2MASS wide-field extinction maps

V. Corona Australis^⋆

¹ University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: joao.alves@univie.ac.at
² University of Milan, Department of Physics, via Celoria 16, 20133 Milan, Italy
³ Harvard-Smithsonian Center for Astrophysics, Mail Stop 42, 60 Garden Street, Cambridge MA 02138, USA

Received: 28 June 2013
Accepted: 6 January 2014

Abstract

We present a near-infrared extinction map of a large region (~870 deg²) covering the isolated Corona Australis complex of molecular clouds. We reach a 1-σ error of 0.02 mag in the K-band extinction with a resolution of 3 arcmin over the entire map. We find that the Corona Australis cloud is about three times as large as revealed by previous CO and dust emission surveys. The cloud consists of a 45 pc long complex of filamentary structure from the well known star forming Western-end (the head, N ≥ 10²³ cm^-2) to the diffuse Eastern-end (the tail, N ≤ 10²¹ cm^-2). Remarkably, about two thirds of the complex both in size and mass lie beneath A_V ~ 1 mag. We find that the probability density function (PDF) of the cloud cannot be described by a single log-normal function. Similar to prior studies, we found a significant excess at high column densities, but a log-normal + power-law tail fit does not work well at low column densities. We show that at low column densities near the peak of the observed PDF, both the amplitude and shape of the PDF are dominated by noise in the extinction measurements making it impractical to derive the intrinsic cloud PDF below A_K < 0.15 mag. Above A_K ~ 0.15 mag, essentially the molecular component of the cloud, the PDF appears to be best described by a power-law with index −3, but could also described as the tail of a broad and relatively low amplitude, log-normal PDF that peaks at very low column densities.