65 research outputs found
Cluster Magnification & the Mass-Richness Relation in CFHTLenS
Gravitational lensing magnification is measured with a significance of 9.7
sigma on a large sample of galaxy clusters in the Canada-France-Hawaii
Telescope Lensing Survey (CFHTLenS). This survey covers ~154 deg^2 and contains
over 18,000 cluster candidates at redshifts 0.2 <= z <= 0.9, detected using the
3D-Matched Filter cluster-finder of Milkeraitis et al. (2010). We fit
composite-NFW models to the ensemble, accounting for cluster miscentering,
source-lens redshift overlap, as well as nearby structure (the 2-halo term),
and recover mass estimates of the cluster dark matter halos in range of ~10^13
M_sun to 2*10^14 M_sun. Cluster richness is measured for the entire sample, and
we bin the clusters according to both richness and redshift. A mass-richness
relation M_200 = M_0 (N_200 / 20)^beta is fit to the measurements. For two
different cluster miscentering models we find consistent results for the
normalization and slope, M_0 = (2.3 +/- 0.2)*10^13 M_sun, beta = 1.4 +/- 0.1
and M_0 = (2.2 +/- 0.2)*10^13 M_sun, beta = 1.5 +/- 0.1. We find that
accounting for the full redshift distribution of lenses and sources is
important, since any overlap can have an impact on mass estimates inferred from
flux magnification.Comment: 11 pages, 8 figures, Accepted to MNRA
Can we use Weak Lensing to Measure Total Mass Profiles of Galaxies on 20 kiloparsec Scales?
Current constraints on dark matter density profiles from weak lensing are
typically limited to radial scales greater than 50-100 kpc. In this paper, we
explore the possibility of probing the very inner regions of galaxy/halo
density profiles by measuring stacked weak lensing on scales of only a few tens
of kpc. Our forecasts focus on scales smaller than the equality radius (Req)
where the stellar component and the dark matter component contribute equally to
the lensing signal. We compute the evolution of Req as a function of lens
stellar mass and redshift and show that Req=7-34 kpc for galaxies with the
stellar mass of 10^{9.5}-10^{11.5} solar masses. Unbiased shear measurements
will be challenging on these scales. We introduce a simple metric to quantify
how many source galaxies overlap with their neighbours and for which shear
measurements will be challenging. Rejecting source galaxies with close-by
companions results in about a 20 per cent decrease in the overall source
density. Despite this decrease, we show that Euclid and WFIRST will be able to
constrain galaxy/halo density profiles at Req with signal-to-noise ratio >20
for the stellar mass of >10^{10} solar masses. Weak lensing measurements at
Req, in combination with stellar kinematics on smaller scales, will be a
powerful means by which to constrain both the inner slope of the dark matter
density profile as well as the mass and redshift dependence of the stellar
initial mass function.Comment: 19 pages, 14 figures, 3 tables, submitted to MNRAS, included the
referee comment
Why do extremely massive disc galaxies exist today?
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 494, Issue 4, June 2020, Pages 5568–5575, https://doi.org/10.1093/mnras/staa970. ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Galaxy merger histories correlate strongly with stellar mass, largely regardless of morphology. Thus, at fixed stellar mass, spheroids and discs share similar assembly histories, both in terms of the frequency of mergers and the distribution of their mass ratios. Since mergers are the principal drivers of disc-to-spheroid morphological transformation, and the most massive galaxies typically have the richest merger histories, it is surprising that discs exist at all at the highest stellar masses (e.g. beyond the knee of the mass function). Using Horizon-AGN, a cosmological hydro-dynamical simulation, we show that extremely massive (M*> 10^11.4 MSun) discs are created via two channels. In the primary channel (accounting for ~70% of these systems and ~8% of massive galaxies) the most recent, significant merger (stellar mass ratio > 1:10) between a massive spheroid and a gas-rich satellite `spins up' the spheroid by creating a new rotational stellar component, leaving a massive disc as the remnant. In the secondary channel (accounting for ~30% of these systems and ~3% of massive galaxies), a system maintains a disc throughout its lifetime, due to an anomalously quiet merger history. Not unexpectedly, the fraction of massive discs is larger at higher redshift, due to the Universe being more gas-rich. The morphological mix of galaxies at the highest stellar masses is, therefore, a strong function of the gas fraction of the Universe. Finally, these massive discs have similar black-hole masses and accretion rates to massive spheroids, providing a natural explanation for why a minority of powerful AGN are surprisingly found in disc galaxies.Peer reviewedFinal Published versio
Relaxed blue ellipticals: accretion-driven stellar growth is a key evolutionary channel for low mass elliptical galaxies
How elliptical galaxies form is a key question in observational cosmology.
While the formation of massive ellipticals is strongly linked to mergers, the
low mass (Mstar < 10^9.5 MSun) regime remains less well explored. In
particular, studying elliptical populations when they are blue, and therefore
rapidly building stellar mass, offers strong constraints on their formation.
Here, we study 108 blue, low-mass ellipticals (which have a median stellar mass
of 10^8.7 MSun) at z < 0.3 in the COSMOS field. Visual inspection of extremely
deep optical HSC images indicates that less than 3 per cent of these systems
have visible tidal features, a factor of 2 less than the incidence of tidal
features in a control sample of galaxies with the same distribution of stellar
mass and redshift. This suggests that the star formation activity in these
objects is not driven by mergers or interactions but by secular gas accretion.
We combine accurate physical parameters from the COSMOS2020 catalog, with
measurements of local density and the locations of galaxies in the cosmic web,
to show that our blue ellipticals reside in low-density environments, further
away from nodes and large-scale filaments than other galaxies. At similar
stellar masses and environments, blue ellipticals outnumber their normal (red)
counterparts by a factor of 2. Thus, these systems are likely progenitors of
not only normal ellipticals at similar stellar mass but, given their high star
formation rates, also of ellipticals at higher stellar masses. Secular gas
accretion, therefore, likely plays a significant (and possibly dominant) role
in the stellar assembly of elliptical galaxies in the low mass regime.Comment: Published in MNRA
Swirling around filaments: are large-scale structure vortices spinning up dark halos?
The kinematic analysis of dark matter and hydrodynamical simulations suggests
that the vorticity in large-scale structure is mostly confined to, and
predominantly aligned with their filaments, with an excess of probability of 20
per cent to have the angle between vorticity and filaments direction lower than
60 degrees relative to random orientations. The cross sections of these
filaments are typically partitioned into four quadrants with opposite vorticity
sign, arising from multiple flows, originating from neighbouring walls. The
spins of halos embedded within these filaments are consistently aligned with
this vorticity for any halo mass, with a stronger alignment for the most
massive structures up to an excess of probability of 165 per cent. On large
scales, adiabatic/cooling hydrodynamical simulations display the same vorticity
in the gas as in the dark matter. The global geometry of the flow within the
cosmic web is therefore qualitatively consistent with a spin acquisition for
smaller halos induced by this large-scale coherence, as argued in Codis et al.
(2012). In effect, secondary anisotropic infall (originating from the
vortex-rich filament within which these lower-mass halos form) dominates the
angular momentum budget of these halos. The transition mass from alignment to
orthogonality is related to the size of a given multi-flow region with a given
polarity. This transition may be reconciled with the standard tidal torque
theory if the latter is augmented so as to account for the larger scale
anisotropic environment of walls and filaments.Comment: 17 pages, 19 figures, 3 tables. accepted for publication in MNRA
Intrinsic alignments of galaxies in the Horizon-AGN cosmological hydrodynamical simulation
The intrinsic alignments of galaxies are recognised as a contaminant to weak
gravitational lensing measurements. In this work, we study the alignment of
galaxy shapes and spins at low redshift () in Horizon-AGN, an
adaptive-mesh-refinement hydrodynamical cosmological simulation box of 100
Mpc/h a side with AGN feedback implementation. We find that spheroidal galaxies
in the simulation show a tendency to be aligned radially towards over-densities
in the dark matter density field and other spheroidals. This trend is in
agreement with observations, but the amplitude of the signal depends strongly
on how shapes are measured and how galaxies are selected in the simulation.
Disc galaxies show a tendency to be oriented tangentially around spheroidals in
three-dimensions. While this signal seems suppressed in projection, this does
not guarantee that disc alignments can be safely ignored in future weak lensing
surveys. The shape alignments of luminous galaxies in Horizon-AGN are in
agreement with observations and other simulation works, but we find less
alignment for lower luminosity populations. We also characterize the
systematics of galaxy shapes in the simulation and show that they can be safely
neglected when measuring the correlation of the density field and galaxy
ellipticities.Comment: 20 pages, 23 figure
Low-Surface-Brightness Galaxies are missing in the observed Stellar Mass Function
We investigate the impact of the surface brightness (SB) limit on the galaxy
stellar mass functions (GSMFs) using mock surveys generated from the Horizon
Run 5 (HR5) simulation. We compare the stellar-to-halo-mass relation, GSMF, and
size-stellar mass relation of the HR5 galaxies with empirical data and other
cosmological simulations. The mean SB of simulated galaxies are computed using
their effective radii, luminosities, and colors. To examine the cosmic SB
dimming effect, we compute -corrections from the spectral energy
distributions of individual simulated galaxy at each redshift, apply the
-corrections to the galaxies, and conduct mock surveys based on the various
SB limits. We find that the GSMFs are significantly affected by the SB limits
at a low-mass end. This approach can ease the discrepancy between the GSMFs
obtained from simulations and observations at . We also find
that a redshift survey with a SB selection limit of \left^e = 28
mag arcsec will miss 20% of galaxies with at . The missing fraction of low-surface-brightness galaxies
increases to 50%, 70%, and 98% at , 1.1, and 1.9, respectively, at the
SB limit.Comment: 27 pages, 30 figures, accepted for publication in Ap
How to Quench a Dwarf Galaxy: The Impact of Inhomogeneous Reionization on Dwarf Galaxies and Cosmic Filaments
We use the SPHINX suite of high-resolution cosmological radiation
hydrodynamics simulations to study how spatially and temporally inhomogeneous
reionization impacts the baryonic content of dwarf galaxies and cosmic
filaments. The SPHINX simulations simultaneously capture the large-scale
process of reionization, model the escape of ionising radiation from thousands
of galaxies, and resolve haloes well below the atomic cooling threshold. This
makes them an ideal tool for examining how reionization impacts star formation
and the gas content of dwarf galaxies. We compare simulations with and without
stellar radiation to isolate the effects of radiation feedback from that of
supernova, cosmic expansion, and numerical resolution. We find that the gas
content of cosmic filaments can be reduced by more than 80% following
reionization. The gas inflow rates into haloes with
are strongly affected and are reduced by more
than an order of magnitude compared to the simulation without reionization. A
significant increase in gas outflow rates is found for halo masses
. Our simulations show that inflow
suppression (i.e. starvation), rather than photoevaporation, is the dominant
mechanism by which the baryonic content of high-redshift dwarf galaxies is
regulated. At fixed redshift and halo mass, there is a large scatter in the
halo baryon fractions that is entirely dictated by the timing of reionization
in the local region surrounding a halo. Finally, although the gas content of
high-redshift dwarf galaxies is significantly impacted by reionization, we find
that most haloes with can remain self-shielded
and form stars long after reionization, until their local gas reservoir is
depleted, suggesting that local group dwarf galaxies do not necessarily exhibit
star formation histories that peak prior to
CFHTLenS: A Weak Lensing Shear Analysis of the 3D-Matched-Filter Galaxy Clusters
We present the cluster mass-richness scaling relation calibrated by a weak
lensing analysis of >18000 galaxy cluster candidates in the
Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). Detected using the
3D-Matched-Filter cluster-finder of Milkeraitis et al., these cluster
candidates span a wide range of masses, from the small group scale up to
, and redshifts 0.2 0.9. The total
significance of the stacked shear measurement amounts to 54. We compare
cluster masses determined using weak lensing shear and magnification, finding
the measurements in individual richness bins to yield 1 compatibility,
but with magnification estimates biased low. This first direct mass comparison
yields important insights for improving the systematics handling of future
lensing magnification work. In addition, we confirm analyses that suggest
cluster miscentring has an important effect on the observed 3D-MF halo
profiles, and we quantify this by fitting for projected cluster centroid
offsets, which are typically 0.4 arcmin. We bin the cluster candidates
as a function of redshift, finding similar cluster masses and richness across
the full range up to 0.9. We measure the 3D-MF mass-richness scaling
relation . We find a normalization , and a logarithmic slope of
, both of which are in 1 agreement with results
from the magnification analysis. We find no evidence for a redshift-dependence
of the normalization. The CFHTLenS 3D-MF cluster catalogue is now available at
cfhtlens.org.Comment: 3D-MF cluster catalog is NOW AVAILABLE at cfhtlens.org.
Magnification-shear mass comparison in Figure 10. 19 pages, 10 figures.
Accepted to MNRA
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