Diffuse Extragalactic Background Light Research Articles

Light scalar explanation for the 18 TeV GRB 221009A

Recent astrophysical transient Swift J1913.1+1946 may be associated with the $\gamma$-ray burst GRB 221009A. The redshift of this event is $z\simeq 0.151$. Very high-energy $\gamma$-rays (up to 18 TeV) followed the transient and were observed by LHAASO, additionally Carpet-2 detected a photon-like air shower of 251 TeV. Photons of such high energy are expected to readily annihilate with the diffuse extragalactic background light (EBL) before reaching Earth. If the $\gamma$-ray identification and redshift measurements are correct, new physics could be necessary to explain these measurements. This letter provides the first CP-even scalar explanation of the most energetic 18 TeV event reported by LHAASO. In this minimal scenario, the light scalar singlet $S$ mixes with the Standard Model (SM) Higgs boson $h$. The highly boosted $S$ particles are produced in the GRB and then undergo the radiative decay di-photon $S\rightarrow \gamma\gamma$ while propagating to Earth. The resulting photons may thus be produced at a remote region without being nullified by the EBL. Hence, the usual exponential reduction of $\gamma$-rays is lifted due to an attenuation that is inverse in the optical depth, which becomes much larger due to the scalar carriers.

Neutrino origin of LHAASO's 18 TeV GRB221009A photon

LHAASO collaboration detected photons with energy above 10 TeV from the most recent gamma-ray burst (GRB), GRB221009A. Given the redshift of this event, z∼0.15, photons of such energy are expected to interact with the diffuse extragalactic background light (EBL) well before reaching Earth. In this paper we provide a novel neutrino-related explanation of the most energetic 18 TeV event reported by LHAASO. We find that the minimal viable scenario involves both mixing and transition magnetic moment portal between light and sterile neutrinos. The production of sterile neutrinos occurs efficiently via mixing while the transition magnetic moment portal governs the decay rate in the parameter space where tree-level decays via mixing to non-photon final states are suppressed. Our explanation of this event, while being consistent with the terrestrial constraints, points to the non-standard cosmology.

SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements: II. First Limits on Diffuse Light at 1.25, 1.4, and 1.6 μm

We present the first results from the HST Archival Legacy project “SKYSURF.” As described in Windhorst et al., SKYSURF utilizes the large HST archive to study the diffuse UV, optical, and near-IR backgrounds and foregrounds in detail. Here, we utilize SKYSURF’s first sky-surface-brightness measurements to constrain the level of near-IR diffuse Extragalactic Background Light (EBL) in three near-IR filters (F125W, F140W, and F160W). This is done by comparing our preliminary sky measurements of >30,000 images to zodiacal light models, carefully selecting the darkest images to avoid contamination from stray light. Our sky-surface-brightness measurements have been verified to an accuracy of better than 1%, which when combined with systematic errors associated with HST, results in sky-brightness uncertainties of ∼ 2%–4% ≃ 0.005 MJy sr−1 in each image. When compared to the Kelsall et al. zodiacal model, an isotropic diffuse background of ∼30 nW m−2 sr−1 remains, whereas using the Wright zodiacal model results in no discernible diffuse background. Based primarily on uncertainties in the foreground model subtraction, we present limits on the amount of diffuse EBL of 29, 40, and 29 nW m−2 sr−1, for F125W, F140W, and F160W, respectively. While this light is generally isotropic, our modeling at this point does not distinguish between a cosmological origin or a solar system origin (such as a dim, diffuse, spherical cloud of cometary dust).

SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-sky Surface-brightness Measurements. I. Survey Overview and Methods

We give an overview and describe the rationale, methods, and testing of the Hubble Space Telescope (HST) Archival Legacy project “SKYSURF.” SKYSURF uses HST’s unique capability as an absolute photometer to measure the ∼0.2–1.7 μm sky-surface brightness (sky-SB) from 249,861 WFPC2, ACS, and WFC3 exposures in ∼1400 independent HST fields. SKYSURF’s panchromatic data set is designed to constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light (ZL), Kuiper Belt Objects (KBOs), Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic Background Light (EBL). We outline SKYSURF’s methods to: (1) measure sky-SB levels between detected objects; (2) measure the discrete EBL, most of which comes from AB≃17–22 mag galaxies; and (3) estimate how much truly diffuse light may exist. Simulations of HST WFC3/IR images with known sky values and gradients, realistic cosmic ray (CR) distributions, and star plus galaxy counts were processed with nine different algorithms to measure the “Lowest Estimated Sky-SB” (LES) in each image between the discrete objects. The best algorithms recover the LES values within 0.2% when there are no image gradients, and within 0.2%–0.4% when there are 5%–10% gradients. We provide a proof of concept of our methods from the WFC3/IR F125W images, where any residual diffuse light that HST sees in excess of zodiacal model predictions does not depend on the total object flux that each image contains. This enables us to present our first SKYSURF results on diffuse light in Carleton et al.

An observational determination of the evolving extragalactic background light from the multiwavelength HST/CANDELS survey in the Fermi and CTA era

ABSTRACT The diffuse extragalactic background light (EBL) is formed by ultraviolet (UV), optical, and infrared (IR) photons mainly produced by star formation processes over the history of the Universe and contains essential information about galaxy evolution and cosmology. Here, we present a new determination of the evolving EBL spectral energy distribution using a novel approach purely based on galaxy data aiming to reduce current uncertainties on the higher redshifts and IR intensities. Our calculations use multiwavelength observations from the UV to the far-IR of a sample of approximately 150 000 galaxies detected up to z ∼ 6 in the five fields of the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey from the Hubble Space Telescope. This is one of the most comprehensive and deepest multiwavelength galaxy data sets ever obtained. These unprecedented resources allow us to derive the overall EBL evolution up to z ∼ 6 and its uncertainties. Our results agree with cosmic observables estimated from galaxy surveys and γ-ray attenuation such as monochromatic luminosity densities, including those in the far-IR, and star formation rate densities, also at the highest redshifts. Optical depths from our EBL approximation, which will be robust at high redshifts and for γ-rays up to tens of TeV, will be reported in a companion paper.

HOW GRAVITATIONAL LENSING HELPS γ-RAY PHOTONS AVOID γ – γ ABSORPTION

We investigate potential $\gamma-\gamma$ absorption of gamma-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess $\gamma-\gamma$ opacity, we consider (1) foreground galaxies, including cases in which this configuration leads to strong gravitational lensing, (2) individual stars within these foreground galaxies, and (3) individual stars within our own galaxy, which may act as lenses for microlensing events. We found that intervening galaxies close to the line-of-sight are unlikely to lead to significant excess $\gamma-\gamma$ absorption. This opens up the prospect of detecting lensed gamma-ray blazars at energies above 10 GeV with their gamma-ray spectra effectively only affected by the EBL. The most luminous stars located either in intervening galaxy or in our galaxy provides an environment in which these gamma-rays could, in principle, be significantly absorbed. However, despite a large microlensing probability due to stars located in intervening galaxies, gamma-rays avoid absorption by being deflected by the gravitational potentials of such intervening stars to projected distances ("impact parameters"') where the resulting $\gamma-\gamma$ opacities are negligible. Thus, neither of the intervening excess photon fields considered here, provide a substantial source of excess $\gamma-\gamma$ opacity beyond the EBL, even in the case of very close alignments between the background blazar and a foreground star or galaxy.

GAMMA-RAYS FROM BLAZARS AND THE EXTRAGALACTIC BACKGROUND LIGHT

Recent observations of blazars at high energy (0.1–100 GeV) and very high energy (> 0.1 TeV) have provided important constraints on the intensity and spectrum of the diffuse extragalactic background light (EBL), shedding light on its main origin. Several issues remain open, however, in particular in the mid- and far-infrared bands and in the blazar emission at multi-TeV energies. This review summarizes the observational and theoretical progress in the study of the EBL with gamma-rays and the most promising future improvements, which are mainly expected from spectra in the multi-TeV range.

The Optical Extragalactic Background Light: Revisions and Further Comments

We revise the measurements in our previous work of foreground zodiacal light (ZL) and diffuse Galactic light (DGL) that were used to measure the extragalactic background light (EBL). These changes result in a decrease of 8 and an increase of 0.3 in units of 10-9 ergs s-1 cm-2 sr-1 A-1 (cgs units) in the ZL and DGL flux, respectively. We therefore obtain revised values for the EBL of 6 ± 4, 10 ± 5, and 7 ± 4 cgs in the HST WFPC2 U (F300W), V (F555W), and I (F814W) bands, respectively, from sources fainter than mV ~ 23 AB mag. The revisions are dominated by the details of the tropospheric scattering models used to measure the ZL. We discuss these results in the context of faint number counts and diffuse EBL measurements at other wavelengths. In particular, we note that unless the slope of the galaxy counts increases beyond mV ~ 30 AB mag, unresolved sources will contribute <0.2 cgs, which is far below the uncertainties achievable for any diffuse EBL measurement in the foreseeable future. Therefore, the best constraints on faint sources come from the resolved sources themselves. As in our earlier work, models are still required to derive the bolometric EBL (0.1-1000 μm) due to uncertainties in the mid-infrared; consequently, our previous discussions of the bolometric EBL are not affected by the revisions presented here. Finally, we discuss the nature of the extended point-spread function (PSF) of ground-based telescopes and its impact on surface brightness measurements. In particular, we show that the slope and amplitude of extended PSFs vary considerably between telescopes and with time. We find no conclusive, single cause of extended PSFs, although atmospheric scattering is ruled out.

A low density of the extragalactic background light revealed by the H.E.S.S. spectra of the BL Lac objects 1ES 1101-232 and H 2356-309

The study of the TeV emission from extragalactic sources is hindered by the uncertainties on the diffuse Extragalactic Background Light (EBL). The recent H.E.S.S. results on the blazars 1ES 1101-232 and H 2356-309 represent a breakthrough on this issue. Their unexpectedly hard spectra allow an upper limit to be derived on the EBL in the optical/near-infrared range, which is very close to the lower limit given by the resolved galaxy counts. This result seems to exclude a large contribution to the EBL from other sources (e.g. Population III stars) and indicates that the intergalactic space is more transparent to γ-rays than previously thought. A discussion of EBL absorption effects and further observational tests with Cherenkov telescopes are presented.

A low level of extragalactic background light as revealed by γ-rays from blazars

The diffuse extragalactic background light consists of the sum of the starlight emitted by galaxies through the history of the Universe, and it could also have an important contribution from the 'first stars', which may have formed before galaxy formation began. Direct measurements are difficult and not yet conclusive, owing to the large uncertainties caused by the bright foreground emission associated with zodiacal light. An alternative approach is to study the absorption features imprinted on the gamma-ray spectra of distant extragalactic objects by interactions of those photons with the background light photons. Here we report the discovery of gamma-ray emission from the blazars H 2356 - 309 and 1ES 1101 - 232, at redshifts z = 0.165 and z = 0.186, respectively. Their unexpectedly hard spectra provide an upper limit on the background light at optical/near-infrared wavelengths that appears to be very close to the lower limit given by the integrated light of resolved galaxies. The background flux at these wavelengths accordingly seems to be strongly dominated by the direct starlight from galaxies, thus excluding a large contribution from other sources-in particular from the first stars formed. This result also indicates that intergalactic space is more transparent to gamma-rays than previously thought.

Subaru Super Deep Field with Adaptive Optics. I. Observations and First Implications

We present a deep K'-band (2.12 μm) imaging of the 1' × 1' Subaru Super Deep Field (SSDF) taken with the Subaru adaptive optics (AO) system. Total integration time of 26.8 hr results in the limiting magnitude of K' ~ 24.7 (5 σ, 02 aperture) for point sources and K' ~ 23.5 (5 σ, 06 aperture) for galaxies, which is the deepest limit ever achieved in the K' band. The average stellar full width at half-maximum (FWHM) of the co-added image is 018. Based on the photometric measurements of detected galaxies, we obtained the differential galaxy number counts, for the first time, down to K' ~ 25, which is more than 0.5 mag deeper than the previous data. We found that the number count slope d log N/dm is about 0.15 at 22 < K' < 25, which is flatter than the previous data. Therefore, detected galaxies in the SSDF have only negligible contribution to the near-infrared extragalactic background light (EBL), and the discrepancy claimed so far between the diffuse EBL measurements and the estimated EBL from galaxy count integration has become more serious. The size distribution of detected galaxies was obtained down to the area size of less than 0.1 arcsec2, which is less than half of that of the previous data in the K' band. We compared the observed size-magnitude relation with a simple pure luminosity evolution model allowing for intrinsic size evolution and found that a model with no size evolution gives the best fit to the data. It implies that the surface brightness of galaxies at high redshift is not much different from that expected from the size-luminosity relation of present-day galaxies.

Constraining the cosmic background light with four BL Lac TeV spectra

The intrinsic BL Lac spectra above few hundreds GeV can be very different from the observed ones due to the absorption effects by the diffuse extragalactic background light (EBL), at present poorly known. With the recent results, there are now four sources with good spectral information: Mkn 421 ( z=0.031), Mkn 501 ( z=0.034), 1ES 1426 + 428 ( z=0.129) and 1ES 1959 + 650 ( z=0.047). Making simple assumptions on the shape of the intrinsic spectra (according to the present blazar knowledge), we have considered the effects of different EBL spectral energy distributions (SED) for the first time on all four objects together, deriving constraints for the EBL fluxes. These resulted significantly lower than many direct estimates.

KsNumber Counts in the Groth and Coppi Fields

We have used William Herschel Telescope/INGRID K_(s) images on two high-latitude fields, the Coppi and Groth strips, to obtain galaxy number counts over similar to 180 arcmin^(2), to a depth of K_(s) similar to 21.0. Detection efficiency corrections as a function of object size have been calculated on each pointing. We have used a signal-to-noise threshold in two complementary half-exposure images to remove spurious detections. Our data cover the range from K_(s) = 14.5 to K_(s) = 21.0, so they are useful for investigating a previously reported change in the number count slope (d log N/dm) at K similar to 17. We find a slope gamma(b) = 0.54 0.63 for K 17.5. A total contribution from galaxies to the extragalactic background light (EBL) in the K band of nuI(nu) = 10.5 nW m^(-2) sr^(-1) has been calculated. This K-band EBL coming from galaxies accounts for only similar to 50% of the recent measurements of the diffuse EBL. Standard number count models fail to reproduce the observed slope change at K similar to 17.5 unless elliptical and spiral formation is pushed to z less than or similar to 2.

The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000 Å. II. Measurement of Foreground Zodiacal Light

We present a measurement of the absolute surface brightness of the zodiacal light (3900-5100 A) toward a fixed extragalactic target at high ecliptic latitude based on moderate-resolution (~1.3 A pixel-1) spectrophotometry obtained with the du Pont 2.5 m Telescope at the Las Campanas Observatory in Chile. This measurement and contemporaneous Hubble Space Telescope data from the Wide Field Planetary Camera 2 and Faint Object Spectrograph comprise a coordinated program to measure the mean flux of the diffuse extragalactic background light (EBL). The zodiacal light at optical wavelengths results from scattering by interplanetary dust so that the zodiacal light flux toward any extragalactic target varies seasonally with the position of the Earth. This measurement of zodiacal light is therefore relevant to the specific observations (date and target field) under discussion. To obtain this result, we have developed a technique that uses the strength of the zodiacal Fraunhofer lines to identify the absolute flux of the zodiacal light in the multiple-component night-sky spectrum. Statistical uncertainties in the result are 0.6% (1 σ). However, the dominant source of uncertainty is systematic errors, which we estimate to be 1.1% (1 σ). We discuss the contributions included in this estimate explicitly. The systematic errors in this result contribute 25% in quadrature to the final error in our coordinated EBL measurement, which is presented in the first paper of this series.

Diffuse Extragalactic Background Light versus Deep Galaxy Counts in the Subaru Deep Field: Missing Light in the Universe?

Deep optical and near-infrared galaxy counts are utilized to estimate the extragalactic background light (EBL) coming from normal galactic light in the universe. Although the slope of the number-magnitude relation of the faintest counts is flat enough for the count integration to converge, a considerable fraction of EBL from galaxies could still have been missed in deep galaxy surveys because of various selection effects, including the cosmological dimming of the surface brightness of galaxies. Here we give an estimate of EBL from galaxy counts, in which these selection effects are quantitatively taken into account for the first time, based on reasonable models of galaxy evolution that are consistent with all available data of galaxy counts, size, and redshift distributions. We show that the EBL from galaxies is best resolved into discrete galaxies in the near-infrared bands (J, K) by using the latest data of the Subaru Deep Field; more than 80%-90% of EBL from galaxies has been resolved in these bands. Our result indicates that the contribution by missing galaxies cannot account for the discrepancy between the count integration and recent tentative detections of diffuse EBL in the K band (2.2 μm), and there may be a very diffuse component of EBL that has left no imprints in known galaxy populations.

The faint galaxy contribution to the diffuse extragalactic background light

view Abstract Citations (38) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Faint Galaxy Contribution to the Diffuse Extragalactic Background Light Cole, Shaun ; Treyer, Marie-Agnes ; Silk, Joseph Abstract Models of the faint galaxy contribution to the diffuse extragalactic background light are presented, which are consistent with current data on faint galaxy number counts and redshifts. We predict the autocorrelation function of surface brightness fluctuations in the extragalactic diffuse light and determine how these predictions depend on the cosmological model and assumptions of biasing. We confirm that the recent deep infrared number counts are most compatible with a high density universe ({OMEGA}_0_ ~ 1) and that the steep blue counts then require an extra population of rapidly evolving blue galaxies. The faintest presently detectable galaxies produce an interesting contribution to the extragalactic diffuse light, and still fainter galaxies may also produce a significant contribution. These faint galaxies still only produce a small fraction of the total optical diffuse background light, but on scales of a few arcminutes to a few degrees, they produce a substantial fraction of the fluctuations in the diffuse light. The amplitude and angular dependence of these fluctuations are dependent on the redshift distribution of the faint galaxies and on the background cosmological model. Measurement of the correlation function of fluctuations in the diffuse background light will place additional constraints on the redshift distribution and spatial clustering of these extremely faint galaxies. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170911 Bibcode: 1992ApJ...385....9C Keywords: Background Radiation; Cosmology; Diffuse Radiation; Galactic Clusters; Light (Visible Radiation); Red Shift; Astronomical Models; Astronomical Photometry; Faint Objects; Luminous Intensity; Night Sky; Astrophysics; COSMOLOGY: DIFFUSE RADIATION; COSMOLOGY: OBSERVATIONS; GALAXIES: PHOTOMETRY full text sources ADS |