A CO Survey of Gravitationally Lensed Quasars with the IRAM Interferometer

We present the results of a CO survey of gravitationally lensed quasars, conducted with the Plateau de Bure Interferometer over the last three years. Among the 18 objects surveyed, one was detected in CO line emission, while six were detected in the continuum at 3mm and three in the continuum at 1mm. The low CO detection rate may at least in part be due to uncertainties in the redshifts derived from quasar broad emission lines. The detected CO source, the z=3.2 radio quiet quasar MG0751+2716, is quite strong in the CO(4-3) line and in the millimeter/submillimeter continuum, the latter being emission from cool dust. The integrated CO line flux is 5.96 +- 0.45 Jy.km/s, and the total molecular gas mass is estimated to be in the range M(H_2) = 1.6-3.1 X 10^9 solar masses.Comment: 5 pages, 2 figures, uses aa.cls and psfig.st

Gas and Dust in the Cloverleaf Quasar at Redshift 2.5

We observed the upper fine structure line of neutral carbon, CI(2-1), the CO(3-2) line and the 1.2mm continuum emission from H1413+117 (Cloverleaf quasar, z=2.5) using the IRAM interferometer. Together with the detection of the lower fine structure line (Barvainis etal. 1997), the Cloverleaf quasar is now only the second extragalactic system, besides M82, where both carbon lines have convincingly been detected. Our analysis shows that the carbon lines are optically thin and have an excitation temperature of ~30 K. CO is subthermally excited and the observed line luminosity ratios are consistent with n(H2)=10^(3-4) cm^(-3) at Tkin=30-50 K. Using three independent methods (CI, dust, CO) we derive a total molecular gas mass (corrected for magnification) of M(H2)=1.2+/-0.3*10^(10) SM. Our observations suggest that the molecular disk extends beyond the region seen in CO(7-6) to a zone of more moderately excited molecular gas that dominates the global emission in CI and the low J CO lines.Comment: 5 pages, 3 figures; accepted by A&

Millimeter-Wave Spectroscopy and Mapping of Quasar Hosts, and the Status of ULIRGs as Quasar 2s

It is becoming possible to detect high redshift quasars in various molecular lines, and to show by mapping lensed objects that the strong dust and molecular emission arises in warm dense ~100 pc-scale "tori." The properties of ULIRGs, at least those with AGN-like narrow line regions, are very similar, as expected in the hidden quasar hypothesis. Several of the latter are in fact confirmed as "Quasar 2s" by spectropolarimetry.Comment: 7 page

Extremely Luminous Water Vapor Emission from a Type 2 Quasar at Redshift z = 0.66

A search for water masers in 47 Sloan Digital Sky Survey Type 2 quasars using the Green Bank Telescope has yielded a detection at a redshift of z = 0.660. This maser is more than an order of magnitude higher in redshift than any previously known and, with a total isotropic luminosity of 23,000 L_sun, also the most powerful. The presence and detectability of water masers in quasars at z ~ 0.3-0.8 may provide a better understanding of quasar molecular tori and disks, as well as fundamental quasar and galaxy properties such as black hole masses. Water masers at cosmologically interesting distances may also eventually provide, via direct distance determinations, a new cosmological observable for testing the reality and properties of dark energy, currently inferred primarily through Type 1a supernova measurements.Comment: 8 pages including 1 figure; accepted for publication in ApJ Letter

New CO and Millimeter Continuum Observations of the z=2.394 Radio Galaxy 53W002

The z=2.39 radio galaxy 53W002 lies in a cluster of Ly-alpha emission line objects and may itself be undergoing a major burst of star formation. CO(3--2) emission, at 102 GHz, was detected from 53W002 by Scoville et al. (1997a), who also reported a possible 30 kpc extension and velocity gradient suggesting a rotating gaseous disk. In this paper we present new interferometric CO(3--2) observations which confirm the previous line detection with improved signal-to-noise ratio, but show no evidence for source extension or velocity gradient. The compact nature of the CO source and the molecular mass found in this object are similar to luminous infrared galaxies and other AGNs previously studied

The essential signature of a massive starburst in a distant galaxy

Observations of carbon monoxide (CO) emission in high redshift (z>2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus (AGN) powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the AGN, or 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; gas densities are n(H2)>105 cm-3 in the cores. 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 is at a much lower density. In galaxies in the local Universe, the HCN(J=1-0) line is an effective tracer of the high-density molecular gas. Here we report observations of HCN emission in the early Universe from the infrared luminous 'Cloverleaf' quasar (at a redshift z=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 that contributes, together with the AGN it harbors, to its high infrared luminosity.Comment: PDF pape

VLBI detection of an AGN pair in the binary black hole candidate SDSS J1536+0441

We present first pc-scale radio imaging of the radio-quiet candidate binary black hole system SDSS J1536+0441. The observations were carried out by the European VLBI Network at the frequency of 5 GHz and allowed to image SDSS J1536+0441 with a resolution of about 10 mas (50 pc). Two compact radio cores are detected at the position of the kpc-scale components VLA-A and VLA-B, proving the presence of two compact active nuclei with radio luminosity about 10^{40} erg/s, thus ruling out the possibility that the two radio sources are both powered by one 0.1 pc binary black hole. From a comparison with published 8.5 GHz flux densities we derived an estimate of the radio spectral index of the two pc-scale cores. Both cores have flat or inverted spectral index and, at least for the case of VLA-A, we can rule out the possibility that synchrotron self-absorption is responsible for the inverted radio spectrum. We suggest that thermal free-free emission from an X-ray heated disk wind may be powering the radio emission in VLA-A.Comment: Accepted for publication in ApJ Letters

Molecular Gas in Quasar Hosts

The study of molecular gas in quasar host galaxies addresses a number of interesting questions pertaining to the hosts' ISM, to unified schemes relating quasars and IR galaxies, and to the processes fueling nuclear activity. In this contribution I review observations of molecular gas in quasar hosts from z=0.06 to z=4.7. The Cloverleaf quasar at z=2.5 is featured as a case where there are now enough detected transitions (four in CO, and one each in CI and HCN) to allow detailed modeling of physical conditions in the molecular ISM. We find that the CO-emitting gas is warmer, denser, and less optically thick than that found in typical Galactic molecular clouds. These differences are probably due to the presence of the luminous quasar in the nucleus of the Cloverleaf's host galaxy