By using the GRAVITY instrument with the near-infrared (NIR) Very Large Telescope Interferometer (VLTI), the structure of the broad (emission-)line region (BLR) in active galactic nuclei (AGNs) can ...be spatially resolved, allowing the central black hole (BH) mass to be determined. This work reports new NIR VLTI/GRAVITY interferometric spectra for four type 1 AGNs (Mrk 509, PDS 456, Mrk 1239, and IC 4329A) with resolved broad-line emission. Dynamical modelling of interferometric data constrains the BLR radius and central BH mass measurements for our targets and reveals outflow-dominated BLRs for Mrk 509 and PDS 456. We present an updated radius-luminosity (R-L) relation independent of that derived with reverberation mapping (RM) measurements using all the GRAVITY-observed AGNs. We find our R-L relation to be largely consistent with that derived from RM measurements except at high luminosity, where BLR radii seem to be smaller than predicted. This is consistent with RM-based claims that high Eddington ratio AGNs show consistently smaller BLR sizes. The BH masses of our targets are also consistent with the standard M BH - σ * relation. Model-independent photocentre fitting shows spatial offsets between the hot dust continuum and the BLR photocentres (ranging from ∼17 μas to 140 μas) that are generally perpendicular to the alignment of the red- and blueshifted BLR photocentres. These offsets are found to be related to the AGN luminosity and could be caused by asymmetric K -band emission of the hot dust, shifting the dust photocentre. We discuss various possible scenarios that can explain this phenomenon.
We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star-forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field ...spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically selected, and 13 submillimeter galaxies (SMGs). We find that rest-frame UV and optically bright (K=5 mJy) have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either the UV or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that a significant fraction of the UV/optically bright galaxies have evolved less violently, either in a series of minor mergers, or in rapid dissipative collapse from the halo, given that either process may leads to the formation of early disks. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) ``Schmidt-Kennicutt'' relation between gas surface density and star formation rate surface density. The best-fit relation suggests that the star formation rate per unit area scales as the surface gas density to a power of ~1.7, and that the star formation efficiency increases by a factor of 4 between non-starbursts and strong starbursts.
This paper reports measurements of Sgr A* made with NACO in L' band (3.80 is a subset of m), Ks band (2.12 is a subset of m), and H band (1.66 is a subset of m), and with VISIR in N band (11.88 is a ...subset of m) at the ESO VLT, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 2007 April 4, a very bright flare was observed from Sgr A* simultaneously at L' band and X-ray wavelengths. No emission was detected using VISIR. The resulting spectral energy distribution has a blue slope ( beta >0 for Delta L Delta Delta beta , consistent with Delta L Delta Delta 0.4) between 12 is a subset of m and 3.8 is a subset of m. For the first time, our high-quality data allow a detailed comparison of infrared (IR) and X-ray light curves with a resolution of a few minutes. The IR and X-ray flares are simultaneous to within 3 minutes. However, the IR flare lasts significantly longer than the X-ray flare (both before and after the X-ray peak), and prominent substructures in the 3.8 is a subset of m light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L'-band light curve, we find that the flaring region must be no more than 1.2RS in size. The high X-ray to IR flux ratio, blue Delta L Delta slope MIR to L' band, and the soft Delta L Delta spectral index of the X-ray flare together place strong constraints on possible flare emission mechanisms. We find that it is quantitatively difficult to explain this bright X-ray flare with inverse Compton processes. A synchrotron emission scenario from an electron distribution with a cooling break is a more viable scenario.
Context. Dynamic model atmospheres of Mira stars predict variabilities in the photospheric radius and in atmospheric molecular layers which are not yet strongly constrained by observations. Aims. ...Here we measure the variability of the oxygen-rich Mira star R Peg in near-continuum and molecular bands. Methods. We used near-infrared K-band spectro-interferometry with a spectral resolution of about 4000 obtained at four epochs between post-maximum and minimum visual phases employing the newly available GRAVITY beam combiner at the Very Large Telescope Interferometer (VLTI). Results. Our observations show a continuum radius that is anti-correlated with the visual lightcurve. Uniform disc (UD) angular diameters at a near-continuum wavelength of 2.25 μm are steadily increasing with values of 8.7 ± 0.1 mas, 9.4 ± 0.1 mas, 9.8 ± 0.1 mas, and 9.9 ± 0.1 mas at visual phases of 0.15, 0.36, 0,45, 0.53, respectively. UD diameters at a bandpass around 2.05 μm, dominated by water vapour, follow the near-continuum variability at larger UD diameters between 10.7 mas and 11.7 mas. UD diameters at the CO 2–0 bandhead, instead, are correlated with the visual lightcurve and anti-correlated with the near-continuum UD diameters, with values between 12.3 mas and 11.7 mas. Conclusions. The observed anti-correlation between continuum radius and visual lightcurve is consistent with an earlier study of the oxygen-rich Mira S Lac, and with recent 1D CODEX dynamic model atmosphere predictions. The amplitude of the variation is comparable to the earlier observations of S Lac, and smaller than predicted by CODEX models. The wavelength-dependent visibility variations at our epochs can be reproduced by a set of CODEX models at model phases between 0.3 and 0.6. The anti-correlation of water vapour and CO contributions at our epochs suggests that these molecules undergo different processes in the extended atmosphere along the stellar cycle. The newly available GRAVITY instrument is suited to conducting longer time series observations, which are needed to provide strong constraints on the model-predicted intra- and inter-cycle variability.
The mean absolute extinction towards the central parsec of the Milky Way is A
K
≃ 3 mag, including both foreground and Galactic Centre dust. Here we present a measurement of dust extinction within ...the Galactic old nuclear star cluster (NSC), based on combining differential extinctions of NSC stars with their υ
l
proper motions along Galactic longitude. Extinction within the NSC preferentially affects stars at its far side, and because the NSC rotates, this causes higher extinctions for NSC stars with negative υ
l
, as well as an asymmetry in the υ
l
-histograms. We model these effects using an axisymmetric dynamical model of the NSC in combination with simple models for the dust distribution. Comparing the predicted asymmetry to data for ∼7100 stars in several NSC fields, we find that dust associated with the Galactic Centre mini-spiral with extinction A
K
≃ 0.15–0.8 mag explains most of the data. The largest extinction A
K
≃ 0.8 mag is found in the region of the Western arm of the mini-spiral. Comparing with total A
K
determined from stellar colours, we determine the extinction in front of the NSC. Finally, we estimate that for a typical extinction of A
K
≃ 0.4 the statistical parallax of the NSC changes by ∼0.4 per cent.
We classify 329 late-type giants within 1 pc of Sgr A*, using the adaptive optics integral field spectrometer SINFONI on the VLT. These observations represent the deepest spectroscopic data set so ...far obtained for the Galactic center, reaching a 50% completeness threshold at the approximate magnitude of the helium-burning red clump (K sub(s) similar to 15.5 mag). Combining our spectroscopic results with NaCo H and K sub(s) photometry, we construct an observed Hertzsprung-Russell diagram, which we quantitatively compare to theoretical distributions of various star formation histories of the inner Galaxy, using a chi super(2) analysis. Our best-fit model corresponds to continuous star formation over the last 12 Gyr with a top-heavy initial mass function (IMF). The similarity of this IMF to the IMF observed for the most recent epoch of star formation is intriguing and perhaps suggests a connection between recent star formation and the stars formed throughout the history of the Galactic center.
We report the first direct observations of neutral, molecular gas streaming in the nucleus of NGC 1068 on scales of <30 pc using SINFONI near-infrared integral field spectroscopy. At a resolution of ...0075, the flux map of 2.12 is a subset of m 1-0 S(1) molecular hydrogen emission around the nucleus in the central arcsec reveals two prominent linear structures leading to the active galactic nucleus from the north and south. The kinematics of the gas in these features are dominated by noncircular motions and indicate that material streams toward the nucleus on highly elliptical or parabolic trajectories, whose orientations are compatible with that of the disk plane of the galaxy. We interpret the data as evidence for fueling of gas to the central region. The radial transport rate from ~30 pc to a few parsecs from the nucleus is ~15 M yr -1. One of the infalling clouds lies directly in front of the central engine. We interpret it as a tidally disrupted streamer that forms the optically thick outer part of an amorphous clumpy molecular/dusty structure which contributes to the nuclear obscuration.
Sagittarius A*, the supermassive compact object at the center of the Galaxy, exhibits outbursts in the near infrared (NIR) and X-ray domains. These flares are likely due to energetic events very ...close to the central object, on a scale of a few Schwarzschild radii. Optical interferometry will soon be able to provide astrometry with an accuracy of this order (10 is a subset of as). In this article, we use recent photometric NIR data observed with the adaptive optics system NACO at the Very Large Telescope combined with simulations in order to deploy a method to test the nature of the flares and to predict the possible outcome of observations with the Very Large Telescope Interferometer. To accomplish this we implement a hot-spot model and investigate its appearance for a remote observer in terms of light curves and centroid tracks, based on general relativistic ray-tracing methods. First, we use a simplified model of a small steady source in order to investigate the relativistic effects qualitatively. A more realistic scenario is then being developed by fitting our model to existing flare data. While indications for the spin of the black hole and multiple images due to lensing effects are marginal in the light curves, astrometric measurements offer the possibility to reveal these high-order general relativistic effects. This study makes predictions on these astrometric measurements and leads us to the conclusion that future infrared interferometers will be able to detect proper motion of hot spots in the vicinity of Sagittarius A*.
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