Kinematics and excitation of the ram pressure stripped ionized gas filaments in the Coma cluster of galaxies

TL;DR

This study investigates the extended ionized gas filaments around galaxies in the Coma cluster, revealing their kinematics, morphology, and star formation activity, consistent with ram pressure stripping effects.

Contribution

It provides detailed observational evidence of ram pressure stripping and star formation in ionized gas filaments in the Coma cluster, supported by spectroscopic and imaging data.

Findings

Radial velocities increase with distance from galaxies, reaching -400 to -800 km/s.

Star formation occurs in knots with high H-alpha equivalent widths.

Shock-like emission spectra indicate shock heating influences ionization.

Abstract

We present the results of deep imaging and spectroscopic observations of very extended ionized gas (EIG) around four member galaxies of the Coma cluster of galaxies: RB199, IC4040, GMP2923 and GMP3071. The EIGs were serendipitously found in an H-alpha narrow band imaging survey of the central region of the Coma cluster. The relative radial velocities of the EIGs with respect to the systemic velocities of the parent galaxies from which they emanate increase almost monotonically with the distance from the nucleus of the respective galaxies, reaching -400 - -800 km/s at around 40 - 80 kpc from the galaxies. The one-sided morphologies and the velocity fields of the EIGs are consistent with the predictions of numerical simulations of ram pressure stripping. We found a very low-velocity filament (v_rel = -1300 km/s) at the southeastern edge of the disk of IC4040. Some bright compact knots in the EIGs of RB199 and IC4040 exhibit blue continuum and strong H-alpha emission. The equivalent widths of the H-alpha emission exceed 200 A, and are greater than 1000 A for some knots. The emission line intensity ratios of the knots are basically consistent with those of sub-solar abundance HII regions. These facts indicate that intensive star formation occurs in the knots. Some filaments, including the low velocity filament of the IC4040 EIG, exhibit shock-like emission line spectra, suggesting that shock heating plays an important role in ionization and excitation of the EIGs.