89 research outputs found
Massive star-forming regions across the Galaxy : Initial stages of massive star formation in infrared high extinction clouds <em>and</em> Trigonometric parallaxes to 6.7GHz methanol masers
Star-forming regions trace the spiral structure of the Galaxy. They are regions of increased column density and therefore traced well by the extinction in the mid-infrared based on the Spitzer/GLIMPSE 3.6-4.5 micron color excess maps. A sample of 25 high extinction clouds (HECs) was studied in the 1.2 mm dust continuum emission, and followed up by observations of ammonia plus several other molecules using the Effelsberg 100m, IRAM 30m and APEX telescopes. With these data we want to investigate the most early stages of massive star formation, which are currently still largely unknown. Three cloud classes were defined from their morphology in the 1.2\,mm continuum maps: the early diffuse HECs, with a low contrast between the clump and cloud emission; the peaked HECs, with an increased contrast; the late multiply peaked HECs, with more than one clump and a high contrast between the clump and the cloud emission. The clouds are cold (T ~ 16 K) and massive (M ~ 800 M_sun) and contain dense clumps (n ~ 10^5 cm^{-3}) of 0.3 pc in size. These clumps were investigated for evidence of gravitational collapse or expansion, for high velocity outflows, and for the presence of young stellar objects. Based on these results we interpret the three cloud classes as an evolutionary sequence of star-forming clouds. Accurate distances are a crucial parameter for establishing the mass, size, and luminosity of an object. Also, for understanding the spiral structure of the Galaxy trustworthy distances are necessary. The most accurate method to measure these is the trigonometric parallax. Using the European Very Large Baseline Interferometry Network of radio antennas we measured, for the first time, parallaxes of 6.7 GHz methanol masers. This transition belongs to the strongest maser species in the Galaxy, it is stable and observed toward numerous massive star-forming regions. We measured distances and proper motions toward L 1287, L 1206, NGC 281-W, ON 1 and S 255, and obtained their 3-dimensional space velocities. Similar to previous studies, these star-forming regions rotate slower than Galactic rotation
A 10- YSO with a Keplerian disk and a nonthermal radio jet
We previously observed the star-forming region G16.590.05 through
interferometric observations of both thermal and maser lines, and identified a
high-mass young stellar object (YSO) which is surrounded by an accretion disk
and drives a nonthermal radio jet. We performed high-angular-resolution (beam
FWHM ~0.15") 1.2-mm continuum and line observations towards G16.590.05 with
the Atacama Large Millimeter Array (ALMA). The main dust clump, with size
~10 au, is resolved into four relatively compact (diameter ~2000 au)
millimeter (mm) sources. The source harboring the high-mass YSO is the most
prominent in molecular emission. By fitting the emission profiles of several
unblended and optically thin transitions of CHOCH and CHOH, we
derived gas temperatures inside the mm-sources in the range 42--131 K, and
calculated masses of 1--5 . A well-defined Local Standard of Rest
velocity (Vlsr) gradient is detected in most of the high-density molecular
tracers at the position of the high-mass YSO, pinpointed by compact 22-GHz
free-free emission. This gradient is oriented along a direction forming a large
(~70 degree) angle with the radio jet, traced by elongated 13-GHz continuum
emission. The butterfly-like shapes of the P-V plots and the linear pattern of
the emission peaks of the molecular lines at high velocity confirm that this
Vlsr gradient is due to rotation of the gas in the disk surrounding the
high-mass YSO. The disk radius is ~500 au, and the Vlsr distribution along the
major axis of the disk is well reproduced by a Keplerian profile around a
central mass of 102 . The position of the YSO is offset by >~
0.1" from the axis of the radio jet and the dust emission peak. To explain this
displacement we argue that the high-mass YSO could have moved from the center
of the parental mm source owing to dynamical interaction with one or more
companions.Comment: 16 pages, 12 figures, accepted by Astronomy & Astrophysics, Main
Journa
ALMA FITS header keywords: a study from the archive User perspective
ALMA products are stored in the Science Archive in the form of FITS images.
It is a common idea that the FITS image headers should collect in their
keywords all the information that an archive User might want to search for in
order to quickly select, compare, or discard datasets. With this perspective in
mind, we first present a short description of the current status of the ALMA
FITS archive and images. We realized that at the moment most of the parameters
that could be useful for a general User are still missing in the archived data.
We then provide a CASA task generating the image header keywords that we
suggest to be relevant for the scientific exploitation of the ALMA archival
data. The proposed tool could be also applied to several types of
interferometer data and part of it is implemented in a web interface. An
example of the scientific application of the keywords is also discussed.Comment: 20 pages, 6 figures, ALMA Memo 613
https://library.nrao.edu/public/memos/alma/main/memo613.pd
Tomography of Galactic star-forming regions and spiral arms with the Square Kilometer Array
© 2014 Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence https://creativecommons.org/licenses/by-nc-sa/3.0/us/. Published by Proceedings of Science http://pos.sissa.it/Very Long Baseline Interferometry (VLBI) at radio wavelengths can provide astrometry accurate to 10 micro-arcseconds or better (i.e. better than the target GAIA accuracy) without being limited by dust obscuration. This means that unlike GAIA, VLBI can be applied to star-forming regions independently of their internal and line-of-sight extinction. Low-mass young stellar objects (particularly T Tauri stars) are often non-thermal compact radio emitters, ideal for astrometric VLBI radio continuum experiments. Existing observations for nearby regions (e.g. Taurus, Ophiuchus, or Orion) demonstrate that VLBI astrometry of such active T Tauri stars enables the reconstruction of both the regions' 3D structure (through parallax measurements) and their internal kinematics (through proper motions, combined with radial velocities). The extraordinary sensitivity of the SKA telescope will enable similar "tomographic mappings" to be extended to regions located several kpc from Earth, in particular to nearby spiral arm segments. This will have important implications for Galactic science, galactic dynamics and spiral structure theories
Methanol Maser Parallaxes and Proper Motions
Due to their compactness, persistence and slow motion, Class II CH3OH masers are excellent targets for parallax and proper motion measurements for massive star-forming regions in the Galactic Disk. These measurements can be used to improve our understanding of the spiral structure and dynamics of the Milky Way. At the same time, Class II CH3OH masers can also be used to study gas kinematics close to the exciting star, tracing rotation, infall and/or outflow motions
KAFE: the Key-analysis Automated FITS-images Explorer
We present KAFE—the Key-analysis Automated FITS-images Explorer. KAFE is a web-based FITS
image postprocessing analysis tool designed to be applicable in the radio to sub-mm wavelength domain. KAFE
was developed to complement selected FITS files with metadata based on a uniform image analysis approach
as well as to provide advanced image diagnostic plots. It is ideally suited for data mining purposes and multiwavelength/multi-instrument data samples that require uniform data diagnostic criteria. We present the code structure and interface, the keyword definitions, the products generated for selected users’ science cases, and application examples
The Forgotten Quadrant Survey
The Forgotten Quadrant Survey (FQS) is an ESO large project at the 12-m Kitt Peak antenna of the Arizona Radio Observatory with the aim to map the Galactic Plane in the range 220\degr12CO (1-0), and 13CO (1-0). FQS will produce a dataset of great legacy value, largely improving the data quality both in terms of sensitivity and spatial resolution over existing datasets, in this poorly studied portion of the outer Galaxy. FQS contributes to the general effort to produce a new generation of high-quality spectroscopic data for the Galactic Plane. Such data, in conjunction with the latest generation continuum surveys, will produce a new and more detailed picture of the plane of the Milky Way
The Hi-GAL compact source catalogue - II. The 360\ub0 catalogue of clump physical properties
We present the 360\ub0 catalogue of physical properties of Hi-GAL compact sources, detected between 70 and 500 m. This release not only completes the analogous catalogue previously produced by the Hi-GAL collaboration for -71\ub0 2 \ue1 2 67\ub0, but also meaningfully improves it because of a new set of heliocentric distances, 120 808 in total. About a third of the 150 223 entries are located in the newly added portion of the Galactic plane. A first classification based on detection at 70 m as a signature of ongoing star-forming activity distinguishes between protostellar sources (23 per cent of the total) and starless sources, with the latter further classified as gravitationally bound (pre-stellar) or unbound. The integral of the spectral energy distribution, including ancillary photometry from λ = 21 to 1100 m, gives the source luminosity and other bolometric quantities, while a modified blackbody fitted to data for m yields mass and temperature. All tabulated clump properties are then derived using photometry and heliocentric distance, where possible. Statistics of these quantities are discussed with respect to both source Galactic location and evolutionary stage. No strong differences in the distributions of evolutionary indicators are found between the inner and outer Galaxy. However, masses and densities in the inner Galaxy are on average significantly larger, resulting in a higher number of clumps that are candidates to host massive star formation. Median behaviour of distance-independent parameters tracing source evolutionary status is examined as a function of the Galactocentric radius, showing no clear evidence of correlation with spiral arm positions
TeraHertz Exploration and Zooming-in for Astrophysics (THEZA): ESA Voyage 2050 White Paper
This paper presents the ESA Voyage 2050 White Paper for a concept of
TeraHertz Exploration and Zooming-in for Astrophysics (THEZA). It addresses the
science case and some implementation issues of a space-borne radio
interferometric system for ultra-sharp imaging of celestial radio sources at
the level of angular resolution down to (sub-) microarcseconds. THEZA focuses
at millimetre and sub-millimetre wavelengths (frequencies above 300~GHz),
but allows for science operations at longer wavelengths too. The THEZA concept
science rationale is focused on the physics of spacetime in the vicinity of
supermassive black holes as the leading science driver. The main aim of the
concept is to facilitate a major leap by providing researchers with orders of
magnitude improvements in the resolution and dynamic range in direct imaging
studies of the most exotic objects in the Universe, black holes. The concept
will open up a sizeable range of hitherto unreachable parameters of
observational astrophysics. It unifies two major lines of development of
space-borne radio astronomy of the past decades: Space VLBI (Very Long Baseline
Interferometry) and mm- and sub-mm astrophysical studies with "single dish"
instruments. It also builds upon the recent success of the Earth-based Event
Horizon Telescope (EHT) -- the first-ever direct image of a shadow of the
super-massive black hole in the centre of the galaxy M87. As an amalgam of
these three major areas of modern observational astrophysics, THEZA aims at
facilitating a breakthrough in high-resolution high image quality studies in
the millimetre and sub-millimetre domain of the electromagnetic spectrum.Comment: White Paper submitted in response to the ESA Call Voyage 205
First M87 Event Horizon Telescope Results and the Role of ALMA
In April 2019, the Event Horizon Telescope (EHT) collaboration revealed the
first image of the candidate super-massive black hole (SMBH) at the centre of
the giant elliptical galaxy Messier 87 (M87). This event-horizon-scale image
shows a ring of glowing plasma with a dark patch at the centre, which is
interpreted as the shadow of the black hole. This breakthrough result, which
represents a powerful confirmation of Einstein's theory of gravity, or general
relativity, was made possible by assembling a global network of radio
telescopes operating at millimetre wavelengths that for the first time included
the Atacama Large Millimeter/ submillimeter Array (ALMA). The addition of ALMA
as an anchor station has enabled a giant leap forward by increasing the
sensitivity limits of the EHT by an order of magnitude, effectively turning it
into an imaging array. The published image demonstrates that it is now possible
to directly study the event horizon shadows of SMBHs via electromagnetic
radiation, thereby transforming this elusive frontier from a mathematical
concept into an astrophysical reality. The expansion of the array over the next
few years will include new stations on different continents - and eventually
satellites in space. This will provide progressively sharper and
higher-fidelity images of SMBH candidates, and potentially even movies of the
hot plasma orbiting around SMBHs. These improvements will shed light on the
processes of black hole accretion and jet formation on event-horizon scales,
thereby enabling more precise tests of general relativity in the truly strong
field regime.Comment: 11 pages + cover page, 6 figure
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