As part of the SINS/zC-SINF surveys of high-z galaxy kinematics, we derive the radial distributions of H alpha surface brightness, stellar mass surface density, and dynamical mass at ~2 kpc ...resolution in 19 z ~ 2 star-forming disks with deep SINFONI adaptive optics spectroscopy at the ESO Very Large Telescope. From these data we infer the radial distribution of the Toomre Q-parameter for these main-sequence star-forming galaxies (SFGs), covering almost two decades of stellar mass (10 super(9,6)-10 super(11.5) M sub(middot in circle)). In more than half of our SFGs, the H alpha distributions cannot be fit by a centrally peaked distribution, such as an exponential, but are better described by a ring, or the combination of a ring and an exponential. At the same time the kinematic data indicate the presence of a mass distribution more centrally concentrated than a single exponential distribution for 5 of the 19 galaxies. The resulting Q-distributions are centrally peaked for all, and significantly exceed unity there for three-quarters of the SFGs. The occurrence of H alpha rings and of large nuclear Q-values appears to be more common for the more massive SFGs. While our sample is small and biased to larger SFGs, and there remain uncertainties and caveats, our observations are consistent with a scenario in which cloud fragmentation and global star formation are secularly suppressed in gas-rich high-z disks from the inside out, as the central stellar mass density of the disks grows.
We report the detection of ubiquitous powerful nuclear outflows in massive (> or =, slanted10 super(11) M sub(middot in circle)) z ~ 2 star-forming galaxies (SFGs), which are plausibly driven by an ...active galactic nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics-assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Halpha and forbidden NII and SII line emission, with typical velocity FWHM ~ 1500 km s super(-1), NII/Halpha ratio approximately 0.6, and intrinsic extent of 2-3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ~60M yr super(-1) and mass loading of ~3. At larger radii, a weaker broad component is detected but with lower FWHM ~485 km s super(-1) and NII/Halpha approximately 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest that the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial in confirming the importance and energetics of the nuclear outflow phenomenon and its connection to AGN activity and bulge growth.
We have studied the properties of giant star-forming clumps in five z {approx} 2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the ...Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad H{alpha}/N II line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10-40 km s{sup -1} kpc{sup -1}, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps.
We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical ...nebular emission line, mainly H Delta *a, SINS represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z ~ 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the 'SINS H Delta *a sample,' consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the H Delta *a and N II emission lines. Only 30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the SINS H Delta *a sample covers a reasonable representation of massive M 1010 M star-forming galaxies at z 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values 3 X 1010 M, 70 M yr-1, and 3 Gyr-1. The ionized gas distribution and kinematics are spatially resolved on scales ranging from 1.5 kpc for adaptive optics assisted observations to typically 4-5 kpc for seeing-limited data. The H Delta *a morphologies tend to be irregular and/or clumpy. About one-third of the SINS H Delta *a sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The H Delta *a luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates.
We present H alpha integral field spectroscopy of well-resolved, UV/optically selected image star-forming galaxies as part of the SINS survey with SINFONI on the ESO VLT. Our laser guide star ...adaptive optics and good seeing data show the presence of turbulent rotating star-forming outer rings/disks, plus central bulge/inner disk components, whose mass fractions relative to the total dynamical mass appear to scale with the N ii/H alpha flux ratio and the star formation age. We propose that the buildup of the central disks and bulges of massive galaxies at image can be driven by the early secular evolution of gas-rich proto-disks. High-redshift disks exhibit large random motions. This turbulence may in part be stirred up by the release of gravitational energy in the rapid 'cold' accretion flows along the filaments of the cosmic web. As a result, dynamical friction and viscous processes proceed on a timescale of <1 Gyr, at least an order of magnitude faster than in image disk galaxies. Early secular evolution thus drives gas and stars into the central regions and can build up exponential disks and massive bulges, even without major mergers. Secular evolution along with increased efficiency of star formation at high surface densities may also help to account for the short timescales of the stellar buildup observed in massive galaxies at image.
The structure of a sample of high-redshift (z ~ 2), rotating galaxies with high star formation rates and turbulent gas velocities of Delta *s 40-80 km s--1 is investigated. Fitting the observed disk ...rotational velocities and radii with a Mo et al. (MMW) model requires unusually large disk spin parameters Delta *l d >0.1 and disk-to-dark halo mass fractions of m d 0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1 <= v max/ Delta *s <= 3, maximum rotational velocities v max<= 200 km s--1, and disk half-light radii r 1/2 1-3 kpc, and rotation-dominated systems with v max> 200 km s--1, v max/ Delta *s>3, and r 1/2 4-8 kpc. For the dispersion-dominated sample, radial pressure gradients partly compensate the gravitational force, reducing the rotational velocities. Including this pressure effect in the MMW model, dispersion-dominated galaxies can be fitted well with spin parameters of Delta *l d = 0.03-0.05 for high disk mass fractions of m d 0.2 and with Delta *l d = 0.01-0.03 for m d 0.05. These values are in good agreement with cosmological expectations. For the rotation-dominated sample, however, pressure effects are small and better agreement with theoretically expected disk spin parameters can only be achieved if the dark halo mass contribution in the visible disk regime (2-3 X r 1/2) is smaller than predicted by the MMW model. We argue that these galaxies can still be embedded in standard cold dark matter halos if the halos do not contract adiabatically in response to disk formation. In this case, the data favor models with small disk mass fractions of m d = 0.05 and disk spin parameters of Delta *l d 0.035. It is shown that the observed high turbulent gas motions of the galaxies are consistent with a Toomre instability parameter Q = 1 which is equal to the critical value, expected for gravitational disk instability to be the major driver of turbulence. The dominant energy source of turbulence is then the potential energy of the gas in the disk.
The kinematics of distant galaxies from z = 0.1 to z > 2 play a key role in our understanding of galaxy evolution from early times to the present. One of the important parameters is the intrinsic, or ...local, velocity dispersion of a galaxy, which allows one to quantify the degree of non-circular motions such as pressure support. However, this is difficult to measure because the observed dispersion includes the effects of (often severe) beam smearing on the velocity gradient. Here we investigate four methods of measuring the dispersion that have been used in the literature, to assess their effectiveness at recovering the intrinsic dispersion. We discuss the biases inherent in each method, and apply them to model disk galaxies in order to determine which methods yield meaningful quantities and under what conditions. All the mean-weighted dispersion estimators are affected by (residual) beam smearing. In contrast, the dispersion recovered by fitting a spatially and spectrally convolved disk model to the data is unbiased by the beam smearing it is trying to compensate. Because of this, and because the bias it does exhibit depends only on the signal-to-noise ratio (S/N), it can be considered reliable. However, at very low S/N, all methods should be used with caution.
Abstract
BL Lac objects emitting in the very high energy (VHE) regime are unique tools to peer into the properties of the extragalactic background light (EBL). However, due to the typical absence of ...features in their spectra, the determination of their redshifts has proven challenging. In this work, we exploit the superb spatial resolution delivered by the new Advanced Rayleigh guided Ground layer adaptive Optics System (ARGOS) at the Large Binocular Telescope to detect the host galaxy of HESS J1943+213, a VHE emitting BL Lac shining through the Galaxy. Deep H-band imaging collected during the ARGOS commissioning allowed us to separate the contribution of the nuclear emission and to unveil the properties of the host galaxy with unprecedented detail. The host galaxy is well fitted by a Sérsic profile with index of n ∼ 2 and total magnitude of HHost ∼ 16.15 mag. Under the assumption that BL Lac host galaxies are standard candles, we infer a redshift of z ∼ 0.21. In the framework of the current model for the EBL, this value is in agreement with the observed dimming of the VHE spectrum due to the annihilation of energetic photons on the EBL
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