The influence of a galaxy's environment on its evolution has been studied and compared extensively in the literature, although differing techniques are often used to define environment. Most methods fall into two broad groups: those that use nearest neighbours to probe the underlying density field and those that use fixed apertures. The differences between the two inhibit a clean comparison between analyses and leave open the possibility that, even with the same data, different properties are actually being measured. In this work, we apply 20 published environment definitions to a common mock galaxy catalogue constrained to look like the local Universe. We find that nearest-neighbour-based measures best probe the internal densities of high-mass haloes, while at low masses the interhalo separation dominates and acts to smooth out local density variations. The resulting correlation also shows that nearest-neighbour galaxy environment is largely independent of dark matter halo mass. Conversely, aperture-based methods that probe superhalo scales accurately identify high-density regions corresponding to high-mass haloes. Both methods show how galaxies in dense environments tend to be redder, with the exception of the largest apertures, but these are the strongest at recovering the background dark matter environment. We also warn against using photometric redshifts to define environment in all but the densest regions. When considering environment, there are two regimes: the 'local environment' internal to a halo best measured with nearest neighbour and 'large-scale environment' external to a halo best measured with apertures. This leads to the conclusion that there is no universal environment measure and the most suitable method depends on the scale being probed.
Carlyle first uses it in his essay Goethe to translate the master's original German Umgebung and to signify not merely surroundings or context (as it had been commonly used before) but rather the vital, ongoing influence of those surroundings upon a person or thing.1 As Ralph Jessop argues, this coinage arises from the “counter-Enlightenment” stance Carlyle took against the forces of mechanization and mechanical thinking: environment is an attempt to convey something of the holistic, “dialogical [and] open-textured” set of influences—physical, social, intellectual, spiritual—at work upon someone.2 We can thus see in it the stirrings of an interdependent, “green” sensibility, though always filtered through Carlyle's peculiar metaphysical division of “substance” from “semblance” and his quasi-reactionary politics. [...]the word ‘environment’ does metaphysical work.” The natural world and human civilization may both be considered “environments,” but in Spencer's system the latter is at a further stage of evolutionary “complexity,” and thus it functions as a stimulus to even more profound kinds of intellectual, moral, and social growth.6 And civilization, as Raymond Williams has shown, had not yet been relativized by the widespread adoption of its plural form: for Spencer, it means Western civilization.7 Thus, such developmentalist arguments reflect the way the concept “environment” was inflected by assumptions of racial and cultural superiority; indeed, as George Stocking notes, to be an “environmentalist” in Victorian anthropological circles was to believe in the profound shaping power of external forces upon human characteristics and capacities and, more often than not, to uphold the ascendancy of European culture on such grounds.8 Moreover, the complete continuity of nature and civilization also makes Spencer—at least in his early writings—famously wary of any “artificial” human intervention in economic and social processes.
By the 1970s, these Victorian practices of accumulation—fixed to physical limits, bound by established lines of connection—came to seem quaint against an emergent economic logic whereby petroleum traveled by tanker along variable routes, and in which the concept of growth itself had become unmoored from “spatial and material processes that had physical limits.” Baby boomers, caught as they were in the whirlwind of the Great Acceleration's money economy—which was, we might note, also the moment that established Victorian Studies as a discipline—thus succeeded in solidifying a notion of environment coextensive with something like “earth” or “nature” conceived as total system. Like the first Earth Day, the Environmental Protection Agency dates from 1970, when it was proposed as an entity able to manage items of legislation, like the Clean Air Act (1970) and the Clean Water Act (1972), directed at more particular earth systems. Devin Griffiths explains how Darwin imagined “a world of nonhuman intent and distributed sentience” that “effectively flattened the natural world, diffusing intentionality as an emergent property shared throughout nature” (Devin Griffiths, The Age of Analogy: Literature and Science Between the Darwins [ Baltimore: Johns Hopkins University Press, 2016 ], 238).