Dense molecular gas toward W49A: A template for extragalactic starbursts?

The HCN, HCO+, and HNC molecules are commonly used as tracers of dense star-forming gas in external galaxies, but such observations are spatially unresolved. Reliably inferring the properties of galactic nuclei and disks requires detailed studies of sources whose structure is spatially resolved. We compare the spatial distributions and abundance ratios of HCN, HCO+, and HNC in W49A, the most massive and luminous star-forming region in the Galactic disk, based on maps of a 2' (6.6 pc) field at 14" (0.83 pc) resolution of the J=4-3 transitions of HCN, H13CN, HC15N, HCO+, H13CO+, HC18O+ and HNC. The kinematics of the molecular gas in W49A appears complex, with a mixture of infall and outflow motions. Both the line profiles and comparison of the main and rarer species show that the main species are optically thick. Two 'clumps' of infalling gas appear to be at ~40 K, compared to ~100 K at the source centre, and may be ~10x denser than the rest of the outer cloud. Chemical modelling suggests that the HCN/HNC ratio probes the current gas temperature, while the HCN/HCO+ ratio and the deuterium fractionation were set during an earlier, colder phase of evolution. The data suggest that W49A is an appropriate analogue of an extragalactic star forming region. Our data show that the use of HCN/HNC/HCO+ line ratios as proxies for the abundance ratios is incorrect for W49A, suggesting the same for galactic nuclei. Our observed isotopic line ratios such as H13CN/H13CO+ approach our modeled abundance ratios quite well in W49A. The 4-3 lines of HCN and HCO+ are much better tracers of the dense star-forming gas in W49A than the 1-0 lines. Our observed HCN/HNC and HCN/HCO+ ratios in W49A are inconsistent with homogeneous PDR or XDR models, indicating that irradiation hardly affects the gas chemistry in W49A. Overall, the W49A region appears to be a useful template for starburst galaxies.Comment: Accepted by A&A; 17 pages, 15 figure

The cooling of atomic and molecular gas in DR21

We present an overview of a high-mass star formation region through the major (sub-)mm, and far-infrared cooling lines to gain insight into the physical conditions and the energy budget of the molecular cloud. We used the KOSMA 3m telescope to map the core ($10'\times 14'$) of the Galactic star forming region DR 21/DR 21 (OH) in the Cygnus X region in the two fine structure lines of atomic carbon CI and four mid-$J$ transitions of CO and $^{13}$CO, and CS J=7\TO6. These observations have been combined with FCRAO J=1\TO0 observations of $^{13}$CO and C$^{18}$O. Five positions, including DR21, DR21 (OH), and DR21 FIR1, were observed with the ISO/LWS grating spectrometer in the \OI 63 and 145 $\mu$m lines, the \CII 158 $\mu$m line, and four high-$J$ CO lines. We discuss the intensities and line ratios at these positions and apply Local Thermal Equilibrium (LTE) and non-LTE analysis methods in order to derive physical parameters such as masses, densities and temperatures. The CO line emission has been modeled up to J=20. From non-LTE modeling of the low- to high-$J$ CO lines we identify two gas components, a cold one at temperatures of T_\RM{kin}\sim 30-40 K, and one with T_\RM{kin}\sim 80-150 K at a local clump density of about n(H$_2$)$\sim 10^4-10^6$ cm$^{-3}$. While the cold quiescent component is massive containing typically more than 94 % of the mass, the warm, dense, and turbulent gas is dominated by mid- and high-$J$ CO line emission and its large line widths. The medium must be clumpy with a volume-filling of a few percent. The CO lines are found to be important for the cooling of the cold molecular gas, e.g. at DR21 (OH). Near the outflow of the UV-heated source DR21, the gas cooling is dominated by line emission of atomic oxygen and of CO

Observations of SNR G328.4+0.2 at 19 GHz

We report on the first polarimetric observations at 19 GHz made with the upgraded Australia Telescope Compact Array. Observations were made of the Galactic supernova remnant (SNR) G328.8+0.2. We find the SNR has circular morphology with a strong central bar, similar to that seen at lower frequencies. The SNR has high linear polarization throughout, with fractional polarization in the bar up to 50 per cent. The orientation of the magnetic field lines follow the filamentary structure of the SNR. The magnetic field at the edge of the SNR is generally toroidal, interspersed with radial fingers, likely caused by Rayleigh-Taylor instabilities. Although the SNR has been identified as Crab-like, we prefer an interpretation in which the bar is a pulsar powered wind nebula with the rest of the SNR consisting of the shell. The proposed pulsar parameters make the SNR / pulsar system more like SNR G11.2--0.3 than the Crab Nebula.Comment: Accepted by MNRAS Letters. 4 pages, 3 figure

Infrared Dark Clouds in the Small Magellanic Cloud?

We have applied the unsharp-masking technique to the 24 $\mu$m image of the Small Magellanic Cloud (SMC), obtained with the Spitzer Space Telescope, to search for high-extinction regions. This technique has been used to locate very dense and cold interstellar clouds in the Galaxy, particularly infrared dark clouds (IRDCs). Fifty five candidate regions of high-extinction, namely high-contrast regions (HCRs), have been identified from the generated decremental contrast image of the SMC. Most HCRs are located in the southern bar region and mainly distributed in the outskirts of CO clouds, but most likely contain a significant amount of H2. HCRs have a peak-contrast at 24 $\mu$m of 2 - 2.5 % and a size of 8 - 14 pc. This corresponds to the size of typical and large Galactic IRDCs, but Galactic IRDCs are 2 - 3 times darker at 24 $\mu$m than our HCRs. To constrain the physical properties of the HCRs, we have performed NH3, N2H+, HNC, HCO+, and HCN observations toward one of the HCRs, HCR LIRS36-EAST, using the Australia Telescope Compact Array and the Mopra single-dish radio telescope. We did not detect any molecular line emission, however, our upper limits to the column densities of molecular species suggest that HCRs are most likely moderately dense with n ~ 10^{3} cm-3. This volume density is in agreement with predictions for the cool atomic phase in low metallicity environments. We suggest that HCRs may be tracing clouds at the transition from atomic to molecule-dominated medium, and could be a powerful way to study early stages of gas condensation in low metallicity galaxies. Alternatively, if made up of dense molecular clumps < 0.5 pc in size, HCRs could be counterparts of Galactic IRDCs, and/or regions with highly unusual abundance of very small dust grains.Comment: accepted for publication in the Astronomical Journa

Dynamic star formation in the massive DR21 filament

The formation of massive stars is a highly complex process in which it is not clear whether the star-forming gas is in global gravitational collapse or in an equilibrium state, supported by turbulence. By studying one of the most massive and dense star-forming regions in the Galaxy at a distance of less than 3 kpc, the filament containing the well-known sources DR21 and DR21(OH), we expect to find observational signatures that allow to discriminate between the two views. We use molecular line data from our 13CO 1-0, CS 2-1, and N2H+ 1-0 survey of the Cygnus X region obtained with the FCRAO and high-angular resolution observations of CO, CS, HCO+, N2H+, and H2CO, obtained with the IRAM 30m telescope. We observe a complex velocity field and velocity dispersion in the DR21 filament in which regions of highest column-density, i.e. dense cores, have a lower velocity dispersion than the surrounding gas and velocity gradients that are not (only) due to rotation. Infall signatures in optically thick line profiles of HCO+ and 12CO are observed along and across the whole DR21 filament. From modelling the observed spectra, we obtain a typical infall speed of 0.6 km/s and mass accretion rates of the order of a few 10^-3 Msun/yr for the two main clumps constituting the filament. These massive (4900 and 3300 Msun) clumps are both gravitationally contracting. All observed kinematic features in the DR21 filament can be explained if it is formed by the convergence of flows at large scales and is now in a state of global gravitational collapse. Whether this convergence of flows originated from self-gravity at larger scales or from other processes can not be settled with the present study. The observed velocity field and velocity dispersion are consistent with results from (magneto)-hydrodynamic simulations where the cores lie at the stagnation points of convergent turbulent flows.Comment: Astronomy and Astrophysics, in pres

Developmental delay in early childhood is associated with visual-constructive skills at school age in a Brazilian cohort

We investigated differences in IQ and visual-constructive skills in school-age children evaluated as developmentally delayed or typically developed in early childhood. Sixty-four participants from a Brazilian cohort were evaluated in IQ (Wechsler Abbreviated Scale of Intelligence) and tasks of visual-spatial memory and visual-constructive skills through the Benton Visual Retention Test (BVRT) at school age. Neuropsychomotor development at 4 years of age was measured by Denver II. Developmentally delayed children showed lower IQs, lower scores, and more errors in copy and memory BVRT tasks when compared to typically developed children. Delay in neuropsychomotor development in early childhood may affect the subsequent cognitive development of children

High resolution HI and radio continuum observations of the SNR G290.1-0.8

We have observed the supernova remnant (SNR) G290.1-0.8 in the 21-cm HI line and the 20-cm radio continuum using the Australia Telescope Compact Array (ATCA). The HI data were combined with data from the Southern Galactic Plane Survey to recover the shortest spatial frequencies. In contrast, HI absorption was analyzed by filtering extended HI emission, with spatial frequencies shorter than 1.1 k-lambda. The low-resolution ATCA radio continuum image of the remnant shows considerable internal structure, resembling a network of filaments across its 13 arcmin diameter. A high-resolution ATCA radio continuum image was also constructed to study the small scale structure in the SNR. It shows that there are no structures smaller than ~17", except perhaps for a bright knot to the south, which is probably an unrelated object. The HI absorption study shows that the gas distribution and kinematics in front of SNR G290.1-0.8 are complex. We estimate that the SNR probably lies in the Carina arm, at a distance 7 (+/- 1) kpc. In addition, we have studied nearby sources in the observed field using archival multiwavelength data to determine their characteristics.Comment: Accepted in Monthly Notices of the Royal Astronomical Societ

Spitzer View of Young Massive Stars in the LMC HII Complexes. II. N159

The HII complex N159 in the Large Magellanic Cloud (LMC) is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their SEDs to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N159B, a maser source, and several ultracompact HII regions. Massive O-type YSOs are found in GMCs N159-E and N159-W, which are associated with ionized gas, i.e., where massive stars formed a few Myr ago. The third GMC, N159-S, has neither O-type YSOs nor evidence of previous massive star formation. This correlation between current and antecedent formation of massive stars suggests that energy feedback is relevant. We present evidence that N159-W is forming YSOs spontaneously, while collapse in N159-E may be triggered. Finally, we compare star formation rates determined from YSO counts with those from integrated H-alpha and 24 micron luminosities and expected from gas surface densities. Detailed dissection of extragalactic GMCs like the one presented here is key to revealing the physics underlying commonly used star formation scaling laws.Comment: 60 pages, 11 figures. Accepted for publication in Astrophysical Journa

Observation of Josephson harmonics in tunnel junctions

Approaches to developing large-scale superconducting quantum processors must cope with the numerous microscopic degrees of freedom that are ubiquitous in solid-state devices. State-of-the-art superconducting qubits employ aluminium oxide (AlO$_x$) tunnel Josephson junctions as the sources of nonlinearity necessary to perform quantum operations. Analyses of these junctions typically assume an idealized, purely sinusoidal current–phase relation. However, this relation is expected to hold only in the limit of vanishingly low-transparency channels in the AlO$_x$ barrier. Here we show that the standard current–phase relation fails to accurately describe the energy spectra of transmon artificial atoms across various samples and laboratories. Instead, a mesoscopic model of tunnelling through an inhomogeneous AlO$_x$ barrier predicts percent-level contributions from higher Josephson harmonics. By including these in the transmon Hamiltonian, we obtain orders of magnitude better agreement between the computed and measured energy spectra. The presence and impact of Josephson harmonics has important implications for developing AlOx-based quantum technologies including quantum computers and parametric amplifiers. As an example, we show that engineered Josephson harmonics can reduce the charge dispersion and associated errors in transmon qubits by an order of magnitude while preserving their anharmonicity