The non-Gaussian Cold Spot in WMAP: significance, morphology and foreground contribution

The non--Gaussian cold spot in the 1-year WMAP data, described in Vielva et al. and Cruz et al., is analysed in detail in the present paper. First of all, we perform a more rigorous calculation of the significance of the non-zero kurtosis detected in WMAP maps by Vielva et al. in wavelet space, mainly generated by the Spot. We confirm the robustness of that detection, since the probability of obtaining this deviation by chance is 0.69%. Afterwards, the morphology of the Spot is studied by applying Spherical Mexican Hat Wavelets with different ellipticities. The shape of the Spot is found to be almost circular. Finally, we discuss if the observed non-Gaussianity in wavelet space can arise from bad subtracted foreground residues in the WMAP maps. We show that the flat frequency dependence of the Spot cannot be explained by a thermal Sunyaev-Zeldovich effect. Based on our present knowledge of Galactic foreground emissions, we conclude that the significance of our detection is not affected by Galactic residues in the region of the Spot. Considering different Galactic foreground estimates, the probability of finding such a big cold spot in Gaussian simulations is always below 1%.Comment: 13 pages, 8 figures, minor changes, accpeted in MNRA

A Cosmic Microwave Background feature consistent with a cosmic texture

The Cosmic Microwave Background provides our most ancient image of the Universe and our best tool for studying its early evolution. Theories of high energy physics predict the formation of various types of topological defects in the very early universe, including cosmic texture which would generate hot and cold spots in the Cosmic Microwave Background. We show through a Bayesian statistical analysis that the most prominent, 5 degree radius cold spot observed in all-sky images, which is otherwise hard to explain, is compatible with having being caused by a texture. From this model, we constrain the fundamental symmetry breaking energy scale to be phi_0 ~ 8.7 x 10^(15) GeV. If confirmed, this detection of a cosmic defect will probe physics at energies exceeding any conceivable terrestrial experiment.Comment: Accepted by Science. Published electronically via Science Express on 25 October 2007, http://www.sciencemag.org/cgi/content/abstract/114869

On the magnetism and dynamics of prominence legs hosting tornadoes

Solar tornadoes are dark vertical filamentary structures observed in the extreme ultraviolet associated with prominence legs and filament barbs. Their true nature and relationship to prominences requires understanding their magnetic structure and dynamic properties. Recently, a controversy has arisen: is the magnetic field organized forming vertical, helical structures or is it dominantly horizontal? And concerning their dynamics, are tornadoes really rotating or is it just a visual illusion? Here, we analyze four consecutive spectropolarimetric scans of a prominence hosting tornadoes on its legs which help us shed some light on their magnetic and dynamical properties. We show that the magnetic field is very smooth in all the prominence, probably an intrinsic property of the coronal field. The prominence legs have vertical helical fields that show slow temporal variation probably related to the motion of the fibrils. Concerning the dynamics, we argue that 1) if rotation exists, it is intermittent, lasting no more than one hour, and 2) the observed velocity pattern is also consistent with an oscillatory velocity pattern (waves).Comment: accepted for publication in Ap

Bias corrections for probit and logit models with two-way fixed effects

In this article, we present the user-written commands probitfe and logitfe, which fit probit and logit panel-data models with individual and time unobserved effects. Fixed-effects panel-data methods that estimate the unobserved effects can be severely biased because of the incidental parameter problem (Neyman and Scott, 1948, Econometrica 16: –32). We tackle this problem using the analytical and jackknife bias corrections derived in Fernández-Val and Weidner (2016, Journal of Econometrics 192: 291–312) for panels where the two dimensions (N and T) are moderately large. We illustrate the commands with an empirical application to international trade and a Monte Carlo simulation calibrated to this application

Near infrared and optical morphology of the dusty galaxy NGC972

Near infrared (NIR) and optical surface photometric analyses of the dusty galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can be fitted with a combination of gaussian and exponential profiles, corresponding to a starburst nucleus and a stellar disk respectively. The exponential scale length in the B-band is 2.8 times larger than in the K-band, which implies a central B-band optical depth as high as 11. A bulge is absent even in the NIR bands and hence the galaxy must be of a morphological type later than the usually adopted Sb type. Relatively low rotational velocity and high gas content also favor a later type, probably Sd, for the galaxy. Only one arm can be traced in the distribution of old stars; the second arm, however, can be traced in the distribution of dust and HII regions. Data suggest a short NIR bar, which ends inside the nuclear ring. The slowly rising nature of the rotation curve rules out a resonance origin of the the nuclear ring. The ring is most likely not in the plane of the galaxy, given its circular appearance in spite of the moderately high inclination of the galaxy. The off-planar nature of the star forming ring, the unusually high fraction (30%) of the total mass in molecular form, the presence of a nuclear starburst and the asymmetry of spiral arms, are probably the result of a merger with a gas-rich companion galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical Journal, October 199