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CO and CI maps of the starburst galaxy M82
The first map of an external galaxy in the 3P₁ - 3P0 fine-structure line of atomic carbon (CI) is presented towards the nucleus of the starbuster M82, and compared with the distinction of the CO J = 4 - 3 molecular emission. The CI traces features that are seen in lower transition CO maps, and shows that CI and the CO are well mixed and have similar spatial distributions. There are small differences between the CO J = 4 - 3 line and lower transition CO data towards the NE part of the molecular ring, where the emission is less prominent. The abundance ratio [CI]/[CO] across M82 is very high, with an average value ~ 0.5 across most of the nucleus, a factor at least 5 times that which is typical of dense molecular cloud cores seen in our own Galaxy. This means that on average, CI is overabundant towards M82. This result can be explained using models which provide enhancements to the CI abundance above normal Interstellar Medium values, a result of a greater cosmic ray flux in M82, or where there is substantial mixing of the gas
Electroweak Bremsstrahlung in Dark Matter Annihilation
A conservative upper bound on the total dark matter (DM) annihilation rate
can be obtained by constraining the appearance rate of the annihilation
products which are hardest to detect. The production of neutrinos, via the
process , has thus been used to set a strong
general bound on the dark matter annihilation rate. However, Standard Model
radiative corrections to this process will inevitably produce photons which may
be easier to detect. We present an explicit calculation of the branching ratios
for the electroweak bremsstrahlung processes and
. These modes inevitably lead to electromagnetic
showers and further constraints on the DM annihilation cross-section. In
addition to annihilation, our calculations are also applicable to the case of
dark matter decay.Comment: 7 pages, 4 figures. New appendix with an extensive discussion of
Majorana fermions and helicity suppression
The Migdal Effect and Photon Bremsstrahlung in effective field theories of dark matter direct detection and coherent elastic neutrino-nucleus scattering
Dark matter direct detection experiments have limited sensitivity to light
dark matter (below a few GeV), due to the challenges of lowering energy
thresholds for the detection of nuclear recoil to below
. While impressive progress has been made on this
front, light dark matter remains the least constrained region of dark-matter
parameter space. It has been shown that both ionization and excitation due to
the Migdal effect and coherently-emitted photon bremsstrahlung from the
recoiling atom can provide observable channels for light dark matter that would
otherwise have been missed owing to the resulting nuclear recoil falling below
the detector threshold. In this paper we extend previous work by calculating
the Migdal effect and photon bremmstrahlung rates for a general set of
interaction types, including those that are momentum-independent or -dependent,
spin-independent or -dependent, as well as examining the rates for a variety of
target materials, allowing us to place new experimental limits on some of these
interaction types. Additionally, we include a calculation of these effects
induced by the coherent scattering on nuclei of solar or atmospheric neutrinos.
We demonstrate that the Migdal effect dominates over the bremsstrahlung effect
for all targets considered for interactions induced by either dark matter or
neutrinos. This reduces photon bremsstrahlung to irrelevancy for future direct
detection experiments.Comment: 17 pages, 6 figure
Searching for Dark Matter at the LHC with a Mono-Z
We investigate a mono-Z process as a potential dark matter search strategy at
the LHC. In this channel a single Z boson recoils against missing transverse
momentum, attributed to dark matter particles, , which escape the
detector. This search strategy is related, and complementary to, monojet and
monophoton searches. For illustrative purposes we consider the process
in a toy dark matter model, where the Z boson is
emitted from either the initial state quarks, or from the internal propagator.
Among the signatures of this process will be a pair of muons with high pT that
reconstruct to the invariant mass of the Z, and large amounts of missing
transverse energy. Being a purely electroweak signal, QCD and other Standard
Model backgrounds are relatively easily removed with modest selection cuts. We
compare the signal to Standard Model backgrounds and demonstrate that, even for
conservative cuts, there exist regions of parameter space where the signal may
be clearly visible above background in future LHC data, allowing either new
discovery potential or the possibility of supplementing information about the
dark sector beyond that available from other observable channels.Comment: 11 pages, 13 figure
Water depletion in the disk atmosphere of Herbig AeBe stars
We present high resolution (R = 100,000) L-band spectroscopy of 11 Herbig
AeBe stars with circumstellar disks. The observations were obtained with the
VLT/CRIRES to detect hot water and hydroxyl radical emission lines previously
detected in disks around T Tauri stars. OH emission lines are detected towards
4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as the
velocity profile of each component of the doublet. Its characteristic
double-peak profile demonstrates that the gas is in Keplerian rotation and
points to an emitting region extending out to ~ 15-30 AU. The OH, emission
correlates with disk geometry as it is mostly detected towards flaring disks.
None of the Herbig stars analyzed here show evidence of hot water vapor at a
sensitivity similar to that of the OH lines. The non-detection of hot water
vapor emission indicates that the atmosphere of disks around Herbig AeBe stars
are depleted of water molecules. Assuming LTE and optically thin emission we
derive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast to
T Tauri disks for which the column density ratio is 0.3 -- 0.4.Comment: Accepted for publication in Ap
Dark Matter Annihilation Signatures from Electroweak Bremsstrahlung
We examine observational signatures of dark matter annihilation in the Milky
Way arising from electroweak bremsstrahlung contributions to the annihilation
cross section. It has been known for some time that photon bremsstrahlung may
significantly boost DM annihilation yields. Recently, we have shown that
electroweak bremsstrahlung of W and Z gauge bosons can be the dominant
annihilation channel in some popular models with helicity-suppressed 2 --> 2
annihilation. W/Z-bremsstrahlung is particularly interesting because the gauge
bosons produced via annihilation subsequently decay to produce large correlated
fluxes of electrons, positrons, neutrinos, hadrons (including antiprotons) and
gamma rays, which are all of importance in indirect dark matter searches. Here
we calculate the spectra of stable annihilation products produced via
gamma/W/Z-bremsstrahlung. After modifying the fluxes to account for the
propagation through the Galaxy, we set upper bounds on the annihilation cross
section via a comparison with observational data. We show that stringent cosmic
ray antiproton limits preclude a sizable dark matter contribution to observed
cosmic ray positron fluxes in the class of models for which the bremsstrahlung
processes dominate.Comment: 11 pages, 6 figures. Updated to match PRD versio
Sub-millimeter images of a dusty Kuiper belt around eta Corvi
We present sub-millimeter and mid-infrared images of the circumstellar disk
around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size
of ~100AU. At 450um the emission is found to be extended at all position
angles, with significant elongation along a position angle of 130+-10deg; at
the highest resolution (9.3") this emission is resolved into two peaks which
are to within the uncertainties offset symmetrically from the star at 100AU
projected separation. Modeling the appearance of emission from a narrow ring in
the sub-mm images shows the observed structure cannot be caused by an edge-on
or face-on axisymmetric ring; the observations are consistent with a ring of
radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are
possible if the dust distribution includes two clumps similar to Vega; we show
how such a clumpy structure could arise from the migration over 25Myr of a
Neptune mass planet from 80-105AU. The inner 100AU of the system appears
relatively empty of sub-mm emitting dust, indicating that this region may have
been cleared by the formation of planets, but the disk emission spectrum shows
that IRAS detected an additional hot component with a characteristic
temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the
emission to be unresolved with no background sources which could be
contaminating the fluxes measured by IRAS. The age of this star is estimated to
be ~1Gyr. It is very unusual for such an old main sequence star to exhibit
significant mid-IR emission. The proximity of this source makes it a perfect
candidate for further study from optical to mm wavelengths to determine the
distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February
2005 issu
Herschel evidence for disk flattening or gas depletion in transitional disks
Transitional disks are protoplanetary disks characterized by reduced near-
and mid-infrared emission with respect to full disks. This characteristic
spectral energy distribution indicates the presence of an optically thin inner
cavity within the dust disk believed to mark the disappearance of the
primordial massive disk. We present new Herschel Space Observatory PACS spectra
of [OI] 63 micron for 21 transitional disks. Our survey complements the larger
Herschel GASPS program "Gas in Protoplanetary Systems" (Dent et al. 2013) by
quadrupling the number of transitional disks observed with PACS at this
wavelength. [OI] 63 micron traces material in the outer regions of the disk,
beyond the inner cavity of most transitional disks. We find that transitional
disks have [OI] 63 micron line luminosities two times fainter than their full
disk counterparts. We self consistently determine various stellar properties
(e.g. bolometric luminosity, FUV excess, etc.) and disk properties (e.g. disk
dust mass, etc.) that could influence the [OI] 63 micron line luminosity and we
find no correlations that can explain the lower [OI] 63 micron line
luminosities in transitional disks. Using a grid of thermo-chemical
protoplanetary disk models, we conclude that either transitional disks are less
flared than full disks or they possess lower gas-to-dust ratios due to a
depletion of gas mass. This result suggests that transitional disks are more
evolved than their full disk counterparts, possibly even at large radii.Comment: Accepted for publication in ApJ; 52 pages, 16 figures, 8 table
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