11 research outputs found
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
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
Theia: Faint objects in motion or the new astrometry frontier
In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 % of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision
Theia: Faint objects in motion or the new astrometry frontier
In the context of the ESA M5 (medium mission) call we proposed a new satellite mission, Theia, based on relative astrometry and extreme precision to study the motion of very faint objects in the Universe. Theia is primarily designed to study the local dark matter properties, the existence of Earth-like exoplanets in our nearest star systems and the physics of compact objects. Furthermore, about 15 of the mission time was dedicated to an open observatory for the wider community to propose complementary science cases. With its unique metrology system and "point and stare" strategy, Theia's precision would have reached the sub micro-arcsecond level. This is about 1000 times better than ESA/Gaia's accuracy for the brightest objects and represents a factor 10-30 improvement for the faintest stars (depending on the exact observational program). In the version submitted to ESA, we proposed an optical (350-1000nm) on-axis TMA telescope. Due to ESA Technology readiness level, the camera's focal plane would have been made of CCD detectors but we anticipated an upgrade with CMOS detectors. Photometric measurements would have been performed during slew time and stabilisation phases needed for reaching the required astrometric precision