THECHANDRADEEP PROTOCLUSTER SURVEY: Lyα BLOBS ARE POWERED BY HEATING, NOT COOLING

Abstract

We present the results of a 400 ks Chandra survey of 29 extended Lyα emitting nebulae (Lyα Blobs, LABs) in the z = 3.09 protocluster in the SS A22 field. We detect luminous X-ray counterparts in five LABs, implying a large fraction of active galactic nuclei (AGN) in LABs, f AGN = 17 +12 −7 % down to L 2-32 keV ∼ 10 44 erg s −1 . All of the AGN appear to be heavily obscured, with spectral indices implying obscuring column densities of N H > 10 23 cm −2 . The AGN fraction should be considered a lower limit, since several more LABs not detected with Chandra show AGN signatures in their mid-infrared (mid-IR) emission. We show that the UV luminosities of the AGN are easily capable of powering the extended Lyα emission via photoionization alone. When combined with the UV flux from a starburst component, and energy deposited by mechanical feedback, we demonstrate that "heating" by a central source, rather than gravitational cooling is the most likely power source of LABs. We argue that all LABs could be powered in this manner, but that the luminous host galaxies are often just below the sensitivity limits of current instrumentation, or are heavily obscured. No individual LABs show evidence for extended X-ray emission, and a stack equivalent to a 9 Ms exposure of an average LAB also yields no statistical detection of a diffuse X-ray component. The resulting diffuse X-ray/Lyα luminosity limit implies there is no hot (T 10 7 K) gas component in these halos, and also rules out inverse Compton scattering of cosmic microwave background photons, or local far-IR photons, as a viable power source for LABs.

ALMA observations of az≈ 3.1 protocluster: star formation from active galactic nuclei and Lyman-alpha blobs in an overdense environment

“…This sample also contains four of the five X-ray-detected LABs in Geach et al (2009). However, there are several X-ray AGNs in the protocluster that we did not observe with ALMA (Tamura et al 2010;Kubo et al 2013;Umehata et al 2015), including LAB 18 from Geach et al (2009). On the basis of optical spectral analyses (Steidel et al 2003;Yamada et al 2012b;Kubo et al 2015), five of the X-ray AGNs in our sample have narrow emission lines and therefore appear to be optically obscured AGNs while three have broad emission lines and are therefore optically unobscured AGNs.…”

“…ALMA targets despite being at least an order of magnitude fainter at X-ray energies (L 2−32 keV 10 43 erg s −1 ; Geach et al 2009). …”

“…2 Our sample includes all six of the X-ray AGNs identified at z ≈ 3.09 in Lehmer et al (2009b) plus two additional X-ray AGNs from Lehmer et al (2009a) that have been spectroscopically identified as lying at z ≈ 3.09 (AGN 7: z = 3.098; Saez et al 2015; AGN 8: z = 3.091; Kubo et al 2015). This sample also contains four of the five X-ray-detected LABs in Geach et al (2009). However, there are several X-ray AGNs in the protocluster that we did not observe with ALMA (Tamura et al 2010;Kubo et al 2013;Umehata et al 2015), including LAB 18 from Geach et al (2009).…”

The environments of Ly α blobs – I. Wide-field Ly α imaging of TN J1338−1942, a powerful radio galaxy at z ≃ 4.1 associated with a giant Ly α nebula★

“…those in the SA 22 protocluster at z = 3.1) have been extensively observed, and are thought to be driven by starburst events in massive galaxies forming galactic winds (e.g. Ohyama et al 2003;Geach et al 2005Geach et al , 2009Wilman et al 2005;Matsuda et al 2006;Uchimoto et al 2008Uchimoto et al , 2012. Moreover, recent surveys targeting Ly α 'blobs' have also suggested a possible connection between their properties (specifically morphologies) and the environments they reside in (Erb, Bogosavljević & Steidel 2011;Matsuda et al 2011Matsuda et al , 2012.…”

“…Even for those Ly α blobs not directly associated with radio sources, these are sometimes found to be harbouring AGNs (e.g. Basu-Zych & Scharf 2004;Geach et al 2009). These results suggest that Ly α nebulae are common phenomena reflecting the interaction between massive galaxies and their surrounding environments, regardless of the presence of AGNs.…”