Diffuse far-infrared and ultraviolet emission in the NGC4435/4438 system: tidal stream or Galactic cirrus?

TL;DR

This study investigates diffuse infrared and ultraviolet emissions near NGC4435/4438, revealing that what appears as tidal debris is actually Galactic cirrus, highlighting the importance of accounting for cirrus contamination in low surface-brightness observations.

Contribution

It provides evidence that diffuse emissions previously attributed to tidal debris are actually Galactic cirrus, emphasizing the need to consider cirrus contamination in extragalactic studies.

Findings

Diffuse emissions are consistent with Galactic cirrus rather than tidal debris.

Strong spatial correlation between far-infrared and ultraviolet cirrus emission observed.

Galactic cirrus contamination can significantly bias low surface-brightness measurements.

Abstract

We report the discovery of diffuse far-infrared and far-ultraviolet emission projected near the interacting pair NGC4435/4438, in the Virgo cluster. This feature spatially coincides with a well known low surface-brightness optical plume, usually interpreted as tidal debris. If extragalactic, this stream would represent not only one of the clearest examples of intracluster dust, but also a rare case of intracluster molecular hydrogen and large-scale intracluster star formation. However, the ultraviolet, far-infrared, HI and CO emission as well as the dynamics of this feature are extremely unusual for tidal streams but are typical of Galactic cirrus clouds. In support to the cirrus scenario, we show that a strong spatial correlation between far-infrared and far-ultraviolet cirrus emission is observed across the center of the Virgo cluster, over a scale of several degrees. This study demonstrates how dramatic Galactic cirrus contamination can be, even at optical and ultraviolet wavelengths and at high galactic latitudes. If ignored, the presence of diffuse light scattered by Galactic dust clouds could significantly bias our interpretation of low surface-brightness features and diffuse light observed around galaxies and in clusters of galaxies.