The galaxies M82, NGC 253, NGC 1068, and NGC 4945 have been detected in gamma-rays by Fermi. Previously, we developed and tested a model for cosmic ray interactions in the starburst galaxy M82. Now, we aim to explore the differences between starburst
and active galactic nuclei (AGN) environments by applying our self-consistent model to the starburst galaxy NGC 253 and the Seyfert galaxy NGC 1068. Assuming constant cosmic-ray acceleration efficiency by supernova remnants with Milky-Way parameters, we calculate the cosmic-ray proton and primary and secondary electron/positron populations, predict the radio and gamma-ray spectra, and compare with published measurements. We find that our models easily fits the observed gamma-ray spectrum for NGC 253 while constraining the cosmic ray source spectral index and acceleration efficiency. However, we encountered difficultly modeling the observed radio data and constraining the speed of the galactic wind and the magnetic field strength, unless the gas mass is less than currently preferred values. Additionally, our starburst model consistently underestimates the observed gamma-ray flux and overestimates the radio flux for NGC 1068; these issues would be resolved if the AGN is the primary source of gamma-rays. We discuss the implications of these results and make predictions for the neutrino fluxes for both galaxies.
We construct a family of models for the evolution of energetic particles in the starburst galaxy M82 and compare them to observations to test the calorimeter assumption that all cosmic ray energy is radiated in the starburst region. Assuming constant
cosmic ray acceleration efficiency with Milky Way parameters, we calculate the cosmic-ray proton and primary and secondary electron/positron populations as a function of energy. Cosmic rays are injected with Galactic energy distributions and electron-to-proton ratio via type II supernovae at the observed rate of 0.07/yr. From the cosmic ray spectra, we predict the radio synchrotron and gamma-ray spectra. To more accurately model the radio spectrum, we incorporate a multiphase interstellar medium in the starburst region of M82. Our model interstellar medium is highly fragmented with compact dense molecular clouds and dense photoionized gas, both embedded in a hot, low density medium in overall pressure equilibrium. The spectra predicted by this one-zone model are compared to the observed radio and gamma-ray spectra of M82. Chi-squared tests are used with radio and gamma-ray observations and a range of model predictions to find the best-fit parameters. The best-fit model yields constraints on key parameters in the starburst zone of M82, including a magnetic field strength of ~250 mu G and a wind advection speed in the range of 300-700 km/s. We find that M82 is a good electron calorimeter but not an ideal cosmic-ray proton calorimeter and discuss the implications of our results for the astrophysics of the far infrared-radio correlation in starburst galaxies.
We present deep WIYN H_alpha SparsePak and DensePak spatially-resolved optical spectroscopy of the dwarf irregular starburst galaxy NGC 1140. The different spatial resolutions and coverage of the two sets of observations have allowed us to investigat
e the properties and kinematics of the warm ionized gas within both the central regions of the galaxy and the inner halo. We find that the position angle of the H_alpha rotation axis for the main body of the galaxy is consistent with the HI rotation axis at PA = 39 deg, but that the ionized gas in the central 20x20 arcsecs (~2x2 kpc) is kinematically decoupled from the rest of the system, and rotates at a PA approximately perpendicular to that of the main body of the galaxy at +40 deg. We find no evidence of coherent large-scale galactic outflows. Instead multiple narrow emission line components seen within a radius of ~1-1.5 kpc, and high [SII]/H_alpha ratios found beyond ~2 kpc implying a strong contribution from shocks, suggest that the intense star formation is driving material outwards from the main star forming zone in the form of a series of interacting superbubbles/shells. A broad component (100<FWHM<230 km/s) to the H_alpha line is identified throughout galaxy disk out to >2 kpc. Based on recent work, we conclude that it is produced in turbulent mixing layers on the surfaces of cool gas knots embedded within the ISM, set up by the feedback from young massive star clusters. Our data suggest a physical limit to the radius where the broad emission line component is significant, and we propose that this limit marks a significant transition point in the development of the galactic outflow, where turbulent motion becomes less dominant. This mirrors what has recently been found in another similar irregular starburst galaxy NGC 1569.
Like other starburst galaxies, M82 hosts compact, massive young star clusters that are interesting both in their own right and as benchmarks for population synthesis models. Can spectral synthesis models at resolutions around 1000 adequately reproduc
e the near-IR spectral features and the energy distribution of these clusters between 0.8 and 2.4 microns? How do the derived cluster properties compare with previous results from optical studies? We analyse the spectra of 5 massive clusters in M82, using data acquired with the spectrograph SpeX on the InfraRed Telescope Facility (NASA/IRTF) and a new population synthesis tool with a highly improved near-IR extension, based on a recent collection of empirical and theoretical spectra of red supergiant stars. We obtain excellent fits across the near-IR with models at quasi-solar metallicity and a solar neighbourhood extinction law. Spectroscopy breaks a strong degeneracy between age and extinction in the near-IR colours in the red supergiant-dominated phase of evolution. The estimated near-IR ages cluster between 9 and 30 Myr, i.e. the ages at which the molecular bands due to luminous red supergiants are strongest in the current models. They do not always agree with optical spectroscopic ages. Adding optical data sometimes leads to the rejection of the solar neighbourhood extinction law. This is not surprising considering small-scale structure around the clusters, but it has no significant effect on the near-IR based spectroscopic ages. [abridged]
