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, 13 CO, HCN, HNC, HCO + , CN, and C 2 H. We also detect HC 3 N J = 10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771, and NGC 1068. The only HC 3 N detections are in objects with HCO + /HCN < 1. Galaxies with the highest HC 3 N/HCN ratios have warm IRAS colours (60/100 μm > 0.8). The brightest HC 3 N 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/ 13 CO ratio is positively correlated with the dust temperature and is generally higher than in our galaxy. The emission of CN and C 18 O is correlated. Conclusions. Bright HC 3 N 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 HC 3 N and faint HCO + could be signatures of embedded starformation, 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.

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We present results of deep echelle spectrophotometry of eight Galactic H II regions located at galactocentric distances between 6.3 and 10.4 kpc. The data have been taken with the Very Large Telescope (VLT) Ultraviolet Echelle Spectrograph (UVES) in the 3100 to 10360Å range. We have derived C ++ and O ++ abundances from recombination lines for all the objects, as well as O + abundances from this kind of lines for three of the nebulae. The intensity of recombination lines is almost independent on the assumed electron temperature as well as on the possible presence of spatial temperature variations or fluctuations inside the nebulae. These data allow the determination of the gas-phase C and O abundance gradients of the Galactic disk, of paramount importance for chemical evolution models. This is the first time the C gradient is derived from a so large number of H II regions and for a so wide range of galactocentric distances. Abundance gradients are found of the form ∆log(O/H) = −0.044±0.010 dex kpc −1 , ∆log(C/H) = −0.103±0.018 dex kpc −1 , and ∆log(C/O) = −0.058±0.018 dex kpc −1 .

We present high resolution observations of the giant extragalactic H II regions NGC 604, NGC 2363, NGC 5461 and NGC 5471, based on observations taken with the ISIS spectrograph on the William Herschel Telescope. We have detected -by the first time-C II and O II recombination lines in these objects. We find that recombination lines give larger C ++ and O ++ abundances than collisionallly excited lines, suggesting that temperature variations can be present in the objects. We detect [Fe IV] lines in NGC 2363 and NGC 5471, the most confident detection of optical lines of this kind in H II regions. Considering the temperature structure we derive their H, He, C, N, O, Ne, S, Ar, and Fe abundances. From the recombination lines of NGC 5461 and NGC 5471 we determine the presence of C/H and O/H gradients in M101. We calculate the ∆Y /∆O and ∆Y /∆Z values considering the presence of temperature variations and under the assumption of constant temperature. We obtain a better agreement with models of galactic chemical evolution by considering the presence of temperature variations than by assuming that the temperature is constant in these nebulae.

We present results of deep echelle spectrophotometry of the brightest knot of the Herbig–Haro object HH 202 in the Orion Nebula – HH 202‐S – using the Ultraviolet Visual Echelle Spectrograph in the spectral range from 3100 to 10 400 Å. The high spectral resolution of the observations has permitted to separate the component associated with the ambient gas from that associated with the gas flow. We derive electron densities and temperatures from different diagnostics for both components, as well as the chemical abundances of several ions and elements from collisionally excited lines, including the first determinations of Ca+ and Cr+ abundances in the Orion Nebula. We also calculate the He+, C2+, O+ and O2+ abundances from recombination lines. The difference between the O2+ abundances determined from collisionally excited and recombination lines – the so‐called abundance discrepancy factor – is 0.35 and 0.11 dex for the shock and nebular components, respectively. Assuming that the abundance discrepancy is produced by spatial variations in the electron temperature, we derive values of the temperature fluctuation parameter, t2, of 0.050 and 0.016 for the shock and nebular components, respectively. Interestingly, we obtain almost coincident t2 values for both components from the analysis of the intensity ratios of He i lines. We find significant departures from case B predictions in the Balmer and Paschen flux ratios of lines of high principal quantum number n. We analyse the ionization structure of HH 202‐S, finding enough evidence to conclude that the flow of HH 202‐S has compressed the ambient gas inside the nebula trapping the ionization front. We measure a strong increase of the total abundances of nickel and iron in the shock component, the abundance pattern and the results of photoionization models for both components are consistent with the partial destruction of dust after the passage of the shock wave in HH 202‐S.