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Register a new userSynchrotron emission and neutral hydrogen in the simulated cosmic web
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We present the first results of a campaign of ENZO cosmological simulations targeting the shocked and the neutral parts of the cosmic web, obtained with Supercomputing facilities provided by the INAF-CINECA agreement.
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Cosmological simulations suggest that most of the matter in the Universe is distributed along filaments connecting galaxies. Illuminated by the cosmic UV background (UVB), these structures are expected to glow in fluorescent Lyman alpha emission with a Surface Brightness (SB) that is well below current observational limits for individual detections. Here, we perform a stacking analysis of the deepest MUSE/VLT data using three-dimensional regions (subcubes) with orientations determined by the position of neighbouring Lyman alpha galaxies (LAEs) at 3<z<4. Our method should increase the probability of detecting filamentary Lyman alpha emission, provided that these structures are Lyman Limit Systems (LLSs). By stacking 390 oriented subcubes we reach a 2 sigma sensitivity level of SB ~ 0.44e-20 erg/s/cm^2/arcsec^2 in an aperture of 1 arcsec^2 x 6.25 Angstrom, which is three times below the expected fluorescent Lyman alpha signal from the Haardt-Madau 2012 (HM12) UVB at z~3.5. No detectable emission is found on intergalactic scales, implying that at least two thirds of our subcubes do not contain oriented LLSs for a HM12 UVB. On the other hand, significant emission is detected in the circum-galactic medium (CGM) of galaxies in the direction of the neighbours. The signal is stronger for galaxies with a larger number of neighbours and appears to be independent of any other galaxy properties such as luminosity, redshift and neighbour distance. We estimate that preferentially oriented satellite galaxies cannot contribute significantly to this signal, suggesting instead that gas densities in the CGM are typically larger in the direction of neighbouring galaxies on cosmological scales.
We explore the characteristics of the cosmic web around Local Group(LG) like pairs using a cosmological simulation in the $Lambda$CDM cosmology. We use the Hessian of the gravitational potential to classify regions on scales of $sim 2$ Mpc as a peak, sheet, filament or void. The sample of LG counterparts is represented by two samples of halo pairs. The first is a general sample composed by pairs with similar masses and isolation criteria as observed for the LG. The second is a subset with additional observed kinematic constraints such as relative pair velocity and separation. We find that the pairs in the LG sample with all constraints are: (i) Preferentially located in filaments and sheets, (ii) Located in in a narrow range of local overdensity $0<delta<2$, web ellipticity $0.1<e<1.0$ and prolateness $-0.4<p<0.4$. (iii) Strongly aligned with the cosmic web. The alignments are such that the pair orbital angular momentum tends to be perpendicular to the smallest tidal eigenvector, $hat{e}_3$, which lies along the filament direction or the sheet plane. A stronger alignment is present for the vector linking the two halos with the vector $hat{e}_3$. Additionally, we fail to find a strong correlation of the spin of each halo in the pair with the cosmic web. All these trends are expected to a great extent from the selection on the LG total mass on the general sample. Applied to the observed LG, there is a potential conflict between the alignments of the different planes of satellites and the numerical evidence for satellite accretion along filaments; the direction defined by $hat{e}_3$. This highlights the relevance of achieving a precise characterization of the place of the LG in the cosmic web in the cosmological context provided by $Lambda$CDM.
We present a search for the synchrotron emission from the synchrotron cosmic web by cross correlating 180MHz radio images from the Murchison Widefield Array with tracers of large scale structure (LSS). We use t
We investigate the alignment of haloes with the filaments of the cosmic web using an unprecedently large sample of dark matter haloes taken from the P-Millennium $Lambda$CDM cosmological N-body simulation. We use the state-of-the-art NEXUS morphological formalism which, due to its multiscale nature, simultaneously identifies structures at all scales. We find strong and highly significant alignments, with both the major axis of haloes and their peculiar velocity tending to orient along the filament. However, the spin - filament alignment displays a more complex trend changing from preferentially parallel at low masses to preferentially perpendicular at high masses. This spin flip occurs at an average mass of $5times10^{11}~h^{-1}M_odot$. This mass increases with increasing filament diameter, varying by more than an order of magnitude between the thinnest and thickest filament samples. We also find that the inner parts of haloes have a spin flip mass that is several times smaller than that of the halo as a whole. These results confirm that recent accretion is responsible for the complex behaviour of the halo spin - filament alignment. Low-mass haloes mainly accrete mass along directions perpendicular to their host filament and thus their spins tend to be oriented along the filaments. In contrast, high-mass haloes mainly accrete along their host filaments and have their spins preferentially perpendicular to them. Furthermore, haloes located in thinner filaments are more likely to accrete along their host filaments than haloes of the same mass located in thicker filaments.
We explore the evolution of halo spins in the cosmic web using a very large sample of dark matter haloes in the $Lambda$CDM Planck-Millennium N-body simulation. We use the NEXUS+ multiscale formalism to identify the hierarchy of filaments and sheets of the cosmic web at several redshifts. We find that at all times the magnitude of halo spins correlates with the web environment, being largest in filaments, and, for the first time, we show that it also correlates with filament thickness as well as the angle between spin-orientation and the spine of the host filament. For example, massive haloes in thick filaments spin faster than their counterparts in thin filaments, while for low-mass haloes the reverse is true. We also have studied the evolution of alignment between halo spin orientations and the preferential axes of filaments and sheets. The alignment varies with halo mass, with the spins of low-mass haloes being predominantly along the filament spine, while those of high-mass haloes being predominantly perpendicular to the filament spine. On average, for all halo masses, halo spins become more perpendicular to the filament spine at later times. At all redshifts, the spin alignment shows a considerable variation with filament thickness, with the halo mass corresponding to the transition from parallel to perpendicular alignment varying by more than one order of magnitude. The environmental dependence of halo spin magnitude shows little evolution for $zleq2$ and is likely a consequence of the correlations in the initial conditions or high redshift effects
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