The spatially resolved PAH characteristics in the Whirlpool Galaxy (M51a)

ABSTRACT We present a detailed study on the spatially resolved polycyclic aromatic hydrocarbon (PAH) emission properties in (circum)nuclear region (NR) and extranuclear regions (ENRs) of M51a using Spitzer-IRS (infrared spectrograph) observations. Correlations among PAH intensity ratios are examined with respect to each other, local physical parameters, galactocentric distance (Rg), very small grain (VSG) emission. Additional comparison is performed mid-infrared features H ii M33 M83. The NR exhibits strongest correlation ratios, whereas ENRs showing increased scatter attributed interstellar medium Overall, radiation field hardness has higher impact than metallicity, latter regulating variance as function Rg. Specifically, different parameters suggests rate small/medium processing compared large PAHs ratio small-to-large formed increasing distance. find similarities between 7.7 $\mu$m carriers M51a’s M83’s regions, 8.6 both types ENRs, M33’s, regions. have identified positive PAH/VSG ratios. conclude that relative abundance VSG not solely driven by field.