LEGO - II. A 3mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way disc
Journal article, 2020

The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60'' (similar to 3pc) resolution observations of many 3mm-band molecular lines across a large map of the W49 massive star-forming region (similar to 100x100pc at 11kpc), which were taken as part of the 'LEGO' IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H-2 column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density (10(22)cm(-2)) and moderate temperatures (35K), whilst e.g. N2H+ emits most efficiently towards lower temperatures (10(22)cm(-2); <20K). We determine XCO(1-0)similar to 0.3 x 10(20)cm(-2)(Kkms(-1))(-1), and alpha(HCN(1-0))similar to 30M(circle dot)(Kkms(-1)pc(2))(-1), which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.

stars: formation

galaxies: star formation

ISM: molecules

galaxies: ISM

ISM: clouds

galaxies: evolution


A. T. Barnes

University of Bonn

J. Kauffmann

Massachusetts Institute of Technology (MIT)

F. Bigiel

University of Bonn

N. Brinkmann

Max Planck Society

D. Colombo

Max Planck Society

A. E. Guzman

National Institutes of Natural Sciences

W. J. Kim

Institut de Radioastronomie Millimétrique (IRAM)

L. Szucs

Max Planck Society

V Wakelam

University of Bordeaux

Susanne Aalto

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics

T. Albertsson

Max Planck Society

N. J. Evans

The University of Texas at Austin

S. C. O. Glover

Heidelberg University

P. F. Goldsmith

California Institute of Technology (Caltech)

C. Kramer

Institut de Radioastronomie Millimétrique (IRAM)

K. Menten

Max Planck Society

Y. Nishimura

University of Tokyo

National Astronomical Observatory of Japan

S. Viti

University College London (UCL)

Y. Watanabe

Shibaura Institute of Technology

A. Weiss

Max Planck Society

M. Wienen

Max Planck Society

University of Exeter

H. Wiesemeyer

Max Planck Society

F. Wyrowski

Max Planck Society

Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 497 2 1972-2001

Subject Categories

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics

Condensed Matter Physics



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