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Register a new userThe GALEX Ultraviolet Virgo Cluster Survey (GUViCS) VIII. Diffuse dust in the Virgo intra-cluster space
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We present the first detection of diffuse dust in the intra-cluster medium of the Virgo cluster out to $sim$0.4 virial radii, and study the radial variation of its properties on a radial scale of the virial radius. Analysing near-UV - $i$ colours for a sample of $sim12000$ background galaxies with redshifts $0.02 < z < 0.8$, we find significant colour reddening and relate it to variation in $E(B-V)$ values. The $E(B-V)$ mean profile shows a dust component characterised by an average reddening $E(B-V)sim0.042 pm 0.004$ mag within 1.5 degrees ($sim0.3, r_{vir}$) from the cluster centre. Assuming a Large Magellanic Cloud extinction law, we derive an average visual extinction $A_{V} = 0.14pm 0.01$ for a total dust mass, $M_{d} = 2.5pm0.2times10^{9}M_{odot}$, hence a dust-to-gas mass ratio $M_{d}/M_{g} = 3.0pm 0.3 times 10^{-4}$. Based on the upper limits on the flux density $mathrm{I_{250mu m} = 0.1, MJy sr^{-1}} $ derived from $Herschel$ data, we estimate an upper limit for the dust temperature of $T_{d} sim 10, K$. However, similar densities can be obtained with dust at higher temperatures with lower emissivities. The Virgo cluster has diffuse dust in its intra-cluster medium characterised by different physical properties as those characterising the Milky Way dust. The diffuse dust in Virgo is transported into the cluster space through similar phenomena (stripping) as those building up the optical intra-cluster light, and it constitutes an additional cooling agent of the cluster gas.
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CONTEXT: The Virgo direction has been observed at many wavelengths in the recent years, in particular in the ultraviolet with GALEX. The far ultraviolet (FUV) diffuse light detected by GALEX bears interesting information on the large scale distribution of Galactic dust, owing to the GALEX FUV band sensitivity and resolution. AIMS: We aim to characterise the ultraviolet large scale distribution of diffuse emission in the Virgo direction. A map of this emission may become useful for various studies by identifying regions where dust affects observations by either scattering light or absorbing radiation. METHODS: We construct mosaics of the FUV and near ultraviolet diffuse emission over a large sky region (RA 12 to 13 hours, DEC 0 to 20 degrees) surrounding the Virgo cluster, using all the GALEX available data in the area. We test for the first time the utilisation of the FUV diffuse light as a Galactic extinction E(B-V) tracer. RESULTS: The FUV diffuse light scattered on cirrus reveals details in their geometry. Despite a large dispersion, the FUV diffuse light correlates roughly with other Galactic dust tracers (coming from IRAS, Herschel, Planck), offering an opportunity to use the FUV emission to locate them in future studies with a better resolution (about 5 arcsec native resolution, 20 arcsec pixels maps presented in this paper) than several usual tracers. Estimating the Galactic dust extinction on the basis of this emission allows us to find a smaller dispersion in the NUV-i colour of background galaxies at a given E(B-V)than with other tracers. The diffuse light mosaics obtained in this work are made publicly available.
We use the GALEX data of the GUViCS survey to construct the 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 type and NUV-i colour, 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 (alpha = -1.19), here sampled down to ~ NUV = -11.5 mag, is significantly flatter than the one measured in other nearby clusters and similar to the field one. Similarly M* = -17.56 is one-to-two magnitudes fainter than measured in Coma, A1367, the Shapley supercluster, and the field. These differences seem 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 notice, however, that the relative contribution of red-to-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. These observational evidences are discussed in the framework of galaxy evolution in dense environments.
We study the role of the environment on galaxy evolution using a sample of 868 galaxies in the Virgo cluster and in its surrounding regions selected from the GUViCS Survey with the purpose of understanding the origin of the red sequence in dense environments. We collected multifrequency data covering the whole electromagnetic spectrum for most of the galaxies. We identify the different dynamical substructures composing the Virgo cluster and we calculate the local density of galaxies using different methods. We then study the distribution of galaxies belonging to the red sequence, the green valley, and the blue cloud within the different cluster substructures. Our analysis indicates that all the most massive galaxies are slow rotators and are the dominant galaxies of the different cluster substructures generally associated with a diffuse X-ray emission. They are probably the result of major merging events that occurred at early epochs. Slow rotators of lower stellar mass are also preferentially located within the different high-density substructures of the cluster. They are virialised within the cluster, thus Virgo members since its formation. They have been shaped by gravitational perturbations occurring within the infalling groups that later formed the cluster. On the contrary, low-mass star-forming systems are extremely rare in the inner regions of the Virgo cluster A, where the density of the intergalactic medium is at its maximum. Our ram pressure stripping models consistently indicate that these star-forming systems can be rapidly deprived of their interstellar medium during their interaction with the intergalactic medium. The lack of gas quenches their star formation activity transforming them into quiescent dwarf ellipticals. This mild transformation does not perturb the kinematic properties of these galaxies which still have rotation curves typical of star-forming systems.
The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering about 40 sq. deg. in the far UV (FUV, lambda_eff=1539A, Delta-lambda=442A) and about 120 sq. deg. in the near UV (NUV, lambda_eff=2316A, Delta-lambda=1060A). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared - submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg. we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early- and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (alpha about -1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference
We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey, a large imaging survey covering Virgos primary subclusters to their virial radii. Using the g, (g-i) color-magnitude diagram of unresolved and marginally-resolved sources, we constructed 2-D maps of the GC distribution. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the extent of the cluster, where the red (metal-rich) GCs are largely located around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a more extended spatial distribution, with significant populations present beyond 83 (215 kpc) along the major axes of M49 and M87. The GC distribution around M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness of the diffuse light surrounding both galaxies. We find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to the locations of Virgo galaxies and the intracluster X-ray gas, and find good agreement between these baryonic structures. The Virgo cluster contains a total population of 67300$pm$14400 GCs, of which 35% are located in M87 and M49 alone. We compute a cluster-wide specific frequency S_N,CL=$2.8pm0.7$, including Virgos diffuse light. The GC-to-baryonic mass fraction is e_b=$5.7pm1.1times10^{-4} $and the GC-to-total cluster mass formation efficiency is e_t=$2.9pm0.5times10^{-5}$, values slightly lower than, but consistent with, those derived for individual galactic halos. Our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the diffuse intracluster light) is an ongoing process.(abridged)
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