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Register a new userCLASH-VLT: Strangulation of cluster galaxies in MACSJ0416.1-2403 as seen from their chemical enrichment
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C. Maier
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(abridged) We explore the Frontier Fields cluster MACS J0416.1-2403 at z=0.3972 with VIMOS/VLT spectroscopy from the CLASH-VLT survey covering a region which corresponds to almost three virial radii. We measure fluxes of 5 emission lines of 76 cluster members enabling us to unambiguously derive O/H gas metallicities, and also SFRs from Halpha. For intermediate massses we find a similar distribution of cluster and field galaxies in the MZR and mass vs. sSFR diagrams. Bulge-dominated cluster galaxies have on average lower sSFRs and higher O/Hs compared to their disk-dominated counterparts. We use the location of galaxies in the projected velocity vs. position phase-space to separate our cluster sample into a region of objects accreted longer time ago and a region of recently accreted and infalling galaxies. We find a higher fraction of accreted metal-rich galaxies (63%) compared to the fraction of 28% of metal-rich galaxies in the infalling regions. Intermediate mass galaxies falling into the cluster for the first time are found to be in agreement with predictions of the fundamental metallicity relation. In contrast, for already accreted star-forming galaxies of similar masses, we find on average metallicities higher than predicted by the models. This trend is intensified for accreted cluster galaxies of the lowest mass bin, that display metallicities 2-3 times higher than predicted by models with primordial gas inflow. Environmental effects therefore strongly influence gas regulations and control gas metallicities of log(M/Msun)<10.2 (Salpeter IMF) cluster galaxies. We also investigate chemical evolutionary paths of model galaxies with and without inflow of gas showing that strangulation is needed to explain the higher metallicities of accreted cluster galaxies. Our results favor a strangulation scenario in which gas inflow stops for log(M/Msun)<10.2 galaxies when accreted by the cluster.
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We present VIMOS-VLT spectroscopy of the Frontier Fields cluster MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~2.2$r_{200}$ (~4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster ($M_{200}$~0.9$times 10^{15} M_{odot}$) presenting two major features: i) a bimodal velocity distribution, showing two central peaks separated by $Delta V_{rf}$~1100 km s$^{-1}$ with comparable galaxy content and velocity dispersion, ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low mass structure at z~0.390, ~10 S of the cluster center, projected at ~3Mpc, with a relative line-of-sight velocity of $Delta V_{rf}$~-1700 km s$^{-1}$. The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the universal NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal overall a complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in line with recent findings from radio and deep X-ray data. With this article we also release the entire redshift catalog of 4386 sources in the field of this cluster.
(Abridged) We explore the Frontier Fields cluster RXJ2248-443 at z~0.35 with VIMOS/VLT spectroscopy from CLASH-VLT, which covers a central region corresponding to almost 2 virial radii. The fluxes of [OII], Hbeta, [OIII], Halpha and [NII] emission lines were measured allowing the derivation of (O/H) gas metallicities, star formation rates based on extinction-corrected Halpha fluxes and active galactic nuclei (AGN) contamination. We compare our sample of cluster galaxies to a population of field galaxies at similar redshifts. We use the location of galaxies in projected phase-space to distinguish between cluster and field galaxies. Both populations follow the star-forming-sequence in the diagnostic diagrams, which allow disentangling between the ionising sources in a galaxy, with only few galaxies classified as Seyfert II. Both field and cluster galaxies follow the Main-Sequence of star forming galaxies, with no substantial difference observed between the two populations. In the Mass - Metallicity (MZ) plane, both high mass field and cluster galaxies show comparable (O/H)s to the local SDSS MZ relation, with an offset of low mass galaxies towards higher metallicities. While both the metallicities of accreted (R < R500) and infalling (R > R500) cluster members are comparable at all masses, the cluster galaxies from the intermediate, mass complete bin show more enhanced metallicities than their field counterparts. The intermediate mass field galaxies are in accordance with the expected (O/H)s from the Fundamental Metallicity relation, while the cluster members deviate strongly from the model predictions. The results of this work are in accordance with studies of other clusters at z < 0.5 and favour the scenario in which the hot halo gas of log(M/Msun)<10.2 cluster galaxies is removed due to mild ram pressure stripping, leading to an increase in their gas-phase metallicity.
Galaxy clusters have long been theorised to quench the star-formation of their members. This study uses integral-field unit observations from the $K$-band Multi-Object Spectrograph (KMOS) - Cluster Lensing And Supernova survey with Hubble (CLASH) survey (K-CLASH) to search for evidence of quenching in massive galaxy clusters at redshifts $0.3<z<0.6$. We first construct mass-matched samples of exclusively star-forming cluster and field galaxies, then investigate the spatial extent of their H$alpha$ emission and study their interstellar medium conditions using emission line ratios. The average ratio of H$alpha$ half-light radius to optical half-light radius ($r_{rm{e},rm{H}alpha}/r_{rm{e},R_c}$) for all galaxies is $1.14pm0.06$, showing that star formation is taking place throughout stellar discs at these redshifts. However, on average, cluster galaxies have a smaller $r_{rm{e},rm{H}alpha}/r_{rm{e},R_c}$ ratio than field galaxies: $langle r_{rm{e},rm{H}alpha}/r_{rm{e},R_c}rangle = 0.96pm0.09$ compared to $1.22pm0.08$ (smaller at a 98% credibility level). These values are uncorrected for the wavelength difference between H$alpha$ emission and $R_c$-band stellar light, but implementing such a correction only reinforces our results. We also show that whilst the cluster and field samples follow indistinguishable mass-metallicity (MZ) relations, the residuals around the MZ relation of cluster members correlate with cluster-centric distance; galaxies residing closer to the cluster centre tend to have enhanced metallicities (significant at the 2.6$sigma$ level). Finally, in contrast to previous studies, we find no significant differences in electron number density between the cluster and field galaxies. We use simple chemical evolution models to conclude that the effects of disc strangulation and ram-pressure stripping can quantitatively explain our observations.
Using the CLASH-VLT survey, we assembled an unprecedented sample of 1234 spectroscopically confirmed members in Abell~S1063, finding a dynamically complex structure at z_cl=0.3457 with a velocity dispersion sigma_v=1380 -32 +26 km s^-1. We investigate cluster environmental and dynamical effects by analysing the projected phase-space diagram and the orbits as a function of galaxy spectral properties. We classify cluster galaxies according to the presence and strength of the [OII] emission line, the strength of the H$delta$ absorption line, and colours. We investigate the relationship between the spectral classes of galaxies and their position in the projected phase-space diagram. We analyse separately red and blue galaxy orbits. By correlating the observed positions and velocities with the projected phase-space constructed from simulations, we constrain the accretion redshift of galaxies with different spectral types. Passive galaxies are mainly located in the virialised region, while emission-line galaxies are outside r_200, and are accreted later into the cluster. Emission-lines and post-starbursts show an asymmetric distribution in projected phase-space within r_200, with the first being prominent at Delta_v/sigma <~-1.5$, and the second at Delta_v/ sigma >~ 1.5, suggesting that backsplash galaxies lie at large positive velocities. We find that low-mass passive galaxies are accreted in the cluster before the high-mass ones. This suggests that we observe as passives only the low-mass galaxies accreted early in the cluster as blue galaxies, that had the time to quench their star formation. We also find that red galaxies move on more radial orbits than blue galaxies. This can be explained if infalling galaxies can remain blue moving on tangential orbits.
We analyzed global properties, radial profiles and 2D maps of the metal abundances and temperature in the cool core cluster of galaxies Hydra A using a deep XMM-Newton exposure. The best fit among the available spectral models is provided by a Gaussian distribution of the emission measure (gdem). We can accurately determine abundances for 7 elements in the cluster core with EPIC and 3 elements with RGS. The gdem model gives lower Fe abundances than a single temperature model. The abundance profiles for Fe, Si, S, but also O are centrally peaked. Combining the Hydra A results with 5 other clusters for which detailed chemical abundance studies are available, we find a significant decrease of O with radius, while the increase in the O/Fe ratio with radius is small within 0.1 r_200. We compare the observed abundance ratios with the mixing of various supernova type Ia and core-collapse yield models in different relative amounts. Producing the estimated O, Si and S peaks in Hydra A requires either an amount of metals ejected by stellar winds 3-8 times higher than predicted by available models or a remaining peak in the enrichment by core-collapse supernovae from the protocluster phase. The temperature map shows cooler gas extending in arm-like structures towards the north and south. These structures appear to be richer in metals than the ambient medium and spatially correlated with the large-scale radio lobes. We estimate the mass of cool gas, which was probably uplifted by buoyant bubbles of relativistic plasma produced by the AGN, to 1.6-6.1x10^9 M_sun, and the energy associated with this uplift to 3.3-12.5x10^58 ergs. The best estimate of the mass of Fe uplifted together with the cool gas is 1.7x10^7 M_sun, 15% of the total mass of Fe in the central 0.5arcmin region.
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