13,859 research outputs found
Strong Clustering of Lyman Break Galaxies around Luminous Quasars at z~4
In the standard picture of structure formation, the first massive galaxies
are expected to form at the highest peaks of the density field, which
constitute the cores of massive proto-clusters. Luminous quasars (QSOs) at z~4
are the most strongly clustered population known, and should thus reside in
massive dark matter halos surrounded by large overdensities of galaxies,
implying a strong QSO-galaxy cross-correlation function. We observed six z~4
QSO fields with VLT/FORS exploiting a novel set of narrow band filters custom
designed to select Lyman Break Galaxies (LBGs) in a thin redshift slice of
Delta_z~0.3, mitigating the projection effects that have limited the
sensitivity of previous searches for galaxies around z>~4 QSOs. We find that
LBGs are strongly clustered around QSOs, and present the first measurement of
the QSO-LBG cross-correlation function at z~4, on scales of 0.1<~R<~9 Mpc/h
(comoving). Assuming a power law form for the cross-correlation function
xi=(r/r0_QG)^gamma, we measure r0_QG=8.83^{+1.39}_{-1.51} Mpc/h for a fixed
slope of gamma=2.0. This result is in agreement with the expected
cross-correlation length deduced from measurements of the QSO and LBG
auto-correlation function, and assuming a linear bias model. We also measure a
strong auto-correlation of LBGs in our QSO fields finding
r0_GG=21.59^{+1.72}_{-1.69} Mpc/h for a fixed slope of gamma=1.5, which is ~4
times larger than the LBG auto-correlation length in random fields, providing
further evidence that QSOs reside in overdensities of LBGs. Our results
qualitatively support a picture where luminous QSOs inhabit exceptionally
massive (M_halo>10^12 M_sun) dark matter halos at z~4.Comment: 25 pages, 22 figures, submitted to the Ap
The circumstellar envelope of AFGL 4106
We present new imaging and spectroscopy of the post-red supergiant binary
AFGL 4106. Coronographic imaging in H-alpha reveals the shape and extent of the
ionized region in the circumstellar envelope (CSE). Echelle spectroscopy with
the slit covering almost the entire extent of the CSE is used to derive the
physical conditions in the ionized region and the optical depth of the dust
contained within the CSE.
The dust shell around AFGL 4106 is clumpy and mixed with ionized gas. H-alpha
and [N II] emission is brightest from a thin bow-shaped layer just outside of
the detached dust shell. On-going mass loss is traced by [Ca II] emission and
blue-shifted absorption in lines of low-ionization species. A simple model is
used to interpret the spatial distribution of the circumstellar extinction and
the dust emission in a consistent way.Comment: 10 pages, 11 figures. Accepted for publication in Astronomy &
Astrophysics Main Journa
Interaction of Human Sperm Acrosomal Proteinase with Human seminal Plasma Proteinase Inhibitors
The Functional Derivation of Master Equations
Master equations describe the quantum dynamics of open systems interacting
with an environment. They play an increasingly important role in understanding
the emergence of semiclassical behavior and the generation of entropy, both
being related to quantum decoherence. Presently we derive the exact master
equation for a homogeneous scalar Higgs or inflaton like field coupled to an
environment field represented by an infinite set of harmonic oscillators. Our
aim is to demonstrate a derivation directly from the path integral
representation of the density matrix propagator. Applications and
generalizations of this result are discussed.Comment: 10 pages; LaTex. - Contribution to the workshop Hadron Physics VI,
March 1998, Florianopolis (Brazil); proceedings, E. Ferreira et al., eds.
(World Scientific). Replaced by slightly modified published versio
Cosmic Structure Traced by Precision Measurements of the X-Ray Brightest Galaxy Clusters in the Sky
The current status of our efforts to trace cosmic structure with 10^6
galaxies (2MASS), 10^3 galaxy clusters (NORAS II cluster survey), and precision
measurements for 10^2 galaxy clusters (HIFLUGCS) is given. The latter is
illustrated in more detail with results on the gas temperature and metal
abundance structure for 10^0 cluster (A1644) obtained with XMM-Newton.Comment: 4 pages; to be published in the Proceedings of the Conference: The
Emergence of Cosmic Structure, College Park, MD (2002), editors: S.S. Holt
and C. Reynolds; also available at http://www.reiprich.ne
Pair Contact Process with Diffusion: Failure of Master Equation Field Theory
We demonstrate that the `microscopic' field theory representation, directly
derived from the corresponding master equation, fails to adequately capture the
continuous nonequilibrium phase transition of the Pair Contact Process with
Diffusion (PCPD). The ensuing renormalization group (RG) flow equations do not
allow for a stable fixed point in the parameter region that is accessible by
the physical initial conditions. There exists a stable RG fixed point outside
this regime, but the resulting scaling exponents, in conjunction with the
predicted particle anticorrelations at the critical point, would be in
contradiction with the positivity of the equal-time mean-square particle number
fluctuations. We conclude that a more coarse-grained effective field theory
approach is required to elucidate the critical properties of the PCPD.Comment: revtex, 8 pages, 1 figure include
The stellar population structure of the Galactic disk
The spatial structure of stellar populations with different chemical
abundances in the Milky Way contains a wealth of information on Galactic
evolution over cosmic time. We use data on 14,699 red-clump stars from the
APOGEE survey, covering 4 kpc <~ R <~ 15 kpc, to determine the structure of
mono-abundance populations (MAPs)---stars in narrow bins in [a/Fe] and
[Fe/H]---accounting for the complex effects of the APOGEE selection function
and the spatially-variable dust obscuration. We determine that all MAPs with
enhanced [a/Fe] are centrally concentrated and are well-described as
exponentials with a scale length of 2.2+/-0.2 kpc over the whole radial range
of the disk. We discover that the surface-density profiles of low-[a/Fe] MAPs
are complex: they do not monotonically decrease outwards, but rather display a
peak radius ranging from ~5 kpc to ~13 kpc at low [Fe/H]. The extensive radial
coverage of the data allows us to measure radial trends in the thickness of
each MAP. While high-[a/Fe] MAPs have constant scale heights, low-[a/Fe] MAPs
flare. We confirm, now with high-precision abundances, previous results that
each MAP contains only a single vertical scale height and that low-[Fe/H],
low-[a/Fe] and high-[Fe/H], high-[a/Fe] MAPs have intermediate (h_Z~300 to 600
pc) scale heights that smoothly bridge the traditional thin- and thick-disk
divide. That the high-[a/Fe], thick disk components do not flare is strong
evidence against their thickness being caused by radial migration. The
correspondence between the radial structure and chemical-enrichment age of
stellar populations is clear confirmation of the inside-out growth of galactic
disks. The details of these relations will constrain the variety of physical
conditions under which stars form throughout the MW disk.Comment: Code available at https://github.com/jobovy/apogee-map
Spin gap and Luttinger liquid description of the NMR relaxation in carbon nanotubes
Recent NMR experiments by Singer et al. [Singer et al. Phys. Rev. Lett. 95,
236403 (2005).] showed a deviation from Fermi-liquid behavior in carbon
nanotubes with an energy gap evident at low temperatures. Here, a comprehensive
theory for the magnetic field and temperature dependent NMR 13C spin-lattice
relaxation is given in the framework of the Tomonaga-Luttinger liquid. The low
temperature properties are governed by a gapped relaxation due to a spin gap (~
30K), which crosses over smoothly to the Luttinger liquid behaviour with
increasing temperature.Comment: 5 pages, 1 figure, 1 tabl
Generating and sustaining long-lived spin states in 15N,15N′-azobenzene
Long-Lived spin States (LLSs) hold a great promise for sustaining non-thermal spin order and investigating various slow processes by Nuclear Magnetic Resonance (NMR) spectroscopy. Of special interest for such application are molecules containing nearly equivalent magnetic nuclei, which possess LLSs even at high magnetic fields. In this work, we report an LLS in trans-15N,15N′-azobenzene. The singlet state of the 15N spin pair exhibits a long-lived character. We solve the challenging problem of generating and detecting this LLS and further increase the LLS population by converting the much higher magnetization of protons into the 15N singlet spin order. As far as the longevity of this spin order is concerned, various schemes have been tested for sustaining the LLS. Lifetimes of 17 minutes have been achieved at 16.4 T, a value about 250 times longer than the longitudinal relaxation time of 15N in this magnetic field. We believe that such extended relaxation times, along with the photochromic properties of azobenzene, which changes conformation upon light irradiation and can be hyperpolarized by using parahydrogen, are promising for designing new experiments with photo-switchable long-lived hyperpolarization
- …