The Survey

We have recently finished an unbiased full survey in the 2mm window of the prototypical nearby starburst galaxy NGC253. This galaxy is one of the favorite extragalactic sources for molecular line studies. In fact, most of the molecules so far detected outside the Galaxy have been detected towards NGC253 (e.g. Mauersberger & Henkel 1993, Rev. Mod. Astron. 6).
Our knowledge of the chemical complexity of outer Galaxies is fairly biased and thus incomplete since the vast majority of the observations are aimed to the study of a few specific molecules. This is then the first time we are able to get a full scan at 2mm which provide us a complete information about the physical conditions and molecular complexity of the matter within the nucleus of NGC253. Such a kind of studies had been succesfully done in different molecular clouds of our Galaxy (e.g. Cummins et al 1986; Sutton 1985, 1991;Turner 1989, 1991; Numelin 2000).

The Source

The Sculptor galaxy NGC253, an almost edge-on spiral (i=78^o, Pence 1981) of type Sc(s) (Sandage & Bedke 1995), is perhaps the best example of a nearby nuclear starburst (Rieke et al. 1988)
At a distance of 2.5Mpc, NGC253 constitutes the nearest starburst spiral galaxy, revealing violent star formation within a region 1000 light-years across. His high starforming rate was first identified by its excess of infrared radiation from warm dust, containing one of the brightest extragalactic IRAS point sources (S₁₀₀=1045Jy, L_IR=25 10⁹L_o).
The nucleus of this galaxy is the most prolific complex molecular source outside the Galaxy, both in terms of the line strenght and the number of molecular species detected.

The Observations

The observations were carried out at the IRAM 30m telescope, during four observing periods in the last two years. This survey had been possible thanks to the new generation 2mm SIS receivers together with the two 256 x 4MHz filterbanks currently working at the 30m telescope. These receivers, operating betweeen 130 and 183GHz provided us with an instantaneous bandwith of 1GHz each. The 2 filterbank spectrometers, with a bandwith of 1GHz each, were tuned to adjacent frequencies, thus covering a 2GHz instantaneous band. These configuration, altogether with the collecting area of the 30m telescope, allowed us to finish the survey in a reasonable period of time. A mean time of 2-3 hours was spent on each frequency, in order to achieve a sensitivity close to the expected confusion limit. A rms of ~3-4 mK was reached in most of the spectra at the lower frequencies, and 5-6 mK at the higher frequencies.

The Authors

Sergio Martin Ruiz : IRAM, Granada
Rainer Mauersberger : IRAM,Granada
Jesus Martin-Pintado : IEM,Madrid
Christian Henkel : MPIfR, Bonn
Santiago Garcia-Burillo : OAN,Madrid

Last Modified 2003-03-20 Sergio Martin Ruiz