The existence of a cosmological magnetic field could be revealed by the effects of nontrivial helicity on large scales. We evaluate a CP odd statistic, Q, using gamma ray data obtained from Fermi satellite observations at high galactic latitudes to search for such a signature. Observed values of Q are found to be non-zero; the probability of a similar signal in Monte Carlo simulations is ∼ 0.2%. Contamination from the Milky Way does not seem to be responsible for the signal since it is present even for data at very high galactic latitudes. Assuming that the signal is indeed due to a helical cosmological magnetic field, our results indicate left-handed magnetic helicity and field strength ∼ 10

We report on the results of a search for γ-ray pair halos with a stacking analysis of low-redshift blazars using data from the Fermi Large Area Telescope. For this analysis we used a number of a-priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of ∼ 1GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift z < 0.5 shows an excess over that of point-like sources. A statistical analysis yields a Bayes factor of log 10 B10 > 2, providing evidence in favor of extended emission against the point-source hypothesis, consistent with expectations for pair halos produced in the IGMF with strength BIGMF ∼ 10 −17 − 10 −15 G. PACS numbers: 95.85.Pw, 98.58.Ay, 98.54.Cm, INTRODUCTIONThe magnetic fields that are observed in galaxies and galaxy clusters are believed to result from the dynamo amplification of weak magnetic field seeds, whose origin remains a mystery. Intergalactic magnetic fields (IGMFs), deep in the voids between galaxies, provide the most accurate image of the weak primordial seed fields and could be linked to the early stages in the evolution of the universe (see e.g.[1] for a recent review). Among the several methods used to study cosmological magnetic fields (see e.g. [2] for a recent review), the observation (or nondetection) of cascade emission from blazars can potentially measure very weak IGMFs. A number of blazars have been observed to emit both very-high-energy (VHE, > 100 GeV) γ-rays with ground-based γ-ray instruments and high-energy (HE, MeV/GeV) γ-rays with the Fermi Gamma-ray Space Telescope [3,4]. Most of the detected TeV γ-rays are from the nearest sources since such high energy γ-rays cannot propagate over long distances in intergalactic space due to interactions with the extragalactic background light (EBL). Of course, some higherredshift sources still have detectable TeV emission (e.g. blazar PKS1424+240, which has redshift lower limit of z > 0.6 [5]), but with highly absorbed spectra consistent with theoretical calculations of the attenuation by the EBL. [6][7][8][9][10]. These interactions of TeV γ-rays with the EBL produce electron-positron pairs that subsequently are cooled by inverse Compton (IC) interactions with the Cosmic Microwave Background (CMB), ultimately leading to GeV γ-ray emission from these pair cascades. Since magnetic fields deflect the electron-positron pairs changing the angular distribution of cascade emission, searches for extended GeV emission around blazars can provide an avenue for constraining the IGMF.Due to the low GeV γ-ray flux from extragalactic sources, it is difficult to examine the angular extent of the photon events from a single blazar or even to assess the joint likelihood for detailed fits to a set of individual sources where individual source parameters are taken to be completely independent. To overcome this limitation, stacking sources has been used to make such statistical analysis feasible. Despite early hints at a signal in the stacking analysis of 1...

Non-vanishing parity-odd correlators of gamma ray arrival directions observed by Fermi-LAT indicate the existence of a helical intergalactic magnetic field (Tashiro et al. 2014). We successfully test this hypothesis using more stringent cuts of the data, Monte Carlo simulations with Fermi-LAT time exposure information, separate analyses for the northern and southern galactic hemispheres, and confirm predictions made in Tashiro & Vachaspati (2014). With some further technical assumptions, we show how to reconstruct the magnetic helicity spectrum from the parity-odd correlators.

We report the detection of a high density of redshift z ≈ 10 galaxies behind the foreground cluster A2744, selected from imaging data obtained recently with NIRCam on board JWST by three programs—GLASS-JWST, UNCOVER, and DDT#2756. To ensure robust estimates of the lensing magnification μ, we use an improved version of our model that exploits the first epoch of NIRCam images and newly obtained MUSE spectra and avoids regions with μ > 5 where the uncertainty may be higher. We detect seven bright z ≈ 10 galaxies with demagnified rest frame −22 ≲ M UV ≲ −19 mag, over an area of ∼37 arcmin2. Taking into account photometric incompleteness and the effects of lensing on luminosity and cosmological volume, we find that the density of z ≈ 10 galaxies in the field is about 10× (3×) larger than the average at M UV ≈ −21 ( −20) mag reported so far. The density is even higher when considering only the GLASS-JWST data, which are the deepest and the least affected by magnification and incompleteness. The GLASS-JWST field contains five out of seven galaxies, distributed along an apparent filamentary structure of 2 Mpc in projected length, and includes a close pair of candidates with M UV < −20 mag having a projected separation of only 16 kpc. These findings suggest the presence of a z ≈ 10 overdensity in the field. In addition to providing excellent targets for efficient spectroscopic follow-up observations, our study confirms the high density of bright galaxies observed in early JWST observations but calls for multiple surveys along independent lines of sight to achieve an unbiased estimate of their average density and a first estimate of their clustering.

Ultraviolet light from early galaxies is thought to have ionized gas in the intergalactic medium. However, there are few observational constraints on this epoch, due to the faintness of those galaxies and the redshift of their optical light into the infrared. We report the observation, in James Webb Space Telescope (JWST) imaging, of a distant galaxy that is magnified by gravitational lensing. JWST spectroscopy of the galaxy, at rest-frame optical wavelengths, detects strong nebular emission lines due to oxygen and hydrogen. The measured redshift is z = 9.51 ± 0.01, corresponding to 510 million years after the Big Bang. The galaxy has a radius of 16.2 − 7.2 + 4.6 parsecs, substantially more compact than galaxies with equivalent luminosity at z ~ 6 to 8, leading to a high star formation rate surface density.