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With infrared luminosities $L_{mathrm{IR}} geq 10^{12} L_{odot}$, Ultra-Luminous Infrared Galaxies (ULIRGs) are the most luminous objects in the infrared sky. They are predominantly powered by starburst regions with star-formation rates $gtrsim 100~ M_{odot}~ mathrm{yr^{-1}}$. ULIRGs can also host an active galactic nucleus (AGN). Both the starburst and AGN environments contain plausible hadronic accelerators, making ULIRGs candidate neutrino sources. We present the results of an IceCube stacking analysis searching for high-energy neutrinos from a representative sample of 75 ULIRGs with redshift $z leq 0.13$. While no significant excess of ULIRG neutrinos is found in 7.5 years of IceCube data, upper limits are reported on the neutrino flux from these 75 ULIRGs as well as an extrapolation for the full ULIRG source population. In addition, constraints are provided on models predicting neutrino emission from ULIRGs.
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Ultra-luminous infrared galaxies (ULIRGs) have infrared luminosities $L_{mathrm{IR}} geq 10^{12} L_{odot}$, making them the most luminous objects in the infrared sky. These dusty objects are generally powered by starbursts with star-formation rates that exceed $100~ M_{odot}~ mathrm{yr}^{-1}$, possibly combined with a contribution from an active galactic nucleus. Such environments make ULIRGs plausible sources of astrophysical high-energy neutrinos, which can be observed by the IceCube Neutrino Observatory at the South Pole. We present a stacking search for high-energy neutrinos from a representative sample of 75 ULIRGs with redshift $z leq 0.13$ using 7.5 years of IceCube data. The results are consistent with a background-only observation, yielding upper limits on the neutrino flux from these 75 ULIRGs. For an unbroken $E^{-2.5}$ power-law spectrum, we report an upper limit on the stacked flux $Phi_{ u_mu + bar{ u}_mu}^{90%} = 3.24 times 10^{-14}~ mathrm{TeV^{-1}~ cm^{-2}~ s^{-1}}~ (E/10~ mathrm{TeV})^{-2.5}$ at 90% confidence level. In addition, we constrain the contribution of the ULIRG source population to the observed diffuse astrophysical neutrino flux as well as model predictions.
We report constraints on the sources of ultra-high-energy cosmic ray (UHECR) above $10^{9}$ GeV, based on an analysis of seven years of IceCube data. This analysis efficiently selects very high energy neutrino-induced events which have deposited energies from $sim 10^6$ GeV to above $10^{11}$ GeV. Two neutrino-induced events with an estimated deposited energy of $(2.6 pm 0.3) times 10^6$ GeV, the highest neutrino energies observed so far, and $(7.7 pm 2.0) times 10^5$ GeV were detected. The atmospheric background-only hypothesis of detecting these events is rejected at 3.6$sigma$. The hypothesis that the observed events are of cosmogenic origin is also rejected at $>$99% CL because of the limited deposited energy and the non-observation of events at higher energy, while their observation is consistent with an astrophysical origin. Our limits on cosmogenic neutrino fluxes disfavor the UHECR sources having cosmological evolution stronger than the star formation rate, e.g., active galactic nuclei and $gamma$-ray bursts, assuming proton-dominated UHECRs. Constraints on UHECR sources including mixed and heavy UHECR compositions are obtained for models of neutrino production within UHECR sources. Our limit disfavors a significant part of parameter space for active galactic nuclei and new-born pulsar models.
The IceCube Neutrino Observatory has recently found compelling evidence for a particular blazar producing high-energy neutrinos and $mathrm{PeV}$ cosmic rays, however the sources of cosmic rays above several $mathrm{EeV}$ remain unidentified. It is believed that the same environments that accelerate ultra-high-energy cosmic rays (UHECRs) also produce high-energy neutrinos via hadronic interactions of lower-energy cosmic rays. Two out of three joint analyses of the IceCube Neutrino Observatory, the Pierre Auger Observatory and the Telescope Array yielded hints for a possible directional correlation of high-energy neutrinos and UHECRs. These hints however became less significant with more data. Recently, an improved analysis with an approach complementary to the other analyses has been developed. This analysis searches for neutrino point sources in the vicinity of UHECRs with search windows estimated from deflections by galactic magnetic fields. We present this new analysis method for searching common hadronic sources, additionally including neutrino data measured by ANTARES in order to increase the sensitivity to possible correlations in the Southern Hemisphere.
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A. Barbano (for the IceCube Collaboration
, the Pierre Augern Collaboration
, the Telescope Array Collaboration
2020
The sources of ultra-high energy cosmic rays (UHECRs) are still one of the main open questions in high-energy astrophysics. If UHECRs are accelerated in astrophysical sources, they are expected to produce high-energy photons and neutrinos due to the interaction with the surrounding astrophysical medium or ambient radiation. In particular, neutrinos are powerful probes for the investigation of the region of production and acceleration of UHECRs since they are not sensitive to magnetic deflections nor to interactions with the interstellar medium. The results of three different analyses that correlate the very high-energy neutrino candidates detected by IceCube and ANTARES and the highest-energy cosmic rays measured by the Pierre Auger Observatory and the Telescope Array will be discussed. The first two analyses use a sample of high-energy neutrinos from IceCube and ANTARES selected to have a significant probability to be of astrophysical origin. The first analysis cross-correlates the arrival directions of these selected neutrino events and UHECRs. The second one is a stacked likelihood analysis assuming as stacked sources the high-energy neutrino directions and looking for excesses in the UHECR data set around the directions of the neutrino candidates. The third analysis instead uses a larger sample of neutrinos selected to look for neutrino point-like sources. It consists of a likelihood method that looks for excesses in the neutrino point-source data set around the directions of the highest-energy UHECRs.
Ultra-Luminous Infrared Galaxies (ULIRGs) are the most luminous objects in the infrared sky. With infrared luminosities exceeding $10^{12}$ solar luminosities, ULIRGs contain strong star formation regions which could power hadronic acceleration. Moreover, a significant fraction of ULIRGs have been found to host Active Galactic Nuclei, which could also be a source of hadronic acceleration. Furthermore, such high infrared luminosities indicate that large amounts of dust are present in these objects. In the presence of hadronic acceleration, this dust not only represents an excellent target for high-energy neutrino production through the pp-channel, but it could also attenuate a significant fraction of the gamma rays that are produced in this process. This could relieve the apparent tension between the diffuse IceCube neutrino flux and the diffuse gamma-ray flux measured by Fermi-LAT. We present our source selection criteria and IceCube sensitivities in view of a search for high-energy neutrinos from these so far unexplored objects.
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