M. A. Requena-Torres

Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines

We have mapped 20 spectral lines in the Central Molecular Zone (CMZ) around the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth University of New South Wales-Mopra Spectrometer (UNSW-MOPS) digital filter bank, obtaining ∼2 km s−1 spectral and ∼40 arcsec spatial resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+, SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+ molecules. The area covered is Galactic longitude −0bsl000647 to 1bsl000648 and latitude −0bsl000643 to 0bsl000642, including the bright dust cores around Sgr A, Sgr B2, Sgr C and G1.6−0.025. We present images from this study and conduct a principal component analysis on the integrated emission from the brightest eight lines. This is dominated by the first component, showing that the large-scale distribution of all molecules is very similar. We examine the line ratios and optical depths in selected apertures around the bright dust cores, as well as for the complete mapped region of the CMZ. We highlight the behaviour of the bright HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues of these species, and compare the behaviour with that found in extragalactic sources where the emission is unresolved spatially. We also find that the isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing redshifted velocity in some locations. Line luminosities are also calculated and compared to that of CO, as well as to line luminosities determined for external galaxies.

Tracing Shocks and Photodissociation in the Galactic Center Region

We present a systematic study of the HNCO, C18O,13CS, and C34S emission toward 13 selected molecular clouds in the Galactic center region. The molecular emission in these positions is used as a template of the different physical and chemical processes claimed to be dominant in the circumnuclear molecular gas of galaxies. The relative abundance of HNCO shows a variation of more than a factor of 20 among the observed sources. The HNCO/13CS abundance ratio is highly contrasted (up to a factor of 30) between the shielded molecular clouds mostly affected by shocks, where HNCO is released to gas phase from grain mantles, and those pervaded by an intense UV radiation field, where HNCO is photodissociated and CS production favored via ion reactions. We propose the relative HNCO to CS abundance ratio as a highly contrasted diagnostic tool to distinguish between the influence of shocks and/or the radiation field in the nuclear regions of galaxies and their relation to the evolutionary state of their nuclear star formation bursts.

A λ = 3 mm molecular line survey of NGC 1068 - Chemical signatures of an AGN environment

Aims. We study the molecular composition of the interstellar medium (ISM) surrounding an active galactic nucleus (AGN), by making an inventory of molecular species and their abundances, to establish a chemical differentiation between starburst galaxies and AGN. Methods. We used the IRAM-30 m telescope to observe the central 1.5–2 kpc region of NGC 1068, covering the frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we calculated the column densities of the detected molecules. We used a chemical model to reproduce the abundances found in the AGN, to determine the origin of each detected species, and to test the influence of UV fields, cosmic rays, and shocks on the ISM. Results. We identified 24 different molecular species and isotopologues, among which HC3N, SO, N2H + ,C H 3CN, NS, 13 CN, and HN 13 C are detected for the first time in NGC 1068. A comparison of the abundances in the nuclear regions of NGC 1068, M 82, and NGC 253 allowed us to establish a chemical differentiation between starburst galaxies and AGN. Two abundant species in starburst galaxies, H2CO and CH3CCH, are not detected in NGC 1068, probably because they are destroyed by UV fields or shocks. On the other hand, species such as CN, SiO, HCO + , and HCN, are enhanced by cosmic ray radiation fields. We obtained the upper limits to the isotopic ratios 12 C/ 13 C = 49, 16 O/ 18 O = 177, and 32 S/ 34 S = 5. These ratios are much lower in this AGN than in starburst galaxies. Our chemical models suggest that the chemistry in the nucleus of NGC 1068 is strongly influenced by cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV) radiation fields also explain the observations well. C-shocks can explain the abundances of C2 Ha nd H 2CO, but do not strongly affect the abundances of the other detected species. Conclusions. The gas in the nucleus of NGC 1068 has a different chemical composition than starburst galaxies. The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas, which allow the nucleus activity to be characterised by its molecular abundances.

GREAT confirms transient nature of the circum-nuclear disk

We report SOFIA/GREAT, Herschel/HIFI, and ground-based velocity-resolved spectroscopy of carbon monoxide (CO) rotational transitions from J = 2–1 to J = 16–15 toward two positions in the circum-nuclear disk (CND) in our Galactic center. Radiative transfer models were used to derive information on the physical state of the gas traced by CO. The excitation of the CO gas cannot be explained by a single physical component, but is clearly the superposition of various warm gas phases. In a two-component approach, our large velocity gradient (LVG) analysis suggests high temperatures of ∼200 K with moderate gas densities of only ∼10 4.5 cm −3 for the bulk of the material. A higher excited phase, carrying ∼20–30% of the column densities, is warmer (∼300–500 K) but only slightly denser (∼10 5.3 cm −3 ). These densities are too low to self-stabilize the clumps against their high internal turbulence and fall below the Roche density (>10 7 cm −3 ) at 1.5 pc galactocentric distance. We conclude that the bulk of the material in the CND is not

GREAT/SOFIA atmospheric calibration

The GREAT observations need frequency-selective calibration across the passband for the residual atmospheric opacity at flight altitude. At these altitudes the atmospheric opacity has both narrow and broad spectral features. To determine the atmospheric transmission at high spectral resolution, GREAT compares the observed atmospheric emission with atmospheric model predictions, and therefore depends on the validity of the atmospheric models. We discuss the problems identified in this comparison with respect to the observed data and the models, and describe the strategy used to calibrate the science data from GREAT/SOFIA during the first observing periods.

Radiative and mechanical feedback into the molecular gas of NGC 253

Starburst galaxies are galaxies or regions of galaxies undergoing intense periods of star formation. Understanding the heating and cooling mechanisms in these galaxies can give us insight to the driving mechanisms that fuel the starburst. Molecular emission lines play a crucial role in the cooling of the excited gas. With Herschel Spectral and Photometric Imaging Receiver we have been able to observe the rich molecular spectrum towards the central region of NGC 253. Carbon monoxide (CO, J = 4 - 3 to 13-12) is the brightest molecule in the Herschel wavelength range and together with ground-based low-J observations, the line fluxes trace the excitation of CO. By studying the CO excitation ladder and comparing the intensities to models, we investigate whether the gas is excited by UV radiation, X-rays, cosmic rays, or turbulent heating. Comparing the 12CO and 13CO observations to large velocity gradient models and photon-dominated region (PDR) models we find three main interstellar medium (ISM) phases. We estimate the density, temperature, and masses of these ISM phases. By adding 13CO, HCN, and HNC line intensities, we are able to constrain these degeneracies and determine the heating sources. The first ISM phase responsible for the low-J CO lines is excited by PDRs, but the second and third phases, responsible for the mid to high-J CO transitions, require an additional heating source. We find three possible combinations of models that can reproduce our observed molecular emission. Although we cannot determine which of these is preferable, we can conclude that mechanical heating is necessary to reproduce the observed molecular emission and cosmic ray heating is a negligible heating source. We then estimate the mass of each ISM phase; 6 × 107M⊙ for phase 1 (low-J CO lines), 3 × 107M⊙ for phase 2 (mid-J CO lines), and 9 × 106M⊙ for phase 3 (high-J CO lines) for a total system mass of 1 × 108M⊙.

Lambda = 3 mm line survey of nearby active galaxies

We used the IRAM 30m telescope to observe the frequency range [86-116]GHz towards the central regions of the starburst galaxies M83, M82, and NGC253, the AGNs M51, NGC1068, and NGC7469, and the ULIRGs Arp220 and Mrk231. Assuming LTE conditions, we calculated the column densities of 27 molecules and 10 isotopologues. Among others, we report the first tentative detections of CH3CHO, HNCO, and NS in M82 and, for the first time in the extragalactic medium, HC5N in NGC253. Halpha recombination lines were only found in M82 and NGC253. Vibrationally excited lines of HC3N were only detected in Arp220. CH3CCH emission is only seen in the starburst-dominated galaxies. By comparison of the fractional abundances among the galaxies, we looked for the molecules that are best suited to characterise the chemistry of starbursts, AGNs and ULIRGs, as well as the differences among galaxies within the same group.

Globules and pillars seen in the [CII] 158 micron line with SOFIA

Molecular globules and pillars are spectacular features, found only in the interface region between a molecular cloud and an HII-region. Impacting Far-ultraviolet (FUV) radiation creates photon dominated regions (PDRs) on their surfaces that can be traced by typical cooling lines. With the GREAT receiver onboard SOFIA we mapped and spectrally resolved the [CII] 158 micron atomic fine-structure line and the highly excited 12CO J=11-10 molecular line from three objects in Cygnus X (a pillar, a globule, and a strong IRAS source). We focus here on the globule and compare our data with existing Spitzer data and recent Herschel Open-Time PACS data. Extended [CII] emission and more compact CO-emission was found in the globule. We ascribe this emission mainly to an internal PDR, created by a possibly embedded star-cluster with at least one early B-star. However, external PDR emission caused by the excitation by the Cyg OB2 association cannot be fully excluded. The velocity-resolved [CII] emission traces the emission of PDR surfaces, possible rotation of the globule, and high-velocity outflowing gas. The globule shows a velocity shift of ~2 km/s with respect to the expanding HII-region, which can be understood as the residual turbulence of the molecular cloud from which the globule arose. This scenario is compatible with recent numerical simulations that emphazise the effect of turbulence. It is remarkable that an isolated globule shows these strong dynamical features traced by the [CII]-line, but it demands more observational studies to verify if there is indeed an embedded cluster of B-stars.

Excitation of the molecular gas in the nuclear region of M 82

We present high-resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M 82. Six ^(12)CO lines, 2 ^(13)CO lines and 4 fine-structure lines have been detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures, and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n = 10^(3.5) cm^(-3)) clouds, with column densities of N_H = 10^(21.5) cm^(-2) and a relatively low UV radiation field (G_0 = 10^2). The remaining gas is predominantly found in clouds with higher densities (n = 10^5 cm^(-3)) and radiation fields (G_0 = 10^(2.75)), but somewhat lower column densities (N_H = 10^(21.2) cm^(-2)). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n = 10^6 cm^(-3)) and UV field (G_0 = 10^(3.25)). These results show the strength of multi-component modelling for interpretating the integrated properties of galaxies.

High-resolution absorption spectroscopy of the OH 2Pi 3/2 ground state line

The chemical composition of the interstellar medium is determined by gas phase chemistry, assisted by grain surface reactions, and by shock chemistry. The aim of this study is to measure the abundance of the hydroxyl radical (OH) in diffuse spiral arm clouds as a contribution to our understanding of the underlying network of chemical reactions. Owing to their high critical density, the ground states of light hydrides provide a tool to directly estimate column densities by means of absorption spectroscopy against bright background sources. We observed onboard the SOFIA observatory the 2Pi3/2, J = 5/2 3/2 2.5 THz line of ground-state OH in the diffuse clouds of the Carina-Sagittarius spiral arm. OH column densities in the spiral arm clouds along the sightlines to W49N, W51 and G34.26+0.15 were found to be of the order of 10^14 cm^-2, which corresponds to a fractional abundance of 10^-7 to 10^-8, which is comparable to that of H_2O. The absorption spectra of both species have similar velocity components, and the ratio of the derived H_2O to OH column densities ranges from 0.3 to 1.0. In W49N we also detected the corresponding line of ^18OH.