Cosmic Radiation Fields - Sources in the early Universe

10 Nov 2010, 08:00 → 12 Nov 2010, 18:00 Europe/Berlin

Auditorium (Building 05) (Desy-Campus)

Conference on the extragalactic infrared background and star formation in the early universe, including dark matter.

Wednesday 10 November

08:30 → 09:15 Registration

09:15 → 09:30 Welcome

09:30 → 11:00 Session 1

09:30 First stars and cosmic reionization

I will discuss our current understanding of the formation and nature of the first stars and their role in driving the cosmic reionization process. I will also outline possible strategies for to directly and indirectly detecting them by exploiting the information embedded in the Cosmic Infrared Background and by searching for their fossil relics in the Milky Way halo.

Speaker: Prof. Andrea Ferrara (Scuola Normale Superiore)

10:00 Cosmic reionization and the LOFAR project

In this talk I will present theoretical models of the cosmic reionization process and discuss ongoing activities within the LOFAR Epoch of Reionization Working Group.

Speaker: Dr Benedetta Ciardi (Max Planck Institute for Astrophysics)

Slides ciardi.pdf

10:30 Pointing the James Webb Space Telescope through lensing clusters - can the first stars and galaxies be detected?

The James Webb Space Telescope (JWST), scheduled for launch in 2014, is expected to revolutionize our understanding of the high-redshift Universe. Even so, many of the first stars and galaxies are predicted to be intrinsically too faint for JWST. Here, we explore the prospects of searching for the first stars (both conventional pop III stars and dark stars) and galaxies at z > 10 by pointing JWST through foreground lensing clusters. Observations of this kind can reach significantly deeper than the currently planned JWST ultra deep field in just a fraction of the exposure time, but at the expense of probing a much smaller volume of the high-redshift Universe. We also present the first spectral synthesis model custom-designed for the first galaxies, and discuss the observational signatures of pop III stars and dark stars within these systems.

Speaker: Dr Erik Zackrisson (Stockholm Observatory)

Slides Hamburg2010_Zackrisson.pdf

11:00 → 11:30 Coffee break

11:30 → 12:30 Session 2

11:30 How the first generations of luminous baryons established the X-ray and UV backgrounds

I will discuss how the first generations of astrophysical objects made a substantial impact on our Universe though their radiation. Due to their large mean free paths, X-rays from the first sources likely quickly heated the IGM. The 2nd generation of 21cm instruments can provide a unique view into these early epoch. The early stages of reionization likely followed, driven by so-called "mini-halos", i.e. molecularly-cooled halos. These small halos are susceptible to complex feedback mechanisms, especially from the soft-UV background which preceded reionization, likely resulting in complex and extended early stages of reionization. When atomically cooled halos emerged as the dominant ionizers, reionization could proceed fairly rapidly, with these being less sensitive to radiative feedback than previously thought. Reionization could have slowed in the final stages when the ionized bubbles grew larger than the separation of absorption systems. The final stages likely involved the (fairly slow) photo-evaporation of Lyman limit systems, which by then regulated the rise of the UV background. I will discuss the theoretical underpinnings of this narrative, as well as how future observations may help shed light on the outstanding uncertainties.

Speaker: Dr Andrei Mesinger (Princeton University)

Slides Mesinger_Hamburg_2010.pdf

11:50 Observational Signatures of Lyman Alpha Emission from Early Galaxy Formation.

The Lyman Alpha (Lya) emission line is robustly predicted to be the most prominent intrinsic spectral feature of the `first’ galaxies that initiated the reionization process in our Universe. Unfortunately, the large Gunn-Peterson optical depth of the surrounding neutral intergalactic medium (IGM) is thought to render this line extremely difficult to detect prior to reionization. However, I will discuss how radiative transfer (RT) effects in the interstellar medium (ISM) can cause Lya flux to emerge from galaxies at frequencies where the Gunn-Peterson optical depth is reduced tremendously. This substantially enhances the prospects for detection of the Lya line at high redshift (say z=10-15) with JWST or ground-based, thirty meter telescopes. Similar RT effects boost the detectability of the Lya line from galaxies during the latter stages of reionization, and quantitatively affect the imprint of cosmic reionization on the observed distribution, and redshift evolution, of Lya selected galaxies.

Speaker: Dr Mark Dijkstra (MPA Garching)

Slides dijkstra.pdf

12:10 Dark Matter effects on high-redshift universe

I will show recent results on the study of decaying/annihilating dark matter (DM) candidate effects in the high-redshift Universe. After a brief introduction to the physics of reionization and the exotic scenario in which DM contributes to reionize the Universe, I will discuss how to constrain this contribution. To this aim, a new numerical code, MEDEA (Monte Carlo Energy Deposition Analysis), was developed, which allows to follow the energy deposition of high-energy cascades produced by leptons injected into the InterGalactic Medium. Results obtained within this approach will be presented and discussed.

Speaker: Dr Carmelo Evoli (SISSA/ISAS, Trieste, Italy)

Slides evoli_crf10.pdf

12:30 → 14:00 Lunch break

14:00 → 15:20 Session 3

14:00 Formation of the First Galaxies

The first stars are thought to be extremely luminous and reside in dark matter halos with masses of approximately a million solar masses. I will present results from radiation hydrodynamics simulations that follow the formation of tens of metal-free stars and their impact on high-redshift galaxy formation and reionization. HII regions created by the first stars are a few kiloparsecs in radius, which then overlap with each other and constitute a volume filling fraction of about a quarter at redshift 15. We also find that the first galaxies are enriched up to 1/1000th of solar metallicity, which is sufficient to transition to lower-mass star formation. I will finish by presenting new results that self-consistently follow the transition from Pop III to II star formation for the first time.

Speaker: John Wise (Princeton University)

Slides Hamburg2010.pdf

14:20 The effect of dust cooling in the fragmentation of star-forming clouds for the transition from Pop. III to Pop. II

The first burst of star formation in the Universe is thought to give rise to 'massive' stars, with current theory predicting masses in the range 20-150 solar masses. This contrasts with the mode of star formation we see today, which tends to yield stars with masses less than 1 solar mass, and so at some point in the evolution of the Universe there was a transition from primordial (POP III) star formation to that the star formation we see today (POP II/I). The most widely accepted cause for this transition is metal enrichment in the interstellar medium by the previous generations of stars, and suggests that there may a 'critical metallicity' at which the mode of star formation changes. We investigate the effects of the cooling due to dust grains on the collapse of low metallicity star forming clouds and the Pop III/II transition. Making use of 3D numerical models to follow the thermal evolution of clouds with different metallicities, we study self-consistently the evolution of the gas and dust temperatures during the collapse, and determine the properties of the cloud at the point at which it undergoes gravitational fragmentation. This allows us to investigate the role that dust cooling may play in the transition from a Pop. III IMF composed predominantly of high-mass stars to the IMF we observe today.

Speaker: Mr Gustavo Dopcke (ITA - Universität Heidelberg)

Slides Dust-cooling04.pdf

14:40 The role of magnetic fields during primordial star formation

Although the initial strength of magnetic fields is very uncertain, they may have a significant impact on the dynamics in case of dynamo amplification. In this talk, I will review recent work regarding magnetic field amplification during primordial star formation, based on analytic calculations and numerical simulations involving MHD and self-gravity. I will discuss the influence of such magnetic fields on fragmentation and accretion in the protostellar disk, which is crucial for the final stellar masses and their observational signatures.

Speaker: Dr Dominik Schleicher (ALMA ARC node Leiden)

Slides Talk

15:00 The generation of strong magnetic fields during the formation of the first stars

Over the course of the last decade, a great deal of progress has been made in understanding the physical processes governing the birth of the first stars and their influence on later epochs of structure formation. These studies have ignored the possible role of magnetic fields primarily because the initial field strengths obtained from either cosmological processes like inflation and phase transition or astrophysical processes like the Biermann battery or the Weibel instability are highly uncertain. However, cosmological hydrodynamical simulations of primordial star formation suggest that the gas within the first star-forming halos is turbulent. This has strong implications on the subsequent evolution, in particular on the generation of magnetic fields via the small-scale dynamo. Using high-resolution numerical simulations, we show that in the presence of turbulence, weak seed magnetic fields are exponentially amplified by the small-scale dynamo during the formation of the first stars. The presence of the small-scale dynamo can only be identified in numerical simulations in which the turbulent motions in the central collapsing core are resolved by at least 32 grid cells. We conclude that strong magnetic fields are generated during the birth of the first stars in the universe, potentially modifying the mass distribution of these stars and influencing the subsequent cosmic evolution.

Speaker: Dr Sharanya Sur (Institute for Theoretical Astrophysics (ITA), Univ. of Heidelberg)

Slides hamburg10_sur.pdf

15:20 → 16:00 Coffee break

16:00 → 17:20 Session 4

16:00 The effects of accretion luminosity from Pop III protostars

While the first stars were long thought to form as isolated, single objects, recent cutting-edge simulations have shown that multiple sites of fragmentation can be formed even in primordial halos. These new results have important consequences for our understanding of the early Universe, and the observational signatures that might be expected from the first stars and protogalaxies. It is therefore important to study this fragmentation in detail, and assess the extent to which it may be suppressed by protostellar feedback. In this contribution, we will discuss the effects of the accretion luminosity from young protostars on their immediate environment. Firstly, we shall show that while the accretion luminosity heats the accretion disk surrounding the first protostar, such radiative feedback is unable to fully stabilise the disk against gravitational instability. Consequently, the disk still fragments, forming a binary or higher-order multiple system. Secondly, we shall discuss the effects of feedback on a small cluster of stars forming in primordial conditions. In particular, we will address whether feedback can reduce or stop fragmentation, and what influence it has on the accretion rates of the young protostars.

Speaker: Dr Rowan J Smith (ITA, University of Heidelberg)

Slides Rowan_Smith.pdf

16:20 The Stellar Initial Mass Function in Low-Metallicity Gas

It is widely believed that the initial mass function (IMF) of stars formed in metal-free gas -- the so-called Population III stars -- was very top-heavy, being dominated by very massive stars. On the other hand, the existence of very low metallicity halo stars demonstrates that it is possible to form low-mass stars with metallicities as small as [Fe/H] ~ -5. This implies that the presence of even a small amount of metals and/or dust may cause the stellar initial mass function to change significantly. Two main theories have been put forward to explain this, one centering on the role of atomic fine structure cooling at low densities, and the other on dust cooling at much higher densities. In this talk, I will discuss both of these theories and show how they can be combined to yield a single coherent picture for the origin of the IMF in low metallicity gas. I will also discuss some recent work that suggests that the Pop. III IMF may not be as different from the Pop. II IMF as previously thought.

Speaker: Dr Simon Glover (Institute for Theoretical Astrophysics, Heidelberg)

Slides Hamburg-Glover.pdf

16:40 Model atmospheres for Dark Stars

I will present the initial results for Dark Star model atmospheres and synthetic spectra computing using the PHOENIX model atmosphere package. There are some interesting features of the spectra that I will discuss.

Speaker: Prof. Peter Hauschildt (Hamburger Sternwarte)

Slides DS.pdf

Thursday 11 November

09:30 → 11:00 Session 5

09:30 Dark matter and the first stars

I will outline the general framework within which self-annihilating, Weakly Interacting massive models of Dark Matter can affect the first stars (Population III). Self annihilation of DM particles during he gas cooling and collapse phase may affect weakly the properties of the cloud; we have found that however even at late stages during star formation this mechanism is not likely to provide an energy source such to stop the collapse of the cloud. Once a pre-MS hydrostatic object is formed, capture of DM particles via weak elastic scattering on the material of the proto-star can drive a DM powered phase that may in principle prolonge the lifetime of the star. I will discuss the general mechanisms as well as a detailed study of the two phases.

Speaker: Dr Fabio Iocco (Institut d'Astrophysique de Paris)

Slides Iocco-CRF.pdf

10:00 Dark stars: structure, evolution and impacts upon the high-redshift Universe

The most compelling and popular models for dark matter predict that it should congregate and annihilate in stellar cores. Stars where annihilation contributes substantially to the total energy budget look very different to those with which we are familiar. I will describe the general features of stars modified by dark matter annihilation with the help of a series of grids of 'dark' stellar evolutionary models, and will detail the public code with which they were computed. I will go on to discuss possible impacts of dark stars on the high-redshift Universe, including the history of reionisation, drawing on dedicated models for dark star atmospheres and the stellar populations to which they would belong.

Speaker: Pat Scott (McGill University)

Slides PS_CRF2010.pdf

10:30 tba

Speaker: Dr Emanuele Ripamonti (Universita' di Milano-Bicocca)

Slides Ripamonti_CRF2010.pdf

11:00 → 11:30 Coffe break

11:30 → 12:30 Session 6

11:30 The Redshift Evolution of LCDM Halo Parameters

We present a detailed study of the redshift evolution of dark matter halo structural parameters in a LambdaCDM cosmology. We study the mass and redshift dependence of the concentration, shape and spin parameter in Nbody simulations spanning masses from 10^{10} Msun/h to 10^{15} Msun/h and redshifts from 0 to 2. We present a series of fitting formulas that accurately describe the time evolution of the concentration-mass relation since z=2. Using arguments based on the spherical collapse model we study the behaviour of the scale length of the density profile during the assembly history of haloes, obtaining physical insights on the origin of the observed time evolution of the concentration mass relation. We also investigate the evolution with redshift of dark matter halo shape and its dependence on mass. Within the studied redshift range the relation between halo shape and mass can be well fitted by a power law. Finally we show that although for z=0 the spin parameter is practically mass independent, at increasing redshift it shows a increasing correlation with mass.

Speaker: Mr Juan Carlos Munoz Cuartas (Astrophysikalisches Institut Potsdam)

Slides CRF2010_Munoz-Cuartas.pdf

11:50 Thermal decoupling of WIMPS: The link between particle physics properties and the small-scale structure of (dark) matter

The kinetic decoupling of weakly interacting massive particles (WIMPs) in the early universe sets a scale that can directly be translated into a small-scale cutoff in the spectrum of matter density fluctuations. I present a formalism which allows to describe this decoupling process in great detail and to determine the cutoff scale to a high accuracy; with decoupling temperatures of several MeV to a few GeV, depending on the details of the underlying WIMP microphysics, the smallest protohalos to be formed range between 10^−11 and almost 10^−3 solar masses. Observational consequences and prospects to probe this small-scale cutoff, which would provide a fascinating new window into the particle nature of dark matter, are discussed.

Speaker: Dr Torsten Bringmann (Hamburg University)

Slides CRF2010_Bringmann.pdf

12:10 Constraints on dark matter powered stars from the extragalactic background light

Recently, it has been proposed that self-annihilating dark matter could have a significant effect on the formation and development of the first stars in the universe. In such a model, the energy from self-annihilation of dark matter particles may be the main power source for this class of young stellar objects called Dark Stars (DS). Their features (e.g. luminosity, temperature, lifetime) differ from normal POP III stars and therefore makes them distinguishable. The contribution of DS to the extragalactic background light considering multiple initial parameters is calculated. By comparing our results with existing data of the EBL we can derive first observational limits on Dark Stars in the early universe. Future observations will improve these constraints.

Speaker: Mr Andreas Maurer (Institute for Experimental Physics, University of Hamburg)

Slides CRF2010_am.pdf

12:30 → 14:00 Lunch break

14:00 → 15:20 Session 7

14:00 Galaxy Evolution and Background Radiations in the Infrared

Speaker: Prof. Alberto FRANCESCHINI

Slides Franceschini.pdf

14:30 Galaxy Build-up and Evolution at z>=7: Early results from ultra-deep WFC3/IR observations over the HUDF and GOODS fields

The new WFC3/IR camera aboard HST enables us to survey the sky in the near-IR data 40x more efficiently than ever before -- permitting us to make enormous strides in our searches for z>=7 galaxies. Already in the first year of observations, we have deep and ultra-deep observation over 52+ arcmin**2 in legacy fields like the HUDF and GOODS. With these data, we have been able to select 80+ z~7 galaxies, 50+ z~8 galaxies, and even a promising z~10 candidate. These new selections have allowed us to quantify the evolution of the UV LF and faint-end slope from z~10, significantly constrain the stellar populations and dust properties of z~7-10 galaxies, and construct a general picture of how galaxies build up early in the universe. In this presentation, I provide a summary of some of the early results -- giving particular emphasis to the implications for reionization and the global star formation rate density.

Speaker: Prof. Rychard Bouwens Bouwens (Leiden University)

Slides hamburg.pdf

15:00 Understanding the Cosmic Infrared Background

The Cosmic Infrared Background (CIB) can provide information about stars and galaxies at high redshifts. I will discuss the constraints that can be attained from observations of the near and far infrared background. Information about background light provides the benefit of giving information of the stellar population as a whole, rather than just bright or common sources, however, it is often very difficult to observe. I will discuss the theory and what properties of stars and galaxies can be constrained by current and future observations, as well as the state of observations.

Speaker: Dr Elizabeth Fernandez (Institut d'astrophysique spatiale)

Slides FernandezHamburgNov2010.pdf

15:20 → 16:00 Coffee break

16:00 → 17:30 Session 8

16:00 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 SED constraints the model 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 will discuss their strengths and weaknesses. 1. The absolute SED was measured by COBE and more recently by Akari. These measurements are limited by the efficiency of 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 counts. The "stacking" method determines the flux emitted at a given wavelength by a population detected at an other 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 (P(k),P(D)...). 3. Finally, upper limits can be derived from the high energy spectra of extragalactic sources. These upper limits give good constraints in the near- and mid-IR.

Speaker: Mr Matthieu Bethermin (IAS (Orsay, France))

Slides CRF2010.pdf

16:30 The Resolved Near-Infrared Extragalactic Background

In our recent paper (Keenan et al. 2010, accepted to ApJ), we present a current best estimate of the integrated near-infrared (NIR) extragalactic background light (EBL) attributable to resolved galaxies in J, H, and Ks. We derive these new limits by combining our deep wide-field NIR photometry from five widely separated fields with other studies from the literature to create a galaxy counts sample that is highly complete and has good counting statistics out to JHKs ~ 27−28. As part of this effort we present new ultradeep Ks−band galaxy counts from 22 hours of observations with the Multi Object Infrared Camera and Spectrograph (MOIRCS) instrument on the Subaru Telescope. We use this MOIRCS Ks−band mosaic to estimate the total missing flux from sources beyond our detection limits. Our new limits to the NIR EBL are in basic agreement with, but 10 − 20% higher than previous estimates, bringing them into better agreement with estimates of the total NIR EBL (resolved + unresolved sources) obtained from TeV gamma−ray opacity measurements and recent direct measurements of the total NIR EBL, as well as recent integrated galaxy light models. We examine field to field variations in our photometry to show that the integrated light from galaxies is isotropic to within uncertainties, consistent with the expected large-scale isotropy of the EBL. Our data also allow for a robust estimate of the NIR light from Galactic stars.

Speaker: Mr Ryan Keenan (University of Wisconsin, Madison)

16:50 Herschel/PEP resolves the far-IR background

Launched in May 2009, Herschel is providing stunning results: the first PACS extragalactic surveys are giving an unprecedented view of the Infra-Red sky, unveiling the far-IR emission of many galaxies, up to redshifts z~2 and beyond. The PACS Evolutionary Probe extragalactic survey (PEP, P.I. Lutz) samples four different layers in the cosmological ``wedding cake'', from shallow wide fields (e.g. COSMOS, 2 deg2) to intermediate areas (e.g. Lockman Hole, ~400 arcmin2), to deep, confusion-limited, pencil-beam observations (e.g. GOODS-N and GOODS-S) and even beyond through lensing galaxy clusters (e.g. Abell 2218). Using the PEP data, we have established 70, 100 and 160 micron source counts, extending between a few mJy (in GOODS-S/N) and ~200 mJy (in COSMOS). The integral of galaxy number counts resolves 70% (55%) of the CIB at 160 micron (100 micron) (see Berta et al. 2010). Including the Abell 2218 lensing cluster, number counts dig down to ~1 mJy, thus breaking the confusion limit in the PACS bands (Altieri et al. 2010). By exploiting stacking of 24 micron sources and statistical analyses such as P(d), we push the knowledge of number counts slopes to sub-mJy regimes. Thanks to the huge ancillary database available in our fields, especially in GOODS-N/S, we attached a detailed shorter wavelength SED and a redshift estimate to each FIR source. In this way, we are able to split number counts and CIB into the contribution from different redshift slices. At z<=0.5 we isolate a class of luminous sources L(IR)~1e11 Lsun), whose SEDs resemble late-spiral galaxies, peaking at ~130 micron restframe and significantly colder than what is expected on the basis of pre-Herschel models. Most of the 100 and 160 microns CIB arises at redshifts z<1, with red sources peaking at higher redshift than blue ones. At the PEP GOODS-N depth, the resolved CIB is mainly due to luminous and ultra-luminous IR galaxies (LIRGs 1e11<= L(IR) <1e12 Lsun, ULIRGs L(IR)>=1e12 Lsun).

Speaker: Dr Stefano Berta (Max Planck Institut fuer Extraterrestrische Physik)

Slides Slides presented at CRF 2010, already in PDF format

17:10 AKARI observation of the fluctuation of the near-infrared background

The fluctuation analysis of the near-infrared background was performed based on the NEP survey at 2.4, 3.2 and 4.1 μm carried out by Japanese infrared astronomy satellite, AKARI. The excess fluctuation powers were detected at the angles larger than 100 arcsec, and they show turnover at tens of arcmin. The excess fluctuating power has a blue stellar spectrum, and correlation between wavelength bands is fairly good. The observed fluctuation is significantly larger than that expected from known foreground sources and could be attributed to pop.III stars origin. The observed angular power spectrum is consistent with theoretical prediction assuming biased star formation that traces the distribution of dark matter.

Speaker: Prof. Toshio Matsumoto (Department of Physics and Astronomy, Seoul National University)

Friday 12 November

09:30 → 10:50 Session 9

09:30 Constraints on the gamma-ray opacity of the Universe with the Fermi-LAT instrument

The Fermi Large Area Telescope is scanning the sky for gamma-rays in the range ~20 MeV to over 300 GeV thereby revealing a wealth of high energy sources. Gamma rays may interact with low-energy photons from the Extragalactic Background Light (EBL) through photon-photon pair production if above the energy threshold. This results in redshift- and energy-dependent attenuation features in extragalactic source spectra such as from blazars and gamma-ray bursts (GRBs). Using photons above 10 GeV collected by the LAT during more than one year of observations from high-redshift blazars and GRBs, the effect of gamma-ray flux attenuation by the EBL is investigated. Several techniques are used to place robust upper limits on the gamma-ray opacity of the Universe at various energies and redshifts. By comparing with predictions from a range of EBL models, high-confidence limits on EBL intensity models at optical-ultraviolet wavelengths are derived.

Speaker: Dr Anita Reimer (Institut für Theoretische Physik, Universität Innsbruck, Austria)

Slides EBL_CRF2010.pdf

10:00 Constraints on Extragalactic Background Light using very high energy gamma rays

Very high energy (VHE, E > 30 GeV) gamma-rays are absorbed via interaction with low-energy photons from the extragalactic background light (EBL) if the involved photon energies are above the threshold for electron-positron pair creation. The VHE gamma-ray absorption, which is energy dependent and increases strongly with redshift, distorts the VHE energy spectra observed from distant objects. The observed energy spectra of the AGNs carry, therefore, an imprint of the EBL. The detection of hard VHE gamma-ray spectra of distant sources (z = 0.11 - 0.54) by H.E.S.S. and MAGIC enabled to set strong upper limits on the EBL density, using certain basic assumptions about blazar physics. These assumptions are, however, under discussion. In this talk, we give an overview of the EBL constraints, their limitations and perspectives for the joint efforts of the Fermi Gamma-Ray Space telescope, current imaging atmospheric Cherenkov telescopes and future projects like the Cherenkov Telescope Array (CTA).

Speaker: Mr Daniel Mazin (IFAE, Barcelona)

Slides EBL_Hamburg2010_mazin.pdf

10:30 Gamma-ray opacity and the high-redshift UV background

The UV-optical photon background is closely related to the cosmological star formation history. I will present recent estimates of this background based on semi-analytic models of galaxy formation and evolution. Observations of extragalactic gamma-ray sources provide a test of UV and IR background fields, through attenuation of gamma rays due to photon-photon pair-production interactions. GeV scale emission from high-redshift gamma-ray bursts (GRBs) can potentially be a valuable probe of the UV background produced by early galaxies. Combined Fermi LAT data on distant blazars and GRBs has already disfavored models with a very high level of background light, and future observations with this instrument and next-generation atmospheric Cherenkov telescopes could provide much stronger limits.

Speaker: Dr Rudy Gilmore (SISSA)

10:50 → 11:30 Coffee break

11:30 → 13:00 Session 10

11:30 TeV blazars and their distance

Recently, a new method to constrain the distance of blazars with unknown redshift using combined observations in the GeV and TeV regimes has been developed, with the underlying assumption that the Very High Energy (VHE) spectrum corrected for the absorption of TeV photons by the Extragalactic Background Light (EBL) via photon-photon interaction should still be softer than the gamma-ray spectrum observed by Fermi/LAT. The constraints found are related to the real redshifts by a simple linear relation, that has been used to infer the unknown distance of blazars. The sample will be revised with the up-to-date spectra in both TeV and GeV bands, the method tested with the more recent EBL models and finally applied to the unknown distance blazars detected at VHE.

Speaker: Ms Elisa Prandini (Padova University & INFN)

Slides CRF2010_prandini.pdf

11:50 Measuring Light from the Epoch of Reionization with CIBER, the Cosmic Infrared Background Experiment

Ultraviolet emission from the first generation of stars in the Universe ionized the intergalactic medium in a process which was completed by z~6; the wavelength of these photons has been redshifted by (1+z) into the near infrared today and can be measured using instruments situated above the Earth's atmosphere. First flying in February 2009, the Cosmic Infrared Background Experiment (CIBER) comprises four instruments housed in a single reusable sounding rocket borne payload. CIBER will measure spatial anisotropies in the extragalactic IR background caused by cosmological structure from the epoch of reionization using two broadband imaging instruments, make a detailed characterization of the spectral shape of the IR background using a low resolution spectrometer, and measure the absolute brightness of the Zodical light foreground with a high resolution spectrometer in each of our six science fields. This talk will present the scientific motivation for CIBER and details of its first two flights, including a discussion of the scientific results from the first flight and an outlook for future reionization science with CIBER data.

Speaker: Dr Michael Zemcov (California Institute of Technology/Jet Propulsion Laboratory)

Slides zemcov_desy.pdf

12:10 Conference summary

Speaker: Mr Martin Raue (Institute for Experimental Physics, University of Hamburg)

Slides crf2010_summary.pdf