152 research outputs found
Observations cosmologiques avec un télescope grand champ spatial: Simulations pixels du spectromètre sans fente d'EUCLID
The observations of the supernovae, the cosmic microwave background, and more recently the measurement of baryon acoustic oscillations and the weak lensing effects, converge to a Lambda CDM model, with an accelerating expansion of the today Universe. This model need two dark components to fit the observations, the dark matter and the dark energy. Two approaches seem particularly promising to measure both geometry of the Universe and growth of dark matter structures, the analysis of the weak distortions of distant galaxies by gravitational lensing and the study of the baryon acoustic oscillations. Both methods required a very large sky surveys of several thousand square degrees. In the context of the spectroscopic survey of the space mission EUCLID, dedicated to the study of the dark side of the universe, I developed a pixel simulation tool for analyzing instrumental performances. The proposed method can be summarized in three steps. The first step is to simulate the observables, ie mainly the sources of the sky. I work up a new method, adapted for spectroscopic simulations, which allows to mock an existing survey of galaxies in ensuring that the distribution of the spectral properties of galaxies are representative of current observations, in particular the distribution of the emission lines. The second step is to simulate the instrument and produce images which are equivalent to the expected real images. Based on the pixel simulator of the HST, I developed a new tool to compute the images of the spectroscopic channel of EUCLID. The new simulator have the particularity to be able to simulate PSF with various energy distributions and detectors which have different pixels. The last step is the estimation of the performances of the instrument. Based on existing tools, I set up a pipeline of image processing and performances measurement. My main results were: 1) to validate the method by simulating an existing survey of galaxies, the WISP survey, 2) to determine the tolerances on the energy distribution of the PSF for the slitless spectrometer of EUCLID, 3) to determine the tolerances on the properties of near-infrared detectors of EUCLID.Les observations des supernovae, du fond diffus cosmologique, et plus récemment la mesure des oscillations acoustiques des baryons et des effets de lentilles gravitationnelles faibles, favorisent le modèle cosmologique Lambda CDM pour lequel l'expansion de l'Univers est actuellement en accélération. Ce modèle fait appel à deux composants insaisissables, la matière sombre et l'énergie sombre. Deux approches semblent particulièrement prometteuses pour sonder à la fois la géométrie de l'Univers et la croissance des structures de matière noire, l'analyse des distorsions faibles des galaxies lointaines par cisaillement gravitationnel et l'étude des oscillations acoustiques des baryons. Ces deux méthodes demandent de très grands relevés du ciel, de plusieurs milliers de degrés carrés, en imagerie et en spectroscopie. Dans le contexte du relevé spectroscopique de la mission spatiale EUCLID, dédiée à l'étude des composantes sombres de l'univers, j'ai réalisé des simulations pixels permettant l'analyse des performances instrumentales. La méthode proposée peut se résumer en trois étapes. La première étape est de simuler les observables, c'est à dire principalement les sources du ciel. Pour cela j'ai développé une nouvelle méthode, adapté à la spectroscopie, qui permet d'imiter un relevé existant, en s'assurant que la distribution des propriétés spectrales des galaxies soit représentative des observations actuelles, en particulier la distribution des raies d'émission. La seconde étape est de simuler l'instrument et de produire des images équivalentes aux images réelles attendues. En me basant sur le simulateur pixel du HST, j'ai développé un nouvel outil permettant de simuler les images en spectroscopie sans fente d'EUCLID. Le nouveau simulateur a la particularité de pouvoir simuler des PSF avec une distribution d'énergie variée et des détecteurs dont chaque pixel est différent. La dernière étape est l'estimation des performances de l'instrument. Encore en me basant sur les outils existant, j'ai mis en place un pipeline de traitement des images et de mesure de performances. Mes résultat principaux ont été : 1) de valider la méthode en simulant un relevé de galaxies existant, le relevé WISP, 2) de déterminer les tolérances sur la distribution d'énergie de la PSF du spectromètre sans fente d'EUCLID, 3) de déterminer les tolérances sur les propriétés de détecteurs proche infrarouge d'EUCLID
The ESO UVES Advanced Data Products Quasar Sample - II. Cosmological Evolution of the Neutral Gas Mass Density
Quasar foreground damped absorbers, associated with HI-rich galaxies allow to
estimate the neutral gas mass over cosmic time, which is a possible indicator
of gas consumption as star formation proceeds. The DLAs and sub-DLAs are
believed to contain a large fraction of neutral gas mass in the Universe. In
Paper I of the series, we present the results of a search for DLAs and sub-DLAs
in the ESO-UVES Advanced Data Products dataset of 250 quasars. Here we use an
unbiased sub-sample of sub-DLAs from this dataset. We build a subset of 122
quasars ranging from 1.5 <z_em < 5.0, suitable for statistical analysis. The
statistical sample is analyzed in conjunction with other sub-DLA samples from
the literature. This makes up a combined sample of 89 sub-DLAs over a redshift
path of . Redshift evolution of the number density and the line
density are derived for sub-DLAs and compared with the LLSs and DLAs
measurements from the literature. The results indicate that these three classes
of absorbers are evolving in the redshift interval 1 < z < 5. The column
density distribution, f(N,z), down to the sub-DLA limit is determined. The
flattening of f_(N,z) in the sub-DLA regime is present in the observations. The
redshift evolution of f_(N,z) down to sub-DLA regime is also presented,
indicating the presence of more sub-DLAs at high-redshift as compared to
low-redshift. f_(N,z) is further used to determine the neutral gas mass
density, Omega_g, at 1.5 < z < 5.0. The complete sample shows that sub-DLAs
contribute 8-20% to the total Omega_g from 1.5 < z < 5.0. In agreement with
previous studies, no evolution of Omega_g is seen from low-redshift to
high-redshift, suggesting that star formation solely cannot explain this
non-evolution and replenishment of gas and/or recombination of ionized gas is
needed. (Abridged)Comment: 20 pages, 10 figures, 7 table
GALEX: a UV telescope to map the star formation history of the universe
The NASA Small Mission EXplorer GALEX (PI: C.Martin, Caltech) is under development at JPL for launch late 2001. It has been designed to map the history of star formation in the Universe over the redshift range 0-2, a major era where galaxies and gas content evolved dramatically. The expected depth and imaging quality matches the Palomar Observatory Surveys, allowing GALEX to provide the astronomical community with a database of FUV photometric and spectroscopic observations of several million galaxies in the nearby and distant Universe. The 1.24 degree FOV, 50 cm aperture compact Ritchey-Chrétien telescope is equipped with two 65 mm photon-counting detectors. It will perform several surveys of different coverage and depths, that will take advantage of a high throughput UV-transmissive Grism newly developed in France to easily switch between imagery and field spectroscopy modes. A thin aspherized fused silica dichroic component provides simultaneous observations in two UV bands (135-185 nm and 185-300 nm) as well as correction for field aberrations. We shall briefly present the mission science goals, and will describe the optical concept, along with the guidelines and compromises used for its optimization in the context of the "Faster, Better, Cheaper" NASA philosophy, and give a brief development status report
Deep GALEX Observations of the Coma Cluster: Source Catalog and Galaxy Counts
We present a source catalog from deep 26 ks GALEX observations of the Coma
cluster in the far-UV (FUV; 1530 A) and near-UV (NUV; 2310 A) wavebands. The
observed field is centered 0.9 deg (1.6 Mpc) south-west of the Coma core, and
has full optical photometric coverage with SDSS. The catalog consists of 9700
galaxies with GALEX and SDSS photometry, including 242
spectroscopically-confirmed Coma member galaxies that range from giant spirals
and elliptical galaxies to dwarf irregular and early-type galaxies. The full
multi-wavelength catalog (cluster plus background galaxies) is ~80% complete to
NUV=23 and FUV=23.5, and has a limiting depth at NUV=24.5 and FUV=25.0 which
corresponds to a star formation rate of ~0.001 Msun/yr at the distance of Coma.
Our deep GALEX observations required a two-fold approach to generating a source
catalog: we used a Bayesian deblending algorithm to measure faint and compact
sources (using SDSS coordinates as a position prior), and relied on the GALEX
pipeline catalog for bright/extended objects. We performed simulations to
assess the influence that systematic effects (e.g. object blends, source
confusion, Eddington Bias) have on source detection and photometry when using
both methods. The Bayesian deblending method roughly doubles the number of
source detections and provides reliable photometry to a few magnitudes deeper
than the GALEX pipeline catalog. This method is also free from source confusion
over the UV magnitude range studied here; conversely, we estimate that the
GALEX pipeline catalogs are confusion limited at magnitudes fainter than NUV~23
and FUV~24. We have measured the total UV galaxy counts using our catalog and
report a ~50% excess of counts across FUV=22-23.5 and NUV=21.5-23 relative to
previous GALEX measurements, which is not attributed to cluster member
galaxies. Our galaxy counts are a better match to deeper UV counts measured
with HST.Comment: 27 pages, 13 figures, 4 tables, accepted for publication in ApJ
Three-dimensional spectroscopy with a fiber-fed NUV spectrograph
In the context of the NASA balloon borne experiment named Fireball (Faint Intergalactic Redshifted Emission BALLoon) dedicated to map the Intergalactic Medium, we designed a fiber-fed near ultraviolet spectrograph to work in the 200 nm atmospheric transmission window. We first describe the system level optimization leading to the atypical use in UV of a fiber Integral Field Unit at the focus of a one meter diameter parabolic mirror. For the qualification of the design we measured the absolute transmission of an UV polyimide 100 microns core fiber. The fiber bundle made of 400 fibers rearranged in a 50 mm slit feeds an F/2.5 spectrograph based on an Offner Littrow mount. We present the optical performances of this design with a high throughput and a well matched aperture ratio
A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - VI. Metallicity and Geometry as Gas Flow Probes
The use of background quasars provides a powerful tool to probe the cool gas
in the circum-galactic medium of foreground galaxies. Here, we present new
observations with SINFONI and X-Shooter of absorbing-galaxy candidates at
z=0.7-1. We report the detection with both instruments of the H-alpha emission
line of one sub-DLA at z_abs=0.94187 with log N(HI)=19.38^+0.10_-0.15 towards
SDSS J002133.27+004300.9. We estimate the star formation rate: SFR=3.6+/-2.2
solar masses per year in that system. A detailed kinematic study indicates a
dynamical mass M_dyn=10^9.9+/-0.4 solar masses and a halo mass
M_halo=10^11.9+/-0.5 solar masses. In addition, we report the OII detection
with X-Shooter of another DLA at z_abs=0.7402 with log N(HI)=20.4+/-0.1 toward
Q0052+0041 and an estimated SFR of 5.3+/-0.7 solar masses per year. Three other
objects are detected in the continuum with X-Shooter but the nature and
redshift of two of these objects are unconstrained due to the absence of
emission lines, while the third object might be at the redshift of the quasar.
We use the objects detected in our whole N(HI)-selected SINFONI survey to
compute the metallicity difference between the galaxy and the absorbing gas,
delta_HI(X), where a positive (negative) value indicates infall (outflow). We
compare this quantity with the quasar line of sight alignment with the galaxy's
major (minor) axis, another tracer of infall (outflow). We find that these
quantities do not correlate as expected from simple assumptions. Additional
observations are necessary to relate these two independent probes of gas flows
around galaxies.Comment: 16 pages, 8 figures, accepted for publication in MNRA
FIREBALL: Detector, data acquisition and reduction
The Faint Intergalactic Redshifted Emission Balloon (FIREBALL) had its first scientific flight in June 2009. The instrument combines microchannel plate detector technology with fiber-fed integral field spectroscopy on an unstable stratospheric balloon gondola platform. This unique combination poses a series of calibration and data reduction challenges that must be addressed and resolved to allow for accurate data analysis. We discuss our approach and some of the methods we are employing to accomplish this task
FIREBALL: Instrument pointing and aspect reconstruction
The Faint Intergalactic Redshifted Emission Balloon (FIREBALL) had its first scientific flight in June 2009. The instrument is a 1 meter class balloon-borne telescope equipped with a vacuum-ultraviolet integral field spectrograph intended to detect emission from the inter-galactic medium at redshifts 0.3 < z < 1.0. The scientific goals and the challenging environment place strict constraints on the pointing and tracking systems of the gondola. In this manuscript we briefly review our pointing requirements, discuss the methods and solutions used to meet those requirements, and present the aspect reconstruction results from the first successful scientific flight
GALEX: a UV telescope to map the star formation history of the universe
The NASA Small Mission EXplorer GALEX (PI: C.Martin, Caltech) is under development at JPL for launch late 2001. It has been designed to map the history of star formation in the Universe over the redshift range 0-2, a major era where galaxies and gas content evolved dramatically. The expected depth and imaging quality matches the Palomar Observatory Surveys, allowing GALEX to provide the astronomical community with a database of FUV photometric and spectroscopic observations of several million galaxies in the nearby and distant Universe. The 1.24 degree FOV, 50 cm aperture compact Ritchey-Chrétien telescope is equipped with two 65 mm photon-counting detectors. It will perform several surveys of different coverage and depths, that will take advantage of a high throughput UV-transmissive Grism newly developed in France to easily switch between imagery and field spectroscopy modes. A thin aspherized fused silica dichroic component provides simultaneous observations in two UV bands (135-185 nm and 185-300 nm) as well as correction for field aberrations. We shall briefly present the mission science goals, and will describe the optical concept, along with the guidelines and compromises used for its optimization in the context of the "Faster, Better, Cheaper" NASA philosophy, and give a brief development status report
Encoding the infrared excess (IRX) in the NUVrK color diagram for star-forming galaxies
We present an empirical method of assessing the star formation rate (SFR) of
star-forming galaxies based on their locations in the rest-frame color-color
diagram (NUV-r) vs (r-K). By using the Spitzer 24 micron sample in the COSMOS
field (~16400 galaxies with 0.2 < z < 1.3) and a local GALEX-SDSS-SWIRE sample
(~700 galaxies with z = <
L_IR / L_UV > can be described by a single vector, NRK, that combines the two
colors. The calibration between and NRK allows us to recover the IR
luminosity, L_IR, with an accuracy of ~0.21 dex for the COSMOS sample and ~0.27
dex for the local one. The SFRs derived with this method agree with the ones
based on the observed (UV+IR) luminosities and on the spectral energy
distribution fitting for the vast majority (~85 %) of the star-forming
population. Thanks to a library of model galaxy SEDs with realistic
prescriptions for the star formation history, we show that we need to include a
two-component dust model (i.e., birth clouds and diffuse ISM) and a full
distribution of galaxy inclinations in order to reproduce the behavior of the
stripes in the NUVrK diagram. In conclusion, the NRK method, based only
on rest-frame UV and optical colors available in most of the extragalactic
fields, offers a simple alternative of assessing the SFR of star-forming
galaxies in the absence of far-IR or spectral diagnostic observations.Comment: 21 pages, 22 figures, in publication in Astronomy & Astrophysic
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