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Infrared observations of Sgr A* probe the region close to the event horizon of the black hole at the Galactic center. These observations can constrain the properties of low-luminosity accretion as well as that of the black hole itself. The GRAVITY instrument at the ESO VLTI has recently detected continuous circular relativistic motion during infrared flares which has been interpreted as orbital motion near the event horizon. Here we analyze the astrometric data from these flares, taking into account the effects of out-of-plane motion and orbital shear of material near the event horizon of the black hole. We have developed a new code to predict astrometric motion and flux variability from compact emission regions following particle orbits. Our code combines semi-analytic calculations of timelike geodesics that allow for out-of-plane or elliptical motions with ray tracing of photon trajectories to compute time-dependent images and light curves. We apply our code to the three flares observed with GRAVITY in 2018. We show that all flares are consistent with a hotspot orbiting at R ~ 9 gravitational radii with an inclination of i ~ 140°. The emitting region must be compact and less than ~5 gravitational radii in diameter. We place a further limit on the out-of-plane motion during the flare. [ABSTRACT FROM AUTHOR]

We use VLTI/GRAVITY near-infrared interferometry measurements of eight bright type 1 AGN to study the size and structure of hot dust that is heated by the central engine. We partially resolve each source, and report Gaussian full width at half-maximum sizes in the range 0:3-0:8 mas. In all but one object, we find no evidence for significant elongation or asymmetry (closure phases .1). The narrow range of measured angular sizes is expected given the similar optical flux of our targets, and implies an increasing effective physical radius with bolometric luminosity, as found from previous reverberation and interferometry measurements. The measured sizes for Seyfert galaxies are systematically larger than for the two quasars in our sample when measured relative to the previously reported R ~ L1=2 relationship, which is explained by emission at the sublimation radius. This could be evidence of an evolving near-infrared emission region structure as a function of central luminosity. [ABSTRACT FROM AUTHOR]

In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high-redshift) Universe efficiently condensed at the centres of dark-matter haloes when gas fractions were high and dark matter was less concentrated. [ABSTRACT FROM AUTHOR]

Spatially- and spectrally-resolved studies have proven very powerful in exploring the processes driving baryonic mass assembly and star formation at redshifts z ∼ 1–3, the heyday of massive galaxy formation. This contribution presents selected key results from near-infrared integral field spectroscopic studies of z ∼ 1–3 galaxies, including from the SINS/zC-SINF and KMOS3D surveys with SINFONI and KMOS at the ESO Very Large Telescope, highlights synergies with observations at other wavelengths, and discusses some of the implications for early galaxy evolution from mass assembly to feedback processes. [ABSTRACT FROM PUBLISHER]

We study the evolution of the dust temperature of galaxies in the SFR-M• plane up to z ~ 2 using far-infrared and submillimetre observations from the Herschel Space Observatory taken as part of the PACS Evolutionary Probe (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes. Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar masses (M•) and redshift estimates, we grid the SFR-M• parameter space in several redshift ranges and estimate the mean dust temperature (Tdust) of each SFR-M•-z bin. Dust temperatures are inferred using the stacked far-infrared flux densities (100-500 µm) of our SFR-M•-z bins. At all redshifts, the dust temperature of galaxies smoothly increases with rest-frame infrared luminosities (LIR), specific SFRs (SSFR; i.e., SFR/M•), and distances with respect to the main sequence (MS) of the SFR-M• plane (i.e., ? log (SSFR)MS = log [SSFR(galaxy)/SSFRMS(M•, z)]). The Tdust-SSFR and Tdust - ?log (SSFR)MS correlations are statistically much more significant than the Tdust-LIR one. While the slopes of these three correlations are redshiftindependent, their normalisations evolve smoothly from z = 0 and z ~ 2. We convert these results into a recipe to derive Tdust from SFR, M• and z, valid out to z ~ 2 and for the stellar mass and SFR range covered by our stacking analysis. The existence of a strong Tdust-?log (SSFR)MS correlation provides us with several pieces of information on the dust and gas content of galaxies. Firstly, the slope of the Tdust-?log (SSFR)MS correlation can be explained by the increase in the star-formation efficiency (SFE; SFR/Mgas) with ? log (SSFR)MS as found locally by molecular gas studies. Secondly, at fixed ? log (SSFR)MS, the constant dust temperature observed in galaxies probing wide ranges in SFR and M• can be explained by an increase or decrease in the number of star-forming regions with comparable SFE enclosed in them. And thirdly, at high redshift, the normalisation towards hotter dust temperature of the Tdust-? log (SSFR)MS correlation can be explained by the decrease in the metallicities of galaxies or by the increase in the SFE of MS galaxies. All these results support the hypothesis that the conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are different. MS galaxies have star-forming regions with low SFEs and thus cold dust, while galaxies situated far above the MS seem to be in a starbursting phase characterised by star-forming regions with high SFEs and thus hot dust. [ABSTRACT FROM AUTHOR]

We present near-infrared integral field observations of the super star cluster in the amorphous galaxy NGC1705. Data have been collected with SINFONI mounted on the VLT. Adaptive optics was used under good seeing conditions. Mosaics of the cluster and its immediate surrounding have been constructed. The cluster is not spatially resolved. Its radius is smaller than 2.85 ± 0.50 pc. The K-band spectrum of the cluster is dominated by strong CO absorption bandheads. It is typical of a Galactic K 4-5 supergiant. Its age is estimated to be 12 ± 6 Myr. The large error bar is rooted in the uncertainties of the input physics and ingredients of different evolutionary models. [ABSTRACT FROM AUTHOR]

Aims. We study the near-infrared properties of the super star cluster NGC 1750-1 to constrain its spatial extent, its stellar population, and its age. Methods. We used adaptive-optics assisted integral field spectroscopy with SINFONI on the Very Large Telescope. We estimated the spatial extent of the cluster and extracted its K-band spectrum from which we constrained the age of the dominant stellar population. Results. Our observations have an angular resolution of about 0.11" , providing an upper limit on the cluster radius of 2.85 ± 0.50 pc depending on the assumed distance. The K-band spectrum is dominated by strong CO absorption bandheads typical of red supergiants. Its spectral type is equivalent to a K4-5I star. Using evolutionary tracks from the Geneva and Utrecht groups, we determine an age of 12 ± 6 Myr. The large uncertainty is rooted in the large difference between the Geneva and Utrecht tracks in the red supergiants regime. The absence of ionized gas lines in the K-band spectrum is consistent with the absence of O and/or Wolf-Rayet stars in the cluster, as expected for the estimated age. [ABSTRACT FROM AUTHOR]

We use the first systematic data sets of CO molecular line emission in z∼ 1–3 normal star-forming galaxies (SFGs) for a comparison of the dependence of galaxy-averaged star formation rates on molecular gas masses at low and high redshifts, and in different galactic environments. Although the current high- z samples are still small and biased towards the luminous and massive tail of the actively star-forming ‘main-sequence’, a fairly clear picture is emerging. Independent of whether galaxy-integrated quantities or surface densities are considered, low- and high- z SFG populations appear to follow similar molecular gas–star formation relations with slopes 1.1 to 1.2, over three orders of magnitude in gas mass or surface density. The gas-depletion time-scale in these SFGs grows from 0.5 Gyr at to 1.5 Gyr at . The average corresponds to a fairly low star formation efficiency of 2 per cent per dynamical time. Because star formation depletion times are significantly smaller than the Hubble time at all redshifts sampled, star formation rates and gas fractions are set by the balance between gas accretion from the halo and stellar feedback. In contrast, very luminous and ultraluminous, gas-rich major mergers at both low and high z produce on average four to 10 times more far-infrared luminosity per unit gas mass. We show that only some fraction of this difference can be explained by uncertainties in gas mass or luminosity estimators; much of it must be intrinsic. A possible explanation is a top-heavy stellar mass function in the merging systems but the most likely interpretation is that the star formation relation is driven by global dynamical effects. For a given mass, the more compact merger systems produce stars more rapidly because their gas clouds are more compressed with shorter dynamical times, so that they churn more quickly through the available gas reservoir than the typical normal disc galaxies. When the dependence on galactic dynamical time-scale is explicitly included, disc galaxies and mergers appear to follow similar gas-to-star formation relations. The mergers may be forming stars at slightly higher efficiencies than the discs. [ABSTRACT FROM AUTHOR]

In this article, we identify and discuss various statistical and systematic effects influencing the astrometric accuracy achievable with Multi-adaptive optics Imaging CAmera for Deep Observations, the near-infrared (NIR) imaging camera proposed for the 42-m European Extremely Large Telescope. These effects are instrumental (e.g. geometric distortion), atmospheric (e.g. chromatic differential refraction) and astronomical (reference source selection). We find that there are several phenomena having impact on scales, meaning they can be substantially larger than the theoretical statistical astrometric accuracy of an optical/NIR 42-m telescope. Depending on type, these effects need to be controlled via dedicated instrumental design properties or via dedicated calibration procedures. We conclude that if this is done properly, astrometric accuracies of 40 μas or better – with 40 μas yr−1 in proper motions corresponding to ≈20 km s−1 at 100 kpc distance – can be achieved in one epoch of actual observations. [ABSTRACT FROM AUTHOR]

Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today’s massive spiral galaxies. The slow decrease between z ≈ 2 and z ≈ 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies. [ABSTRACT FROM AUTHOR]

Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks—the primary components of present-day galaxies—were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger. [ABSTRACT FROM AUTHOR]

The evolution of the content of heavy elements in galaxies, the relative chemical abundances, their spatial distribution, and how these scale with various galactic properties, provide unique information on the galactic evolutionary processes across the cosmic epochs. In recent years major progress has been made in constraining the chemical evolution of galaxies and inferring key information relevant to our understanding of the main mechanisms involved in galaxy evolution. In this review we provide an overview of these various areas. After an overview of the methods used to constrain the chemical enrichment in galaxies and their environment, we discuss the observed scaling relations between metallicity and galaxy properties, the observed relative chemical abundances, how the chemical elements are distributed within galaxies, and how these properties evolve across the cosmic epochs. We discuss how the various observational findings compare with the predictions from theoretical models and numerical cosmological simulations. Finally, we briefly discuss the open problems and the prospects for major progress in this field in the nearby future. [ABSTRACT FROM AUTHOR]

The model of the galaxy is considered as a structure of the baryonic matter embedded into the hot dark matter. The dark matter is supposed to come into being from the decaying matter after the epoch of structure formation. The galaxy is divided into two regions. In the inner region, the baryonic matter predominates over the hot dark matter while in the outer region, the hot dark matter predominates over the baryonic matter. The motion of the test particle is bounded in the inner region (elliptic orbit) and unbounded in the outer region (parabolic orbit). Observational constraints on the proposed model are considered from the rotation curves of the galaxies: Milky Way, M33, NGC 2366 and IC 2574. [ABSTRACT FROM AUTHOR]