106 research outputs found
Impact of Cosmic Variance on the Galaxy-Halo Connection for Lyman- Emitters
In this paper we study the impact of cosmic variance and observational
uncertainties in constraining the mass and occupation fraction, ,
of dark matter halos hosting Ly- Emitting Galaxies (LAEs) at high
redshift. To this end, we construct mock catalogs from an N-body simulation to
match the typical size of observed fields at (). In
our model a dark matter halo with mass in the range can only host one detectable LAE at most. We proceed to explore
the parameter space determined by , and
with a Markov Chain Monte-Carlo algorithm using the angular correlation
function (ACF) and the LAEs number density as observational constraints. We
find that the preferred minimum and maximum masses in our model span a wide
range , ; followed by a wide range in the
occupation fraction . As a consequence the
median mass, , of all the consistent models has a large uncertainty
. However,
we find that the same individual models have a relatively tight
scatter around the median mass dex.
We are also able to show that \focc\ is uniquely determined by ,
regardless of . We argue that upcoming large surveys covering at
least deg should be able to put tighter constraints on
and through the LAE number density distribution width constructed
over several fields of deg.Comment: 7 Pages, 5 figures. Accepted for publication in Ap
Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes
We study the alignment of dark matter haloes with the cosmic web
characterized by the tidal and velocity shear fields. We focus on the alignment
of their shape, angular momentum and peculiar velocities. We use a cosmological
N-body simulation that allows to study dark matter halos spanning almost five
orders of magnitude in mass (-) and
spatial scales of - Mpc to define the cosmic web. We find
that the halo shape presents the strongest alignment along the smallest tidal
eigenvector, e.g. along filaments and walls, with a signal that gets stronger
as the halo mass increases. In the case of the velocity shear field only
massive halos tend to have their shapes aligned
along the largest tidal eigenvector; that is, perpendicular to filaments and
walls. For the angular momentum we find alignment signals only for halos more
massive than both in the tidal and velocity shear
webs where the preferences are for it to be parallel to the middle eigenvector;
perpendicular to filaments and parallel to walls. Finally, the peculiar
velocities show a strong alignment along the smallest tidal eigenvector for all
halo masses; halos move along filaments and walls. In the velocity shear the
same alignment is present but weaker and only for haloes less massive than
. Our results clearly show that the two different
algorithms we used to define the cosmic web describe different physical aspects
of non-linear collapse and should be used in a complementary way to understand
the effect of the cosmic web on galaxy evolution.Comment: 14 pages, 5 figures, MNRAS accepte
Systematic uncertainties from halo asphericity in dark matter searches
Although commonly assumed to be spherical, dark matter halos are predicted to
be non-spherical by N-body simulations and their asphericity has a potential
impact on the systematic uncertainties in dark matter searches. The evaluation
of these uncertainties is the main aim of this work, where we study the impact
of aspherical dark matter density distributions in Milky-Way-like halos on
direct and indirect searches. Using data from the large N-body cosmological
simulation Bolshoi, we perform a statistical analysis and quantify the
systematic uncertainties on the determination of local dark matter density and
the so-called factors for dark matter annihilations and decays from the
galactic center. We find that, due to our ignorance about the extent of the
non-sphericity of the Milky Way dark matter halo, systematic uncertainties can
be as large as 35%, within the 95% most probable region, for a spherically
averaged value for the local density of 0.3-0.4 GeV/cm. Similarly,
systematic uncertainties on the factors evaluated around the galactic
center can be as large as 10% and 15%, within the 95% most probable region, for
dark matter annihilations and decays, respectively.Comment: 29 pages, 6 artistic figures, version accepted for publication in
JCA
The kinematics of the Local Group in a cosmological context
Recent observations constrained the tangential velocity of M31 with respect
to the Milky Way (MW) to be v_tan<34.4 km/s and the radial velocity to be in
the range v_rad=-109+/- 4.4 km/s (van der Marel et al. 2012). In this study we
use a large volume high resolution N-body cosmological simulation (Bolshoi)
together with three constrained simulations to statistically study this
kinematics in the context of the LCDM. The comparison of the ensembles of
simulated pairs with the observed LG at the 1-sigma level in the uncertainties
has been done with respect to the radial and tangential velocities, the reduced
orbital energy (e_tot), angular momentum (l_orb) and the dimensionless spin
parameter, lambda. Our main results are: (i) the preferred radial and
tangential velocities for pairs in LCDM are v_rad=-80+/-20 km/s, v_tan=50+/-10
km/s, (ii) pairs around that region are 3 to 13 times more common than pairs
within the observational values, (iii) 15%to 24% of LG-like pairs in LCDM have
energy and angular momentum consistent with observations while (iv) 9% to 13%
of pairs in the same sample show similar values in the inferred dimensionless
spin parameter. It follows that within current observational uncertainties the
quasi-conserved quantities that characterize the orbit of the LG, i.e. e_tot,
r_orb and lambda, do not challenge the standard LCDM model, but the model is in
tension with regard to the actual values of the radial and tangential
velocities. This might hint to a problem of the LCDM model to reproduce the
observed LG.Comment: 6 pages, 2 figures, 3 tables, accepted for publication in ApJ
Letters. For full data and source code (IPython notebook) to reproduce the
results, see: https://github.com/forero/LG_Kinematic
Modelling the gas kinematics of an atypical Lyman-alpha emitting compact dwarf galaxy
Star-forming Compact Dwarf Galaxies (CDGs) resemble the expected pristine
conditions of the first galaxies in the Universe and are the best systems to
test models on primordial galaxy formation and evolution. Here we report on one
of such CDGs, Tololo 1214-277, which presents a broad, single peaked, highly
symmetric Ly emission line that had evaded theoretical interpretation
so far. In this paper we reproduce for the first time these line features with
two different physically motivated kinematic models: an interstellar medium
composed by outflowing clumps with random motions and an homogeneous gaseous
sphere undergoing solid body rotation. The multiphase model requires a clump
velocity dispersion of km s with outflows of
km s, while the bulk rotation velocity is constrained to be
km s. We argue that the results from the multiphase
model provide a correct interpretation of the data. In that case the clump
velocity dispersion implies a dynamical mass of M,
ten times its baryonic mass. If future kinematic maps of Tololo 1214-277
confirm the velocities suggested by the multiphase model, it would provide
additional support to expect such kinematic state in primordial galaxies,
opening the opportunity to use the models and methods presented in this paper
to constrain the physics of star formation and feedback in the early generation
of Ly- emitting galaxies.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in MNRA
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