Scientific Objectives for UV/Visible Astrophysics Investigations: A Summary of Responses by the Community (2012)

Following several recommendations presented by the Astrophysics Decadal Survey 2010 centered around the need to define "a future ultraviolet-optical space capability," on 2012 May 25, NASA issued a Request for Information (RFI) seeking persuasive ultraviolet (UV) and visible wavelength astrophysics science investigations. The goal was to develop a cohesive and compelling set of science objectives that motivate and support the development of the next generation of ultraviolet/visible space astrophysics missions. Responses were due on 10 August 2012 when 34 submissions were received addressing a number of potential science drivers. A UV/visible Mission RFI Workshop was held on 2012 September 20 where each of these submissions was summarized and discussed in the context of each other. We present a scientific analysis of these submissions and presentations and the pursuant measurement capability needs, which could influence ultraviolet/visible technology development plans for the rest of this decade. We also describe the process and requirements leading to the inception of this community RFI, subsequent workshop and the expected evolution of these ideas and concepts for the remainder of this decade.Comment: 22 pages, 1 figure, 3 table

Instability of toroidal magnetic field in jets and plerions

Jets and pulsar-fed supernova remnants (plerions) tend to develop highly organized toroidal magnetic field. Such a field structure could explain the polarization properties of some jets, and contribute to their lateral confinement. A toroidal field geometry is also central to models for the Crab Nebula - the archetypal plerion - and leads to the deduction that the Crab pulsar's wind must have a weak magnetic field. Yet this `Z-pinch' field configuration is well known to be locally unstable, even when the magnetic field is weak and/or boundary conditions slow or suppress global modes. Thus, the magnetic field structures imputed to the interiors of jets and plerions are unlikely to persist. To demonstrate this, I present a local analysis of Z-pinch instabilities for relativistic fluids in the ideal MHD limit. Kink instabilities dominate, destroying the concentric field structure and probably driving the system toward a more chaotic state in which the mean field strength is independent of radius (and in which resistive dissipation of the field may be enhanced). I estimate the timescales over which the field structure is likely to be rearranged and relate these to distances along relativistic jets and radii from the central pulsar in a plerion. I conclude that a concentric toroidal field is unlikely to exist well outside the Crab pulsar's wind termination shock. There is thus no dynamical reason to conclude that the magnetic energy flux carried by the pulsar wind is much weaker than the kinetic energy flux. Abandoning this inference would resolve a long-standing puzzle in pulsar wind theory.Comment: 28 pages, plain TeX. Accepted for publication in Ap

Bipolar molecular outflows driven by hydromagnetic protostellar winds

We demonstrate that magnetically-collimated protostellar winds will sweep ambient material into thin, radiative, momentum-conserving shells whose features reproduce those commonly observed in bipolar molecular outflows. We find the typical position-velocity and mass-velocity relations to occur in outflows in a wide variety of ambient density distributions, regardless of the time histories of their driving winds.Comment: 4 pages, 1 figure, submitted to ApJ

Sensitive Radio Observations of High Redshift Dusty QSOs

We present sensitive radio continuum imaging at 1.4 GHz and 4.9 GHz of seven high redshift QSOs selected for having a 240 GHz continuum detection, which is thought to be thermal dust emission. We detect radio continuum emission from four of the sources: BRI 0952-0115, BR 1202-0725, LBQS 1230+1627B, and BRI 1335-0417. The radio source in BR 1202-0725 is resolved into two components, coincident with the double mm and CO sources. We compare the results at 1.4 GHz and 240 GHz to empirical and semi-analytic spectral models based on star forming galaxies at low redshift. The radio-to-submm spectral energy distribution for BR 1202-0725, LBQS 1230+1627B, and BRI 1335-0417 are consistent with that expected for a massive starburst galaxy, with implied massive star formation rates of order 1000 solar masses per year (without correcting for possible amplification by gravitational lensing). The radio-to-submm spectral energy distribution for BRI 0952-0115 suggests a low-luminosity radio jet source driven by the AGN.Comment: 12 pages, Latex emulateapj format, including 1 table and 3 figures. The Astrophysical Journal, to appear in the January 2000 issu

The thermodynamics of urban population flows

Orderliness, reflected via mathematical laws, is encountered in different frameworks involving social groups. Here we show that a thermodynamics can be constructed that macroscopically describes urban population flows. Microscopic dynamic equations and simulations with random walkers underlie the macroscopic approach. Our results might be regarded, via suitable analogies, as a step towards building an explicit social thermodynamics

350 Micron Dust Emission from High Redshift Objects

We report observations of a sample of high redshift sources (1.8<z<4.7), mainly radio-quiet quasars, at 350 microns using the SHARC bolometer camera at the Caltech Submillimeter Observatory. Nine sources were detected (>4-sigma) and upper limits were obtained for 11 with 350 micron flux density limits (3-sigma) in the range 30-125mJy. Combining published results at other far-infrared and millimeter wavelengths with the present data, we are able to estimate the temperature of the dust, finding relatively low values, averaging 50K. From the spectral energy distribution, we derive dust masses of a few 10^8 M_sun and luminosities of 4-33x10^{12} L_sun (uncorrected for any magnification) implying substantial star formation activity. Thus both the temperature and dust masses are not very different from those of local ultraluminous infrared galaxies. For this redshift range, the 350 micron observations trace the 60-100 micron rest frame emission and are thus directly comparable with IRAS studies of low redshift galaxies.Comment: 5 pages, 2 PS figures. Accepted for publication in Astrophysical Journal Letter

The X-ray jet in the Crab Nebula: radical implications for pulsar theory?

The recent Chandra image of the Crab nebula shows a striking, axisymmetric polar jet. It is shown that jets are formed in axisymmetric, magnetized pulsar winds and that the jet luminosity scales relative to the total as (\gamma_0\sigma_{eq})^{-4/3}, where \sigma_{eq} is the ratio of Poynting flux to particle kinetic energy output at the equator at the base of the flow and \gamma_0 the initial Lorentz factor of the flow. The results are applied to the image of the Crab nebula, and the limit is set for the Crab pulsar of \sigma_{eq} \leq 100. It is argued that conventional pulsar theory needs to be reexamined in light of these limits.Comment: 13 page

First Astronomical Use of Multiplexed Transition Edge Bolometers

We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE'S detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Δλ/λ= 1/7 at a resolution of δλ/λ ≈ 1/1200 can be acquired. This spectral resolution is sufficient to resolve Doppler-broadened line emission from external galaxies. FIBRE operates in the 350 µm and 450 µm bands. These bands cover line emission from the important star formation tracers neutral carbon [Cl] and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry

Characterization of a submillimeter high-angular-resolution camera with a monolithic silicon bolometer array for the Caltech Submillimeter Observatory

We constructed a 24-pixel bolometer camera operating in the 350- and 450-µm atmospheric windows for the Caltech Submillimeter Observatory (CSO). This instrument uses a monolithic silicon bolometer array that is cooled to approximately 300 mK by a single-shot 3 He refrigerator. First-stage amplification is provided by field-effect transistors at approximately 130 K. The sky is imaged onto the bolometer array by means of several mirrors outside the Dewar and a cold off-axis elliptical mirror inside the cryostat. The beam is defined by cold aperture and field stops, which eliminates the need for any condensing horns. We describe the instrument, present measurements of the physical properties of the bolometer array, describe the performance of the electronics and the data-acquisition system, and demonstrate the sensitivity of the instrument operating at the observatory. Approximate detector noise at 350 µm is 5 x 10^-15 W/√Hz, referenced to the entrance of the Dewar, and the CSO system noise-equivalent flux density is approximately 4 Jy/√Hz. These values are within a factor of 2.5 of the background limit