24 research outputs found
Photon Mass Bound Destroyed by Vortices
The Particle Data Group gives an upper bound on the photon mass eV from a laboratory experiment and lists, but does not adopt, an
astronomical bound eV, both of which are based on the
plausible assumption of large galactic vector-potential. We argue that the
interpretations of these experiments should be changed, which alters
significantly the bounds on . If arises from a Higgs effect, both limits
are invalid because the Proca vector-potential of the galactic magnetic field
may be neutralized by vortices giving a large-scale magnetic field that is
effectively Maxwellian. In this regime, experiments sensitive to the Proca
potential do not yield a useful bound on . As a by-product, the non-zero
photon mass from Higgs effect predicts generation of a primordial magnetic
field in the early universe. If, on the other hand, the galactic magnetic field
is in the Proca regime, the very existence of the observed large-scale magnetic
field gives kpc, or eV.Comment: 9 pages, discussion of primordial magnetic field adde
Understanding the nature of the optically faint radio sources and their connection to the submillimeter population
We present a sample of 43 submillimeter sources detected (at >3 sigma), drawn
from our program to follow-up optically faint radio sources with SCUBA. These
sources already have associated radio and in many cases optical
identifications, and many are also detected at 450 microns. We compare these
with 12 submillimeter sources drawn from the literature, which were discovered
in blank field mapping campaigns, but also have radio detections. We then use
this total sample (55 sources) to study and model the evolution of dusty
galaxies. A correlation is observed in the sub-mm/radio color-magnitude
diagram, which can be modeled by strong luminosity evolution. The selection
effects of the radio/optical pre-selection technique are determined from the
models, and a corrected redshift distribution is constrained using a range of
model assumptions. The temperature/redshift effects on the 450 microns detected
subset of our sample are studied in relation to the models, and prospects for
improved measurements in the shorter sub-mm wavelength windows (450 microns and
350 microns) are explored.Comment: to appear in ApJ, 19 pages, 9 figure
The evolution of the specific star formation rate of massive galaxies to z ~ 1.8 in the E-CDFS
We study the evolution of the star formation rate (SFR) of mid-infrared (IR)
selected galaxies in the extended Chandra Deep Field South (E-CDFS). We use a
combination of U-K GaBoDS and MUSYC data, deep IRAC observations from SIMPLE,
and deep MIPS data from FIDEL. This unique multi-wavelength data set allows us
to investigate the SFR history of massive galaxies out to redshift z ~ 1.8. We
determine star formation rates using both the rest-frame ultraviolet luminosity
from young, hot stars and the total IR luminosity of obscured star formation
obtained from the MIPS 24 um flux. We find that at all redshifts the galaxies
with higher masses have substantially lower specific star formation rates than
lower mass galaxies. The average specific star formation rates increase with
redshift, and the rate of incline is similar for all galaxies (roughly
(1+z)^{n}, n = 5.0 +/- 0.4). It does not seem to be a strong function of galaxy
mass. Using a subsample of galaxies with masses M_*> 10^11 M_sun, we measured
the fraction of galaxies whose star formation is quenched. We consider a galaxy
to be in quiescent mode when its specific star formation rate does not exceed
1/(3 x t_H), where t_H is the Hubble time. The fraction of quiescent galaxies
defined as such decreases with redshift out to z ~ 1.8. We find that, at that
redshift, 19 +/-9 % of the M_* > 10^11 M_sun sources would be considered
quiescent according to our criterion.Comment: 7 pages, 6 figures, accepted for publication in Ap
Differential Morphology Between Rest-frame Optical and UV Emission from 1.5 < z < 3 Star-forming Galaxies
We present the results of a comparative study of the rest-frame optical and
rest-frame ultraviolet morphological properties of 117 star-forming galaxies
(SFGs), including BX, BzK, and Lyman break galaxies with B<24.5, and 15 passive
galaxies in the region covered by the Wide Field Camera 3 Early Release Science
program. Using the internal color dispersion (ICD) diagnostic, we find that the
morphological differences between the rest-frame optical and rest-frame UV
light distributions in 1.4<z<2.9 SFGs are typically small (ICD~0.02). However,
the majority are non-zero (56% at >3 sigma) and larger than we find in passive
galaxies at 1.4<z<2, for which the weighted mean ICD is 0.013. The lack of
morphological variation between individual rest-frame ultraviolet bandpasses in
z~3.2 galaxies argues against large ICDs being caused by non-uniform dust
distributions. Furthermore, the absence of a correlation between ICD and galaxy
UV-optical color suggests that the non-zero ICDs in SFGs are produced by
spatially distinct stellar populations with different ages. The SFGs with the
largest ICDs (>~0.05) generally have complex morphologies that are both
extended and asymmetric, suggesting that they are mergers-in-progress or very
large galaxies in the act of formation. We also find a correlation between
half-light radius and internal color dispersion, a fact that is not reflected
by the difference in half-light radii between bandpasses. In general, we find
that it is better to use diagnostics like the ICD to measure the morphological
properties of the difference image than it is to measure the difference in
morphological properties between bandpasses.Comment: 11 pages, 9 figures, accepted to Ap
Lyman-Alpha-Emitting Galaxies at z = 2.1 in ECDF-S: Building Blocks of Typical Present-day Galaxies?
We discovered a sample of 250 Ly-Alpha emitting (LAE) galaxies at z=2.1 in an
ultra-deep 3727 A narrow-band MUSYC image of the Extended Chandra Deep
Field-South. LAEs were selected to have rest-frame equivalent widths (EW) > 20
A and emission line fluxes > 2.0 x 10^(-17)erg /cm^2/s, after carefully
subtracting the continuum contributions from narrow band photometry. The median
flux of our sample is 4.2 x 10^(-17)erg/cm^2/s, corresponding to a median Lya
luminosity = 1.3 x 10^(42) erg/s at z=2.1. At this flux our sample is > 90%
complete. Approximately 4% of the original NB-selected candidates were detected
in X-rays by Chandra, and 7% were detected in the rest-frame far-UV by GALEX.
At luminosity>1.3 x 10^42 erg/s, the equivalent width distribution is unbiased
and is represented by an exponential with scale-length of 83+/-10 A. Above this
same luminosity threshold, we find a number density of 1.5+/-0.5 x 10^-3
Mpc^-3. Neither the number density of LAEs nor the scale-length of their EW
distribution show significant evolution from z=3 to z=2. We used the rest frame
UV luminosity to estimate a median star formation rate of 4 M_(sun) /yr. The
median rest frame UV slope, parametrized by B-R, is that typical of dust-free,
0.5-1 Gyr old or moderately dusty, 300-500 Myr old populations. Approximately
40% of the sample occupies the z~2 star-forming galaxy locus in the UVR two
color diagram. Clustering analysis reveals that LAEs at z=2.1 have
r_0=4.8+/-0.9 Mpc and a bias factor b=1.8+/-0.3. This implies that z=2.1 LAEs
reside in dark matter halos with median masses
Log(M/M_(sun))=11.5^(+0.4)_(-0.5), which are among of the lowest-mass halos yet
probed at this redshift. We used the Sheth-Tormen conditional mass function to
study the descendants of these LAEs and found that their typical present-day
descendants are local galaxies with L* properties, like the Milky Way.Comment: 35 pages, 9 figures, ApJ, in pres
Initial Results from the LIGO Newtonian Calibrator
The precise calibration of the strain readout of the LIGO gravitational wave
observatories is paramount to the accurate interpretation of gravitational wave
events. This calibration is traditionally done by imparting a known force on
the test masses of the observatory via radiation pressure. Here we describe the
implementation of an alternative calibration scheme: the Newtonian Calibrator.
This system uses a rotor consisting of both quadrupole and hexapole mass
distributions to apply a time-varying gravitational force on one of the
observatory's test masses. The force produced by this rotor can be predicted to
relative uncertainty and is well-resolved in the readout of the
observatory. This system currently acts as a cross-check of the existing
absolute calibration system
US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report
This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in
Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic