Gamma-Ray Emission from Galaxies Hosting Molecular Outflows

Abstract

Many star-forming galaxies and those hosting active galactic nuclei show evidence of massive outflows of material in a variety of phases including ionized, neutral atomic, and molecular. Molecular outflows in particular have been the focus of recent interest as they may be responsible for removing gas from the galaxy, thereby suppressing star formation. As material is ejected from the cores of galaxies, interactions of the outflowing material with the interstellar medium can accelerate cosmic rays and produce high-energy gamma rays. In this work, we search for gamma-ray emission from a sample of local galaxies known to host molecular outflows using data collected by the Fermi Large Area Telescope. We employ a stacking technique in order to search for and characterize the average gamma-ray emission properties of the sample. Gamma-ray emission is detected from the galaxies in our sample at the 4.4σ level with a power-law photon index of Γ ≈ 2 in the 1–800 GeV energy range. The emission is found to correlate with tracers of star formation activity, namely the 8–1000 μm infrared luminosity. We also find that the observed signal can be predominantly attributed to H ii galaxies hosting energy-driven outflows. While we do not find evidence suggesting that the outflows are accelerating charged particles directly, galaxies with molecular outflows may produce more gamma rays than galaxies without outflows. In particular, the set consisting of gamma-ray-detected galaxies with molecular outflows are nearly perfect calorimeters and may be future targets for searches of high-energy neutrinos.

Disentangling the Hadronic Components in NGC 1068

“…Assuming that the starburst region is nearly calorimetric (see, e.g., McDaniel et al 2023), we calculate the gamma-ray emission produced by cosmic rays via inelastic pp interactions with interstellar gas, adopting the method used in Murase (2022). The normalization of the starburst model is set by the L γ -L IR relation obtained by Ajello et al (2020), where = L log 10.97 10 IR 7 is used for NGC 1068 (Sanders et al 2003).…”

Constraining Annihilating Dark Matter Using the Multifrequency Radio Flux Profiles of the M33 Galaxy

“…However, our limits for the b, τ, and W channels are less stringent than those in gamma-ray analysis (H.E.S.S. Collaboration et al 2021;McDaniel et al 2023). Overall, analyzing the radio flux profile data with different frequencies can give good limits for leptophilic channels, especially for the μ channel.…”

Characterizing the γ-Ray Emission from FR0 Radio Galaxies

“…The two individually detected galaxies (SDSS J153016.15 +270551.0 and SDSS J162846.13+252940.9) can be best modeled with photon fluxes of 2.0 0.3 0.4 , and with a TS of 35 and 24, respectively, consistent with P21. To characterize the γ-ray emission from the subthreshold sample, we utilized a stacking analysis technique, which has been successfully implemented in a number of previous studies (Ackermann et al 2011;Abdollahi et al 2018;Paliya et al 2019;Ajello et al 2020bAjello et al , 2021McDaniel et al 2023). We find that the subthreshold sample can be best described with an average photon flux of -+ 7.94 3.96 4.64 × 10 −12 photons cm −2 s −1 , an average photon index of -+ 2.4 0.3 0.4 , with a detection significance of 3.99σ.…”