Abstract
Although first considered as too diluted for the formation of moleculesin-situand too harsh an environment for their survival, the interstellar medium has turned out to host a rich palette of molecular species: to date, 256 species, not counting isotopologues, have been identified. The last decade, and more particularly the last 2 years, have seen an explosion of new detections, including those of a number of complex organic species, which may be dubbed as prebiotic. Organic molecules have been discovered not just in interstellar clouds from the Solar neighbourhood, but also throughout the Milky-Way, as well as in nearby galaxies, or some of the most distant quasars. These discoveries were made possible by the completion of large sub-millimetre and radio facilities. Equipped with new generation receivers, those instruments have provided the orders of magnitude leap in sensitivity required to detect the vanishingly weak rotational lines that allowed the molecule identifications. Last 2 years, 30 prebiotic molecules have been detected in TMC-1, a dust-enshrouded gaseous cloud located at 400 light-years from the Sun in the Taurus constellation. Ten new molecular species, have been identified in the arm of a spiral galaxy seven billion light-yr distant, and 12 molecular species observed in a quasar at 11 billion light-yr. We present the latest spectral observations of this outlying quasar and discuss the implications of those detections in these 3 archetypal sources. The basic ingredients involved in the Miller-Urey experiment and related experiments (H2, H2O, CH4, NH3, CO, H2S, … ) appeared early after the formation of the first galaxies and are widespread throughout the Universe. The chemical composition of the gas in distant galaxies seems not much different from that in the nearby interstellar clouds. It presumably comprises, like for TMC-1, aromatic rings and complex organic molecules putative precursors of the RNA nucleobases, except the lines of such complex species are too weak to be detected that far.
Highlights
The question of extraterrestrial life arose as soon as Earth was recognized as one amid a myriad of celestial bodies
It was argued that extraterrestrial life could be based on silicium or germanium, instead of carbon, and take surprising forms
A decisive advantage of a phased array of mobile antennas is that its angular resolution can be much better. The latter, which scales with the instrument largest dimension D as λ/D, is a critical parameter in the radio domain. Another advantage of interferometers vs single-dish telescopes is that they yield spectra with much flatter baselines, as they filter out intensity fluctuations caused by amplifier instabilities and by the Earth atmosphere
Summary
The question of extraterrestrial life arose as soon as Earth was recognized as one amid a myriad of celestial bodies. The EMIR SIS junction receivers on the IRAM 30-m diameter telescope, located at an altitude of 2,900 m on Pico Veleta, near Granada, Spain (Figure 1), allow to simultaneously observe a 32 GHz-wide band with a spectral resolution of 200 kHz within the 73–375 GHz (λ 4 to 0.8 mm) atmospheric windows. Another advantage of interferometers vs single-dish telescopes is that they yield spectra with much flatter baselines, as they filter out intensity fluctuations caused by amplifier instabilities and by the Earth atmosphere This is valuable for the detection of the broad (broadened by Doppler effect) and very weak lines, such as those observed in remote galaxies: this makes it possible to detect, with proper integration time, molecular lines 105 times weaker than the receiver noise throughout a 8 GHz-wide spectrum without removing any baseline. Its SIS junction receivers and its wide band XF Fast Fourier Transform correlator make it well suited for extragalactic spectral surveys, since it can instantaneously cover a 32 GHz-wide bandwidth with 2 MHz-wide (2.6 kms−1 at 230 GHz) spectral channels (see Figure 5)
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