Rui-Qing Mao

Molecular Superbubbles in the Starburst Galaxy NGC 253

The central 2; 1 kpc of the starburst galaxy NGC 253 have been imaged using the Submillimeter Array at a 60 pc resolution in the J = 2 - 1 transitions of (12)CO, (13)CO, and C(18)O, as well as in the 1.3 mm continuum. Molecular gas and dust are distributed mainly in a circumnuclear disk of similar to 500 pc radius, with warm (similar to 40 K) and high area filling factor gas in its central part. Two gas shells or cavities have been discovered in the circumnuclear disk. They have similar to 100 pc diameters and have large velocity widths of 80 - 100 km s(-1), suggestive of expansion at similar to 50 km s(-1) . Modeled as an expanding bubble, each shell has an age of similar to 0.5 Myr and needed kinetic energy of similar to 1; 10(46) J, as well as mean mechanical luminosity of similar to 1; 10(33) W, for its formation. The large energy allows each to be called a superbubble. A similar to 10(6) M circle dot super star cluster can provide the luminosity and could be a building block of the nuclear starburst in NGC 253. Alternatively, a hypernova can also be the main source of energy for each superbubble, not only because it can provide the mechanical energy and luminosity but also because the estimated rate of superbubble formation and that of hypernova explosions are comparable. Our observations indicate that the circumnuclear molecular disk harboring the starburst is highly disturbed on 100 pc or smaller scales, presumably by individual young clusters and stellar explosions, in addition to being globally disturbed in the form of the well-known superwind.

The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9

Based on measurements with the Effelsberg 100-m telescope, a multi-line study of molecular species is presented toward the gravitational lens system PKS 1830-211, which is by far the best known target to study dense cool gas in absorption at intermediate redshift. Determining average radial velocities and performing Large Velocity Gradient radiative transfer calculations, the aims of this study are (1) to determine the density of the gas, (2) to constrain the temperature of the cosmic microwave background (CMB), and (3) to evaluate the proton-to-electron mass ratio at redshift z ˜ 0.89. Analyzing data from six rotational HC3N transitions (this includes the J=7≤ftarrow6 line, which is likely detected for the first time in the interstellar medium) we obtain n(H2) ~ 2600 cm-3 for the gas density of the south-western absorption component, assuming a background source covering factor, which is independent of frequency. With a possibly more realistic frequency dependence proportional to ν0.5 (the maximal exponent permitted by observational boundary conditions), n(H2) ~ 1700 cm-3. Again toward the south-western source, excitation temperatures of molecular species with optically thin lines and higher rotational constants are, on average, consistent with the expected temperature of the cosmic microwave background, T_CMB = 5.14 K. However, individually, there is a surprisingly large scatter which far surpasses expected uncertainties. A comparison of CS J =1 ≤ftarrow0 and 4≤ftarrow3 optical depths toward the weaker north-western absorption component results in T_ex = 11 K and a 1-σ error of 3 K. For the main component, a comparison of velocities determined from ten optically thin NH3 inversion lines with those from five optically thin rotational transitions of HC3N, observed at similar frequencies, constrains potential variations of the proton-to-electron mass ratio μ to Δμ / μ < 1.4 × 10 -6 with 3-σ confidence. Also including optically thin rotational lines from other molecular species, it is emphasized that systematic errors are Δ V < 1 km s-1, corresponding to Δμ/μ< 1.0× 10-6.

Ammonia cores in high mass star formation regions

We observed a sample of 35 water masers not coincident with known HII regions and/or low mass young stellar objects (YSOs) with the Effelsberg 100 m telescope in the NH3(J,K) = (1,1), (2,2), (3,3) and (4,4) transitions. Sixteen sources were detected in the NH3 emission. The detection rate is 46%. All these sixteen sources have NH3 (1,1) and (2,2) emission, among which four sources have NH3 (3,3) emission. Comparing with the IRAS and the 2MASS data, we analyzed the relationship between the detection rate and the infrared color, the dust temperature and the source distance. All the detected sources were mapped and 17 cores were obtained (one source IRAS 20215+3725 has two cores). From the detected sources five cores do not coincide with radio continuum or IRAS and MSX point sources. Excluding one core that has no MSX data available, the remaining eleven cores are coincident with IRAS or MSX point sources. The typical size and mass of the cores are 1.6 pc and 1.5 x 10(3) M-circle dot, respectively. The average line widths of the NH3 (1,1) and (2,2) are 1.54 and 1.73 km s(-1). The average kinetic temperature of the gas is about 19 K. These values are much larger than those of low mass cores. The NH3 cores that coincide with IRAS sources (referred to as Group I) have slightly larger line widths (1.65 and 1.75 km s(-1) for the (1,1) and (2,2) lines, respectively) and larger masses (1.8 x 10(3) M-circle dot) than the mean values of the sample. For this type of core the kinetic temperature correlates with the line width. The line width appears to correlate with the bolometric luminosity and the core size. Despite the average luminosity of 2.9 x 10(4) L-circle dot, there is no detectable 6 cm emission. These are candidates for high mass protostars or precursors of UC HII regions. The NH3 cores with peaks onset from infrared sources (referred to as Group II) have an average size of 1.7 pc and an average line width of 1.50 km s(-1) for the (1,1) line. The line width of the (1,1) emission is smaller than that of the group I. The average mass is 9.4 x 10(2) M-circle dot. One possible explanation for the deviation is that the NH3 peak and the infrared source correspond to different clumps. These cores are potential high mass star formation sites and may be at an earlier evolutionary stage than those with IRAS point sources. This type of core is seen in mapping observations, and can be easily missed by single-spectrum observations toward the IRAS position.

A 1.3 cm line survey toward Orion KL

Orion KL has served as a benchmark for spectral line searches throughout the (sub)millimeter regime. The main goal is to systematically study spectral characteristics of Orion KL in the 1.3 cm band. We carried out a spectral line survey (17.9 GHz to 26.2 GHz) with the Effelsberg-100 m telescope towards Orion KL. We find 261 spectral lines, yielding an average line density of about 32 spectral features per GHz above 3

Star-forming regions of the Aquila rift cloud complex - I. NH3 tracers of dense molecular cores

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VLA NH3 observations of regions of massive star formation in protostellar cores

. The identified lines include 164 radio recombination lines (RRLs) and 97 molecular lines. A total of 23 molecular transitions from species known to exist in Orion KL are detected for the first time in the interstellar medium. Non-metastable 15NH3 transitions are detected in Orion KL for the first time. Based on the velocity information of detected lines and the ALMA images, the spatial origins of molecular emission are constrained and discussed. A narrow feature is found in SO2 (

Submillimeter Array12CO ([FORMULA][F]J=3-2[/F][/FORMULA]) Interferometric Observations of the Central Region of M51

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ASIAA EXTRAGALACTIC STUDY WITH THE SMA

), possibly suggesting the presence of a maser line. Column densities and fractional abundances relative to H2 are estimated for 12 molecules with LTE methods. Rotational diagrams of non-metastable 14NH3 transitions with J=K+1 to J=K+4 yield different results; metastable 15NH3 is found to have a higher excitation temperature than non-metastable 15NH3, indicating that they may trace different regions. Elemental and isotopic abundance ratios are estimated: 12C/13C=63+-17, 14N/15N=100+-51, D/H=0.0083+-0.0045. The dispersion of the He/H ratios derived from H

Submillimeter Array 12CO (J = 3-2) Interferometric Observations of the Central Region of M51

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AN EXTRAGALACTIC 12CO J = 3-2 SURVEY WITH THE HEINRICH HERTZ TELESCOPE

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