Context. The Galactic center is the closest region where we can study star formation under extreme physical conditions like those in high-redshift galaxies. Aims. We measure the temperature of the ...dense gas in the central molecular zone (CMZ) and examine what drives it. Methods. We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3–2 para-formaldehyde (p - H2CO) transitions. We used the 32,1−22,0/ 30,3−20,2 line ratio to determine the gas temperature in n ~ 104−105 cm-3 gas. We have produced temperature maps and cubes with 30′′ and 1 km s-1 resolution and published all data in FITS form. Results. Dense gas temperatures in the Galactic center range from ~60 K to >100 K in selected regions. The highest gas temperatures TG> 100 K are observed around the Sgr B2 cores, in the extended Sgr B2 cloud, the 20 km s-1 and 50 km s-1 clouds, and in “The Brick” (G0.253+0.016). We infer an upper limit on the cosmic ray ionization rate ζCR< 10-14s-1. Conclusions. The dense molecular gas temperature of the region around our Galactic center is similar to values found in the central regions of other galaxies, in particular starburst systems. The gas temperature is uniformly higher than the dust temperature, confirming that dust is a coolant in the dense gas. Turbulent heating can readily explain the observed temperatures given the observed line widths. Cosmic rays cannot explain the observed variation in gas temperatures, so CMZ dense gas temperatures are not dominated by cosmic ray heating. The gas temperatures previously observed to be high in the inner ~75 pc are confirmed to be high in the entire CMZ.
ABSTRACT We present a statistical study of the distribution and physical properties of cold, dense material in and around the inner Galactic Plane near-infrared bubbles as cataloged by the Milky Way ...Project citizen scientists. Using data from the Atacama Pathfinder Experiment (APEX) Telescope Large Area Survey of the Galaxy 870 m survey, we show that 48 2% of all cold clumps in the studied survey region ( , ) are found in close proximity to a bubble, and 25 2% appear directly projected toward a bubble rim. A two-point correlation analysis confirms the strong correlation of massive cold clumps with expanding bubbles. It shows an overdensity of clumps along bubble rims that grows with increasing bubble size, which shows how interstellar medium material is reordered on large scales by bubble expansion around regions of massive star formation. The highest column density clumps appear to be resistent to the expansion, remaining overdense toward the bubbles' interior rather than being swept up by the expanding edge. Spectroscopic observations in ammonia show that cold dust clumps near bubbles appear to be denser, hotter, and more turbulent than those in the field, offering circumstantial evidence that bubble-associated clumps are more likely to be forming stars. These observed differences in physical conditions persist beyond the region of the bubble rims.
GRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular ...resolution and a collecting area of 200 m2. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual-beam operation, and laser metrology. GRAVITY opens up to optical/infrared interferometry the techniques of phase referenced imaging and narrow angle astrometry, in many aspects following the concepts of radio interferometry. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase-tracking on stars as faint as mK ≈ 10 mag, phase-referenced interferometry of objects fainter than mK ≈ 15 mag with a limiting magnitude of mK ≈ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25%, and spectro-differential phase and closure phase accuracy better than 0.5°, corresponding to a differential astrometric precision of better than ten microarcseconds (μas). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 μas when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the Galactic center supermassive black hole and its fast orbiting star S2 for phase referenced dual-beam observations and infrared wavefront sensing, the high mass X-ray binary BP Cru and the active galactic nucleus of PDS 456 for a few μas spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, ξ Tel and 24 Cap for high accuracy visibility observations, and η Car for interferometric imaging with GRAVITY.
Context
. The Medium-Resolution Spectrometer (MRS) provides one of the four operating modes of the Mid-Infrared Instrument (MIRI) on board the
James Webb
Space Telescope (JWST). The MRS is an ...integral field spectrometer, measuring the spatial and spectral distributions of light across the 5–28 µm wavelength range with a spectral resolving power between 3700 and 1300.
Aims
. We present the MRS’s optical, spectral, and spectro-photometric performance, as achieved in flight, and we report on the effects that limit the instrument’s ultimate sensitivity.
Methods
. The MRS flight performance has been quantified using observations of stars, planetary nebulae, and planets in our Solar System. The precision and accuracy of this calibration was checked against celestial calibrators with well-known flux levels and spectral features.
Results
. We find that the MRS geometric calibration has a distortion solution accuracy relative to the commanded position of 8 mas at 5 µm and 23 mas at 28 µm. The wavelength calibration is accurate to within 9 km s
−1
at 5 µm and 27 km s
−1
at 28 µm. The uncertainty in the absolute spectro-photometric calibration accuracy was estimated at 5.6 ± 0.7%. The MIRI calibration pipeline is able to suppress the amplitude of spectral fringes to below 1.5% for both extended and point sources across the entire wavelength range. The MRS point spread function (PSF) is 60% broader than the diffraction limit along its long axis at 5 µm and is 15% broader at 28 µm.
Conclusions
. The MRS flight performance is found to be better than prelaunch expectations. The MRS is one of the most subscribed observing modes of JWST and is yielding many high-profile publications. It is currently humanity’s most powerful instrument for measuring the mid-infrared spectra of celestial sources and is expected to continue as such for many years to come.
Carbon dioxide (CO
) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO
is an indicator of the metal enrichment (that is, elements ...heavier than helium, also called 'metallicity')
, and thus the formation processes of the primary atmospheres of hot gas giants
. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets
. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO
, but have not yielded definitive detections owing to the lack of unambiguous spectroscopic identification
. Here we present the detection of CO
in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science programme
. The data used in this study span 3.0-5.5 micrometres in wavelength and show a prominent CO
absorption feature at 4.3 micrometres (26-sigma significance). The overall spectrum is well matched by one-dimensional, ten-times solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide and hydrogen sulfide in addition to CO
, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 micrometres that is not reproduced by these models.
The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy
. However, these efforts have been hampered by ...modelling degeneracies between composition and cloud properties that are caused by limited data quality
. Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6-2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and signatures of clouds. The precision and broad wavelength coverage of NIRISS/SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favouring a heavy-element enhancement ('metallicity') of about 10-30 times the solar value, a sub-solar carbon-to-oxygen (C/O) ratio and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet's terminator.
Abstract
Exoplanets with radii between those of Earth and Neptune have stronger surface gravity than Earth, and can retain a sizable hydrogen-dominated atmosphere. In contrast to gas giant planets, ...we call these planets gas dwarf planets. The James Webb Space Telescope (JWST) will offer unprecedented insight into these planets. Here, we investigate the detectability of ammonia (NH
3
, a potential biosignature) in the atmospheres of seven temperate gas dwarf planets using various JWST instruments. We use
petitRadTRANS
and
PandExo
to model planet atmospheres and simulate JWST observations under different scenarios by varying cloud conditions, mean molecular weights (MMWs), and NH
3
mixing ratios. A metric is defined to quantify detection significance and provide a ranked list for JWST observations in search of biosignatures in gas dwarf planets. It is very challenging to search for the 10.3–10.8
μ
m NH
3
feature using eclipse spectroscopy with the Mid-Infrared Instrument (MIRI) in the presence of photon and a systemic noise floor of 12.6 ppm for 10 eclipses. NIRISS, NIRSpec, and MIRI are feasible for transmission spectroscopy to detect NH
3
features from 1.5–6.1
μ
m under optimal conditions such as a clear atmosphere and low MMWs for a number of gas dwarf planets. We provide examples of retrieval analyses to further support the detection metric that we use. Our study shows that searching for potential biosignatures such as NH
3
is feasible with a reasonable investment of JWST time for gas dwarf planets given optimal atmospheric conditions.
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