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Register a new userGas filaments of the cosmic web located around active galaxies in a proto-cluster
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Cosmological simulations predict the Universe contains a network of intergalactic gas filaments, within which galaxies form and evolve. However, the faintness of any emission from these filaments has limited tests of this prediction. We report the detection of rest-frame ultraviolet Lyman-alpha radiation from multiple filaments extending more than one megaparsec between galaxies within the SSA 22 proto-cluster at a redshift of 3.1. Intense star formation and supermassive black-hole activity is occurring within the galaxies embedded in these structures, which are the likely sources of the elevated ionizing radiation powering the observed Lyman-alpha emission. Our observations map the gas in filamentary structures of the type thought to fuel the growth of galaxies and black holes in massive proto-clusters.
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Distant powerful radio-loud active galactic nuclei (RLAGN) tend to reside in dense environments and are commonly found in proto-clusters at z > 1.3. We examine whether this occurs because RLAGN are hosted by massive galaxies, which preferentially reside in rich environments. We compare the environments of powerful RLAGN at 1.3 < z < 3.2 from the CARLA survey to a sample of radio-quiet galaxies matched in mass and redshift. We find the environments of RLAGN are significantly denser than those of radio-quiet galaxies, implying that not more than 50% of massive galaxies in this epoch can host powerful radio-loud jets. This is not an observational selection effect as we find no evidence to suggest it is easier to observe the radio emission when the galaxy resides in a dense environment. We therefore suggest that the dense Mpc-scale environment fosters the formation of a radio-jet from an AGN. We show that the number density of potential RLAGN host galaxies is consistent with every > 10^14 solar mass cluster having experienced powerful radio-loud feedback of duration ~60 Myr during 1.3 < z < 3.2. This feedback could heat the intracluster medium to the extent of 0.5-1 keV per gas particle, which could limit the amount of gas available for further star formation in the proto-cluster galaxies.
We investigate the role of the environment in processing molecular gas in radio galaxies (RGs). We observed five RGs at $z=0.4-2.6$ in dense Mpc-scale environment with the IRAM-30m telescope. We set four upper-limits and report a tentative CO(7$rightarrow$6) detection for COSMOS-FRI 70 at $z=2.63$, which is the most distant brightest cluster galaxy (BCG) candidate detected in CO. We speculate that the cluster environment might have played a role in preventing the refueling via environmental mechanisms such as galaxy harassment, strangulation, ram-pressure, or tidal stripping. The RGs of this work are excellent targets for ALMA as well as next generation telescopes such as the James Webb Space Telescope.
We investigate whether the satellite luminosity function (LF) of primary galaxies identified in the Sloan Digital Sky Survey (SDSS) depends on whether the host galaxy is in a filament or not. Isolated primary galaxies are identified in the SDSS spectroscopic sample while potential satellites (that are up to 4 magnitudes fainter than their hosts) are searched for in the much deeper photometric sample. Filaments are constructed from the galaxy distribution by the Bisous process. Isolated primary galaxies are divided into two subsamples: those in filaments and those not in filaments. We examine the stacked mean satellite LF of both the filament and non-filament sample and find that, on average, the satellite LFs of galaxies in filaments is significantly higher than those of galaxies not in filaments. The filamentary environment can increases the abundance of the brightest satellites ($M_mathrm{sat.} < M_mathrm{prim.} + 2.0$), by a factor of $sim 2$ compared with non-filament isolated galaxies. This result is independent of primary galaxy magnitude although the satellite LF of galaxies in the faintest magnitude bin, is too noisy to determine if such a dependence exists. Since our filaments are extracted from a spectroscopic flux-limited sample, we consider the possibility that the difference in satellite LF is due to a redshift, colour or environmental bias, finding these to be insufficient to explain our result. The dependence of the satellite LF on the cosmic web suggests that the filamentary environment may have a strong effect on the efficiency of galaxy formation.
Galaxies have different morphology, gas content, and star formation rate (SFR) in dense environments like galaxy clusters. The impact of environmental density extends to several virial radii, and galaxies are pre-processed in filaments and groups, before falling into the cluster. Our goal is to quantify this pre-processing, in terms of gas content and SFR, as a function of density in cosmic filaments. We have observed the two first CO transitions in 163 galaxies with the IRAM-30m telescope, and added 82 measurements from the literature, for a sample of 245 galaxies in the filaments around Virgo. We gathered HI-21cm measurements from the literature, and observed 69 galaxies with the Nanc{c}ay telescope, to complete our sample. We compare our filament galaxies with comparable samples from the Virgo cluster and with the isolated galaxies of the AMIGA sample. We find a clear progression from field, to filament, and cluster galaxies for decreasing SFR, increasing fraction of galaxies in the quenching phase, increasing proportion of early-type galaxies and decreasing gas content. Galaxies in the quenching phase, defined as having SFR below 1/3 of the main sequence rate, are between 0-20% in the isolated sample, while they are 20-60% in the filaments and 30-80% in the Virgo cluster. Processes that lead to star formation quenching are already at play in filaments. They depend mostly on the local galaxy density, while the distance to filament spine is a secondary parameter. While the HI to stellar mass ratio decreases with local density by ~1 dex in the filaments, and ~2 dex in the Virgo cluster with respect to the field, the decrease is much less for the H$_2$ to stellar mass ratio. As the environmental density increases, the gas depletion time decreases, since the gas content decreases faster than the SFR. This suggests that gas depletion significantly precedes star formation quenching.
The strikingly anisotropic large-scale distribution of matter made of an extended network of voids delimited by sheets, themselves segmented by filaments, within which matter flows towards compact nodes where they intersect, imprints its geometry on the dynamics of cosmic flows, ultimately shaping the distribution of galaxies and the redshift evolution of their properties. The (filament-type) saddle points of this cosmic web provide a local frame in which to quantify the induced physical and morphological evolution of galaxies on large scales. The properties of virtual galaxies within the Horizon-AGN simulation are stacked in such a frame. The iso-contours of the galactic number density, mass, specific star formation rate (sSFR), kinematics and age are clearly aligned with the filament axis with steep gradients perpendicular to the filaments. A comparison to a simulation without feedback from active galactic nuclei (AGN) illustrates its impact on quenching star formation of centrals away from the saddles. The redshift evolution of the properties of galaxies and their age distribution are consistent with the geometry of the bulk flow within that frame. They compare well with expectations from constrained Gaussian random fields and the scaling with the mass of non-linearity, modulo the redshift dependent impact of feedback processes. Physical properties such as sSFR and kinematics seem not to depend only on mean halo mass and density: the residuals trace the geometry of the saddle, which could point to other environment-sensitive physical processes, such as spin advection, and AGN feedback at high mass.
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