arXiv subjects

J. Martín-Pintado

Publications and source records attributed to J. Martín-Pintado.

42 records · Page 3Linked to original sources

arXiv2008

Tracing high density gas in M 82 and NGC 4038

We present the first detection of CS in the Antennae galaxies towards the NGC 4038 nucleus, as well as the first detections of two high-J (5-4 and 7-6) CS lines in the center of M 82. The CS(7-6) line in M 82 shows a profile that is surprisingly different to those of other low-J CS transitions we observed. This implies the presence of a separate, denser and warmer molecular gas component. The derived physical properties and the likely location of the CS(7-6) emission suggests an association with the supershell in the centre of M 82.

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arXiv2006

Organic chemistry in the dark clouds L1448 and L183. A Unique grain mantle composition

We present high sensitivity observations of the complex organic molecules (COMs) CH3OH, C2H5OH, HCOOCH3, HCOOH and H2CO and of SiO toward the quiescent dark cloud L183 and the molecular outflow L1448-mm. We have not detected C2H5OH, HCOOCH3 and SiO in L183 and in the quiescent gas of L1448-mm. The abundances of CH3OH, H2CO and SiO are enhanced by factors 4-20 in the shock precursor component, and those of CH3OH and SiO by 3 and 4 orders of magnitude in the shocked gas, without substantial changes (< factor of 2) in the abundances of C2H5OH and HCOOCH3 relative to that of CH3OH. The large enhancements of SiO and CH3OH can be explained by the shock ejection of an important fraction of the grain mantle material into gas phase. Our upper limits to the C2H5OH/CH3OH and HCOOCH3/CH3OH ratios are consistent with the rather constant ratios measured in hot cores and Galactic center clouds. However, the upper limits to the HCOOCH3/CH3OH and the HCOOH/CH3OH ratios are at least one order of magnitude smaller than those found in"hot corinos" surrounding low mass protostars. We speculate that the observed abundances of COMs in different objects are consistent with a sort of "universal" grain mantle composition which is locally changed by the processes of low mass star formation.

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arXiv2006

Organic Molecules in the Galactic Center. Hot Core Chemistry without Hot Cores

We study the origin of large abundances of complex organic molecules in the Galactic center (GC). We carried out a systematic study of the complex organic molecules CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules.The CH3OH abundance between clouds varies by nearly two orders of magnitude from 2.4x10^{-8} to 1.1x10^{-6}. The abundance of the other complex organic molecules relative to that of CH3OH is basically independent of the CH3OH abundance, with variations of only a factor 4-8. The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant. We find that both the abundance and the abundance ratios of the complex molecules relative to CH3OH in hot cores are similar to those found in the GC clouds. However, hot corinos show different abundance ratios than observed in hot cores and in GC clouds. The rather constant abundance of all the complex molecules relative to CH3OH suggests that all complex molecules are ejected from grain mantles by shocks. Frequent (similar 10^{5}years) shocks with velocities >6km/s are required to explain the high abundances in gas phase of complex organic molecules in the GC molecular clouds. The rather uniform abundance ratios in the GC clouds and in Galactic hot cores indicate a similar average composition of grain mantles in both kinds of regions. The Sickle and the Thermal Radio Arches, affected by UV radiation, show different relative abundances in the complex organic molecules due to the differentially photodissociation of these molecules.

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arXiv2006

Methanol detection in M82

We present a multilevel study of the emission of methanol, detected for the first time in this galaxy, and discuss the origin of its emission. The high observed methanol abundance of a few 10^-9 can only be explained if injection of methanol from dust grains is taken into account. While the overall [CH3OH]/[NH3] ratio is much larger than observed towards other starbursts, the dense high excitation component shows a similar value to that found in NGC 253 and Maffei 2. Our observations suggest the molecular material in M 82 to be formed by dense warm cores, shielded from the UV radiation and similar to the molecular clouds in other starbursts, surrounded by a less dense photodissociated halo. The dense warm cores are likely the location of recent and future star formation within M 82.

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arXiv2006

A 2 mm spectral line survey of the starburst galaxy NGC 253

We present the first unbiased molecular line survey towards an extragalactic source, namely the nuclear region of the starburst galaxy NGC 253. The scan covers the frequency band from 129.1 to 175.2 GHz, i.e. most of the 2mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers 34SO and HC18O+. Tentative detections of two deuterated species, DNC and N2D+, are reported for the first time from a target beyond the Magellanic Clouds. Additionally, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC 253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC 342 and NGC 4945 to that of NGC 253. On the other hand, the chemistries characterizing NGC 253 and M 82 are clearly different. We also present a comparison of the chemical composition of NGC 253 with those observed in Galactic prototypical sources. The chemistry of NGC 253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC 253 is dominated by the same mechanism as that in the central region of the Milky Way.

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arXiv2004

Sulfur chemistry and isotopic ratios in the starburst galaxy NGC 253

Based on observations of the most abundant sulfur-bearing molecules (H2S, CS, NS, SO, H2CS, OCS, and SO2) carried out with the IRAM 30m telescope and SEST, we present the first analysis of the sulfur chemistry of an extragalactic source, the nuclear region of the starburst galaxy NGC 253. This is the first time that H2S and, tentatively, H2CS are detected towards the nucleus of a starburst galaxy. Source averaged fractional abundances of these molecules are a few 10^-9, except for CS and OCS which are more abundant (10^-8). Sulfur isotopic ratios, 32S/34S~8+-2 and 34S/33S>9, are measured through observations of 13CS, C34S, and C33S. A comparison with the observed relative abundances towards different prototypical Galactic sources suggests that the chemical composition of NGC 253 is similar to that found towards the molecular clouds complexes like Sgr B2 in the nuclear region of the Milky Way. The large overabundance of OCS compared to the predictions of time-dependent sulfur chemistry models supports the idea that OCS is likely injected into the gas phase from the grain mantles by low velocity shocks.

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