arXiv subjects

Andy Fabian

Publications and source records attributed to Andy Fabian.

20 records · Page 2Linked to original sources

arXiv2007

An infrared survey of brightest cluster galaxies: Paper I

We report on an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission. These galaxies are located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky Survey. We find that about half of these sources have a sign of excess infrared emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8 micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0. Altogether 35 of 62 objects in our survey exhibit at least one of these signs of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at 8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol and so can be classified as luminous infrared galaxies (LIRGs). Excluding the four systems hosting dusty AGNs, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation.

astro-ph↗

arXiv2006

Discovery of the low-energy cutoff in a powerful giant radio galaxy

The lobes of radio galaxies and quasars, fed by jets and hotspots, represent a significant, and currently ill-constrained, source of energy input into the inter-galactic medium (IGM). How much energy is input into the IGM depends on the minimum energy to which the power-law distribution of relativistic particles is accelerated in the hotspots. This has hitherto been unknown to within three orders of magnitude. We present direct evidence for the discovery of this low-energy cutoff in the lobe of a Mpc-sized radio galaxy via the existence of extended X-ray emission, inverse-Compton scattered from aged radio plasma, and its separation by 80kpc from regions containing freshly accelerated plasma from the hotspot. The low-energy cutoff of gamma ~ 10^4 in the hotspot is higher than previously thought, but reconciles discrepancies with magnetic field estimates which had been systematically lower than equipartition values. The inverse Compton scattering of the spent synchrotron plasma is at the expense of cosmic microwave background (CMB) photons; we comment on the importance of such giant radio galaxies as contaminants of CMB anisotropies.

astro-ph↗