Galactic Spur Research Articles

BEYONDPLANCK

Using the Planck Low Frequency Instrument (LFI) and WMAP data within the global Bayesian BEYONDPLANCK framework, we constrained the polarized foreground emission between 30 and 70 GHz. We combined, for the first time, full-resolution Planck LFI time-ordered data with low-resolution WMAP sky maps at 33, 40, and 61 GHz. The spectral parameters were fit with a likelihood defined at the native resolution of each frequency channel. This analysis represents the first implementation of true multi-resolution component separation applied to CMB observations for both amplitude and spectral energy distribution (SED) parameters. For the synchrotron emission, we approximated the SED as a power-law in frequency and we find that the low signal-to-noise ratio of the current data strongly limits the number of free parameters that can be robustly constrained. We partitioned the sky into four large disjoint regions (High Latitude; Galactic Spur; Galactic Plane; and Galactic Center), each associated with its own power-law index. We find that the High Latitude region is prior-dominated, while the Galactic Center region is contaminated by residual instrumental systematics. The two remaining regions appear to be signal-dominated, and for these we derive spectral indices of βsSpur = −3.17 ± 0.06 and βsPlane = −3.03 ± 0.07, which is in good agreement with previous results. For the thermal dust emission, we assumed a modified blackbody model and we fit a single power-law index across the full sky. We find βd = 1.64 ± 0.03, which is slightly steeper than the value reported in Planck HFI data, but still statistically consistent at the 2σ confidence level.

Asymmetry of the CMB map: local and global anomalies

We investigate the sources of parity asymmetry in the CMB temperature maps using a pixel domain approach. We demonstrate that this anomaly is mainly associated with the presence of two pairs of high asymmetry regions. The first pair of peaks with Galactic coordinates (l, b) = (212°, -21°) and (32°, 21°) is associated with the Northern Galactic Spur and the direction of the dipole modulation of the power spectrum of the CMB anisotropy. The other pair ((l, b)=(332°, -8°) and (152°, 8°)) is located within the Galactic plane (the Galactic Cold Spot and its antipodal partner). Similar asymmetric peaks, but with smaller amplitudes, belong to the WMAP/Planck Cold Spot and its partner in the Northern Galactic Spur. These local anomalies increase the odd-multipole power to a level consistent with Gaussian simulations. In contrast, the deficit of symmetric peaks is accompanied by a deficit in the even-multipole power and is the source of the parity asymmetry of the CMB temperature maps at the level of about 3 sigma. We also evaluate the influence of the quadrupole, which is another source of the even-multipole deficit. If the low quadrupole is an intrinsic feature of the theoretical model, it will reduce the significance of the parity asymmetry to around the 2 sigma level. We also investigate the relationship between the asymmetry of the power spectrum and the level of the parity asymmetry in the framework of a model with dipole modulation of a statistically uniform Gaussian signal. We show that these two anomalies are innately linked to each other.

Origin of Galactic Spurs: New Insight from Radio/X-Ray All-sky Maps

Abstract In this study, we analyze giant Galactic spurs seen in both radio and X-ray all-sky maps to reveal their origins. We discuss two types of giant spurs: one is the brightest diffuse emission near the map’s center, which is likely to be related to Fermi bubbles (NPSs/SPSs, north/south polar spurs, respectively), and the other is weaker spurs that coincide positionally with local spiral arms in our Galaxy (LAS, Local Arm spur). Our analysis finds that the X-ray emissions, not only from the NPS but also from the SPS, are closer to the Galactic center by ∼5° compared with the corresponding radio emission. Furthermore, larger offsets of 10°–20° are observed in the LASs; however, they are attributed to different physical origins. Moreover, the temperature of the X-ray emission is kT ≃ 0.2 keV for the LAS, which is systematically lower than those of the NPS and SPS (kT ≃ 0.3 keV) but consistent with the typical temperature of Galactic halo gas. We argue that the radio/X-ray offset and the slightly higher temperature of the NPS/SPS X-ray gas are due to the shock compression/heating of halo gas during a significant Galactic explosion in the past, whereas the enhanced X-ray emission from the LAS may be due to the weak condensation of halo gas in the arm potential or star formation activity without shock heating.

Three‐YearWilkinson Microwave Anisotropy Probe(WMAP) Observations: Foreground Polarization

We present a full-sky model of polarized Galactic microwave emission based on 3 years of observations by the Wilkinson Microwave Anisotropy Probe (WMAP) at frequencies from 23 to 94 GHz. The model compares maps of the Stokes Q and U components from each of the five WMAP frequency bands in order to separate synchrotron from dust emission, taking into account the spatial and frequency dependence of the synchrotron and dust components. This simple two-component model of the interstellar medium accounts for at least 97% of the polarized emission in the WMAP maps of the microwave sky. Synchrotron emission dominates the polarized foregrounds at frequencies below 50 GHz, and is comparable to the dust contribution at 65 GHz. The spectral index of the synchrotron component, derived solely from polarization data, is -3.2 averaged over the full sky, with a modestly flatter index on the Galactic plane. The synchrotron emission has mean polarization fraction 2%-4% in the Galactic plane and rising to over 20% at high latitude, with prominent features such as the north Galactic spur more polarized than the diffuse component. Thermal dust emission has polarization fraction 1% near the Galactic center, rising to 6% at the anticenter. Diffuse emission from high-latitude dust is also polarized with mean fractional polarization 0.036 ± 0.011.

Observations of the galactic radio structure CTB 63 (G47.5 + 6.0)

view Abstract Citations (2) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the Galactic Radio Structure CTB 63 (G47.5+6.0) Caswell, J. L. ; Landecker, T. L. ; Roger, R. S. Abstract The radio source CTB 63 is extended and diffuse and has been regarded as a possible galactic supernova remnant. We present new observations at 408 and 1420 MHz made with the DRAO synthesis telescope that delineate the boundary and suggest that it is a galactic spur rather than a discrete supernova remnant. The spur has a length of ~6^deg^ and at one extremity merges with the diffuse galactic disk emission; it is clearly nonthermal and we explore some possibilities for its origin. We also catalog small-diameter sources in the region, most of which are extragalactic background sources. Publication: The Astronomical Journal Pub Date: June 1989 DOI: 10.1086/115111 Bibcode: 1989AJ.....97.1721C Keywords: Extragalactic Radio Sources; Galactic Radio Waves; Galactic Structure; Supernova Remnants; Astronomical Spectroscopy; Brightness Temperature; High Resolution; Radio Galaxies; Astrophysics; NEBULAE: SUPERNOVA REMNANTS; GALAXIES: THE GALAXY full text sources ADS | data products SIMBAD (150) NED (149)

New Theory for Giant Loops

FOUR very large, shell-shaped features are known from the surveys of radio emission from the Galaxy. Ranging in angular diameter from 40° (Loop IV) to 116° (Loop I, the North Polar Spur), they are polarized, nonthermal radio sources that appear to be associated with faint optical emission nebulae. These objects, formerly known as the galactic spurs, have recently been reviewed by the group at Manchester which has been responsible for much of the observational and theoretical work on them1. The term “spurs” seems to have given way to that of “loops”. We prefer to call them “giant loops”, because we believe that these objects represent a different phenomenon from that typified by the much smaller Cygnus Loop to which they are frequently compared.

Galactic Spurs as Possible Sources of Soft X-radiation

SOFT thermal X-radiation from the Cygnus Loop has been discovered recently1. One of us2 has predicted the existence of such radiation from supernova remnants on theoretical grounds. It is possible that the source Vela X-1 has a similar origin3.

Observations at 178 MHz of the North Galactic Spur

Observations at 178 MHz of the North Galactic Spur

Magnetic Fields in the Galactic Spurs

Magnetic Fields in the Galactic Spurs

A Survey of the Southern Sky at 85 MHz

A survey at 85 MHz is presented of the sky south of declination 0 = _20�,and of the northern galactic spur region to 0 = +20�. The survey was made withthe 210 ft telescope at Parkes, New South Wales. At this frequency the observedbeamwidth was 3.5� by 3� 8� to half-power points. The radiation characteristics ofthe survey aerial and of scaled aerial models were studied to enable corrections to bemade for radiation received by the aerial from regions outside the main beam.Absolute beam temperatures derived from the observed aerial temperatures had anr.m.s. accuracy of better than 7%.

The Galactic Spurs as a Single Feature

The Galactic Spurs as a Single Feature

First-Epoch Proper Motion Radio Observations on the Galactic Spur.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS First-Epoch Proper Motion Radio Observations on the Galactic Spur. Ellis, Fred Edward Abstract or any large arc-like object, implies proper motion if the object is not too old. The proper motion would be proportional directly to the tangent of the angular radius and inversely to the age. For example, if the Spur were associated with the "supernova" of A.D. 1006 the proper motion would be about 4 min of arc per year. Background radiation maps are not suitable as proper motion material. Scan profiles are desired. To be along the direction of greatest anticipated proper motion the scan path must follow a radius of the circle which best fits the obj ect. If the observation includes a discrete source as a coordinate marker and only relative position measures attempted, precession, correction for time constant, and conversion from indicated to true coordinates are unnecessary. The observing program is more self-contained if it includes pairs of scans made in opposite directions through the same discrete source. Such pairs of proper motion observations simultaneously carry information on telescope pointing errors, time constant, and antenna beam. To investigate observing techniques and to obtain first-epoch material for the Spur, observations were made in spring 1965 using the National Radio Astronomy Observatory 300-ft meridian telescope at 750 and 1415 Mc/sec. Declination scans at 2.5 min of arc per second included north-going and south- going scans through 3C310, 3C315, and 3C318. On 750 Mc/sec the ridge, seen on lower frequencies in this region at 180 declination, is conspicuous but because of the faintness of the Spur, an individual scan would not be useful for a position measurement. Only noise is seen on any individual 1415 Mc/sec record. Averaging of the digital records is in progress. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109658 Bibcode: 1965AJ.....70S.674E full text sources ADS |

The Galactic Spur

New observations have been made of the radio emission from the galactic spur at lII = 30° at 237 Mc/s to investigate the detailed structure of the sharp edges and the distribution of emission over the declination range observable from Jodrell Bank. The weak radio emission at 1415 Mc/s was measured at three sections of the northern edge of the spur, and the results were also compared with the 38 Mc/s survey of the region obtained by Costain and Smith (1960). This data allows a rediscussion of the nature of the spur. The spur has a characteristic sharp outer edge which in places falls to half intensity in 0°.5. Also it has structure parallel to the edge which indicates that the source is a multiple shell like the Cygnus Loop which it resembles in brightness temperature, spectrum and structure. If its radius is taken as 20 pc its centre lies at a distance of 30 pc and is composed of shells each with a thickness of about 2 pc. The observed emission from both the Cygnus Loop and the galactic spur is rather more than expected from background cosmic ray electrons alone, emitting in the enhanced magnetic field of the expanding envelope, and suggests that some of the emission comes from cosmic rays generated within the shell sources. The polarization of the main ridge of the spur confirms that it is close to the Sun and also that it radiates by the synchrotron process. It is concluded that the galactic spur, like the Cygnus Loop, is a supernova remnant.

Some Attempts to Detect Linear Polarization of the Spur of Galactic Radio Emission at lII = 30

Experiments have been carried out in an attempt to detect linearly polarized radiation from the galactic spur at lII = 30°. Five observational methods are discussed and the results of experiments using these methods are given. The frequencies used were 160, 178 and 408 Mc/s and the region of observation covered the more intense parts of the spur. All the experiments agree in fixing a low upper limit of a few per cent on linearly polarized radiation from the spur.