We present a multiwavelength morphological analysis of star forming clouds and filaments in the central ( \mathrel { < \kern - 10.0 pt \lower 3.87 pt \hbox { $ \sim$ } } 50 kpc ) regions of 16 low redshift ( z < 0.3 ) cool core brightest cluster galaxies ( BCGs ) .
The sample spans decades-wide ranges of X-ray mass deposition and star formation rates as well as active galactic nucleus ( AGN ) mechanical power , encompassing both high and low extremes of the supposed intracluster medium ( ICM ) cooling and AGN heating feedback cycle .
New Hubble Space Telescope ( HST ) imaging of far ultraviolet continuum emission from young ( \mathrel { < \kern - 10.0 pt \lower 3.87 pt \hbox { $ \sim$ } } 10 Myr ) , massive ( \mathrel { > \kern - 10.0 pt \lower 3.87 pt \hbox { $ \sim$ } } 5 M _ { \odot } ) stars reveals filamentary and clumpy morphologies , which we quantify by means of structural indices .
The FUV data are compared with X-ray , Ly \alpha , narrowband H \alpha , broadband optical/IR , and radio maps , providing a high spatial resolution atlas of star formation locales relative to the ambient hot ( \sim 10 ^ { 7 - 8 } K ) and warm ionised ( \sim 10 ^ { 4 } K ) gas phases , as well as the old stellar population and radio-bright AGN outflows .
Nearly half of the sample possesses kpc-scale filaments that , in projection , extend toward and around radio lobes and/or X-ray cavities .
These filaments may have been uplifted by the propagating jet or buoyant X-ray bubble , or may have formed in situ by cloud collapse at the interface of a radio lobe or rapid cooling in a cavity ’ s compressed shell .
Many other extended filaments , however , show no such spatial correlation , and the dominant driver of their morphology remains unclear .
We nevertheless show that the morphological diversity of nearly the entire FUV sample is reproduced by recent hydrodynamical simulations in which the AGN powers a self-regulating rain of thermally unstable star forming clouds that precipitate from the hot atmosphere .
In this model , precipitation triggers where the cooling-to- freefall time ratio is t _ { \mathrm { cool } } / t _ { \mathrm { ff } } \sim 10 .
This condition is roughly met at the maxmial projected FUV radius for more than half of our sample , and clustering about this ratio is stronger for sources with higher star formation rates .