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Register a new userEvidence for HI replenishment in massive galaxies through gas accretion from the cosmic web
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We examine the HI-to-stellar mass ratio (HI fraction) for galaxies near filament backbones within the nearby Universe ($d <$ 181 Mpc). This work uses the 6 degree Field Galaxy Survey and the Discrete Persistent Structures Extractor to define the filamentary structure of the local cosmic web. HI spectral stacking of HI Parkes all sky survey observations yields the HI fraction for filament galaxies and a field control sample. The HI fraction is measured for different stellar masses and fifth nearest neighbour projected densities ($Sigma_{5}$) to disentangle what influences cold gas in galaxies. For galaxies with stellar masses log($M_{star}$) $<$ 11 M$_{odot}$ in projected densities 0 $leq$ $Sigma_{5}$ $<$ 3 galaxies Mpc$^{-2}$, all HI fractions of galaxies near filaments are statistically indistinguishable from the control sample. Galaxies with stellar masses log($M_{star}$) $geq$ 11 M$_{odot}$ have a systematically higher HI fraction near filaments than the control sample. The greatest difference is 0.75 dex, which is 5.5$sigma$ difference at mean projected densities of 1.45 galaxies Mpc$^{-2}$. We suggest that this is evidence for massive galaxies accreting cold gas from the intrafilament medium that can replenish some HI gas. This supports cold mode accretion where filament galaxies with a large gravitational potential can draw gas from the large-scale structure.
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We present neutral hydrogen (HI) and ionized hydrogen (H${alpha}$) observations of ten galaxies out to a redshift of 0.1. The HI observations are from the first epoch (178 hours) of the COSMOS HI Large Extragalactic Survey (CHILES). Our sample is HI biased and consists of ten late-type galaxies with HI masses that range from $1.8times10^{7}$ M$_{odot}$ to $1.1times10^{10}$ M$_{odot}$. We find that although the majority of galaxies show irregularities in the morphology and kinematics, they generally follow the scaling relations found in larger samples. We find that the HI and H${alpha}$ velocities reach the flat part of the rotation curve. We identify the large-scale structure in the nearby CHILES volume using DisPerSE with the spectroscopic catalog from SDSS. We explore the gaseous properties of the galaxies as a function of location in the cosmic web. We also compare the angular momentum vector (spin) of the galaxies to the orientation of the nearest cosmic web filament. Our results show that galaxy spins tend to be aligned with cosmic web filaments and show a hint of a transition mass associated with the spin angle alignment.
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.
We study the mass-metallicity relation for 19 members of a spectroscopically-confirmed protocluster in the COSMOS field at $z=2.2$ (CC2.2), and compare it with that of 24 similarly selected field galaxies at the same redshift. Both samples are $rm Halpha$ emitting sources, chosen from the HiZELS narrow-band survey, with metallicities derived from $rm N2 (frac{rm [NII] lambda 6584}{rm H alpha})$ line ratio. For the mass-matched samples of protocluster and field galaxies, we find that protocluster galaxies with $10^{9.9} rm M_odot leq M_* leq 10^{10.9} rm M_odot$ are metal deficient by $0.10 pm 0.04$ dex ($2.5sigma$ significance) compared to their coeval field galaxies. This metal deficiency is absent for low mass galaxies, $rm M_* < 10^{9.9} rm M_odot$. Moreover, relying on both SED-derived and $rm {Halpha}$ (corrected for dust extinction based on $rm {M_*}$) SFRs, we find no strong environmental dependence of SFR-$rm {M_*}$ relation, however, we are not able to rule out the existence of small dependence due to inherent uncertainties in both SFR estimators. The existence of $2.5sigma$ significant metal deficiency for massive protocluster galaxies favors a model in which funneling of the primordial cold gas through filaments dilutes the metal content of protoclusters at high redshifts ($z gtrsim 2$). At these redshifts, gas reservoirs in filaments are dense enough to cool down rapidly and fall into the potential well of the protocluster to lower the gas-phase metallicity of galaxies. Moreover, part of this metal deficiency could be originated from galaxy interactions which are more prevalent in dense environments.
Galaxies that have fallen into massive haloes may no longer be able to accrete gas from their surroundings, a process referred to as starvation or strangulation of satellites. We study the environmental dependence of gas accretion onto galaxies using the cosmological, hydrodynamical EAGLE simulation. We quantify the dependence of gas accretion on stellar mass, redshift, and environment, using halo mass and galaxy overdensity as environmental indicators. We find a strong suppression, by many orders of magnitude, of the gas accretion rate in dense environments, primarily for satellite galaxies. This suppression becomes stronger at lower redshift. However, the scatter in accretion rates is very large for satellites. This is (at least in part) due to the variation in halocentric radius, since gas accretion is more suppressed at smaller radii. Central galaxies are influenced less strongly by their environment and exhibit less scatter in their gas accretion rates. The star formation rates of both centrals and satellites show similar behaviour to their gas accretion rates. The relatively small differences between gas accretion and star formation rates demonstrate that galaxies generally exhaust their gas reservoir somewhat faster at higher stellar mass, lower redshift, and in denser environments. We conclude that the environmental suppression of gas accretion could directly result in the quenching of star formation.
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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