TAILS OF IONISED GAS IN NGC 4569

Image: The colour image of the galaxy NGC 4569 in the Virgo cluster, obtained with MegaCam at the CFHT. The red filaments at the right of the galaxy show the ionised gas removed by ram pressure. This is about 95% of the gas reservoir of the galaxy needed to feed the formation of new stars  Credit: CFHT/Coelum

Messier 90 (also known as M90 and NGC 4569) is a member of the Virgo cluster and one of its largest and brightest spiral galaxies, about 60 million light-years away.

The environment plays a fundamental role in galaxy evolution. In fact, as a consequence of the galaxy's interaction with the intracluster medium in the Virgo Cluster, the galaxy NGC 4569 has lost much of its interstellar medium.

In the paper (Boselli et al. 2013, A&A) the authors analyze the image of NGC 4569 obtained with MegaCam at the CFHT and reveal the presence of a long tails of diffuse ionised gas without any associated stellar component extending from the disc of the galaxy up to ~ 80 kpc. This tail is referred to as ram-pressure stripping. The image also shows a prominent 8 kpc spur of ionised gas associated to the nucleus that spectroscopic data identify as an outflow.

Image: NGC 4569. Credit: NOAO/AURA/NSF.

The gas is ionised within the tail during the stripping process. The lack of star forming regions suggests that mechanisms other than photoionisation are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves).

This analysis indicates that ram pressure stripping is efficient in massive (M_star ~ 30 billion M_sun) galaxies located in intermediate mass (~10¹⁴ M_sun) clusters under formation.

The authors conclude that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism responsible for the quenching of the star formation activity of galaxies in high density environments.

• Boselli et al. 2013, A&A - Spectacular tails of ionised gas in the Virgo cluster galaxy NGC 4569 (arXiv)
• NGC 4569 - (cfht.hawaii.edu)(Wikipedia)