Molecules as tracers of galaxy evolution: an EMIR survey I. Presentation of the data and first results
Artikel i vetenskaplig tidskrift, 2011

Aims. We investigate the molecular gas properties of a sample of 23 galaxies in order to find and test chemical signatures of galaxy evolution and to compare them to IR evolutionary tracers. Methods. Observation at 3 mm wavelengths were obtained with the EMIR broadband receiver, mounted on the IRAM 30 m telescope on Pico Veleta, Spain. We compare the emission of the main molecular species with existing models of chemical evolution by means of line intensity ratios diagrams and principal component analysis. Results. We detect molecular emission in 19 galaxies in two 8 GHz-wide bands centred at 88 and 112 GHz. The main detected molecules are CO, (CO)-C-13, HCN, HNC, HCO+, CN, and C2H. We also detect HC3N J = 10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771, and NGC 1068. The only HC3N detections are in objects with HCO+/HCN < 1. Galaxies with the highest HC3N/HCN ratios have warm IRAS colours (60/100 mu m > 0.8). The brightest HC3N emission is found in IC 860, where we also detect the molecule in its vibrationally excited state. We find low HNC/HCN line ratios (<0.5), that cannot be explained by existing PDR or XDR chemical models. The intensities of HCO+ and HNC appear anti-correlated. No correlation is found between the HNC/HCN line ratio and dust temperature. All HNC-bright objects are either luminous IR galaxies (LIRG) or Seyferts. Galaxies with bright polycyclic aromatic hydrocarbons (PAH) emission show low HNC/HCO+ ratios. The CO/(CO)-C-13 ratio is positively correlated with the dust temperature and is generally higher than in our galaxy. The emission of CN and (CO)-O-18 is correlated. Conclusions. Bright HC3N emission in HCO+-faint objects may imply that these are not dominated by X-ray chemistry. Thus the HCN/HCO+ line ratio is not, by itself, a reliable tracer of XDRs. Bright HC3N and faint HCO+ could be signatures of embedded star-formation, instead of AGN activity. Mechanical heating caused by supernova explosions may be responsible for the low HNC/HCN and high HCO+/HCN ratios in some starbursts. We cannot exclude, however, that the discussed trends are largely caused by optical depth effects or excitation. Chemical models alone cannot explain all properties of the observed molecular emission. Better constraints to the gas spacial distribution and excitation are needed to distinguish abundance and excitation effects.

arp 220

dense gas


ISM: molecules


nearby galaxies

vibrationally excited hc3n

luminous infrared galaxies



hnc line emission


galaxies: active

galaxies: evolution

galaxies: ISM



Francesco Costagliola

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

M. I. Rodriguez

CSIC - Instituto de Astrof&amp;iacute;sica de Andaluc&amp;iacute;a (IAA)

Sebastien Muller

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

H. W. W. Spoon

Cornell University

S. Martin

European Southern Observatory Santiago

Miguel Angel Perez-Torres

CSIC - Instituto de Astrof&amp;iacute;sica de Andaluc&amp;iacute;a (IAA)

Antxon Alberdi

CSIC - Instituto de Astrof&amp;iacute;sica de Andaluc&amp;iacute;a (IAA)

Johan Lindberg

Onsala Space Observatory

Kobenhavns Universitet

Fabien Batejat

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

E. Jutte

Ruhr-Universität Bochum

P. van der Werf

University of Edinburgh

Leiden University

F. Lahuis

Leiden University

SRON Netherlands Institute for Space Research

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 528 A30


Astronomi, astrofysik och kosmologi


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