Gas stripping in galaxy groups - the case of the starburst spiral NGC 2276

Abstract

Ram‐pressure stripping of galactic gas is generally assumed to be inefficient in galaxy groups due to the relatively low density of the intragroup medium (IGM) and the small velocity dispersions of groups. To test this assumption, we obtained Chandra X‐ray data of the starbursting spiral NGC 2276 in the NGC 2300 group of galaxies, a candidate for a strong galaxy interaction with hot intragroup gas. The data reveal a shock‐like feature along the western edge of the galaxy and a low surface brightness tail extending to the east, similar to the morphology seen in other wavebands. Spatially resolved spectroscopy shows that the data are consistent with intragroup gas being pressurized at the leading western edge of NGC 2276 due to the galaxy moving supersonically through the IGM at a velocity ∼850 km s−1. Detailed modelling of the gravitational potential of NGC 2276 shows that the resulting ram pressure could significantly affect the morphology of the outer gas disc but is probably insufficient to strip large amounts of cold gas from the disc. We estimate the mass‐loss rates due to turbulent viscous stripping and starburst outflows being swept back by ram pressure, showing that both mechanisms could plausibly explain the presence of the X‐ray tail. Comparison to existing H i measurements shows that most of the gas escaping the galaxy is in a hot phase. With a total mass‐loss rate of ∼5 M⊙ yr−1, the galaxy could be losing its entire present H i supply within a Gyr. This demonstrates that the removal of galactic gas through interactions with a hot IGM can occur rapidly enough to transform the morphology of galaxies in groups. Implications of this for galaxy evolution in groups and clusters are briefly discussed.

The SAMI Galaxy Survey: spatially resolving the environmental quenching of star formation in GAMA galaxies

“…Ram pressure stripping is commonly cited as a mechanism to remove gas from the edges of discs in group (Rasmussen, Ponman, & Mulchaey 2006) and cluster galaxies (Koopmann & Kenney 2004a,b). The removal of cold gas from a galaxy by this method is possible only if the velocity of the galaxy through the intergalactic medium is such that the ram pressure force exerted on the interstellar medium is sufficient to overcome the gravitational potential of the galaxy.…”

Metal distribution in sloshing galaxy clusters: the case of A496

“…Thermal conduction is the most efficient mechanism to erase temperature differences. In the Spitzer (Spitzer 1962) regime, thermal conduction operates on a timescale of t S ∼ k 2 n e /κ S ∼ 1.3 × 10 −2 n e,2 2 100 (T 10 ) −5/2 Gyr (1) (Markevitch et al 2003a;Rasmussen et al 2006), where k is the Boltzmann constant, κ S is the Spitzer heat conductivity, T 10 is the temperature in units of 10 keV, 100 the region width in units of 100 kpc, n e,2 the electron density n e in units of 2 × 10 −3 cm −3 . In our case, can vary from few kpc (the typical width of a cold front if we wish to estimate the timescale to erase discontinuities) to some tens of kpc if we wish to bring the whole spiral in thermal equilibrium.…”

Hot gas in Mach cones around Virgo cluster spiral galaxies

“…In particular, there is no detection of the leading bow shock of a cluster spiral galaxy in the literature to our knowledge. Rasmussen et al (2006) detected a shock-like feature in NGC 2276 which is part of the NGC 2300 group of galaxies. Since galaxies move with velocities between 1000 and 2000 km s −1 and the sound speed in the intracluster medium of the Virgo cluster is ∼500-700 km s −1 , a bow shock with an associated Mach cone is expected.…”