TY - JOUR
T1 - ALCHEMI, an AL MA Comprehensive High-resolution Extragalactic Molecular Inventory
T2 - Survey presentation and first results from the ACA array
AU - Martín, S.
AU - Mangum, J. G.
AU - Harada, N.
AU - Costagliola, F.
AU - Sakamoto, K.
AU - Muller, S.
AU - Aladro, R.
AU - Tanaka, K.
AU - Yoshimura, Y.
AU - Nakanishi, K.
AU - Herrero-Illana, R.
AU - Mühle, S.
AU - Aalto, S.
AU - Behrens, E.
AU - Colzi, L.
AU - Emig, K. L.
AU - Fuller, G. A.
AU - García-Burillo, S.
AU - Greve, T. R.
AU - Henkel, C.
AU - Holdship, J.
AU - Humire, P.
AU - Hunt, L.
AU - Izumi, T.
AU - Kohno, K.
AU - König, S.
AU - Meier, D. S.
AU - Nakajima, T.
AU - Nishimura, Y.
AU - Padovani, M.
AU - Rivilla, V. M.
AU - Takano, S.
AU - Van Der Werf, P. P.
AU - Viti, S.
AU - Yan, Y. T.
N1 - Publisher Copyright:
© ESO 2021.
PY - 2021
Y1 - 2021
N2 - 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.
AB - 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.
KW - Galaxies: individual: NGC 253
KW - Galaxies: ISM
KW - Galaxies: starburst
KW - ISM: molecules
KW - Line: identification
KW - Submillimeter: ISM
U2 - 10.1051/0004-6361/202141567
DO - 10.1051/0004-6361/202141567
M3 - Journal article
AN - SCOPUS:85117289568
SN - 0004-6361
VL - 656
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A46
ER -