409 research outputs found
Interstellar H_2 in M 33 detected with FUSE
FUSE spectra of the four brightest H II regions in M 33 show absorption by interstellar gas in the Galaxy and in M 33. On three lines of sight molecular hydrogen in M 33 is detected. This is the first measurement of diffuse H_2 in absorption in a Local Group galaxy other than the Magellanic Clouds. A quantitative analysis is difficult because of the low signal to noise ratio and the systematic effects produced by having multiple objects in the FUSE aperture. We use the M 33 FUSE data to demonstrate in a more general manner the complexity of interpreting interstellar absorption line spectra towards multi-object background sources. We derive H_2 column densities of approximately 10^16 to 10^17 cm^{-2} along 3 sight lines (NGC 588, NGC 592, NGC 595). Because of the systematic effects, these values most likely represent upper limits and the non-detection of H_2 towards NGC 604 does not exclude the existence of significant amounts of molecular gas along this sight line
Intermediate scale structure of the interstellar medium towards NGC 6231 in Sco OB1 with FUSE
The FUSE far-ultraviolet interstellar spectra toward seven targets in NGC
6231 show that the molecules H_2, HD, and CO as well as various atomic species
are distributed in several clouds. The main absorption component found on the
sight lines lies in the Lupus cloud region at a distance of about 150 pc, and
there is a weaker second one, presumably in the Sco OB1 shell surrounding NGC
6231 (d~1.8 kpc). H_2 excitation modelling is used to constrain the radiation
field and the density in the gas; HD is used to estimate the abundance of H+.
The small angular separation of the target stars allows column density
variations to be probed over the field of view, on scales of 0.05 pc in the
case of the Lupus cloud distance. They are 40% for H_2 and 60% for H I. A
rather strong radiation field inside the molecular clouds suggests a separation
of the gas into smaller cloudlets also along the line of sight.Comment: 12 pages, accepted for publication in Astronomy & Astrophysic
ORFEUS echelle spectra: Molecular hydrogen in disk, IVC, and HVC gas in front of the LMC
In front of the LMC molecular hydrogen is found in absorption near 0 km/s,
being local disk gas, near +60 km/s in an intermediate velocity cloud, and near
+120 km/s, in a high velocity halo cloud. The nature of the gas is discussed
based on four ORFEUS far UV spectra of LMC stars and including data from the
ground and from the IUE satellite. The local gas is cool and, given a span of
sight lines of only 2.5 deg, rather fluffy. The fractional abundance of H_2
varies from log(f)=-5.4 to -3.3. Metal depletions (up to -1.7 dex for Fe) are
typical for galactic disk gas. In the IV and HV gas an apparent underabundance
of neutral oxygen points to an ionization level of the gas of about 90%. H_2 is
detected in IV and HV gas toward HD 269546. In the IV gas we find an H_2 column
density of log(N)\simeq15.6. The H_2 excitation indicates that the line of
sight samples a cloud at a temperature below 150 K. Column densities are too
small to detect the higher UV pumped excitation levels. The high velocity H_2
(log(N)\simeq15.6) is highly excited and probably exposed to a strong radiation
field. Its excitation temperature exceeds 1000 K. Due to the radial velocity
difference between the halo gas and the Milky Way disk, the unattenuated disk
radiation is available for H_2 excitation in the halo. We do not find evidence
for an intergalactic origin of this gas; a galactic as well as a Magellanic
Cloud origin is possible.Comment: 12 pages, 5 figures, accepted for publication in A&
The massive binary companion star to the progenitor of supernova 1993J
The massive star which underwent core-collapse to produce SN1993J was
identified as a non-variable red supergiant star in images of the galaxy M81
taken before explosion. However the stellar source showed an excess in UV and
B-band colours that suggested it had either a hot, massive companion star or
was embedded in an unresolved young stellar association. The spectra of SN1993J
underwent a remarkable transformation between a hydrogen-rich Type II supernova
and a helium-rich (hydrogen-deficient) Type Ib. The spectral and photometric
peculiarities were explained by models in which the 13-20 solar mass supergiant
had lost almost its entire hydrogen envelope to a close binary companion. The
binary scenario is currently the best fitting model for the production of such
type IIb supernovae, however the hypothetical massive companion stars have so
far eluded discovery. Here we report the results of new photometric and
spectroscopic observations of SN1993J, 10 years after explosion. At the
position of the fading SN we detect the unambiguous signature of a massive
star, the binary companion to the progenitor. This is evidence that this type
of SN originate in interacting binary systems.Comment: 18 pages (3 figures
Extending empirical constraints on the SZ-mass scaling relation to higher redshifts via HST weak lensing measurements of nine clusters from the SPT-SZ survey at z >= 1
Galaxie
Euclid: the selection of quiescent and star-forming galaxies using observed colours
The Euclid mission will observe well over a billion galaxies out to z ⌠6 and beyond. This will offer an unrivalled opportunity to investigate several key questions for understanding galaxy formation and evolution. The first step for many of these studies will be the selection of a sample of quiescent and star-forming galaxies, as is often done in the literature by using well-known colour techniques such as the âUVJâ diagram. However, given the limited number of filters available for the Euclid telescope, the recovery of such rest-frame colours will be challenging. We therefore investigate the use of observed Euclid colours, on their own and together with ground-based u-band observations, for selecting quiescent and star-forming galaxies. The most efficient colour combination, among the ones tested in this work, consists of the (u â VIS) and (VIS â J) colours. We find that this combination allows users to select a sample of quiescent galaxies complete to above âŒ70 per cent and with less than 15 per cent contamination at redshifts in the range 0.75 65 per cent completeness level and contamination below 20 per cent at 1 < z < 2 for finding quiescent galaxies. In comparison, the sample of quiescent galaxies selected with the traditional UVJ technique is only âŒ20 per cent complete at z < 3, when recovering the rest-frame colours using mock Euclid observations. This shows that our new methodology is the most suitable one when only Euclid bands, along with u-band imaging, are available
Euclid: the selection of quiescent and star-forming galaxies using observed colours
The Euclid mission will observe well over a billion galaxies out to z ⌠6 and beyond. This will offer an unrivalled opportunity to investigate several key questions for understanding galaxy formation and evolution. The first step for many of these studies will be the selection of a sample of quiescent and star-forming galaxies, as is often done in the literature by using well-known colour techniques such as the âUVJâ diagram. However, given the limited number of filters available for the Euclid telescope, the recovery of such rest-frame colours will be challenging. We therefore investigate the use of observed Euclid colours, on their own and together with ground-based u-band observations, for selecting quiescent and star-forming galaxies. The most efficient colour combination, among the ones tested in this work, consists of the (u â VIS) and (VIS â J) colours. We find that this combination allows users to select a sample of quiescent galaxies complete to above âŒ70 per cent and with less than 15 per cent contamination at redshifts in the range 0.75 65 per cent completeness level and contamination below 20 per cent at 1 < z < 2 for finding quiescent galaxies. In comparison, the sample of quiescent galaxies selected with the traditional UVJ technique is only âŒ20 per cent complete at z < 3, when recovering the rest-frame colours using mock Euclid observations. This shows that our new methodology is the most suitable one when only Euclid bands, along with u-band imaging, are available
Euclid preparation: XVII. Cosmic Dawn Survey: Spitzer Space Telescope observations of the Euclid deep fields and calibration fields
We present a new infrared survey covering the three Euclid deep fields and four other Euclid calibration fields using Spitzer Space Telescope's Infrared Array Camera (IRAC). We combined these new observations with all relevant IRAC archival data of these fields in order to produce the deepest possible mosaics of these regions. In total, these observations represent nearly 11 % of the total Spitzer Space Telescope mission time. The resulting mosaics cover a total of approximately 71.5 deg^{2} in the 3.6 and 4.5 ÎŒm bands, and approximately 21.8 deg^{2} in the 5.8 and 8 ÎŒm bands. They reach at least 24 AB magnitude (measured to 5Ï, in a 2âłââ.5 aperture) in the 3.6 ÎŒm band and up to âŒ5 mag deeper in the deepest regions. The astrometry is tied to the Gaia astrometric reference system, and the typical astrometric uncertainty for sources with 16 "< "[3.6]< 19 is âČ 0âłââ.15. The photometric calibration is in excellent agreement with previous WISE measurements. We extracted source number counts from the 3.6 ÎŒm band mosaics, and they are in excellent agreement with previous measurements. Given that the Spitzer Space Telescope has now been decommissioned, these mosaics are likely to be the definitive reduction of these IRAC data. This survey therefore represents an essential first step in assembling multi-wavelength data on the Euclid deep fields, which are set to become some of the premier fields for extragalactic astronomy in the 2020s
Euclid: On the reduced shear approximation and magnification bias for Stage IV cosmic shear experiments
Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, previously ignored systematic effects must be addressed. In this work, we evaluate the impact of the reduced shear approximation and magnification bias, on the information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities, in high-magnification regions. The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculate the impact of neglecting these effects on the cosmological parameters that would be determined from Euclid, using cosmic shear tomography. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach. These effects cause significant biases in Omega_m, n_s, sigma_8, Omega_DE, w_0, and w_a of -0.51 sigma, -0.36 sigma, 0.37 sigma, 1.36 sigma, -0.66 sigma, and 1.21 sigma, respectively. We then show that these lensing biases interact with another systematic: the intrinsic alignment of galaxies. Accordingly, we develop the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to Euclid, we find that the additional terms introduced by this correction are sub-dominant
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