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DOE OSTI2012

SPITZER AND HERSCHEL MULTIWAVELENGTH CHARACTERIZATION OF THE DUST CONTENT OF EVOLVED H II REGIONS

We have analyzed a uniform sample of 16 evolved H II regions located in a 2 Degree-Sign Multiplication-Sign 2 Degree-Sign Galactic field centered at (l,b) = (30 Degree-Sign , 0 Degree-Sign ) and observed as part of the Herschel Hi-GAL survey. The evolutionary stage of these H II regions was established using ancillary radio-continuum data. By combining Hi-GAL PACS (70 {mu}m, 160 {mu}m) and SPIRE (250 {mu}m, 350 {mu}m, and 500 {mu}m) measurements with MIPSGAL 24 {mu}m data, we built spectral energy distributions of the sources and showed that a two-component gray-body model is a good representation of the data. In particular, wavelengths >70 {mu}m appear to trace a cold dust component, for which we estimated an equilibrium temperature of the big grains (BGs) in the range 20-30 K, while for {lambda} < 70 {mu}m, the data indicate the presence of a warm dust component at temperatures of the order of 50-90 K. This analysis also revealed that dust is present in the interior of H II regions, although likely not in a large amount. In addition, the data seem to corroborate the hypothesis that the main mechanism responsible for the (partial) depletion of dust in H II regions is radiation-pressure-driven drift. In this framework, we speculated that the 24 {mu}m emission that spatially correlates with ionized gas might be associated with either very small grain or BG replenishment, as recently proposed for the case of wind-blown bubbles. Finally, we found that evolved H II regions are characterized by distinctive far-IR and submillimeter colors, which can be used as diagnostics for their identification in unresolved Galactic and extragalactic regions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

SIZE BIAS AND DIFFERENTIAL LENSING OF STRONGLY LENSED, DUSTY GALAXIES IDENTIFIED IN WIDE-FIELD SURVEYS

We address two selection effects that operate on samples of gravitationally lensed dusty galaxies identified in millimeter- and submillimeter-wavelength surveys. First, we point out the existence of a ''size bias'' in such samples: due to finite source effects, sources with higher observed fluxes are increasingly biased toward more compact objects. Second, we examine the effect of differential lensing in individual lens systems by modeling each source as a compact core embedded in an extended diffuse halo. Considering the ratio of magnifications in these two components, we find that at high overall magnifications, the compact component is amplified by a much larger factor than the diffuse component, but at intermediate magnifications ({approx}10) the probability of a larger magnification for the extended region is higher. Lens models determined from multi-frequency resolved imaging data are crucial to correct for this effect.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A MULTI-WAVELENGTH STUDY OF THE SUNYAEV-ZEL'DOVICH EFFECT IN THE TRIPLE-MERGER CLUSTER MACS J0717.5+3745 WITH MUSTANG AND BOLOCAM

We present 90, 140, and 268 GHz subarcminute resolution imaging of the Sunyaev-Zel'dovich effect (SZE) in the disturbed, intermediate-redshift (z 0.5458) galaxy cluster MACS J0717.5+3745, a triple-merger system comprising four distinct, optically detected subclusters. Our 90 GHz SZE data result in a sensitive, 34 {mu}Jy beam{sup -1} map of the SZE at 13'' effective resolution using the MUSTANG bolometer array on the Green Bank Telescope (GBT). Our 140 and 268 GHz SZE imaging, with resolutions of 58'' and 31'' and sensitivities of 1.8 and 3.3 mJy beam{sup -1}, respectively, was obtained through observations from the Caltech Submillimeter Observatory using Bolocam. We compare these maps to a two-dimensional pressure map derived from Chandra X-ray observations. Our MUSTANG SZE data confirm previous indications from Chandra of a pressure enhancement due to shock-heated, {approx}> 20 keV gas immediately adjacent to extended radio emission seen in low-frequency radio maps of this cluster. MUSTANG also detects pressure substructure that is not well constrained by the Chandra X-ray data in the remnant core of a merging subcluster. We find that the small-scale pressure enhancements in the MUSTANG data amount to {approx}2% of the total pressure measured in the 140 GHz Bolocam observations. The X-ray inferred pseudo-pressure template also fails on larger scales to accurately describe the Bolocam data, particularly at the location of the subcluster with a remnant core known to have a high line-of-sight optical velocity of {approx}3200 km s{sup -1}. Our Bolocam data are adequately described when we add an additional component-not described by a thermal SZE spectrum-to the X-ray template coincident with this subcluster. Using flux densities extracted from our model fits, and marginalizing over the X-ray spectroscopic temperature constraints for the region, we fit a thermal + kinetic SZE spectrum to our Bolocam data and find that the subcluster has a best-fit line-of-sight proper velocity v{sub z} 3600{sup +3440}{sub -{sub 2160}} km s{sup -1}, in agreement with the optical velocity estimates for the subcluster. The probability v{sub z} {<=} 0 given our measurements is 2.1%. Repeating this analysis using flux densities measured directly from our maps results in a 3.4% probability v{sub z} {<=} 0. We note that this tantalizing result for the kinetic SZE is on resolved, subcluster scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A REDSHIFT SURVEY OF HERSCHEL FAR-INFRARED SELECTED STARBURSTS AND IMPLICATIONS FOR OBSCURED STAR FORMATION

We present Keck spectroscopic observations and redshifts for a sample of 767 Herschel-SPIRE selected galaxies (HSGs) at 250, 350, and 500 {mu}m, taken with the Keck I Low Resolution Imaging Spectrometer and the Keck II DEep Imaging Multi-Object Spectrograph. The redshift distribution of these SPIRE sources from the Herschel Multitiered Extragalactic Survey peaks at z = 0.85, with 731 sources at z < 2 and a tail of sources out to z {approx} 5. We measure more significant disagreement between photometric and spectroscopic redshifts (({Delta}z/(1 + z{sub spec})) = 0.29) than is seen in non-infrared selected samples, likely due to enhanced star formation rates and dust obscuration in infrared-selected galaxies. The infrared data are used to directly measure integrated infrared luminosities and dust temperatures independent of radio or 24 {mu}m flux densities. By probing the dust spectral energy distribution (SED) at its peak, we estimate that the vast majority (72%-83%) of z < 2 Herschel-selected galaxies would drop out of traditional submillimeter surveys at 0.85-1 mm. We find that dust temperature traces infrared luminosity, due in part to the SPIRE wavelength selection biases, and partially from physical effects. As a result, we measure no significant trend in SPIRE color with redshift; if dust temperature were independent of luminosity or redshift, a trend in SPIRE color would be expected. Composite infrared SEDs are constructed as a function of infrared luminosity, showing the increase in dust temperature with luminosity, and subtle change in near-infrared and mid-infrared spectral properties. Moderate evolution in the far-infrared (FIR)/radio correlation is measured for this partially radio-selected sample, with q{sub IR}{proportional_to}(1 + z){sup -0.30{+-}0.02} at z < 2. We estimate the luminosity function and implied star formation rate density contribution of HSGs at z < 1.6 and find overall agreement with work based on 24 {mu}m extrapolations of the LIRG, ULIRG, and total infrared contributions. This work significantly increased the number of spectroscopically confirmed infrared-luminous galaxies at z >> 0 and demonstrates the growing importance of dusty starbursts for galaxy evolution studies and the build-up of stellar mass throughout cosmic time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DIFFUSE HARD X-RAY EMISSION IN STARBURST GALAXIES AS SYNCHROTRON FROM VERY HIGH ENERGY ELECTRONS

The origin of the diffuse hard X-ray (2-10 keV) emission from starburst galaxies is a long-standing problem. We suggest that synchrotron emission of 10-100 TeV electrons and positrons (e {sup {+-}}) can contribute to this emission, because starbursts have strong magnetic fields. We consider three sources of e {sup {+-}} at these energies: (1) primary electrons directly accelerated by supernova remnants, (2) pionic secondary e {sup {+-}} created by inelastic collisions between cosmic ray (CR) protons and gas nuclei in the dense interstellar medium of starbursts, and (3) pair e {sup {+-}} produced between the interactions between 10 and 100 TeV {gamma}-rays and the intense far-infrared (FIR) radiation fields of starbursts. We create one-zone steady-state models of the CR population in the Galactic center (R {<=} 112 pc), NGC 253, M82, and Arp 220's nuclei, assuming a power-law injection spectrum for electrons and protons. We consider different injection spectral slopes, magnetic field strengths, CR acceleration efficiencies, and diffusive escape times, and include advective escape, radiative cooling processes, and secondary and pair e {sup {+-}}. We compare these models to extant radio and GeV and TeV {gamma}-ray data for these starbursts, and calculate the diffuse synchrotron X-ray and inverse Compton (IC) luminosities of these starbursts in the models which satisfy multiwavelength constraints. If the primary electron spectrum extends to {approx}PeV energies and has a proton/electron injection ratio similar to the Galactic value, we find that synchrotron emission contributes 2%-20% of their unresolved, diffuse hard X-ray emission. However, there is great uncertainty in this conclusion because of the limited information on the CR electron spectrum at these high energies. IC emission is likewise a minority of the unresolved X-ray emission in these starbursts, from 0.1% in the Galactic center to 10% in Arp 220's nuclei, with the main uncertainty being the starbursts' magnetic field. We also model generic starbursts, including submillimeter galaxies, in the context of the FIR-X-ray relation, finding that anywhere between 0% and 16% of the total hard X-ray emission is synchrotron for different parameters, and up to 2% in the densest starbursts assuming an E {sup -2.2} injection spectrum and a diffusive escape time of 10 Myr (E/3 GeV){sup -1/2} (h/100 pc). Neutrino observations by IceCube and TeV {gamma}-ray data from HESS, VERITAS, and CTA can further constrain the synchrotron X-ray emission of starbursts. Our models do not constrain the possibility of hard, second components of primary e {sup {+-}} from sources like pulsars in starbursts, which could enhance the synchrotron X-ray emission further.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SPIRAL ARMS IN THE ASYMMETRICALLY ILLUMINATED DISK OF MWC 758 AND CONSTRAINTS ON GIANT PLANETS

We present the first near-IR scattered light detection of the transitional disk associated with the Herbig Ae star MWC 758 using data obtained as part of the Strategic Exploration of Exoplanets and Disks with Subaru, and 1.1 {mu}m Hubble Space Telescope/NICMOS data. While submillimeter studies suggested there is a dust-depleted cavity with r = 0.''35, we find scattered light as close as 0.''1 (20-28 AU) from the star, with no visible cavity at H, K', or K{sub s} . We find two small-scaled spiral structures that asymmetrically shadow the outer disk. We model one of the spirals using spiral density wave theory, and derive a disk aspect ratio of h {approx} 0.18, indicating a dynamically warm disk. If the spiral pattern is excited by a perturber, we estimate its mass to be 5{sup +3} {sub -4} M{sub J} , in the range where planet filtration models predict accretion continuing onto the star. Using a combination of non-redundant aperture masking data at L' and angular differential imaging with Locally Optimized Combination of Images at K' and K{sub s} , we exclude stellar or massive brown dwarf companions within 300 mas of the Herbig Ae star, and all but planetary mass companions exterior to 0.''5. We reach 5{sigma} contrasts limiting companions to planetary masses, 3-4 M{sub J} at 1.''0 and 2 M{sub J} at 1.''55, using the COND models. Collectively, these data strengthen the case for MWC 758 already being a young planetary system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE FAR-INFRARED, UV, AND MOLECULAR GAS RELATION IN GALAXIES UP TO z = 2.5

We use the infrared excess (IRX) FIR/UV luminosity ratio to study the relation between the effective UV attenuation (A {sub IRX}) and the UV spectral slope ({beta}) in a sample of 450 1 < z < 2.5 galaxies. The FIR data are from very deep Herschel observations in the GOODS fields that allow us to detect galaxies with star formation rates (SFRs) typical of galaxies with log(M {sub *}) > 9.3. Thus, we are able to study galaxies on and even below the main SFR-stellar mass relation (main sequence). We find that main-sequence galaxies form a tight sequence in the IRX-{beta} plane, which has a flatter slope than commonly used relations. This slope favors a Small-Magellanic-Cloud-like UV extinction curve, though the interpretation is model dependent. The scatter in the A {sub IRX}-{beta} plane correlates with the position of the galaxies in the SFR-M {sub *} plane. Using a smaller sample of galaxies with CO gas masses, we study the relation between the UV attenuation and the molecular gas content. We find a very tight relation between the scatter in the IRX-{beta} plane and the specific attenuation S{sub A} , a quantity that represents the attenuation contributed by the molecular gas mass per young star. S{sub A} is sensitive to both the geometrical arrangement of stars and dust and to the compactness of the star-forming regions. We use this empirical relation to derive a method for estimating molecular gas masses using only widely available integrated rest-frame UV and FIR photometry. The method produces gas masses with an accuracy between 0.12 and 0.16 dex in samples of normal galaxies between z {approx} 0 and z {approx} 1.5. Major mergers and submillimeter galaxies follow a different S{sub A} relation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CHEMICAL AND PHYSICAL CONDITIONS IN MOLECULAR CLOUD CORE DC 000.4-19.5 (SL42) IN CORONA AUSTRALIS

Chemical reactions in starless molecular clouds are heavily dependent on interactions between gas phase material and solid phase dust and ices. We have observed the abundance and distribution of molecular gases in the cold, starless core DC 000.4-19.5 (SL42) in Corona Australis using data from the Swedish ESO Submillimeter Telescope. We present column density maps determined from measurements of C{sup 18}O (J = 2-1, 1-0) and N{sub 2}H{sup +} (J = 1-0) emission features. Herschel data of the same region allow a direct comparison to the dust component of the cloud core and provide evidence for gas phase depletion of CO at the highest extinctions. The dust color temperature in the core calculated from Herschel maps ranges from roughly 10.7 to 14.0 K. This range agrees with the previous determinations from Infrared Space Observatory and Planck observations. The column density profile of the core can be fitted with a Plummer-like density distribution approaching n(r) {approx} r {sup -2} at large distances. The core structure deviates clearly from a critical Bonnor-Ebert sphere. Instead, the core appears to be gravitationally bound and to lack thermal and turbulent support against the pressure of the surrounding low-density material: it may therefore be in the process of slow contraction. We test two chemical models and find that a steady-state depletion model agrees with the observed C{sup 18}O column density profile and the observed N(C{sup 18}O) versus A{sub V} relationship.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CHANGES OF DUST OPACITY WITH DENSITY IN THE ORION A MOLECULAR CLOUD

We have studied the opacity of dust grains at submillimeter wavelengths by estimating the optical depth from imaging at 160, 250, 350, and 500 {mu}m from the Herschel Gould Belt Survey and comparing this to a column density obtained from the Two Micron All Sky Survey derived color excess E(J - K {sub s}). Our main goal was to investigate the spatial variations of the opacity due to 'big' grains over a variety of environmental conditions and thereby quantify how emission properties of the dust change with column (and volume) density. The central and southern areas of the Orion A molecular cloud examined here, with N {sub H} ranging from 1.5 Multiplication-Sign 10{sup 21} cm{sup -2} to 50 Multiplication-Sign 10{sup 21} cm{sup -2}, are well suited to this approach. We fit the multi-frequency Herschel spectral energy distributions (SEDs) of each pixel with a modified blackbody to obtain the temperature, T, and optical depth, {tau}{sub 1200}, at a fiducial frequency of 1200 GHz (250 {mu}m). Using a calibration of N {sub H}/E(J - K{sub s} ) for the interstellar medium (ISM) we obtained the opacity (dust emission cross-section per H nucleon), {sigma}{sub e}(1200), for every pixel. From a value {approx}1 Multiplication-Sign 10{sup -25} cm{sup 2} H{sup -1} at the lowest column densities that is typical of the high-latitude diffuse ISM, {sigma}{sub e}(1200) increases as N {sup 0.28} {sub H} over the range studied. This is suggestive of grain evolution. Integrating the SEDs over frequency, we also calculated the specific power P (emission power per H) for the big grains. In low column density regions where dust clouds are optically thin to the interstellar radiation field (ISRF), P is typically 3.7 Multiplication-Sign 10{sup -31} W H{sup -1}, again close to that in the high-latitude diffuse ISM. However, we find evidence for a decrease of P in high column density regions, which would be a natural outcome of attenuation of the ISRF that heats the grains, and for localized increases for dust illuminated by nearby stars or embedded protostars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

HIERARCHICAL FRAGMENTATION OF THE ORION MOLECULAR FILAMENTS

We present a high angular resolution map of the 850 {mu}m continuum emission of the Orion Molecular Cloud-3 (OMC 3) obtained with the Submillimeter Array (SMA); the map is a mosaic of 85 pointings covering an approximate area of 6.'5 Multiplication-Sign 2.'0 (0.88 Multiplication-Sign 0.27 pc). We detect 12 spatially resolved continuum sources, each with an H{sub 2} mass between 0.3-5.7 M {sub Sun} and a projected source size between 1400-8200 AU. All the detected sources are on the filamentary main ridge (n{sub H{sub 2}}{>=}10{sup 6} cm{sup -3}), and analysis based on the Jeans theorem suggests that they are most likely gravitationally unstable. Comparison of multi-wavelength data sets indicates that of the continuum sources, 6/12 (50%) are associated with molecular outflows, 8/12 (67%) are associated with infrared sources, and 3/12 (25%) are associated with ionized jets. The evolutionary status of these sources ranges from prestellar cores to protostar phase, confirming that OMC-3 is an active region with ongoing embedded star formation. We detect quasi-periodical separations between the OMC-3 sources of Almost-Equal-To 17''/0.035 pc. This spatial distribution is part of a large hierarchical structure that also includes fragmentation scales of giant molecular cloud ( Almost-Equal-To 35 pc), large-scale clumps ( Almost-Equal-To 1.3 pc), and small-scale clumps ( Almost-Equal-To 0.3 pc), suggesting that hierarchical fragmentation operates within the Orion A molecular cloud. The fragmentation spacings are roughly consistent with the thermal fragmentation length in large-scale clumps, while for small-scale cores it is smaller than the local fragmentation length. These smaller spacings observed with the SMA can be explained by either a helical magnetic field, cloud rotation, or/and global filament collapse. Finally, possible evidence for sequential fragmentation is suggested in the northern part of the OMC-3 filament.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE ANATOMY OF AN EXTREME STARBURST WITHIN 1.3 Gyr OF THE BIG BANG REVEALED BY ALMA

We present further analysis of the [C II] 158 {mu}m fine structure line and thermal dust continuum emission from the archetype extreme starburst/active galactic nucleus (AGN) group of galaxies in the early universe, BRI 1202-0725 at z = 4.7, using the Atacama Large Millimeter Array. The group has long been noted for having a closely separated (26 kpc in projection) FIR-hyperluminous quasar host galaxy and an optically obscured submillimeter galaxy (SMG). A short ALMA test observation reveals a rich laboratory for the study of the myriad processes involved in clustered massive galaxy formation in the early universe. Strong [C II] emission from the SMG and the quasar have been reported earlier by Wagg et al. based on these observations. In this paper, we examine in more detail the imaging results from the ALMA observations, including velocity channel images, position-velocity plots, and line moment images. We present detections of [C II] emission from two Ly{alpha}-selected galaxies in the group, demonstrating the relative ease with which ALMA can detect the [C II] emission from lower star formation rate galaxies at high redshift. Imaging of the [C II] emission shows a clear velocity gradient across the SMG, possibly indicating rotation or a more complex dynamical system on a scale {approx}10 kpc. There is evidence in the quasar spectrum and images for a possible outflow toward the southwest, as well as more extended emission (a {sup b}ridge{sup )}, between the quasar and the SMG, although the latter could simply be emission from Ly{alpha}-1 blending with that of the quasar at the limited spatial resolution of the current observations. These results provide an unprecedented view of a major merger of gas-rich galaxies driving extreme starbursts and AGN accretion during the formation of massive galaxies and supermassive black holes within 1.3 Gyr of the big bang.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NON-ZEEMAN CIRCULAR POLARIZATION OF MOLECULAR ROTATIONAL SPECTRAL LINES

We present measurements of circular polarization from rotational spectral lines of molecular species in Orion KL, most notably {sup 12}CO (J = 2 {yields} 1), obtained at the Caltech Submillimeter Observatory with the Four-Stokes-Parameter Spectral Line Polarimeter. We find levels of polarization of up to 1%-2% in general; for {sup 12}CO (J = 2 {yields} 1) this level is comparable to that of linear polarization also measured for that line. We present a physical model based on resonant scattering in an attempt to explain our observations. We discuss how slight differences in scattering amplitudes for radiation polarized parallel and perpendicular to the ambient magnetic field, responsible for the alignment of the scattering molecules, can lead to the observed circular polarization. We also show that the effect is proportional to the square of the magnitude of the plane of the sky component of the magnetic field and therefore opens up the possibility of measuring this parameter from circular polarization measurements of Zeeman insensitive molecules.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few Multiplication-Sign 10{sup 22} cm{sup -2} (N {sub H2}) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to {approx}10 K from values {approx}14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

RESOLVED DEPLETION ZONES AND SPATIAL DIFFERENTIATION OF N{sub 2}H{sup +} AND N{sub 2}D{sup +}

We present a study on the spatial distribution of N{sub 2}D{sup +} and N{sub 2}H{sup +} in 13 protostellar systems. Eight of thirteen objects observed with the IRAM 30 m telescope show relative offsets between the peak N{sub 2}D{sup +} (J = 2 {yields} 1) and N{sub 2}H{sup +} (J = 1 {yields} 0) emission. We highlight the case of L1157 using interferometric observations from the Submillimeter Array and Plateau de Bure Interferometer of the N{sub 2}D{sup +} (J = 3 {yields} 2) and N{sub 2}H{sup +} (J = 1 {yields} 0) transitions, respectively. Depletion of N{sub 2}D{sup +} in L1157 is clearly observed inside a radius of {approx}2000 AU (7'') and the N{sub 2}H{sup +} emission is resolved into two peaks at radii of {approx}1000 AU (3.''5), inside the depletion region of N{sub 2}D{sup +}. Chemical models predict a depletion zone in N{sub 2}D{sup +} and N{sub 2}H{sup +} due to destruction of H{sub 2}D{sup +} at T {approx} 20 K and the evaporation of CO off dust grains at the same temperature. However, the abundance offsets of 1000 AU between the two species are not reproduced by chemical models, including a model that follows the infall of the protostellar envelope. The average abundance ratios of N{sub 2}D{sup +} to N{sub 2}H{sup +} have been shown to decrease as protostars evolve by Emprechtinger et al., but this is the first time depletion zones of N{sub 2}D{sup +} have been spatially resolved. We suggest that the difference in depletion zone radii for N{sub 2}H{sup +} and N{sub 2}D{sup +} is caused by either the CO evaporation temperature being above 20 K or an H{sub 2} ortho-to-para ratio gradient in the inner envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CO J = 2-1 EMISSION FROM EVOLVED STARS IN THE GALACTIC BULGE

We observe a sample of eight evolved stars in the Galactic bulge in the CO J = 2-1 line using the Submillimeter Array with angular resolution of 1''-4''. These stars have been detected previously at infrared wavelengths, and several of them have OH maser emission. We detect CO J = 2-1 emission from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and [SLO2003] A51. We do not detect the remaining five stars in the sample because of heavy contamination from the galactic CO emission. Combining CO data with observations at infrared wavelengths constraining dust mass loss from these stars, we determine the gas-to-dust ratios of the Galactic bulge stars for which CO emission is detected. For OH 359.943 +0.260, we determine a gas mass-loss rate of 7.9 ({+-}2.2) Multiplication-Sign 10{sup -5} M {sub Sun} yr{sup -1} and a gas-to-dust ratio of 310 ({+-}89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 ({+-}2.8) Multiplication-Sign 10{sup -5} M {sub Sun} yr{sup -1} and a gas-to-dust ratio of 220 ({+-}110). For [SLO2003] A51, we find a gas mass-loss rate of 3.4 ({+-}3.0) Multiplication-Sign 10{sup -5} M {sub Sun} yr{sup -1} and a gas-to-dust ratio of 160 ({+-}140), reflecting the low quality of our tentative detection of the CO J = 2-1 emission from A51. We find that the CO J = 2-1 detections of OH/IR stars in the Galactic bulge require lower average CO J = 2-1 backgrounds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

H{sub 2}CO AND N{sub 2}H{sup +} IN PROTOPLANETARY DISKS: EVIDENCE FOR A CO-ICE REGULATED CHEMISTRY

We present Submillimeter Array (SMA) observations of H{sub 2}CO and N{sub 2}H{sup +} emission in the disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296 at 2''-6'' resolution and discuss the distribution of these species with respect to CO freezeout. The H{sub 2}CO and N{sub 2}H{sup +} emission toward HD 163296 does not peak at the continuum emission center that marks the stellar position but is instead significantly offset. Using a previously developed model for the physical structure of this disk, we show that the H{sub 2}CO observations are reproduced if H{sub 2}CO is present predominantly in the cold outer disk regions. A model where H{sub 2}CO is present only beyond the CO snow line (estimated at a radius of 160 AU) matches the observations well. We also show that the average H{sub 2}CO excitation temperature, calculated from two transitions of H{sub 2}CO observed in these two disks and a larger sample of disks around T Tauri stars in the DISCS (the Disk Imaging Survey of Chemistry with SMA) program, is consistent with the CO freezeout temperature of {approx}20 K. In addition, we show that N{sub 2}H{sup +} and H{sub 2}CO line fluxes in disks are strongly correlated, indicative of co-formation of these species across the sample. Taken together, these results imply that H{sub 2}CO and N{sub 2}H{sup +} are generally present in disks only at low temperatures where CO depletes onto grains, consistent with fast destruction of N{sub 2}H{sup +} by gas-phase CO, and in situ formation of H{sub 2}CO through hydrogenation of CO ice. In this scenario H{sub 2}CO, CH{sub 3}OH, and N{sub 2}H{sup +} emission in disks should appear as rings with the inner edge at the CO midplane snow line. This prediction can be tested directly using observations from ALMA with higher resolution and better sensitivity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

AN ANALYSIS OF THE DEUTERIUM FRACTIONATION OF STAR-FORMING CORES IN THE PERSEUS MOLECULAR CLOUD

We have performed a pointed survey of N{sub 2}D{sup +} 2-1 and N{sub 2}D{sup +} 3-2 emission toward 64 N{sub 2}H{sup +}-bright starless and protostellar cores in the Perseus molecular cloud using the Arizona Radio Observatory Submillimeter Telescope and Kitt Peak 12 m telescope. We find a mean deuterium fractionation in N{sub 2}H{sup +}, R{sub D} = N(N{sub 2}D{sup +})/N(N{sub 2}H{sup +}), of 0.08, with a maximum R{sub D} = 0.2. In detected sources, we find no significant difference in the deuterium fractionation between starless and protostellar cores, nor between cores in clustered or isolated environments. We compare the deuterium fraction in N{sub 2}H{sup +} with parameters linked to advanced core evolution. We only find significant correlations between the deuterium fraction and increased H{sub 2} column density, as well as with increased central core density, for all cores. Toward protostellar sources, we additionally find a significant anticorrelation between R{sub D} and bolometric temperature. We show that the Perseus cores are characterized by low CO depletion values relative to previous studies of star-forming cores, similar to recent results in the Ophiuchus molecular cloud. We suggest that the low average CO depletion is the dominant mechanism that constrains the average deuterium fractionation in the Perseus cores to small values. While current equilibrium and dynamic chemical models are able to reproduce the range of deuterium fractionation values we find in Perseus, reproducing the scatter across the cores requires variation in parameters such as the ionization fraction or the ortho-to-para-H{sub 2} ratio across the cloud, or a range in core evolution timescales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

VERY LARGE ARRAY MAPPING OF THE CO(1-0) LINE IN SMM J14011+0252

We present high-resolution CO(1-0) observations of the lensed submillimeter galaxy (SMG) SMM J14011+0252 at z = 2.6. Comparison to the previously detected CO(3-2) line gives an intensity ratio of r {sub 3,1} = 0.97 {+-} 0.16 in temperature units, larger than is typical for SMGs but within the range seen in the low-z ultraluminous infrared galaxy population. Combining our new data with previous mid-J CO observations, we perform a single-phase large velocity gradient (LVG) analysis to constrain the physical conditions of the molecular gas. Acceptable models have significant degeneracies between parameters, even when we rule out all models that produce optically thin emission, but we find that the bulk of the molecular gas has T {sub kin} = 20-60 K, n{sub H{sub 2}}{approx}10{sup 4}-10{sup 5} cm{sup -3}, and N {sub CO}/{Delta}v = 10{sup 17.00{+-}0.25} cm{sup -2} km{sup -1} s. For our best-fit models to self-consistently recover a typical CO-to-H{sub 2} abundance and a plausible degree of virialization, the local velocity gradient in the molecular gas must be substantially larger than its galaxy-wide average. This conclusion is consistent with a scenario in which SMM J14011+0252 has a fairly face-on orientation and a molecular interstellar medium composed of many unresolved clouds. Using previous H{alpha} observations, we find that SMM J14011+0252 has a spatially resolved star formation rate versus molecular gas surface density relation inconsistent with those of 'normal' local star-forming galaxies, even if we adopt a local 'disk-like' CO-to-H{sub 2} conversion factor as motivated by our LVG analysis. This discrepancy supports the inference of a star formation relation for high-z starbursts distinct from the local relation that is not solely due to differing choices of gas mass conversion factor.

79 ASTRONOMY AND ASTROPHYSICS↗