Astronomy Department Faculty Publication Series

A high-resolution line survey of IRC +10216 with Herschel/HIFI *,** First results: Detection of warm silicon dicarbide (SiC)

Cernicharo, J et al. — Thu, 23 Aug 2012 10:06:14 PDT

We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901 GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5–636.5 GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal-to-noise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and, surprisingly, silicon dicarbide (SiC₂). We identified 55 SiC₂ transitions involving energy levels between 300 and 900 K. By analysing these rotational lines, we conclude that SiC₂ is produced in the inner dust formation zone, with an abundance of ~ 2 × 10^-7 relative to molecular hydrogen. These SiC₂ lines have been observed for the first time in space and have been used to derive an SiC₂ rotational temperature of ~204 K and a source-averaged column density of ~ 6.4 × 10¹⁵ cm^-2. Furthermore, the high quality of the HIFI data set was used to improve the spectroscopic rotational constants of SiC₂.

Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C*

Lis, DC et al. — Thu, 23 Aug 2012 10:06:12 PDT

We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H₂¹⁶O and H₂¹⁸O in absorption towards Sagittarius B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of 2.35 ± 0.35, corresponding to a spin temperature of ~27 K, towards Sagittarius B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust.

Detection of OH+ and H2O+ towards Orion KL

Gupta, M et al. — Thu, 23 Aug 2012 10:06:10 PDT

We report observations of the reactive molecular ions OH⁺, H₂O⁺, and H₃O⁺ towards Orion KL with Herschel/HIFI. All three N = 1-0 fine-structure transitions of OH⁺ at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H₂O⁺ 1₁₁–0₀₀ transition at 1115 and 1139 GHz were detected; an upper limit was obtained for H₃O⁺. OH⁺ and H₂O⁺ are observed purely in absorption, showing a narrow component at the source velocity of 9 km s^-1, and a broad blueshifted absorption similar to that reported recently for HF and para-H₂¹⁸O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH⁺ and H₂O⁺ for the 9 km s^-1 component of 9 ± 3 × 10¹² cm^-2 and 7 ± 2 × 10¹² cm^-2, and those in the outflow of 1.9 ± 0.7 × 10¹³ cm^-2 and 1.0 ± 0.3 × 10¹³ cm^-2. Upper limits of 2.4 × 10¹² cm^-2 and 8.7 × 10¹² cm^-2 were derived for the column densities of ortho and para-H₃O⁺ from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate.

Herschel observations of ortho- and para-oxidaniumyl (H2O+) in spiral arm clouds toward Sagittarius B2(M) *,**

Schilke, P et al. — Thu, 23 Aug 2012 10:06:08 PDT

H₂O⁺ has been observed in its ortho- and para- states toward the massive star forming core Sgr B2(M), located close to the Galactic center. The observations show absorption in all spiral arm clouds between the Sun and Sgr B2. The average o/p ratio of H₂O⁺ in most velocity intervals is 4.8, which corresponds to a nuclear spin temperature of 21 K. The relationship of this spin temperature to the formation temperature and current physical temperature of the gas hosting H₂O⁺ is discussed, but no firm conclusion is reached. In the velocity interval 0–60 km s^-1, an ortho/para ratio of below unity is found, but if this is due to an artifact of contamination by other species or real is not clear.

Strong CH+ J = 1–0 emission and absorption in DR21*

Falgarone, E et al. — Thu, 23 Aug 2012 10:06:07 PDT

We report the first detection of the ground-state rotational transition of the methylidyne cation CH⁺ towards the massive star-forming region DR 21 with the HIFI instrument onboard the Herschel satellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR 21 molecular ridge and foreground gas. These observations allow us to determine a ¹²CH⁺J = 1–0 line frequency of ν = 835 137 ± 3 MHz, in good agreement with a recent experimental determination. We estimate the CH⁺ column density to be a few 10¹³ cm^-2 in the gas seen in emission, and >10¹⁴ cm^-2 in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH⁺] /[H] > 1.2 × 10^-8. We show that the CH⁺ column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines.

Kinematics of Protostellar Objects in the ρ Ophiuchus A Region

Narayanan, Gopal et al. — Thu, 23 Aug 2012 10:06:06 PDT

We present the detection of infall, rotation, and outflow kinematic signatures toward both a protostellar source, VLA 1623, and what was initially thought to be a pre-protostellar core, SM 1N, in the ρ Ophiuchus A region. The kinematic signatures of early star formation were detected in the dense molecular gas surrounding the embedded sources using high signal-to-noise ratio millimeter and submillimeter data. Centroid velocity maps made with HCO⁺ J = 4 → 3 and J = 1 → 0 line emission exhibit the blue bulge signature of infall, which is predicted to be seen when infall motion dominates over rotational motion. Further evidence for infalling gas is found in the HCO⁺ blue asymmetric line profiles and red asymmetric opacity profiles. We also performed CO J = 3 → 2 and J = 1 → 0 observations to determine the direction, orientation, and extent of molecular outflows, and we report the discovery of a new bipolar outflow possibly driven by SM 1N.

SuperCam: a 64-pixel heterodyne imaging array for the 870-micron atmospheric window (Proceedings Paper)

Groppi, C et al. — Mon, 09 May 2011 16:21:43 PDT

We report on the development of SuperCam, a 64 pixel, superheterodyne camera designed for operation in the astrophysically important 870 μm atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The advent of such a system will provide an order of magnitude increase in mapping speed over what is now available and revolutionize how observational astronomy is performed in this important wavelength regime. Unlike the situation with bolometric detectors, heterodyne receiver systems are coherent, retaining information about both the amplitude and phase of the incident photon stream. From this information a high resolution spectrum of the incident light can be obtained without multiplexing. SuperCam will be constructed by stacking eight, 1×8 rows of fixed tuned, SIS mixers. The IF output of each mixer will be connected to a low-noise, broadband MMIC amplifier integrated into the mixer block. The instantaneous IF bandwidth of each pixel will be ~2 GHz, with a center frequency of 5 GHz. A spectrum of the central 500 MHz of each IF band will be provided by the array spectrometer. Local oscillator power is provided by a frequency multiplier whose output is divided between the pixels by using a matrix of waveguide power dividers. The mixer array will be cooled to 4K by a closed-cycle refrigeration system. SuperCam will reside at the Cassegrain focus of the 10m Heinrich Hertz telescope (HHT). A prototype single row of the array will be tested on the HHT in 2006, with the first engineering run of the full array in late 2007. The array is designed and constructed so that it may be readily scaled to higher frequencies.

Detection of Infall Signatures toward Serpens SMM4

Narayanan, Gopal et al. — Mon, 09 May 2011 16:21:31 PDT

We present the detection of kinematic infall signatures toward the Class 0 protostellar system SMM4 in the Serpens cloud core. We have observed the dense molecular gas toward the embedded source using millimeter and submillimeter line transitions of density sensitive molecular tracers. High signal-to-noise ratio maps obtained in HCO⁺ J = 1 → 0, J = 3 → 2, and J = 4 → 3, and CS J = 2 → 1 show the blue-bulge infall signature. The blue-bulge infall signature can be observed in the centroid velocity maps of protostellar objects when infall dominates over rotation. The line profiles of HCO⁺ and CS exhibit the characteristic blue asymmetric line profile signature consistent with infall. In addition, HCO⁺ and CS optical depth profiles obtained using isotopic observations show a red asymmetry also consistent with an infall interpretation. Using three-dimensional radiative transfer models based on the rotating, collapse model of Terebey, Shu, & Cassen, we derive infall parameters of the source. To determine the direction and orientation of molecular outflows in the larger Serpens cluster, wide-field mapping of CO J = 1 → 0 emission was also performed.

Physical parameter eclipse mapping of the quiescent disc in V2051 Ophiuchi

Vrielmann, S et al. — Mon, 09 May 2011 16:21:18 PDT

We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping (PPEM) method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions, and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13 500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has temperatures of 9000 to 6500 K.

A complete view of galaxy evolution: panchromatic luminosity functions and the generation of metals

Blain, AW et al. — Fri, 29 Apr 2011 12:49:53 PDT

When and how did galaxies form and their metals accumulate? Over the last decade, this has moved from an archeological question to a live investigation: there is now a broad picture of the evolution of galaxies in dark matter halos: their masses, stars, metals and supermassive blackholes. Galaxies have been found and studied in which these formation processes are taking place most vigorously, all the way back in cosmic time to when the intergalactic medium (IGM) was still largely neutral. However, the details of how and why the interstellar medium (ISM) in distant galaxies cools, is processed, recycled and enriched in metals by stars, and fuels active galactic nuclei (AGNs) remain uncertain. In particular, the cooling of gas to fuel star formation, and the chemistry and physics of the most intensely active regions is hidden from view at optical wavelengths, but can be seen and diagnosed at mid- & far-infrared (IR) wavelengths. Rest-frame IR observations are important first to identify the most luminous, interesting and important galaxies, secondly to quantify accurately their total luminosity, and finally to use spectroscopy to trace the conditions in the molecular and atomic gas out of which stars form. In order to map out these processes over the full range of environments and large-scale structures found in the universe - from the densest clusters of galaxies to the emptiest voids - we require tools for deep, large area surveys, of millions of galaxies out to z~5, and for detailed follow-up spectroscopy. The necessary tools can be realized technically. Here, we outline the requirements for gathering the crucial information to build, validate and challenge models of galaxy evolution.