The extraordinary outburst in the massive protostellar system NGC 6334 I-MM1 : strong increase in mid-infrared continuum emission

Financial support for this work was provided by NASA through award #07_0156 issued by USRA. Based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 089.C-0852(A).In recent years, dramatic outbursts have been identified toward massive protostars via infrared and millimeter dust continuum and molecular maser emission. The longest lived outburst (>6 yr) persists in NGC 6334 I-MM1, a deeply embedded object with no near-IR counterpart. Using FORCAST and HAWC+ on SOFIA, we have obtained the first mid-IR images of this field since the outburst began. Despite being undetected in pre-outburst ground-based 18 μm images, MM1 is now the brightest region at all three wavelengths (25, 37, and 53 μm), exceeding the UCHII region MM3 (NGC 6334 F). Combining the SOFIA data with ALMA imaging at four wavelengths, we construct a spectral energy distribution of the combination of MM1 and the nearby hot core MM2. The best-fit Robitaille radiative transfer model yields a luminosity of (4.9 ± 0.8) × 104 L⊙. Accounting for an estimated pre-outburst luminosity ratio MM1:MM2 = 2.1 ± 0.4, the luminosity of MM1 has increased by a factor of 16.3 ± 4.4. The pre-outburst luminosity implies a protostar of mass 6.7 M⊙, which can produce the ionizing photon rate required to power the pre-outburst HCHII region surrounding the likely outbursting protostar MM1B. The total energy and duration of the outburst exceed the S255IR-NIRS3 outburst by a factor of 3, suggesting a different scale of event involving expansion of the protostellar photosphere (to 20 R⊙), thereby supporting a higher accretion rate (0.0023 M⊙ yr−1) and reducing the ionizing photon rate. In the grid of hydrodynamic models of Meyer et al., the combination of outburst luminosity and magnitude (3) places the NGC 6334 I-MM1 event in the region of moderate total accretion (~0.1–0.3 M⊙) and hence long duration (~40–130 yr).PostprintPeer reviewe

Mission Concept for the Single Aperture Far-Infrared (SAFIR) Observatory

The Single Aperture Far-InfraRed (SAFIR) Observatory's science goals are driven by the fact that the earliest stages of almost all phenomena in the universe are shrouded in absorption by and emission from cool dust and gas that emits strongly in the far-infrared and submillimeter. Over the past several years, there has been an increasing recognition of the critical importance of this spectral region to addressing fundamental astrophysical problems, ranging from cosmological questions to understanding how our own Solar System came into being. The development of large, far-infrared telescopes in space has become more feasible with the combination of developments for the James Webb Space Telescope and of enabling breakthroughs in detector technology. We have developed a preliminary but comprehensive mission concept for SAFIR, as a 10 m-class far-infrared and submillimeter observatory that would begin development later in this decade to meet the needs outlined above. Its operating temperature (<4K) and instrument complement would be optimized to reach the natural sky confusion limit in the far-infrared with diffraction-limited peformance down to at least 40 microns. This would provide a point source sensitivity improvement of several orders of magnitude over that of Spitzer or Herschel, with finer angular resolution, enabling imaging and spectroscopic studies of individual galaxies in the early universe. We have considered many aspects of the SAFIR mission, including the telescope technology, detector needs and technologies, cooling method and required technology developments, attitude and pointing, power systems, launch vehicle, and mission operations. The most challenging requirements for this mission are operating temperature and aperture size of the telescope, and the development of detector arrays.Comment: 36 page

The magnetic field in the Flame nebula

International audienceContext. Star formation drives the evolution of galaxies and the cycling of matter between different phases of the interstellar medium and stars. The support of interstellar clouds against gravitational collapse by magnetic fields has been proposed as a possible explanation for the low observed star formation efficiency in galaxies and the Milky Way. The Planck satellite provided the first all-sky map of the magnetic field geometry in the diffuse interstellar medium on angular scales of 5–15′. However, higher spatial resolution observations are required to understand the transition from diffuse, subcritical gas to dense, gravitationally unstable filaments.Aims. NGC 2024, also known as the Flame nebula, is located in the nearby Orion B molecular cloud. It contains a young, expanding H II region and a dense supercritical filament. This filament harbors embedded protostellar objects and is likely not supported by the magnetic field against gravitational collapse. Therefore, NGC 2024 provides an excellent opportunity to study the role of magnetic fields in the formation, evolution, and collapse of dense filaments, the dynamics of young H II regions, and the effects of mechanical and radiative feedback from massive stars on the surrounding molecular gas.Methods. We combined new 154 and 216 μm dust polarization measurements carried out using the HAWC+ instrument aboard SOFIA with molecular line observations of 12CN(1−0) and HCO+(1−0) from the IRAM 30-m telescope to determine the magnetic field geometry, and to estimate the plane of the sky magnetic field strength across the NGC 2024 H II region and the surrounding molecular cloud.Results. The HAWC+ observations show an ordered magnetic field geometry in NGC 2024 that follows the morphology of the expanding H II region and the direction of the main dense filament. The derived plane of the sky magnetic field strength is moderate, ranging from 30 to 80 μG. The strongest magnetic field is found at the eastern edge of the H II region, characterized by the highest gas densities and molecular line widths. In contrast, the weakest field is found toward the main, dense filament in NGC 2024.Conclusions. We find that the magnetic field has a non-negligible influence on the gas stability at the edges of the expanding H II shell (gas impacted by stellar feedback) and the filament (site of current star formation)

Deep Herschel view of obscured star formation in the Bullet cluster

We use deep, five band (100–500 μm) data from the Herschel Lensing Survey (HLS) to fully constrain the obscured star formation rate, SFRFIR, of galaxies in the Bullet cluster (z = 0.296), and a smaller background system (z = 0.35) in the same field. Herschel detects 23 Bullet cluster members with a total SFRFIR = 144±14 yr-1. On average, the background system contains brighter far-infrared (FIR) galaxies, with ~50% higher SFRFIR (21 galaxies; 207± 9 yr-1). SFRs extrapolated from 24 μm flux via recent templates (SFR24 µm) agree well with SFRFIR for ~60% of the cluster galaxies. In the remaining ~40%, SFR24 µm underestimates SFRFIR due to a significant excess in observed S100/S24 (rest frame S75/S18) compared to templates of the same FIR luminosity

Low Q^2 Jet Production at HERA and Virtual Photon Structure

The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure

Hadron Production in Diffractive Deep-Inelastic Scattering

Characteristics of hadron production in diffractive deep-inelastic positron-proton scattering are studied using data collected in 1994 by the H1 experiment at HERA. The following distributions are measured in the centre-of-mass frame of the photon dissociation system: the hadronic energy flow, the Feynman-x (x_F) variable for charged particles, the squared transverse momentum of charged particles (p_T^{*2}), and the mean p_T^{*2} as a function of x_F. These distributions are compared with results in the gamma^* p centre-of-mass frame from inclusive deep-inelastic scattering in the fixed-target experiment EMC, and also with the predictions of several Monte Carlo calculations. The data are consistent with a picture in which the partonic structure of the diffractive exchange is dominated at low Q^2 by hard gluons.Comment: 16 pages, 6 figures, submitted to Phys. Lett.

Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA

An investigation of the hadronic final state in diffractive and non--diffractive deep--inelastic electron--proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo --rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep--inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep--inelastic $ep$ scattering, in which a sizeable diffractive contribution is present because of non--perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil

Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD

With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.

A Search for Selectrons and Squarks at HERA

Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure

Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA

Deep--inelastic scattering events with a leading baryon have been detected by the H1 experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi--inclusive cross sections have been measured in the kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T <= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV, or a neutron with energy E' >= 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.