43 research outputs found
Measurements of the spectral energy distribution of the cosmic infrared background
The extragalactic background light (EBL) is the relic emission of all
processes of structure formation in the Universe. About half of this
background, called the Cosmic Infrared Background (CIB) is emitted in the
8-1000 microns range, and peaks around 150 microns. It is due to the dust
reemission from star formation processes and AGN emission. The CIB spectral
energy distribution (SED) constraints the models of star formation in the
Universe. It is also useful to compute the opacity of the Universe to the TeV
photons.
We present the different types of measurements of the CIB and discuss their
strengths and weaknesses.
1. The absolute SED was measured by COBE, and by other experiments. These
measurements are limited by the accuracy of the component separation, i.e. the
foreground subtraction.
2. Robust lower limits are determined from the extragalactic number counts of
infrared galaxies. These lower limits are very stringent up to 100 microns. At
larger wavelengths, the rather low angular resolution of the instruments limits
strongly the depth of the number counts. The "stacking" method determines the
flux emitted at a given wavelength by a population detected at another
wavelength, and provides stringent lower limits in the sub-mm range. It is
complementary with other methods based on the statistical analysis of the map
properties like the P(D) analysis.
3. Finally, upper limits can be derived from the high energy spectra of
extragalactic sources. These upper limits give currently good constraints in
the near- and mid-IR.
Progress have been amazing since the CIB discovery about 15 years ago: the
SED is much better known, and most of it can be accounted for by galaxies
(directly or indirectly). Prospects are also exciting, with fluctuation
analysis with Planck&Herschel, and forthcoming missions.Comment: 9 pages, 1 figure, 1 table, proceedings of invited talk at CRF2010,
DESY Hamburg, Nov 9-12 201
Inversion de données infrarouges issues du télescope SPITZER
Nous nous intéressons dans ce papier à l'inversion de données infrarouges issues du télescope spatial SPITZER avec l'imageur MIPS à 160 microns. Le principal problÚme rencontré est la perturbation des mesures sur le ciel par le dépÎt d'énergie des rayons cosmiques dans le détecteur. Ces particules de haute énergie peuvent modifier temporairement les gains des capteurs en altérant la structure du semiconducteur. Nous avons donc développé un algorithme d'estimation conjointe du gain et de l'image infrarouge du ciel. Cet algorithme repose sur la minimisation d'un critÚre par une approche de type gradient conjugué
Exploratory Visualization of Astronomical Data on Ultra-high-resolution Wall Displays
International audienceUltra-high-resolution wall displays feature a very high pixel density over a large physical surface, which makes them well-suited to the collaborative, exploratory visualization of large datasets. We introduce FITS-OW, an application designed for such wall displays, that enables astronomers to navigate in large collections of FITS images, query astronomical databases, and display detailed, complementary data and documents about multiple sources simultaneously. We describe how astronomers interact with their data using both the wall's touch-sensitive surface and handheld devices. We also report on the technical challenges we addressed in terms of distributed graphics rendering and data sharing over the computer clusters that drive wall displays
Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 micron Imaging
The absolute calibration and characterization of the Multiband Imaging
Photometer for Spitzer (MIPS) 70 micron coarse- and fine-scale imaging modes
are presented based on over 2.5 years of observations. Accurate photometry
(especially for faint sources) requires two simple processing steps beyond the
standard data reduction to remove long-term detector transients. Point spread
function (PSF) fitting photometry is found to give more accurate flux densities
than aperture photometry. Based on the PSF fitting photometry, the calibration
factor shows no strong trend with flux density, background, spectral type,
exposure time, or time since anneals. The coarse-scale calibration sample
includes observations of stars with flux densities from 22 mJy to 17 Jy, on
backgrounds from 4 to 26 MJy sr^-1, and with spectral types from B to M. The
coarse-scale calibration is 702 +/- 35 MJy sr^-1 MIPS70^-1 (5% uncertainty) and
is based on measurements of 66 stars. The instrumental units of the MIPS 70
micron coarse- and fine-scale imaging modes are called MIPS70 and MIPS70F,
respectively. The photometric repeatability is calculated to be 4.5% from two
stars measured during every MIPS campaign and includes variations on all time
scales probed. The preliminary fine-scale calibration factor is 2894 +/- 294
MJy sr^-1 MIPS70F^-1 (10% uncertainty) based on 10 stars. The uncertainty in
the coarse- and fine-scale calibration factors are dominated by the 4.5%
photometric repeatability and the small sample size, respectively. The 5-sigma,
500 s sensitivity of the coarse-scale observations is 6-8 mJy. This work shows
that the MIPS 70 micron array produces accurate, well calibrated photometry and
validates the MIPS 70 micron operating strategy, especially the use of frequent
stimulator flashes to track the changing responsivities of the Ge:Ga detectors.Comment: 19 pages, PASP, in pres
The redshift evolution of the distribution of star formation among dark matter halos as seen in the infrared
Recent studies revealed a strong correlation between the star formation rate (SFR) and stellar mass of star-forming galaxies, the so-called star-forming main sequence. An empirical modeling approach (2-SFM) which distinguishes between the main sequence and rarer starburst galaxies is capable of reproducing most statistical properties of infrared galaxies. In this paper, we extend this approach by establishing a connection between stellar mass and halo mass with the technique of abundance matching. Based on a few, simple assumptions and a physically motivated formalism, our model successfully predicts the (cross-)power spectra of the cosmic infrared background (CIB), the cross-correlation between CIB and cosmic microwave background (CMB) lensing, and the correlation functions of bright, resolved infrared galaxies measured by Herschel, Planck, ACT and SPT. We use this model to infer the redshift distribution these observables, as well as the level of correlation between CIB-anisotropies at different wavelengths. We also predict that more than 90% of cosmic star formation activity occurs in halos with masses between 10^11.5 and 10^13.5 Msun. Taking into account subsequent mass growth of halos, this implies that the majority of stars were initially (at z>3) formed in the progenitors of clusters, then in groups at 0.5<z<3 and finally in Milky-Way-like halos at z<0.5. At all redshifts, the dominant contribution to the star formation rate density stems from halos of mass ~10^12 Msun, in which the instantaneous star formation efficiency is maximal (~70%). The strong redshift-evolution of SFR in the galaxies that dominate the CIB is thus plausibly driven by increased accretion from the cosmic web onto halos of this characteristic mass scale
Dusty Infrared Galaxies: Sources of the Cosmic Infrared Background
The discovery of the Cosmic Infrared Background (CIB) in 1996, together with
recent cosmological surveys from the mid-infrared to the millimeter have
revolutionized our view of star formation at high redshifts. It has become
clear, in the last decade, that a population of galaxies that radiate most of
their power in the far-infrared (the so-called ``infrared galaxies'')
contributes an important part of the whole galaxy build-up in the Universe.
Since 1996, detailed (and often painful) investigations of the high-redshift
infrared galaxies have resulted in the spectacular progress covered in this
review. We outline the nature of the sources of the CIB including their
star-formation rate, stellar and total mass, morphology, metallicity and
clustering properties. We discuss their contribution to the stellar content of
the Universe and their origin in the framework of the hierarchical growth of
structures. We finally discuss open questions for a scenario of their evolution
up to the present-day galaxies.Comment: To appear in Annual Reviews of Astronomy and Astrophysics, 2005, vol
43. 31 pages, 12 color figure
Spitzer 70/160 ÎŒm observations of high-redshift ULIRGs and HyLIRSs in the Boötes field
We present new 70 and 160 ÎŒm observations of a sample of extremely red (R â [24] âł 15 mag), mid-infrared bright, high-redshift (1.7 ⟠z ⟠2.8) galaxies. All targets detected in the far-infrared exhibit rising spectral energy distributions (SEDs) consistent with dust emission from obscured active galactic nuclei (AGNs) and/or star-forming regions in luminous IR galaxies (LIRGs). We find that the SEDs of the high-redshift sources are more similar to canonical AGN-dominated local ultraluminous IR galaxies (ULIRGs) with significant warm dust components than to typical local star-forming ULIRGs. The inferred IR (8-1000 ÎŒm) bolometric luminosities are found to be Lbol ~ 4 Ă 10^12 Lâ to ~3 Ă 10^13 Lâ (ULIRGs/hyper-luminous IR galaxies (HyLIRGs)), representing the first robust constraints on Lbol for this class of object
SWIRE: The SIRTF WideâArea Infrared Extragalactic Survey
The SIRTF Wide-Area Infrared Extragalactic Survey (SWIRE), the largest SIRTF Legacy program, is a wide-area imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and active galactic nuclei (AGNs) as a function of environment, from redshifts to the current z ⌠3 epoch. SWIRE will survey seven high-latitude fields, totaling 60â65 deg2 in all seven SIRTF bands: Infrared Array Camera (IRAC) 3.6, 4.5, 5.6, and 8 mm and Multiband Imaging Photometer for SIRTF (MIPS) 24, 70, and 160 mm. Extensive modeling suggests that the Legacy Extragalactic Catalog may contain in excess of 2 million IR-selected galaxies, dominated by (1) âŒ150,000 luminous infrared galaxies (LIRGs; LFIR 1 1011 L,) detected by MIPS (and significantly more detected by IRAC), âŒ7000 of these with ; (2) 1 million IRAC- z 1 2 detected early-type galaxies (⌠with and âŒ10,000 with ); and (3) âŒ20,000 classical AGNs 5 2 # 10 z 1 1 z 1 2 detected with MIPS, plus significantly more dust-obscured quasi-stellar objects/AGNs among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGNs.
The key scientific goals of SWIRE are (1) to determine the evolution of actively star forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts, and AGNs in the key redshift range over which much of cosmic evolution has occurred; and (3) to 0.5 ! z ! 3 determine the evolutionary relationship between ânormal galaxiesâ and AGNs and the contribution of AGN accretion energy versus stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e., in the context of structure formation. The large volume is also optimized for finding rare objects.
The SWIRE fields are likely to become the next generation of large âcosmic windowsâ into the extragalactic sky. They have been uniquely selected to minimize Galactic cirrus emission over large scales. The Galaxy Evolution Explorer will observe them as part of its deep 100 deg2 survey, as will Herschel. SWIRE includes âŒ9 deg2 of the unique large-area XMM Large Scale Structure hard X-ray imaging survey and is partly covered by the UKIDSS deep J and K survey. An extensive optical/near-IR imaging program is underway from the ground. The SWIRE data are nonproprietary; catalogs and images will be released twice yearly, beginning about 11 months after SIRTF launch. Details of the data products and release schedule are presented
An Earth-system prediction initiative for the twenty-first century
International audienceSome scientists have proposed the Earth-System Prediction Initiative (EPI) at the 2007 GEO Summit in Cape Town, South Africa. EPI will draw upon coordination between international programs for Earth system observations, prediction, and warning, such as the WCRP, WWRP, GCOS, and hence contribute to GEO and the GEOSS. It will link with international organizations, such as the International Council for Science (ICSU), Intergovernmental Oceanographic Commission (IOC), UNEP, WMO, and World Health Organization (WHO). The proposed initiative will provide high-resolution climate models that capture the properties of regional high-impact weather events, such as tropical cyclones, heat wave, and sand and dust storms associated within multi-decadal climate projections of climate variability and change. Unprecedented international collaboration and goodwill are necessary for the success of EPI