31 research outputs found
Galaxy Quenching from Cosmic Web Detachment
We propose the Cosmic Web Detachment (CWD) model, a framework to interpret
the star-formation history of galaxies in a cosmological context. The CWD model
unifies several starvation mechanisms known to disrupt or stop star formation
into one single physical framework. Galaxies begin accreting star-forming gas
at early times via a network of primordial filaments, simply related to the
pattern of density fluctuations in the initial conditions. But when
shell-crossing occurs on intergalactic scales, this pattern is disrupted, and
the galaxy detaches from its primordial filaments, ending the accretion of cold
gas. We argue that CWD encompasses known external processes halting star
formation, such as harassment, strangulation and starvation. On top of these
external processes, internal feedback processes such as AGN contribute to stop
in star formation as well.
By explicitly pointing out the non-linear nature of CWD events we introduce a
simple formalism to identify CWD events in N-body simulations. With it we
reproduce and explain, in the context of CWD, several observations including
downsizing, the cosmic star formation rate history, the galaxy mass-color
diagram and the dependence of the fraction of red galaxies with mass and local
density.Comment: 20 pages, accepted for publication in OJA. High-res version:
http://skysrv.pha.jhu.edu/~miguel/Papers/CWD/ms.pd
A halo bias function measured deeply into voids without stochasticity
We study the relationship between dark-matter haloes and matter in the MIP
-body simulation ensemble, which allows precision measurements of this
relationship, even deeply into voids. What enables this is a lack of
discreteness, stochasticity, and exclusion, achieved by averaging over hundreds
of possible sets of initial small-scale modes, while holding fixed large-scale
modes that give the cosmic web. We find (i) that dark-matter-halo formation is
greatly suppressed in voids; there is an exponential downturn at low densities
in the otherwise power-law matter-to-halo density bias function. Thus, the
rarity of haloes in voids is akin to the rarity of the largest clusters, and
their abundance is quite sensitive to cosmological parameters. The exponential
downturn appears both in an excursion-set model, and in a model in which
fluctuations evolve in voids as in an open universe with an effective
proportional to a large-scale density. We also find that (ii) haloes
typically populate the average halo-density field in a super-Poisson way, i.e.
with a variance exceeding the mean; and (iii) the rank-order-Gaussianized halo
and dark-matter fields are impressively similar in Fourier space. We compare
both their power spectra and cross-correlation, supporting the conclusion that
one is roughly a strictly-increasing mapping of the other. The MIP ensemble
especially reveals how halo abundance varies with `environmental' quantities
beyond the local matter density; (iv) we find a visual suggestion that at fixed
matter density, filaments are more populated by haloes than clusters.Comment: Changed to version accepted by MNRA
Sub-Megaparsec Individual Photometric Redshift Estimation from Cosmic Web Constraints
We present a method, PhotoWeb, for estimating photometric redshifts of
individual galaxies, and their equivalent distance, with megaparsec and even
sub-megaparsec accuracy using the Cosmic Web as a constraint over photo-z
estimates. PhotoWeb redshift errors for individual galaxies are of the order of
delta_z = 0.0007, compared to errors of delta_z = 0.02 for current photo-z
techniques. The mean redshift error is of the order of 0.00005-0.0004 compared
to mean errors in the range delta_z =z 0.001-0.01 for the best available
photo-z estimates in the literature. Current photo-z techniques based on the
spectral energy distribution of galaxies and projected clustering produce
redshift estimates with large errors due to the poor constraining power the
galaxy's spectral energy distribution and projected clustering can provide. The
Cosmic Web, on the other hand, provides the strongest constraints on the
position of galaxies. The network of walls, filaments and voids occupy ~%10 of
the volume of the Universe, yet they contain ~%95 of galaxies. The cosmic web,
being a cellular system with well-defined boundaries, sets a restricted set of
intermittent positions a galaxy can occupy along a given line-of-sight. Using
the information in the density field computed from spectroscopic redshifts we
can narrow the possible locations of a given galaxy along the line of sight
from a single broad probability distribution (from photo-z) to one or a few
narrow peaks. Our first results improve previous photo-z errors by more than
one order of magnitude allowing sub-megaparsec errors in some cases. Such
accurate estimates for tens of millions of galaxies will allow unprecedented
galaxy-LSS studies. In this work we apply our technique to the SDSS photo-z
galaxy sample and discuss its performance and future improvements.Comment: Final version submitted to MNRA