[show abstract][hide abstract] ABSTRACT: The Molecular Hydrogen Explorer, H2 EX, was proposed in response to the ESA 2015 - 2025 Cosmic Vision Call as a medium class space mission with NASA and CSA participations. The mission, conceived to understand the formation of galaxies, stars and planets from molecular hydrogen, is designed to observe the first rotational lines of the H2 molecule (28.2, 17.0, 12.3 and 9.7 mum) over a wide field, and at high spectral resolution. H2 EX can provide an inventory of warm (>= 100 K) molecular gas in a broad variety of objects, including nearby young star clusters, galactic molecular clouds, active galactic nuclei, local and distant galaxies. The rich array of molecular, atomic and ionic lines, as well as solid state features available in the 8 to 29 mum spectral range brings additional science dimensions to H2 EX. We present the optical and mechanical design of the H2 EX payload based on an innovative Imaging Fourier Transform Spectrometer fed by a 1.2 m telescope. The 20'Ã20' field of view is imaged on two 1024Ã1024 Si:As detectors. The maximum resolution of 0.032 cm - 1 (full width at half maximum) means a velocity resolution of 10 km s - 1 for the 0 - 0 S(3) line at 9.7 mum. This instrument offers the large field of view necessary to survey extended emission in the Galaxy and local Universe galaxies as well as to perform unbiased extragalactic and circumstellar disks surveys. The high spectral resolution makes H2 EX uniquely suited to study the dynamics of H2 in all these environments. The mission plan is made of seven wide-field spectro-imaging legacy programs, from the cosmic web to galactic young star clusters, within a nominal two years mission. The payload has been designed to re-use the Planck platform and passive cooling design.
[show abstract][hide abstract] ABSTRACT: Fourier phases contain a vast amount of information about structure in direct space, that most statistical tools never tap into. We address ALMA's ability to detect and recover this information, using the probability distribution function (PDF) of phase increments, and the related concepts of phase entropy and phase structure quantity. We show that ALMA, with its high dynamical range, is definitely needed to achieve significant detection of phase structure, and that it will do so even in the presence of a fair amount of atmospheric phase noise. We also show that ALMA should be able to recover the actual "amount" of phase structure in the noise-free case, if multiple configurations are used.
[show abstract][hide abstract] ABSTRACT: VO Paris Federation is a partnership between Paris Observatory, IAP,
IPSL and CEA. Its objectives are to provide VO access to its databases
ressources, contribute to international standards developments,
implement VO compliant simulation codes and data visualisation and
analysis software. The various activities are organised into portals
whose functions are (i) to provide visibility and information on the
projects and (ii) to encourage collaborations. The portals are linked to
thematic activities and resources: solar system (ephemerides,
astrometry, physical characteristic of small bodies of the solar system,
planetology), reference systems, exoplanet database, legacy (archives
from the Nançcay Radio Telescope, some specific data from the
DENIS and EROS surveys, MAMA), solar physics, stellar and galactic
databases and services, atomic and molecular databases and services,
simulation codes and data analysis.
[show abstract][hide abstract] ABSTRACT: Most statistical tools used to characterize the complex structures of the interstellar medium can be related to the power spectrum, and therefore to the Fourier amplitudes of the observed fields. To tap into the vast amount of information contained in the Fourier phases, one may consider the probability distribution function (PDF) of phase increments, and the related concepts of phase entropy and phase structure quantity. We use these ideas here with the purpose of assessing the ability of radio-interferometers to detect and recover this information. By comparing current arrays such as the VLA and Plateau de Bure to the future ALMA instrument, we show that the latter is definitely needed to achieve significant detection of phase structure, and that it will do so even in the presence of a fair amount of atmospheric phase fluctuations. We also show that ALMA will be able to recover the actual "amount'' of phase structure in the noise-free case, if multiple configurations are used. Comment: Accepted for publication in "Astronomy & Astrophysics"
[show abstract][hide abstract] ABSTRACT: Interferometric observations of molecular clouds in M31 and M33 are presented. We detected clouds with properties : brightness, line width, size, mass and association with massive star forming regions, similar to those of galactic giant molecular clouds. The application of the virial theorem indicates that the NH2/WCO ratio in M31 and M33 is comparable to the Galactic value.
[show abstract][hide abstract] ABSTRACT: We present Infrared Space Observatory Camera (ISOCAM) Circular Variable Filter scans of three giant HII regions in M33. IC 133, NGC 595, and CC 93 span a wide range of metallicity, luminosity, nebular excitation, and infrared excess; three other emission regions (CC 43, CC 99, and a region to the northeast of the core of NGC 595) are luminous enough in the mid-infrared to be detected in the observed fields. ISOCAM CVF observations provide spatially resolved observations (5'') of 151 wavelengths between 5.1 and 16.5 microns with a spectral resolution R = 35 to 50. We observe atomic emission lines ([Ne II], [Ne III], and [S IV]), several "unidentified infrared bands" (UIBs; 6.2, 7.7, 8.6, 11.3, 12.0, and 12.7 microns), and in some cases a continuum which rises steeply at longer wavelengths. We conclude that the spectra of these three GHRs are well explained by combinations of ionized gas, PAHs, and very small grains in various proportions and with different spatial distributions. Comparisons between observed ratios of the various UIBs with model ratios indicate that the PAHs in all three of the GHRs are dehydrogenated and that the small PAHs have been destroyed in IC 133 but have survived in NGC 595 and CC 93. The [Ne III]/[Ne II] ratios observed in IC 133 and NGC 595 are consistent with their ages of 5 and 4.5 Myr, respectively; the deduced ionization parameter is higher in IC 133, consistent with its more compact region of emission.
[show abstract][hide abstract] ABSTRACT: We present new observations of the merging system Arp 299 obtained with the IRAM Plateau de Bure interferometer. We have observed the (12)CO(1-0), (12)CO(2-1), (13)CO(1-0) and HCN(1-0) lines. For the (12)CO(1-0) line, short spacings were recovered by using 30m data; about half of the total flux is found in weak and extended emission filtered out by the interferometer. The (12)CO(1-0) map shows three bright regions associated with the nuclei of the galaxies (IC 694=A and NGC 3690=B) and to a star-forming region, C-C', which contains about one-third of the CO emission, but also extended emission and several ``filaments'' joining the bright regions. We find a south-east extension (A2) in IC 694 which corresponds to bright H_2 and Brgamma emission. The (12)CO(2-1) map which has 0.7arcsec x0.6arcsec resolution but does not include short spacings shows the same gross features and is dominated by extremely bright emission in the nucleus of IC 694. Strong HCN emission is also observed in the nucleus of IC 694 (A), indicating the presence of large amounts of dense gas; weaker emission is found in B, C and C': the (12)CO(1-0)d/HCN ratio varies between 20 and 40 in the body of Arp 299, while it is about 7 in nucleus A. B is weak in (13)CO(1-0) emission, with a (12)CO(1-0)d/(13)CO(1-0)t ratio of about 30, while A and C-C' exhibit more ``normal'' ratios (11-16). Globally, C, C' and A2 exhibit line ratios that are typical of galactic disks, while A and B are clearly peculiar, with in particular HCN stronger than (13)CO(1-0)t. We find in the CO(1-0) line a regular velocity gradient over the south-east part of IC 694, which apparently extends to the C-C' region. The other regions of Arp 299 have more complex dynamics; from the high-resolution (12)CO(2-1) maps, we are able to locate the dynamical center of NGC 3690 at the position of the radiocontinuum peak. We see clear indications that there is some gas flowing between IC 694 and NGC 3690. The three main regions are then dynamically and physically connected. In Arp 299, gas transfers have thus already occcured at an early stage of the merger. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).
[show abstract][hide abstract] ABSTRACT: We analyse the integrated properties of the Mid-IR emission of a complete, optically selected sample of galaxies in the Virgo cluster observed with the ISOCAM instrument on board the ISO satellite. The analysis shows that the Mid-IR emission up to 15 mic of optically-selected, normal early-type galaxies (E, S0 and S0a) is dominated by the Rayleigh-Jeans tail of the cold stellar component. The Mid-IR emission of late-type galaxies is instead dominated by the thermal emission from dust. The small dust grains emitting in the Mid-IR have an excess of emission if compared to big grains emitting in the Far-IR. While the Far-IR emission increases with the intensity of the interstellar radiation field, their Mid-IR emission is non--linearly related to the UV radiation field. The spectral energy distributions of the target galaxies indicate that there is a linear relationship between the UV radiation field and the Mid-IR emission of galaxies for low or intermediate activities of star formation, while the emission from the hot dust seems to drop for strong UV fields. The Mid-IR colour of late-type galaxies is not related to their activity of star formation. The properties of the dust emission in the Mid-IR seem more related to the mass than to the morphological type of the target galaxy. Since the activity of star formation is anticorrelated to the mass of galaxies, this reflects a relationship between the emission of dust in the Mid-IR and the UV radiation field: galaxies with the lowest Mid-IR emission for a given UV field are low mass, dwarf galaxies. These observational evidences are easily explained if the carriers of the Unidentified Infrared Bands that dominate the 6.75 mic emission are destroyed by the intense UV radiation field of dwarf galaxies, although abundance effects can also play a role. Comment: 17 pages, Latex, 7 figures; to be published in Astronomy & Astrophysics, Main Journal; Figure legend should be corrected in: 1 - 1a; 2 - 1b; 3 - 2; 4 - 3a; 5 - 3b; 6 - 3c; 7 - 3d; 8 - 3e; 9 - 4; 10 - 5; 11 - 6; 12 - 7
[show abstract][hide abstract] ABSTRACT: We present observations of the global emission of a sample of spiral and
irregular galaxies in the Virgo cluster and the Coma supercluster. These
observations have been made with the camera ISOCAM on board the Infrared
Space Observatory, through two broad filters centered respectively at
6.75 and 15.0μm. The corresponding fluxes are corrected for the
stellar contribution in order to obtain the pure interstellar
contribution; the stellar contribution is estimated from the
near-infrared fluxes using as template some S0 and elliptical galaxies
observed by chance in the ISO fields. The fluxes at 6.75 and 15.0μm
are then normalized to the stellar mass of the galaxy, and compared to
the normalized far-UV fluxes at 2000Å which are good indicators of
the star-formation rate (SFR). We find that, while the mid-IR fluxes are
proportional to the SFR when it is not too large, the galaxies with a
high SFR have relatively less emission at 6.75 and 15μm. It appears
that the carriers of the Unidentified Infrared Bands which are
responsible for almost all the emission at 6.75μm and for a part of
the emission at 15μm have different properties in these galaxies or
are partly destructed by the UV field. At 15μm, there is a
contribution of very small, three-dimensional grains in galaxies with a
Astronomy and Astrophysics 07/1997; 324:L13-L16. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The dwarf emission line galaxy IZw 18 has one of the lowest known O/H
abundances ratios (O/H=1.75 10-5) deduced from its emission
lines. Its two main emission patches are associated with two extended HI
clouds with very high column densities (N(HI)=1022 H atoms/sq
cm). We have obtained spectra of the NW emission region with the Goddard
High Resolution Spectrograph (GHRS) on the Hubble Space Telescope in a
spectral range containing OI lambda(1302)A and SiII lambda(1304)A and
another range around Lyman-alpha. The GHRS spectrum combined with a
lower resolution IUE spectrum shows that the HI column density in front
of the NW emission patch is N(HI)=3.5 x 1021/sq cm.
Accordingly, the absorption spectrum of IZw 18 would be classified as
being a 'damped Lyman-alpha' system. No Lyman-alpha emission is detected
from IZW 18 due to multiple scattering in the HI gas. Absorption lines
due to OI and SiII were detected at the redshift of IZw 18. The
abundances are very uncertain but the best values are O/H=7.9 x
10-7 and Si/H=7.5 x 10-8. We show that most of the
observed OI is produced in the HI gas in IZw 18 and very little in the
transition region of the HI gas. Our new results strengthen the
importance of IZw 18 determine the primordial He abundance. We also
detected OI and SiII absorption at a velocity of -160 km/s due to a
Galactic high velocity cloud. We derive abundance ratios O/H and Si/H
which are about 1/10 that in the local interstellar gas, illustrating
that the high velocity clouds are not composed of primordial material.
Astronomy and Astrophysics 01/1994; 282:709-716. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: The study presents H I and radio continuum observations of the Scd
galaxy NGC 6946 at about 25-arcsec resolution, obtained with the
Westerbork Synthesis Radio Telescope and the Penticton interferometer.
The data from the two interferometers are combined to measure the
emission of the galaxy on all angular scales down to 25 arcsec. It is
shown that about one-third of the 21- and 50-cm radio-continuum emission
comes from the spiral arms; this emission, which has an average spectral
index of 0.55, is mainly nonthermal. The other two-thirds of the
emission comes from an exponential disk which has a spectral index of
0.8 and a scale-length of 1.7 arcmin similar to the one measured for the
blue light. The highest concentrations of H I emission coincide with the
spiral arms of the galaxy. The H I spiral arms are fragmented in giant
complexes with masses of a few 10 exp 7 solar masses and lengths of a
Astronomy and Astrophysics 11/1992; 266:37-56. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: A field of one arcmin diameter on the eastern edge of the H II region
NGC 604 has been mapped in the J = 2-1 and J = 1-0 transitions of the
(C-12)O molecule. The distribution of the CO emission, which is observed
all over that field, is characterized by two prominent concentrations
plus a diffuse component with complex kinematics. The (C-13)O molecule
in the (2-1) and the (1-0) transitions has also been observed. From
these observations, the physical conditions of these concentrations are
derived. Although NGC 604 is known to be deficient in heavy elements as
compared to the metallicity in the solar neighborhood, the CO luminosity
to virial mass ratio is typical of those for giant molecular clouds in
Astronomy and Astrophysics 10/1992; 265:437-446. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Deep infrared images of the Small Magellanic Cloud have been produced and compared to an ultraviolet image at an angular resolution of 8 min. There is a strong correlation between the far infrared and the ultraviolet emission but the dispersion in this correlation is unrelated to infrared colors. Comparing with the results for the nearby spiral M33 at different radial distances, it is suggested that the population of dust grains in the Small Magellanic Cloud has very different properties.
[show abstract][hide abstract] ABSTRACT: IRAS spatial observations of M33 are presented and compared to UV optical, and radio wavelength data. At 12, 25, 60, and 100 microns the emission appears as two bright spiral arms superposed on a diffuse disk, with localized sources at the position of the nucleus and the brightest H II region complexes. The global IR properties of M33 are characteristic of quiescent spirals. The 8-30 micron mid-IR global emission is about 20 percent of the far-IR emission, similar to the ratio of these fluxes found for the local ISM. The local IR excess of M33 is about 2-3 times larger than the excess derived for H II regions in the Galaxy. The radial distributions of the IR colors are flat or nearly flat, implying near-constant dust temperatures across the diffuse disk. The integrated F(IR)-to-radio continuum emission of M33 follows the relation seen in other galaxies, but the radial distribution of the two emission components differ. A striking correlation is seen between the IR emission structure and the distribution of H II regions.
The Astrophysical Journal 09/1990; · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: A study of the kinematics and mass distribution of NGC 6946 is presented
from Westerbork H I line observations. It is found that the H I
distribution is not symmetric but is more extended on the NE side
compared to the SW side by about 25 percent in radius. The overall
velocity field is fairly regular, with some signs of noncircular motions
associated with the optical and H I spiral arms. A well defined rotation
curve is derived which is essentially flat from 4 to 10 arcmin. At
larger radii, the H I runs out on the SW side. The kinematical
parameters are Vsys = 47 km/s, i = 38 deg, and PA = 240 deg. An analysis
of the mass distribution yields a well defined ratio of dark-to-luminous
matter of about 0.75 at the Holmberg radius.
Astronomy and Astrophysics 07/1990; 234:43-52. · 5.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: Observations of 12CO(1-0) and 12CO(2-1) found in the disk of the Scd
galaxy NGC 6946 are presented. These observations were performed with
the IRAM 30-m telescope. The ratio of the CO(2-1) to CO(1-0)
emissivities amounted to about 0.4, which is characteristic of a
low-excitation state. It is suggested that the CO lines observed at a
scale of 500 pc are mainly emitted in the low-density optically thick
envelopes of molecular clouds.
Astronomy and Astrophysics 06/1990; 233:357-371. · 5.08 Impact Factor