243 research outputs found
Growth of Linear Perturbations before the Era of the First Galaxies
We calculate the evolution of linear density and temperature perturbations in
a universe with dark matter, baryons, and radiation, from cosmic recombination
until the epoch of the first galaxies. In addition to gravity, the
perturbations are effected by electron scattering with the radiation, by
radiation pressure, and by gas pressure. We include the effect of spatial
fluctuations in the baryonic sound speed and show that they induce a >10%
change in the baryonic density power spectrum on small scales, and a larger
change on all scales in the power spectrum of gas temperature fluctuations. A
precise calculation of the growth of linear perturbations is essential since
they provide the initial conditions for the formation of galaxies and they can
also be probed directly via cosmological 21cm fluctuations. We also show that
in general the thermal history of the cosmic gas can be measured from 21cm
fluctuations using a small-scale anisotropic cutoff due to the thermal width of
the 21cm line.Comment: 8 pages, 6 figures, MNRAS, accepte
The Supersonic Project: Shining Light on SIGOs - a New Formation Channel for Globular Clusters
Supersonically induced gas objects (SIGOs) with little to no dark matter
component are predicted to exist in patches of the Universe with non-negligible
relative velocity between baryons and the dark matter at the time of
recombination. Using {\sc arepo} hydrodynamic simulations we find that the gas
densities inside these objects are high enough to allow stars to form. An
estimate of the luminosity of the first star clusters formed within these SIGOs
suggests that they may be observed at high redshift using future HST and JWST
observations. Furthermore, our simulations indicate that SIGOs lie in a
distinct place in the luminosity-radius parameter space, which can be used
observationally to distinguish SIGOs from dark-matter hosting gas systems.
Finally, as a proof-of-concept, we model star formation before reionization and
evolve these systems to current times. We find that SIGOs occupy a similar part
of the magnitude-radius parameter space as globular clusters. These results
suggest that SIGOs may be linked with present-day metal-poor local globular
clusters. Since the relative velocity between the baryons and dark matter is
coherent over a few Mpc scales, we predict that if this is the dominant
mechanism for the formation of globular clusters, their abundance should vary
significantly over these scales.Comment: 9 pages, 5 figures, submitted to ApJ
Detecting Early Galaxies Through Their 21-cm Signature
New observations over the next few years of the emission of distant objects
will help unfold the chapter in cosmic history around the era of the first
galaxies. These observations will use the neutral hydrogen emission or
absorption at a wavelength of 21-cm as a detector of the hydrogen abundance. We
predict the signature on the 21-cm signal of the early generations of galaxies.
We calculate the 21-cm power spectrum including two physical effects that were
neglected in previous calculations. The first is the redistribution of the UV
photons from the first galaxies due to their scattering off of the neutral
hydrogen, which results in an enhancement of the 21-cm signal. The second is
the presence of an ionized hydrogen bubble near each source, which produces a
cutoff at observable scales. We show that the resulting clear signature in the
21-cm power spectrum can be used to detect and study the population of galaxies
that formed just 200 million years after the Big Bang.Comment: 5 pages, 3 figures, submitted to MNRAS Let
The First Stars in The Universe
Large telescopes have allowed astronomers to observe galaxies that formed as
early as 850 million years after the Big Bang. We predict when the first star
that astronomers can observe formed in the universe, accounting for the first
time for the size of the universe and for three essential ingredients: the
light travel time from distant galaxies, Poisson and density fluctuations on
all scales, and the effect of very early cosmic history on galaxy formation. We
find that the first observable star is most likely to have formed 30 million
years after the Big Bang (at redshift 65), much earlier than previously
expected. Also, the first galaxy as massive as our own Milky Way likely formed
when the universe was only 400 Myr old (at redshift 11). We also show that
significant modifications are required in current methods of numerically
simulating the formation of galaxies at redshift 20 and above.Comment: 5 pages, 4 figures, MNRAS Letters, revised versio
An Observational Limit on the Earliest GRBs
We predict the redshift of the first observable (i.e., in our past light
cone) Gamma Ray Burst (GRB) and calculate the GRB-rate redshift distribution of
the Population III stars at very early times (z=20-60). Using the last 2 years
of data from Swift we place an upper limit on the efficiency (\eta_{GRB}) of
GRB production per solar mass from the first generation of stars. We find that
the first observable GRB is most likely to have formed at redshift 60. The
observed rate of extremely high redshift GRBs (XRGs) is a subset of a group of
15 long GRBs per year, with no associated redshift and no optical afterglow
counterparts, detected by Swift. Taking this maximal rate we get that
\eta_{GRB}<1.1~10^{-4} GRBs per solar mass in stars. A more realistic
evaluation, e.g., taking a subgroup of 5% of the total sample of Swift gives an
upper limit of \eta_{GRB}<3.2~10^{-5} GRBs per solar mass.Comment: 6 Pages, 3 figures, submitted to MNRA
Suppression of small baryonic structures due to a primordial magnetic field
We investigate the impact of the existence of a primordial magnetic field on
the filter mass, characterizing the minimum baryonic mass that can form in dark
matter (DM) haloes. For masses below the filter mass, the baryon content of DM
haloes are severely depressed. The filter mass is the mass when the baryon to
DM mass ratio in a halo is equal to half the baryon to DM ratio of the
Universe. The filter mass has previously been used in semianalytic calculations
of galaxy formation, without taking into account the possible existence of a
primordial magnetic field. We examine here its effect on the filter mass. For
homogeneous comoving primordial magnetic fields of or 2 nG and a
reionization epoch that starts at a redshift and is completed at
, the filter mass is increased at redshift 8, for example, by factors
4.1 and 19.8, respectively. The dependence of the filter mass on the parameters
describing the reionization epoch is investigated. Our results are particularly
important for the formation of low mass galaxies in the presence of a
homogeneous primordial magnetic field. For example, for B_0\sim 1\nG and a
reionization epoch of and , our results indicate that
galaxies of total mass M\sim5 \times 10^8\msun need to form at redshifts
, and galaxies of total mass M\sim10^8\msun at redshifts
.Comment: 5 pages, 3 figures, accepted for publication in MNRA
The signature of the first stars in atomic hydrogen at redshift 20
Dark and baryonic matter moved at different velocities in the early Universe,
which strongly suppressed star formation in some regions. This was estimated to
imprint a large-scale fluctuation signal of about 2 mK in the 21-cm spectral
line of atomic hydrogen associated with stars at a redshift of 20, although
this estimate ignored the critical contribution of gas heating due to X-rays
and major enhancements of the suppression. A large velocity difference reduces
the abundance of halos and requires the first stars to form in halos of about a
million solar masses, substantially greater than previously expected. Here we
report a simulation of the distribution of the first stars at z=20 (cosmic age
of ~180 Myr), incorporating all these ingredients within a 400 Mpc box. We find
that the 21-cm signature of these stars is an enhanced (10 mK) fluctuation
signal on the 100-Mpc scale, characterized by a flat power spectrum with
prominent baryon acoustic oscillations. The required sensitivity to see this
signal is achievable with an integration time of a thousand hours with an
instrument like the Murchison Wide-field Array or the Low Frequency Array but
designed to operate in the range of 50-100 MHz.Comment: 27 pages, 5 figures, close (but not exact) match to accepted version.
Basic results unchanged from first submitted version, but justification
strengthened, title and abstract modified, and substantial Supplementary
Material added. Originally first submitted for publication on Oct. 12, 201
Effects of an eccentric inner Jupiter on the dynamical evolution of icy body reservoirs in a planetary scattering scenario
Aims. We analyze the dynamics of small body reservoirs under the effects of an eccentric inner giant planet resulting from a planetary scattering event around a 0.5 M⊙ star. Methods. First, we used a semi-analytical model to define the properties of the protoplanetary disk that lead to the formation of three Jupiter-mass planets. Then, we carried out N-body simulations assuming that the planets are close to their stability limit together with an outer planetesimal disk. In particular, the present work focused on the analysis of N-body simulations in which a single Jupiter-mass planet survives after the dynamical instability event. Results. Our simulations produce outer small body reservoirs with particles on prograde and retrograde orbits, and other ones whose orbital plane flips from prograde to retrograde and back again along their evolution (“Type-F particles”). We find strong correlations between the inclination i and the ascending node longitude Ω of Type-F particles. First, Ω librates around 90° or/and 270°. This property represents a necessary and sufficient condition for the flipping of an orbit. Moreover, the libration periods of i and Ω are equal and they are out to phase by a quarter period. We also remark that the larger the libration amplitude of i, the larger the libration amplitude of Ω. We analyze the orbital parameters of Type-F particles immediately after the instability event (post IE orbital parameters), when a single Jupiter-mass planet survives in the system. Our results suggest that the orbit of a particle can flip for any value of its post IE eccentricity, although we find only two Type-F particles with post IE inclinations i ≲ 17°. Finally, our study indicates that the minimum value of the inclination of the Type-F particles in a given system decreases with an increase in the eccentricity of the giant planet.Fil: Zanardi, Macarena. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: de Elia, Gonzalo Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Di Sisto, Romina Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Naoz, S.. University of California at Los Angeles; Estados UnidosFil: Li, G.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Guilera, O. M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Brunini, A.. Universidad Nacional de la Patagonia Austral; Argentin
Where can we really find the First Stars' Remnants today?
A number of recent numerical investigations concluded that the remnants of
rare structures formed at very high redshift, such as the very first stars and
bright redshift z~6 QSOs, are preferentially located at the center of the most
massive galaxy clusters at redshift z=0. In this paper we readdress this
question using a combination of cosmological simulations of structure formation
and extended Press-Schechter formalism and we show that the typical remnants of
Population III stars are instead more likely to be found in a group
environment, that is in dark matter halos of mass ~2x10^{13} h^{-1}M_sun.
Similarly, the descendants of the brightest z~6 QSOs are expected to be in
medium-sized clusters (mass of a few 10^{14} h^{-1}M_sun), rather than in the
most massive superclusters (M>10^{15} h^{-1}M_sun) found within the typical 1
Gpc^3 cosmic volume where a bright z~6 QSO lives. The origin of past claims
that the most massive clusters preferentially host these remnants is rooted in
the numerical method used to initialize their numerical simulations: Only a
small region of the cosmological volume of interest was simulated with
sufficient resolution to identify low-mass halos at early times, and this
region was chosen to host the most massive halo in the cosmological volume at
late times. The conclusion that the earliest structures formed in the entire
cosmological volume evolve into the most massive halo at late times was thus
arrived at by construction. We demonstrate that, to the contrary, the first
structures to form in a cosmological region evolve into relatively typical
objects at later times. We propose alternative numerical methods for simulating
the earliest structures in cosmological volumes.Comment: 18 pages, 5 figures, ApJ accepted, high resolution version of the
paper available at http://www.stsci.edu/~trenti/papers/halo_evolution.pd
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