Recent studies have found a positive correlation between the star-formation rate of galaxies and their gamma-ray luminosity. Galaxies with a high star-formation rate are expected to produce a large amount of high-energy cosmic rays, which emit gamma-rays when interacting with the interstellar medium and radiation fields. We search for gamma-ray emission from a sample of galaxies within and beyond the Local Group with data from the LAT instrument onboard the Fermi satellite. We exclude recently detected galaxies (NGC 253, M82, NGC 4945, NGC 1068, NGC 2146, Arp 220) and use seven years of cumulative Pass 8 data from the LAT in the 100 MeV to 100 GeV range. No new detections are seen in the data and upper limits for the gamma- ray fluxes are calculated. The correlation between gamma-ray luminosity and infrared luminosity for galaxies obtained using our new upper limits is in agreement with a previously published correlation, but the new upper limits imply that some galaxies are not as efficient gamma-ray emitters as previously thought.
The interaction between a supernova ejecta and the circum-stellar medium drives a strong shock wave which accelerates particles (i.e., electrons and protons). The radio and X-ray emission observed after the supernova explosion constitutes the evidence of the electron acceleration. The accelerated protons are expected to produce GeV-TeV gamma-ray emission via $pp$ collisions, but the flux is usually low since only a small fraction of the supernova kinetic energy is converted into the shock energy at the very early time. The low gamma-ray flux of the nearest supernova explosion, SN 1987A, agrees…
Cosmic ray accelerators like supernova and hypernova remnants in star forming galaxies are one of the most plausible sources of the IceCube observed diffuse astrophysical neutrinos. The neutrino producing hadronic processes will also produce a diffuse gamma ray flux, constrained by the Fermi-LAT bounds. The fact that point sources like blazars also contribute to the diffuse gamma ray flux implies large gamma opacity of the neutrino sources. Indeed, for these high redshift star forming galaxies the gamma absorption during the intergalactic propagation can be significant. In addition, large gamm…
Probing the $γ$-ray Emission Origin of Two Star-forming Galaxies NGC 2403 and NGC 3424 with the Fermi-LAT
Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；University of the Chinese Academy of Sciences（中国科学院大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；TIANFU Cosmic Ray Research Center（天府宇宙线研究中心）；IRAP, Université de Toulouse, CNRS, UPS, CNES（图卢兹大学IRAP研究所）
We present a new theoretical modeling to predict luminosity and spectrum of gamma-ray and neutrino emission of a star-forming galaxy, from star formation rate ($ψ$), gas mass ($M_{\rm gas}$), stellar mass, and disk size, taking into account production, propagation and interactions of cosmic rays. The model reproduces the observed gamma-ray luminosities of nearby galaxies detected by {\it Fermi} better than the simple power-law models as a function of $ψ$ or $ψM_{\rm gas}$. Then this model is used to predict the cosmic background flux of gamma-ray and neutrinos from star-forming galaxies, by us…
In this work, we reanalyzed 11 years of spectral data from the \textit{Fermi} Large Area Telescope (\textit{Fermi}-LAT) of currently observed starburst galaxies (SBGs) and star-forming galaxies (SFGs). We used a one-zone model provided by \textbf{NAIMA} and the hadronic origin to explain the GeV observation data of the SBGs and SFGs. We found that a protonic distribution of a power-law form with an exponential cutoff can explain the spectra of most SBGs and SFGs. However, it cannot explain the spectral hardening components of NGC 1068 and NGC 4945 in the GeV energy band. Therefore, we consider…
We report the detection of high-energy gamma-ray signal towards the young star-forming region, W40. Using 10-year Pass 8 data from the Fermi Large Area Telescope (Fermi-LAT), we extracted an extended gamma-ray excess region with a significance of about 18sigma. The radiation has a spectrum with a photon index of 2.49 +/- 0.01. The spatial correlation with the ionized gas content favors the hadronic origin of the gamma-ray emission. The total cosmic-ray (CR) proton energy in the gamma-ray production region is estimated to be the order of 10^47 erg. However, this could be a small fraction of the…
We report the Fermi Large Area Telescope (Fermi-LAT) detection of the $γ$-ray emission toward the massive star forming region of Carina Nebula Complex (CNC). Using the latest source catalog and diffuse background models, we found that the GeV $γ$-ray emission in this region can be resolved into three different components. The GeV $γ$-ray emission from the central point source is considered to originate from the Eta Carina ($η$ Car). We further found the diffuse GeV $γ$-ray emission around the CNC which can be modelled by two Gaussian disks with radii of 0.4°(region A) and 0.75°(region B), resp…
GeV γ-ray emission in the low-mass star-forming region AFGL 490
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area, Sun Yat-Sen University（中山大学粤港澳大湾区宇宙线科学中心）
We present a detailed study of the gamma-ray emission from the direction of the star-forming region W30 based on a decade of the Fermi Large Area Telescope data in the 0.3-300 GeV photon energy range. The morphological and spectral analyses allow us to resolve the gamma-ray emission into two extended structures from different origins. One of them mostly overlaps with the supernova remnant (SNR) G8.7-0.1 and has a soft spectrum that resembles with the spectra of other middle-aged SNRs interacting with molecular clouds. The other shows remarkable spatial and spectral consistency with the TeV emi…
The origin of Galactic cosmic rays remains unconfirmed, but promising candidates for their sources are found in star-forming regions. We report a series of X-ray observations, with Suzaku, toward the nearby star-forming region of Cygnus X. They aim at comparing diffuse X-ray emissions on and off the $γ$-ray cocoon of hard cosmic rays revealed by Fermi LAT. After excluding point sources and small-scale structures and subtracting the non-X-ray and cosmic X-ray backgrounds, the 2--10~keV X-ray intensity distribution is found to monotonically decrease with increasing Galactic latitude. This indica…
The origin of the Isotropic Diffuse $γ$-Ray Background (IGRB) is one of the most intriguing mystery in astrophysics. Recently the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope has measured the IGRB spectrum from 100 MeV to 820 GeV. Thousands of extragalactic sources are detected at $γ$-ray energies and, thanks to Fermi-LAT catalogs and to population studies, we show that the IGRB can be explained, in the entire energy range, by the $γ$-ray emission from unresolved misaligned Active Galactic Nuclei, blazars and Star Forming Galaxies. Finally we derive, with a dedicated…
Star-forming galaxies have been predicted to contribute considerably to the diffuse gamma-ray background as they are guaranteed reservoirs of cosmic rays. Assuming that the hadronic interactions responsible for high-energy gamma rays also produce high-energy neutrinos and that O(100) PeV cosmic rays can be produced and confined in starburst galaxies, we here discuss the possibility that star-forming galaxies are also the main sources of the high-energy neutrinos observed by the IceCube experiment. First, we compute the diffuse gamma-ray background from star-forming galaxies, adopting the lates…
More than 30 % of $γ$-ray sources detected in the last source catalog of the Fermi satellite have no observational counterpart at other frequencies. A significant fraction of these sources is positionally in agreement with star-forming regions dominated by associations of T Tauri stars. Rho Ophiuchi, which is one of the closest star-forming regions, matches the unidentified Fermi source 4FGL J1625.3-2338. In this work we modeled the spectral energy distribution considering some dominant radiative processes in T Tauri stars. Accounting for a total of 22 Class III T Tauri stars in the region, in…
The Fermi Gamma-ray Space Telescope has revealed a diffuse $γ$-ray background at energies from 0.1 GeV to 1 TeV, which can be separated into Galactic emission and an isotropic, extragalactic component. Previous efforts to understand the latter have been hampered by the lack of physical models capable of predicting the $γ$-ray emission produced by the many candidate sources, primarily active galactic nuclei and star-forming galaxies, leaving their contributions poorly constrained. Here we present a calculation of the contribution of star-forming galaxies to the $γ$-ray background that does not …
Star-forming galaxies produce gamma-rays primarily via pion production, resulting from inelastic collisions between cosmic ray protons and the interstellar medium (ISM). The dense ISM and high star formation rates of luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs) imply that they should be strong gamma-ray emitters, but so far only two LIRGs have been detected. Theoretical models for their emission depend on the unknown fraction of cosmic ray protons that escape these galaxies before interacting. We analyze Fermi-LAT data for 82 of the brightest IRAS LIRGs and ULIRGs. We exami…
Star-forming and starburst galaxies, which are well-known cosmic-rays reservoirs, are expected to emit gamma-rays and neutrinos predominantly via hadronic collisions. In this Letter, we analyze the 10-year Fermi-LAT spectral energy distributions of 13 nearby galaxies by means of a physical model which accounts for high-energy proton transport in starburst nuclei and includes the contribution of primary and secondary electrons. In particular, we test the hypothesis that the observed gamma-ray fluxes are mostly due to star-forming activity, in agreement with the available star formation rates co…
Star-forming regions on different scales, such as giant molecular clouds in our Galaxy and star-forming galaxies, emit GeV gamma-rays. These are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. It has recently been shown that the gamma-ray luminosity ($L_γ$) of star-forming galaxies is well correlated with their star formation rates (SFR). We investigated \textsl{Fermi} data of eight Galactic molecular clouds in the Gould belt and found that molecular clouds do not follow the $L_γ-{\rm SFR}$ correlation of star-forming galaxies. We also co…
We derive the contribution to the extragalactic gamma-ray background (EGB) from AGN winds and star-forming galaxies by including a physical model for the gamma-ray emission produced by relativistic protons accelerated by AGN-driven and supernova-driven shocks into a state-of-the-art semi-analytic model of galaxy formation. This is based on galaxy interactions as triggers of AGN accretion and starburst activity and on expanding blast wave as the mechanism to communicate outwards the energy injected into the interstellar medium by the active nucleus. We compare the model predictions with the lat…
A majority of the $γ$-ray emission from star-forming galaxies is generated by the interaction of high-energy cosmic rays with the interstellar gas and radiation fields. Star-forming galaxies are expected to contribute to both the extragalactic $γ$-ray background and the IceCube astrophysical neutrino flux. Using roughly 10\,years of $γ$-ray data taken by the {\it Fermi} Large Area Telescope, in this study we constrain the $γ$-ray properties of star-forming galaxies. We report the detection of 11 bona-fide $γ$-ray emitting galaxies and 2 candidates. Moreover, we show that the cumulative $γ$-ray…
We present low frequency wide band observations (300-500 MHz) of the star forming complex G351.7-1.2 using upgraded Giant Metrewave Radio Telescope (uGMRT), India. Combining this with the optical, infrared and submillimeter data, we analyse the large scale diffuse radio emission associated with the region that exhibits a broken shell morphology. The spectral index of the emission in the shell is -0.8, indicating non-thermal emission. H-alpha emission that mimics the morphology of the radio shell on a smaller scale is also detected here. Based on the non-thermal emission from the radio shell an…
Despite the influx of unprecedented-quality data from the Fermi Gamma-Ray Space Telescope that have been collected over nine years of operation, the contribution of normal star-forming galaxies to the extragalactic gamma-ray background (EGRB) remains poorly constrained. Different estimates are discrepant both their underlying physical assumptions and their results. With several detections and many upper limits for the gamma-ray fluxes of nearby starforming galaxies now available, estimates that rely on empirical scalings between gamma-ray and longer-wavelength luminosities have become possible…
Fermi LAT detection of two high Galactic latitude gamma-ray sources, Fermi J1049.7+0435 and J1103.2+1145
第二个费米LAT源目录（Nolan et al. 2012）包括多达1，873个源，但最初尝试识别其他波长的对应物导致575个源仍然未被识别。2FGL目录是基于自2008年推出以来的前24个月LAT观测，但LAT现在已经积累了超过5年的高能伽马射线数据，几乎没有任何变化，这表明有可能找到新的来源，这些来源太微弱而无法在前两年的数据中检测到，或者在目录创建后显示出耀斑活动。在本文中，我们报告两个新的伽玛射线源偶然发现的星座狮子座和讨论可能的对应物的基础上无线电观测。
