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Feasting black holes caught in galactic spiderweb


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Spiderweb galaxy field: Feasting black holes caught in galactic spiderweb

by Chandra X-ray Center:

Often, a spiderweb conjures the idea of captured prey soon to be consumed by a waiting predator. In the case of the "Spiderweb" protocluster, however, objects that lie within a giant cosmic web are feasting and growing, according to data from NASA's Chandra X-ray Observatory.

The Spiderweb galaxy, officially known as J1140-2629, gets its nickname from its web-like appearance in some optical light images. This likeness can be seen in the inset box where data from NASA's Hubble Space Telescope shows galaxies in orange, white, and blue, and data from Chandra is in purple. Located about 10.6 billion light years from Earth, the Spiderweb galaxy is at the center of a protocluster, a growing collection of galaxies and gas that will eventually evolve into a galaxy cluster.

To look for growing black holes in the Spiderweb protocluster a team of researchers observed it for over eight days with Chandra. In the main panel of this graphic, a composite image of the Spiderweb protocluster shows X-rays detected by Chandra (also in purple) that have been combined with optical data from the Subaru telescope on Mauna Kea in Hawaii (red, green, and white). The large image is 11.3 million light years across.

more at link............

the paper:



The 700 ks Chandra Spiderweb Field I: evidence for widespread nuclear activity in the Protocluster:


Aims. We present an analysis of the 700 ks Chandra ACIS-S observation of the field around the radio galaxy J1140-2629 (the Spiderweb Galaxy) at z = 2.156, focusing on the nuclear activity in the associated large-scale environment. Methods. We identify unresolved X-ray sources in the field down to flux limits of 1.3 × 10−16 and 3.9 × 10−16 erg/s/cm2 in the soft (0.5-2.0 keV) and hard (2-10 keV) band, respectively. We search for counterparts in the optical, NIR and submm catalogs available in the literature to identify X-ray sources belonging to the protocluster and derive their X-ray properties. Results. We detect 107 X-ray unresolved sources within 5 arcmin (corresponding to 2.5 Mpc) of J1140-2629, among which 13 have optical counterparts with spectroscopic redshift 2.11 < z < 2.20, and 1 source with photometric redshift consistent with this range. The X-ray emitting protocluster members are distributed approximately over a ∼ 3.2 × 1.3 Mpc2 rectangular region. An X-ray spectral analysis for all the sources within the protocluster, shows that their intrinsic spectral slope is consistent with an average hΓi ∼ 1.84 ± 0.04. Excluding the Spiderweb Galaxy, the best-fit intrinsic absorption for 5 protocluster X-ray members is NH > 1023 cm−2 , while other 6 have upper limits of the order of few×1022 cm−2 . Two sources can only be fitted with very flat Γ ≤ 1, and are therefore considered Compton-thick candidates. The 0.5-10 keV rest frame luminosities of the 11 Compton-thin protocluster members, corrected for intrinsic absorption, are greater than 2×1043 erg/s. These values are typical for the bright end of a Seyfert-like distribution and significantly greater than X-ray luminosities expected from star formation activity. The X-ray luminosity function of AGN in the volume associated to the Spiderweb protocluster in the range 1043 < LX < 1044.5 erg/s, is at least 10 times higher than that in the field at the same redshift and significantly flatter, implying an increasing excess at the bright end. The X-ray AGN fraction is measured to be 25.5 ± 4.5% of the spectroscopically confirmed members in the stellar mass range log(M∗/M) > 10.5. This value corresponds to an enhancement factor of 6.0 +9.0 −3.0 for the nuclear activity with L0.5−10keV > 4 × 1043 erg/s with respect to the COSMOS field at comparable redshifts and stellar mass range. Conclusions. We conclude that the galaxy population in the Spiderweb Protocluster is characterized by enhanced X-ray nuclear activity triggered by environmental effects on Mpc scales.


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