Pre-peak ram pressure stripping in the Virgo cluster spiral galaxy NGC 4501

TL;DR

This study presents multi-wavelength observations of NGC 4501 in the Virgo cluster, revealing early-stage ram pressure stripping effects, including gas truncation and compression, consistent with dynamical simulations.

Contribution

It provides detailed observational evidence and analysis of pre-peak ram pressure stripping in a large spiral galaxy, supported by comparison with dynamical models.

Findings

Gas disk is sharply truncated within the stellar disk.

A low surface-density gas region extends northeast of the galaxy.

Ram pressure stripping explains observed gas and polarization features.

Abstract

VIVA HI observations of the Virgo spiral galaxy NGC 4501 are presented. The HI disk is sharply truncated to the southwest, well within the stellar disk. A region of low surface-density gas, which is more extended than the main HI disk, is discovered northeast of the galaxy center. These data are compared to existing 6cm polarized radio continuum emission, Halpha, and optical broad band images. We observe a coincidence between the western HI and polarized emission edges, on the one hand, and a faint Halpha emission ridge, on the other. The polarized emission maxima are located within the gaps between the spiral arms and the faint Halpha ridge. Based on the comparison of these observations with a sample of dynamical simulations with different values for maximum ram pressure and different inclination angles between the disk and the orbital plane,we conclude that ram pressure stripping can account for the main observed characteristics. NGC 4501 is stripped nearly edge-on, is heading southwest, and is ~200-300 Myr before peak ram pressure, i.e. its closest approach to M87. The southwestern ridge of enhanced gas surface density and enhanced polarized radio-continuum emission is due to ram pressure compression. It is argued that the faint western Halpha emission ridge is induced by nearly edge-on ram pressure stripping. NGC 4501 represents an especially clear example of early stage ram pressure stripping of a large cluster-spiral galaxy.