Planck data when combined with ancillary data provide a unique opportunity to separate the diuse emission components of the inner Galaxy.The purpose of the paper is to elucidate the morphology of the various emission components in the strong star-formation region lying inside thesolar radius and to clarify the relationship between the various components. The region of the Galactic plane covered is l = 300 ! 0 ! 60where star-formation is highest and the emission is strong enough to make meaningful component separation. The latitude widths in this longituderange lie between 1 and 2, which correspond to FWHM z-widths of 100–200 pc at a typical distance of 6 kpc. The four emission componentsstudied here are synchrotron, free-free, anomalous microwave emission (AME), and thermal (vibrational) dust emission. These components areidentified by constructing spectral energy distributions (SEDs) at positions along the Galactic plane using the wide frequency coverage of Planck(28.4–857 GHz) in combination with low-frequency radio data at 0.408–2.3 GHz plus WMAP data at 23–94 GHz, along with far-infrared (FIR) datafrom COBE-DIRBE and IRAS. The free-free component is determined from radio recombination line (RRL) data. AME is found to be comparablein brightness to the free-free emission on the Galactic plane in the frequency range 20–40 GHz with a width in latitude similar to that of the thermaldust; it comprises 45 1% of the total 28.4 GHz emission in the longitude range l = 300 ! 0 ! 60. The free-free component is the narrowest,reflecting the fact that it is produced by current star-formation as traced by the narrow distribution of OB stars. It is the dominant emission on theplane between 60 and 100 GHz. RRLs from this ionized gas are used to assess its distance, leading to a free-free z-width of FWHM 100 pc. Thenarrow synchrotron component has a low-frequency brightness spectral index β synch ≈-2.7 that is similar to the broad synchrotron componentindicating that they are both populated by the cosmic ray electrons of the same spectral index. The width of this narrow synchrotron component issignificantly larger than that of the other three components, suggesting that it is generated in an assembly of older supernova remnants that haveexpanded to sizes of order 150 pc in 3 105 yr; pulsars of a similar age have a similar spread in latitude. The thermal dust is identified in the SEDswith average parameters of Tdust = 20:40:4 K, FIR = 1:940:03 (> 353 GHz), and β mm = 1:670:02 (< 353 GHz). The latitude distributions ofgamma-rays, CO, and the emission in high-frequency Planck bands have similar widths, showing that they are all indicators of the total gaseousmatter on the plane in the inner Galaxy.
- Galaxy: general
- ISM: general
- Radiation mechanisms: general
- Radio continuum: ISM
- Submillimeter: ISM