Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6

The existence of massive (10¹¹ solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z > 6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z > 6 are, with one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than 10⁹ solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C ii] at a wavelength of 158 micrometres) in four galaxies at z > 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [C ii] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [C ii] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of the twenty-five z > 6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [C ii] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.

The heating of gas in a galaxy cluster by X-ray cavities and large-scale shock fronts

Most of the baryons in galaxy clusters reside between the galaxies in a hot, tenuous gas. The densest gas in their centres should cool and accrete onto giant central galaxies at rates of 10-1,000 solar masses per year. No viable repository for this gas, such as clouds or new stars, has been found. New X-ray observations, however, have revealed far less cooling below X-ray temperatures than expected, altering the previously accepted picture of cooling flows. As a result, most of the gas must be heated to and maintained at temperatures above approximately 2 keV (ref. 3). The most promising heating mechanism is powerful radio jets emanating from supermassive black holes in the central galaxies of clusters. Here we report the discovery of giant cavities and shock fronts in a distant (z = 0.22) cluster caused by an interaction between a radio source and the hot gas surrounding it. The energy involved is approximately 6 x 10(61) erg, the most powerful radio outburst known. This is enough energy to quench a cooling flow for several Gyr, and to provide approximately 1/3 keV per particle of heat to the surrounding cluster.

The essential signature of a massive starburst in a distant quasar

Observations of carbon monoxide emission in high-redshift (zeta > 2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the active galactic nucleus, from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds, where gas densities are n(H2) > 10(5) cm(-3) (refs 1, 2). Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations, however, is at a much lower density. For galaxies in the local Universe, the HCN molecule is an effective tracer of high-density molecular gas. Here we report observations of HCN emission from the infrared-luminous 'Cloverleaf' quasar (at a redshift zeta = 2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst, which contributes, together with the active galactic nucleus it harbours, to its high infrared luminosity.

A massive reservoir of low-excitation molecular gas at high redshift

Molecular hydrogen (H2) is an important component of galaxies because it fuels star formation and the accretion of gas onto active galactic nuclei (AGN), the two processes that can generate the large infrared luminosities of gas-rich galaxies. Observations of spectral-line emission from the tracer molecule carbon monoxide (CO) are used to probe the properties of this gas. But the lines that have been studied in the local Universe-mostly the lower rotational transitions of J = 1 --> 0 and J = 2 --> 1-have hitherto been unobservable in high-redshift galaxies. Instead, higher transitions have been used, although the densities and temperatures required to excite these higher transitions may not be reached by much of the gas. As a result, past observations may have underestimated the total amount of molecular gas by a substantial amount. Here we report the discovery of large amounts of low-excitation molecular gas around the infrared-luminous quasar APM08279+5255 at redshift z = 3.91, using the two lowest excitation lines of 12 CO (J = 1 --> 0 and J = 2 --> 1). The maps confirm the presence of hot and dense gas near the nucleus, and reveal an extended reservoir of molecular gas with low excitation that is 10 to 100 times more massive than the gas traced by the higher-excitation observations. This raises the possibility that significant amounts of low-excitation molecular gas may exist in the environments of high-redshift (z > 3) galaxies.

Infusion of recombinant human prorenin into rhesus monkeys. Effects on hemodynamics, renin-angiotensin-aldosterone axis and plasma testosterone

Prorenin, the biosynthetic precursor of active renin, is present in high concentrations in the kidney and reproductive organs. We have proposed that prorenin may be the vehicle of local renin systems, separating the functions of circulating and tissue renin. In the present study, we investigated the effect of increasing plasma prorenin 3- to 4-fold by infusing recombinant prorenin, 400 ng/min for 40 min, into male rhesus monkeys. The prorenin was first warmed to 37 degrees C to reduce the endogenous renin activity to a minimum. The study included a 20 min baseline and a 40 min recovery period. Plasma prorenin increased from 72 +/- 14 ng/mL/h to a maximum of 246 +/- 18 ng/mL/h during the infusion (P less than .001) and fell to 169 +/- 23 ng/mL/h 40 min after the infusion was stopped. Active renin did not change significantly. Plasma aldosterone increased slightly during the prorenin infusion (by 13%) and returned to baseline during the recovery period (P less than .05 compared to the infusion period). Plasma testosterone fell significantly from 1.9 +/- 0.1 ng/mL to 1.6 +/- 0.1 ng/mL during the infusion and further to 1.4 +/- 0.1 ng/mL during the post-infusion period (P less than .05). Blood pressure fell slightly but not significantly. Heart rate, glomerular filtration rate and renal blood flow, as well as urine flow and urine sodium and potassium excretion showed no significant change. These results demonstrate that human recombinant prorenin is not converted to active renin in the circulation of rhesus monkeys.(ABSTRACT TRUNCATED AT 250 WORDS)

Human renin is correctly processed and targeted to the regulated secretory pathway in mouse pituitary AtT-20 cells

Renin is formed by intracellular processing of prorenin and catalyzes the conversion of angiotensinogen to angiotensin I, the precursor to angiotensin II. Several tissues synthesize prorenin. However, in man, the kidney is the only known source of circulating renin, raising the possibility that the processing enzyme is unique to that tissue. We have transfected a gene that directs prorenin synthesis in pituitary AtT-20 cells, which are capable of processing other prohormones. The results demonstrate that transfected AtT-20 cells can secrete inactive prorenin, accurately process prorenin to active renin, and be stimulated to release active renin in response to a secretagogue. These data imply that cellular elements capable of directing the processing of prorenin to renin and its correct subcellular compartmentalization may be present in nonrenal cell types and that critical elements of the regulated release of renin that occur in the kidney can be reconstituted in cells in culture.