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Abstract:

The ultraluminous infrared Seyfert 1 galaxy Mrk 231 has been spectrally imaged in the K band with the new three-dimensional MPE integral field spectrometer. The combined images of the H2 emission lines show, for the first time in an ultraluminous infrared galaxy, the presence of an extended circumnuclear structure of hot molecular gas. The H2 emitting region has a size of ∼2.4 kpc and a hot molecular gas mass MH2^hot ∼ 2 × 10⁴ M⊙. The H2 emission-line ratios indicate that the gas is most likely thermally excited. If as in NGC 7469 star formation is associated with the H2 emission, the starburst would have a far-IR luminosity LFIR ∼ 1 × 10¹² L⊙. This value represents an upper limit, since a fraction of the hot molecular gas may be excited by the radiation field emerging from the nucleus. The K-band three-dimensional data cube also shows for the first time the presence of extended narrow Paα emission blueshifted by ∼1400 km s^-1 with respect to the systemic velocity, and located ∼0.6 kpc northwest of the nucleus. The detection of CO absorption bands with a spatial distribution peaking on the K-band continuum provides evidence for a central stellar concentration. The low CO spectroscopic index indicates, however, dilution by hot dust emission or by a nonthermal active galactic nucleus. The Paα/Hα ratio confirms previous extinction measurements based on Balmer line ratios, i.e., visual extinction of AV ∼ 2.0-6.6 mag. The quasar-type nucleus of Mrk 231 should then be transparent at 2 μm and also in hard X-rays. A weak nuclear He I λ2.058 μm (He I/Paα = 0.032) is detected, and no detection of [Si VI] λ1.962 μm is made, placing an upper limit of 4 × 10^-18 Wm^-2 for the coronal gas emission. The ionizing source could either be a far-UV and X-ray quiet quasar or else a nuclear starburst with an upper mass limit ≥60 M⊙. © 1997. The American Astronomical Society. All rights reserved.

Abstract:

We present source counts at 6.7 and 15 μm from our maps of the Hubble Deep Field (HDF) region, reaching 38.6 μJy at 6.7 μm and 255 μJy at 15 μm. These are the first ever extragalactic number counts to be presented at 6.7 μm, and are three decades fainter than IRAS at 12 μm. Both source counts and a P(D) analysis suggest that we have reached the Infrared Space Obsen'atory (ISO) confusion limit at 15 μm: this will have important implications for future space missions. These data provide an excellent reference point for other ongoing ISO surveys. A no-evolution model at 15 μm is ruled out at > 3σ, while two models which fit the steep IRAS 60-μm counts are acceptable. This provides important confirmation of the strong evolution seen in IRAS surveys. One of these models can then be ruled out from the 6.7-μm data. © 1997 RAS.

Abstract:

We describe the construction of catalogues of galaxy clusters from the APM Galaxy survey using an automated algorithm based on Abell-like selection criteria. We investigate the effects of varying several parameters in our selection algorithm, including the magnitude range and radius from the cluster centre used to estimate the cluster richnesses. We quantify the accuracy of the photometric distance estimates by comparing them with measured redshifts, and we investigate the stability and completeness of the resulting catalogues. We find that the angular correlation functions for different cluster catalogues are in good agreement with one another, and are also consistent with the observed amplitude of the spatial correlation function of rich clusters. © 1997 RAS.

Abstract:

We present new near-infrared speckle and adaptive optics imaging and integral field spectroscopy of the nuclear region of NGC 1068. Ninety-four percent of the K-band light in the central 1" originates from a ≤30 milliarcsecond diameter source whose position we determine to coincide within ± 0''15 with the apex of the cone structure seen in the optical narrow emission lines, as well as the location of the flat spectrum radio component SI and the 12 μm emission peak. We interpret the compact source as hot dust near the sublimation temperature within ∼ 1 pc of the true nucleus of the galaxy. The remaining 6% of the light in the central 1″ comes from a moderately extincted stellar core centered on the nuclear position and of intrinsic size ∼50 pc. We show that this nuclear stellar core is probably 5-16 × 108 yr in age and contributes at least 7% of the total nuclear luminosity of ~1 × 1011 L⊙. © 1997. The American Astronomical Society. All rights reserved.

Abstract:

In the deepest optically identified X-ray survey yet performed, we have identified 32 X-ray-selected QSOs to a flux limit of 2 × 10-15 erg cm-2 s-1 (0.5-2 keV). The survey, performed with the ROSAT Position Sensitive Proportional Counter (PSPC), has 89 per cent spectroscopic completeness. The QSO log(N)-log(S) relation is found to have a break to a flat slope at faint fluxes. The surface density of QSOs at the survey limit is 230 ± 40 per square degree, the largest so far of any QSO survey. We use this survey to measure the QSO X-ray luminosity function at low luminosities (LX<1044.5 erg s-1) and high redshifts (2