1,144 research outputs found
The Impact of Galaxy Formation on the Diffuse Background Radiation
The far infrared background is a sink for the hidden aspects of galaxy
formation. At optical wavelengths, ellipticals and spheroids are old, even at
Neither the luminous formation phase nor their early evolution is
seen in the visible. We infer that ellipticals and, more generally, most
spheroids must have formed in dust-shrouded starbursts. In this article, we
show how separate tracking of disk and spheroid star formation enables us to
infer that disks dominate near the peak in the cosmic star formation rate at z
\lapproxeq 2 and in the diffuse ultraviolet/optical/infrared background,
whereas spheroid formation dominates the submillimetre background.Comment: 12 pages, 5 figures, to appear in proceedings of IAU symp.204, "The
Extragalactic Infrared Background and its Cosmological Implications", Martin
Harwit and Michael G. Hauser, ed
Galaxy Modelling - II. Multi-Wavelength Faint Counts from a Semi-Analytic Model of Galaxy Formation
(Abridged) This paper predicts self-consistent faint galaxy counts from the
UV to the submm wavelength range. The STARDUST spectral energy distributions
described in Devriendt et al. (1999) are embedded within the explicit
cosmological framework of a simple semi-analytic model of galaxy formation and
evolution. We build a class of models which capture the luminosity budget of
the universe through faint galaxy counts and redshift distributions in the
whole wavelength range spanned by our spectra. In contrast with a rather stable
behaviour in the optical and even in the far-IR, the submm counts are
dramatically sensitive to variations in the cosmological parameters and changes
in the star formation history. Faint submm counts are more easily accommodated
within an open universe with a low value of , or a flat universe with
a non-zero cosmological constant. This study illustrates the implementation of
multi-wavelength spectra into a semi-analytic model. In spite of its
simplicity, it already provides fair fits of the current data of faint counts,
and a physically motivated way of interpolating and extrapolating these data to
other wavelengths and fainter flux levels.Comment: 13 pages, 10 figures, to appear in A&
The spectral appearance of primeval galaxies
The current and forthcoming observations of large samples of high-redshift
galaxies selected according to various photometric and spectroscopic criteria
can be interpreted in the context of galaxy formation, by means of models of
evolving spectral energy distributions (SEDs). We hereafter present STARDUST
which gives synthetic SEDs from the far UV to the submm wavelength range. These
SEDs are designed to be implemented into semi-analytic models of galaxy
formation.Comment: 10 pages, Latex, 8 postscript figures, to be published in the
Proceedings of the meeting ``Clustering at High Redshift'', ASP Conference
Serie
Building Merger Trees from Cosmological N-body Simulations
Although a fair amount of work has been devoted to growing Monte-Carlo merger
trees which resemble those built from an N-body simulation, comparatively
little effort has been invested in quantifying the caveats one necessarily
encounters when one extracts trees directly from such a simulation. To somewhat
revert the tide, this paper seeks to provide its reader with a comprehensive
study of the problems one faces when following this route. The first step to
building merger histories of dark matter haloes and their subhaloes is to
identify these structures in each of the time outputs (snapshots) produced by
the simulation. Even though we discuss a particular implementation of such an
algorithm (called AdaptaHOP) in this paper, we believe that our results do not
depend on the exact details of the implementation but extend to most if not all
(sub)structure finders. We then highlight different ways to build merger
histories from AdaptaHOP haloes and subhaloes, contrasting their various
advantages and drawbacks. We find that the best approach to (sub)halo merging
histories is through an analysis that goes back and forth between
identification and tree building rather than one which conducts a
straightforward sequential treatment of these two steps. This is rooted in the
complexity of the merging trees which have to depict an inherently dynamical
process from the partial temporal information contained in the collection of
instantaneous snapshots available from the N-body simulation.Comment: 19 pages, 28 figure
Galaxy Modelling -- I. Spectral Energy Distributions from Far-UV to Sub-mm Wavelengths
(abridged) We present STARDUST, a new self-consistent modelling of the
spectral energy distributions (SEDs) of galaxies from far-UV to radio
wavelengths. In order to derive the SEDs in this broad spectral range, we first
couple spectrophotometric and (closed-box) chemical evolutions to account for
metallicity effects on the spectra of synthetic stellar populations. We then
use a phenomenological fit for the metal-dependent extinction curve and a
simple geometric distribution of the dust to compute the optical depth of
galaxies and the corresponding obscuration curve. This enables us to calculate
the fraction of stellar light reprocessed in the infrared range. In a final
step, we define a dust model with various components and we fix the weights of
these components in order to reproduce the IRAS correlation of IR colours with
total IR luminosities. This allows us to compute far-IR SEDs that
phenomenologically mimic observed trends. We are able to predict the spectral
evolution of galaxies in a broad wavelength range, and we can reproduce the
observed SEDs of local spirals, starbursts, luminous infrared galaxies (LIRGs)
and ultra luminous infrared galaxies (ULIRGs). This modelling is so far kept as
simple as possible and depends on a small number of free parameters, namely the
initial mass function (IMF), star formation rate (SFR) time scale, gas density,
and galaxy age, as well as on more refined assumptions on dust properties and
the presence (or absence) of gas inflows/outflows.Comment: 20 pages, 23 figures, Accepted for publication in Astronomy and
Astrophysics Main Journa
The FIR/submm window on galaxy formation
Our view on the deep universe has been so far biased towards optically bright
galaxies. Now, the measurement of the Cosmic Infrared Background in FIRAS and
DIRBE residuals, and the observations of FIR/submm sources by the ISOPHOT and
SCUBA instruments begin unveiling the ``optically dark side'' of galaxy
formation. Though the origin of dust heating is still unsolved, it appears very
likely that a large fraction of the FIR/submm emission is due to
heavily-extinguished star formation. Consequently, the level of the CIRB
implies that about 2/3 of galaxy/star formation in the universe is hidden by
dust shrouds. In this review, we introduce a new modeling of galaxy formation
and evolution that provides us with specific predictions in FIR/submm
wavebands. These predictions are compared with the current status of the
observations. Finally, the capabilities of current and forthcoming instruments
for all-sky and deep surveys of FIR/submm sources are briefly described.Comment: 10 pages, Latex, 5 postscript figures, to appear in ``The Birth of
Galaxies'', 1999, B. Guiderdoni, F.R. Bouchet, T.X. Thuan & J. Tran Thanh Van
(eds), Editions Frontiere
LeMoMaF: Lensed Mock Map Facility
We present the Lensed Mock Map Facility (LeMoMaF), a tool designed to perform
mock weak lensing measurements on numerically simulated chunks of the universe.
Coupling N-body simulations to a semi-analytical model of galaxy formation,
LeMoMaF can create realistic lensed images and mock catalogues of galaxies, at
wavelengths ranging from the UV to the submm. To demonstrate the power of such
a tool we compute predictions of the source-lens clustering effect on the
convergence statistics, and quantify the impact of weak lensing on galaxy
counts in two different filters. We find that the source-lens clustering effect
skews the probability density function of the convergence towards low values,
with an intensity which strongly depends on the redshift distribution of
galaxies. On the other hand, the degree of enhancement or depletion in galaxy
counts due to weak lensing is independent of the source-lens clustering effect.
We discuss the impact on the two-points shear statistics to be measured by
future missions like SNAP and LSST. The source-lens clustering effect would
bias the estimation of sigma_8 from two point statistics by 2% -5%. We conclude
that accurate photometric redshifts for individual galaxies are necessary in
order to quantify and isolate the source-lens clustering effect.Comment: 14 pages, 11 figures, submitted to MNRA
Cloud Dispersal in Turbulent Flows
Cold clouds embedded in warm media are very common objects in astrophysics.
Their disruption timescale depends strongly on the dynamical configuration. We
discuss the evolution of an initially homogeneous cold cloud embedded in warm
turbulent gas. Within a couple of dynamical timescales, the filling factor of
the cold gas within the original cloud radius drops below 50%. Turbulent
diffusivities estimated from the time evolution of radial filling factor
profiles are not constant with time. Cold and warm gas are bodily transported
by turbulence and mixed. This is only mildly indicated by column density maps.
The radiation field within the cloud, however, increases by several orders of
magnitudes due to the mixing, with possible consequences for cloud chemistry
and evolution within a few dynamical timescales.Comment: 11 pages, 12 figures, accepted by MNRA
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