ALCHEMI, an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory: Survey presentation and first results from the ACA array
Journal article, 2021
Context. The interstellar medium is the locus of physical processes affecting the evolution of galaxies which drive or are the result of star formation activity, supermassive black hole growth, and feedback. The resulting physical conditions determine the observable chemical abundances that can be explored through molecular emission observations at millimeter and submillimeter wavelengths. Aims. Our goal is to unveiling the molecular richness of the central region of the prototypical nearby starburst galaxy NGC 253 at an unprecedented combination of sensitivity, spatial resolution, and frequency coverage. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA), covering a nearly contiguous 289 GHz frequency range between 84.2 and 373.2 GHz, to image the continuum and spectral line emission at 1.6″(∼28 pc) resolution down to a sensitivity of 30 - 50 mK. This article describes the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program. We focus on the analysis of the spectra extracted from the 15″ (∼255 pc) resolution ALMA Compact Array data. Results. We modeled the molecular emission assuming local thermodynamic equilibrium with 78 species being detected. Additionally, multiple hydrogen and helium recombination lines are identified. Spectral lines contribute 5 to 36% of the total emission in frequency bins of 50 GHz. We report the first extragalactic detections of C2H5OH, HOCN, HC3HO, and several rare isotopologues. Isotopic ratios of carbon, oxygen, sulfur, nitrogen, and silicon were measured with multiple species. Concluison. Infrared pumped vibrationaly excited HCN, HNC, and HC3N emission, originating in massive star formation locations, is clearly detected at low resolution, while we do not detect it for HCO+. We suggest high temperature conditions in these regions driving a seemingly "carbon-rich"chemistry which may also explain the observed high abundance of organic species close to those in Galactic hot cores. The Lvib/LIR ratio was used as a proxy to estimate a 3% contribution from the proto super star cluster to the global infrared emission. Measured isotopic ratios with high dipole moment species agree with those within the central kiloparsec of the Galaxy, while those derived from 13C/18O are a factor of five larger, confirming the existence of multiple interstellar medium components within NGC 253 with different degrees of nucleosynthesis enrichment. The ALCHEMI data set provides a unique template for studies of star-forming galaxies in the early Universe.
Galaxies: individual: NGC 253
Line: identification
Galaxies: starburst
Galaxies: ISM
Submillimeter: ISM
ISM: molecules
Author
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
J. G. Mangum
National Radio Astronomy Observatory
N. Harada
Academia Sinica
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
Francesco Costagliola
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
K. Sakamoto
Academia Sinica
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Rebeca Aladro
Max Planck Society
Kunihiko Tanaka
Keio University
Y. Yoshimura
University of Tokyo
K. Nakanishi
National Astronomical Observatory of Japan
The Graduate University for Advanced Studies (SOKENDAI)
R. Herrero-Illana
European Southern Observatory Santiago
Institute of Space Sciences (ICE) - CSIC
S. Muhle
University of Bonn
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
E. Behrens
University of Virginia
L. Colzi
Centro de Astrobiologia (CAB)
Arcetri Astrophysical Observatory
K.L. Emig
National Radio Astronomy Observatory
G. A. Fuller
Institute of Astrophysics of Andalusia (IAA)
University of Manchester
S. G. Burillo
Spanish National Observatory (OAN)
T. R. Greve
Technical University of Denmark (DTU)
University College London (UCL)
C. Henkel
Chinese Academy of Sciences
Max Planck Society
King Abdulaziz University
Jonathan Holdship
University College London (UCL)
Leiden University
Pedro Humire
Max Planck Society
L. K. Hunt
Arcetri Astrophysical Observatory
T. Izumi
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
K. Kohno
Research Center for the Early Universe
University of Tokyo
Sabine König
Chalmers, Space, Earth and Environment, Onsala Space Observatory
D. S. Meier
National Radio Astronomy Observatory Socorro
New Mexico Institute of Mining and Technology
T. Nakajima
Nagoya University
Y. Nishimura
University of Tokyo
National Astronomical Observatory of Japan
M. Padovani
Arcetri Astrophysical Observatory
Víctor M. Rivilla
Arcetri Astrophysical Observatory
Centro de Astrobiologia (CAB)
S. Takano
Nihon University
P. van der Werf
Leiden University
Serena Viti
University College London (UCL)
Leiden University
Y. T. Yan
Max Planck Society
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 656 A46Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Physical Geography
DOI
10.1051/0004-6361/202141567