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At least 1,603 records · Page 89
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DOE OSTI2013

FAINT END OF 1.3 mm NUMBER COUNTS REVEALED BY ALMA

We present the faint end of number counts at 1.3 mm (238 GHz) obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). Band 6 observations were carried out targeting 20 star-forming galaxies at z ∼ 1.4 in the Subaru/XMM-Newton Deep Survey field. In the observations, we serendipitously detect 15 sources (≥3.8σ, S{sub 1.3} {sub mm} = 0.15-0.61 mJy) other than the targeted sources. We create number counts by using these ''sub-mJy sources'', which probe the faintest flux range among surveys at millimeter wavelengths. The number counts are consistent with (flux-scaled) number counts at 850 μm and 870 μm obtained with gravitational lensing clusters. The ALMA number counts agree well with model predictions, which suggest that these sub-mJy populations are more like ''normal'' star-forming galaxies than ''classical'' submillimeter galaxies with intense star-forming activity. In this flux range, ∼80% of the extragalactic background light at 1.3 mm is resolved into individual sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ALMA FOLLOWS STREAMING OF DENSE GAS DOWN TO 40 pc FROM THE SUPERMASSIVE BLACK HOLE IN NGC 1097

We present a kinematic analysis of the dense molecular gas in the central 200 pc of the nearby galaxy NGC 1097, based on Cycle 0 observations with the Atacama Large Millimeter/submillimeter Array (ALMA). We use the HCN(4-3) line to trace the densest interstellar molecular gas (n{sub H{sub 2}}{approx}10{sup 8} cm{sup -3}), and quantify its kinematics, and estimate an inflow rate for the molecular gas. We find a striking similarity between the ALMA kinematic data and the analytic spiral inflow model that we have previously constructed based on ionized gas velocity fields on larger scales. We are able to follow dense gas streaming down to 40 pc distance from the supermassive black hole in this Seyfert 1 galaxy. In order to fulfill marginal stability, we deduce that the dense gas is confined to a very thin disk, and we derive a dense gas inflow rate of 0.09 M{sub Sun} yr{sup -1} at 40 pc radius. Combined with previous values from the H{alpha} and CO gas, we calculate a combined molecular and ionized gas inflow rate of {approx}0.2 M{sub Sun} yr{sup -1} at 40 pc distance from the central supermassive black hole of NGC 1097.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

CARBON MONOXIDE IN THE COLD DEBRIS OF SUPERNOVA 1987A

We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M{sub Sun} of CO at a temperature >14 K, confined within at most 35% of a spherical volume expanding at {approx}2000 km s{sup -1}. Moreover, we locate the emission within 1'' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

HIGH-n HYDROGEN RECOMBINATION LINES FROM THE FIRST GALAXIES

We investigate the prospects of blind and targeted searches in the radio domain (10 MHz to 1 THz) for high-n hydrogen recombination lines from the first generation of galaxies, at z ∼< 10. The expected optically thin spontaneous α-line luminosities are calculated as a function of the absolute AB magnitude of a galaxy at 1500 Å. For a blind search, semi-empirical luminosity functions are used to calculate the number of galaxies whose expected flux densities exceed an assumed detectability threshold. Plots of the minimum sky area, within which at least one detectable galaxy is expected at a given observing frequency, in the fiducial instantaneous passband of 10{sup 4} km s{sup –1}, allow us to assess the blind search time necessary for detection by a given facility. We show that the chances for detection are the highest in the millimeter and submillimeter domains, but finding spontaneous emission in a blind search, especially from redshifts z >> 1, is a challenge even with powerful facilities, such as the Actama Large Millimeter/Submillimeter Array and Square Kilometre Array. The probability of success is higher for a targeted search of lines with principal quantum number n ∼ 10 in Lyman-break galaxies amplified by gravitational lensing. Detection of more than one hydrogen line in such a galaxy will allow for line identification and a precise determination of the galaxy's redshift.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: HOT CORE AND MOLECULAR OUTFLOWS

We have observed a cluster forming clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the 1.3 mm continuum and the CH{sub 3}OH, CS, {sup 13}CS, SiO, CH{sub 3}CH{sub 2}CN, and HCOOCH{sub 3} lines with the Atacama Large Millimeter/submillimeter Array and in K-band with the Keck telescope. We have found a young outflow toward the center of this clump in the SiO, CS, and CH{sub 3}OH lines. This outflow is likely driven by a protostar embedded in a hot core, which is traced by the CH{sub 3}CH{sub 2}CN, HCOOCH{sub 3}, {sup 13}CS, and high excitation CH{sub 3}OH lines. The size of the hot core is about 800 × 300 AU in spite of its low mass (<1.1 M {sub ☉}), suggesting a high accretion rate or the presence of multiple star system harboring a few hot corinos. The outflow is highly collimated, and the dynamical timescale is estimated to be less than 740 yr. In addition, we have also detected extended emission of SiO, CS, and CH{sub 3}OH, which is not associated with the hot core and the outflow. This emission may be related to past star formation activity in the clump. Although G34.43+00.24 MM3 is surrounded by a dark feature in infrared, it has already experienced active formation of low-mass stars in an early stage of clump evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ALMA CONTINUUM OBSERVATIONS OF A 30 Myr OLD GASEOUS DEBRIS DISK AROUND HD 21997

Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examples of old (30-40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present Atacama Large Millimeter/Submillimeter Array (ALMA) and Herschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution and origin of the dust and its connection to the gas. Our ALMA continuum images at 886 μm clearly resolve a broad ring of emission within a diameter of ∼4.''5, adding HD 21997 to the dozen debris disks resolved at (sub)millimeter wavelengths. Modeling the morphology of the ALMA image with a radiative transfer code suggests inner and outer radii of ∼55 and ∼150 AU, and a dust mass of 0.09 M {sub ⊕}. Our data and modeling hints at an extended cold outskirt of the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gas nevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is of secondary origin and is produced by planetesimals. Since the gas component is probably primordial, HD 21997 is one of the first known examples of a hybrid circumstellar disk, a thus-far little studied late phase of circumstellar disk evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A RECENT ACCRETION BURST IN THE LOW-MASS PROTOSTAR IRAS 15398-3359: ALMA IMAGING OF ITS RELATED CHEMISTRY

Low-mass protostars have been suggested to show highly variable accretion rates throughout their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C{sup 17}O, H{sup 13}CO{sup +}, CH{sub 3}OH, C{sup 34}S and C{sub 2}H toward the low-mass protostar IRAS 15398-3359 on 0.''5 (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array at 340 GHz. The resolved images show that the emission from H{sup 13}CO{sup +} is only present in a ring-like structure with a radius of about 1-1.''5 (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO{sup +} is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 yr increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH{sub 3}OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other protostars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA WILL DETERMINE THE SPECTROSCOPIC REDSHIFT z > 8 WITH FIR [O III] EMISSION LINES

We investigate the potential use of nebular emission lines in the rest-frame far-infrared (FIR) for determining spectroscopic redshift of z > 8 galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA). After making a line emissivity model as a function of metallicity, especially for the [O III] 88 μm line which is likely to be the strongest FIR line from H II regions, we predict the line fluxes from high-z galaxies based on a cosmological hydrodynamics simulation of galaxy formation. Since the metallicity of galaxies reaches at ∼0.2 Z {sub ☉} even at z > 8 in our simulation, we expect the [O III] 88 μm line as strong as 1.3 mJy for 27 AB objects, which is detectable at a high significance by <1 hr integration with ALMA. Therefore, the [O III] 88 μm line would be the best tool to confirm the spectroscopic redshifts beyond z = 8.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

DUST PRODUCTION AND PARTICLE ACCELERATION IN SUPERNOVA 1987A REVEALED WITH ALMA

Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/Submillimeter Array to observe SN 1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 μm, 870 μm, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (>0.2 M {sub ☉}). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

VARYING [C II]/[N II] LINE RATIOS IN THE INTERACTING SYSTEM BR1202-0725 AT z = 4.7

We study the properties of the interstellar medium in the interacting system BR1202-0725 at z = 4.7 via its [N II] and [C II] fine-structure line emission. This system consists of a QSO, a sub-mm galaxy (SMG), and two Lyα emitters (LAEs). Such a diversity in galaxy properties makes BR1202-0725 a unique laboratory of star formation and galaxy evolution at high redshift. We present ionized nitrogen ([N II] 205 μm) observations of this system, obtained with the IRAM Plateau de Bure Interferometer. We find no [N II] emission at the quasar location, but tentative [N II] line detections associated with the SMG and one of the LAEs. Together with available ionized carbon ([C II] 158 μm) Atacama Large Millimeter Array observations of this system, we find the following: the [C II]/[N II] luminosity ratio is >5.5 for the QSO and the SMG, but it is as low as ∼2 in the LAE, suggesting that, in this source, most of the [C II] emission is associated with the ionized medium (H II regions) rather than the neutral one (photon-dominated regions). This study demonstrates the importance of combined studies of multiple fine-structure lines in order to pin down the physical properties of the interstellar medium in distant galaxies.

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DOE OSTI2014

A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I

We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H{sub 2}O lines at 321 GHz (10{sub 2,} {sub 9}-9{sub 3,} {sub 6}) and 336 GHz (ν{sub 2} = 1, 5{sub 2,} {sub 3}-6{sub 1,} {sub 6}) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.''4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0.''2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H{sub 2}O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M{sub ☉} and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of ∼100 AU scale.

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DOE OSTI2014

JUPITER AS A GIANT COSMIC RAY DETECTOR

We explore the feasibility of using the atmosphere of Jupiter to detect ultra-high-energy cosmic rays (UHECRs). The large surface area of Jupiter allows us to probe cosmic rays of higher energies than previously accessible. Cosmic ray extensive air showers in Jupiter's atmosphere could in principle be detected by the Large Area Telescope (LAT) on the Fermi observatory. In order to be observed, these air showers would need to be oriented toward the Earth, and would need to occur sufficiently high in the atmosphere that the gamma rays can penetrate. We demonstrate that, under these assumptions, Jupiter provides an effective cosmic ray ''detector'' area of 3.3 × 10{sup 7} km{sup 2}. We predict that Fermi-LAT should be able to detect events of energy >10{sup 21} eV with fluence 10{sup –7} erg cm{sup –2} at a rate of about one per month. The observed number of air showers may provide an indirect measure of the flux of cosmic rays ≳ 10{sup 20} eV. Extensive air showers also produce a synchrotron signature that may be measurable by Atacama Large Millimeter/submillimeter Array (ALMA). Simultaneous observations of Jupiter with ALMA and Fermi-LAT could be used to provide broad constraints on the energies of the initiating cosmic rays.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

EXTREME DUST DISKS IN Arp 220 AS REVEALED BY ALMA

We present new images of Arp 220 from the Atacama Large Millimeter/submillimeter Array with the highest combination of frequency (691 GHz) and resolution (0.''36 × 0.''20) ever obtained for this prototypical ultraluminous infrared galaxy. The western nucleus is revealed to contain warm (200 K) dust that is optically thick (τ{sub 434} {sub μm} = 5.3), while the eastern nucleus is cooler (80 K) and somewhat less opaque (τ{sub 434} {sub μm} = 1.7). We derive full width at half-maximum diameters of 76 × ≤ 70 pc and 123 × 79 pc for the western and eastern nucleus, respectively. The two nuclei combined account for (83{sub −38}{sup +65} (calibration) {sub −34}{sup +0} (systematic))% of the total infrared luminosity of Arp 220. The luminosity surface density of the western nucleus (log (σT{sup 4})=14.3±0.2{sub −0.7}{sup +0} in units of L {sub ☉} kpc{sup –2}) appears sufficiently high to require the presence of an active galactic nucleus (AGN) or a ''hot starburst'', although the exact value depends sensitively on the brightness distribution adopted for the source. Although the role of any central AGN remains open, the inferred mean gas column densities of (0.6-1.8) × 10{sup 25} cm{sup –2} mean that any AGN in Arp 220 must be Compton-thick.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA HINTS AT THE PRESENCE OF TWO COMPANIONS IN THE DISK AROUND HD 100546

HD 100546 is a well-studied Herbig Be star-disk system that likely hosts a close-in companion with compelling observational evidence for an embedded protoplanet at 68 AU. We present Atacama Large Millimeter/Submillimeter Array observations of the HD 100546 disk which resolve the gas and dust structure at (sub)millimeter wavelengths. The CO emission (at 345.795 GHz) originates from an extensive molecular disk (390 ± 20 AU in radius) whereas the continuum emission is more compact (230 ± 20 AU in radius), suggesting radial drift of the millimeter-sized grains. The CO emission is similar in extent to scattered light images indicating well-mixed gas and micrometer-sized grains in the disk atmosphere. Assuming azimuthal symmetry, a single-component power-law model cannot reproduce the continuum visibilities. The visibilities and images are better reproduced by a double-component model: a compact ring with a width of 21 AU centered at 26 AU and an outer ring with a width of 75 ± 3 AU centered at 190 ± 3 AU. The influence of a companion and protoplanet on the dust evolution is investigated. The companion at 10 AU facilitates the accumulation of millimeter-sized grains within a compact ring, ≈20-30 AU, by ≈10 Myr. The injection of a protoplanet at 1 Myr hastens the ring formation (≈1.2 Myr) and also triggers the development of an outer ring (≈100-200 AU). These observations provide additional evidence for the presence of a close-in companion and hint at dynamical clearing by a protoplanet in the outer disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A CHEMICAL VIEW OF PROTOSTELLAR-DISK FORMATION IN L1527

Subarcsecond images of the rotational line emissions of CCH, CS, H{sub 2}CO, and CH{sub 3}OH have been obtained toward the low-mass protostar IRAS 04368+2557 in L1527 as one of the early science projects of the Atacama Large Millimeter/submillimeter Array. The intensity distributions of CCH and CS show a double-peaked structure along the edge-on envelope with a dip toward the protostar position, whereas those of H{sub 2}CO and CH{sub 3}OH are centrally peaked. By analyzing the position-velocity diagrams along the envelope, CCH and CS are found to reside mainly in the envelope, where the gas is infalling with conservation of its angular momentum. They are almost absent inward of the centrifugal barrier (a half of the centrifugal radius). Although H{sub 2}CO exists in the infalling rotating envelope, it also resides in the disk component inside the centrifugal barrier to some extent. On the other hand, CH{sub 3}OH seems to exist around the centrifugal barrier and in the disk component. Hence, the drastic chemical change occurs at the centrifugal barrier. A discontinuous infalling motion as well as the gas-grain interaction would be responsible for the chemical change. This result will put an important constraint on initial chemical compositions for chemical evolution of protostellar disks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: 278 GHz CLASS I METHANOL MASERS

We have observed a molecular clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} E, 5{sub 0}-4{sub 0} E, and 5{sub –1}-4{sub –1} E lines at sub-arcsecond resolution by using the Atacama Large Millimeter/submillimeter Array. By comparing the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} E emission with the CH{sub 3}OH 5{sub 0}-4{sub 0} E and 5{sub –1}-4{sub –1} E emission, we have found that the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} E emission is masing. We have clearly shown that the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} masers arise from the post shocked gas in the interacting regions between the outflows and ambient dense gas. Toward the strongest peak of the CH{sub 3}OH maser emission, SiO J = 6-5 emission is very weak. This indicates that the CH{sub 3}OH maser emission traces relatively old shocks or weak shocks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

TURBULENCE SETS THE INITIAL CONDITIONS FOR STAR FORMATION IN HIGH-PRESSURE ENVIRONMENTS

Despite the simplicity of theoretical models of supersonically turbulent, isothermal media, their predictions successfully match the observed gas structure and star formation activity within low-pressure (P/k < 10{sup 5} K cm{sup –3}) molecular clouds in the solar neighborhood. However, it is unknown whether or not these theories extend to clouds in high-pressure (P/k > 10{sup 7} K cm{sup –3}) environments, like those in the Galaxy's inner 200 pc central molecular zone (CMZ) and in the early universe. Here, we present Atacama Large Millimeter/submillimeter Array 3 mm dust continuum emission within a cloud, G0.253+0.016, which is immersed in the high-pressure environment of the CMZ. While the log-normal shape and dispersion of its column density probability distribution function (PDF) are strikingly similar to those of solar neighborhood clouds, there is one important quantitative difference: its mean column density is one to two orders of magnitude higher. Both the similarity and difference in the PDF compared to those derived from solar neighborhood clouds match predictions of turbulent cloud models given the high-pressure environment of the CMZ. The PDF shows a small deviation from log-normal at high column densities confirming the youth of G0.253+0.016. Its lack of star formation is consistent with the theoretically predicted, environmentally dependent volume density threshold for star formation which is orders of magnitude higher than that derived for solar neighborhood clouds. Our results provide the first empirical evidence that the current theoretical understanding of molecular cloud structure derived from the solar neighborhood also holds in high-pressure environments. We therefore suggest that these theories may be applicable to understand star formation in the early universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALMA MEASUREMENTS OF THE HNC AND HC{sub 3}N DISTRIBUTIONS IN TITAN'S ATMOSPHERE

We present spectrally and spatially resolved maps of HNC and HC{sub 3}N emission from Titan's atmosphere, obtained using the Atacama Large Millimeter/submillimeter Array on 2013 November 17. These maps show anisotropic spatial distributions for both molecules, with resolved emission peaks in Titan's northern and southern hemispheres. The HC{sub 3}N maps indicate enhanced concentrations of this molecule over the poles, consistent with previous studies of Titan's photochemistry and atmospheric circulation. Differences between the spectrally integrated flux distributions of HNC and HC{sub 3}N show that these species are not co-spatial. The observed spectral line shapes are consistent with HNC being concentrated predominantly in the mesosphere and above (at altitudes z ≳ 400 km), whereas HC{sub 3}N is abundant at a broader range of altitudes (z ≈ 70-600 km). From spatial variations in the HC{sub 3}N line profile, the locations of the HC{sub 3}N emission peaks are shown to be variable as a function of altitude. The peaks in the integrated emission from HNC and the line core (upper atmosphere) component of HC{sub 3}N (at z ≳ 300 km) are found to be asymmetric with respect to Titan's polar axis, indicating that the mesosphere may be more longitudinally variable than previously thought. The spatially integrated HNC and HC{sub 3}N spectra are modeled using the NEMESIS planetary atmosphere code and the resulting best-fitting disk-averaged vertical mixing ratio profiles are found to be in reasonable agreement with previous measurements for these species. Vertical column densities of the best-fitting gradient models for HNC and HC{sub 3}N are 1.9 × 10{sup 13} cm{sup –2} and 2.3 × 10{sup 14} cm{sup –2}, respectively.

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