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تسجيل مستخدم جديدEvidence of Fermi acceleration of Lyman alpha in the Radio Galaxy 1243+036
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L. Binette UNAM
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The high redshift radiogalaxy 1243+036 (z=3.6) presents an asymmetric Lyman alpha profile of FWHM 1550 km/s as measured by van Ojik et al. We propose that the blue asymmetry in the Lyman alpha profile is not due to narrow absorption dips but consists of narrow emission peaks. We interpret the blueshifted peaks near -1130, -850 and -550 km/s (relative to the peak of full profile) as being the result of Fermi acceleration of Lyman alpha produced by jet-induced star formation in the wake of a 300 km/s shock. This shock would be caused by the deflection of the radio-jet at the observed position of the radio bend which also coincides spatially with the excess Lyman alpha emission reported by van Ojik et al
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We report results of our new spatially-resolved, optical spectroscopy of the giant Ly$alpha$ nebula around a powerful radio galaxy 1243+036 (4C+03.24) at $z=3.57$. The nebula is extended over $sim 30$ kpc from the nucleus, and forms a pair of cones o
r elongated bubbles. The high-velocity ($sim -1000$ km s$^{-1}$; blueshifted with respect to the systemic velocity) Ly$alpha$-emitting components are detected at both sides of the nucleus along its major axis. The northwestern nebula is more spectacular in its velocity shift (blueshifted by -1000 km s$^{-1}$ to -1400 km s$^{-1}$) and in its width ($simeq 1900$ km s$^{-1}$ FWHM) over $simeq 30$ kpc scale. We discuss possible origin of the nebula; 1) the shock-heated expanding bubble or outflowing cone associated with the superwind activity of the host galaxy, 2) halo gas photoionized by the anisotropic radiation from the active galactic nuclei (AGN), and 3) the jet-induced star-formation or shock. The last possibility may not be likely because Ly$alpha$ emission is distributed out of the narrow channel of the radio jet. We show that the superwind model is most plausible since it can explain both the characteristics of the morphology (size and shape) and the kinematical structures (velocity shift and line width) of the nebula although the photoionization by AGN may contribute to the excitation to some extent.
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, two have clear detections and an additional two are barely detected (~2-sigma). The clear detections are within ~0.5 kpc of the centroid of the corresponding rest-UV continuum source, suggesting that the line-emitting gas and young stars in LAEs are spatially coincident. The brightest object exhibits extended emission with a half-light radius of ~1.5 kpc, but a stack of the remaining LAE surface brightness profiles is consistent with the WFPC2 point spread function. This suggests that the Lyman Alpha emission in these objects originates from a compact (<~2 kpc) region and cannot be significantly more extended than the far-UV continuum emission (<~1 kpc). Comparing our WFPC2 photometry to previous ground-based measurements of their monochromatic fluxes, we find at 95% (99.7%) confidence that we cannot be missing more than 22% (32%) of the Lyman Alpha emission.
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Lyman-$alpha$ blobs (LABs) are spatially extended nebulae of emission in the Ly$alpha$ line of hydrogen, seen at high redshifts$^{1,2}$, and most commonly found in the dense environment of star-forming galaxies$^{3,4}$. The origin of Ly$alpha$ emissi
on in the LABs is still unclear and under debate$^{5}$. Proposed powering sources generally fall into two categories: (1) photoionization, galactic super-winds/outflows, resonant scattering of Ly$alpha$ photons from starbursts or active galactic nuclei (AGNs)$^{6,7,8,9,10}$ and (2) cooling radiation from cold streams of gas accreting onto galaxies$^{12}$. Here we analyze the gas kinematics within a LAB providing rare observational evidence for infalling gas. This is consistent with the release of gravitational accretion energy as cold streams radiate Ly$alpha$ photons. It also provides direct evidence for possible cold streams feeding the central galaxies. The infalling gas is not important by mass but hints at more than one mechanism to explain the origin of the extended Ly$alpha$ emission around young galaxies. It is also possible that the infalling gas may represent material falling back to the galaxy from where it originated, forming a galactic fountain.
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