Astronomical instrumentation

Abstract:

We present K, L and M diffraction-limited images of NGC 1068 obtained with NAOS+CONICA at VLT/YEPUN over a 3.5" field around the central engine. Hot dust (Tcol = 550-650 K) is found in three different regions : (a) in the true nucleus, seen as a slightly NS elongated, core of extremely hot dust, "resolved" in K and L with respective diameters of ~5 pc and 8.5 pc ; (b) along the NS direction, as a "spiral arm" and a southern tongue ; (c) as a set of parallel elongated nodules ("wave-like") bracketting the jet. Several structures observed on radio maps, mid-IR or HST UV-visible maps are seen, so that a precise registration can be done from UV to 6 cm. These results do support the current interpretion that source (a) corresponds to emission from dust near sublimation temperature delimiting the walls of the cavity in the central obscuring torus. Structure (b) is thought to be a mixture of hot dust and active star forming regions along a micro spiral structure that could trace the tidal mechanism bringing matter to the central engine. Structure c)which was not known, exhibits too high a temperature for "classical'' grains ; it is most probably the signature of transiently heated very small dust grains (VSG) : "nano-diamonds", which are resistant and can form in strong UV field or in shocks, are very attractive candidates. The "waves'' can be condensations triggered by jet induced shocks, as predicted by recent models. First estimates, based on a simple VSG model and on a detailed radiative transfer model, do agree with those interpretations, both qualitatively and quantitatively.

Abstract:

We present a detailed analysis of the two-point correlation function, ξ (σ, π) from the 2dF Galaxy Redshift purvey (2dFGRS). The large size of the catalogue, which contains ∼220 000 redshifts, allows us to make high-precision measurements of various properties of the galaxy clustering pattern. The effective redshift at which our estimates are made is z s ≈ 0.15, and similarly the effective luminosity, Ls ≈ 1.4L*. We estimate the redshift-space correlation function, ξ(s), from which we measure the redshift-space clustering length, S0 = 6. 82 ± 0.28 h-1 Mpc. We also estimate the projected correlation function, Ξ (σ), and the real-space correlation function, ξ(r), which can be fit by a power law (r/r0)-γr, with r0 = 5.05 ± 0.26 h-1 Mpc, γr = 1.67 ± 0.03. For r ≳ 20 h-1 Mpc, ξ drops below a power law as, for instance, is expected in the popular A cold dark matter model. The ratio of amplitudes of the real- and redshift-space correlation functions on scales of 8-30 h-1 Mpc gives an estimate of the redshift-space distortion parameter β. The quadrupole moment of ξ(σ, π) on scales 30-40 h-1 Mpc provides another estimate of β. We also estimate the distribution function of pairwise peculiar velocities, f(v), including rigorously the significant effect due to the infall velocities, and we find that the distribution is well fit by an exponential form. The accuracy of our ξ(σ, π) measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of ξ(r) and the two redshift-space distortion effects parametrized by β and velocity dispersion, a. We find β= 0.49 ± 0.09 and a = 506 ± 52 km s-1, although the best-fitting values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(σ), and find that the shape is consistent with models and simulations. This is the first time that β and f(v) have been estimated from a self-consistent model of galaxy velocities. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that β (L = L*,z = 0) = 0.47 ± 0.08, and that the present-day matter density of the Universe, Ωm ≈ 0.3, consistent with other 2dFGRS estimates and independent analyses.

Abstract:

Results of optical identification of the ASCA Lynx Deep Survey are presented. Six X-ray sources are detected in the 2-7 keV band using the Solid-State Imaging Spectrometer in a ∼20′ × 20′ field of view with fluxes larger than ∼4 × 10-14 ergs s -1 cm-2 in the band. Follow-up optical spectroscopic observations were made, and five out of six sources are identified with active galactic nuclei/quasi-stellar objects (AGNs/QSOs) at redshifts of 0.5-1.3. We also identify two more additional X-ray sources detected in a soft X-ray band with AGNs/QSOs. We find that three QSOs identified are located at z ∼ 1.3. Two rich clusters and several groups of galaxies are also placed at the same redshift in the surveyed field, and projected separations between the QSOs and the clusters are 3-8 Mpc at the redshift.