低频射电观测弥散同步加速辐射为研究银河系内从弥散星际介质（ISM）到恒星形成区的结构形成过程中气体与磁场之间的复杂关系提供了独特视角。实现这一关键目标取决于对宇宙线性质的全面理解，宇宙线决定了相对论电子（主要是可观测同步加速辐射的来源）的有效能量分布。值得注意的是，能量在100 MeV至10 GeV之间的宇宙线电子（CRe）在决定GHz以下大部分天空亮度方面起着关键作用。然而，由于太阳调制的存在，它们的能量通量（$j_e$）仍然难以捉摸。我们提出通过低频射电辐射的亮温谱指数（此处记为$β_{\ m obs}$）来推导星际CRe这一能量间隙的观测约束。我们引入了一个新的参数化解析模型，该模型拟合了$j_e$的现有数据，与文献中测量的银河系弥散发射在50 MHz至1 GHz之间的$β_{\ m obs}$值一致。我们的模型能够考虑多种观测，磁场强度与低于10 $μ$G的现有测量一致。我们首次展示了垂直于视线方向的平均磁场分量的全天图，并针对弥散ISM的最先进数值模拟验证了我们的方法。这项研究在利用实用的参数化形式建模银河系弥散发射方面取得了进展，为即将到来的平方千米阵（SKA）提供了重要见解。
英文摘要：
Low-frequency radio observations of diffuse synchrotron radiation offer a unique vantage point for investigating the intricate relationship between gas and magnetic fields in the formation of structures within the Galaxy, spanning from the diffuse interstellar medium (ISM) to star-forming regions. Achieving this pivotal objective hinges on a comprehensive understanding of cosmic-ray properties, which dictate the effective energy distribution of relativistic electrons, primarily responsible for the observable synchrotron radiation. Notably, cosmic-ray electrons (CRe) with energies between 100 MeV and 10 GeV play a crucial role in determining the majority of the sky brightness below the GHz range. However, their energy flux ($j_e$) remains elusive due to solar modulation. We propose deriving observational constraints on this energy gap of interstellar CRe through the brightness temperature spectral index of low-frequency radio emission, here denoted as $β_{\rm obs}$. We introduce a new parametric analytical model that fits available data of $j_e$ in accordance with the $β_{\rm obs}$ values measured in the literature between 50 MHz to 1 GHz for diffuse emission in the Milky Way. Our model allows to account for multiple observations considering magnetic-field strengths consistent with existing measurements below 10 $μ$G. We present a first all-sky map of the average component of the magnetic field perpendicular to the line of sight and validate our methodology against state-of-the art numerical simulations of the diffuse ISM. This research makes headway in modeling Galactic diffuse emission with a practical parametric form. It provides essential insights in preparation for the imminent arrival of the Square Kilometre Array.
We present an upper limit of galactic diffuse gamma-ray flux, measured with the GAMMA experiment at energy about 175 TeV. The results were obtained using selection of muon poor extensive air showers at mountain level (700 g/cm^2, Mt. Aragats, Armenia) for 5 GeV muon energy threshold. An upper limit for the differential flux at energy E=175+/-25 TeV is equal to (5.8-7.0)x10^-12 [erg m^2 s sr]^-1 for 95% confidence level.
We study the change in cosmic-ray pressure, the change in cosmic-ray density, and the level of cosmic-ray induced heating via Alfven-wave damping when cosmic rays move from a hot ionized plasma to a cool cloud embedded in that plasma. The general analysis method outlined here can apply to diffuse clouds in either the ionized interstellar medium or in galactic winds. We introduce a general-purpose model of cosmic-ray diffusion building upon the hydrodynamic approximation for cosmic rays (from McKenzie & Voelk and Breitschwerdt and collaborators). Our improved method self-consistently derives th…
A shock-accelerated particle flux \propto p^-s, where p is the particle momentum, follows from simple theoretical considerations of cosmic-ray acceleration at nonrelativistic shocks followed by rigidity-dependent escape into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with s ~ 2.8 provides an adequate fit to the Fermi-LAT gamma-ray emission spectra of high-latitude and molecular cloud gas when uncertainties in nuclear production models are considered. A break in the spectrum of cosmic-ray protons claimed by Neronov, Semikoz, & Taylor (PRL, 108, 051105, 2012) when fitting …
The gamma-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi-LAT mission and compare with models of the diffuse gamma-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas and r…
The origin of the Galactic center diffuse X-ray emission (GCDX) is still under intense investigation. We have found a clear excess in a longitudinal GCDX profile over a stellar number density profile in the nuclear bulge region, suggesting a significant contribution of diffuse, interstellar hot plasma to the GCDX. We have estimated that contributions of an old stellar population to the GCDX are about 50 % and 20 % in the nuclear stellar disk and nuclear star cluster, respectively. Our near-infrared polarimetric observations show that the GCDX region is permeated by a large scale, toroidal magn…
It has been indicated that low-luminosity active galactic nuclei (LLAGNs) are accelerating high-energy cosmic-ray (CR) protons in their radiatively inefficient accretion flows (RIAFs). If this is the case, Sagittarius A* (Sgr A*) should also be generating CR protons, because Sgr A* is a LLAGN. Based on this scenario, we calculate a production rate of CR protons in Sgr A* and their diffusion in the central molecular zone (CMZ) around Sgr A*. The CR protons diffusing in the CMZ create gamma-rays through pp interaction. We show that the gamma-ray luminosity and spectrum are consistent with observ…
We have used Voyager and Galex observations to map the diffuse Galactic light near the Galactic equator. We find that most of the observations are relatively faint with surface brightnesses of less than 5,000 photon units. This is important because many ultraviolet telescopes have not observed at low Galactic latitudes because of the fear of a bright diffuse emission. Our data are consistent with emission from interstellar dust grains with albedo ($a$) of 0.2 -- 0.3 and phase function ($g$) $ < 0.7$ at 1100 Å; $0.2 < a < 0.5; g < 0.8$ at 1500 Å; and $0.4 < a < 0.6; g < 0.4$ at 2300 Å.
I report on progress in my ongoing work with Professor Jayant Murthy concerning the origin and nature of the diffuse ultraviolet background radiation over the sky. We have obtained and are reducing a vast trove of Voyager ultraviolet spectrometer observations of the diffuse background shortward of Lyman alpha, including for the first time measurements made from the outermost regions of the solar system, where noise from solar-system scattered (and then grating-scattered) solar Lyman alpha is lowest. Also, we have obtained and are investigating the complete set of GALEX observations of the diff…
The spectrum of any star viewed through a sufficient quantity of diffuse interstellar material reveals a number of absorption features collectively called diffuse interstellar bands (DIBs). The first DIBs were reported 90 years ago, and currently well over 500 are known. None of them has been convincingly identified with any specific element or molecule, although recent studies suggest that the DIB carriers are polyatomic molecules containing carbon. Most of the DIBs currently known are at visible and very near-infrared wavelengths, with only two previously known at wavelengths beyond one micr…
Can galactic magnetic fields diffuse into the voids?
Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University（斯德哥尔摩大学）；Nordita, KTH Royal Institute of Technology and Stockholm University（诺迪塔；皇家理工学院和斯德哥尔摩大学）；McWilliams Center for Cosmology & Department of Physics, Carnegie Mellon University（卡内基梅隆大学）；School of Natural Sciences and Medicine, Ilia State University（伊利亚国立大学）；Theoretical Physics Department, CERN（欧洲核子研究中心）；Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève（日内瓦大学）；Université Paris Cité, CNRS, Astroparticule et Cosmologie（巴黎西岱大学）；Laboratory of Astrophysics, École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院）；Dipartimento di Fisica e Astronomia, Universitá di Bologna（博洛尼亚大学）
The potential of diffuse Galactic Ridge neutrino measurements to constrain dark matter
Instituto de Fisica Teorica UAM-CSIC, Universidad Autonoma de Madrid（马德里自治大学理论物理研究所）；Departamento de Fisica Teorica, M-15, Universidad Autonoma de Madrid（马德里自治大学理论物理系）；Department of Information Technology, Escuela Politécnica Superior, Universidad San Pablo-CEU（圣巴勃罗ceu大学高等理工学院信息技术系）
We have used GALEX observations of the North and South Galactic poles to study the diffuse ultraviolet background at locations where the Galactic light is expected to be at a minimum. We find offsets of 230 -- 290 photon units in the FUV (1531 Å) and 480 -- 580 photon units in the NUV (2361 Å). Of this, approximately 120 photon units can be ascribed to dust scattered light and another 110 (190 in the NUV) photon units to extragalactic radiation. The remaining radiation is, as yet, unidentified and amounts to $120 -- 180$ photon units in the FUV and $300 -- 400$ photon units in the NUV. We find…
The Galactic gamma-ray diffuse emission is currently observed in the GeV-TeV energy range with unprecedented accuracy by the Fermi satellite. Understanding this component is crucial as it provides a background to many different signals such as extragalactic sources or annihilating dark matter. It is timely to reinvestigate how it is calculated and to assess the various uncertainties which are likely to affect the accuracy of the predictions. The Galactic gamma-ray diffuse emission is mostly produced above a few GeV by the interactions of cosmic ray primaries impinging on the interstellar mater…
We analyze the diffuse Fe I K-alpha line generated in the diffuse interstellar molecular hydrogen by primary photons or subrelativistic protons injected by Sagittarius (Sgr) A*. We showed that unlike emission from compact molecular clouds, this emission can be permanently observed in the directions of the Galactic center. We conclude that the diffuse emission of 6.4 keV line observed at present is probably due to Fe I K-alpha vacancy production by primary photons if the X-ray luminosity of Sgr A* was about Lx ~ 10^39-10^40 erg/s. In principle these data can also be described in the framework o…
We present an all sky map of the diffuse Galactic far ultraviolet (1344-1786 Angstroms) background using GALEX data, covering 65% of the sky with 11.79 arcmin square pixels. We investigate the dependence of the background on Galactic coordinates, finding that a standard cosecant model of intensity is not a valid fit. Furthermore, we compare our map to Galactic all sky maps of 100 micron emission, N_HI column, and H-alpha intensity. We measure a consistent low level FUV intensity at zero-points for other Galactic quantities, indicating a 300 CU non-scattered isotropic component to the diffuse F…
With the help of 3D AMR hydrodynamical simulations we aim at understanding G2's nature, recent evolution and fate in the coming years. By exploring the possible parameter space of the diffuse cloud scenario, we find that a starting point within the disc of young stars is favoured by the observations, which may hint at G2 being the result of stellar wind interactions.
Observational study on near-infrared (IR) scattering properties of interstellar dust grains has been limited due to its faintness. Using all-sky maps obtained from Diffuse Infrared Background Experiment (DIRBE), we investigate the scattering property from diffuse Galactic light (DGL) measurements at 1.25, 2.2, and 3.5 μm in addition to our recent analyses of diffuse near-IR emission (Sano et al. 2015; Sano et al. 2016). As a result, we first find that the intensity ratios of near-IR DGL to 100 μm emission increase toward low Galactic latitudes at 1.25 and 2.2 μm. The derived latitude dependenc…
Search for Diffuse Galactic Neutrinos with the Full ANTARES Telescope Dataset
Université de Strasbourg（斯特拉斯堡大学）；CNRS（法国国家科学研究中心）；Université de Haute Alsace（上阿尔萨斯大学）；IFIC - Instituto de Física Corpuscular (CSIC - Universitat de València)（IFIC-粒子物理研究所（瓦伦西亚大学-西班牙高等科学研究委员会））；Technical University of Catalonia（加泰罗尼亚理工大学）；Institut d’Investigació per a la Gestió Integrada de les Zones Costaneres (IGIC) - Universitat Politècnica de València（海岸综合管理研究所(IGIC)-巴伦西亚理工大学）；Aix Marseille Univ（艾克斯-马赛大学）；CNRS/IN2P3；CPPM；Université Paris Cité（巴黎西岱大学）；Astroparticule et Cosmologie（天体粒子与宇宙学）；CNES（法国国家空间研究中心）；LAM；National Center for Energy Sciences and Nuclear Techniques（国家能源科学与核技术研究中心）；INFN - Sezione di Bologna（意大利国家核物理研究所-博洛尼组分所）；Dipartimento di Fisica e Astronomia dell’Università di Bologna（博洛尼亚大学物理与天文系）
We first obtained the spectrum of the diffuse Galactic light (DGL) at general interstellar space in 1.8-5.3 um wavelength region with the low-resolution prism spectroscopy mode of the AKARI Infra-Red Camera (IRC) NIR channel. The 3.3 um PAH band is detected in the DGL spectrum at Galactic latitude |b| < 15 deg, and its correlations with the Galactic dust and gas are confirmed. The correlation between the 3.3 um PAH band and the thermal emission from the Galactic dust is expressed not by a simple linear correlation but by a relation with extinction. Using this correlation, the spectral shape of…
Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray ionization rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H3+ observations to 50, with detections in 21 of those. Ionization rates inferred from these observations are in the range (1.7+-1.3)x10^-16 s^-1<zeta_2<(10.6+-8.2)x10^-16 s^-1 with a mean value of zeta_2=(3.5^+5.3_-3.0)x10^-16 s^-1. Upper limits (3 sigma) derived from non-detections o…
Radio recombination lines (RRLs) can be used to determine the emission measure unambiguously along the Galactic plane. We use the deep (2100s per beam) HI Parkes Zone of Avoidance survey which includes 3 RRLs (H$166α$, H$167α$ and H$168α$) within its bandwidth. The region $\ell = 36\degr$ to $44\degr$, $b = -4\degr$ to $+4\degr$ is chosen to include emission from the Local, Sagittarius and Scutum arms. An $8\degr \times 8\degr$ data cube centred at $(\ell, b) = (40\degr, 0\degr)$ is constructed of RRL spectra with velocity and spatial resolution of 27$\kms$ and 15.5 arcmin, respectively. Well-…
We determine the source of the diffuse [CII] emission by studying its spatial (radial and vertical) distributions. We used the HIFI [CII] Galactic survey (GOT C+), along with HI, 12CO, and 13CO data toward 354 lines of sight, and several HIFI [CII] and [CI] position-velocity maps. We quantified the emission in each spectral line profile by evaluating the intensities in 3 km/s wide velocity bins, 'spaxels'. Using the detection of [CII] with CO or [CI], we separated the dense and diffuse gas components. We derived 2-D Galactic disk maps using the spaxel velocities for kinematic distances. We sep…
Absorption lines from the molecules OH+, H2O+, and H3+ have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH+ and H2O+ are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray ionization rate of atomic hydrogen. H3+ is used to infer the cosmic-ray ionization rate of H2 in the molecular interior of the cloud, which we find to be zeta_2=(4.8+-3.4)x10^-16 per second. Combining the res…
We report the discovery of diffuse far-infrared and far-ultraviolet emission projected near the interacting pair NGC4435/4438, in the Virgo cluster. This feature spatially coincides with a well known low surface-brightness optical plume, usually interpreted as tidal debris. If extragalactic, this stream would represent not only one of the clearest examples of intracluster dust, but also a rare case of intracluster molecular hydrogen and large-scale intracluster star formation. However, the ultraviolet, far-infrared, HI and CO emission as well as the dynamics of this feature are extremely unusu…
The excess of neutrino candidate events detected by IceCube from the direction of TXS 0506+056 has generated a great deal of interest in blazars as sources of high-energy neutrinos. In this study, we analyze the publicly available portion of the IceCube dataset, performing searches for neutrino point sources in spatial coincidence with the blazars and other active galactic nuclei contained in the Fermi 3LAC and the Roma BZCAT catalogs, as well as in spatial and temporal coincidence with flaring sources identified in the Fermi Collaboration's All-Sky Variability Analysis (FAVA). We find no evid…
Understanding the effects of dust extinction is important to properly interpret observations. The optical total-to-selective extinction ratio, Rv = Av/E(B-V), is widely used to describe extinction variations in ultraviolet and optical bands. Since the Rv=3.1 extinction curve adequately represents the average extinction law of diffuse regions in the Milky Way, it is commonly used to correct observational measurements along sightlines toward diffuse regions in the interstellar medium. However, the Rv value may vary even along different diffuse interstellar medium sightlines. In this paper, we in…
Using the Archeops and WMAP data we perform a study of the anti-center Galactic diffuse emissions - thermal dust, synchrotron, free-free and anomalous emission - at degree scales. The high frequency data are used to infer the thermal dust electromagnetic spectrum and spatial distribution allowing us to precisely subtract this component at lower frequencies. After subtraction of the thermal dust component a mixture of standard synchrotron and free-free emissions does not account for the residuals at these low frequencies. Including the all-sky 408 MHz Haslam data we find evidences for anomalous…
Near-infrared (IR) diffuse Galactic light (DGL) consists of scattered light and thermal emission from interstellar dust grains illuminated by interstellar radiation field (ISRF). At 1.25 and 2.2um, recent observational study shows that intensity ratios of the DGL to interstellar 100um dust emission steeply decrease toward high Galactic latitudes (b). In this paper, we investigate origin(s) of the b-dependence on the basis of models of thermal emission and scattered light. Combining a thermal emission model with regional variation of the polycyclic aromatic hydrocarbon abundance observed with P…
