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

Abstract

We exploit ALMA 870 µm observations to measure the star-formation rates (SFRs) of eight X-ray detected Active Galactic Nuclei (AGNs) in a z ≈ 3.1 protocluster, four of which reside in extended Ly α haloes (often termed Ly α blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ≈ 220-410 M yr −1 ; the non detection of the other five AGNs places SFR upper limits of < ∼ 210 M yr −1 . The mean SFR of the protocluster AGNs (≈ 110-210 M yr −1 ) is consistent (within a factor of ≈ 0.7-2.3) with that found for co-eval AGNs in the field, implying that the galaxy growth is not significantly accelerated in these systems. However, when also considering ALMA data from the literature, we find evidence for elevated mean SFRs (up-to a factor of ≈ 5.9 over the field) for AGNs at the protocluster core, indicating that galaxy growth is significantly accelerated in the central regions of the protocluster. We also show that all of the four protocluster LABs are associated with an ALMA counterpart within the extent of their Ly α emission. The SFRs of the ALMA sources within the LABs (≈ 150-410 M yr −1 ) are consistent with those expected for co-eval massive star-forming galaxies in the field. Furthermore, the two giant LABs (with physical extents of > ∼ 100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Ly α emission. We use these results to discuss star formation as the power source of LABs.

Deep Submillimeter and Radio Observations in the SSA22 Field. I. Powering Sources and the Lyα Escape Fraction of Lyα Blobs

“…References: (1) Umehata et al density of 0.91 ± 0.10 mJy at 350GHz, coincident with the X-ray counterpart (Geach et al 2009). Our observation does not confirm the presence of a second continuum source (see Figure 4) marginally detected by Alexander et al (2016) with a flux of 1.11 ± 0.25 mJy at 0.87 mm, which is significantly higher than our 3σ ALMA limit of 0.23 mJy. This may be due to the presence of extended structure that is resolved out by our higher angular resolution observations or it may be a spurious source.…”

“…While the LABs' preferential location in over-dense environments indicates an association with massive galaxy formation, the origin of their Lyα emission is still unclear and under debate (Faucher-Giguère et al 2010;Cen & Zheng 2013;Yajima et al 2013). Proposed sources have generally fallen into two categories: (1) cooling radiation from cold streams of gas accreting onto galaxies (e.g., Haiman et al 2000;Dijkstra & Loeb 2009;Faucher-Giguère et al 2010) and (2) photoionization and/or galactic superwinds/outflows from starbursts or AGNs (e.g., Taniguchi & Shioya 2000;Furlanetto et al 2005;Wilman et al 2005;Colbert et al 2006;Mori & Umemura 2006;Matsuda et al 2007;Zheng et al 2011;Cen & Zheng 2013;Ao et al 2015;Prescott et al 2015;Alexander et al 2016;Hine et al 2016). All of the above mentioned energy supplying sources may trigger Lyα emission in an environment where violent interactions are frequent between gas rich galaxies as expected in over-dense regions at high redshift (Matsuda et al 2009(Matsuda et al , 2011Prescott et al 2012aPrescott et al , 2013Kubo et al 2013).…”

“…Even in the recent deep SCUBA-2 observations, only 2 out of 34 LABs are detected at 850μm (Hine et al 2016). A few LABs have been observed and detected in the dust continuum with the Atacama Large Millimeter/Submillimeter Array (ALMA; Umehata et al 2015;Alexander et al 2016;Geach et al 2016). In this paper, we present deep submillimeter results from new JCMT/SCUBA-2 data (Holland et al 2013) together with ALMA data, and deep radio images from the Karl G. Jansky Very Large Array (VLA) 21 observations to study the LABs in the SSA22 field.…”

ALMA OBSERVATIONS OF Lyα BLOB 1: HALO SUBSTRUCTURE ILLUMINATED FROM WITHIN

“…The observed Lyα surface brightness and morphology is highly orientation dependent Lyα sources-the emission need not be symmetric about the central sources that are the source of the Lyα photons. This is simiular to the situation in real LABs, for example, the next largest LAB in SSA22, SSA22-LAB02 contains an X-ray luminous AGN (Geach et al 2009;Alexander et al 2016) that is significantly offset from the peak and geometric center of the LAB. This has important implications for correctly identifying potential luminous galaxy counterparts to LABs, the apparent absence of which in some systems has previously been argued in favor of cold mode acceretion (e.g., Nilsson et al 2006, but see also Prescott et al 2015).…”

“…LABs are intriguing objects: the origin of the extended Lyα emission could be due to gravitational cooling radiation, with pristine hydrogen at T∼10 4-5 K cooling primarily via collisionally excited Lyα as it flows into young galaxies (Katz et al 1996;Haiman et al 2000;Fardal et al 2001). Alternatively, galactic winds, photoionization, fluorescence, or scattering processes have been proposed (Taniguchi & Shioya 2000;Geach et al 2009Geach et al , 2014Alexander et al 2016;Hine et al 2016). In any scenario, the picture is one of an extended circumgalactic medium (CGM) that is rich in cool gas (be it clumpy or smoothly distributed), and so LABs reveal astrophysics associated with the environment on scales comparable to the virial radius of the massive dark matter halos they trace.…”