75 Kiloparsec Trails of Ionized Gas behind Two Irregular Galaxies in A1367

Boissier

Voyer

et al. 2015

A&A

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We use the GALEX data of the GUViCS survey to construct the near-ultraviolet (NUV) luminosity function of the Virgo cluster over ∼300 deg 2 , an area covering the cluster and its surrounding regions up to ∼1.8 virial radii. The NUV luminosity function is also determined for galaxies of different morphological types and NUV − i colours, and for the different substructures within the cluster. These luminosity functions are robust vs. statistical corrections since based on a sample of 833 galaxies mainly identified as cluster members with spectroscopic redshift (808) or high-quality optical scaling relations (10). We fit these luminosity functions with a Schechter function, and compare the fitted parameters with those determined for other nearby clusters and for the field. The faint end slope of the Virgo NUV luminosity function (α = −1.19), here sampled down to ∼NUV = −11.5 mag, is significantly flatter than the value measured in other nearby clusters and similar to the field value. Similarly, M * = −17.56 is one to two magnitudes fainter than measured in Coma, A1367, the Shapley supercluster, and the field. These differences seem to be due to the quite uncertain statistical corrections and the small range in absolute magnitude sampled in these clusters. We do not observe strong systematic differences in the overall NUV luminosity function of the core of the cluster with respect to that of its periphery. We note, however, that the relative contribution of red and blue galaxies at the faint end is inverted, with red quiescent objects dominating the core of the cluster and star forming galaxies dominating beyond one virial radius. This observational evidence is discussed in the framework of galaxy evolution in dense environments.

Section: Figmentioning

confidence: 84%

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)

Boissier

Voyer

et al. 2015

A&A

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“…8), indicate small (a few kpc) low surface-brightness features that are perpendicular to the disc on the south east side of the galaxy or on the north suggesting a possible bridge with IC 3583. A minor gravitational interaction might also have contributed flattening the potential well of the two galaxies, weakening their gravitational binding forces, which keep the diffuse gas of the ISM anchored to the stellar disc, thus making ram pressure stripping more efficient (Gavazzi et al 2001). Further evidence of a ram pressure stripping event is the presence of a polarised radio ridge, southwest of the galaxy centre, which was probably produced by a local compression of the gas that was able to organise the magnetic field (Wezgowiec et al 2012).…”

Section: The Evolution Of Ngc 4569 In the Clustermentioning

confidence: 99%

“…Deep Hα imaging is used to search for long tails of ionized gas, the most direct evidence of an ongoing ram pressure stripping event (e.g. Gavazzi et al 2001). At the same time, the impact of feedback can be quantified by studying the properties of the ionized gas that is associated with the nuclear outflow.…”

Section: Introductionmentioning

confidence: 99%

Spectacular tails of ionized gas in the Virgo cluster galaxy NGC 4569

Cuillandre

Fossati

et al. 2016

A&A

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128

169

Using MegaCam at the CFHT, we obtained a deep narrow band Hα+ [NII] wide-field image of NGC 4569 (M90), the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of long tails of diffuse ionized gas, without any associated stellar component extending from the disc of the galaxy up to 80 kpc (projected distance) and with a typical surface brightness of a few 10 −18 erg s −1 cm −2 arcsec −2 . These features provide direct evidence that NGC 4569 is undergoing a ram-presure stripping event. The image also shows a prominent 8 kpc spur of ionized gas that is associated with the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Hα surface brightness of these extended low-surface brightness features to derive the density and the mass of the gas that has been stripped during the interaction of the galaxy with the intracluster medium. The comparison with ad hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Hα emitting gas in the tail is a large fraction of that of the cold phase that has been stripped from the disc, suggesting that the gas is ionized within the tail during the stripping process. The lack of star-forming regions suggests that mechanisms other than photoionization 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 10 10.5 M ) galaxies located in intermediate-mass ( 10 14 M ) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is only ∼1% than that removed during the ram pressure stripping event. Together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism that is responsible for the quenching of the star formation activity of galaxies in high density environments.Key words. galaxies: individual: NGC 4569 -galaxies: clusters: general -galaxies: clusters: individual: Virgo -galaxies: evolutiongalaxies: interactions -galaxies: ISM Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canadian-French-Hawaii Telescope (CFHT) which is operated by the

“…Multiphase hydrodynamical simulations indicate that gas ablation in all its phases (from diffuse atomic to dense molecular gas) can take place at all galactic radii if ram pressure stripping is sufficiently strong, as indeed is the case in rich clusters of galaxies such as Virgo (Tonnesen & Bryan 2009). There is also observational evidence indicating that ram pressure stripping is efficient up to the cluster virial radius (Scott et al 2012;Gavazzi et al 2001;Yagi et al 2010;Fossati et al 2012). It is thus reasonable to assume that ram pressure stripping can completely remove the gas of the ISM on timescales of 1.5 Gyr in galaxies within the virial radius 5 .…”

Section: Implications On the Star Formation History Of Cluster Galaxiesmentioning

confidence: 99%

Cold gas properties of theHerschelReference Survey

Cortese

Boquien

et al. 2014

A&A

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176

250

The Herschel Reference Survey is a complete volume-limited, K-band-selected sample of nearby objects including Virgo cluster and isolated objects. Using a recent compilation of Hi and CO data for this sample we study the effects of the cluster environment on the molecular gas content of spiral galaxies. With the subsample of unperturbed field galaxies, we first identify the stellar mass as the scaling variable that traces the total molecular gas mass of galaxies better. We show that, on average, Hi-deficient galaxies are significantly offset (4σ) from the M(H 2 ) vs. M star relation for Hi-normal galaxies. We use the M(H 2 ) vs. M star scaling relation to define the H 2 -deficiency parameter as the difference, on logarithmic scale, between the expected and observed molecular gas mass for a galaxy of given stellar mass. The H 2 -deficiency parameter shows a weak and scattered relation with the Hi-deficiency parameter, here taken as a proxy for galaxy interactions with the surrounding cluster environment. We also show that, as for the atomic gas, the extent of the molecular disc decreases with increasing Hi-deficiency. All together, these results show that cluster galaxies have, on average, a lower molecular gas content than similar objects in the field. Our analysis indicates that ram pressure stripping is the physical process responsible for this molecular gas deficiency. The slope of the H 2 − de f vs. Hi − de f relation is less than unity, while the D(Hi)/D(i) vs. Hi − de f relation is steeper than the D(CO)/D(i) vs. Hi − de f relation, thereby indicating that the molecular gas is removed less efficiently than the atomic gas. This result can be understood if the atomic gas is distributed on a relatively flat disc that is more extended than the stellar disc. It is thus less anchored to the gravitational potential well of the galaxy than the molecular gas phase, which is distributed on an exponential disc with a scalelength r CO 0.2r 24.5 (g). There is a clear trend between the NUV-i colour index, which is a proxy for the specific star formation activity, and the H 2 -deficiency parameter, which suggests that molecular gas removal quenches the activity of star formation. This causes galaxies migrate from the blue cloud to the green valley and, eventually, to the red sequence. The total gas-consumption timescale of gas deficient cluster galaxies is comparable to that of isolated, unperturbed systems. The total gas depletion timescale determined by considering the recycled fraction is τ gas,R 3.0−3.3 Gyr, which is significantly larger than the typical timescale for total gas removal in a ram pressure stripping process, indicated by recent hydrodynamical simulations to be τ RP 1.5 Gyr. The comparison of these timescales suggests that ram pressure, rather than a simple stop of the infall of pristine gas from the halo, will be the dominant process driving the future evolution of these cluster galaxies.