large Magellanic Cloud.

Methods. The pilot field is divided into equal-size grid elements. We compare the stellar population in every element with the population in nearby control fields by creating K_s/(Y−K_s) Hess diagrams; the observed density excesses over the local field population are used to classify the stellar populations.

Results. Our analysis recovers all known star formation complexes in this pilot field (N 44, N 51, N 148, and N 138) and for the first time reveals their true spatial extent. In total, around 2260 PMS candidates with ages ≲10 Myr are found in the pilot field. PMS structures, identified as areas with a significant density excess of PMS candidates, display a power-law distribution of the number of members with a slope of −0.86 ± 0.12. We find a clustering of the young stellar populations along ridges and filaments where dust emission in the far-infrared (FIR) (70 μm–500 μm) is bright. Regions with young populations lacking massive stars show a lower degree of clustering and are usually located in the outskirts of the star formation complexes. At short FIR wavelengths (70 μm,100 μm) we report a strong dust emission increase in regions hosting young massive stars, which is less pronounced in regions populated only by less massive (≲4 M_⊙) PMS stars.