556 research outputs found
Report from the Tri-Agency Cosmological Simulation Task Force
The Tri-Agency Cosmological Simulations (TACS) Task Force was formed when
Program Managers from the Department of Energy (DOE), the National Aeronautics
and Space Administration (NASA), and the National Science Foundation (NSF)
expressed an interest in receiving input into the cosmological simulations
landscape related to the upcoming DOE/NSF Vera Rubin Observatory (Rubin),
NASA/ESA's Euclid, and NASA's Wide Field Infrared Survey Telescope (WFIRST).
The Co-Chairs of TACS, Katrin Heitmann and Alina Kiessling, invited community
scientists from the USA and Europe who are each subject matter experts and are
also members of one or more of the surveys to contribute. The following report
represents the input from TACS that was delivered to the Agencies in December
2018.Comment: 36 pages, 3 figures. Delivered to NASA, NSF, and DOE in Dec 201
On the puzzling plateau in the specific star formation rate at z=2-7
The observational indications for a constant specific star-formation rate
(sSFR) in the redshift range z=2-7 are puzzling in the context of current
galaxy-formation models. Despite the tentative nature of the data, their marked
conflict with theory motivates a study of the possible implications. The
plateau at sSFR ~ 2 Gyr^-1 is hard to reproduce because (a) its level is low
compared to the cosmological specific accretion rate at z > 6, (b) it is higher
than the latter at z ~ 2, (c) the natural correlation between SFR and stellar
mass makes it difficult to manipulate their ratio, and (d) a low SFR at high z
makes it hard to produce enough massive galaxies by z ~ 2. Using a flexible
semi-analytic model, we explore ad-hoc modifications to the standard physical
recipes trying to obey the puzzling observational constraints. Successful
models involve non-trivial modifications, such as (a) a suppressed SFR at z > 4
in galaxies of all masses, by enhanced feedback or reduced SFR efficiency,
following an initial active phase at z > 7, (b) a delayed gas consumption into
stars, allowing the gas that was prohibited from forming stars or ejected at
high z to form stars later in more massive galaxies, and (c) enhanced growth of
massive galaxies, in terms of either faster assembly or more efficient
starbursts in mergers, or by efficient star formation in massive haloes.Comment: 17 pages, 11 figures. MNRAS accepted. References added, small changes
to text after referee report. Results and conclusions unchange
Dark-ages reionization and galaxy formation simulation XI: Clustering and halo masses of high redshift galaxies
We investigate the clustering properties of Lyman-break galaxies (LBGs) at
- . Using the semi-analytical model {\scshape Meraxes} constructed
as part of the Dark-ages Reionization And Galaxy-formation Observables from
Numerical Simulation (DRAGONS) project, we predict the angular correlation
function (ACF) of LBGs at - . Overall, we find that the predicted
ACFs are in good agreement with recent measurements at and from observations consisting of the Hubble eXtreme Deep Field (XDF), the
Hubble Ultra-Deep Field (HUDF) and Cosmic Assembly Near-infrared Deep
Extragalactic Legacy Survey (CANDELS) field. We confirm the dependence of
clustering on luminosity, with more massive dark matter haloes hosting brighter
galaxies, remains valid at high redshift. The predicted galaxy bias at fixed
luminosity is found to increase with redshift, in agreement with observations.
We find that LBGs of magnitude at reside in dark matter haloes of mean mass -
, and this dark matter halo mass does not evolve
significantly during reionisation.Comment: 14 pages, 10 figures, published in MNRA
The Millennium Run Observatory: First Light
Simulations of galaxy evolution aim to capture our current understanding as
well as to make predictions for testing by future experiments. Simulations and
observations are often compared in an indirect fashion: physical quantities are
estimated from the data and compared to models. However, many applications can
benefit from a more direct approach, where the observing process is also
simulated and the models are seen fully from the observer's perspective. To
facilitate this, we have developed the Millennium Run Observatory (MRObs), a
theoretical virtual observatory which uses virtual telescopes to `observe'
semi-analytic galaxy formation models based on the suite of Millennium Run dark
matter simulations. The MRObs produces data that can be processed and analyzed
using the standard software packages developed for real observations. At
present, we produce images in forty filters from the rest-frame UV to IR for
two stellar population synthesis models, three different models of IGM
absorption, and two cosmologies (WMAP1/7). Galaxy distributions for a large
number of mock lightcones can be `observed' using models of major ground- and
space-based telescopes. The data include lightcone catalogues linked to
structural properties of galaxies, pre-observation model images, mock telescope
images, and Source Extractor products that can all be traced back to the higher
level dark matter, semi-analytic galaxy, and lightcone catalogues available in
the Millennium database. Here, we describe our methods and announce a first
public release of simulated surveys (e.g., SDSS, CFHT-LS, GOODS, GOODS/ERS,
CANDELS, and HUDF). The MRObs browser, an online tool, further facilitates
exploration of the simulated data. We demonstrate the benefits of a direct
approach through a number of example applications (galaxy number counts in
CANDELS, clusters, morphologies, and dropout selections).Comment: MNRAS, in press. Millennium Run Observatory data products, online
tools, and more available through http://galformod.mpa-garching.mpg.de/mrobs
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