2MASS wide field extinction maps

I. The Pipe nebula

¹ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany e-mail: mlombard@eso.org
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: 2 December 2004
Accepted: 3 March 2006

Abstract

Context.

Aims. We present a , high resolution extinction map of the Pipe nebula using 4.5 million stars from the Two Micron All Sky Survey (2MASS) point source catalog.

Methods. The use of Nicer (Lombardi & Alves 2001, A&A, 377, 1023), a robust and optimal technique to map the dust column density, allows us to detect a extinction at a 3-σ level with a resolution.

Results. (i ) We find for the Pipe nebula a normal reddening law, . (ii ) We measure the cloud distance using Hipparchos and Tycho parallaxes, and obtain . This, together with the total estimated mass, , makes the Pipe the closest massive cloud complex to Earth. (iii ) We compare the Nicer extinction map to the NANTEN CO observations and derive with unprecedented accuracy the relationship between the near-infrared extinction and the ¹²CO column density and hence (indirectly) the ¹²CO X-factor, that we estimate to be in the range . (iv ) We identify approximately 1500 OH/IR stars located within the Galactic bulge in the direction of the Pipe field. This represents a significant increase of the known numbers of such stars in the Galaxy.

Conclusions. Our analysis confirms the power and simplicity of the color excess technique to study molecular clouds. The comparison with the NANTEN CO data corroborates the insensitivity of CO observations to low column densities (up to approximately  in A_V), and shows also an irreducible uncertainty in the dust-CO correlation of about of visual extinction.