On the Nature of the NGC 1275 System

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Abstract
Subarcsecond images, taken in B, R, and Hα filters, and area spectroscopy obtained with the WIYN 3.5 m telescope provide the basis for an investigation of the unusual structures in the stellar body and ionized gas in and around the Perseus Cluster central galaxy NGC 1275. Our Hα filter is tuned to gas at the velocity of NGC 1275, revealing complex, probably unresolved, small-scale features in the extended ionized gas, located up to 50 h kpc from NGC 1275. The mean Hα surface brightness varies little along the outer filaments; this, together with the complex excitation state demonstrated by spectra, imply that the filaments are likely to be tubes, or ribbons, of gas. The morphology, location, and inferred physical parameters of the gas in the filaments are consistent with a model, whereby the filaments form through compression of the intracluster gas by relativistic plasma emitted from the active nucleus of NGC 1275. Imaging spectroscopy with the DensePak fiber array on WIYN suggests partial rotational support of the inner component of low-velocity ionized gas. Our broadband data is used to derive color maps of the stellar distribution and also to investigate asymmetries in the stellar surface brightness. We confirm and extend evidence for features in the stellar body of NGC 1275 and identify outer stellar regions containing very blue, probably very young, star clusters. We interpret these as evidence for recent accretion of a gas-rich system, with subsequent star formation. Other star clusters are identified, some of which are possibly associated with the high-velocity 8200 km s-1 emission-line system being in the same projected location. We suggest that two main processes, which may be causally connected, are responsible for the rich phenomenology of the NGC 1275 system—NGC 1275 experienced a recent merger and/or interaction with a group of gas-rich galaxies, and recent outflows from its AGN have compressed the intracluster gas and perhaps the gas in the infalling galaxies to produce a complex web of filaments.
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