We report 350 and 230 GHz observations of molecular gas and dust in the starburst nucleus of NGC 253 at 20-40 pc (1''-2'') resolution. The data contain CO(3-2), HCN(4-3), CO(2-1), 13CO(2-1), ...C18O(2-1), and continuum at 0.87 mm and 1.3 mm toward the central kiloparsec. The CO(2-1) size of the galaxy's central molecular zone (CMZ) is measured to be about 300 pcX100 pc at the half-maximum of intensity. Five clumps of dense and warm gas stand out in the CMZ at arcsecond resolution, and they are associated with compact radio sources due to recent massive star formation. They contribute one-third of the CO emission in the central 300 pc and have 12CO peak brightness temperatures around 50 K, molecular gas column densities on the order of 104 M pc--2, gas masses on the order of 107 M in the size scale of 20 pc, volume-averaged gas densities of cm--3, and high HCN-to-CO ratios suggestive of higher fractions of dense gas than in the surrounding environment. It is suggested that these are natal molecular cloud complexes of massive star formation. The CMZ of NGC 253 is also compared with that of our Galaxy in CO(2-1) at the same 20 pc resolution. Their overall gas distributions are strikingly similar. The five molecular cloud complexes appear to be akin to such molecular complexes as Sgr A, Sgr B2, Sgr C, and the l = 13 cloud in the Galactic center. On the other hand, the starburst CMZ in NGC 253 has higher temperatures and higher surface (and presumably volume) densities than its non-starburst cousin.
Infrared pumping and its effect on the excitation of HCN molecules can be important when using rotational lines of HCN to probe dense molecular gas in galaxy nuclei. We report the first extragalactic ...detection of (sub)millimeter rotational lines of vibrationally excited HCN, in the dust-enshrouded nucleus of the luminous infrared galaxy NGC 4418. We estimate the excitation temperature of Tvib 230 K between the vibrational ground and excited (v 2 = 1) states. This excitation is most likely due to infrared radiation. At this high vibrational temperature the path through the v 2 = 1 state must have a strong impact on the rotational excitation in the vibrational ground level, although it may not be dominant for all rotational levels. Our observations also revealed nearly confusion-limited lines of CO, HCN, HCO+, H13CN, HC15N, CS, N2H+, and HC3N at Delta *l ~ 1 mm. Their relative intensities may also be affected by the infrared pumping.
We report ~100 pc (03) resolution observations of (sub)millimeter HCO+ and CO lines in the ultraluminous infrared galaxy Arp 220. The lines peak at two merger nuclei, with HCO+ being more spatially ...concentrated than CO. Asymmetric line profiles with blueshifted absorption and redshifted emission are discovered in HCO+(3-2) and (4-3) toward the two nuclei and in CO(3-2) toward one nucleus. We suggest that these P Cygni profiles are due to ~100 km s-1 outward motion of molecular gas from the nuclei. This gas is most likely outflowing from the inner regions of the two nuclear disks rotating around individual nuclei, clearing the shroud around the luminosity sources there.
We have observed the nucleus of the nearby luminous infrared galaxy NGC 4418 with subarcsec resolution at 860 and 450 mu m for the first time to characterize its hidden power source. A ~20 pc (0".1) ...hot dusty core was found inside a 100 pc scale concentration of molecular gas at the galactic center. The 860 mu m continuum core has a deconvolved (peak) brightness temperature of 120-210 K. The CO(3-2) peak brightness temperature there is as high as 90 K at 50 pc resolution. The core has a bolometric luminosity of about 10 super(11) L sub(middot in circle), which accounts for most of the galaxy luminosity. It is Compton thick (N sub(H) gap 10 super(25) cm super(-2)) and has a high luminosity-to-mass ratio (L/M) ~ 500 L sub(middot in circle) M sub(middot in circle) super(-1) as well as a high luminosity surface density 10 super(8.5+ or -0.5) L sub(middot in circle) pc super(-2). These parameters are consistent with an active galactic nucleus to be the main luminosity source (with an Eddington ratio about 0.3), while they can be also due to a young starburst near its maximum L/M. We also found an optical color (reddening) feature that we attribute to an outflow cone emanating from the nucleus. The hidden hot nucleus thus shows evidence of both an inflow, previously seen with absorption lines, and the new outflow reported here in a different direction. The nucleus must be rapidly evolving with these gas flows.
The design, fabrication and measurement of a 2 × 2 local oscillator beam divider for pumping a hot electron bolometer based heterodyne array at 1.37 THz is presented. The WR0.65 rectangular ...waveguide-based H -plane and E -plane junctions are used to construct the feeding network. The divider comprises two 400-<inline-formula><tex-math notation="LaTeX">\mu </tex-math></inline-formula>m thick silicon wafers with multilayer deep reactive-ion etching micromachined circuits, and a Pickett-Potter horn array manufactured in aluminum (AI) using computer numerical control machining. The two silicon plates and the AI plate were assembled with a special process using multilayer stacking technology to ensure an assembling misalignment lower than 10 μm. The radiation patterns of the beam divider are measured at 1.34 THz and 1.37 THz and compared to simulations. This is the first prototype of the multilayer stacked waveguide-based 2 × 2 beam divider at 1.37 THz ever fabricated.
This paper presents a novel diagonal horn design with improved performance over a standard diagonal horn. This is achieved by applying a spline curve to the vertical cutting axis of the "V" cutting ...tool, while retaining the ease of direct machining into a split block. The smooth curve does not present step changes, enabling a large radius cutter to be used. The cross polarization is reduced from -10 to <;-20 dB and copolar sidelobes are also reduced. Power coupling to a single linear polarization fundamental Gaussian mode is improved from 84% to approximately 97%, similar to smooth-walled spline horns and only slightly worse than a conventional corrugated horn.
The Heterodyne Receiver for the Origins Space Telescope (HERO) is a proposed design for a heterodyne focal plane array for a large space mission. The Origins Space Telescope (OST) is one of the four ...missions selected to be studied by NASA for the 2020 Astronomy and Astrophysics Decadal survey. HERO is designed to observe the trail of water from the interstellar medium (ISM) to disks around protostars. In Concept 1, HERO provides continuous frequency coverage from 468 to 2700 GHz in five bands and a sixth band to cover 4700 GHz. Most bands include 2 × 64 pixels providing at least an order of magnitude higher mapping speeds than available with today's instruments. Receiver sensitivities are expected to be close to the quantum limit. HERO Concept 2, highly constrained by cost and denoted Little-HERO, includes four bands with continuous coverage from 486 to 2700 GHz and with focal plane arrays having only 2 × 9 pixels per band. Both of these THz receiver concepts will be described and the designs will be motivated by the science drivers, the space craft constraints and the latest technological developments. The HERO design builds on the highly successful Herschel/Heterodyne Instrument for the Far-Infrared, on Stratospheric Observatory for Far-Infrared Astronomy/upGREAT and many other heterodyne receivers, but surpasses these in terms of frequency coverage, array size and sensitivity, thanks to the latest technical advances. HERO can be considered an example of a new generation of heterodyne focal plane arrays for future space missions.
•First 0.3-1.3 mm spectra of Jupiter and Satrun obtained from the ground.•Lowest rotational transitions of PH3 and NH3 detected.•Standard Radiative Transfer models at 0.3–1.3 for both planets ...verified.•Extensive and complex calibration procedure described.•Results can be a calibration reference for sub-millimeter observatories.
One of the legacies of the now retired Caltech Submillimeter Observatory (CSO) is presented in this paper. We measured for the first time the emission of the giant planets Jupiter and Saturn across the 0.3 to 1.3 mm wavelength range using a Fourier Transform Spectrometer mounted on the 10.4 m dish of the CSO at Mauna Kea, Hawaii, 4100 m above sea level. A careful calibration, including the evaluation of the antenna performance over such a wide wavelength range and the removal of the Earth’s atmosphere effects, has allowed the detection of broad absorption lines on those planets’ atmospheres. The calibrated data allowed us to verify the predictions of standard models for both planets in this spectral region, and to confirm the absolute radiometry in the case of Jupiter. Besides their physical interest, the results are also important as both planets are calibration references in the current era of operating ground-based and space-borne submillimeter instruments.
One of the legacies of the now retired Caltech Submillimeter Observatory (CSO) is presented in this paper. We measured for the first time the emission of the giant planets Jupiter and Saturn across ...the 0.3 to 1.3 mm wavelength range using a Fourier Transform Spectrometer mounted on the 10.4-meter dish of the CSO at Mauna Kea, Hawaii, 4100 meters above sea level. A careful calibration, including the evaluation of the antenna performance over such a wide wavelength range and the removal of the Earth's atmosphere effects, has allowed the detection of broad absorption lines on those planets' atmospheres. The calibrated data allowed us to verify the predictions of standard models for both planets in this spectral region, and to confirm the absolute radiometry in the case of Jupiter. Besides their physical interest, the results are also important as both planets are calibration references in the current era of operating ground-based and space-borne submillimeter instruments.
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