118401675
The Diskionary: A Glossary of Terms Commonly Used for Disks and Related Objects, First Edition
Based on a panel discussion at the meeting "New Light on Young Stars: Spitzer's View of Circumstellar Disks", we provide some definitions of common usage of terms describing disks and related objects.
17826176
The Mass Distribution And Lifetime Of Prestellar Cores In Perseus, Serpens, And Ophiuchus
We present an unbiased census of starless cores in Perseus, Serpens, and Ophiuchus, assembled by comparing large-scale Bolocam 1.1 mm continuum emission maps with Spitzer c2d surveys. We use the c2d catalogs to separate 108 starless from 92 protostellar cores in the 1.1 mm core samples from Enoch and Young and their coworkers. A comparison of these populations reveals the initial conditions of the starless cores. Starless cores in Perseus have similar masses but larger sizes and lower densities on average than protostellar cores, with sizes that suggest density profiles substantially flatter than ρ∝r^-2. By contrast, starless cores in Serpens are compact and have lower masses than protostellar cores; future star formation will likely result in lower mass objects than the currently forming protostars. Comparison to dynamical masses estimated from the NH3 survey of Perseus cores by Rosolowsky and coworkers suggests that most of the starless cores are likely to be gravitationally bound, and thus prestellar. The combined prestellar core mass distribution includes 108 cores and has a slope of α = -2.3 ± 0.4 for M > 0.8 M☉. This slope is consistent with recent measurements of the stellar initial mass function, providing further evidence that stellar masses are directly linked to the core formation process. We place a lower limit on the core-to-star efficiency of 25%. There are approximately equal numbers of prestellar and protostellar cores in each cloud; thus the dense prestellar core lifetime must be similar to the lifetime of embedded protostars, or 4.5 x 10^5 yr, with a total uncertainty of a factor of 2. Such a short lifetime suggests a dynamic, rather than quasi-static, core evolution scenario, at least at the relatively high mean densities (n > 2 x 10^4 cm^-3) to which we are sensitive.
29731360
Submillimeter Follow-up of WISE-selected Hyperluminous Galaxies
We have used the Caltech Submillimeter Observatory (CSO) to follow-up a sample of Wide-field Infrared Survey Explorer (WISE) selected, hyperluminous galaxies, the so-called W1W2-dropout galaxies. This is a rare (∼1000 all-sky) population of galaxies at high redshift (peaks at z = 2–3), which are faint or undetected by WISE at 3.4 and 4.6 μm, yet are clearly detected at 12 and 22 μm. The optical spectra of most of these galaxies show significant active galactic nucleus activity. We observed 14 high-redshift ( z> 1.7) W1W2-dropout galaxies with SHARC-II at 350–850 μm, with nine detections, and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer follow-up of 25 targets at 3.6 and 4.5 μm, as well as optical spectra of 12 targets, are also presented in the paper. Combining WISE data with observations from warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral energy distributions (SEDs). These SEDs have a consistent shape, showing significantly higher mid-IR to submillimeter ratios than other galaxy templates, suggesting a hotter dust temperature. We estimate their dust temperatures to be 60–120 K using a single-temperature model. Their infrared luminosities are well over 10 13 L� . These SEDs are not well fitted with existing galaxy templates, suggesting they are a new population with very high luminosity and hot dust. They are likely among the most luminous galaxies in the universe. We argue that they are extreme cases of luminous, hot dust-obscured galaxies (DOGs), possibly representing a short evolutionary phase during galaxy merging and evolution. A better understanding of their long-wavelength properties needs ALMA as well as Herschel data.
119231909
THE SPITZER c2d SURVEY OF NEARBY DENSE CORES. IX. DISCOVERY OF A VERY LOW LUMINOSITY OBJECT DRIVING A MOLECULAR OUTFLOW IN THE DENSE CORE L673-7
We present new infrared, submillimeter, and millimeter observations of the dense core L673-7 and report the discovery of a low-luminosity, embedded Class 0 protostar driving a molecular outflow. L673-7 is seen in absorption against the mid-infrared background in 5.8, 8, and 24 {mu}m Spitzer images, allowing for a derivation of the column density profile and total enclosed mass of L673-7, independent of dust temperature assumptions. Estimates of the core mass from these absorption profiles range from 0.2to4.5 M{sub sun}. Millimeter continuum emission indicates a mass of {approx}2 M{sub sun}, both from a direct calculation assuming isothermal dust and from dust radiative transfer models constrained by the millimeter observations. We use dust radiative transfer models to constrain the internal luminosity of L673-7, defined to be the luminosity of the central source and excluding the luminosity from external heating, to be L{sub int} = 0.01-0.045 L{sub sun}, with L{sub int} {approx} 0.04 L{sub sun} the most likely value. L673-7 is thus classified as a very low luminosity object (VeLLO), and is among the lowest luminosity VeLLOs yet studied. We calculate the kinematic and dynamic properties of the molecular outflow in the standard manner. From the outflow properties and standard assumptions regarding themore » driving of outflows, we calculate the time-averaged protostellar mass accretion rate, total protostellar mass accreted, and expected accretion luminosity to be {>=}1.2 x 10{sup -6} (sin i)/(co{sup 2} i) M{sub sun} yr{sup -1}, M{sub acc{>=}}0.07 1/cos i M{sub sun}, and L{sub acc} {>=} 0.36 L{sub sun}, respectively. The discrepancy between this calculated L{sub acc} and the L{sub int} derived from dust radiative transfer models indicates that the current accretion rate is much lower than the average rate over the lifetime of the outflow. Although the protostar embedded within L673-7 is consistent with currently being substellar, it is unlikely to remain as such given the substantial mass reservoir remaining in the core.« less
119498034
Submillimeter Dust Continuum Studies of Low and High Mass Star Formation
Studying the physical environments of low mass and high mass cores using dust continuum emission provides important observational constraints on theoretical models of star formation. The motivation and procedure for modeling dust continuum emission is reviewed and the results of recent surveys towards low mass and high mass star forming regions are compared.
209907524
Photon - dominated regions in low UV fields : a study of the peripheral regions of L1204 /S140
15575800
Flavor universal dynamical electroweak symmetry breaking
The top condensate seesaw mechanism of Dobrescu and Hill allows electroweak symmetry to be broken while deferring the problem of flavor to an electroweak singlet, massive sector. We provide an extended version of the singlet sector that naturally accommodates realistic masses for all the standard model fermions, which play an equal role in breaking electroweak symmetry. The models result in a relatively light composite Higgs sector with masses typically in the range of (400{endash}700) GeV. In more complete models the dynamics will presumably be driven by a broken gauged family or flavor symmetry group. As an example of the higher scale dynamics a fully dynamical model of the quark sector with a GIM mechanism is presented, based on an earlier top condensation model of King using broken family gauge symmetry interactions (that model was itself based on a technicolor model of Georgi). The crucial extra ingredient is a reinterpretation of the condensates that form when several gauge groups become strong close to the same scale. A related technicolor model of Randall which naturally includes the leptons too may also be adapted to this scenario. We discuss the low energy constraints on the massive gauge bosons and scalars of these modelsmore » as well as their phenomenology at the TeV scale. thinsp thinsp {copyright} {ital 1999} {ital The American Physical Society}« less
8365482
Non-equilibrium physics at a holographic chiral phase transition
The D3/D7 system holographically describes an $ \mathcal{N} = 2 $ gauge theory which spontaneously breaks a chiral symmetry by the formation of a quark condensate in the presence of a magnetic field. At finite temperature it displays a first order phase transition. We study out of equilibrium dynamics associated with this transition by placing probe D7 branes in a geometry describing a boost-invariant expanding or contracting plasma. We use an adiabatic approximation to track the evolution of the quark condensate in a heated system and reproduce the phase structure expected from equilibrium dynamics. We then study solutions of the full partial differential equation that describes the evolution of out of equilibrium configurations to provide a complete description of the phase transition including describing aspects of bubble formation.
6065903
Exact results and soft breaking masses in supersymmetric gauge theory
Abstract We give an explicit formalism connecting softly broken supersymmetric gauge theories (with QCD as one limit) to N = 2 and N = 1 supersymmetric theories possessing exact solutions, using spurion fields to embed these models in an enlarged N = 1 model. The functional forms of effective lagrangian terms resulting from soft supersymmetry breaking are constrained by the symmetries of the enlarged model, although not well enough to fully determine the vacuum structure of generic softly broken models. Nevertheless, by perturbing the exact N = 1 model results with sufficiently small soft breaking masses, we show that there exist nonsupersymmetric models that exhibit monopole condensation and confinement in the same modes as the N = 1 case.
119208225
The baryonic phase in holographic descriptions of the QCD phase diagram
A bstractWe study holographic models of the QCD temperature-chemical potential phase diagram based on the D3/D7 system with chiral symmetry breaking. The baryonic phase may be included through linked D5-D7 systems. In a previous analysis of a model with a running gauge coupling a baryonic phase was shown to exist to arbitrarily large chemical potential. Here we explore this phase in a more generic phenomenological setting with a step function dilaton profile. The change in dilaton generates a linear confining qq potential and opposes the screening effect of temperature. We show that the persistence of the baryonic phase depends on the step size and that QCD-like phase diagrams can be described. The baryonic phase’s existence is qualitatively linked to the existence of confinement in Wilson loop computations in the background.
118357465
Decoupling dynamical electroweak symmetry breaking
The modern precision accelerator data has essentially ruled out the most obvious model of dynamical electroweak symmetry breaking, technicolour. The idea is though well motivated and it is important to construct models compatible with the precision data of this ilk to motivate experimental searches. We describe the top-see-saw and flavour universal symmetry breaking models that break electroweak symmetry dynamically yet have a decoupling limit for all new physics. Limits on the scale of such new physics may be placed using precision data and direct search results from the Tevatron.