arXiv subjects

J. Martin-Pintado

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

At least 73 records · Page 4Linked to original sources

arXiv2006

First Measurements of the Electron Density Enhancements Expected in C-shocks

Magnetic precursors of C-shocks accelerate, compress and heat molecular ions, modifying the kinematics and the physical conditions of the ion fluid with respect to the neutral one. Electron densities are also expected to be significantly enhanced in shock precursors. In this Letter, we present observations of strongly polar ion and neutral molecules such as SiO, H13CO+, HN13C and H13CN, which reveal the electron density enhancements associated with the precursor of the young L1448-mm outflow. While in the ambient gas the excitation of the ions and neutrals is explained by collisional excitation by H2 with a single density of 10E5cmE-3, H13CO+ shows an over excitation in the shock precursor component that requires H2 densities of a factor of >10 larger than those derived from the neutral species. This over excitation in H13CO+ can be explained if we consider an additional excitation by collisions with electrons and an electron density enhancement in the precursor stage by a factor of 500, i.e. a fractional ionization of 5x10E-5. These results show that multiline observations can be used to study the evolution of the ion and electron fluids at the first stages of the C-shock interaction.

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arXiv2006

Extragalactic chemistry of molecular gas: lessons from the local universe

Observational constraints provided by high resolution and high sensitivity observations of external galaxies made in the millimeter and submillimeter range have started to put on a firm ground the study of extragalactic chemistry of molecular gas. In particular, the availability of multi-species and multi-line surveys of nearby galaxies is central to the interpretation of existent and forthcoming millimeter observations of the high redshift universe. Probing the physical and chemical status of molecular gas in starbursts and active galaxies (AGN) requires the use of specific tracers of the relevant energetic phenomena that are known to be at play in these galaxies: large-scale shocks, strong UV fields, cosmic rays and X-rays. We present below the first results of an ongoing survey, allying the IRAM 30m telescope with the Plateau de Bure interferometer(PdBI), devoted to study the chemistry of molecular gas in a sample of starbursts and AGN of the local universe. These observations highlight the existence of a strong chemical differentiation in the molecular disks of starbursts and AGN.

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arXiv2005

Large-scale molecular shocks in galaxies: the SiO interferometer map of IC342

(Abridged) We present the first high-resolution (5.6''x5.1'') images of the emission of silicon monoxide (SiO) in the nearby spiral IC342, obtained with the IRAM Plateau de Bure Interferometer. We have mapped the emission of the SiO(2-1) and H13CO+(1-0) lines in a 0.9kpcx1.3kpc region around the nucleus of IC342. The bulk of the line emission comes from a 290pc spiral arm and a r~80pc nuclear ring. The distribution of SiO clouds is mostly anticorrelated with the continuum emission at 87GHz, dominated by thermal free-free bremsstrahlung. The SiO/H13CO+ intensity ratio increases by an order of magnitude from the nuclear ring to the spiral arm. Furthermore the gas kinematics show significant differences between SiO and H13CO+ over the spiral arm, where the linewidths of SiO are 2 times larger than that of H13CO+. The average abundance of SiO in the inner r~320pc, X(SiO)>2x10^{-10}, evidences that shock chemistry is at work in IC342. We have compared the emission of SiO with another tracer of molecular shocks: the emission of methanol (CH3OH). The significant difference of the X(SiO) measured between the spiral arm (~a few 10^{-9}) and the nuclear ring (~10^{-10}) is not echoed by a comparable variation in the SiO/CH3OH intensity ratio. This implies that the typical shock velocities should be similar in both regions. In contrast, the fraction of shocked molecular gas should be 5-7 times larger in the spiral arm (up to ~10% of the available molecular gas mass over the arm region) compared to the nuclear ring. We conclude that the large-scale shocks revealed by the SiO map of IC342 are mostly unrelated with star formation and arise instead in a pre-starburst phase. Shocks are driven by cloud-cloud collisions along the potential well of the IC342 bar. The general implications for the current understanding of galaxy evolution are discussed.

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arXiv2005

A new intermediate mass protostar in the Cepheus A HW2 region

We present the discovery of the first molecular hot core associated with an intermediate mass protostar in the CepA HW2 region. The hot condensation was detected from single dish and interferometric observations of several high excitation rotational lines (from 100 to 880K above the ground state) of SO2 in the ground vibrational state and of HC3N in the vibrationally excited states v7=1 and v7=2. The kinetic temperature derived from both molecules is 160K. The high-angular resolution observations (1.25'' x 0.99'') of the SO2 J=28(7,21)-29(6,24) line (488K above the ground state) show that the hot gas is concentrated in a compact condensation with a size of 0.6''(430AU), located 0.4'' (300AU) east from the radio-jet HW2. The total SO2 column density in the hot condensation is 10E18cm-2, with a H2 column density ranging from 10E23 to 6 x 10E24cm-2. The H2 density and the SO2 fractional abundance must be larger than 10E7cm-3 and 2 x 10E-7 respectively. The most likely alternatives for the nature of the hot and very dense condensation are discussed. From the large column densities of hot gas, the detection of the HC3N vibrationally excited lines and the large SO2 abundance, we favor the interpretation of a hot core heated by an intermediate mass protostar of 10E3 Lo. This indicates that the CepA HW2 region contains a cluster of very young stars.

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arXiv2005

Grain Evolution across the Shocks in the L1448-mm Outflow

The recent detection of shock-precursors toward the very young L1448-mm outflow offers us the possibility to study the grain chemistry during the first stages of the shock evolution, constraining the molecules ejected from grains and the species formed in gas phase. Observations of key molecules in the grain chemistry such as SiO, CH3OH, SO, CS, H2S, OCS, and SO2 toward this outflow are presented. The line profiles and the derived abundances show three distinct velocity regimes that trace the shock evolution: the preshock, the shock-precursor and the postshock gas. The SiO, CH3OH, SO, and CS abundances are enhanced with respect to the quiescent gas by 1 order of magnitude in the shock-precursor component, and by 3 orders of magnitude in the postshock gas. The derived SiO and CH3OH abundances are consistent with the recent ejection of these molecules from grains. Since H2S is only enhanced in the shock-precursor component, and OCS and SO2 are undetected, SO and CS are the most abundant sulfur-bearing species in the grain mantles of L1448-mm. The ejection of mainly SO and CS rather than H2S or OCS from grains, suggests that the sulfur chemistry will depend on the chemical "history" of the grain mantles in outflows and hot cores.

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arXiv2004

Q0957+561 revised: CO emission from a disk at z=1.4

Based on additional interferometric observations, we reanalysed the CO(2-1) and 3mm continuum emission of Q0957+561, a lensed QSO at a redshift of z=1.4141. The emission in the CO(2-1) lines reveals a gas-rich host galaxy with a peculiar double-peaked profile at one of the two lensed images. Our new interferometric CO maps of the host galaxy agree well with HST images obtained by Keeton et al. (2000) and we thus argue that the two velocity components arise from molecular gas in the disk of the host galaxy. We also present new model calculations, all in excellent agreement with recent time delay measurements and simulations.

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arXiv2004

ISO observations of the Galactic center Interstellar Medium: ionized gas

(Abridged) We present fine structure and recombination lines observations of the ionized gas toward a sample of 18 sources located within 300 pc of the center of the Galaxy (GC). The fine structure lines from [NII] and [SIII] have been detected in 16 sources. In 10 sources we have even detected the [OIII] 88 $μ$m line. The measured N, S and Ne abundances are similar to those measured in the HII regions in the 5-kpc ring and in the nuclei of starburst galaxies. The fine structure lines ratios measured for all the sources can be explained by photo-ionization with an effective temperature of 32000-37000 K and an ionization parameter, $U$, of $-1>\log U > -3$. The highest excitation is found in the Radio Arc region but there must be more ionizing sources distributed over the Galactic center than the known clusters of massive stars. Most of the clouds are located far from the prominent continuum complexes (Sgr C, B ...). However, it is possible that the clouds are ionized by escaped photons from those complexes. The excitation ratios, effective temperature and ionization parameter measured in the GC are similar to those found in some low excitation starburst galaxies. The [NeIII]/[NeII] line ratios measured in the GC sources are consistent with the results of the Thornely et al. (2000) model for a short burst of massive star formation less than 8 Myr ago. We have also found that the [NeII] 13 $μ$m ~ to far-infrared continuum ratio measured for the GC sources is similar to that of external galaxies, supporting the idea by Sturm et al. (2002) that the far-infrared continuum in Active Galaxies is dominated by dust heated by stellar radiation rather than by the AGN.

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arXiv2004

ISO observations of the Galactic center Interstellar Medium: neutral gas and dust

The 500 central pc of the Galaxy (hereafter GC) exhibit a widespread gas component with a kinetic temperature of 100-200 K. The bulk of this gas is not associated to the well-known thermal radio continuum or far infrared sources like Sgr A or Sgr B. How this gas is heated has been a longstanding problem. With the aim of studying the thermal balance of the neutral gas and dust in the GC, we have observed 18 molecular clouds located at projected distances far from thermal continuum sources with the Infrared Space Observatory (ISO). In this paper we present observations of several fine structure lines and the full continuum spectra of the dust between 40 and 190 microns. A warm dust component with a temperature between 27 and 42 K is needed to fit the spectra. We have compared the gas and the dust emission with the predictions from J-type and C-type shocks and photodissociation region (PDRs) models. We conclude that the dust and the fine structure lines observations are best explained by a PDR with a density of 10$^3$ cm^-3 and an incident far-ultraviolet field 10$^3$ times higher than the local interstellar radiation field. PDRs can naturally explain the discrepancy between the gas and the dust temperatures. However, these PDRs can only account for 10-30% of the total H2 column density with a temperature of ~ 150 K. We discuss other possible heating mechanisms (short version).

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arXiv2004

Molecular Gas Chemistry in AGN I. The IRAM Survey of NGC1068

There is observational evidence that nuclear winds and X-rays can heavily influence the physical conditions and chemical abundances of molecular gas in the circumnuclear disks (CND) of Active Galactic Nuclei (AGN). In this paper we probe the chemical status of molecular gas in the CND of NGC1068, a prototypical Seyfert 2 galaxy. Precedent claims that the chemistry of molecular gas in the nucleus of NGC1068 is abnormal by galactic standards were based on the high HCN/CO luminosity ratio measured in the CND. Results from new observations obtained in this survey have served to derive abundances of molecular species such as SiO, CN, HCO+, HOC+, H13CO+ and HCO. These estimates are complemented by a re-evaluation of molecular abundances for HCN, CS and CO, based on previously published single-dish and interferometer observations of NGC1068. We report on the first detection of SiO emission in the CND of NGC1068. The estimated large abundance of SiO in the CND, X(SiO)~5-10x10^{-9}, cannot be attributed to shocks related to star formation, as there is little evidence of a recent starburst in the nucleus of NGC1068. Alternatively, we propose that silicon chemistry is driven by intense X-ray processing of molecular gas. We also report on the first extragalactic detection of the reactive ion HOC+. Most remarkably, the estimated HCO+/HOC+ abundance ratio in the nucleus of NGC1068, ~30-80, is the smallest ever measured in molecular gas. The abundances derived for all molecules that have been the subject of this survey are compared with the predictions of models invoking either oxygen-depletion or X-ray chemistry in molecular gas. Our conclusions favour an overall scenario where the CND of NGC1068 has become a giant X-ray Dominated Region (XDR).

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arXiv2004

The Galactic center interstellar medium as seen by ISO

This paper deals with the heating and the ionization of the interstellar medium (ISM) in the 500 central pc of the Milky Way (hereafter Galactic center, GC). We review the results of the Infrared Space Observatory (ISO) observations of a sample of GC molecular clouds located far from thermal radiocontinuum or far-infrared sources. For the first time, we have been able to study in detail the dust continuum spectra from 40 to 190 microns founding a warm (30-40 K) dust component in addition to the well known 15-20 K component. Fine-structure lines observations have revealed the presence of diffuse ionized gas associated with the molecular clouds. The effective temperature of the ionizing radiation is higher than 33000 K. ISO has also allow us to measure the fraction of warm (~ 150 K) H2 in the GC clouds, which is on average of 30 %. The observations of the warm (a few 100 K) neutral gas are compatible with a Photon Dominated Region (PDR) scenario.

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arXiv2004

Tracing the shock precursors in the L1448-mm/IRS3 outflows

We present the detection of the SiO v=0 J=2-1 and J=3-2 lines, and of the HCO 101-000 J=3/2-1/2 F=2-1 line at ambient velocities towards the molecular outflows in L1448-mm and L1448-IRS3. This is the first detection of HCO in a dark cloud. We have also measured lines of H13CO+, H13CN, HN13C, CH3OH, and N2H+. While the HCO and the SiO lines have the narrowest profiles with linewidths of 0.5 km s-1, the other lines have widths of 1km s-1. Towards L1448-mm, all lines except those of SiO and HCO, show two distinct velocity components centered at 4.7 and 5.2 km s-1. HCO is only observed in the 4.7 km s-1 cloud, and SiO in the 5.2 km s-1 component. The SiO abundance is 10E-11 in the 5.2 km s-1 clouds, one order of magnitude larger than in the 4.7 km s-1 component and in other dark clouds. The HCO abundance is 10E-11, similar to that predicted by the ion-molecule reactions models for the quiescent gas in dark clouds. The large change in the SiO/HCO abundance ratio (>150) from the 4.7 to the 5.2 km s-1 component, and the distribution and kinematics of the SiO emission towards L1448-mm suggest that the ambient SiO is associated with the molecular outflows. We propose that the narrow linewidths and the abundances of SiO in the ambient gas are produced by the interaction of the magnetic and/or radiative precursors of the shocks with the clumpy pre-shocked ambient gas.

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arXiv2003

The quasar Q0957+561: Lensed CO emission from a disk at z~1.4?

In recent years large efforts have been made to detect molecular gas towards high redshifted objects. Up to now the literature reports on only two cases of CO-detection in quasars at a redshift between 1 and 2 - Q0957+561, a gravitationally lensed system at z=1.41 (Planesas et al. 1999), and HR10 at z=1.44 (Andreani et al. 2000). According to Planesas et al. (1999), 12CO(2-1) emission was detected towards both the lensed images of Q0957+561 with the IRAM Plateau de Bure Interferometer (PdBI). In contrast to the optical spectra of the two images which support the idea that they are images of one and the same object, the CO-spectra were surprisingly different: the southern image (named CO-B) shows a single blueshifted line whereas a double-peaked line profile with a blue- and a redshifted part appears towards the northern image (CO-A). Based on the observations and on simulations with a gravitational lens program, we are tempted to argue that the line profile traces the presence of molecular gas of a disk in the host galaxy around the quasar. We have now new observations with the PdBI providing the necessary sensitivity to corroborate our disk model.

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arXiv2003

XDR Chemistry in the Circumnuclear Disk of NGC 1068

We have studied the feedback influence that the central engine of the Seyfert 2 galaxy NGC 1068 may have on the chemistry of the 200 pc circumnuclear gas disk (CND). With this purpose, we have conducted a multi-species/multi-transition survey of molecular gas in the CND of NGC 1068 using the IRAM 30m telescope. Abundances of several molecular species have been estimated, including HCN, CN, CS, HCO+, SiO and HOC+. We report on the detection of significant SiO emission in this galaxy, as well as on the first extragalactic detection of the active radical HOC+. We conclude that the chemistry of the molecular gas reservoir in the CND can be best explained in the framework of X-rays Dominated Regions (XDR) models.

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arXiv2003

Molecular Gas Chemistry in Starbursts and AGN

We present the main results of an extragalactic survey aiming to study the chemistry of molecular gas in a limited sample of starburst galaxies (SB) and AGN hosts. Observations have been carried out with the IRAM 30m telescope and the Plateau de Bure Interferometer (PdBI). The high resolution/sensitivity of the PdBI has made possible to obtain high quality images of the galaxies using specific molecular gas tracers of Shock Chemistry, Photon Dominated Regions (PDR) and X-ray Dominated Regions (XDR). The occurrence of large-scale shocks and the propagation of PDR chemistry in starbursts can be studied. We also discuss the onset of XDR chemistry in AGN.

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arXiv2003

First detections of extragalactic SO2, NS and NO

We report the first detections of SO_2, NS and NO in an extragalactic source, the nucleus of the starburst galaxy NGC 253. Five SO_2 transitions, three groups of hyperfine components of NO and five of NS were detected. All three species show large abundances averaged over the inner 200 pc of NGC 253. With a relative abundance of a few 10^-7, the emission of the NO molecule is similar or even larger than that found in Galactic star forming regions. The derived relative molecular abundances for each molecule have been compared with those of prototypical Galactic molecular clouds. These results seem to confirm that large scale shocks dominate the chemistry of these molecules in the nucleus of NGC 253, ruling out a chemistry dominated by PDRs for the bulk of the gas.

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arXiv2003

Shocked gas layers surrounding the WR nebula NGC 2359

NGC 2359 is a Wolf-Rayet (W-R) nebula partially bound by a rather dense and warm molecular cloud. We present the results derived from CO and $^{13}$CO fully sampled maps of the molecular material with angular resolutions up to 12". We have detected three different velocity components, and determined their spatial distribution and physical properties. The kinematics, morphology, mass and density are clearly stratified with respect to the W-R star. These features allow us to learn about the recent evolutionary history of HD 56925, because the multiple layers could be associated to several energetic events which have acted upon the surrounding circumstellar medium. Hence, a careful study of the different shockfronts contain clues in determining the present and past interaction of this evolved massive star with its surroundings. From the analysis of the mass-loss history in massive stars like HD 56925, we suggest that the multiple layers of shocked molecular gas are likely to be produced during the earlier LBV phase and/or the actual W-R stage of HD 56925.

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arXiv2003

Warm molecular gas, dust and ionized gas in the 500 central pc of the Galaxy

We present infrared and millimeter observations of molecular gas, dust and ionized gas towards a sample of clouds distributed along the 500 central pc of the Galaxy. The clouds were selected to investigate the physical state, in particular the high gas temperatures, of the Galactic center region (GCr) clouds located far from far-infrared of thermal radio continuum sources. We have found that there is ionized gas associated with the molecular gas. The ionizing radiation is hard (~35000 K) but diluted due to the inhomogeneity of the medium. We estimate that ~30 % of the warm molecular gas observed in the GCr clouds is heated by ultra-violet radiation in photo-dissociation regions.

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arXiv2002

Widespread HCO emission in the M82's nuclear starburst

We present a high-resolution (~ 5'') image of the nucleus of M82 showing the presence of widespread emission of the formyl radical (HCO). The HCO map, the first obtained in an external galaxy, reveals the existence of a structured disk of ~ 650 pc full diameter. The HCO distribution in the plane mimics the ring morphology displayed by other molecular/ionized gas tracers in M82. More precisely, rings traced by HCO, CO and HII regions are nested, with the HCO ring lying in the outer edge of the molecular torus. Observations of HCO in galactic clouds indicate that the abundance of HCO is strongly enhanced in the interfaces between the ionized and molecular gas. The surprisingly high overall abundance of HCO measured in M82 (X(HCO) ~ 4x10^{-10}) indicates that its nuclear disk can be viewed as a giant Photon Dominated Region (PDR) of ~ 650 pc size. The existence of various nested gas rings, with the highest HCO abundance occurring at the outer ring (X(HCO) ~ 0.8x10^{-9}), suggests that PDR chemistry is propagating in the disk. We discuss the inferred large abundances of HCO in M82 in the context of a starburst evolutionary scenario, picturing the M82 nucleus as an evolved starburst.

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