Excitation Of CO Research Articles

Herschel ★ -ATLAS: correlations between dust and gas in local submm-selected galaxies

We present an analysis of CO molecular gas tracers in a sample of 500{\mu}m-selected Herschel-ATLAS galaxies at z<0.05 (cz<14990km/s). Using 22-500{\mu}m photometry from WISE, IRAS and Herschel, with HI data from the literature, we investigate correlations between warm and cold dust, and tracers of the gas in different phases. The correlation between global CO(3-2) line fluxes and FIR-submillimetre fluxes weakens with increasing IR wavelength ({\lambda}>60{\mu}m), as a result of colder dust being less strongly associated with dense gas. Conversely, CO(2-1) and HI line fluxes both appear to be better correlated with longer wavelengths, suggesting that cold dust is more strongly associated with diffuse atomic and molecular gas phases, consistent with it being at least partially heated by radiation from old stellar populations. The increased scatter at long wavelengths implies that submillimetre fluxes are a poorer tracer of SFR. Fluxes at 22 and 60{\mu}m are also better correlated with diffuse gas tracers than dense CO(3-2), probably due to very-small-grain emission in the diffuse interstellar medium, which is not correlated with SFR. The FIR/CO luminosity ratio and the dust mass/CO luminosity ratio both decrease with increasing luminosity, as a result of either correlations between mass and metallicity (changing CO/H2) or between CO luminosity and excitation [changing CO(3-2)/CO(1-0)].

Herschelobservations of the Sagittarius B2 cores: Hydrides, warm CO, and cold dust

Sagittarius B2 (Sgr B2) is one of the most massive and luminous star-forming regions in the Galaxy and shows chemical and physical conditions similar to those in distant extragalactic starbursts. We present large-scale far-IR/submm photometric images and spectroscopic maps taken with the PACS and SPIRE instruments onboard Herschel. The spectra towards the Sgr B2 star-forming cores, B2(M) and B2(N), are characterized by strong CO line emission, emission lines from high-density tracers (HCN, HCO+, and H2S), [N II] 205 um emission from ionized gas, and absorption lines from hydride molecules (OH+, H2O+, H2O, CH+, CH, SH+, HF, NH, NH2, and NH3). The rotational population diagrams of CO suggest the presence of two gas temperature components: an extended warm component, which is associated with the extended envelope, and a hotter component, which is seen towards the B2(M) and B2(N) cores. As observed in other Galactic Center clouds, the gas temperatures are significantly higher than the dust temperatures inferred from photometric images. We determined far-IR and total dust masses in the cores. Non-local thermodynamic equilibrium models of the CO excitation were used to constrain the averaged gas density in the cores. A uniform luminosity ratio is measured along the extended envelope, suggesting that the same mechanism dominates the heating of the molecular gas at large scales. The detection of high-density molecular tracers and of strong [N II] 205 um line emission towards the cores suggests that their morphology must be clumpy to allow UV radiation to escape from the inner HII regions. Together with shocks, the strong UV radiation field is likely responsible for the heating of the hot CO component. At larger scales, photodissociation regions models can explain both the observed CO line ratios and the uniform L(CO)/LFIR luminosity ratios.

High-JCO survey of low-mass protostars observed withHerschel-HIFI

The evolution of deeply embedded young stellar objects (YSOs) has traditionally been traced through dust continuum spectral energy distributions (SEDs), but the use of CO excitation as an evolutionary probe has not yet been explored due to lack of high-J CO observations. The aim is to constrain the physical characteristics (excitation, kinematics, column density) of the warm gas toward 26 low-mass Class 0 and I YSOs using spectrally-resolved Herschel Space Observatory data of high-J lines of CO. Data are complemented by ground-based observations from APEX and the JCMT to compare those with the colder gas traced by lower-J CO lines. This is the first large spectrally resolved high-J CO survey conducted for these types of sources. The median excitation temperatures for 12CO, 13CO and C18O derived from single-temperature fits to the J_u=2-10 integrated intensities are ~70K, 48K and 37K, respectively, with no significant difference between Class 0 and I sources and no trend with M_env or L_bol. Thus, in contrast with the continuum SEDs, the spectral line energy distributions (SLEDs) do not show an evolution during the embedded stage. In contrast, the integrated line intensities of all CO isotopologs show a clear decrease with evolutionary stage as the envelope is dispersed. The H2O 110-101/CO 10-9 intensity ratio does not change significantly with velocity, in contrast with the H2O/CO 3-2 ratio, indicating that CO 10-9 is the lowest transition for which the line wings probe the same warm shocked gas as H2O. Modeling of the full suite of C18O lines indicates an abundance profile for Class 0 sources that is consistent with a freeze-out zone below 25 K and evaporation at higher temperatures, with but some fraction of the CO transformed into other species in the cold phase. In contrast, observations for two Class I sources in Ophiuchus are consistent with a constant high CO abundance profile.

STAR FORMATION ON SUBKILOPARSEC SCALE TRIGGERED BY NON-LINEAR PROCESSES IN NEARBY SPIRAL GALAXIES

We report a super-linear correlation for the star formation law based on new CO($J$=1-0) data from the CARMA and NOBEYAMA Nearby-galaxies (CANON) CO survey. The sample includes 10 nearby spiral galaxies, in which structures at sub-kpc scales are spatially resolved. Combined with the star formation rate surface density traced by H$\alpha$ and 24 $\mu$m images, CO($J$=1-0) data provide a super-linear slope of $N$ = 1.3. The slope becomes even steeper ($N$ = 1.8) when the diffuse stellar and dust background emission is subtracted from the H$\alpha$ and 24 $\mu$m images. In contrast to the recent results with CO($J$=2-1) that found a constant star formation efficiency (SFE) in many spiral galaxies, these results suggest that the SFE is not independent of environment, but increases with molecular gas surface density. We suggest that the excitation of CO($J$=2-1) is likely enhanced in the regions with higher star formation and does not linearly trace the molecular gas mass. In addition, the diffuse emission contaminates the SFE measurement most in regions where star formation rate is law. These two effects can flatten the power law correlation and produce the apparent linear slope. The super linear slope from the CO($J$=1-0) analysis indicates that star formation is enhanced by non-linear processes in regions of high gas density, e.g., gravitational collapse and cloud-cloud collisions.

SOFIA: first science highlights and future science potential

AbstractSOFIA, the Stratospheric Observatory for Infrared Astronomy, is a joint project between NASA and the German Aerospace Agency (DLR) to develop and operate a 2.5 m airborne telescope in a highly modified Boeing 747SP aircraft that can fly as high as 45000 feet (13.7 km). This is above 99.8 % of the precipitable water vapor which blocks much of the midand far‐infrared radiation from reaching ground‐based telescopes. In this review, we briefly discuss the characteristics of the Observatory and present a number of early science highlights obtained with the FORCAST camera in 5–40 micron spectral region and with the GREAT heterodyne spectrometer in the 130–240 micron spectral region. The FORCAST images in Orion show the discovery of a new high‐mass protostar (IRc4), while GREAT observations at 1 km s–1 velocity resolution detected velocity‐resolved, redshifted ammonia spectra at 1.81 THz in absorption against several strong farinfrared dust continuum sources, clear evidence of substantial protostellar infall onto massive (non‐ionizing) protostars. These powerful new data allow us to determine how massive stars form in our Galaxy. Another highlight is the stunning image taken by FORCAST that reveals the transient circumnuclear 1.5 pc radius (dust) ring around our Galactic center, heated by hundreds of massive stars in the young nuclear star cluster. The GREAT heterodyne spectrometer also observed the circumnuclear ring in highly excited CO rotational lines, indicative of emission from warm dense molecular gas with broad velocity structure, perhaps due to local shock heating. GREAT also made superb mapping observations of the [C II] fine structure cooling line at 158 microns, for example in M17‐SW molecular cloud–star cluster interface, observations which disprove the simple canonical photodissociation models. The much better baseline stability of the GREAT receivers (compared to Herschel HIFI) allows efficient on‐the‐fly mapping of extended [C II] emission in our galaxy and also in other nearby spiral galaxies. Of particular note is the GREAT discovery of two new molecules outside the solar system: OD (the deuterated OH hydroxyl radical) as well as mercapto radical SH, both in absorption near 1.4 THz, a frequency gap where Herschel was blind. A special highlight was the 2011 June 23 UT stellar occultation by Pluto using the HIPO high speed photometer and the FDC fast diagnostic camera. This difficult but successful observation, which was both space‐critical (within 100 km) and time‐critical (within 1 min), proved that SOFIA can be in the right place at the right time, when important transient events occur. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Evolution of CO lines in time-dependent models of protostellar disk formation

(Abridged) Star and planet formation theories predict an evolution in the density, temperature, and velocity structure as the envelope collapses and forms an accretion disk. The aim of this work is to model the evolution of the molecular excitation, line profiles, and related observables during low-mass star formation. Specifically, the signatures of disks during the deeply embedded stage are investigated. Semi-analytic 2D axisymmetric models have been used to describe the evolution of the density, stellar mass, and luminosity from the pre-stellar to the T-Tauri phase. A full radiative transfer calculation is carried out to accurately determine the time-dependent dust temperatures and CO abundance structure. We present non-LTE near-IR, FIR, and submm lines of CO have been simulated at a number of time steps. In contrast to the dust temperature, the CO excitation temperature derived from submm/FIR lines does not vary during the protostellar evolution, consistent with C18O observations obtained with Herschel and from ground-based telescopes. The near-IR spectra provide complementary information to the submm lines by probing not only the cold outer envelope but also the warm inner region. The near-IR high-J (>8) absorption lines are particularly sensitive to the physical structure of the inner few AU, which does show evolution. High signal-to-noise ratio subarcsec resolution data with ALMA are needed to detect the presence of small rotationally supported disks during the Stage 0 phase and various diagnostics are discussed.

Rate coefficients for electron impact excitation of CO

Rate coefficients for electron impact excitation of the CO molecule have been calculated both for equilibrium and non-equilibrium conditions in the presence of electric and magnetic fields. The rate coefficients have been determined for all relevant non-elastic processes: rotational excitation, vibrational excitation, electronic excitation into singlet and triplet states and particularly for ionization. In the case of non-equilibrium conditions, we had to determine electron energy distribution functions needed for rate coefficients calculations. The distribution functions were obtained by employing a Monte Carlo simulation developed in our laboratory. The simulations were performed for moderate values of electric field over gas number density ratios, E/N, from 0 to 1000Td. Also, the rate coefficients have been determined in presence of magnetic field for typical values of magnetic field over gas number density ratios, B/N, from 500 to 3000 Hx. The results of equilibrium rate coefficients along with non-equilibrium ones have been shown.

MOLECULAR GAS AND STAR FORMATION IN NEARBY DISK GALAXIES

We compare molecular gas traced by 12CO(2-1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between Sig_mol and Sig_SFR but also find important second-order systematic variations in the apparent molecular gas depletion time, t_dep^mol = Sig_mol / Sig_SFR. At our 1 kpc common resolution, CO correlates closely with many tracers of the recent SFR. Weighting each line of sight equally and using a fixed, Milky Way alpha_CO, our data yield a molecular gas depletion time, t_dep^mol=Sig_mol/Sig_SFR ~ 2.2 Gyr with 0.3 dex scatter, in good agreement with literature data. We apply a forward-modeling approach to constrain the power-law index, N, that relates the SFR surface density and the molecular gas surface density and find N=1+/-0.15 for our full data set with some variation from galaxy to galaxy. However, we caution that a power law treatment oversimplifies the topic given that we observe correlations between t_dep^mol and other local and global quantities. The strongest of these are a decreased t_dep^mol in low-mass, low-metallicity galaxies and a correlation of the kpc-scale t_dep^mol with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H2 conversion factor that depends on D/G in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes it a conservative one. After applying a D/G-dependent alpha_CO, some weak correlations between t_dep^mol and local conditions persist. In particular, we observe lower t_dep^mol and enhanced CO excitation associated with some nuclear gas concentrations. These appear to reflect real enhancements in the SFR/H2 and t_dep appears multivalued at fixed Sig_mol, supporting the the idea of "disk" and "starburst" modes driven by environmental factors.

Vibronic effects on the low-lying electronic excitations in CO2 induced by electron impact

We report an angle-resolved electron energy loss spectroscopy (EELS) study on the valence-shell electronic excitations of CO2. Experimentally, momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles for low-lying electronic excitations have been derived from EELS spectra measured at incident electron energy of 3 keV. Theoretically, we have calculated GOS profiles using wave functions at the equation-of-motion coupled-cluster singles and doubles level. In the calculation, vibronic effects are taken into account by evaluating the electronic transition amplitudes along the individual normal coordinates. The calculation satisfactorily reproduces the experiment for the (1)Πg and (1)Δu transitions and reveals prominent roles of strong coupling between the associated mixed-Rydberg-valence and valence excited states through the bending vibration of CO2. Vibronic effects on GOS profiles have also been examined for the (1)Σu (+), (1)Πu, and 2(1)Πg transitions.

Selective Ultrafast Probing of Transient Hot Chemisorbed and Precursor States of CO on Ru(0001)

We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process.

Modeling Analysis of the Photoreduction of Cobalt(III) Speciation via (CoIII-I-) Ion Pair Formation in Water-1,4-Dioxane Mixtures with XRPD and Voltammetric Studies

Ion pair charge transfer (IPCT) reaction has been studied on the reduction of Co III centre in coordination compounds with reference to solvent medium and structure of the complex. A series of Co III (L) 3 3+ (L = (NH 3)2, en, pn, tn and bn) were prepared, characterized and the structures of the complexes were refined using powder XRD data. Co III (L) 3 3+ crystallizes in distorted monoclinic system with � = 92.93 (1)° to 113.00 (2)°. A combination of powder XRD and cyclic voltammetric technique is shown to be methodologically important and complementary for the understanding of reduction property of Co III centre. The voltammetric measurements of Co III (L)3 3+ have shown one irreversible Co(III) � Co(II) reduction of metal centre and the peak positions of the complexes are localized due to strained ligand. Quantum yield for 254 nm excitation of Co III (L) 3 3+ (L = (NH 3)2, en, pn, tn and bn) in water-1,4-dioxane mixtures (Diox = 0, 5, 10, 15, 20, 25 and 30% (v/v)) were also derived for all the complexes in presence of added iodide ion, in which Co III is reduced via {Co III L3 3+ , I - } ion-pair formation. The photoactive state is ion-pair charge transfer transition state and the quantum efficiency is solvent dependent. That is, �Co(II) in water Diox (100:0 (v/v)) is less than that in water Diox (70:30 (v/v)). That is, change inCo(II) is consistent with observed increase in x Diox of the medium. An elaboration on binary solvent modifiedCo(II) in terms of correlation relationships using solvent empirical parametersr, Y, E T N , DN N , �, � and �* provides a model to understand solvent medium participation. Application of this method involving model equation of the form Y S = Y 0 + � n i=1 aiXi helps the binary solvent effect on {Co III (L) 3 3+ , I - } ion pair into Co II product formation efficiency. The photoreduction proceeds through long-range and short range solvation mechanisms. Regression methods were attempted to quantify the solvation effect.

Isotope effect in the photochemical decomposition of CO2 (ice) by Lyman-α radiation

The photochemical decomposition of CO2(ice) at 75 K by Lyman-α radiation (10.2 eV) has been studied using transmission infrared spectroscopy. An isotope effect in the decomposition of the CO2 molecule in the ice has been discovered, favoring (12)CO2 photodecomposition over (13)CO2 by about 10%. The effect is caused by electronic energy transfer from the excited CO2 molecule to the ice matrix, which favors quenching of the heavier electronically-excited (13)CO2 molecule over (12)CO2. The effect is similar to the Menzel-Gomer-Redhead isotope effect in desorption from adsorbed molecules on surfaces when electronically excited. An enhancement of the rate of formation of lattice-trapped CO and CO3 species is observed for the photolysis of the (12)CO2 molecule compared to the (13)CO2 molecule in the ice. Only 0.5% of the primary photoexcitation results in O-CO bond dissociation to produce trapped-CO and trapped-CO3 product molecules and the majority of the electronically-excited CO2 molecules return to the ground state. Here either vibrational relaxation occurs (majority process) or desorption of CO2 occurs (minority process) from highly vibrationally-excited CO2 molecules in the ice. The observation of the (12)C∕(13)C isotope effect in the Lyman-α induced photodecomposition of CO2 (ice) suggests that over astronomical time scales the isotope enrichment effect may distort historical information derived from isotope ratios in space wherever photochemistry can occur.

Infrared Spectroscopy of CO Ro-Vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915

Abstract We present high-resolution spectroscopy of gaseous CO absorption in the fundamental ro-vibrational band toward the heavily obscured active galactic nucleus (AGN) IRAS 08572$ +$ 3915. We have detected absorption lines up to highly excited rotational levels ($ J$$ \leqq$ 17). The velocity profiles reveal three distinct components, the strongest and broadest ($ \Delta v$$ &amp;gt;$ 200 km s$ ^{-1}$ ) of which is due to blueshifted ($-$ 160 km s$ ^{-1}$ ) gas at a temperature of $ \sim$ 270 K absorbing at velocities as high as $-$ 400 km s$ ^{-1}$ . A much weaker but even warmer ($ \sim$ 700 K) component, which is highly redshifted ($ +$ 100 km s$ ^{-1}$ ), is also detected, in addition to a cold ($ \sim$ 20 K) component centered at the systemic velocity of the galaxy. On the assumption of local thermodynamic equilibrium, the column density of CO in the 270 K component is $ N_{\rm {CO}}$$ \sim$ 4.5 $ \times$ 10$ ^{18}$ cm$ ^{-2}$ , which in fully molecular gas corresponds to an H$ _2$ column density of $ N_{\rm {H_2}}$$ \sim$ 2.5 $ \times$ 10$ ^{22}$ cm$ ^{-2}$ . The thermal excitation of CO up to the observed high rotational levels requires a density greater than $ n_{\rm c}$ (H$ _2$ ) $ &amp;gt;$ 2 $ \times$ 10$ ^{7}$ cm$ ^{-3}$ , implying that the thickness of the warm absorbing layer is extremely small ($ \Delta d$$ &amp;lt;$ 4 $ \times$ 10$ ^{-2}$ pc), even if it is highly clumped. The large column densities and high radial velocities associated with these warm components, as well as their temperatures, indicate that they originate in molecular clouds near the central engine of the AGN.

Observation of direct vibrational excitation in gas-surface collisions of CO with Au(111): a new model system for surface dynamics

We report vibrational excitation of CO from its ground (v = 0) to first excited (v = 1) vibrational state in collision with Au(111) at an incidence energy of translation of E(I) = 0.45 eV. Unlike past work, we can exclude an excitation mechanism involving temporary adsorption on the surface followed by thermalization and desorption. The angular distributions of the scattered CO molecules are narrow, consistent with direct scattering occurring on a sub-ps time scale. The absolute excitation probabilities are about 3% of those expected from thermal accommodation. The surface temperature dependence of excitation, which was measured between 373 and 973 K, is Arrhenius-like with an activation energy equal to the energy required for vibrational excitation. Our measurements are consistent with a vibrational excitation mechanism involving coupling of thermally excited electron-hole pairs of the solid to CO vibration.

TDDFT studies on CO in a linear polarized femtosecond laser field

We present a theoretical study on the ionization and excitation dynamics of CO in various linear-polarized laser fields with in the frame work of the time-dependent density functional theory (TDDFT), applied to valence electrons, coupled non-adiabatically with molecular dynamics of the ions. It is found that the stronger the laser intensity, the more the energies are absorbed by CO and the earlier the ionization takes place with more electrons emitted. Moreover, the bond length of CO is stretched associated with more violent contraction vibration. The dipole moment along the laser polarization is enlarged when the laser intensity is enhanced. This study on the influence of the polarization of laser pulse on the excitation of CO indicates that the ionization of CO is maximized and the contraction vibration becomes most violent when the laser is polarized along the molecular axis. Ionization is restrained when the polarization angle is increased and the dipole vibration shows a strong dependence on the laser polarization. Furthermore, it is found that the electron density surrounding the carbon atom is distributed along the molecular axis particularly when the dispersion of the electrons around the oxygen atom is greatly influenced by the laser polarization.

New observation of the quintet states of CO excited by glow discharge

Emission from the lowest quintet state of CO is observed in low power glow discharge. Intersystem crossing from the state to the state makes transition from the state to lower lying states possible. The term values for the three lower vibrational levels of the state are found to be , and above the ground level. The fundamental vibrational frequency of the state is found to be . Analysis of the relaxation pathways of excited CO molecules via the state is carried out and transition lines assigned.

Influence of Vibrational States on CO2 Splitting by Dielectric Barrier Discharges

In this paper, the splitting of CO2 in a pulsed plasma system, such as a dielectric barrier discharge (DBD), is evaluated from a chemical point of view by means of numerical modeling. For this purpose, a chemical reaction set of CO2 in an atmospheric pressure plasma is developed, including the vibrational states of CO2, O2, and CO. The simulated pulses are matched to the conditions of a filament (or microdischarge) and repeated with intervals of 1 μs. The influence of vibrationally excited CO2 as well as other neutral species, ions, and electrons on the CO2 splitting is discussed. Our calculations predict that the electrons have the largest contribution to the CO2 splitting at the conditions under study, by electron impact dissociation. The contribution of vibrationally excited CO2 levels in the splitting of CO2 is found be 6.4%, when only considering one microdischarge pulse and its afterglow, but it can be much higher for consecutive discharge pulses, as is typical for a filamentary DBD, when the interp...

The molecular gas in luminous infrared galaxies - I. CO lines, extreme physical conditions and their drivers

We report results from a large molecular line survey of Luminous Infrared Galaxies (L_{IR} >= 10^{11} L_sol) in the local Universe (z<=0.1), conducted during the last decade with the James Clerk Maxwell Telescope (JCMT) and the IRAM 30-m telescope. This work presents the CO and {13}CO line data for 36 galaxies, further augmented by multi-J total CO luminosities available for other IR-bright galaxies from the literature. This yields a sample of N=70 galaxies with the star-formation (SF) powered fraction of their IR luminosities spanning L_{IR} (10^{10}-2x10^{12}) L_sol and a wide range of morphologies. Simple comparisons of their available CO Spectral Line Energy Distributions (SLEDs) with local ones, as well as radiative transfer models discern a surprisingly wide range of average ISM conditions, with most of the surprises found in the high-excitation regime. These take the form of global CO SLEDs dominated by a very warm (T_{kin}>=100 K) and dense (n>=10^4 cm^{-3}) gas phase, involving galaxy-sized (~(few)x10^9 M_sol) gas mass reservoirs under conditions that would otherwise amount only ~1% of mass per typical SF molecular cloud in the Galaxy. Some of the highest excitation CO SLEDs are found in the so-called Ultra Luminous Infrared Galaxies and seem irreducible to ensembles of ordinary SF-powered regions. Highly supersonic turbulence and high cosmic ray (CR) energy densities rather than far-UV/optical photons or SNR-induced shocks from individual SF sites can globally warm the large amounts of dense gas found in these merger-driven starbursts and easily power their extraordinary CO line excitation.....

SUBMILLIMETER LINE SPECTRUM OF THE SEYFERT GALAXY NGC 1068 FROM THEHERSCHEL-SPIRE FOURIER TRANSFORM SPECTROMETER

The first complete submillimetre spectrum (190-670um) of the Seyfert 2 galaxy NGC1068 has been observed with the SPIRE Fourier Transform Spectrometer onboard the {\it Herschel} Space Observatory. The sequence of CO lines (Jup=4-13), lines from water, the fundamental rotational transition of HF, two o-H_2O+ lines and one line each from CH+ and OH+ have been detected, together with the two [CI] lines and the [NII]205um line. The observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components, one due to the compact circum-nuclear disk (CND) and one from the extended region encompassing the star forming ring (SF-ring). Radiative transfer models show that the two CO components are characterized by density of n(H_2)=10^4.5 and 10^2.9 cm^-3 and temperature of T=100K and 127K, respectively. The comparison of the CO line intensities with photodissociation region (PDR) and X-ray dominated region (XDR) models, together with other observational constraints, such as the observed CO surface brightness and the radiation field, indicate that the best explanation for the CO excitation of the CND is an XDR with density of n(H_2) 10^4 cm^-3 and X-ray flux of 9 erg s^-1 cm^-2, consistent with illumination by the active galactic nucleus, while the CO lines in the SF-ring are better modeled by a PDR. The detected water transitions, together with those observed with the \her \sim PACS Spectrometer, can be modeled by an LVG model with low temperature (T_kin \sim 40K) and high density (n(H_2) in the range 10^6.7-10^7.9 cm^-3).

MEASUREMENTS OF CO REDSHIFTS WITH Z-SPEC FOR LENSED SUBMILLIMETER GALAXIES DISCOVERED IN THE H-ATLAS SURVEY

We present new observations from Z-Spec, a broadband 185-305 GHz spectrometer, of five sub-millimeter bright lensed sources selected from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) science demonstration phase (SDP) catalog. We construct a redshift finding algorithm using combinations of the signal-to-noise of all the lines falling in the Z-Spec bandpass to determine redshifts with high confidence, even in cases where the signal-to-noise in individual lines is low. We measure the dust continuum in all sources and secure CO redshifts for four out of five (z~1.5-3). In one source, SDP.17, we tentatively identify two independent redshifts and a water line, confirmed at z=2.308. Our sources have properties characteristic of dusty starburst galaxies, with magnification-corrected star formation rates of 10^(2-3) M_sun/yr. Lower limits for the dust masses (~a few 10^8 M_sun) and spatial extents (~1 kpc equivalent radius) are derived from the continuum spectral energy distributions, corresponding to dust temperatures between 54 and 69K. In the LTE approximation, we derive relatively low CO excitation temperatures (< 100 K) and optical depths (tau<1). Performing a non-LTE excitation analysis using RADEX, we find that the CO lines measured by Z-Spec (from J=4->3 to 10->9, depending on the galaxy) localize the best solutions to either a high-temperature / low-density region, or a low-temperature / high-density region near the LTE solution, with the optical depth varying accordingly. Observations of additional CO lines, CO(1-0) in particular, are needed to constrain the non-LTE models.