2MASS wide field extinction maps

Free access article

Issue		A&A Volume 454, Number 3, August II 2006


Page(s)		781 - 796
Section		Interstellar and circumstellar matter
DOI		http://dx.doi.org/10.1051/0004-6361:20042474

A&A 454, 781-796 (2006)
DOI: 10.1051/0004-6361:20042474

I. The Pipe nebula

M. Lombardi^{1, 2}, J. Alves¹ and C. J. Lada³

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 $8^\circ\times6^\circ$ , 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 $A_{\rm V} = 0.5~\mbox{mag}$ extinction at a 3- $\sigma$ level with a $1~\mbox{ arcmin}$ resolution.
Results. (i ) We find for the Pipe nebula a normal reddening law, $E(J - H) = (1.85 \pm 0.15) E(H - K)$ . (ii ) We measure the cloud distance using Hipparchos and Tycho parallaxes, and obtain $130^{+24}_{-58}~\mbox{ pc}$ . This, together with the total estimated mass, $10^4~{M}_\odot$ , makes the Pipe the closest massive cloud complex to Earth. (iii ) We compare the NICER extinction map to the NANTEN ¹²CO 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 $2.91 \times 10^{20}~\mbox{cm}^{-2}\,\mbox{K}^{-1}\,\mbox{km}^{-1}\,\mbox{s}$ in the range $A_{\rm V} \in [0.9, 5.4]~\mbox{mag}$ . (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 ¹²CO data corroborates the insensitivity of CO observations to low column densities (up to approximately $2~\mbox{mag}$ in $A_{\rm V}$ ), and shows also an irreducible uncertainty in the dust-CO correlation of about $1~\mbox{mag}$ of visual extinction.

Key words: ISM: clouds -- ISM: dust, extinction -- ISM: structure -- ISM: individual objects: Pipe molecular complex -- methods: data analysis

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