T. G. Phillips

SHARC-2 350 μm Observations of Distant Submillimeter-selected Galaxies

We present 350 μm observations of 15 Chapman et al. submillimeter galaxies (SMGs) with radio counterparts and optical redshifts. We detect 12 and obtain sensitive upper limits for three, providing direct, precise measurements of their far-infrared luminosities and characteristic dust temperatures. With these, we verify the linear radio-far-infrared correlation at redshifts of z ~ 1-3 and luminosities of 10^(11)-10^(13) L_☉, with a power-law index of 1.02 ± 0.12 and rms scatter of 0.12 dex. However, either the correlation constant q or the dust emissivity index β is lower than measured locally. The best-fitting q ≃2.14 is consistent with SMGs being predominantly starbust galaxies, without significant AGN contribution, at far-infrared wavelengths. Gas-to-dust mass ratios are estimated at 54^(+14)_(-11)(κ_(850μm)/0.15 m^2 kg^(-1)), depending on the absoption efficiency κ_ν, with intrinsic dispersion ≃40% around the mean value. Dust temperatures consistent with 34.6 ± 3 K (1.5/β)^(0.71), at z ~ 1.5-3.5, suggest that far-infrared photometric redshifts may be viable, and perhaps accurate to 10% ≲ dz/(1 + z), for up to 80% of the SMG population in this range, if the above temperature characterizes the full range of SMGs. However, observed temperature evolution of T_d ∝ (1 + z) is also plausible and could result from selection effects. From the observed luminosity-temperature (L-T) relation, L ∝ T^(2.82±0.29)_(obs), we derive scaling relations for dust mass versus dust temperature, and we identify expressions to interrelate the observed quantities. These suggest that measurements at a single wavelength, in the far-infrared, submillimeter, or radio wave bands, might constrain dust temperatures and far-infrared luminosities for most SMGs with redshifts at z ~ 0.5-4.

In-orbit performance of Herschel-HIFI

Aims. In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described. Methods. The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources. Results. The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies.

The edges of molecular clouds - Fractal boundaries and density structure

This paper continues a discussion of the manifestations of the highly nonlinear physical equations underlying the dynamics of the dense interstellar medium. Previously, Falgarone and Phillips confirmed that the velocity field in non-star-forming regions could be explained as a turbulent phenomenon, showing the Kolmogorov scaling of velocity dispersion with spatial extent, and proposed that the excess of large velocity deviations (line wings stronger than predicted by a Gaussian distribution) corresponds to the fundamental property of turbulent flows called intermittency. In the present work we inspect the spatial structure of the dense medium. The observations of clouds at two different distances were carried out at high angular resolution using several transitions of the carbon monoxide molecule. Cloud edge regions were selected for the study to avoid the spatial crowding of emitting components, which obscures the structure of cloud cores

A Line Survey of Orion KL from 325 to 360 GHz

We present a high-sensitivity spectral line survey of the high-mass star-forming region Orion KL in the 325-360 GHz frequency band. The survey was conducted at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii. The sensitivity achieved is typically 0.1-0.5 K and is limited mostly by the sideband separation method utilized. We find 717 resolvable features consisting of 1004 lines, among which 60 are unidentified. The identified lines are due to 34 species and various isotopomers. Most of the unidentified lines are weak, and many of them most likely due to isotopomers or vibrationally or torsionally excited states of known species with unknown line frequencies, but a few reach the 2-5 K level. No new species have been identified, but we were able to strengthen evidence for the identification of ethanol in Orion and found the first nitrogen sulfide line in this source. The molecule dominating the integrated line emission is S02, which emits twice the intensity of CO, followed by SO, which is only slightly stronger than CO. In contrast, the largest number of lines is emitted from heavy organic rotors like HCOOCH3, CH3CH2CN, and CH3OCH3, but their contribution to the total flux is unimportant. CH3OH is also very prominent, both in the number of lines and in integrated flux. An interesting detail of this survey is the first detection of vibrationally excited HCN in the v2 = 2 state, 2000 K above ground. Clearly this is a glimpse into the very inner part of the Orion hot core.

A Line Survey of Orion-KL from 607 to 725 GHz

With the Caltech Submillimeter Telescope, we have performed an unbiased line survey of Orion-KL in the frequency range 607-725 GHz. We were able to identify lines down to a threshold of 1-2 K in main beam brightness temperature units, and we found 1064 spectral features consisting of 2032 lines, partially blended. Apart from the abundant diatomic rotors such as CO, CS, SO, the spectrum is dominated by CH3OH and SO2, both in terms of numbers of lines and integrated flux. The number of unidentified lines is 155 or 14%. We also report the tentative identification of the new molecule SiH in our data. For some complex organic molecules, we find rotation temperatures and column densities which are much higher than those found in earlier studies. It is likely the cause of this is a significant contribution from a very compact, hot component of the Orion molecular cloud core which was not visible in lower frequency surveys.

Long-term Evolution of the Outgassing of Comet Hale-Bopp From Radio Observations

C/1995 O1 (Hale-Bopp) has been observed on a regular basis since August 1995 at millimetre and submillimetre wavelengths using IRAM, JCMT, CSO and SEST radio telescopes. The production rates of eight molecular species (CO, HCN, CH3OH, H2CO,H2S, CS, CH3CN,HNC) have been monitored as a function of heliocentric distance(rh from 7 AU pre-perihelion to 4 AU post-perihelion. As comet Hale-Bopp approached and receded from the Sun, these species displayed different behaviours. Far from the Sun, the most volatile species were found in general relatively more abundant in the coma. In comparison to other species, HNC, H2CO and CS showed a much steeper increase of the production rate with decreasing rh. Less than 1.5 AU from the Sun, the relative abundances were fairly stable and approached those found in other comets near 1 AU.The kinetic temperature of the coma, estimated from the relative intensities of the CH3OH and CO lines, increased with decreasing rh, from about10 K at 7 AU to 110 K around perihelion. The expansion velocity of the gaseous species, derived from the line shapes, also increased with a law close torh3.

Low-noise 115-GHz mixing in superconducting oxide-barrier tunnel junctions

Small‐area (≲1 μm2) oxide‐barrier tunnel junctions have been made of thermally cyclable superconducting Pb alloys for use as high‐frequency mixers. A single‐sideband mixer noise temperature of <100 K has been achieved at 115 GHz. This result was achieved in the quasiparticle (classical) mixing mode.

Interstellar OH+, H2O+ and H3O+ along the sight-line to G10.6–0.4

We report the detection of absorption lines by the reactive ions OH + ,H 2O + and H3O + along the line of sight to the submillimeter continuum source G10.6−0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH + at 971 GHz, H2O + at 1115 and 607 GHz, and H3O + at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6−0.4 as well as in the molecular gas directly associated with that source. The OH + spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O + lines remains lower than 1 in the same velocity range, and the H3O + line shows only weak absorption. For LSR velocities between 7 and 50 kms −1 we estimate total column densities of N(OH + ) ≥ 2.5 × 10 14 cm −2 , N(H2O + ) ∼6 × 10 13 cm −2 and N(H3O + ) ∼4.0 × 10 13 cm −2 . These detections confirm the role of O + and OH + in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH + by the H2O + column density implies that these species predominantly trace low-density gas with a small fraction of

Detection of Triply Deuterated Ammonia in the Barnard 1 Cloud

We report the detection of the ground-state rotational transition JK = 10 → 00 (0a → 0s) of triply deuterated ammonia at 309.91 GHz in the Barnard 1 cloud, obtained with the Caltech Submillimeter Observatory. The observed, integrated, line intensity of 0.307 ± 0.019 K km s-1 implies an ND3 column density of (2 ± 0.9) × 1012 cm-2, for excitation temperatures in the range 5-10 K. Using previously published H2 and NH3 column density estimates in this source, we derive an ND3 fractional abundance with respect to H2 of (1.5 ± 1) × 10-11 and an ND3-to-NH3 abundance ratio of ~8 × 10-4. The observed abundance ratios can be explained in the framework of gas-phase chemical models, in which the dissociative recombination of partially deuterated ions results in a somewhat higher probability for the ejection of hydrogen atoms than deuterium.

A signature of the intermittency of interstellar turbulence - The wings of molecular line profiles

Ensembles of line profiles of molecular clouds are presented, and it is shown that most of the profiles can be fitted by a strong and narrow Gaussian plus a weak and broad Gaussian. The remarkably self-similar scaling of the wing widths to that of the cores is shown and the available information on the density and velocity structure of the fast gas is discussed. It is shown that the line wings can be used as tracers of the probability distribution of the projected velocity field within the cloud volume sampled by the profile. The statistical properties of this distribution are compared with that of the velocity in atmospheric turbulence and recent duct flow measurements. 62 refs.