3,401 research outputs found
Chaotic diffusion of particles with finite mass in oscillating convection flows
Deterministic diffusion in temporally oscillating convection is studied for
particles with finite mass. The particles are assumed to obey a simple
dissipative dynamical system and the particle diffusion is induced by the
strange attractor. The diffusion constants are numerically calculated for
convection models with free and rigid boundary conditions.Comment: 5 figure
Where are the z=4 Lyman Break Galaxies? Results from Conditional Luminosity Function Models of Luminosity-dependent Correlation Functions
Using the conditional luminosity function (CLF) -- the luminosity distribution of galaxies in a dark matter halo -- as a way to model galaxy statistics, we study how z=4 Lyman Break Galaxies (LBGs) are distributed in dark matter halos. For this purpose, we measure luminosity-dependent clustering of LBGs in the Subaru/XMM-Newton Deep Field by separating a sample of 16,920 galaxies to three magnitude bins in i'-band between 24.5 and 27.5. Our models fits to data show a possible trend for more luminous galaxies to appear as satellites in more massive halos. The satellite fraction of galaxies at z=4 in these magnitude bins is 0.13 to 0.3, 0.09 to 0.22, and 0.03 to 0.14, respectively, where the 1 sigma ranges account for differences coming from two different estimates of the z=4 LF from the literature. To jointly explain the LF and the large-scale linear bias factor of z=4 LBGs as a function of rest-UV luminosity requires central galaxies to be brighter in UV at z =4 than present-day galaxies in same dark matter mass halos. Moreover, UV luminosity of central galaxies in halos with total mass greater than roughly 10^{12} M_sun must decrease from z=4 to today by an amount more than the luminosity change for galaxies in halos below this mass. This mass-dependent luminosity evolution is preferred at more than 3 sigma confidence level compared to a pure-luminosity evolution scenario where all galaxies decrease in luminosity by the same amount from z=4 to today. The scenario preferred by the data is consistent with the ``down-sizing'' picture of galaxy evolution
Tracing early structure formation with massive starburst galaxies and their implications for reionization
Cosmological hydrodynamic simulations have significantly improved over the
past several years, and we have already shown that the observed properties of
Lyman-break galaxies (LBGs) at z=3 can be explained well by the massive
galaxies in the simulations. Here we extend our study to z=6 and show that we
obtain good agreement for the LBGs at the bright-end of the luminosity function
(LF). Our simulations also suggest that the cosmic star formation rate density
has a peak at z= 5-6, and that the current LBG surveys at z=6 are missing a
significant number of faint galaxies that are dimmer than the current magnitude
limit. Together, our results suggest that the universe could be reionized at
z=6 by the Pop II stars in ordinary galaxies. We also estimate the LF of
Lyman-alpha emitters (LAEs) at z=6 by relating the star formation rate in the
simulation to the Ly-alpha luminosity. We find that the simulated LAE LFs agree
with the observed data provided that the net escape fraction of Ly-alpha photon
is f_{Ly-alpha} <= 0.1. We investigate two possible scenarios for this effect:
(1) all sources in the simulation are uniformly dimmer by a factor of 10
through attenuation, and (2) one out of ten LAEs randomly lights up at a given
moment. We show that the correlation strength of the LAE spatial distribution
can possibly distinguish the two scenarios.Comment: 9 pages, 4 figures. Summary of the talk given at the "First Light &
Reionization" workshop at UC Irvine, May 2005. The published article is
available from http://dx.doi.org/10.1016/j.newar.2005.11.00
Evidence for Low Extinction in Actively Star Forming Galaxies at z6.5
We present a search for the [CII] 158micron fine structure line (a main
cooling line of the interstellar medium) and the underlying far-infrared (FIR)
continuum in three high-redshift (6.6<z<8.2) star-forming galaxies using the
IRAM Plateau de Bure interferometer. We targeted two Lyman-Alpha-selected
galaxies (Lyman-Alpha-Emitters, LAEs) with moderate UV-based star formation
rates (SFR~20 M_sun/yr; Himiko at z=6.6 and IOK-1 at z=7.0) and a Gamma Ray
Burst (GRB) host galaxy (GRB 090423 at z~8.2). Based on our 3 sigma rest-frame
FIR continuum limits, previous (rest-frame) UV continuum measurements and
spectral energy distribution (SED) fitting, we rule out SED shapes similar to
highly obscured galaxies (e.g. Arp220, M82) and less extreme dust-rich nearby
spiral galaxies (e.g. M51) for the LAEs. Conservatively assuming a SED shape
typical of local spiral galaxies we derive upper limits for the FIR-based star
formation rates (SFRs) of ~70 M_sun/yr, ~50 M_sun/yr and ~40 M_sun/yr for
Himiko, IOK-1 and GRB 090423, respectively. For the LAEs these limits are only
a factor ~3 higher than the published UV-based SFRs (uncorrected for
extinction). This indicates that the dust obscuration in the z>6 LAEs studied
here is lower by a factor of a few than what has recently been found in some
LAEs at lower redshift (2<z<3.5) with similar UV-based SFRs. A low obscuration
in our z>6 LAE sample is consistent with recent rest-frame UV studies of z~7
Lyman-Break-Galaxies (LBGs).Comment: Accepted for publication in the Astrophysical Journa
Very blue UV-continuum slopes of low luminosity z~7 galaxies from WFC3/IR: Evidence for extremely low metallicities?
We use the ultra-deep WFC3/IR data over the HUDF and the Early Release
Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband
spectral properties of candidate star-forming galaxies at z~7. We determine the
UV-continuum slope beta in these galaxies, and compare the slopes with galaxies
at later times to measure the evolution in beta. For luminous L*(z=3) galaxies,
we measure a mean UV-continuum slope beta of -2.0+/-0.2, which is comparable to
the beta~-2 derived at similar luminosities at z~5-6. However, for the lower
luminosity 0.1L*(z=3) galaxies, we measure a mean beta of -3.0+/-0.2. This is
substantially bluer than is found for similar luminosity galaxies at z~4, just
800 Myr later, and even at z~5-6. In principle, the observed beta of -3.0 can
be matched by a very young, dust-free stellar population, but when nebular
emission is included the expected beta becomes >~-2.7. To produce these very
blue beta's (i.e., beta~-3), extremely low metallicities and mechanisms to
reduce the red nebular emission are likely required. For example, a large
escape fraction (i.e., f_{esc}>~0.3) could minimize the contribution from this
red nebular emission. If this is correct and the escape fraction in faint z~7
galaxies is >~0.3, it may help to explain how galaxies reionize the universe.Comment: 5 pages, 5 figures, accepted for publication in Astrophysical Journal
Letter
Large Cosmic Variance in the Clustering Properties of Lyman Alpha Emitters at z~5
We reported in a previous paper the discovery of large-scale structure of
Lyman Alpha emitters (LAEs) at z=4.86+-0.03 with a projected size of 20 Mpc x
50 Mpc in narrow-band data of a 25' x 45' area of the Subaru Deep Field
(Omega_0=0.3, lambda_0=0.7, H0=70 km/s/Mpc). However, the surveyed area, which
corresponds to 55 Mpc x 100 Mpc, was not large enough that we can conclude that
we are seeing a typical distribution of z~5 LAEs. In this Letter, we report the
results of follow-up imaging of the same sky area using a new narrow-band
filter (NB704, lambda_c=7046 A and FWHM=100 A) to detect LAEs at z=4.79, i.e.,
LAEs lying closer to us by 39 Mpc on average than the z=4.86 objects. We detect
51 LAEs at z=4.79+-0.04 down to NB704=25.7, and find that their sky
distribution is quite different from the z=4.86 LAEs'. The clustering of z=4.79
LAEs is very weak on any scales and there is no large-scale high- contrast
structure. The shape and the amplitude of the angular correlation function are
thus largely different between the two samples. These results demonstrate a
large cosmic variance in the clustering properties of LAEs on scales of ~ 50
Mpc.Comment: 4 pages (uses emulateapj5.sty), accepted for ApJ
Large-scale structure of Lyman break galaxies around a radio galaxy protocluster at z~4
We present broad-band imaging with the Subaru Telescope of a 25'x25' field
surrounding the radio galaxy TN J1338-1942 at redshift z=4.1. The field
contains excesses of Lyman-alpha emitters (LAEs) and Lyman break galaxies
(LBGs) identified with a protocluster surrounding the radio galaxy. Our new
wide-field images provide information about the boundary of the protocluster
and its surroundings. There are 874 candidate LBGs within our field, having
redshifts in the range z=3.5-4.5. An examination of the brightest of these
(with i'< 25.0) shows that the most prominent concentration coincides with the
previously discovered protocluster. The diameter of this galaxy overdensity
corresponds to ~2 Mpc at z=4, consistent with the previous estimation using
LAEs. Several other concentrations of LBGs are observed in the field, some of
which may well be physically connected with the z=4.1 protocluster. The
observed structure in the smoothed LBG distribution can be explained as the
projection of large-scale structure, within the redshift range z=3.5-4.5,
comprising compact overdensities and prominent larger voids. If the 5-8
observed compact overdensities are associated with protoclusters, the observed
protocluster volume density is ~5x10^-6 Mpc^-3, similar to the volume density
of rich clusters in the local Universe.Comment: 5 pages, 4 figures. Accepted for publication in A&A. Full resolution
version available at
http://www.strw.leidenuniv.nl/~intema/files/AA_2006_4812.zi
Constraining the Lyα escape fraction with far-infrared observations of Lyα emitters
We study the far-infrared properties of 498 Lyα emitters (LAEs) at z = 2.8, 3.1, and 4.5 in the Extended Chandra Deep Field-South, using 250, 350, and 500μm data from the Herschel Multi-tiered Extragalactic Survey and 870μm data from the LABOCA ECDFS Submillimeter Survey. None of the 126, 280, or 92 LAEs at z = 2.8, 3.1, and 4.5, respectively, are individually detected in the far-infrared data. We use stacking to probe the average emission to deeper flux limits, reaching 1σ depths of ∼0.1 to 0.4 mJy. The LAEs are also undetected at ?3σ in the stacks, although a 2.5σ signal is observed at 870μm for the z = 2.8 sources. We consider a wide range of far-infrared spectral energy distributions (SEDs), including an M82 and an Sd galaxy template, to determine upper limits on the far-infrared luminosities and far-infrared-derived star formation rates of the LAEs. These star formation rates are then combined with those inferred from the Lyα and UV emission to determine lower limits on the LAEs’ Lyα escape fraction (f esc (Lyα)). For the Sd SED template, the inferred LAEs f esc (Lyα) are ?30% (1σ) at z = 2.8, 3.1, and 4.5, which are all significantly higher than the global f esc (Lyα) at these redshifts. Thus, if the LAEs f esc (Lyα) follows the global evolution, then they have warmer far-infrared SEDs than the Sd galaxy template. The average and M82 SEDs produce lower limits on the LAE f esc (Lyα) of ∼10%–20% (1σ), all of which are slightly higher than the global evolution of f esc (Lyα), but consistent with it at the 2σ–3σ level
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