ShantanuT01/DACTYL-Pretraining huggingface dataset:
We have obtained Gemini/GMOS spectra of 28 regions located across the interacting group NGC 6845, spanning from the inner regions of the four major galaxies (NGC 6845A, B, C, D) to the tidal tails of NGC 6845A. All regions in the tails are star-forming objects with ages younger than 10 Myr. We derived the gas-phase metallicity gradients across NGC 6845A and its two tails and we find that these are shallower than those for isolated galaxies. NGC 6845A has a gas-phase oxygen central metallicity of \mbox{12+log(O/H)$\sim$8.5} and a flat gas-phase metallicity gradient ($\beta$=0.002$\pm$0.004 dex kpc$^{-1}$) out to $\sim$4 $\times$ R$_{25}$ (to the end of the longest tidal tail). Considering the mass-metallicity relation, the central region of NGC 6845A displays a lower oxygen abundance than the expected for its mass. Taking into account this fact and considering the flat oxygen distribution measured along the eastern tidal tail, we suggest that an interaction event has produced a dilution in the central metallicity of this galaxy and the observed flattening in its metal distribution. We found that the star formation process along the eastern tidal structure has not been efficient enough to increase the oxygen abundances in this place, suggesting that this structure was formed from enriched material.
The evolution of nuclear shell structure is investigated for the first time within density-dependent relativistic Hartree-Fock theory and the role of $\pi$-exchange potential is studied in detail. The energy differences between the neutron orbits $\Lrb{\nu1h_{9/2},\nu 1i_{13/2}}$ in the N=82 isotones and between the proton ones $\Lrb{\pi1g_{7/2},\pi1h_{11/2}}$ in the Z=50 isotopes are extracted as a function of neutron excess $N-Z$. A kink around $Z = 58$ for the N=82 isotones is found as an effect resulting from pion correlations. It is shown that the inclusion of $\pi$-coupling plays a central role to provide realistic isospin dependence of the energy differences. In particular, the tensor part of the $\pi$-coupling has an important effect on the characteristic isospin dependence observed in recent experiments.
Observations and modeling for the light curve (LC) and spectra of supernova (SN) 2005bf are reported. This SN showed unique features: the LC had two maxima, and declined rapidly after the second maximum, while the spectra showed strengthening He lines whose velocity increased with time. The double-peaked LC can be reproduced by a double-peaked $^{56}$Ni distribution, with most $^{56}$Ni at low velocity and a small amount at high velocity. The rapid post-maximum decline requires a large fraction of the $\gamma$-rays to escape from the $^{56}$Ni-dominated region, possibly because of low-density ``holes''. The presence of Balmer lines in the spectrum suggests that the He layer of the progenitor was substantially intact. Increasing $\gamma$-ray deposition in the He layer due to enhanced $\gamma$-ray escape from the $^{56}$Ni-dominated region may explain both the delayed strengthening and the increasing velocity of the He lines. The SN has massive ejecta ($\sim6-7\Msun$), normal kinetic energy ($\sim 1.0-1.5\times 10^{51}$ ergs), high peak bolometric luminosity ($\sim 5\times 10^{42}$ erg s$^{-1}$) for an epoch as late as $\sim$ 40 days, and a large $^{56}$Ni mass ($\sim0.32\Msun$). These properties, and the presence of a small amount of H suggest that the progenitor was initially massive (M$\sim 25-30 \Msun$) and had lost most of its H envelope, and was possibly a WN star. The double-peaked $^{56}$Ni distribution suggests that the explosion may have formed jets that did not reach the He layer. The properties of SN 2005bf resemble those of the explosion of Cassiopeia A.
I examine a variety snow crystal growth experiments performed at temperatures near -2 C, as a function of supersaturation, background gas pressure, and crystal morphology. Although the different experimental data were obtained using quite diverse experimental techniques, the resulting measurements can all be reasonably understood using a single comprehensive physical model for the basal and prism attachment kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. As with the previous paper in this series, comparing and reconciling different data sets at a single temperature yields significant insights into the underlying physical processes that govern snow crystal growth dynamics.
Let $G$ be a smooth connected linear algebraic group and $X$ be a $G$-torsor. Totaro asked: if $X$ admits a zero-cycle of degree $d \geq 1$, then does $X$ have a closed \'etale point of degree dividing $d$? This question is entirely unexplored in the literature for algebraic tori. We settle Totaro's question affirmatively for algebraic tori of rank $\leq 2$.
GRB 080607 has provided the first strong observational signatures of molecular absorption bands toward any galaxy hosting a gamma-ray burst. Despite the identification of dozens of features as belonging to various atomic and molecular (H_2 and CO) carriers, many more absorption features remained unidentified. Here we report on a search among these features for absorption from vibrationally-excited H_2, a species that was predicted to be produced by the UV flash of a GRB impinging on a molecular cloud. Following a detailed comparison between our spectroscopy and static, as well as dynamic, models of H_2* absorption, we conclude that a column density of 10^{17.5+-0.2} cm^{-2} of H_2* was produced along the line of sight toward GRB 080607. Depending on the assumed amount of dust extinction between the molecular cloud and the GRB, the model distance between the two is found to be in the range 230--940 pc. Such a range is consistent with a conservative lower limit of 100 pc estimated from the presence of Mg I in the same data. These distances show that substantial molecular material is found within hundreds of pc from GRB 080607, part of the distribution of clouds within the GRB host galaxy.
We consider a model for gravity that is invariant under global scale transformations. It includes one extra real scalar field coupled non-minimally to the gravity fields. In this model all the dimensionful parameters like the gravitational constant and the cosmological constant etc. are generated by a solution of the classical equations of motion which breaks scale invariance. In this paper we demonstrate the stability of such a solution against small perturbations in a flat FRW background by making a perturbative expansion around this solution and solving the resulting equations linear in the perturbations.
We present a comparison of Doppler-shifted H-alpha line emission observed by the Global Jet Watch from freshly-launched jet ejecta at the nucleus of the Galactic microquasar SS433 with subsequent ALMA imaging at mm-wavelengths of the same jet ejecta. There is a remarkable similarity between the transversely-resolved synchrotron emission and the prediction of the jet trace from optical spectroscopy: this is an a priori prediction not an a posteriori fit, confirming the ballistic nature of the jet propagation. The mm-wavelength of the ALMA polarimetry is sufficiently short that the Faraday rotation is negligible and therefore that the observed E-vector directions are accurately orthogonal to the projected local magnetic field. Close to the nucleus the B-field vectors are perpendicular to the direction of propagation. Further out from the nucleus, the B-field vectors that are coincident with the jet instead become parallel to the ridge line; this occurs at a distance where the jet bolides are expected to expand into one another. X-ray variability has also been observed at this location; this has a natural explanation if shocks from the expanding and colliding bolides cause particle acceleration. In regions distinctly separate from the jet ridge line, the fractional polarisation approaches the theoretical maximum for synchrotron emission.
We consider approximation of vectors $\mathbf{z}\in F\otimes\mathbb{R}\cong\mathbb{R}^r\times\mathbb{C}^s$ by elements of a number field $F$ and construct examples of badly approximable vectors. These examples come from compact subspaces of $SL_2(\mathcal{O}_F)\backslash SL_2(F\otimes\mathbb{R})$ naturally associated to (totally indefinite, anisotropic) $F$-rational binary quadratic and Hermitian forms, a generalization of the well-known fact that quadratic irrationals are badly approximable over $\mathbb{Q}$.
The successful operation of dedicated detectors has brought us valuable information for understanding the central engine and the progenitor of gamma-ray bursts (GRBs). For instance, the giant X-ray and optical bumps found in some long-duration GRBs (e.g. GRBs 121027A and 111209A) imply that some extended central engine activities, such as the late X-ray flares, are likely due to the fall-back of progenitor envelope materials. Here we systemically search for long GRBs that consist of a giant X-ray or optical bump from the Swift GRB sample, and eventually we find 19 new possible candidates. The fall-back accretion model could well interpret the X-ray and optical bump for all candidates within a reasonable parameter space. Six candidates showing simultaneous bump signatures in both X-ray and optical observations, which could be well fitted at the same time when scaling down the X-ray flux into optical by one order of magnitude, are consistent with the standard $F_{\nu}\propto\nu^{1/3}$ synchrotron spectrum. The typical fall-back radius is distributed around $10^{10}\rm-10^{12}$ cm, which is consistent with the typical radius of a Wolf-Rayet star. The peak fall-back accretion rate is in the range of $\sim 10^{-11}-10^{-4}M_{\odot} \ \text{s} ^{-1}$ at time $\sim10^{2}- 10^{5}~\rm s$, which is relatively easy to fulfill as long as the progenitor's metallicity is not too high. Combined with the sample we found, future studies of the mass supply rate for the progenitors with different mass, metallicity, and angular momentum distribution would help us to better constrain the progenitor properties of long GRBs.
Vast sound waves traveling through the relativistic plasma during the first million years of the universe imprint a preferred scale in the density of matter. We now have the ability to detect this characteristic fingerprint in the clustering of galaxies at various redshifts and use it to measure the acceleration of the expansion of the Universe. The Wide-Field Multi-Object Spectrograph (WFMOS) would use this test to shed significant light on the true nature of dark energy, the mysterious source of this cosmic acceleration. WFMOS would also revolutionise studies of the kinematics of the Milky Way and provide deep insights into the clustering of galaxies at redshifts up to z~4. In this article we discuss the recent progress in large galaxy redshift surveys and detail how WFMOS will help unravel the mystery of dark energy.
A well-known precursor of an imminent solar eruption is the appearance of a hot S-shaped loop, also known as sigmoid, in an active region (AR). Classically, the formation of such an S-shaped loop is envisaged to be implemented by magnetic reconnection of two oppositely oriented J-shaped loops. However, the details of reconnection are elusive due to weak emission and subtle evolution during the pre-eruptive phase. In this paper, we investigate how a single J-shaped loop transforms into an S-shaped one through the slippage of one of its footpoints in NOAA AR 11719 on 2013 April 11. During an interval of about 16 min, the J-shaped loop slips through a low-corona region of strong electric current density in a bursty fashion, reaching a peak apparent speed as fast as over 1000 km s$^{-1}$, at the slipping footpoint. The enhancement of electric current density, as suggested by non-linear force-free field modeling, indicates that the "non-idealness" of coronal plasma becomes locally important, which may facilitate magnetic reconnection. The loop segment undergoing slipping motions is heated; meanwhile, above the fixed footpoint coronal emission dims due to a combination effect of the lengthening and heating of the loop, the latter of which is manifested in the temporal variation of dimming slope and of emission measure. These features together support an asymmetric scenario of sigmoid formation through slipping reconnection of a single J-shaped loop, which differs from the standard tether-cutting scenario involving a double J-shaped loop system.
The Sh2-294 HII region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in the region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 HII region at 3.6, 4.5, 5.8, and 8.0 microns observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H2 (2.12 microns) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the HII region and associated with enhanced H2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (< 4 solar masses) YSOs; however, we also detected a massive YSO (~9 solar masses) of Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present analysis suggests that the Class I sources are indeed younger population of the region relative to Class II sources (age ~ 4.5 x 10^6 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the HII region powered by a ~ 4 x 10^6 yr B0 main-sequence star.
The similarity between Finsler and Riemann geometry is an intriguing starting point to extend general relativity. The lack of quadratic restriction over the line element (color) naturally generalize the Riemannian case and breaks the local symmetries of general relativity. In addition, the Finsler manifold is enriched with new geometric entities and all the classical identities are suitably extended. We investigate the covariant kinematics of a medium formed by a time-like congruence. After a brief view in the general case we impose particular geometric restrictions to get some analytic insight. Central role to our analysis plays the Lie derivative where even in case of irrotational Killing vectors the bundle still deforms. We demonstrate an example of an isotropic and exponentially expanding cross-section that finally deflates or forms a caustic. Furthermore, using the 1+3 covariant formalism we investigate the expansion dynamics of the congruence. For certain geometric restrictions we retrieve the Raychaudhuri equation where a color-curvature coupling is revealed. The condition to prevent the focusing of neighboring particles is given and is more likely to fulfilled in highly curved regions. Then, we introduce the Levi-Civita connection for the osculating Riemannian metric and develop a (spatially) isotropic and homogeneous dust-like model with a non-singular bounce.
Magnetic skyrmions are topological quasi particles of great interest for data storage applications because of their small size, high stability, and ease of manipulation via electric current. Theoretically, however, skyrmions are poorly understood since existing theories are not applicable to small skyrmion sizes and finite material thicknesses. Here, we present a complete theoretical framework to determine the energy of any skyrmion in any material, assuming only a circular symmetric 360$^\circ$ domain wall profile and a homogeneous magnetization profile in the out-of-plane direction. Our model precisely agrees with existing experimental data and micromagnetic simulations. Surprisingly, we can prove that there is no topological protection of skyrmions. We discover and confirm new phases, such as bi-stability, a phenomenon unknown in magnetism so far. The outstanding computational performance and precision of our model allow us to obtain the complete phase diagram of static skyrmions and to tackle the inverse problem of finding materials corresponding to given skyrmion properties, a milestone of skyrmion engineering.
In this work, FRW universe filled with dark matter (perfect fluid with negligible pressure) along with dark energy in the background of Galileon gravity is considered. Four dark energy models with different EoS parametrizations have been employed namely, Linear, CPL, JBP and Logarithmic parametrizations. From Stern, Stern+BAO and Stern+BAO+CMB joint data analysis, we have obtained the bounds of the arbitrary parameters $\omega_{0}$ and $\omega_{1}$ by minimizing the $\chi^{2}$ test. The best-fit values and bounds of the parameters are obtained at 66\%, 90\% and 99\% confidence levels which are shown by closed confidence contours in the figures. For the logarithmic model unbounded confidence contours are obtained and hence the model parameters could not be finitely constrained. The distance modulus $\mu$(z) against redshift $z$ has also been plotted for our predicted theoretical models for the best fit values of the parameters and compared with the observed Union2 data sample and SNe Type Ia 292 data and we have shown that our predicted theoretical models permits the observational data sets. From the data fitting it is seen that at lower redshifts $(z<0.3)$ the SNe Type Ia 292 data gives a better fit with our theoretical models compared to the Union2 data sample. So, from the data analysis, SNe Type Ia 292 data is the more favoured data sample over its counterpart given the present choice of free parameters. From the study, it is also seen that the logarithmic parametrization model is less supported by the observational data. Finally we have generated the plot for the deceleration parameter against the redshift parameter for all the theoretical models and compared the results with the work of Farooq et al, 2013.
We discuss the near-infrared properties of the nuclei in the 11 merging galaxies of the Toomre sequence, based on high spatial resolution J, H, and K imaging data using NICMOS onboard the Hubble Space Telescope (HST). The observations are less affected by dust extinction than our previous HST/WFPC2 observations and offer higher spatial resolution than existing ground-based near-IR data. We see a marginal trend for the nuclei to become bluer with advancing merger stage, which we attribute to a dispersal of dust at late times in the merging process. Our data also indicate a statistically significant trend for the nuclei in the sequence to become more luminous, within an aperture of fixed physical size and after correcting for dust extinction, with advancing merger stage. We derive K-band surface brightness profiles for those nuclei for which the morphology allows a meaningful isophotal analysis, and fit the profiles with a ``Nuker law'' for comparison with other samples of galaxies observed with HST. The majority of the nuclei have steep profiles that can be characterized as power-law type. In general, the Toomre sequence galaxies tend to have steeper profiles and higher central luminosity surface densities than E/S0's. We derive V-K color profiles for the nuclei to further address this possibility, but find that the large amounts of dust extinction complicate their interpretation. Overall, our results are consistent with the generic predictions of N-body simulations of spiral galaxy mergers. If left to evolve and fade for several Gyrs, it is possible that the properties of the Toomre sequence nuclei would resemble theproperties of the nuclei of normal E/S0 galaxies. Our results therefore support the view that mergers of spiral galaxies can lead to the formation of early-type galaxies (Abridged).
The problem of a linear damped noisy oscillator is treated in the presence of two multiplicative sources of noise which imply a random mass and random damping. The additive noise and the noise in the damping are responsible for an influx of energy to the oscillator and its dissipation to the surrounding environment. A random mass implies that the surrounding molecules not only collide with the oscillator but may also adhere to it, thereby changing its mass. We present general formulas for the first two moments and address the question of mean and energetic stabilities. The phenomenon of stochastic resonance, i.e. the expansion due to the noise of a system response to an external periodic signal, is considered for separate and joint action of two sources of noise and their characteristics.
This is the abstract of the revised paper. The integrable XXZ model with a special open boundary condition is considered. We study Sklyanin transfer matrices after quantum group reduction in roots of unity. In this case Sklyanin transfer matrices satisfy a closed system of truncated functional equations. The algebraic reason for the truncation is found.The important role in proving of the result is performed by Zamolodchikov algebra introduced in the paper.
A theoretical scheme which relates multiparticle states generated in ultrarelativistic nuclear collisions to a QCD phase transition is considered in the framework of the universality class provided by the 3-D Ising model. Two different evolution scenarios for the QGP system are examined. The statistical mechanics of the critical state is accounted for in terms of (critical) cluster formation consistent with suitably cast effective action functionals, one for each considered type of expansion. Fractal properties associated with these clusters, characterizing the density fluctuations near the QCD critical point, are determined. Monte-Carlo simulations are employed to generate events, pertaining to the total system, which correspond to signals associated with unconventional sources of pion production.
We address the problem of how particles that are accelerated by solar flares can escape promptly into the heliosphere, on time scales of an hour or less. Impulsive solar energetic particles (SEP) bursts are generally observed in association with so-called eruptive flares consisting of a coronal mass ejection (CME) and a flare. These highly prompt SEPs are believed to be accelerated directly by the flare, rather than by the CME shock, although the precise mechanism by which the particles are accelerated remains controversial. Whatever their origin, within the magnetic geometry of the standard eruptive-flare model, the accelerated particles should remain trapped in the closed magnetic fields of the coronal flare loops and the ejected flux rope. In this case the particles would reach the Earth only after a delay of many hours to a few days, when the bulk ejecta arrive at Earth. We propose that the external magnetic reconnection intrinsic to the breakout model for CME initiation can naturally account for the prompt escape of flare-accelerated energetic particles onto open interplanetary magnetic flux tubes. We present detailed 2.5D MHD simulations of a breakout CME/flare event with a background isothermal solar wind. Our calculations demonstrate that if the event occurs sufficiently near a coronal-hole boundary, interchange reconnection between open and closed field can occur, which allows particles from deep inside the ejected flux rope to access solar wind field lines soon after eruption. We compare these results with the standard observations of impulsive SEPs and discuss the implications of the model for further observations and calculations.