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Register a new userConcurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters
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We present results from a ~100 ks Chandra observation of the 2QZ Cluster 1004+00 structure at z = 2.23 (hereafter, 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four optically-selected QSOs at z = 2.23 within a 15x15 arcmin^2 region. Narrow-band imaging in the near-IR revealed that the structure contains an additional overdensity of 22 z = 2.23 Halpha-emitting galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs. Our Chandra observations reveal that 3 HAEs in addition to the 4 QSOs harbor powerfully accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of ~(8-60) x 10^43 ergs/s and X-ray spectral slopes consistent with unobscured AGN. Using a large comparison sample of 210 HAEs in Chandra-COSMOS (C-COSMOS), we find suggestive evidence that the AGN fraction increases with local HAE galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment (a factor of ~2 times over the field), and after excluding optically-selected QSOs, we find the AGN fraction is a factor of ~3.5^+3.8_-2.2 times higher than C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra data and Herschel SPIRE observations at 250 um, we respectively estimate mean SMBH accretion rates (Mdot) and star-formation rates (SFRs) for the 2QZ Clus and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked 2-10 keV luminosity is QSO-like (~6-10 x 10^43 ergs/s), and the implied Mdot/SFR sim (1.6-3.2) x10^-3 is broadly consistent with the local MBH/M* relation and z ~ 2 X-ray selected AGN. The C-COSMOS HAEs are on average an order of magnitude less X-ray luminous and have Mdot/SFR sim (0.2-0.4) x10^-3, comparable to z ~ 1-2 star-forming galaxies with similar mean X-ray luminosities. We estimate that a periodic QSO phase with duty cycle ~2-8% would be sufficient to bring the star-forming galaxies onto the local MBH/M* relation.
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We present the results of a narrow-band (H2S1, 2.121/0.021um) imaging search with WFCAM/UKIRT for H-alpha emitters around several potential signposts of rare (10^-7-10^-8 Mpc^-3) over-dense regions at z=2.23: an over-density of QSOs (2QZ cluster), a powerful, high-redshift radio galaxy (HzRG), and a concentration of submillimetre galaxies (SMGs) and optically faint radio galaxies (OFRGs). In total, we detect 137 narrow-band emitter candidates down to emission-line fluxes of 0.5-1 x 10^-16 erg s^-1 cm^-2, across a total area of 0.56 sq. degrees (2.1 x 10^5 comoving Mpc at z=2.23) in these fields. The BzK colours of the emitters suggest that at least 80% of our sample are likely to be H-alpha emitters (HAEs) at z=2.23. This is one of the largest HAE samples known at z>2. We find modest (~3-sigma) local over-densities of emitters associated with all the three targets. In the 2QZ cluster field, the emitters show a striking filamentary structure connecting four of the z=2.23 QSOs extending over 30Mpc (comoving). In the HzRG and SMG/OFRG fields, the structures appear to be smaller and seen only in the vicinities of the targets. The K-band magnitudes and the H-alpha equivalent widths of the emitters are weakly correlated with the over-density of the emitters: emitters in over-dense region are more evolved systems compared to those in under-dense regions at z=2.23. We find several examples of extended HAEs in our target fields, including a striking example with a spatial extent of 7.5 arcsec (60 kpc at z=2.23) in the 2QZ field, suggesting that these are relatively common in high-density regions. We conclude that narrow-band H-alpha surveys are efficient routes to map over-dense regions at high-z and thus to understand the relation between the growth of galaxies and their surrounding large-scale structures.
The formation, accretion and growth of supermassive black holes in the early universe are investigated. The accretion rate ${dot M}$ is calculated using the Bondi accretion rate onto black holes. Starting with initial seed black holes with masses $M_{rm BH}sim 10^2-10^3M_{odot}$, the Bondi accretion rate can evolve into a supermassive black hole with masses $M_{rm BH}sim 10^9-10^{10}M_{odot}$ and with a young quasar lifetime $sim 10^5-10^6$ years by super-Eddington accretion.
We present the detection of four far-infrared fine-structure oxygen lines, as well as strong upper limits for the CO(2-1) and [N II] 205 um lines, in 3C 368, a well-studied radio-loud galaxy at z = 1.131. These new oxygen lines, taken in conjunction with previously observed neon and carbon fine-structure lines, suggest a powerful active galactic nucleus (AGN), accompanied by vigorous and extended star formation. A starburst dominated by O8 stars, with an age of ~6.5 Myr, provides a good fit to the fine-structure line data. This estimated age of the starburst makes it nearly concurrent with the latest episode of AGN activity, suggesting a link between the growth of the supermassive black hole and stellar population in this source. We do not detect the CO(2-1) line, down to a level twelve times lower than the expected value for star forming galaxies. This lack of CO line emission is consistent with recent star formation activity if the star-forming molecular gas has low metallicity, is highly fractionated (such that CO is photodissociated through much of the clouds), or is chemically very young (such that CO has not yet had time to form). It is also possible, though we argue unlikely, that the ensemble of fine structure lines are emitted from the region heated by the AGN.
We use data from large surveys of the local Universe (SDSS+Galaxy Zoo) to show that the galaxy-black hole connection is linked to host morphology at a fundamental level. The fraction of early-type galaxies with actively growing black holes, and therefore the AGN duty cycle, declines significantly with increasing black hole mass. Late-type galaxies exhibit the opposite trend: the fraction of actively growing black holes increases with black hole mass.
We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous Halpha (Ha) emitters at z~0.8-2.23, which evolve strongly in number density over this period, and compare them to more typical Ha emitters. We study 59 luminous Ha emitters with $L_{Halpha}>L_{Halpha}^*$, roughly equally split per redshift slice at z~0.8, 1.47 and 2.23 from the HiZELS and CF-HiZELS surveys. We find that, overall, 30$pm$8% are AGN (80$pm$30% of these AGN are broad-line AGN, BL-AGN), and we find little to no evolution in the AGN fraction with redshift, within the errors. However, the AGN fraction increases strongly with Ha luminosity and correlates best with $L_{Halpha}/L_{Halpha}^*(z)$. While $L_{Halpha}<L_{rm Halpha}^*(z)$ Ha emitters are largely dominated by star-forming galaxies (>80%), the most luminous Ha emitters ($L_{Halpha}>10L_{Halpha}^*(z)$) at any cosmic time are essentially all BL-AGN. Using our AGN-decontaminated sample of luminous star-forming galaxies, and integrating down to a fixed Ha luminosity, we find a factor of ~1300x evolution in the star formation rate density from z=0 to z=2.23. This is much stronger than the evolution from typical Ha star-forming galaxies and in line with the evolution seen for constant luminosity cuts used to select Ultra-Luminous Infrared Galaxies and/or sub-millimetre galaxies. By taking into account the evolution in the typical Ha luminosity, we show that the most strongly star-forming Ha-selected galaxies at any epoch ($L_{Halpha}>L^*_{Halpha}(z)$) contribute the same fractional amount of ~15% to the total star-formation rate density, at least up to z=2.23.
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