We present Herschel observations of six fine-structure lines in 25 Ultraluminous Infrared Galaxies at z < 0.27. The lines, [O III]52µm, [N III]57µm, [O I]63µm, [N II]122µm, [O I]145µm, and [C II]158µm, are mostly single gaussians with widths <600 km s −1 and luminosities of 10 7 − 10 9 L ⊙ . There are deficits in the [O I]63/L IR , [N II]/L IR , [O I]145/L IR , and [C II]/L IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from PDRs or the ISM. We derive relations between far-IR line luminosities and both IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10 1 < n < 10 2.5 and 10 2.2 < G 0 < 10 3.6 , respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters; AGN activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.
A Large Quasar Group (LQG) of particularly large size and high membership has been identified in the DR7QSO catalogue of the Sloan Digital Sky Survey. It has characteristic size (volume 1/3 ) ∼ 500 Mpc (proper size, present epoch), longest dimension ∼ 1240 Mpc, membership of 73 quasars, and mean redshiftz = 1.27. In terms of both size and membership it is the most extreme LQG found in the DR7QSO catalogue for the redshift range 1.0 z 1.8 of our current investigation. Its location on the sky is ∼ 8.8 • north (∼ 615 Mpc projected) of the Clowes & Campusano LQG at the same redshift,z = 1.28, which is itself one of the more extreme examples. Their boundaries approach to within ∼ 2 • (∼ 140 Mpc projected). This new, huge LQG appears to be the largest structure currently known in the early universe. Its size suggests incompatibility with the Yadav et al. scale of homogeneity for the concordance cosmology, and thus challenges the assumption of the cosmological principle.
We investigate the relation between star formation rates (Ṁ s ) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find thatṀ s remains approximately constant with redshift, at 300 ± 100 M ⊙ yr −1 . Conversely,Ṁ s increases with AGN luminosity, up to a maximum of ∼ 600 M ⊙ yr −1 , and with C iv FWHM. In context with previous results, this is consistent with a relation betweenṀ s and black hole accretion rate (Ṁ bh ) existing in only parts of the z −Ṁ s −Ṁ bh plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations betweenṀ s and both AGN luminosity and C iv FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C iv equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; M i is not a linear tracer of L 2500 , the Baldwin effect changes form at high AGN luminosities, and high C iv EW values signpost a change in the relation betweenṀ s andṀ bh . Finally, there is no strong relation betweenṀ s and Eddington ratio, or the asymmetry of the C iv line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C iv asymmetries arising from orientation effects.
We explore the relationship between active galactic nuclei and star formation in a sample of 513 optically luminous type 1 quasars up to redshifts of ∼4 hosting extremely high star formation rates (SFRs). The quasars are selected to be individually detected by the Herschel SPIRE instrument at > 3σ at 250 µm, leading to typical SFRs of order of 1000 M yr −1 . We find the average SFRs to increase by almost a factor 10 from z ∼ 0.5 to z ∼ 3, mirroring the rise in the comoving SFR density over the same epoch. However, we find that the SFRs remain approximately constant with increasing accretion luminosity for accretion luminosities above 10 12 L . We also find that the SFRs do not correlate with black hole mass. Both of these results are most plausibly explained by the existence of a self-regulation process by the starburst at high SFRs, which controls SFRs on time-scales comparable to or shorter than the AGN or starburst duty cycles. We additionally find that SFRs do not depend on Eddington ratio at any redshift, consistent with no relation between SFR and black hole growth rate per unit black hole mass. Finally, we find that high-ionisation broad absorption line (HiBAL) quasars have indistinguishable far-infrared properties to those of classical quasars, consistent with HiBAL quasars being normal quasars observed along a particular line of sight, with the outflows in HiBAL quasars not having any measurable effect on the star formation in their hosts.
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