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Register a new userQUIJOTE Scientific Results. II. Polarisation Measurements of the Microwave Emission in the Galactic molecular complexes W43 and W47 and supernova remnant W44
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Ricardo Genova-Santos
Publication date
2016
fields
Physics
and research's language is
English
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We present Q-U-I JOint TEnerife (QUIJOTE) intensity and polarisation maps at 10-20 GHz covering a region along the Galactic plane 24<l<45 deg, |b|<8 deg. These maps result from 210 h of data, have a sensitivity in polarisation of ~40 muK/beam and an angular resolution of ~1 deg. Our intensity data are crucial to confirm the presence of anomalous microwave emission (AME) towards the two molecular complexes W43 (22 sigma) and W47 (8 sigma). We also detect at high significance (6 sigma) AME associated with W44, the first clear detection of this emission towards a SNR. The new QUIJOTE polarisation data, in combination with WMAP, are essential to: i) Determine the spectral index of the synchrotron emission in W44, beta_sync =-0.62 +/-0.03, in good agreement with the value inferred from the intensity spectrum once a free-free component is included in the fit. ii) Trace the change in the polarisation angle associated with Faraday rotation in the direction of W44 with rotation measure -404 +/- 49 rad/m2. And iii) set upper limits on the polarisation of W43 of Pi_AME <0.39 per cent (95 per cent C.L.) from QUIJOTE 17~GHz, and <0.22 per cent from WMAP 41 GHz data, which are the most stringent constraints ever obtained on the polarisation fraction of the AME. For typical physical conditions (grain temperature and magnetic field strengths), and in the case of perfect alignment between the grains and the magnetic field, the models of electric or magnetic dipole emissions predict higher polarisation fractions.
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Anomalous microwave emission (AME) has been observed in numerous sky regions, in the frequency range ~10-60 GHz. One of the most scrutinized regions is G159.6-18.5, located within the Perseus molecular complex. In this paper we present further observations of this region (194 hours in total over ~250 deg^2), both in intensity and in polarization. They span four frequency channels between 10 and 20 GHz, and were gathered with QUIJOTE, a new CMB experiment with the goal of measuring the polarization of the CMB and Galactic foregrounds. When combined with other publicly-available intensity data, we achieve the most precise spectrum of the AME measured to date, with 13 independent data points being dominated by this emission. The four QUIJOTE data points provide the first independent confirmation of the downturn of the AME spectrum at low frequencies, initially unveiled by the COSMOSOMAS experiment in this region. We accomplish an accurate fit of these data using models based on electric dipole emission from spinning dust grains, and also fit some of the parameters on which these models depend. We also present polarization maps with an angular resolution of ~1 deg and a sensitivity of ~25 muK/beam. From these maps, which are consistent with zero polarization, we obtain upper limits of Pi<6.3% and <2.8% (95% C.L.) respectively at 12 and 18 GHz, a frequency range where no AME polarization observations have been reported to date. These constraints are compatible with theoretical predictions of the polarization fraction from electric dipole emission originating from spinning dust grains. At the same time, they rule out several models based on magnetic dipole emission from dust grains ordered in a single magnetic domain, which predict higher polarization levels. Future QUIJOTE data in this region may allow more stringent constraints on the polarization level of the AME.
We present new intensity and polarization observations of the Taurus molecular cloud (TMC) region in the frequency range 10-20 GHz with the Multi-Frequency Instrument (MFI) mounted on the first telescope of the QUIJOTE experiment. From the combination of the QUIJOTE data with the WMAP 9-yr data release, the Planck second data release, the DIRBE maps and ancillary data, we detect an anomalous microwave emission (AME) component with flux density $S_{rm AME, peak} = 43.0 pm 7.9,$Jy in the Taurus Molecular Cloud (TMC) and $S_{rm AME, peak} = 10.7 pm 2.7,$Jy in the dark cloud nebula L1527, which is part of the TMC. In the TMC the diffuse AME emission peaks around a frequency of 19 GHz, compared with an emission peak about a frequency of 25 GHz in L1527. In the TMC, the best constraint on the level of AME polarisation is obtained at the Planck channel of 28.4 GHz, with an upper limit $pi_{rm AME}<$4.2$,%$ (95$,%$ C. L.), which reduces to $pi_{rm AME} <$3.8$,%$ (95$,%$ C.L.) if the intensity of all the free-free, synchrotron and thermal dust components are negligible at this frequency. The same analysis in L1527 leads to $pi_{rm AME}<$5.3$%$ (95$,%$C.L.), or $pi_{rm AME}<$4.5$,%$ (95$%$C.L.) under the same assumption. We find that in the TMC and L1527 on average about $80%$ of the HII gas should be mixed with thermal dust. Our analysis shows how the QUIJOTE-MFI 10-20 GHz data provides key information to properly separate the synchrotron, free-free and AME components.
Anomalous Microwave Emission (AME) is a significant component of Galactic diffuse emission in the frequency range $10$-$60,$GHz and a new window into the properties of sub-nanometre-sized grains in the interstellar medium. We investigate the morphology of AME in the $approx10^{circ}$ diameter $lambda$ Orionis ring by combining intensity data from the QUIJOTE experiment at $11$, $13$, $17$ and $19,$GHz and the C-Band All Sky Survey (C-BASS) at $4.76,$GHz, together with 19 ancillary datasets between $1.42$ and $3000,$GHz. Maps of physical parameters at $1^{circ}$ resolution are produced through Markov Chain Monte Carlo (MCMC) fits of spectral energy distributions (SEDs), approximating the AME component with a log-normal distribution. AME is detected in excess of $20,sigma$ at degree-scales around the entirety of the ring along photodissociation regions (PDRs), with three primary bright regions containing dark clouds. A radial decrease is observed in the AME peak frequency from $approx35,$GHz near the free-free region to $approx21,$GHz in the outer regions of the ring, which is the first detection of AME spectral variations across a single region. A strong correlation between AME peak frequency, emission measure and dust temperature is an indication for the dependence of the AME peak frequency on the local radiation field. The AME amplitude normalised by the optical depth is also strongly correlated with the radiation field, giving an overall picture consistent with spinning dust where the local radiation field plays a key role.
We present the AGILE gamma-ray observations in the energy range 50 MeV - 10 GeV of the supernova remnant (SNR) W44, one of the most interesting systems for studying cosmic-ray production. W44 is an intermediate-age SNR (20, 000 years) and its ejecta expand in a dense medium as shown by a prominent radio shell, nearby molecular clouds, and bright [SII] emitting regions. We extend our gamma-ray analysis to energies substantially lower than previous measurements which could not conclusively establish the nature of the radiation. We find that gamma-ray emission matches remarkably well both the position and shape of the inner SNR shocked plasma. Furthermore, the gamma-ray spectrum shows a prominent peak near 1 GeV with a clear decrement at energies below a few hundreds of MeV as expected from neutral pion decay. Here we demonstrate that: (1) hadron-dominated models are consistent with all W44 multiwavelength constraints derived from radio, optical, X-ray, and gamma-ray observations; (2) ad hoc lepton-dominated models fail to explain simultaneously the well-constrained gamma-ray and radio spectra, and require a circumstellar density much larger than the value derived from observations; (3) the hadron energy spectrum is well described by a power-law (with index s = 3.0 pm 0.1) and a low-energy cut-off at Ec = 6 pm 1 GeV. Direct evidence for pion emission is then established in an SNR for the first time.
(Abridged) We have investigated two evolutionary scenarios advanced to explain the centrally-brightened X-ray morphology of the supernova remnant (SNR) W44: (1) a model involving the slow thermal evaporation of clouds engulfed by a supernova blast wave as it propagates though a clumpy interstellar medium (ISM), and (2) a hydrodynamical simulation of a blast wave propagating through a homogeneous ISM, including the effects of radiative cooling. Both models can have their respective parameters tuned to approximate the remnants morphology. The mean temperature of the hot plasma in W44 (~0.9 keV) as determined by our nonequilibrium ionization X-ray spectral analysis provides the essential key to discriminate between these scenarios. Based on the size (using the well established distance of 3 kpc) and temperature of W44, the dynamical evolution predicted by the cloud evaporation model gives an age for the SNR of merely 6500 yr. We argue that, because this age is inconsistent with the characteristic age (approx. 20000 yr) of the associated PSR 1853+01, this model cannot provide the explanation for the center-filled morphology. We favor the radiative-phase shock model since it can reproduce both the morphology and age of W44 assuming reasonable values for the initial explosion energy in the range 0.7E51 to 0.9E51 ergs and the ambient ISM density of between 3 and 4 cm**-3.
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