14 research outputs found
Detection and classification of supernovae beyond z~2 redshift with the James Webb Space Telescope
Future time-domain surveys for transient events in the near- and mid-infrared
bands will significantly extend our understanding about the physics of the
early Universe. In this paper we study the implications of a deep (~27 mag),
long-term (~3 years), observationally inexpensive survey with the James Webb
Space Telescope (JWST) within its Continuous Viewing Zone, aimed at discovering
luminous supernovae beyond z~2 redshift. We explore the possibilities for
detecting Superluminous Supernovae (SLSNe) as well as Type Ia supernovae at
such high redshifts and estimate their expected numbers within a relatively
small (~0.1 deg^2) survey area. It is found that we can expect ~10 new SLSNe
and ~50 SNe Ia discovered in the 1 < z < 4 redshift range. We show that it is
possible to get relatively accurate (sigma_z < 0.25) photometric redshifts for
Type Ia SNe by fitting their Spectral Energy Distributions (SED), redshifted
into the observed near-IR bands, with SN templates. We propose that Type Ia SNe
occupy a relatively narrow range on the JWST F220W-F440W vs F150W-F356W
color-color diagram between +/- 7 rest-frame days around maximum light, which
could be a useful classification tool for such type of transients. We also
study the possibility of extending the Hubble-diagram of Type Ia SNe beyond
redshift 2 up to z~4. Such high-z SNe Ia may provide new observational
constraints for their progenitor scenario.Comment: accepted for publication in Ap
Detecting Pair-Instability Supernovae at z<5 with the James Webb Space Telescope
Pair-instability supernovae (PISNe) are the ultimate cosmic lighthouses,
capable of being observed at z<25 and revealing the properties of primordial
stars at cosmic dawn. But it is now understood that the spectra and light
curves of these events evolved with redshift as the universe became polluted
with heavy elements because chemically enriched stars in this mass range
typically lose most of their hydrogen envelopes and explode as bare helium
cores. The light curves of such transients can be considerably dimmer in the
near infrared (NIR) today than those of primordial PISNe of equal energy and
progenitor mass. Here, we calculate detection rates for PISNe whose progenitors
lost their outer layers to either line-driven winds or rotation at z<10, their
detection limit in redshift for the James Webb Space Telescope (JWST). We find
that JWST may be able to detect only Pop II (metal-poor) PISNe over the
redshift range of z<4, but not their Pop III (metal-free) counterparts.Comment: Accepted for ApJ, in pres
Structure Formation with Cold + Hot Dark Matter
We report results from high-resolution particle-mesh (PM) N-body simulations
of structure formation in an cosmological model with a mixture of
Cold plus Hot Dark Matter (C+HDM) having ,
, and . We present analytic fits to
the C+HDM power spectra for both cold and hot () components, which provide
initial conditions for our nonlinear simulations. In order to sample the
neutrino velocities adequately, these simulations included six times as many
neutrino particles as cold particles. Our simulation boxes were 14, 50, and
200~Mpc cubes (with km s Mpc); we also did comparison
simulations for Cold Dark Matter (CDM) in a 50~Mpc box. C+HDM with linear bias
factor is consistent both with the COBE data and with the galaxy
correlations we calculate. We find the number of halos as a function of mass
and redshift in our simulations; our results for both CDM and C+HDM are well
fit by a Press-Schechter model. The number density of galaxy-mass halos is
smaller than for CDM, especially at redshift , but the numbers of
cluster-mass halos are comparable. We also find that on galaxy scales the
neutrino velocities and flatter power spectrum in C+HDM result in galaxy
pairwise velocities that are in good agreement with the data, and about 30\%
smaller than in CDM with the same biasing factor. On scales of several tens of
Mpc, the C+HDM streaming velocities are considerably larger than CDM. Thus
C+HDM looks promising as a model of structure formation.Comment: 33pp., 16+ figures not included (available by mail), SCIPP-92/5
Could Edge-Lit Type Ia Supernovae be Standard Candles
The progenitors of Type Ia supernovae (SNe Ia) have not been identified.
Though they are no longer fashionable we investigate the consequences if a
significant number of SNe Ia were edge-lit detonations (ELDs) of carbon/oxygen
white dwarfs that have accreted a critical mass of helium. Our best
understanding of the Phillips relation between light curve speed and peak
luminosity assigns both these phenomena to the amount of Ni produced. In
ELDs there are two sites of Ni synthesis. If the peak luminosity is
determined primarily by the C/O ratio in the core it is primarily a function of
its progenitor's initial mass. If the light curve decay speed is determined by
the total mass of iron group elements ejected this is a function of the total
mass of the ELD at the time of explosion. In general these two masses are
correlated and an empirical relation between peak luminosity and light curve
shape can be expected. However when we perform population synthesis for
progenitors of different metallicities we find a systematic shift in this
relation that would make distant SNe Ia fainter than those nearby. The
abundances of alpha-rich isotopes, such as Ca, in the solar system
indicate that only about 40 per cent of SNe Ia are edge-lit so any systematic
effect that could be present would be correspondingly diluted. If we examine
only the small subset of ELDs that accrete from a naked helium star, rather
than a He white dwarf, the systematic effect disappears.Comment: 14 pages, 3figure
Casimir effect: running Newton constant or cosmological term
We argue that the instability of Euclidean Einstein gravity is an indication
that the vacuum is non perturbative and contains a condensate of the metric
tensor in a manner reminiscent of Yang-Mills theories. As a simple step toward
the characterization of such a vacuum the value of the one-loop effective
action is computed for Euclidean de Sitter spaces as a function of the
curvature when the unstable conformal modes are held fixed. Two phases are
found, one where the curvature is large and gravitons should be confined and
another one which appears to be weakly coupled and tends to be flat. The
induced cosmological constant is positive or negative in the strongly or weakly
curved phase, respectively. The relevance of the Casimir effect in
understanding the UV sensitivity of gravity is pointed out.Comment: Final, slightly extended version, to appear in Classical and Quantum
Gravit
How far can we trust type Ia supernovae as standard candles?
We review the various possibilities that have been proposed as progenitors of Type Ia supernovae (SNe Ia) from the point of view of binary evolution and population synthesis. Depending on the nature of the progenitor, there may be systematic effects that cannot be calibrated by local observations that could undermine their use as standard candles
Forecast of Cosmological Constraints with Type Ia Supernovae from the Chinese Space Station Telescope
The 2-m aperture Chinese Space Station Telescope (CSST), which observes at
wavelengths ranging from 255 to 1000 nm, is expected to start science
operations in 2024. An ultra-deep field observation program covering
approximately 10 square degrees is proposed with supernovae (SNe) and other
transients as one of its primary science drivers. This paper presents the
simulated detection results of type Ia supernovae (SNe Ia) and explores the
impact of new datasets on the determinations of cosmological parameters. The
simulated observations are conducted with an exposure time of 150 s and
cadences of 10, 20, and 30 days. The survey mode covering a total of 80
observations but with a random cadence in the range of 4 to 14 days is also
explored. Our simulation results indicate that the CSST can detect up to SNe Ia at z 1.3. The simulated SNe Ia are then used to constrain the
cosmological parameters. The constraint on can be improved by 37.5%
using the 10-day cadence sample in comparison with the Pantheon sample. A
deeper measurement simulation with a 300 s exposure time together with the
Pantheon sample improves the current constraints on by 58.3% and
by 47.7%. Taking future ground-based SNe Ia surveys into
consideration, the constraints on can be improved by 59.1%. The CSST
ultra-deep field observation program is expected to discover large amounts of
SNe Ia over a broad redshift span and enhance our understanding of the nature
of dark energy.Comment: 10 pages, 6 figures, 2 tables, accepted for publication in SCIENCE
CHINA Physics, Mechanics & Astronom