arXiv subjects

Isaac Shlosman

Publications and source records attributed to Isaac Shlosman.

At least 19 recordsLinked to original sources

arXiv2026

The Limited Lifetime of Self-Gravitating Accretion Disks In Galactic Centers

Globally self-gravitating accretion disks in active galactic nuclei (AGN) have been frequently discussed in the literature, but never observed. Few dozen mega-masering accretion disks in AGN have been detected, which display a clear Keplerian rotation on scales of 0.1-1 pc, allowing to estimate their masses within the sphere of influence (SoI) of the central supermassive black holes (SMBHs) to be smaller by more than a factor of 10, compared with the parent SMBH masses. Furthermore, the stellar components, deep inside the SoI, are dwarfed by the SMBH masses of M_BH ~ few X 10^6 - few X 10^7 Mo. Theoretically, no limit exists on sizes and masses of gaseous disks in AGN, which in principle, can exceed masses of their central compact objects. We analyze instabilities which can operate in gaseous disks, i.e., fragmentation for a locally dominant self-gravity and spontaneous breaking of axial symmetry for the globally self-gravitating disks. We invoke the gas response to the latter instability which leads to gravitational collapse, leaving a negligible mass behind and dynamically stable remnants. Consequently, the characteristic timescale for globally self-gravitating disks to exist in AGN should not exceed few rotations, t_phi ~ 10^{3-4} yrs for M_BH ~ 10^{6-8} Mo. Disk rebuilding is expected to be > 10^7 yrs, meaning that probability of finding is < 10^{-3}, which explains their lack of detection. We conclude that observed sub-parsec disks in AGN, at least the Keplerian masering ones, can be remnants of globally self-gravitating accretion disks, and the instability timescale can be related to the duty cycle of AGN, t_duty ~ 10t_phi ~ 10^{4-5} yr.

astro-ph.GA↗

arXiv2026

The Impact of Seyfert Jets on Galaxy Evolution Across Major Scaling Relations

We analyze a suite of high-resolution cosmological zoom-in simulations of jetted Seyfert galaxies over $z\leq10$ projected on the major scaling relations, comparing trajectories of `normal' versus jet-hosting galaxies. Models include thermal and mechanical jet feedback launched from supermassive black holes (SMBHs) seeded at $z\sim9.1$ and $z\sim3.7$ with $M_\bullet\sim10^6\,M_\odot$ in galaxies within dark matter halos of ${\rm log}\,M_{\rm halo}/M_\odot\sim11.8$ at $z=0$. A single parameter, the SMBH accretion efficiency, has been varied resulting in $L_{\rm jet}\sim10^{40-42}\,{\rm erg\,s^{-1}}$, and SMBH accretion rates range between $\sim 0.2-10^{-4}$ of the Eddington rate. We find that jet feedback (1) suppresses central star formation rates (SFRs), redistributes gas to larger radii, (2) generates long-lived expanding shocks that couple to the ISM and CGM, (3) reduces stellar mass ($M_*$), shifting galaxies toward lower central concentrations, and (4) alters host trajectories on the $M_{\rm halo}-M_*$, specific SFR$-M_*$, $M_\bullet-\sigma_{\rm bulge}$, Mass$-$Metallicity, Kennicutt-Schmidt, and baryonic Tully-Fisher relation planes. Specifically, we find that jetted Seyferts live longer in the green valley and more frequently move to the quenched region in comparison to the non-jetted galaxies. Despite producing only transient quenching, Seyfert jets cause persistent structural, kinematic and chemical signatures, including flatter rotation curves, elevated CGM metallicities, and reduced cold gas clumping. (5) Early SMBH seeding and stronger jets amplify these effects, yielding galaxies that lie systematically closer to some of the empirical relations, e.g., $M_{\rm halo}-M_*$, while showing offsets for others, e.g., Kennicutt-Schmidt, and demonstrating that low-luminosity Seyfert jets can exert a significant long-term influence on galaxy evolution.

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arXiv2025

Modeling Cosmological Evolution of Jetted Seyfert Galaxies for z<10

We use high-resolution cosmological zoom-in simulations to model mechanical and thermal feedback from AGN onto the evolution of Seyfert-type galaxies, studying the morphology of central galaxies growing within dark matter (DM) halos with masses logM/Mo ~11.8 at z=0. In Paper I, we focused on the end products at z=0, here we analyze evolution for z<10. Black holes (SMBHs) of ~10^6 Mo were seeded at z~9.1 and z~3.7, producing jets along their spin axes. Obtained SMBH accretion rates vary in the range ~0.3-10^(-4) of the Eddington rate. We compared the basic properties of galaxies, such as star formation rate, masses, gas and stellar fractions, bulge-to-disk mass ratios, SMBH masses, etc., over the range of redshifts. Our results indicate that jets and associated over-pressured bubbles have substantial effects on Seyfert galaxy evolution, including properties of the interstellar and circumgalactic medium (ISM and CGM), and even beyond. This feedback can suppress and even quench star formation, reduce stellar mass and gas fraction, modify the bulge-to-disk ratios, drive outflows from galaxies and host DM halos, and metal-enrich the CGM. The jets are largely but not exclusively contained within galaxies. However, over-pressured bubbles cross and modify the composition of the CGM and IGM, their thermodynamic and dynamic state, and generate vorticity. The CGM emerges as a complex region, where action of galactic outflows and jet-formed bubbles combines with the influx from cosmological filaments and diffuse accretion. Ultimately, the above processes affect the gas balance within the galaxy, its morphology, and gas supply to the SMBH, limiting its growth.

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arXiv2025

Direct Collapse Pre-supermassive Black Hole Objects as Ly$\alpha$ Emitters

The Direct Collapse scenario to form the supermassive black hole (SMBH) seeds offers the most promising way to explain the origin of quasars at $z>7$. Assuming atomic primordial gas, can Ly$\alpha$ photons escape from the central regions of the collapse and serve as a diagnostic for the detection of these pre-SMBH objects? Models of spherical collapse have found these photons to be trapped and destroyed. We use Ly$\alpha$ radiation transfer within the inflow-outflow geometry, based on earlier zoom-in cosmological modeling involving radiation transfer and magnetic forces. Adopting geometry that includes ongoing disk and spherical accretion, and formation of a biconical outflow funnel, we obtain the formation of a dense radiatively driven expanding shell. The Ly$\alpha$ transfer is performed using a Monte Carlo algorithm, accounting for the destruction of Ly$\alpha$ photons and the emergence of two-photon emission. We find that a substantial fraction of Ly$\alpha$ photons can escape through the funnel and calculate the line profiles, the line peak velocity shift, asymmetry, and cuspiness, by varying basic model parameters. The escaping Ly$\alpha$ emission is anisotropic and sensitive to the overall inflow-outflow geometry. The escaping fraction of Ly$\alpha$ radiation exceeds 95% from a $z=10$ pre-SMBH object -- in principle detectable by the JWST NIRSpec in the MOS mode, during $\sim 10^4$ seconds for a $10\sigma$ signal-to-noise ratio. Moreover, comparisons with line shapes from high-$z$ galaxies and quasars allow us to separate them from pre-SMBH objects based on the line shape: the pre-SMBH lines show a profound asymmetry and extended red tail.

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arXiv2024

Jetted Seyfert Galaxies at z = 0: Simulating Feedback Effects on Galactic Morphology and Beyond

We use high-resolution cosmological zoom-in simulations to model feedback from Seyfert-type supermassive black hole (SMBH) jets onto galaxies with identical dark matter (DM) halos of log(M/M$_\odot$) ~ 11.8. The low mass, ~10$^6$ M$_\odot$, seed SMBHs, have been introduced when the parent DM halos have reached log(M/M$_\odot$) ~ 11, at z ~ 3.7. In a controlled experiment, we vary only the efficiency of the SMBH accretion and focus on galaxies and their immediate environment properties. Our results show that the AGN jet feedback has a substantial effect on the basic properties of Seyfert-type galaxies, such as morphology, gas fraction and distribution, star formation rate and distribution, bulge-to-disk ratio, DM halo baryon fraction, and properties of circumgalactic medium (CGM) and beyond. These have been compared to a galaxy with supernovae only feedback. We focus on the energy deposition by the jet in the ISM and IGM, and follow the expansion of the multiple jet cocoons to 2 Mpc. We find that the jet-ISM interaction gradually pushes the star formation to larger radii with increasing accretion efficiency, which results in increased mass of the outer stellar disk, which is best fit as a double-exponential disk. Furthermore, we compare our galaxies and their properties with the observed nearby Seyfert galaxies, including the scaling relations, and find a close agreement, although statistical analysis of observed Seyferts is currently missing. In a forthcoming paper, we focus on evolution of these objects at z<10 and study the effect of the SMBH seeding redshift on galaxy evolution.

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arXiv2024

Direct Collapse Accretion Disks Within Dark Matter Halos: Saturation of the Magnetorotational Instability and the Field Expulsion

We have used high-resolution zoom-in simulations of direct collapse to supermassive black hole (SMBH) seeds within dark mater (DM) halos in the presence of magnetic fields generated during the collapse, down to $10^{-5}$ pc or 2 AU. We confirm an efficient amplification of magnetic field during collapse, the formation of a geometrically thick self-gravitating accretion disk inside 0.1 pc, and damping of fragmentation in the disk by the field. This disk differs profoundly from SMBH accretion disks. We find the following: (1) The accretion disk is subject to the magnetorotational instability which further amplifies the field to near equipartition. No artificial seeding of the disk field has been used. (2) The equipartition toroidal field changes its polarity in the midplane. (3) The nonlinear Parker instability develops, accompanied by the vertical buckling of the field lines, which injects material above the disk, leading to an increase in the disk scale height; (4) With the Coriolis force producing a coherent helicity above the disk, vertical poloidal field has been generated and amplified. (5) We estimate that the associated outflow will be most probably squashed by accretion. The resulting configuration consists of a magnetized disk with $\beta > 0.1$ and its magnetosphere with $\beta << 1$, where $\beta = P_{\rm th}/P_{\rm B}$ is the ratio of thermal to magnetic energy density. (6) The disk is highly variable, due to feeding by variable accretion flow, and strong vortical motions are present. (7) Finally, the negative gradient of the total vertical stress drives an equatorial outflow sandwiched by an inward accretion flow.

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arXiv2024

Metal-Poor Stars in the MW Disk: Resonant Cooling of Vertical Oscillations of Halo Stars in Barred Galaxies

Using numerical simulations of barred disk galaxy embedded in nonspinning and spinning dark matter (DM) halos, we present a novel mechanism of `cooling' the vertical oscillations of DM particles, which acquire the disk kinematics. The underlying mechanism consists of resonant interactions between halo particles and the stellar bar, facilitated by chaotic phase space of the system. The cooling mechanism acts both on dynamical and secular timescales, from $\sim 0.5$\,Gyr to few Gyr. The stellar bar acts to absorb kinetic energy of the vertical motions. Using Milky Way-type stellar halo, we estimate the population of metal-poor disk stars trapped by the MW disk and analyze its kinematics. We find that population of metal-poor MW disk stars with $|z|\ltorder 3$\,kpc detected by the Gaia DR3 and other surveys can have their origin in the stellar halo. The cooled population also migrates radially outwards by exchanging energy and angular momentum with the spinning bar, and prograde-moving stars have a different distribution from the retrograde ones. Next, we have calculated the ratio of the prograde-to-retrograde orbits of the cooled population and found that this ratio varies radially, with the fast-spinning stellar halo resulting in the shallower radial increase of this ratio outside of the corotation. The nonspinning stellar halo shows a monotonic increase of this ratio with radius outside the corotation. Together with analyzed radial migration of these halo stars, the cooling phenomenon of halo metal-poor stars can explain their current disk population, and has corollaries for chemical evolution of disk galaxies in general.

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arXiv2023

Evolution of Stellar Bars in Spinning Dark Matter Halos and Stellar Bulges

We use high-resolution numerical simulations to follow the barred disk evolution in a suite of models with progressively more massive stellar bulges, with bulge-to-total (disk$+$bulge) mass ratios of $B/T\sim 0-0.25$, embedded in dark matter (DM) halos with the spin $λ\sim 0 - 0.09$. We focus on models with a sequence of initial rotational support for bulges, and analyze their spinup and spindown. We find that (1) the presence of a bulge affects the evolution of stellar bars, i.e., the timescale of bar instability, bar pattern speed and its decay, and the vertical buckling instability. The bar strength is nearly independent of $B/T$ in halos with spin $λ= 0$, and is suppressed by a factor $\sim 2$ for halos with $λ= 0.09$; (2) The main effect of the bulge is the destruction of the harmonic core which affects the buckling; (3) The bulge plays a minor role in the exchange of angular momentum between the barred disk and the DM halo, during its spinup and spindown; (4) Most interestingly, the buckling process triggers different response above/below the disk midplane, which anti-correlates with the bulge mass; (5) In spinning halos, the buckling process has a prolonged amplitude tail, extending by few Gyr, as verified by measuring distortions in the Laplace plane; (6) Furthermore, as verified by orbital spectral analysis, the bulge gains its spin from the bar mainly via the inner Lindblad resonance, while losing it via a number of resonances lying between the outer and inner Lindblad resonance.

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arXiv2023

Dissecting Cosmological Filaments at High Redshifts: Emergence of Spaghetti-type Flow Inside DM Haloes

We use high-resolution zoom-in simulations to study the fueling of the central galaxies by gas accretion from cosmological filaments at high redshifts, z>=2. Their parent haloes with similar DM masses of log(M_vir/M})~11.65, have been chosen at z=6, 4, and 2, in high/low overdensity environments, with the goal of comparing evolution within similar M at different z, under dual action of cosmological accretion and galactic outflows -- forming the circumgalactic medium (CGM). We focus on the filamentary and diffuse gas accretion within few virial radii, R_vir, down to the central galaxy. Using a hybrid d-web/entropy method we have mapped the gaseous filaments, and invoking particle kinematics allowed us to separate inflows from outflows, thus resolving thermodynamic and kinematic signatures of the CGM. We find that (1) The CGM is multiphase and not in thermodynamic or dynamic equilibrium; (2) accretion rates via individual filaments display a lower accretion rate and densities at lower redshifts. The inflow velocities along the filaments decrease with redshift, z~ 6-2, from 200-30 kms^-1 by a factor of 2; (3) Temperature within the filaments increases inside R_vir, faster at lower redshifts, in tandem with decrease in the accretion rate; (4) The filaments show a complex structure along their spines: a core radial flow surrounded by a lower density envelope. The core exhibits an elevated density and lower temperature, with no obvious metallicity gradient in the filament cross sections. It also tends to separate the filament into different infall velocity regions and density cores, thus producing a spaghetti-type flow; (6) Inside the inner ~ 30\,h^-1 kpc, the filaments develop the Kelvin-Helmholtz instability which ablates and dissolves them, and triggers turbulence along the filament spine; (7) Finally, the galactic outflows affect mostly the inner ~ 0.5R_vir~ 100 h^-1 kpc of the CGM.

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arXiv2023

Direct Collapse to Precursors of Supermassive Black Hole Seeds:Radiation-feedback-generated Outflows

We use high-resolution zoom-in cosmological simulations to model outflow triggered by radiation and thermal drivers around the central mass accumulation during direct collapse within the dark matter (DM) halo. The maximal resolution is $1.3\times 10^{-5}$\,pc, and no restrictions are put on the geometry of the inflow/outflow. The central mass is considered {\it prior} to the formation of the supermassive black hole seed at a redshift of $z\sim 15.9$, and can constitute either a supermassive star (SMS) of $\sim 10^5\,M_\odot$ surrounded by a growing accretion disk or a self-gravitating disk. The radiation transfer is modeled using the ray-tracing algorithm. Due to the high accretion rate of $\sim 1\,M_\odot\,{\rm yr^{-1}}$ determined by the DM halo, accretion is mildly supercritical, resulting in mildly super-critical luminosity which has only a limited effect on the accretion rate, with the duty cycle of $\sim 0.9$. We observe a fast development of hot cavities, which quickly extend into polar funnels and expand dense shells. Within the funnels, fast winds, $\sim 10^3\,{\rm km\,s^{-1}}$, are mass-loaded by the accreting gas. We follow the expanding shells to $\sim 1$\,pc, when the shell velocity remains substantially, $\sim 5$ times, above the escape speed. The ionization cones formed by the central UV/X-ray completely ionize the cavities. Extrapolating the outflow properties shows that the halo material outside the shell will have difficulty stopping it. We therefore conclude that the expanding wind-driven shell will break out of the central parsec and will reach the halo virial radius. Finally, the anisotropic accretion flow on sub-parsec scales will attenuate the UV/soft X-rays on the H$_2$. Hence, the formation of funnels and powerful outflows around, e.g., SMS, can have interesting observational corollaries.

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arXiv2023

Stellar Bars in Spinning Halos: Delayed Buckling and Absence of Slowdown

We use high resolution numerical simulations in order to analyze the stellar bar evolution in spinning dark matter (DM) halos. Previous works have shown that the halo spin has a substantial effect on the bar evolution and can lead to bar dissolution following the vertical buckling instability. Here, we invoke the DM spin sequence, $λ=0-0.09$, and study the effect of DM density along this $λ$-sequence by varying the compactness of DM halo. We find that (1) varying the DM density has a profound effect on the stellar bar evolution along the $λ$-sequence, namely, on its amplitude, pattern speed, buckling time, etc.; (2) For $λ\gtrsim 0.04$, the buckling instability has been delayed progressively, and does not occur when the bar has reached its maximal strength; (3) Instead, stellar bars remain near maximal strength, and their amplitude plateau stage extends over $\sim 1-7$ Gyr, terminating with the buckling instability; (4) Although stellar bars remain strong during the plateau, their pattern speed stays nearly constant. The reason for this unusual behavior of stellar bars follows from the highly reduced gravitational torques which they experience due to the DM bar being aligned with the stellar bar. The performed orbital analysis shows that the delayed buckling results from a slow evolution of stellar oscillations along the bar major and vertical axes -- thus postponing the action of the vertical 2:1 resonance which pumps the rotational energy into vertical motions; (5) Peanut/boxy shaped bulges form at the beginning of the plateau and grow with time; (6) Strong stellar bars in spinning halos can avoid fast braking, resolving the long standing discrepancy between observations and $N$-body simulations. This behavior of stellar bars along the $λ$- and DM density-sequences, reveals a wealth of stellar bar properties which require additional study.

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arXiv2023

The Origin of Buckling Instability in Galactic Bars: Searching for the Scapegoat

The buckling process in stellar bars is full of unsolved issues. We analyze the origin of the buckling instability in stellar bars using high-resolution N-body simulations. Previous studies have promoted the nonresonant firehose instability to be responsible for the vertical buckling. We have analyzed the buckling process in terms of the resonant excitation of stellar orbits in the bar, which pumps energy into vertical oscillations. We find that (1) the buckling is associated with an abrupt increase in the central mass concentration and triggers velocities along the bar and along its rotation axis. The velocity field projected on one of the main axes forms circulation cells and increases vorticity, which are absent in firehose instability; (2) The bending amplitude is nonlinear when measured by isodensity contours or curvature of the Laplace plane, which has a substantial effect on the stellar motions; (3) In the linear description, the planar and vertical 2:1 resonances appear only with the buckling and quickly reach the overlapping phase, thus supporting the energy transfer; (4) Using nonlinear orbit analysis, we analyze the stellar oscillations along the bar and along the rotation axis and find that stars cross the vertical 2:1 resonance simultaneously with the buckling. The overlapping planar and vertical 2:1 resonances trapping more than 25% of the bar particles provide the 'smoking gun' pointing to a close relationship between the bending of stellar orbits and the resonant action -- these particles provide the necessary ingredient assuring the cohesive response in the growing vertical asymmetry. We conclude that resonant excitation is important in triggering the buckling instability, and the contribution from the firehose instability should be reevaluated. Finally, we discuss some observational implications of buckling.

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arXiv2022

Modeling Evolution of Galactic Bars at Cosmic Dawn

We study evolution of galactic bars using suite of very high-resolution zoom-in cosmological simulations of galaxies at z ~ 9-2. Our models were chosen to lie within similar mass DM halos, log(Mvir/Mo) ~ 11.65 +- 0.05, at z=6, 4, and 2, in high and low overdensity environments. We apply two galactic wind feedback mechanisms for each model. All galaxies develop sub-kpc stellar bars differing in their properties. We find that (1) The high-z bars form in response to various perturbations: mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) These bars account for large-mass fraction of galaxies; (3) Bars display large corotation-to-bar-size ratios, and are weaker compared to their low-redshift counterparts, by measuring their Fourier amplitudes, and are very gas-rich; (4) Their pattern speed does not exhibit monotonic decline with time due to braking against DM, as at low z; (5) Bar properties, including their stellar population (SFRs and metal enrichment) depend sensitively on prevailing feedback; (6) Finally, we find that bars can weaken substantially during cosmological evolution, becoming weak oval distortions -- hence bars are destroyed and reformed multiple times unlike their low-z counterparts. In all cases, bars in our simulations have been triggered by interactions. In summary, stellar bars appear to be not only contemporary phenomenon, but based on increased frequency of mergers, flybys and the strength of cold accretion flows at high z, we expect them to be ubiquitous at redshifts > 2 -- the epoch of rapid galaxy growth and larger stellar dispersion velocities.

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arXiv2021

Emergence of Galactic Morphologies at Cosmic Dawn: Input from Numerical Modeling

We employ high-resolution zoom-in cosmological simulations to analyze the emerging morphology of galaxies in dark matter halos at redshifts z > 2. We choose DM halos of similar masses of log (Mvir/Mo) ~11.65 +- 0.05 at the target redshifts of z_f = 6, 4 and 2. The rationale for this choice, among others, allows us to analyze how the different growth rate in these halos propagates down to galaxy scales. Halos were embedded in high or low overdensity regions, and two different versions of a galactic wind feedback have been employed. Our main results are: (1) Although our galaxies evolve in different epochs, their global parameters remain within a narrow range. Their morphology, kinematics and stellar populations differ substantially, yet all of them host sub-kpc stellar bars; (2) The SFRs appear higher for larger z_f, in tandem with their energy and momentum feedback; (3) The stellar kinematics allowed separation of bulge from the stellar spheroid. The existence of disk-like bulges has been revealed based on stellar surface density and photometry, but displayed a mixed disk-like and classical bulges based on their kinematics. The bulge-to-total mass ratios appear independent of the last merger time for all z_f. The stellar spheroid-to-total mass ratios of these galaxies lie in the range of ~0.5-0.8; (4) The synthetic redshifted, pixelized and PSF-degraded JWST images allow to detect stellar disks at all z_f. Some bars disappear in degraded images, but others remain visible; (5) Based on the kinematic decomposition, for stellar disks separated from bulges and spheroids. we observe that rotational support in disks depends on the feedback type, but increases with decreasing z_f; (6) Finally, the ALMA images detect disks at all z_f, but their spiral structure is only detectable in z_f=2 galaxies.

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arXiv2020

Direct collapse to supermassive black hole seeds: the critical conditions for suppression of $\rm H_2$ cooling

Observations of high-redshift quasars imply the presence of supermassive black holes already at z~ 7.5. An appealing and promising pathway to their formation is the direct collapse scenario of a primordial gas in atomic-cooling haloes at z ~ 10 - 20, when the $\rm H_2$ formation is inhibited by a strong background radiation field, whose intensity exceeds a critical value, $J_{\rm crit}$. To estimate $J_{\rm crit}$, typically, studies have assumed idealized spectra, with a fixed ratio of $\rm H_{2}$ photo-dissociation rate $k_{\rm H_2}$ to the $\rm H^-$ photo-detachment rate $k_{\rm H^-}$. This assumption, however, could be too narrow in scope as the nature of the background radiation field is not known precisely. In this work we argue that the critical condition for suppressing the $\rm H_2$ cooling in the collapsing gas could be described in a more general way by a combination of $k_{\rm H_2}$ and $k_{\rm H^-}$ parameters. By performing a series of cosmological zoom-in simulations with an encompassing set of $k_{\rm H_2}$ and $k_{\rm H^-}$, we examine the gas flow by following evolution of basic parameters of the accretion flow. We test under what conditions the gas evolution is dominated by $\rm H_{2}$ and/or atomic cooling. We confirm the existence of a critical curve in the $k_{\rm H_2}-k_{\rm H^-}$ plane, and provide an analytical fit to it. This curve depends on the conditions in the direct collapse, and reveals domains where the atomic cooling dominates over the molecular cooling. Furthermore, we have considered the effect of $\rm H_{2}$ self-shielding on the critical curve, by adopting three methods for the effective column density approximation in $\rm H_{2}$. We find that the estimate of the characteristic length-scale for shielding can be improved by using $λ_{\rm Jeans25}$, which is 0.25 times that of the local Jeans length.

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arXiv2019

Stellar Bars in Counter-Rotating Dark Matter Halos: The Role of Halo Orbit Reversals

Disk galaxies can exchange angular momentum and baryons with their host dark matter (DM) halos. These halos possess internal spin, `lambda', which is insignificant rotationally but does affect interactions between the baryonic and DM components. While statistics of prograde and retrograde spinning halos in galaxies is not available at present, the existence of such halos is important for galaxy evolution. In the previous works, we analyzed dynamical and secular evolution of stellar bars in prograde spinning halos and the DM response to the bar perturbation, and found that it is modified by the resonant interactions between the bar and the DM halo orbits. In the present work, we follow the evolution of stellar bars in retrograde halos. We find, that this evolution differs substantially from evolution in rigid unresponsive halos, discussed in the literature. First, we confirm that the bar instability is delayed progressively along the retrograde `lambda' sequence. Second, the bar evolution in the retrograde halos differs also from that in the prograde halos, in that the bars continue to grow substantially over the simulation time of 10 Gyr. The DM response is also substantially weaker compared to this response in the prograde halos. Third, using orbital spectral analysis of the DM orbital structure, we find a phenomenon we call the orbit reversal --- when retrograde DM orbits interact with the stellar bar, reverse their streaming and precession, and become prograde. This process dominates the inner halo region adjacent to the bar and allows these orbits to be trapped by the bar, thus increasing efficiency of angular momentum transfer by the Inner Lindblad Resonance. We demonstrate this reversal process explicitly in a number of examples.

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arXiv2019

Dark Matter Bars in Spinning Halos

We study nonlinear response of spinning dark matter (DM) halos to dynamic and secular evolution of stellar bars in the embedded galactic disks, using high-resolution numerical simulations. For a sequence of halos with the cosmological spin parameter lambda=0-0.09, and a representative angular momentum distribution, we analyze evolution of induced DM bars amplitude and quantify parameters of the response as well as trapping of DM orbits and angular momentum transfer by the main and secondary resonances. We find that (1) maximal amplitude of DM bars depends strongly on `lambda', while that of the stellar bars is indifferent to `lambda'; (2) Efficiency of resonance trapping of DM orbits by the bar increases with `lambda', and so is the mass and the volume of DM bars; (3) Contribution of resonance transfer of angular momentum to the DM halo increases with `lambda', and for larger spin, the DM halo `talks' to itself, by moving the angular momentum to larger radii --- this process is maintained by resonances; (4) Prograde and retrograde DM orbits play different roles in angular momentum transfer. The `active' part of the halo extends well beyond the bar region, up to few times the bar length in equatorial plane and away from this plane. (5) We model evolution of diskless DM halos and halos with frozen disks, and found them to be perfectly stable to any Fourier modes. Finally, further studies adopting a range of mass and specific angular momentum distributions of the DM halo will generalize the dependence of DM response on the halo spin and important implications for direct detection of DM and that of the associated stellar tracers, such as streamers.

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arXiv2019

Lyman alpha Properties of Simulated Galaxies in Overdense Regions: Effects of Galactic Winds at z > 6

We perform Monte-Carlo radiative transfer calculations to model the Lyman alpha properties of galaxies in high-resolution, zoom-in cosmological simulations at z ~ 6.6. The simulations include both constrained and unconstrained runs, representing respectively a highly overdense region and an average field. Different galactic wind models are used in the simulations in order to investigate the effects of these winds on the apparent Ly alpha properties of galaxies. We find that, for models including galactic winds, the Ly alpha properties of massive galaxies residing in the overdense region match well recent observations of luminous Ly alpha emitters (LAEs) at z ~ 6-7, in terms of apparent Ly alpha luminosity, Ly alpha line width and Ly alpha equivalent width distributions. Without winds, the same galaxies appear less Ly alpha bright as a result of both differences in the line profile emerging from galaxies themselves, and, in the distributions of neutral gas in the circumgalactic (CGM) and intergalactic medium (IGM). We also study the relations between apparent Ly alpha luminosity and various galaxy properties: stellar mass, star formation rate (SFR) and host halo mass. At fixed halo mass, the apparent Ly alpha luminosity of galaxies appears to depend on the large-scale environment while this is no longer true for galaxies at a given stellar mass or SFR. We provide simple linear fits to these relations that can be used for quickly constructing mock LAE samples from N-body simulations. Our results suggest that the observed luminous LAEs at z ~ 6.6 are hosted by ~10^{12} h^{-1} Mo, dark matter haloes, residing in large, overdense ionized regions.

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