Global Jet Watch

Abstract:

We describe a new, independent method for breaking the deadlock of measuring the cosmologically very important Cosmic Infrared Background. Our method measures the energy density of the Cosmic Infrared Background at the location of radio galaxies by using Fermi Gamma-ray and multiwavelength observations of their radio lobes. We present an application of our method for the well-studied radio galaxy Fornax A, showing that Fermi observations will provide us with a direct, model independent measurement of the Cosmic Infrared Background. © 2009 American Institute of Physics.

Abstract:

One of the six extended X-ray sources found in the Chandra DeepField North is centred on HDF130, which has recently been shown to be a massive galaxy at z=1.99 with a compact radio nucleus. The X-ray source has a roughly double-lobed structure with each lobe about 41 arcsec long, or 345 kpc at the redshift of HDF130. We have analyzed the 2 Ms X-ray image and spectrum of the source and find that it is well fit by a power-law continuum of photon index 2.65 and has a 2--10 keV luminosity of 5.4x10^{43}ergps (if at z=1.99). Any further extended emission within a radius of 60 arcsec has a luminosity less than half this value, which is contrary to what is expected from a cluster of galaxies. The source is best explained as an inverse Compton ghost of a giant radio source, which is no longer being powered, and for which Compton losses have downgraded the energetic electrons, \gamma> 10^4, required for high-frequency radio emission. The lower energy electrons, \gamma~1000, produce X-rays by inverse Compton scattering on the Cosmic Microwave Background. Depending on the magnetic field strength, some low frequency radio emission may remain. Further inverse Compton ghosts may exist in the Chandra deep fields.

Abstract:

Using deep J, H and Ks-band observations, we have studied the near-infrared (nIR) extinction of the Nuclear Bulge (NB) and we find significant, complex variations on small physical scales. We have applied a new variable nIR colour excess method, V-NICE, to measure the extinction; this method allows for variation in both the extinction law parameter alpha and the degree of absolute extinction on very small physical scales. We see significant variation in both these parameters on scales of 5 arcsec. In our observed fields, representing a random sample of sight lines to the NB, we measure alpha to be 2.64 +- 0.52, compared to the canonical "universal" value of 2. Our measured levels of A_Ks are similar to previously measured results (1 < A_Ks < 4.5); however, the steeper extinction law results in higher values for A_J (4.5 < A_J < 10) and A_H (1.5 < A_H < 6.5). Only when the extinction law is allowed to vary on the smallest scales can we recover self-consistent measures of the absolute extinction at each wavelength, allowing accurate reddening corrections for field star photometry in the NB. The steeper extinction law slope also suggests that previous conversions of nIR extinction to A_V may need to be reconsidered. Finally, we find that the measured values of extinction are significantly dependent on the filter transmission functions of the instrument used to obtain the data. This effect must be taken into account when combining or comparing data from different instruments.