Search

Context. Observations of $\rm ^{14}N/^{15}N$ in the interstellar medium are becoming more frequent thanks to the increased telescope capabilities. However, interpreting these data is still puzzling. In particular, measurements of $\rm ^{14}N/^{15}N$ in diazenylium revealed high levels of anti-fractionation in cold cores. Aims. Furuya & Aikawa (2018), using astrophysical simulations coupled with a gas-grain chemical code, concluded that the $^{15}$N-depletion in prestellar cores could be inherited from the initial stages, when $\rm ^{14}N^{15}N$ is selectively photodissociated and 15N atoms deplete onto the dust grain, forming ammonia ices. We aim to test this hypothesis. Methods. We targeted three sources (the prestellar core L1544, the protostellar envelope IRAS4A, and the shocked region L1157-B1) with distinct degrees of desorption or sputtering of the ammonia ices. We observed the NH3 isotopologues with the GBT, and we inferred the $\rm ^{14}N/^{15}N$ via a spectral fitting of the observed inversion transitions. Results. $^{15}$NH3(1,1) is detected in L1544 and IRAS4A, whilst only upper limits are deduced in L1157-B1. The NH3 isotopic ratio is significantly lower towards the protostar than at the centre of L1544, where it is consistent with the elemental value. We also present the first spatially resolved map of NH3 nitrogen isotopic ratio towards L1544. Conclusions. Our results are in agreement with the hypothesis that ammonia ices are enriched in $^{15}$N, leading to a decrease of the $\rm ^{14}N/^{15}N$ ratio when the ices are sublimated into the gas phase for instance due to the temperature rise in protostellar envelopes. The ammonia $\rm ^{14}N/^{15}N$ value at the centre of L1544 is a factor of 2 lower than that of N2H+, suggesting that the dominant formation pathway is hydrogenation of N atoms on dust grains, followed by non-thermal desorption., Comment: Accepted for publication in A&A on 29/05/23

The formyl cation (HCO+) is one of the most abundant ions in molecular clouds and plays a major role in the interstellar chemistry. For this reason, accurate collisional rate coefficients for the rotational excitation of HCO+ and its isotopes due to the most abundant perturbing species in interstellar environments are crucial for non-local thermal equilibrium models and deserve special attention. In this work, we determined the first hyperfine resolved rate coefficients of HC17O+ in collision with H2 (j=0). Indeed, despite no scattering calculations on its collisional parameters have been performed so far, the HC17O+ isotope assumes a prominent role for astrophysical modelling applications. Computations are based on a new four dimensional (4D) potential energy surface, obtained at the CCSD(T)-F12a/aug-cc-pVQZ level of theory. A test on the corresponding cross section values pointed out that, to a good approximation, the influence of the coupling between rotational levels of H2 can be ignored. For this reason, the H2 collider has been treated as a spherical body and an average of the potential based on five orientations of H2 has been employed for scattering calculations. State-to-state rate coefficients resolved for the HC17O+ hyperfine structure for temperature ranging from 5 to 100 K have been computed using recoupling techniques. This study provides the first determination of HC17O+/H2 inelastic rate coefficients directly computed from full quantum close-coupling equations, thus supporting the reliability of future radiative transfer modellings of HC17O+ in interstellar environments., Comment: 9 pages, 6 figures

Isotopologue abundance ratios are important to understand the evolution of astrophysical objects and ultimately the origins of a planetary system like our own. Being nitrogen a fundamental ingredient of pre-biotic material, understanding its chemistry and inheritance is of fundamental importance to understand the formation of the building blocks of life. We present here single-dish observations of the ground state rotational transitions of the $^{13}$C and $^{15}$N isotopologues of HCN, HNC and CN with the IRAM 30m telescope. We analyse their column densities and compute the $^{14}$N/$^{15}$N ratio map for HCN. The $^{15}$N-fractionation of CN and HNC is computed towards different offsets across L1544. The $^{15}$N-fractionation map of HCN shows a clear decrease of the $^{14}$N/$^{15}$N ratio towards the southern edge of L1544, where carbon chain molecules present a peak, strongly suggesting that isotope-selective photodissociation has a strong effect on the fractionation of nitrogen across pre-stellar cores. The $^{14}$N/$^{15}$N ratio in CN measured towards four positions across the core also shows a decrease towards the South-East of the core, while HNC shows opposite behaviour. The uneven illumination of the pre-stellar core L1544 provides clear evidence that $^{15}$N-fractionation of HCN and CN is enhanced toward the region more exposed to the interstellar radiation field. Isotope-selective photodissociation of N$_2$ is then a crucial process to understand $^{15}$N fractionation, as already found in protoplanetary disks. Therefore, the $^{15}$N-fractionation in pre-stellar material is expected to change depending on the environment within which pre-stellar cores are embedded. The $^{12}$CN/$^{13}$CN ratio also varies across the core, but its variation does not affect our conclusions on the effect of the environment on the fractionation of nitrogen., Comment: Accepted for publication in A&A Letters

Nitriles play a key role as molecular precursors in prebiotic experiments based on the RNA-world scenario for the origin of life. These chemical compounds could have been partially delivered to the young Earth from extraterrestrial objects, stressing the importance of establishing the reservoir of nitriles in the interstellar medium. We report here the detection towards the molecular cloud G+0.693-0.027 of several nitriles, including cyanic acid (HOCN), and three C$_4$H$_3$N isomers (cyanoallene, CH$_2$CCHCN; propargyl cyanide, HCCCH$_2$CN; and cyanopropyne (CH$_3$CCCN), and the tentative detections of cyanoformaldehyde (HCOCN), and glycolonitrile (HOCH$_2$CN). We have also performed the first interstellar search of cyanoacetaldehyde (HCOCH$_2$CN), which was not detected. Based on the derived molecular abundances of the different nitriles in G+0.693-0.027 and other interstellar sources, we have discussed their formation mechanisms in the ISM. We propose that the observed HOCN abundance in G+0.693-0.027 is mainly due to surface chemistry and subsequent shock-induced desorption, while HCOCN might be mainly formed through gas-phase chemistry. In the case of HOCH$_2$CN, several grain-surface routes from abundant precursors could produce it. The derived abundances of the three C$_4$H$_3$N isomers in G+0.693-0.027 are very similar, and also similar to those previously reported in the dark cold cloud TMC-1. This suggests that the three isomers are likely formed through gas-phase chemistry from common precursors, possibly unsaturated hydrocarbons (CH$_3$CCH and CH$_2$CCH$_2$) that react with the cyanide radical (CN). The rich nitrile feedstock found towards G+0.693-0.027 confirms that interstellar chemistry is able to synthesize in space molecular species that could drive the prebiotic chemistry of the RNA-world., Comment: Accepted in Frontiers in Astronomy and Space Sciences

Spectral lines of ammonia, NH$_3$, are useful probes of the physical conditions in dense molecular cloud cores. In addition to advantages in spectroscopy, ammonia has also been suggested to be resistant to freezing onto grain surfaces, which should make it a superior tool for studying the interior parts of cold, dense cores. Here we present high-resolution NH$_3$ observations with the Very Large Array (VLA) and Green Bank Telescope (GBT) towards a prestellar core. These observations show an outer region with a fractional NH$_3$ abundance of X(NH$_3$) = (1.975$\pm$0.005)$\times 10^{-8}$ ($\pm 10\%$ systematic), but it also reveals that after all, the X(NH$_3$) starts to decrease above a H$_2$ column density of $\approx 2.6 \times 10^{22}$ cm$^{-2}$. We derive a density model for the core and find that the break-point in the fractional abundance occurs at the density n(H$_2$) $\sim 2\times10^5$ cm$^{-3}$, and beyond this point the fractional abundance decreases with increasing density, following the power law $n^{-1.1}$. This power-law behavior is well reproduced by chemical models where adsorption onto grains dominates the removal of ammonia and related species from the gas at high densities. We suggest that the break-point density changes from core to core depending on the temperature and the grain properties, but that the depletion power law is anyway likely to be close to $n^{-1}$ owing to the dominance of accretion in the central parts of starless cores., Comment: Accepted for publication in AJ. 18 Pages, 16 Figures, 3 Tables

We present the first detection of ($Z$)-1,2-ethenediol, (CHOH)$_2$, the enol form of glycolaldehyde, in the interstellar medium towards the G+0.693-0.027 molecular cloud located in the Galactic Center. We have derived a column density of (1.8$\pm$0.1)$\times$10$^{13}$ cm$^{-2}$, which translates into a molecular abundance with respect to molecular hydrogen of 1.3$\times$10$^{-10}$. The abundance ratio between glycolaldehyde and ($Z$)-1,2-ethenediol is $\sim$5.2. We discuss several viable formation routes through chemical reactions from precursors such as HCO, H$_2$CO, CHOH or CH$_2$CHOH. We also propose that this species might be an important precursor in the formation of glyceraldehyde (HOCH$_2$CHOHCHO) in the interstellar medium through combination with the hydroxymethylene (CHOH) radical., Comment: Accepted for publication in The Astrophysical Journal Letters

Pre-stellar cores represent the initial conditions in the process of star and planet formation. Their low temperatures ($<$10 K) allow the formation of thick icy dust mantles, which will be partially preserved in the future protoplanetary disks, ultimately affecting the chemical composition of planetary systems. Previous observations have shown that carbon- and oxygen-bearing species, in particular CO, are heavily depleted in pre-stellar cores due to the efficient molecular freeze-out onto the surface of cold dust grains. However, N-bearing species such as NH$_3$ and, in particular, its deuterated isotopologues, appear to maintain high abundances where CO molecules are mainly in solid phase. Thanks to ALMA, we present here the first clear observational evidence of NH$_2$D freeze-out toward the L1544 pre-stellar core, suggestive of the presence of a"complete-depletion zone" within a $\simeq$1800 au radius, in agreement with astrochemical pre-stellar core model predictions. Our state-of-the-art chemical model coupled with a non-LTE radiative transfer code demonstrates that NH$_2$D becomes mainly incorporated in icy mantles in the central 2000 au and starts freezing-out already at $\simeq$7000 au. Radiative transfer effects within the pre-stellar core cause the NH$_2$D(1$_{11}$-1$_{01}$) emission to appear centrally concentrated, with a flattened distribution within the central $\simeq$3000 au, unlike the 1.3 mm dust continuum emission which shows a clear peak within the central $\simeq$1800 au. This prevented NH$_2$D freeze-out to be detected in previous observations, where the central 1000 au cannot be spatially resolved., Comment: accepted for publication in The Astrophysical Journal

Small imines containing up to three carbon atoms are present in the interstellar medium. As alkynyl compounds are abundant in this medium, propargylimine thus represents a promising candidate for a new interstellar detection. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of propargylimine in its ground vibrational state in order to obtain a highly precise set of rest-frequencies and to search it in space. The rotational spectra of $E$ and $Z$ geometrical isomers of propargylimine have been recorded in laboratory in the 83-500 GHz frequency interval. The measurements have been performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic quantities. The improved spectral data allow us to perform a successful search for this new imine in the quiescent G+0.693-0.027 molecular cloud. Eighteen lines of $Z$-propargylimine have been detected at level $>2.5 \sigma$, resulting in a column density estimate of $N = (0.24\pm 0.02)\times 10^{14}$ cm$^{-2}$. An upper limit was retrieved for the higher-energy $E$ isomer, which was not detected in the data. The fractional abundance (w.r.t. H$_2$) derived for $Z$-propargylimine is $1.8\times 10^{-10}$. We discuss the possible formation routes by comparing the derived abundance with those measured in the source for possible chemical precursors., Comment: 15 pages, 6 figures. Accepted for publication in Astronomy & Astrophysics

Observations of ammonia in interstellar environments have revealed high levels of deuteration, and all its D-containing variants, including ND$_3$, have been detected in cold prestellar cores and around young protostars. The observation of these deuterated isotopologues is very useful to elucidate the chemical and physical processes taking place during the very early stages of star formation, as the abundance of deuterated molecules is highly enhanced in dense and cold gas. Nitrogen hydride radicals are key species lying at the very beginning of the reaction pathway leading to the formation of NH$_3$ and organic molecules of pre-biotic interest, but relatively little information is known about their D-bearing isotopologues. To date, only ND has been detected in the interstellar gas. To aid the identification of further deuterated nitrogen radicals, we have thoroughly re-investigated the rotational spectrum of NHD employing two different instruments: a frequency-modulation submillimetre spectrometer operating in the THz region and a synchrotron-based Fourier Transform infrared spectrometer operating in the 50-240 cm$^{-1}$ wavelength range. NHD was produced in a plasma of NH$_3$ and D$_2$. A wide range of rotational energy levels has been probed thanks to the observation of high $N$ (up to 15) and high $K_a$ (up to 9) transitions. A global analysis including our new data and those already available in the literature has provided a comprehensive set of very accurate spectroscopic parameters. A highly reliable line catalogue has been generated to assist archival data searches and future astronomical observations of NHD at submillimetre and THz regimes., Comment: 16 pages, 3 figures

Phosphorus-bearing species are an essential key to form life on Earth, however they have barely been detected in the interstellar medium. Since only PN and PO have been identified so far towards star-forming regions, the chemical formation pathways of P-bearing molecules are not easy to constrain and are thus highly debatable. An important factor still missing in the chemical models is the initial elemental abundance of phosphorus, i.e. the depletion level of P. In order to overcome this problem, we study P-bearing species in diffuse/translucent clouds. In these objects phosphorus is mainly in the gas phase and therefore the elemental initial abundance needed in our chemical simulations corresponds to the cosmic one and is thus well constrained. An advanced chemical model with an updated P-chemistry network has been used. Single-pointing observations were performed with the IRAM 30m telescope towards the line of sight to the blazar B0355+508 aiming for the (2-1) transitions of PN, PO, HCP and CP. This line of sight incorporates five diffuse/translucent clouds. The (2-1) transitions of the PN, PO, HCP and CP were not detected. We report detections of the (1-0) lines of $\mathrm{^{13}CO}$, HNC and CN along with a first detection of $\mathrm{C^{34}S}$. We have reproduced the observations of HNC, CN, CS and CO in every cloud by applying typical conditions for diffuse/translucent clouds. According to our best-fit model, the most abundant P-bearing species are HCP and CP ($\sim10^{-10}$), followed by PN, PO and $\mathrm{PH_3}$ ($\sim10^{-11}$). We show that the production of P-bearing species is favoured towards translucent rather than diffuse clouds, where the environment provides a stronger shielding from the interstellar radiation. Based on our improved model, the (1-0) transitions of HCP, CP, PN and PO are expected to be detectable with estimated intensities up to $\sim200$ mK.

Context. The deuterium fraction in low-mass prestellar cores is a good diagnostic indicator of the initial phases of star formations, and it is also a fundamental quantity to infer the ionisation degree in these objects. Aims. With the analysis of multiple transitions of $\rm N_2H^+$, $\rm N_2D^+$, $\rm HC^{18}O^+$ and $\rm DCO^+$ we are able to determine the molecular column density maps and the deuterium fraction in $\rm N_2H^+$ and $\rm HCO^+$ toward the prototypical prestellar core L1544. This is the preliminary step to derive the ionisation degree in the source. Methods. We use a non-local thermodynamic equilibrium (non-LTE) radiative transfer code, combined with the molecular abundances derived from a chemical model, to infer the excitation conditions of all the observed transitions, which allows us to derive reliable maps of each molecule's column density. The ratio between the column density of a deuterated species and its non-deuterated counterpart gives the searched deuteration level. Results. The non-LTE analysis confirms that, for the analysed molecules, higher-J transitions are characterised by excitation temperatures $\approx 1-2\,$K lower than the lower-J ones. The chemical model that provides the best fit to the observational data predict the depletion of $\rm N_2H^+$ and to a lesser extent of $\rm N_2D^+$ in the innermost region. The peak values for the deuterium fraction that we find are $\mathrm{D/H_{N_2H^+}} = 0.26^{+0.15}_{-0.14}$ and $\mathrm{D/H_{HCO^+}} = 0.035^{+0.015}_{-0.012}$, in good agreement with previous estimates in the source., Comment: Accepted for publication on A&A on 18/7/19

We present ALMA maps of the starless molecular cloud core Ophiuchus/H-MM1 in the lines of deuterated ammonia (ortho-NH2D), methanol (CH3OH), and sulphur monoxide (SO). The dense core is seen in NH2D emission, whereas the CH3OH and SO distributions form a halo surrounding the core. Because methanol is formed on grain surfaces, its emission highlights regions where desorption from grains is particularly efficient. Methanol and sulphur monoxide are most abundant in a narrow zone that follows the eastern side of the core. This side is sheltered from the stronger external radiation field coming from the west. We show that photodissociation on the illuminated side can give rise to an asymmetric methanol distribution, but that the stark contrast observed in H-MM1 is hard to explain without assuming enhanced desorption on the shaded side. The region of the brightest emission has a wavy structure that rolls up at one end. This is the signature of Kelvin-Helmholtz instability occurring in sheared flows. We suggest that in this zone, methanol and sulphur are released as a result of grain-grain collisions induced by shear vorticity., Comment: Accepted for publication in the Astrophysical Journal

The rotational spectrum of $^{15}$ND in its ground electronic $X^{3}\Sigma^{-}$ state has been observed for the first time. Forty-three hyperfine-structure components belonging to the ground and v = 1 vibrational states have been recorded with a frequency-modulation millimeter-/submillimeter-wave spectrometer. These new measurements, together with the ones available for the other isotopologues NH, ND, and $^{15}$NH, have been simultaneously analysed using the Dunham model to represent the ro-vibrational, fine, and hyperfine energy contributions. The least-squares fit of more than 1500 transitions yielded an extensive set of isotopically independent $U_{lm}$ parameters plus 13 Born--Oppenheimer Breakdown coefficients $\Delta_{lm}$. As an alternative approach, we performed a Dunham analysis in terms of the most abundant isotopologue coefficients $Y_{lm}$ and some isotopically dependent Born--Oppenheimer Breakdown constants $\delta_{lm}$ [R. J. Le Roy, J. Mol. Spectrosc. 194, 189 (1999)]. The two fits provide results of equivalent quality. The Born--Oppenheimer equilibrium bond distance for the imidogen radical has been calculated [$r_e^{BO}$ =103.606721(13) pm] and zero point energies have been derived for all the isotopologues., Comment: 11 pages, 1 figure, 8 tables. Accepted for publication in Phys. Chem. Chem. Phys

Protonated molecular species have been proven to be abundant in the interstellar gas. This class of molecules is also pivotal for the determination of important physical parameters for the ISM evolution (e.g. gas ionisation fraction) or as tracers of non-polar, hence not directly observable, species. The identification of these molecular species through radioastronomical observations is directly linked to a precise laboratory spectral characterisation. The goal of the present work is to extend the laboratory measurements of the pure rotational spectrum of the ground electronic state of protonated carbonyl sulfide (HSCO$^+$) and its deuterium substituted isotopomer (DSCO$^+$). At the same time, we show how implementing different laboratory techniques allows the determination of different spectroscopical properties of asymmetric-top protonated species. Three different high-resolution experiments were involved to detected for the first time the $b-$type rotational spectrum of HSCO$^+$, and to extend, well into the sub-millimeter region, the $a-$type spectrum of the same molecular species and DSCO$^+$. The electronic ground-state of both ions have been investigated in the 273-405 GHz frequency range, allowing the detection of 60 and 50 new rotational transitions for HSCO$^+$ and DSCO$^+$, respectively. The combination of our new measurements with the three rotational transitions previously observed in the microwave region permits the rest frequencies of the astronomically most relevant transitions to be predicted to better than 100 kHz for both HSCO$^+$ and DSCO$^+$ up to 500 GHz, equivalent to better than 60 m/s in terms of equivalent radial velocity. The present work illustrates the importance of using different laboratory techniques to spectroscopically characterise a protonated species at high frequency, and how a similar approach can be adopted when dealing with reactive species., Comment: 7 pages, 4 figures. Accepted for publication in Astronomy and Astrophysics

A fraction of Narrow Line Seyfert 1 galaxies (NLS1) are hosted by galaxies that present a disturbed morphology, in some cases hinting for merger processes, that are putative sources of gas replenishment. We have been investigating the poorly studied population of radio loud NLS1 (RL-NLS1) showing a flat radio spectrum, assumed to be the manifestation of the presence of a radio jet. In some of the objects the infrared emission is well fitted by a combination of an AGN component and an "active" host galaxy component like M82, the estimate SFR being in the LIRG/ULIRG range (10-500 Msun/year). In order to better characterize that component, we have been investigating the sub-millimeter/millimeter emission of the sources using APEX. Here we present the results concerning a pilot sample of 2 representative objects., Comment: 5 pages, published on Proceedings of Science - volume "Revisiting narrow-line Seyfert 1 galaxies and their place in the Universe"

Context: The $^{15}$N fractionation has been observed to show large variations among astrophysical sources, depending both on the type of target and on the molecular tracer used. These variations cannot be reproduced by the current chemical models. Aims: Until now, the $^{14}$N/$^{15}$N ratio in N$_2$H$^+$ has been accurately measured in only one prestellar source, L1544, where strong levels of fractionation, with depletion in $^{15}$N, are found ($^{14}$N/$^{15}$N$\: \approx 1000$). In this paper we extend the sample to three more bona fide prestellar cores, in order to understand if the antifractionation in N$_2$H$^+$ is a common feature of this kind of sources. Methods: We observed N$_2$H$^+$,N$^{15}$NH$^+$ and $^{15}$NNH$^+$ in L183, L429 and L694-2 with the IRAM 30m telescope. We modeled the emission with a non-local radiative transfer code in order to obtain accurate estimates of the molecular column densities, including the one for the optically thick N$_2$H$^+$. We used the most recent collisional rate coefficients available, and with these we also re-analysed the L1544 spectra previously published. Results: The obtained isotopic ratios are in the range $630-770$ and significantly differ with the value, predicted by the most recent chemical models, of $\approx 440$, close to the protosolar value. Our prestellar core sample shows high level of depletion of $^{15}$N in diazenylium, as previously found in L1544. A revision of the N chemical networks is needed in order to explain these results., Comment: Accepted for publication in A&A

We report molecular gas observations of IRAS 20100-4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using ALMA and PdBI observations, we spatially resolve the CO(1-0) emission from the outflowing molecular gas in both and find maximum outflow velocities of $ v_{\rm max} \sim 1600$ and $\sim 1700$ km/s for IRAS 20100-4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates of $\dot M_{\rm OF} \sim 670$ and $\sim 350$ Msun/yr, respectively, corresponding to molecular gas depletion timescales $\tau^{\rm dep}_{\rm OF} \sim 11$ and $\sim 16$ Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, $\tau^{\rm dep}_{\rm SFR} \sim 33$ and $\sim 46$ Myr, respectively. To determine the outflow driving mechanism, we compare the starburst ($L_{*}$) and AGN ($L_{\rm AGN}$) luminosities to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern $L_{\rm AGN}$. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with $L_{*}$ and $L_{\rm IR}$ as with $L_{\rm AGN}$, indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows., Comment: 29 pages, 17 figures, 6 tables, accepted to ApJ

Towards the pre-stellar core L1544, the methanol (CH$_3$OH) emission forms an asymmetric ring around the core centre, where CH$_3$OH is mostly in solid form, with a clear peak 4000~au to the north-east of the dust continuum peak. As part of the NOEMA Large Project SOLIS (Seeds of Life in Space), the CH$_3$OH peak has been spatially resolved to study its kinematics and physical structure and to investigate the cause behind the local enhancement. We find that methanol emission is distributed in a ridge parallel to the main axis of the dense core. The centroid velocity increases by about 0.2~km~s$^{-1}$ and the velocity dispersion increases from subsonic to transonic towards the central zone of the core, where the velocity field also shows complex structure. This could be indication of gentle accretion of material onto the core or interaction of two filaments, producing a slow shock. We measure the rotational temperature and show that methanol is in local thermodynamic equilibrium (LTE) only close to the dust peak, where it is significantly depleted. The CH$_3$OH column density, $N_{tot}({\rm CH_3OH})$, profile has been derived with non-LTE radiative transfer modelling and compared with chemical models of a static core. The measured $N_{tot}({\rm CH_3OH})$ profile is consistent with model predictions, but the total column densities are one order of magnitude lower than those predicted by models, suggesting that the efficiency of reactive desorption or atomic hydrogen tunnelling adopted in the model may be overestimated; or that an evolutionary model is needed to better reproduce methanol abundance., Comment: 19 pages, 18 figures. Accepted by ApJ

HC$_3$N is an ubiquitous molecule in interstellar environments, from external galaxies, to Galactic interstellar clouds, star forming regions, and planetary atmospheres. Observations of its rotational and vibrational transitions provide important information on the physical and chemical structure of the above environments. We present the most complete global analysis of the spectroscopic data of HC$_3$N. We have recorded the high-resolution infrared spectrum from 450 to 1350 cm$^{-1}$, a region dominated by the intense $\nu_5$ and $\nu_6$ fundamental bands, located at 660 and 500 cm$^{-1}$, respectively, and their associated hot bands. Pure rotational transitions in the ground and vibrationally excited states have been recorded in the millimetre and sub-millimetre regions in order to extend the frequency range so far considered in previous investigations. All the transitions from the literature and from this work involving energy levels lower than 1000 cm$^{-1}$ have been fitted together to an effective Hamiltonian. Because of the presence of various anharmonic resonances, the Hamiltonian includes a number of interaction constants, in addition to the conventional rotational and vibrational l-type resonance terms. The data set contains about 3400 ro-vibrational lines of 13 bands and some 1500 pure rotational lines belonging to 12 vibrational states. More than 120 spectroscopic constants have been determined directly from the fit, without any assumption deduced from theoretical calculations or comparisons with similar molecules. An extensive list of highly accurate rest frequencies has been produced to assist astronomical searches and data interpretation. These improved data, have enabled a refined analysis of the ALMA observations towards Sgr B2(N2)., Comment: 35 pages, 14 figures, accepted for pubblication in ApJ Supplement

HOCO$^+$ is a polar molecule that represents a useful proxy for its parent molecule CO$_2$, which is not directly observable in the cold interstellar medium. This cation has been detected towards several lines of sight, including massive star forming regions, protostars, and cold cores. Despite the obvious astrochemical relevance, protonated CO$_2$ and its deuterated variant, DOCO$^+$, still lack an accurate spectroscopic characterisation. The aim of this work is to extend the study of the ground-state pure rotational spectra of HOCO$^+$ and DOCO$^+$ well into the sub-millimetre region. Ground-state transitions have been recorded in the laboratory using a frequency-modulation absorption spectrometer equipped with a free-space glow-discharge cell. The ions were produced in a low-density, magnetically-confined plasma generated in a suitable gas mixture. The ground-state spectra of HOCO$^+$ and DOCO$^+$ have been investigated in the 213-967 GHz frequency range, with the detection of 94 new rotational transitions. Additionally, 46 line positions taken from the literature have been accurately remeasured. The newly-measured lines have significantly enlarged the available data sets for HOCO$^+$ and DOCO$^+$, thus enabling the determination of highly accurate rotational and centrifugal distortion parameters. Our analysis showed that all HOCO$^+$ lines with Ka $\geq$ 3 are perturbed by a ro-vibrational interaction that couples the ground state with the v$_ 5$ = 1 vibrationally-excited state. This resonance has been explicitly treated in the analysis in order to obtain molecular constants with clear physical meaning. The improved sets of spectroscopic parameters provide enhanced lists of very accurate, sub-millimetre rest-frequencies of HOCO$^+$ and DOCO$^+$ for astrophysical applications. These new data challenges a recent tentative identification of DOCO$^+$ toward a pre-stellar core., Comment: 7 pages, 1 figure, accepted for publication in A&A

Because of the very peculiar conditions of chemistry in many astrophysical gases (low densities, mostly low temperatures, kinetics-dominated chemical evolution), great efforts have been devoted to study molecular signatures and chemical evolution. While experiments are being performed in many laboratories, it appears that the efforts directed towards theoretical works are not as strong. This report deals with the present status of chemical physics/physical chemistry theory, for the qualitative and quantitative understanding of kinetics of molecular scattering, being it reactive or inelastic. By gathering several types of expertise, from applied mathematics to physical chemistry, dialog is made possible, as a step towards new and more adapted theoretical frameworks, capable of meeting the theoretical, methodological and numerical challenges of kinetics-dominated gas phase chemistry in astrophysical environments. A state of the art panorama is presented, alongside present-day strengths and shortcomings. However, coverage is not complete, being limited in this report to actual attendance of the workshop. Some paths towards relevant progress are proposed., Comment: 24 pages, 7 figures. White paper reporting a workshop held in Garching, Nov 23-Dec 4, 2015

Dense cloud cores present chemical differentiation due to the different distribution of C-bearing and N-bearing molecules, the latter being less affected by freeze-out onto dust grains. In this letter we show that two C-bearing molecules, CH$_3$OH and $c$-C$_3$H$_2$, present a strikingly different (complementary) morphology while showing the same kinematics toward the prestellar core L1544. After comparing their distribution with large scale H$_2$ column density N(H$_2$) map from the Herschel satellite, we find that these two molecules trace different environmental conditions in the surrounding of L1544: the $c$-C$_3$H$_2$ distribution peaks close to the southern part of the core, where the surrounding molecular cloud has a N(H$_2$) sharp edge, while CH$_3$OH mainly traces the northern part of the core, where N(H$_2$) presents a shallower tail. We conclude that this is evidence of chemical differentiation driven by different amount of illumination from the interstellar radiation field: in the South, photochemistry maintains more C atoms in the gas phase allowing carbon chain (such as $c$-C$_3$H$_2$) production; in the North, C is mainly locked in CO and methanol traces the zone where CO starts to freeze out significantly. During the process of cloud contraction, different gas and ice compositions are thus expected to mix toward the central regions of the core, where a potential Solar-type system will form. An alternative view on carbon-chain chemistry in star-forming regions is also provided., Comment: Accepted for publication in A&A Letters

The Star formation rate (SFR) is a crucial parameter to investigate galaxy evolution. At low redshift the cosmic SFR density declines smoothly, and massive active galaxies become passive, reducing their star formation activity. This implies that the bulk of the SFR density at low redshift is mainly driven by low mass objects. We investigate the properties of a sample of low luminosity Far-Infrared (FIR) sources selected at 250 microns from Pappalardo et al. (2015). We have collected data from Ultraviolet to FIR to perform a multi-wavelengths analysis. The main goal is to investigate the correlation between SFR, stellar mass, and dust mass for a galaxy population with a wide range in dust content and stellar mass, including the low mass regime that most probably dominates the SFR density at low z. We define a main sample of ~800 sources with full Spectral Energy Distribution (SED) coverage between 0.15 < lambda < 500 microns and an extended sample with ~5000 sources in which we remove the constraints on the Ultraviolet and Near-Infrared bands. We analyze both samples with two different SED fitting methods: MAGPHYS and CIGALE. In the SFR versus stellar mass plane our samples occupy a region included between local spirals and higher redshift star forming galaxies. The galaxies subsample with the higher masses (M* > 3e10 Msol) does not lie on the main sequence, but shows a small offset, as a consequence of the decreased star formation. Low mass galaxies (M* < 1e10 Msol) settle in the main sequence with SFR and stellar mass consistent with local spirals. Deep Herschel data allow the identification of a mixed galaxy population, with galaxies still in an assembly phase, or galaxies at the beginning of their passive evolution. We find that the dust luminosity is the parameter that discriminates these two galaxy populations., Comment: Corrected to match the published version

We present three independent catalogs of point-sources extracted from SPIRE images at 250, 350, and 500 micron as a part of the Herschel Virgo Cluster Survey (HeViCS). The source positions are determined by estimating the likelihood to be a real source for each peak on the maps and the flux densities are estimated using the sourceExtractorTimeline, a timeline-based point source fitter. Afterwards, each source is subtracted from the maps, removing a Gaussian function in every position with the full width half maximum equal to that estimated in sourceExtractorTimeline. This procedure improves the robustness of our algorithm in terms of source identification. The HeViCS catalogs contain about 52000, 42200, and 18700 sources selected at 250, 350, and 500 micron above 3sigma and are ~ 75%, 62%, and 50% complete at flux densities of 20 mJy at 250, 350, 500 micron, respectively. We then measured source number counts at 250, 350, and 500 micron and we also cross-correlated the catalogs with the Sloan Digital Sky Survey to investigate the redshift distribution of the nearby sources. From this cross-correlation, we select ~2000 sources with reliable fluxes and a high signal-to-noise ratio, finding an average redshift z~0.3+/-0.22. The number counts at 250, 350, and 500 micron show an increase in the slope below 200 mJy, indicating a strong evolution in number of density for galaxies at these fluxes. In general, models tend to overpredict the counts at brighter flux densities, underlying the importance of studying the Rayleigh-Jeans part of the spectral energy distribution to refine the theoretical recipes of the models. Our iterative method for source identification allowed the detection of a family of 500 micron sources that are not foreground objects belonging to Virgo and not found in other catalogs., Comment: Accepted for publication in Astronomy and Astrophysics

Using the IRAM 30m telescope, we mapped the methanol emission in the pre-stellar core L1544 and observed singly deuterated methanol (CH$_2$DOH and CH$_3$OD) towards the dust peak of L1544. Non-LTE radiative transfer modelling was performed on three CH$_3$OH emissions lines at 96.7 GHz, using a Bonnor-Ebert sphere as a model for the source. We have also assumed a centrally decreasing abundance profile to take the molecule freeze-out in the inner core into account. The column density of CH$_2$DOH was derived assuming LTE excitation and optically thin emission. The CH$_3$OH emission has a highly asymmetric morphology, resembling a non-uniform ring surrounding the dust peak, where CO is mainly frozen onto dust grains. The observations provide an accurate measure of methanol deuteration in the cold pre-stellar gas. The derived abundance ratio is [CH$_2$DOH]/[CH$_3$OH] $= 0.10\pm 0.03$, which is significantly smaller than the ones found in low-mass Class 0 protostars and smaller than the deuterium Fraction measured in other molecules towards L1544. The low deuterium fractionation observed in L1544 and the morphology of the CH$_3$OH emission suggest that we are mainly tracing the outer parts of the core, where CO just started to freeze-out onto dust grains., Comment: 8 pages, 9 figures. Accepted in A&A

We present a catalogue of bulgeless galaxies, which includes 19225 objects selected in four of the deepest, largest multi-wavelength datasets available -- COSMOS, AEGIS, GEMS and GOODS -- at intermediate redshift ($0.4 \leq z \leq 1.0$). The morphological classification was provided by the Advanced Camera for Surveys General Catalogue (ACS-GC), which used publicly available data obtained with the ACS instrument on the Hubble Space Telescope. Rest-frame photometric quantities were derived using kcorrect. We analyse the properties of the sample and the evolution of pure-disc systems with redshift. Very massive [$\log (M_\star/M_{\odot}) > 10.5$] bulgeless galaxies contribute to ~30% of the total galaxy population number density at $z \geq 0.7$, but their number density drops substantially with decreasing redshift. We show that only a negligible fraction of pure discs appear to be quiescent systems, and red sequence bulgeless galaxies show indications of dust-obscured star formation. X-ray catalogues were used to search for X-ray emission within our sample. After visual inspection and detailed parametric morphological fitting we identify 30 AGN that reside in galaxies without a classical bulge. The finding of such peculiar objects at intermediate redshift shows that while AGN growth in merger-free systems is a rare event (0.2% AGN hosts in this sample of bulgeless galaxies), it can indeed happen relatively early in the Universe history., Comment: 49 pages, 13 figures

Samples of pristine Solar System material found in meteorites and interplanetary dust particles are highly enriched in (15)N. Conspicuous nitrogen isotopic anomalies have also been measured in comets, and the (14)N/(15)N abundance ratio of the Earth is itself larger than the recognised pre-solar value by almost a factor of two. Ion--molecules, low-temperature chemical reactions in the proto-solar nebula have been repeatedly indicated as responsible for these (15)N-enhancements. We have searched for (15)N variants of the N2H+ ion in L1544, a prototypical starless cloud core which is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion. The goal is the evaluation of accurate and reliable (14)N/(15)N ratio values for this species in the interstellar gas. A deep integration of the (15)NNH+ (1-0) line at 90.4 GHz has been obtained with the IRAM 30 m telescope. Non-LTE radiative transfer modelling has been performed on the J=1-0 emissions of the parent and (15)N-containing dyazenilium ions, using a Bonnor--Ebert sphere as a model for the source. A high-quality fit of the N2H+ (1--0) hyperfine spectrum has allowed us to derive a revised value of the N2H+ column density in L1544. Analysis of the observed N(15)NH+ and (15)NNH+ spectra yielded an abundance ratio N[N(15)NH+]/N[(15)NNH+] = 1.1 +/- 0.3. The obtained (14)N/(15)N ratio is ~ 1000 +/- 200, suggestive of a sizeable (15)N depletion in this molecular ion. Such a result is not consistent with the prediction of present nitrogen chemical models. As chemical models predict large (15)N fractionation of N2H+, we suggest that (15)N(14)N, or (15)N in some other molecular form, is preferentially depleted onto dust grains., Comment: 12 pages, 9 figures, manuscript accepted in A&A

Excess levels of 15N isotopes which have been detected in primitive solar system materials are explained as a remnant of interstellar chemistry which took place in regions of the protosolar nebula. Chemical models of nitrogen fractionation in cold clouds predict an enhancement in the gas-phase abundance of 15N-bearing molecules, thus we have searched for 15N variants of the N2H+ ion in L1544, which is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion. With the IRAM 30m telescope we have obtained deep integrations of the N2H+(1-0) line at 91.2 GHz. The N2H+(1-0) line has been detected toward the dust emission peak of L1544. The 14N/15N abundance ratio in N2H+ resulted 446+/-71, very close to the protosolar value of ~450, higher than the terrestrial ratio of ~270, and significantly lower than the lower limit in L1544 found by Gerin et al. (2009, ApJ, 570, L101) in the same object using ammonia isotopologues., Comment: Accepted for publication in Astronomy and Astrophysics