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A recently-discovered class of outflows, extremely high-velocity outflows (EHVOs), may be key to understanding feedback processes as it is likely the most powerful in terms of mass-energy. These EHVOs have been observed at redshifts 1.052 < z_em < 7.641, but the potential connection with outflows in emission had not been studied. We find that EHVOs, albeit their small numbers at the moment, appear to show distinct CIV and HeII properties. In particular, EHVOs are more predominant in quasars with large blueshifts of the CIV emission line, suggesting a connection between emission and absorption outflowing signatures for these extreme outflows. We also find incipient trends with the maximum velocity of the outflows, which is similar to what has been previously found in BALQSOs, but now extending previous studies to speeds up to ~0.2c. We find the bolometric luminosities, Eddington ratios, and black hole masses of our sample are overall very similar from the general quasar population upon considering their CIV emission properties. This is close to the case for HeII EW as we observe a tentative upper limit to the HeII strength for a quasar to host an EHVO. This study shows that extreme outflows such as EHVOs appear in quasars that are clearly a distinct class from the overall BALQSO population, and solidify the relation between outflows observed in emission and in absorption., Comment: 10 pages, 5 figures, accepted for publication in the Astrophysical Journal Letters (submitted Sept 3rd 2022; accepted Sept 26th 2022)

The warm absorbers observed in more than half of all nearby active galactic nuclei (AGN) are tracers of ionized outflows located at parsec scale distances from the central engine. If the smallest inferred ionization parameters correspond to plasma at a few $10^4$~K, then the gas undergoes a transition from being bound to unbound provided it is further heated to $\sim 10^6$~K at larger radii. Dannen et al. recently discovered that under these circumstances, thermally driven wind solutions are unsteady and even show very dense clumps due to thermal instability. To explore the observational consequences of these new wind solutions, we compute line profiles based on the one-dimensional simulations of Dannen et al. We show how the line profiles from even a simple steady state wind solution depend on the ionization energy (IE) of absorbing ions, which is a reflection of the wind ionization stratification. To organize the diversity of the line shapes, we group them into four categories: weak Gaussians, saturated boxy profiles with and without an extended blue wing, and broad weak profiles. The lines with profiles in the last two categories are produced by ions with the highest IE that probe the fastest regions. Their maximum blueshifts agree with the highest flow velocities in thermally unstable models, both steady state and clumpy versions. In contrast, the maximum blueshifts of the most high IE lines in thermally stable models can be less than half of the actual solution velocities. Clumpy solutions can additionally imprint distinguishable absorption troughs at widely separated velocities., Comment: Accepted for publication in ApJ, 20 pages, 15 figures, 3 tables, videos and FITS files of line profiles available on: http://www.physics.unlv.edu/astro/clumpywindsims-lps.html

We present a survey of extremely high-velocity outflows (EHVOs) in quasars, defined by speeds between 0.1c and 0.2c. This region of the parameter space has not been included in previous surveys, but it might present the biggest challenge for theoretical models and it might be a large contributor to feedback due to the outflows' potentially large kinetic power. Using the Sloan Digital Sky Survey, we find 40 quasar spectra with broad EHVO CIV absorption, 10 times more than the number of previously known cases. We characterize the EHVO absorption and find that in 26 cases, CIV is accompanied by NV and/or OVI absorption. We find that EHVO quasars lack HeII emission and have overall larger bolometric luminosities and black hole masses than those of their parent sample and BALQSOs, while we do not find significant differences in their Eddington ratios. We also report a trend toward larger black hole masses as the velocity of the outflowing gas increases in the BALQSOs in our sample. The overall larger Lbol and lack of HeII emission of EHVO quasars suggest that radiation is likely driving these outflows. We find a potential evolutionary effect as EHVO quasars seem to be more predominant at large redshifts. We estimate that the kinetic power of these outflows may be similar to or even larger than that of the outflows from BALQSOs as the velocity factor increases this parameter by 1-2.5 orders of magnitude. Further study of EHVO quasars will help improve our understanding of quasar physics., Comment: 26 pages, accepted for publication in the Astrophysical Journal

The stability of annular electromagnetic pumps (EMPs) is investigated through 3D direct numerical simulations. When induction effects dominate dissipative processes, linear induction EMPs become unstable and lead to non-axisymmetric states relatively different from what was predicted by previous theoretical models. We show that the 3D destabilization of the flow is deeply connected to the axisymmetric state, and always appears as a secondary bifurcation from a locally stalled flow, even if the applied magnetic field is axisymmetric. Finally, we model a configuration aiming to optimize the efficiency of the pump, by imposing electrical currents on both sides (inner and outer cylinders) of the pump. This configuration increases the efficiency of the pump, but generates a complex dynamics, associated to periodic oscillation of a large vortex flow localized in the active region of the pump. Finally, we demonstrate the existence of an upper bound on the efficiency of such electromagnetic pump, which can never exceed 50%.

We isolate a set of quasars that exhibit emergent C iv broad absorption lines (BALs) in their spectra by comparing spectra in the SDSS Data Release 7 and the SDSS/BOSS Data Releases 9 and 10. After visually defining a set of emergent BALs, follow-up observations were obtained with the Gemini Observatory for 105 quasars. We find an emergence rate consistent with the previously reported disappearance rate of BAL quasars given the relative numbers of non-BAL and BAL quasars in the SDSS. We find candidate newly emerged BALs are preferentially drawn from among BALs with smaller balnicity indices, shallower depths, larger velocities, and smaller widths. Within two rest-frame years (average) after a BAL has emerged, we find it equally likely to continue increasing in equivalent width in an observation six months later (average) as it is to start decreasing. From the time separations between our observations, we conclude the coherence time-scale of BALs is less than 100 rest-frame days. We observe coordinated variability among pairs of troughs in the same quasar, likely due to clouds at different velocities responding to the same changes in ionizing flux; and the coordination is stronger if the velocity separation between the two troughs is smaller. We speculate the latter effect may be due to clouds having on average lower densities at higher velocities due to mass conservation in an accelerating flow, causing the absorbing gas in those clouds to respond on different timescales to the same ionizing flux variations., Comment: 37 pages, 25 figures

In a previous paper, we have reported numerical simulations of the MHD flow driven by a travelling magnetic field (TMF) in an annular channel, at low Reynolds number. It was shown that the stalling of such induction pump is strongly related to magnetic flux expulsion. In the present article, we show that for larger hydrodynamic Reynolds number, and with more realistic boundary conditions, this instability takes the form of a large axisymmetric vortex flow in the (r,z)-plane, in which the fluid is locally pumped in the direction opposite to the one of the magnetic field. Close to the marginal stability of this vortex flow, a low-frequency pulsation is generated. Finally, these results are compared to theoretical predictions and are discussed within the framework of experimental annular linear induction electromagnetic pumps.

We present the discovery of the highest velocity CIV broad absorption line to date in the z=2.47 quasar SDSS J023011.28+005913.6, hereafter J0230. In comparing the public DR7 and DR9 spectra of J0230, we discovered an emerging broad absorption trough outflowing at ~60,000 km/s, which we refer to as trough A. In pursuing follow up observations of trough A, we discovered a second emergent CIV broad absorption trough outflowing at ~40,000 km/s, namely trough B. In total, we collected seven spectral epochs of J0230 that demonstrate emergent and rapidly (~10 days in the rest-frame) varying broad absorption. We investigate two possible scenarios that could cause these rapid changes: bulk motion and ionization variability. Given our multi-epoch data, we were able to rule out some simple models of bulk motion, but have proposed two more realistic models to explain the variability of both troughs. Trough A is likely an augmented `crossing disk' scenario with the absorber moving at 10,000 < v (km/s) < 18,000. Trough B can be explained by a flow-tube feature travelling across the emitting region at 8,000 < v (km/s) < 56,000. If ionization variability is the cause for the changes observed, trough A's absorber has n_e >= 724 cm^-3 and is at r_{equal} >=2.00 kpc, or is at r < 2.00 kpc with no constraint on the density; trough B's absorber either has n_e >= 1540 cm^-3 and is at r_{equal} >= 1.37 kpc, or is at r < 1.37 kpc with no constraint on the density., Comment: 16 pages, 14 figures, 3 tables

We present the detection of a rare case of dramatic strengthening in the UV absorption profiles in the spectrum of the quasar J115122.14+020426.3 between observations ~2.86 years apart in the quasar rest-frame. A 2001 spectrum from the Sloan Digital Sky Survey (SDSS) shows a CIV "mini-broad" absorption line (FWHM=1,220 km/s) with a maximum blueshift velocity ~9,520 km/s, while a later spectrum from the Very Large Telescope (VLT) shows significantly broader and stronger absorption line, with a maximum blueshift velocity of ~12,240 km/s, that qualifies as a broad absorption line. A similar variability pattern is observed in two additional systems at lower blueshifted velocities and in the Lya and NV transitions as well. One of the absorption systems appears to be resolved and shows evidence for partial covering of the quasar continuum source (Cf~0.65), indicating a transverse absorber size of, at least, ~6 x 10^(16) cm. In contrast, a cluster of narrower CIV lines appears to originate in gas that fully covers the continuum and broad emission line sources. There is no evidence for changes in the centroid velocity of the absorption troughs. This case suggests that, at least some of the absorbers that produce "mini-broad" and broad absorption lines in quasar spectra do not belong to intrinsically separate classes. Here, the "mini-broad" absorption line is most likely interpreted as an intermediate phase before the appearance of a broad absorption line due to their similar velocity. While the current observations do not provide enough constraints to discern among the possible causes for this variability, future monitoring of multiple transitions at high resolution will help achieve this goal., Comment: 12 pages, 8 figures, accepted for publication in the Astrophysical Journal

Quasar accretion disk winds observed via broad absorption lines (BALs) in the UV produce strong continuous absorption in X-rays. The X-ray absorber is believed to serve critically as a radiative shield to enable radiative driving. However, "mini-BAL" and narrow absorption line outflows have dramatically less X-ray absorption than BALs. Here we examine X-ray and rest-frame UV spectra of 8 mini-BAL quasars with outflow speeds in the range 0.1c to 0.2c to test whether extreme speeds require a strong shield. We find that the X-ray absorption is weak or moderate, with neutral-equivalent column densities N_H < few times 10^22 cm^-2, consistent with mini-BALs at lower speeds. We use photoionization models to show that this amount of shielding is too weak to control the outflow ionizations and, therefore, it is not important for the acceleration. Shielding in complex geometries also seems unlikely because the alleged shield would need to extinguish the ionizing far-UV flux while avoiding detection in X-rays and the near-UV. We argue that the outflow ionizations are kept moderate, instead, by high gas densities in small clouds. If the mini-BALs form at radial distances of order R ~ 2 pc from the central quasar (broadly consistent with theoretical models and with the mini-BAL variabilities observed here and in previous work), and the total column densities in the mini-BAL gas are N_H ~< 10^21 cm^-2, then the total radial extent of outflow clouds is only Delta-R_clouds ~< 3 x 10^13 cm and the radial filling factor is Delta-R_clouds/R ~< 5 x 10^-6 for weak/negligible shielding. Compared to the transverse sizes >~ 8 x 10^15 cm (based on measured line depths), the outflows have shapes like thin "pancakes" viewed face-on, or they occupy larger volumes like a spray of many dense clouds with a small volume filling factor. These results favor models with magnetic confinement in magnetic disk winds., Comment: 18 pages, 5 figures, accepted for publication in the MNRAS

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics., Comment: Submitted in response to the call for White Papers for the definition of the L2 and L3 missions in the ESA Science program. More information: http://www.the-athena-x-ray-observatory.eu/. 19 pages, 12 figures, 4 tables

We describe two studies designed to characterize the total column densities, kinetic energies, and acceleration physics of broad absorption line (BAL) outflows in quasars. The first study uses new Chandra X-ray and ground-based rest-frame UV observations of 7 quasars with mini-BALs at extreme high speeds, in the range 0.1c to 0.2c, to test the idea that strong radiative shielding is needed to moderate the mini-BAL ionizations and facilitate their acceleration to extreme speeds. We find that the X-ray absorption is weak or absent, with generally N_H < few x 10^22 mc^-2, and that radiative shielding is not important. We argue that the mini-BAL ionizations are controlled, instead, by high gas densities of order n_H ~ 4 x 10^8 cm^-3 in small outflow substructures. If we conservatively assume that the total column density in the mini-BAL gas is N_H < 10^22 cm^-2, covering >15% of the UV continuum source along our lines of sight (based on measured line depths), then the radial thickness of these outflows is only Delta_R < 3 x 10^13 cm and their transverse size is > 8 x 10^15 cm. Thus the outflow regions have the shape of very thin "pancakes" viewed face-on, or they occupy larger volumes like a spray of dense cloudlets with a very small volume filling factor. We speculate that this situation (with ineffective shielding and small dense outflow substructures) applies to most quasar outflows, including BALs. Our second study focuses from BALs of low-abundance ions, mainly PV 1118,1128 A, whose significant strengths imply large column densities, N_H > 10^22 cm^-2, that can further challenge models of the outflow acceleration. In spite of the difficulties of finding this line in the Ly-alpha forest, a search through the SDSS DR9 quasar catalog reveals >50 BAL sources at redshifts z>2.3 with strong PV BALs, which we are now using to characterize the general properties of high-column outflows., Comment: proceedings article for Nuclei of Seyfert galaxies and QSOs - Central engine & conditions of star formation, Bonn, Germany, 2012

We present a study of the evolution of several classes of MgII absorbers, and their corresponding FeII absorption, over a large fraction of cosmic history: 2.3 to 8.7 Gyrs from the Big Bang. Our sample consists of 87 strong (Wr(MgII)>0.3 A) MgII absorbers, with redshifts 0.21 A) with small ratios of equivalent widths of FeII to MgII. At high z, very strong MgII absorbers with both small and large Wr(FeII)/Wr(MgII) values are present. We compare our findings to a sample of 100 weak MgII absorbers (Wr(MgII)<0.3 A) found in the same quasar spectra by Narayanan et al. (2007). The main effect driving the evolution of very strong MgII systems is the difference between the kinematic profiles at low and high redshifts. At high z, we observe that, among the very strong MgII absorbers, all of the systems with small ratios of Wr(FeII)/Wr(MgII) have relatively large velocity spreads, resulting in less saturated profiles. At low z, such kinematically spread systems are absent, and both FeII and MgII are saturated, leading to Wr(FeII)/Wr(MgII) values that are all close to 1. The high redshift, small Wr(FeII)/Wr(MgII) systems could correspond to sub-DLA systems, many of which have large velocity spreads and are possibly linked to superwinds in star forming galaxies. In addition to the change in saturation due to kinematic evolution, the smaller Wr(FeII)/Wr(MgII) values could be due to a lower abundance of Fe at high z, which would indicate relatively early stages of star formation in those environments., Comment: 20 pages, 14 figures (figure 1 is a set of 87 figures, which is available on the online version), accepted for publication in the MNRAS

We study how helicity affects the spectrum of a passive scalar in rotating turbulent flows, using numerical simulations of turbulent flows with or without rotation, and with or without injection of helicity. Scaling laws for energy and passive scalar spectra in the direction perpendicular to the rotation axis differ in rotating helical flows from the ones found in the non-helical case, with the spectrum of passive scalar variance in the former case being shallower than in the latter. A simple phenomenological model that links the effects of helicity on the energy spectrum with the passive scalar spectrum is presented., Comment: 16 pages, 8 figures, proceeding for the Third International Conference Turbulent Mixing and Beyond 2011, International Centre for Theoretical Physics, Trieste, Italy

Broad absorption lines (BALs) in quasar spectra identify high velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. Studying the variability in these BALs can help us understand the structure, evolution, and basic physical properties of these outflows. We are conducting a BAL monitoring program, which so far includes 163 spectra of 24 luminous quasars, covering time-scales from \sim 1 week to 8 years in the quasar rest-frame. We investigate changes in both the CIV {\lambda}1550 and SiIV {\lambda}1400 BALs, and we report here on some of the results from this program., Comment: 5 pages, proceedings for the conference "AGN Winds in Charleston", Charleston, S.C., 2011

Narrow absorption line (NAL) outflows are an important yet poorly understood part of the quasar outflow phenomenon. We discuss one particular NAL outflow that has high speeds, time variability, and moderate ionizations like typical BAL flows, at an estimated location just ~5 pc from the quasar. It also has a total column density and line widths (internal velocity dispersions) ~100 times smaller than BALs, with no substantial X-ray absorption. We argue that radiative shielding (in the form of an X-ray/warm absorber) is not critical for the outflow acceleration and that the moderate ionizations occur in dense substructures that have an overall small volume filling factor in the flow. We also present new estimates of the overall incidence of quasar outflow lines; e.g., ~43% of bright quasars have a C IV NAL outflow while ~68% have a C IV outflow line of any variety (NAL, BAL, or mini-BAL)., Comment: 5 pages, proceedings for the conference "AGN Winds in Charleston", Charleston, S.C., 2011

We report the results of several programs to study the variability of high-velocity (up to 0.2c) mini-"broad absorption lines" (mini-BALs) and BALs in quasar spectra, and thus to better characterize the structural and physical properties of these outflows. After the report of a highly variable mini-BAL outflow at a speed of ~0.17c in the quasar PG0935+417, we created the first systematic accounting of outflows in Sloan Digital Sky Survey (SDSS) quasar spectra that includes mini-BALs and extremely high velocity outflows (up to 0.2c) to measure their frequency. Following this study, we began a monitoring campaign to study the location, and dynamical and evolutionary effects of these outflows. This program covers a range of 0.9-3.3 years in the quasars' rest-frame by comparing new spectra (using facilities at the Kitt Peak National Observatory and MDM Observatory) with archival SDSS spectra. We find that ~57% of quasars with mini-BALs and BALs varied between just two observations. This variability tends to occur in complex ways; however, all the variable lines vary in intensity and not in velocity, not finding evidence for acceleration/deceleration in these outflows. Due to the variations in strength, mini-BALs can become BALs and vice versa, suggesting they share a similar nature. We include as an example the discovery of the transition of a mini-BAL into a BAL in the spectra of the SDSS quasar J115122+020426., Comment: 6 pages, 2 figures, To appear in the proceedings of the "AGN Winds in Charleston" conference, Charleston SC, Oct 15-18 2011. To be published by ASP

Broad absorption lines (BALs) in quasar spectra indicate high-velocity outflows that may be present in all quasars and could be an important contributor to feedback to their host galaxies. Variability studies of BALs help illuminate the structure, evolution, and basic physical properties of the outflows. Here we present further results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2 < z < 2.9. We directly compare the variabilities in the CIV 1549 and SiIV 1400 absorption to try to ascertain the cause(s) of the variability. We find that SiIV BALs are more likely to vary than CIV BALs. When looking at flow speeds >-20 000 km/s, 47 per cent of quasars exhibited SiIV variability while 31 per cent exhibited CIV variability. Furthermore, ~50 per cent of the variable SiIV regions did not have corresponding CIV variability at the same velocities. When both CIV and SiIV varied, those changes always occurred in the same sense (either getting weaker or stronger). We also include our full data set so far in this paper, which includes up to 10 epochs of data per quasar. The multi-epoch data show that the BAL changes were not generally monotonic across the full ~5 to ~8 yr time span of our observations, suggesting that the characteristic time-scale for significant line variations, and (perhaps) for structural changes in the outflows, is less than a few years. Coordinated variabilities between absorption regions at different velocities in individual quasars seems to favor changing ionization of the outflowing gas as the cause of the observed BAL variability. However, variability in limited portions of broad troughs fits naturally in a scenario where movements of individual clouds, or substructures in the flow, across our lines-of-sight cause the absorption to vary. The actual situation may be a complex mixture of changing ionization and cloud movements., Comment: 21 pages, 11 figures (2 in color), accepted for publication in MNRAS

We review the main results from axisymmetric, time-dependent hydrodynamical simulations of radiation driven disk winds in AGN. We illustrate the capability of such simulations to provide useful insights into the three domains of observational astronomy: spectroscopy, time-variability, and imaging. Specifically, the synthetic line profiles predicted by the simulations resemble the broad absorption lines observed in quasars. The intrinsically time dependent nature of radiation driven disk winds that have been predicted by the simulations can be supported by a growing number of the observed dramatic variability in the UV absorption lines. And finally, the intensity maps predicted by the simulations give physical and geometrical justification to the phenomenologically deduced fact that a proper interpretation of the observed line absorption requires the wind covering factor to be considered as being partial, inhomogeneous, and velocity dependent., Comment: 5 pages, 1 figure, Conference proceedings for "AGN Winds in Charleston," Charleston, SC, Oct 15-18, 2011. To be published by ASP

We present results of direct numerical simulations of passive scalar advection and diffusion in turbulent rotating flows. Scaling laws and the development of anisotropy are studied in spectral space, and in real space using an axisymmetric decomposition of velocity and passive scalar structure functions. The passive scalar is more anisotropic than the velocity field, and its power spectrum follows a spectral law consistent with $\sim k_\perp^{-3/2}$. This scaling is explained with phenomenological arguments that consider the effect of rotation. Intermittency is characterized using scaling exponents and probability density functions of velocity and passive scalar increments. In the presence of rotation, intermittency in the velocity field decreases more noticeably than in the passive scalar. The scaling exponents show good agreement with Kraichnan's prediction for passive scalar intermittency in two-dimensions, after correcting for the observed scaling of the second order exponent., Comment: 10 pages, 15 figures

Broad absorption lines (BALs) in quasar spectra identify high velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. The variability of BALs can help us understand the structure, evolution, and basic physical properties of the outflows. Here we report on our first results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2

We report the detection of OVI 1031,1037 and NV 1238,1242 absorption in a system of "mini-broad" absorption lines (mini-BALs) previously reported to have variable CIV 1548,1550 in the quasar PG0935+417. The formation of these lines in an extreme high-velocity quasar outflow (with v ~ -50000 km/s) is confirmed by the line variability, broad smooth absorption profiles, and partial covering of the background light source. HI and lower ionization metals are not clearly present. The resolved OVI doublet indicates that these lines are moderately saturated, with the absorber covering ~80% of the quasar continuum source (C_f~0.8). We derive ionic column densities of order 1015 cm^(-2) in CIV and several times larger in OVI, indicating an ionization parameter of log U >~ -0.5. Assuming solar abundances, we estimate a total column density of N(H) ~5 x 10^(19) cm^(-2). This outflow emerged sometime between 1982 and 1993. Our examination of the CIV data from 1993 to 2007 shows that there is variable complex absorption across a range of velocities from -45000 to -54000 km/s. There is no clear evidence for acceleration or deceleration of the outflow gas. Outflows are common in Active Galactic Nuclei (AGN), but extreme speeds such as those reported here are extremely rare. It is not clear what properties of PG0935+417 might produce this unusual outflow. In fact, PG0935+417 has significantly less X-ray absorption than typical BAL quasars even though its outflow has a degree of ionization typical of BALs at speeds that are 2-3 times larger than most BALs. These results might present a challenge to theoretical models that invoke strong radiative shielding in the X-rays/far-UV to moderate the outflow ionization and thus enable its radiative acceleration to high speeds., Comment: 15 pages, 9 figures, accepted for publication in the MNRAS

Helicity is a quadratic invariant of the Euler equation in three dimensions. As the energy, when present helicity cascades to smaller scales where it dissipates. However, the role played by helicity in the energy cascade is still unclear. In non-helical flows, the velocity and the vorticity tend to align locally creating patches with opposite signs of helicity. Also in helical flows helicity changes sign rapidly in space. Not being a positive definite quantity, global studies considering its spectral scaling in the inertial range are inconclusive, except for cases where one sign of helicity is dominant. We use the cancellation exponent to characterize the scaling laws followed by helicity fluctuations in numerical simulations of helical and non-helical turbulent flows, with different forcing functions and spanning a range of Reynolds numbers from approximately 670 to 6200. The exponent is a measure of sign-singularity and can be related to the fractal dimension as well as to the first order helicity scaling exponent. The results are consistent with the geometry of helical structures being filamentary. Further analysis indicates that statistical properties of helicity fluctuations do not depend on the global helicity of the flow., Comment: 9 pages, 4 figures

High velocity (HV) outflows are an important but poorly understood aspect of quasar/SMBH evolution. Outflows during the luminous accretion phase might play a critical role in "unveiling" young dusty AGN and regulating star formation in the host galaxies. Most quasar studies have focussed on the broad absorption lines (BALs). We are involved in a program to study a nearly unexplored realm of quasar outflow parameter space: HV winds with v>10,000 km/s up to v~0.2c but small velocity dispersions (narrow absorption lines), such that (Delta v)/v << 1. Narrow-line HV flows merit specific attention because they complement the BAL work and pose unique challenges for models of the wind acceleration, mass loss rates, launch radii, geometry, etc. We have selected the brightest quasars at 1.8

The warm absorbers observed in more than half of all nearby active galactic nuclei are tracers of ionized outflows located at parsec-scale distances from the central engine. If the smallest inferred ionization parameters correspond to plasma at a few 104 K, then the gas undergoes a transition from being bound to unbound, provided it is further heated to ∼106 K at larger radii. Dannen et al. recently discovered that, under these circumstances, thermally driven wind solutions are unsteady and even show very dense clumps due to thermal instability. To explore the observational consequences of these new wind solutions, we compute line profiles based on the one-dimensional simulations of Dannen et al. We show how the line profiles from even a simple steady-state wind solution depend on the ionization energy (IE) of absorbing ions, which is a reflection of the wind ionization stratification. To organize the diversity of the line shapes, we group them into four categories: weak Gaussians, saturated boxy profiles with and without an extended blue wing, and broad weak profiles. The lines with profiles in the last two categories are produced by ions with the highest IE that probe the fastest regions. Their maximum blueshifts agree with the highest flow velocities in thermally unstable models, both steady-state and clumpy versions. In contrast, the maximum blueshifts of the highest-IE lines in thermally stable models can be less than half of the actual solution velocities. Clumpy solutions can additionally imprint distinguishable absorption troughs at widely separated velocities.