Thermal and nonthermal infrared emission from M87

We discuss images of M87 from 3.6 to 160 μm obtained with Spitzer. As found previously, there is an excess in the far-infrared over a simple power-law interpolation from the radio to the resolved nonthermal features in the midinfrared and optical. We show that this excess is most likely due to warm dust in the galaxy itself and that the properties of this emission component are similar to the far-infrared emission of normal giant elliptical galaxies. The new observations allow us to determine the spectrum of the jet and surrounding lobes of nonthermal emission. We find that even in the lobes, the synchrotron break frequency is in the optical, probably requiring in situ particle acceleration not only in the jet but in the lobes as well.