59 research outputs found
The far-IR view of Sgr B2 and Orion KL
We summarize the main highlights from ISO observations towards Sgr B2 and
Orion KL in the far-IR domain (~43 to 197 um). Both Star-Forming Regions are
among the best sources to construct a template for more distant and unresolved
regions (e.g., extragalactic). We stress some peculiarities in the
interpretation (excitation and radiative transfer) of far-IR spectral lines and
dust continuum emission.Comment: ''Far-Infrared and Submillimeter Emission of the Interstellar Medium:
Models meet extragalactic and Galactic Observations''. Proceedings of the FIR
Workshop 2007. Eds. C. Kramer, R. Simon et a
SPICA: the next generation Infrared Space Telescope
We present an overview of SPICA, the Space Infrared Telescope for Cosmology
and Astrophysics, a world-class space observatory optimized for mid- and far-IR
astronomy (from 5 to ~210um) with a cryogenically cooled ~3.2m telescope (<6
K). Its high spatial resolution and unprecedented sensitivity in both
photometry and spectroscopy modes will enable us to address a number of key
problems in astronomy. SPICA's large, cold aperture will provide a two order of
magnitude sensitivity advantage over current far-IR facilities (lambda>30 um
wavelength). In the present design, SPICA will carry mid-IR camera,
spectrometers and coronagraph (by JAXA institutes) and a far-IR imager
FTS-spectrometer, SAFARI (~34-210 um, provided by an European/Canadian
consortium lead by SRON). Complementary instruments such as a far-IR/submm
spectrometer (proposed by NASA) are also being discussed. SPICA will be the
only space observatory of its era to bridge the far-IR wavelength gap between
JWST and ALMA, and carry out unique science not achievable at visible or submm
wavelengths. In this contribution we summarize some of the scientific advances
that will be made possible by the large increase in sensitivity compared to
previous infrared space missions.Comment: 6 pages; to appear in the proceedings of the conference: "Conditions
and impact of star formation: New results with Herschel and beyond" (The 5th
Zermatt ISM Symposium
A high-resolution line survey of IRC+10216 with Herschel/HIFI. First results: Detection of warm silicon dicarbide (SiC2)
Compact jets as probes for sub-parsec scale regions in AGN
Compact relativistic jets in active galactic nuclei offer an effective tool
for investigating the physics of nuclear regions in galaxies. The emission
properties, dynamics, and evolution of jets in AGN are closely connected to the
characteristics of the central supermassive black hole, accretion disk and
broad-line region in active galaxies. Recent results from studies of the
nuclear regions in several active galaxies with prominent outflows are reviewed
in this contribution.Comment: AASLaTeX, 5 pages, 4 figures. Accepted in Astrophysics and Space
Scienc
The magnetic field in the Flame nebula
International audienceContext. Star formation drives the evolution of galaxies and the cycling of matter between different phases of the interstellar medium and stars. The support of interstellar clouds against gravitational collapse by magnetic fields has been proposed as a possible explanation for the low observed star formation efficiency in galaxies and the Milky Way. The Planck satellite provided the first all-sky map of the magnetic field geometry in the diffuse interstellar medium on angular scales of 5â15âČ. However, higher spatial resolution observations are required to understand the transition from diffuse, subcritical gas to dense, gravitationally unstable filaments.Aims. NGC 2024, also known as the Flame nebula, is located in the nearby Orion B molecular cloud. It contains a young, expanding H II region and a dense supercritical filament. This filament harbors embedded protostellar objects and is likely not supported by the magnetic field against gravitational collapse. Therefore, NGC 2024 provides an excellent opportunity to study the role of magnetic fields in the formation, evolution, and collapse of dense filaments, the dynamics of young H II regions, and the effects of mechanical and radiative feedback from massive stars on the surrounding molecular gas.Methods. We combined new 154 and 216 ÎŒm dust polarization measurements carried out using the HAWC+ instrument aboard SOFIA with molecular line observations of 12CN(1â0) and HCO+(1â0) from the IRAM 30-m telescope to determine the magnetic field geometry, and to estimate the plane of the sky magnetic field strength across the NGC 2024 H II region and the surrounding molecular cloud.Results. The HAWC+ observations show an ordered magnetic field geometry in NGC 2024 that follows the morphology of the expanding H II region and the direction of the main dense filament. The derived plane of the sky magnetic field strength is moderate, ranging from 30 to 80 ÎŒG. The strongest magnetic field is found at the eastern edge of the H II region, characterized by the highest gas densities and molecular line widths. In contrast, the weakest field is found toward the main, dense filament in NGC 2024.Conclusions. We find that the magnetic field has a non-negligible influence on the gas stability at the edges of the expanding H II shell (gas impacted by stellar feedback) and the filament (site of current star formation)
Star Formation and Dynamics in the Galactic Centre
The centre of our Galaxy is one of the most studied and yet enigmatic places
in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre
(GC) is the ideal environment to study the extreme processes that take place in
the vicinity of a supermassive black hole (SMBH). Despite the hostile
environment, several tens of early-type stars populate the central parsec of
our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and
inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the
SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The
formation of such early-type stars has been a puzzle for a long time: molecular
clouds should be tidally disrupted by the SMBH before they can fragment into
stars. We review the main scenarios proposed to explain the formation and the
dynamical evolution of the early-type stars in the GC. In particular, we
discuss the most popular in situ scenarios (accretion disc fragmentation and
molecular cloud disruption) and migration scenarios (star cluster inspiral and
Hills mechanism). We focus on the most pressing challenges that must be faced
to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in
expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A.,
'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201
Herschel observations of EXtra-Ordinary Sources (HEXOS): Observations of H2O and its isotopologues towards Orion KL
We report the detection of more than 48 velocity-resolved ground rotational state transitions of H 16
2 O, H 18
2 O, and H 17
2 O â most for the first time
â in both emission and absorption toward Orion KL using Herschel/HIFI. We show that a simple fit, constrained to match the known emission
and absorption components along the line of sight, is in excellent agreement with the spectral profiles of all the water lines. Using the measured
H 18
2 O line fluxes, which are less affected by line opacity than their H 16
2 O counterparts, and an escape probability method, the column densities
of H 18
2 O associated with each emission component are derived. We infer total water abundances of 7.4 Ă 10â5, 1.0Ă 10â5, and 1.6 Ă 10â5 for the
plateau, hot core, and extended warm gas, respectively. In the case of the plateau, this value is consistent with previous measures of the Orion-KL
water abundance as well as those of other molecular outflows. In the case of the hot core and extended warm gas, these values are somewhat higher
than water abundances derived for other quiescent clouds, suggesting that these regions are likely experiencing enhanced water-ice sublimation
from (and reduced freeze-out onto) grain surfaces due to the warmer dust in these sources
Water in star-forming regions: physics and chemistry from clouds to disks as probed by <i>Herschel</i> spectroscopy
Herschel observations of deuterated water towards Sgr B2(M)
Observations of HDO are an important complement for studies of water, because they give strong constraints on the formation processes â grain
surfaces versus energetic process in the gas phase, e.g. in shocks. The HIFI observations of multiple transitions of HDO in Sgr B2(M) presented
here allow the determination of the HDO abundance throughout the envelope, which has not been possible before with ground-based observations
only. The abundance structure has been modeled with the spherical Monte Carlo radiative transfer code RATRAN, which also takes radiative
pumping by continuum emission from dust into account. The modeling reveals that the abundance of HDO rises steeply with temperature from
a low abundance (2.5 Ă 10â11) in the outer envelope at temperatures below 100 K through a medium abundance (1.5 Ă 10â9) in the inner
envelope/outer core at temperatures between 100 and 200 K, and finally a high abundance ( 3.5 Ă 10â9) at temperatures above 200 K in the hot
core
Herschel observations of EXtra-Ordinary Sources (HEXOS): Detection of hydrogen fluoride in absorption towards Orion KL
We report a detection of the fundamental rotational transition of hydrogen fluoride in absorption towards Orion KL using Herschel/HIFI. After the
removal of contaminating features associated with common molecules (âweedsâ), the HF spectrum shows a P-Cygni profile, with weak redshifted
emission and strong blue-shifted absorption, associated with the low-velocity molecular outflow. We derive an estimate of 2.9 Ă 1013 cmâ2 for the
HF column density responsible for the broad absorption component. Using our best estimate of the H2 column density within the low-velocity
molecular outflow, we obtain a lower limit of âŒ1.6 Ă 10â10 for the HF abundance relative to hydrogen nuclei, corresponding to âŒ0.6% of the solar
abundance of fluorine. This value is close to that inferred from previous ISO observations of HF J = 2â1 absorption towards Sgr B2, but is in
sharp contrast to the lower limit of 6 Ă 10â9 derived by Neufeld et al. for cold, foreground clouds on the line of sight towards G10.6-0.4
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