Table of contents

We investigate the effects of a magnetic dipole moment of asymmetric dark matter (DM) in the evolution of the Sun. The dipole interaction can lead to a sizable DM scattering cross section even for light DM, and asymmetric DM can lead to a large DM number density in the Sun. We find that solar model precision tests, using as diagnostic the sound speed profile obtained from helioseismology data, exclude dipolar DM particles with a mass larger than 4.3 GeV and magnetic dipole moment larger than 1.6 × 10⁻¹⁷ e cm.

We describe a new method for measuring galaxy magnification due to weak gravitational lensing. Our method makes use of a tight scaling relation between galaxy properties that are modified by gravitational lensing, such as apparent size, and other properties that are not, such as surface brightness. In particular, we use a version of the well-known fundamental plane relation for early-type galaxies. This modified "photometric fundamental plane" uses only photometric galaxy properties, eliminating the need for spectroscopic data. We present the first detection of magnification using this method by applying it to photometric catalogs from the Sloan Digital Sky Survey. This analysis shows that the derived magnification signal is within a factor of three of that available from conventional methods using gravitational shear. We suppress the dominant sources of systematic error and discuss modest improvements that may further enhance the lensing signal-to-noise available with this method. Moreover, some of the dominant sources of systematic error are substantially different from those of shear-based techniques. With this new technique, magnification becomes a useful measurement tool for the coming era of large ground-based surveys intending to measure gravitational lensing.

Determination of the nitrogen isotopic ratios in different bodies of the solar system provides important information regarding the solar system's origin. We unambiguously identified emission lines in comets due to the ¹⁵NH₂ radical produced by the photodissociation of ¹⁵NH₃. Analysis of our data has permitted us to measure the ¹⁴N/¹⁵N isotopic ratio in comets for a molecule carrying the amine (–NH) functional group. This ratio, within the error, appears similar to that measured in comets in the HCN molecule and the CN radical, and lower than the protosolar value, suggesting that N₂ and NH₃ result from the separation of nitrogen into two distinct reservoirs in the solar nebula. This ratio also appears similar to that measured in Titan's atmospheric N₂, supporting the hypothesis that, if the latter is representative of its primordial value in NH₃, these bodies were assembled from building blocks sharing a common formation location.

We investigate the potential use of nebular emission lines in the rest-frame far-infrared (FIR) for determining spectroscopic redshift of z > 8 galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA). After making a line emissivity model as a function of metallicity, especially for the [O iii] 88 μm line which is likely to be the strongest FIR line from H ii regions, we predict the line fluxes from high-z galaxies based on a cosmological hydrodynamics simulation of galaxy formation. Since the metallicity of galaxies reaches at ∼0.2 Z_☉ even at z > 8 in our simulation, we expect the [O iii] 88 μm line as strong as 1.3 mJy for 27 AB objects, which is detectable at a high significance by <1 hr integration with ALMA. Therefore, the [O iii] 88 μm line would be the best tool to confirm the spectroscopic redshifts beyond z = 8.

A strong indication that fast reconnection regimes exist within resistive magnetohydrodynamics was given by the proof that the Sweet–Parker current sheet, maintained by a flow field with an appropriate inflow–outflow structure, could be unstable to a reconnecting instability which grows without bound as the Lundquist number, S, tends to infinity. The requirement of a minimum value for S in order for the plasmoid instability to kick in does little to resolve the paradoxical nature of the result. Here we argue against the realizability of Sweet–Parker current sheets in astrophysical plasmas with very large S by showing that an "ideal" tearing mode takes over before current sheets reach such a thickness. While the Sweet–Parker current sheet thickness scales as ∼S^−1/2, the tearing mode becomes effectively ideal when a current sheet collapses to a thickness of the order of ∼S^−1/3, up to 100 times thicker than S^−1/2, when (as happens in many astrophysical environments) S is as large as 10¹². Such a sheet, while still diffusing over a very long time, is unstable to a tearing mode with multiple x-points: here we detail the characteristics of the instability and discuss how it may help solve the flare trigger problem and effectively initiate the turbulent disruption of the sheet.

As early as 10 Gyr ago, galaxies with more than 10¹¹ M_☉ of stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction (≲0.1%) may have survived untouched until today. Searches for such relic galaxies, useful windows to explore the early universe, have been inconclusive to date: galaxies with masses and sizes like those observed at high redshift (M_⋆ ≳ 10¹¹ M_☉; R_e ≲ 1.5 kpc) have been found in the local universe, but their stars are far too young for the galaxy to be a relic galaxy. This paper explores the first case of a nearby galaxy, NGC 1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfills many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H] = 0.20 ± 0.04 with a smooth decline toward the outer regions) and α-enriched ([α/Fe] = 0.4 ± 0.1). This suggests a very short formation time scale for the bulk of the stars in this galaxy. This object also rotates very fast (V_rot ∼ 300 km s⁻¹) and has a large central velocity dispersion (σ > 300 km s⁻¹). NGC 1277 allows the exploration in full detail of properties such as the structure, internal dynamics, metallicity, and initial mass function as they were at ∼10–12 Gyr ago when the first massive galaxies were built.

The physical nature of fast radio bursts (FRBs), a new type of cosmological transient discovered recently, is not known. It has been suggested that FRBs can be produced when a spinning supra-massive neutron star loses centrifugal support and collapses to a black hole. Here, we suggest that such implosions can happen in supra-massive neutron stars shortly (hundreds to thousands of seconds) after their births, and an observational signature of such implosions may have been observed in the X-ray afterglows of some long and short gamma-ray bursts (GRBs). Within this picture, a small fraction of FRBs would be physically connected to GRBs. We discuss possible multi-wavelength electromagnetic signals and gravitational wave signals that might be associated with FRBs, and propose an observational campaign to unveil the physical nature of FRBs. In particular, we strongly encourage a rapid radio follow-up observation of GRBs starting from 100 s after a GRB trigger.

We report the discovery of an azimuthal dynamo wave of a low-order (m = 1) mode in direct numerical simulations (DNS) of turbulent convection in spherical shells. Such waves are predicted by mean-field dynamo theory and have been obtained previously in mean-field models. An azimuthal dynamo wave has been proposed as a possible explanation for the persistent drifts of spots observed on several rapidly rotating stars, as revealed through photometry and Doppler imaging. However, this has been judged unlikely because evidence for such waves from DNS has been lacking. Here we present DNS of large-scale magnetic fields showing a retrograde m = 1 mode. Its pattern speed is nearly independent of latitude and does not reflect the speed of the differential rotation at any depth. The extrema of magnetic m = 1 structures coincide reasonably well with the maxima of m = 2 structures of the temperature. These results provide direct support for the observed drifts being due to an azimuthal dynamo wave.

We have analyzed daily microwave images of the Sun at 17 GHz obtained with the Nobeyama Radioheliograph (NoRH) in order to study the solar cycle variations of the enhanced brightness in the polar regions. Unlike in previous works, the averaged brightness of the polar regions is obtained from individual images rather than from synoptic maps. We confirm that the brightness is anti-correlated with the solar cycle and that it has generally declined since solar cycle 22. Including images up to 2013 October, we find that the 17 GHz brightness temperature of the south polar region has decreased noticeably since 2012. This coincides with a significant decrease in the average magnetic field strength around the south pole, signaling the arrival of solar maximum conditions in the southern hemisphere more than a year after the northern hemisphere. We do not attribute the enhanced brightness of the polar regions at 17 GHz to the bright compact sources that occasionally appear in synthesized NoRH images. This is because they have no correspondence with small-scale bright regions in images from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory with a broad temperature coverage. Higher-quality radio images are needed to understand the relationship between microwave brightness and magnetic field strength in the polar regions.

We report the observation of an outflow perpendicular to the radio jet in near-infrared integral field spectra of the inner 250 pc of the Seyfert 2 galaxy NGC 5929. The observations were obtained with the Gemini Near-infrared Integral Field Spectrograph at a spatial resolution of ∼20 pc and spectral resolution of R ≈ 5300 and reveal a region ∼50 pc wide crossing the nucleus and extending by ∼300 pc perpendicularly to the known radio jet in this galaxy. Along this structure—which we call the south-east–north-west (SE–NW) strip—the emission line profiles show two velocity components, one blueshifted and the other redshifted by −150 km s⁻¹ and 150 km s⁻¹, respectively, relative to the systemic velocity. We interpret these two components as being due to an outflow perpendicular to the radio jet, which is supported by low-frequency radio emission observed along the same region. We attribute this feature to the interaction of ambient gas with an "equatorial outflow" predicted in recent accretion disk and torus wind models. Perpendicularly to the SE–NW strip, thus approximately along the radio jet, single-component profiles show blueshifts of ≈ − 150 km s⁻¹ to the north-east and similar redshifts to the south-west, which can be attributed to gas counter-rotating relative to the stellar kinematics. More double-peaked profiles are observed in association with the two radio hot spots, attributed to interaction of the radio jet with the surrounding gas.

We present the light curve of the old nova V603 Aql (Nova Aql 1918) from 1898–1918 and 1934–2013 using 22,721 archival magnitudes. All of our magnitudes are either in, or accurately transformed into, the Johnson B and V magnitude systems. This is vital because offsets in old sequences and the visual-to-V transformation can cause errors of 0.1–1.0 mag if not corrected. Our V603 Aql light curve is the first time that this has been done for any nova. Our goal was to see the evolution of the mass accretion rate on a century timescale, and to test the long-standing prediction of the Hibernation model that old novae should be fading significantly in the century after their eruption is over. The 1918 nova eruption was completely finished by 1938 when the nova decline stopped, and when the star had faded to fainter than its pre-nova brightness of B = 11.43 ± 0.03 mag. We find that the nova light from 1938 to 2013 was significantly fading, with this being seen consistently in three independent data sets (the Sonneberg plates in B, the American Association of Variable Star Observers (AAVSO) V light curve, and the non-AAVSO V light curve). We find that V603 Aql has been declining in brightness at an average rate of 0.44 ± 0.04 mag per century since 1938. This work provides remarkable confirmation of an important prediction of the Hibernation model.

Novae are generally considered to be "hot" astronomical objects which show effective temperatures of 10,000 K or higher at their visual maximum. However, theoretical predictions suggest that the outer envelope of the nova outflow can become cool enough to form molecules which would be dissociated at such high temperatures. We detected strong C₂ and CN absorption bands in the optical spectrum of the nova V2676 Oph, a very slow nova with dust formation. This is the first report of the detection of C_2, and the second of CN, in novae during an outburst. Although, based on previous studies, such simple molecules are predicted form in the envelope of the outflow, there are few reports of their detection thus far. The presence of the molecular envelope is considered to be very transient, with a duration of only a few days, in the case of V2676 Oph.

The X-ray emission mechanism in large-scale jets of powerful radio quasars has been a source of debate in recent years, with two competing interpretations: either the X-rays are of synchrotron origin, arising from a different electron energy distribution than that producing the radio to optical synchrotron component, or they are due to inverse Compton scattering of cosmic microwave background photons (IC/CMB) by relativistic electrons in a powerful relativistic jet with bulk Lorentz factor Γ ∼ 10–20. These two models imply radically different conditions in the large-scale jet in terms of jet speed, kinetic power, and maximum energy of the particle acceleration mechanism, with important implications for the impact of the jet on the large-scale environment. A large part of the X-ray origin debate has centered on the well-studied source 3C 273. Here we present new observations from Fermi which put an upper limit on the gamma-ray flux from the large-scale jet of 3C 273 that violates at a confidence greater that 99.9% the flux expected from the IC/CMB X-ray model found by extrapolation of the UV to X-ray spectrum of knot A, thus ruling out the IC/CMB interpretation entirely for this source when combined with previous work. Further, this upper limit from Fermi puts a limit on the Doppler beaming factor of at least δ < 9, assuming equipartition fields, and possibly as low as δ < 5, assuming no major deceleration of the jet from knots A through D1.

We report observations of white-light ejecta in the low corona, for two X-class flares on 2013 May 13, using data from the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory. At least two distinct kinds of sources appeared (chromospheric and coronal), in the early and later phases of flare development, in addition to the white-light footpoint sources commonly observed in the lower atmosphere. The gradual emissions have a clear identification with the classical loop-prominence system, but are brighter than expected and possibly seen here in the continuum rather than line emission. We find the HMI flux exceeds the radio/X-ray interpolation of the bremsstrahlung produced in the flare soft X-ray sources by at least one order of magnitude. This implies the participation of cooler sources that can produce free-bound continua and possibly line emission detectable by HMI. One of the early sources dynamically resembles "coronal rain", appearing at a maximum apparent height and moving toward the photosphere at an apparent constant projected speed of 134 ± 8 km s⁻¹. Not much literature exists on the detection of optical continuum sources above the limb of the Sun by non-coronagraphic instruments and these observations have potential implications for our basic understanding of flare development, since visible observations can in principle provide high spatial and temporal resolution.

Progress in understanding star formation requires detailed observational constraints on the initial conditions, i.e., dense clumps and cores in giant molecular clouds that are on the verge of gravitational instability. Such structures have been studied by their extinction of near-infrared and, more recently, mid-infrared (MIR) background light. It has been somewhat more of a surprise to find that there are regions that appear as dark shadows at far-infrared (FIR) wavelengths as long as ∼100 μm! Here we develop analysis methods of FIR images from Spitzer-MIPS and Herschel-PACS that allow quantitative measurements of cloud mass surface density, Σ. The method builds on that developed for MIR extinction mapping by Butler & Tan, in particular involving a search for independently saturated, i.e., very opaque, regions that allow measurement of the foreground intensity. We focus on three massive starless core/clumps in the Infrared Dark Cloud (IRDC) G028.37+00.07, deriving mass surface density maps from 3.5 to 70 μm. A by-product of this analysis is the measurement of the spectral energy distribution of the diffuse foreground emission. The lower opacity at 70 μm allows us to probe to higher Σ values, up to ∼1 g cm⁻² in the densest parts of the core/clumps. Comparison of the Σ maps at different wavelengths constrains the shape of the MIR–FIR dust opacity law in IRDCs. We find that it is most consistent with the thick ice mantle models of Ossenkopf & Henning. There is tentative evidence for grain ice mantle growth as one goes from lower to higher Σ regions.

We present near-infrared high-contrast imaging photometry and integral field spectroscopy of ROXs 42B, a binary M0 member of the 1–3 Myr old ρ Ophiuchus star-forming region, from data collected over 7 years. Each data set reveals a faint companion—ROXs 42Bb—located ∼116 (r_proj ≈ 150 AU) from the primaries at a position angle consistent with a point source identified earlier by Ratzka et al.. ROXs 42Bb's astrometry is inconsistent with a background star but consistent with a bound companion, possibly one with detected orbital motion. The most recent data set reveals a second candidate companion at ∼05 of roughly equal brightness, though preliminary analysis indicates it is a background object. ROXs 42Bb's H and K_s band photometry is similar to dusty/cloudy young, low-mass late M/early L dwarfs. K band VLT/SINFONI spectroscopy shows ROXs 42Bb to be a cool substellar object (M8–L0; T_eff ≈ 1800–2600 K), not a background dwarf star, with a spectral shape indicative of young, low surface gravity planet-mass companions. We estimate ROXs 42Bb's mass to be 6–15 M_J, either below the deuterium-burning limit and thus planet mass or straddling the deuterium-burning limit nominally separating planet-mass companions from other substellar objects. Given ROXs 42b's projected separation and mass with respect to the primaries, it may represent the lowest mass objects formed like binary stars or a class of planet-mass objects formed by protostellar disk fragmentation/disk instability, the latter slightly blurring the distinction between non-deuterium-burning planets like HR 8799 bcde and low-mass, deuterium-burning brown dwarfs.

Debris disks and asteroid belts are expected to form around young pulsars due to fallback material from their original supernova explosions. Disk material may migrate inward and interact with a pulsar's magnetosphere, causing changes in torque and emission. Long-term monitoring of PSR J0738−4042 reveals both effects. The pulse shape changes multiple times between 1988 and 2012. The torque, inferred via the derivative of the rotational period, changes abruptly from 2005 September. This change is accompanied by an emergent radio component that drifts with respect to the rest of the pulse. No known intrinsic pulsar processes can explain these timing and radio emission signatures. The data lead us to postulate that we are witnessing an encounter with an asteroid or in-falling debris from a disk.

We present polarization images of Comet ISON (C/2012 S1) taken with the Hubble Space Telescope (HST) on UTC 2013 May 8 (r_h = 3.81 AU, Δ = 4.34 AU), when the phase angle was α ≈ 1216. This phase angle is approximately centered in the negative polarization branch for cometary dust. The region beyond 1000 km (∼0.32 arcsec ≈ 6 pixels) from the nucleus shows a negative polarization amplitude of p% ∼ −1.6%. Within 1000 km of the nucleus, the polarization position angle rotates to be approximately perpendicular to the scattering plane, with an amplitude p% ∼ +2.5%. Such positive polarization has been observed previously as a characteristic feature of cometary jets, and we show that Comet ISON does indeed harbor a jet-like feature. These HST observations of Comet ISON represent the first visible light, imaging polarimetry with subarcsecond spatial resolution of a Nearly Isotropic Comet beyond 3.8 AU from the Sun at a small phase angle. The observations provide an early glimpse of the properties of the cometary dust preserved in this Oort-Cloud comet.

Recently, Thornton and coworkers confirmed a class of millisecond radio bursts likely of extragalactic origin that is well-suited for estimating dispersion measures (DMs). We calculate the probability distribution of DM(z) in different models for how the cosmic baryons are distributed (both analytically and with cosmological simulations). We show that the distribution of DM is quite sensitive to whether the "missing" baryons lie around the virial radius of 10¹¹–10¹³ M_☉ halos or further out, which is not easily constrained with other observational techniques. The intrinsic contribution to DM from each source could complicate studies of the extragalactic contribution. This difficulty is avoided by stacking based on the impact parameter to foreground galaxies. We show that a stacking analysis using a sample of ∼100 DM measurements from arcminute-localized, z ≳ 0.5 sources would place interesting constraints at 0.2–2 halo virial radii on the baryonic mass profile surrounding different galaxy types. Conveniently for intergalactic studies, sightlines that intersect intervening galactic disks should be easily identified owing to scattering. A detectable level of scattering may also result from turbulence in the circumgalactic medium.

X-ray measurements suggest that the abundance of calcium in the intracluster medium is higher than can be explained using favored models for core-collapse and Type Ia supernovae alone. We investigate whether the "calcium conundrum" in the intracluster medium can be alleviated by including a contribution from the recently discovered subclass of supernovae known as calcium-rich gap transients. Although the calcium-rich gap transients make up only a small fraction of all supernovae events, we find that their high calcium yields are sufficient to reproduce the X-ray measurements found for nearby rich clusters. We find the χ² goodness-of-fit metric improves from 84 to 2 by including this new class. Moreover, calcium-rich supernovae preferentially occur in the outskirts of galaxies making it easier for the nucleosynthesis products of these events to be incorporated in the intracluster medium via ram-pressure stripping. The discovery of calcium-rich gap transients in clusters and groups far from any individual galaxy suggests that supernovae associated with intracluster stars may play an important role in enriching the intracluster medium. Calcium-rich gap transients may also help explain anomalous calcium abundances in many other astrophysical systems including individual stars in the Milky Way, the halos of nearby galaxies, and the circumgalactic medium. Our work highlights the importance of considering the diversity of supernovae types and corresponding yields when modeling the abundance of the intracluster medium and other gas reservoirs.