Vicinity Of Galaxies Research Articles

The nature of dark matter and a comprehensive solution

Dark matter has been postulated to explain the excess of gravitation in relation to Newtonian physics in the vicinity of galaxies. At present, two theories are under discussion: the assumption that undetected heavy but weakly interacting particles exist, and a modification of Newtonian gravity (MOND). Both theories are unsatisfying because they can only explain certain cases and conflict with others. Recent extended observations have now given a spectacular indication of the nature of dark matter. These observations show an identical spatial distribution of dark matter on the one hand and photons on the other hand. In the following, we will check the possibility of the solution that photons are in fact the particles that explain the phenomenon.

Gas infall and radial transport in cosmological simulations of milky way-mass discs

ABSTRACT Observations indicate that a continuous supply of gas is needed to maintain observed star formation rates in large, discy galaxies. To fuel star formation, gas must reach the inner regions of such galaxies. Despite its crucial importance for galaxy evolution, how and where gas joins galaxies is poorly constrained observationally and rarely explored in fully cosmological simulations. To investigate gas accretion in the vicinity of galaxies at low redshift, we analyse the FIRE-2 cosmological zoom-in simulations for 4 Milky Way mass galaxies (Mhalo ∼ 1012M⊙), focusing on simulations with cosmic ray physics. We find that at z ∼ 0, gas approaches the disc with angular momentum similar to the gaseous disc edge and low radial velocities, piling-up near the edge and settling into full rotational support. Accreting gas moves predominately parallel to the disc and joins largely in the outskirts. Immediately prior to joining the disc, trajectories briefly become more vertical on average. Within the disc, gas motion is complex, being dominated by spiral arm induced oscillations and feedback. However, time and azimuthal averages show slow net radial infall with transport speeds of 1–3 km s−1 and net mass fluxes through the disc of ∼M⊙ yr−1, comparable to the galaxies’ star formation rates and decreasing towards galactic centre as gas is sunk into star formation. These rates are slightly higher in simulations without cosmic rays (1–7 km s−1, ∼4–5 M⊙ yr−1). We find overall consistency of our results with observational constraints and discuss prospects of future observations of gas flows in and around galaxies.

PHOTOMETRIC RESEARCH OF SEYFERT GALAXIES MRK 766, MRK 6, MRK 1040, MRK 1513

The paper presents the results of the photometric observations of the Seyfert galaxies from theMarkarian list: MRK 766, MRK 6, MRK 1040, MRK 1513. The observations were carried out on “the Eastern“ 1-meter telescope, located at the Tien-Shan Astronomical Observatory of the Fesenkov Astrophysical Institute. Theobservational data were processed using the MaximDL6 software package. The brightness was estimated bydifferential photometry, using standard stars in the vicinity of galaxies. This paper presents the light curves of thegalaxies: Mrk 766, Mrk 6, Mrk 1040, Mrk 1513. It has been noted, that in Mrk 766, there is a tendency to a gradualweakening of the brightness in the three filters. Photometric changes of the galaxy Mrk 6 during 2016-2019 occurredsynchronously in all three filters. The weakening of its brightness began in 2017and by 2019 it reached ~ 0m.9.During the investigation period, irregular brightness fluctuations were registered in galaxies Mrk 1040 and Mrk 1513with amplitudes of ~ 1m 0 and 0m.8, respectively.

SlicerAstro: A 3-D interactive visual analytics tool for HI data

Abstract SKA precursors are capable of detecting hundreds of galaxies in HI in a single 12 h pointing. In deeper surveys one will probe more easily faint HI structures, typically located in the vicinity of galaxies, such as tails, filaments, and extraplanar gas. The importance of interactive visualization in data exploration has been demonstrated by the wide use of tools (e.g. Karma , Casaviewer , VISIONS ) that help users to receive immediate feedback when manipulating the data. We have developed SlicerAstro , a 3-D interactive viewer with new analysis capabilities, based on traditional 2-D input/output hardware. These capabilities enhance the data inspection, allowing faster analysis of complex sources than with traditional tools. SlicerAstro is an open-source extension of 3DSlicer , a multi-platform open source software package for visualization and medical image processing. We demonstrate the capabilities of the current stable binary release of SlicerAstro , which offers the following features: (i) handling of FITS files and astronomical coordinate systems; (ii) coupled 2-D/3-D visualization; (iii) interactive filtering; (iv) interactive 3-D masking; (v) and interactive 3-D modeling. In addition, SlicerAstro has been designed with a strong, stable and modular C++ core, and its classes are also accessible via Python scripting, allowing great flexibility for user-customized visualization and analysis tasks.

Finding faint HI structure in and around galaxies: Scraping the barrel

Soon to be operational HI survey instruments such as APERTIF and ASKAP will produce large datasets. These surveys will provide information about the HI in and around hundreds of galaxies with a typical signal-to-noise ratio of $\sim$ 10 in the inner regions and $\sim$ 1 in the outer regions. In addition, such surveys will make it possible to probe faint HI structures, typically located in the vicinity of galaxies, such as extra-planar-gas, tails and filaments. These structures are crucial for understanding galaxy evolution, particularly when they are studied in relation to the local environment. Our aim is to find optimized kernels for the discovery of faint and morphologically complex HI structures. Therefore, using HI data from a variety of galaxies, we explore state-of-the-art filtering algorithms. We show that the intensity-driven gradient filter, due to its adaptive characteristics, is the optimal choice. In fact, this filter requires only minimal tuning of the input parameters to enhance the signal-to-noise ratio of faint components. In addition, it does not degrade the resolution of the high signal-to-noise component of a source. The filtering process must be fast and be embedded in an interactive visualization tool in order to support fast inspection of a large number of sources. To achieve such interactive exploration, we implemented a multi-core CPU (OpenMP) and a GPU (OpenGL) version of this filter in a 3D visualization environment ($\tt{SlicerAstro}$).

First-Order Light Deflection by Einstein-Strauss Vacuole Method

We resolve here an outstanding problem plaguing conformal gravity in its role in making consistent astrophysical predictions. Though its static spherically symmetric solution incorporates all the successes of Schwarzschild gravity, the fit to observed galactic rotation curves requires γ>0, while the observed increase in the Schwarzschild light deflection by galaxies appears to demand γ<0. Here we show that, contrary to common knowledge, there is an increase in the Schwarzschild deflection angle in the vicinity of galaxies due purely to the effect of γ>0, when the idea of the Einstein-Strauss vacuole model is employed. With the inconsistency now out of the way, conformal gravity should be regarded as a good theory explaining light deflection by galaxies.

The unchanging circumgalactic medium over the past 11 billion years

This paper examines how the circumgalactic medium (CGM) evolves as a function of time by comparing results from different absorption-line surveys that have been conducted in the vicinities of galaxies at different redshifts. Despite very different star formation properties of the galaxies considered in these separate studies and different intergalactic radiation fields at redshifts between z~2.2 and z~0, I show that both the spatial extent and mean absorption equivalent width of the CGM around galaxies of comparable mass have changed little over this cosmic time interval.

Are strong MgII Absorbers Signatures of Outflows?

Low-ionization transitions such as the Mg iiλ2796/2803 doublet trace cold gas in the vicinity of galaxies. The exact physical origin of this cold gas traced by QSO absorption lines is debated. Does it trace gas in disks, halos, merger tails, and even in outflows? Recent studies of strong starbursts and post-starbursts at intermediate redshifts have shown that Mg ii are seen in outflows, with blue-shifted velocities ∼500 − 1500km s −1 . Strong intervening Mg ii absorbers (with equivalent width W r λ2796 > 1A) may be tracing the denser and colder gas of starburst-driven outflows. Indeed, based on Mg ii statistics, our clustering analysis has shown that the host-galaxy mass is anti-correlated with the line-of-sight velocity Δ v (as measured from W r λ2796 ). If Mg ii absorbers were virialized in galaxy halos, a positive M h – W r correlation would have been observed. Our result thus shows that the Mg ii clouds are not virialized in the gaseous halos of the host-galaxies.

The SINFONI Mg ii Program for Line Emitters (SIMPLE): Discovering Starbursts near QSO Sight Lines

Low-ionization transitions such as the Mg II λ2796/2803 doublet trace cold gas in the vicinity of galaxies. It is not clear whether this gas is part of the interstellar medium of large protodisks, part of dwarfs, or part of entrained material in supernova-driven outflows. Studies based on Mg II statistics, e.g., stacked images and clustering analysis, have invoked starburst-driven outflows where Mg II absorbers are tracing the denser and colder gas of the outflow. A consequence of the outflow scenario is that the strongest absorbers ought to be associated with starbursts. We use the near-IR integral field spectrograph SINFONI to test whether starbursts are found around z ~ 1 Mg II absorbers. For 67% (14 out of 21) of the absorbers with rest-frame equivalent width W > 2 A, we do detect Hα in emission within ±200 km s-1 of the predicted wavelength based on the Mg II redshift, and with impact parameter ranging from 0.2'' to 6.7'' from the QSO. The star formation rate (SFR) inferred from Hα is 1-20 M☉ yr-1, i.e., showing a level of star formation larger than in M82 by a factor of >4 on average. Our flux limit (3 σ) is fHα 95%) for a correlation between SFR and equivalent width, indicating a physical connection between starburst phenomena and gas seen in absorption. In the cases where we can extract the velocity field, the host galaxies of Mg II absorbers with W > 2 A reside in halos with mean mass log Mh(M☉) ~ 11.2, in good agreement with clustering measurements.

Lyman Break Galaxies and the Lyα Forest

We use hydrodynamic cosmological simulations to predict correlations between Lyα forest absorption and the galaxy distribution at redshift z ≈ 3. The probability distribution function (PDF) of Lyα flux decrements shifts systematically toward higher values in the vicinity of galaxies, reflecting the overdense environments in which these galaxies reside. The predicted signal remains strong in spectra smoothed over 50-200 km s-1, allowing tests with moderate-resolution quasar spectra. The strong bias of high-redshift galaxies toward high-density regions imprints a clear signature on the flux PDF, but the predictions are not sensitive to galaxy baryon mass or star formation rate, and they are similar for galaxies and dark matter halos. The dependence of the flux PDF on galaxy proximity is sensitive to redshift determination errors, with rms errors of 150-300 km s-1 substantially weakening the predicted trends. On larger scales, the mean galaxy overdensity in a cube of 5 or 10 h-1 Mpc (comoving) is strongly correlated with the mean Lyα flux decrement on a line of sight through the cube center. The slope of the correlation is ~3 times steeper for galaxies than for dark matter as a result of galaxy bias. The predicted large-scale correlation is in qualitative agreement with recently reported observational results. However, observations also show a drop in the average absorption in the immediate vicinity of galaxies, which our models do not predict even if we allow the galaxies or active galactic nuclei within them to be ionizing sources. This decreased absorption could be a signature of galaxy feedback on the surrounding intergalactic medium, perhaps via galactic winds. We find that a simplified wind model that eliminates neutral hydrogen in spheres around the galaxies can marginally explain the data. However, because peculiar velocities allow gas at large distances to produce saturated absorption at the galaxy redshift, these winds (or any other feedback mechanism) must extend to comoving radii of ~1.5 h-1 Mpc to reproduce the observations. We also discuss the possibility that extended Lyα emission from the target galaxies fills in the expected Lyα forest absorption at small angular separations.

The Multiphase Intracluster Medium in Galaxy Groups Probed by the Ly Forest

The case is made that the intracluster medium (ICM) in present-day spiral-rich galaxy groups probably has undergone a much slower evolution than that in elliptical-rich groups and clusters. The environments of protoclusters and protogroups at z > 2 are likely similar to spiral-rich group environments at lower redshift. Therefore, like the ICM in spiral-rich groups today, the ICM in protogroups and protoclusters at z > 2 is predicted to be significantly multiphased. The QSO Lyα forest in the vicinity of galaxies is an effective probe of the ICM at a wide range of redshift. Two recent observations of Lyα absorption around galaxies by Adelberger et al. and by Pascarelle et al. are reconciled, and it is shown that observations support the multiphase ICM scenario. Galaxy redshifts must be very accurate for such studies to succeed. This scenario can also explain the lower metallicity and lower hot gas fraction in groups.

Cosmological Implications of the Planck Aether Model for a Unified Field Theory

Abstract In the previously proposed Planck aether model of a unified theory, the vacuum ground state consists of a dense assembly of positive and negative Planck masses obeying an exactly nonrelativistic law of motion. The Planck aether is superfluid, and it can without expenditure of energy form a tangle of quantized vortex filamants permitting the transmission of two types of waves: One associated with a symmetric displacement of the vortex lattice leading to gravitational waves, and one associated with an antisymmetric displacement leading to electromagnetic waves. Dirac spinors are explained in this model as excitons made up from positive and negative energy resonances of the vortex lattice. Because the number of positive and negative Planck masses is assumed to be equal, the cosmological constant is equal to zero. With the Dirac spinors formed as bound states from the Planck aether, the sum of the positive kinetic energy and negative gravitational energy must remain exactly equal to zero, resulting in ß = l as the exact value for the cosmological mass parameter. To make up for the unobserved missing mass, estimated to be about 10 times larger than the baryonic mass, it is conjectured that this mass consists of rotons, which in the superfluid Planck aether would come from the cut-off of the energy spectrum near the Planck energy. Because of their unusual dispersion relation, rotons possess a large momentum, even if their velocity vanishes. They are, for this reason, a promising candidate for the nonbaryonic dark matter, combining properties of hot and cold dark matter. The critical value Ω = 1 requires that the number density of the rotons is equal to nr ≃ 2 x 10-25 cm-3 . This value corresponds to an average distance of separation between the rotons of the order nr -1/3 ≃ 6000 km. The small number of rotons per unit volume combined with their weak gravitational coupling constant would make it difficult to detect them directly, but the gravitational field these roton masses generate in the vicinity of galaxies could explain the observed flat rotation curves of disc galaxies. Finally, because the gravitational waves have a cut-off at the vortex lattice scale at 1015 -1016 GeV, there can be no singularity in the course of a gravitational collapse, as it happens for solutions of Einstein's gravitational field equations. A generalization of Einstein's gravitational field Lagrangian, taking into account the existence of a smallest wave length, rather predicts a conversion of all mass into electromagnetic (or gravitational) radiation in approaching the singularity. The predicted conversion of mass into radiation in the course of gravitational collapse may provide an explanation for the large energy release of quasars.

Forbidden O II and O III emission 29 arcsec from a QSO absorption-line region

QSO 0453-423 (z QSO = 2.66) was imaged with a narrow-band filter centered on forbidden O II 3727 A at the redshift of a strong intervening absorption complex (z abs = 0.7256). Comparison with a broadband exposure revealed a small nonstellar object 29 arcsec (140/h kpc, H0 = 100 h km/s Mpc) from the QSO line of sight with total flux 1.8 + or - 0.4 x 10 to the -16th ergs/sq cm s in one emission line. Spectroscopic follow-up confirmed the forbidden O II emission and detected forbidden O III 5007 A. It is suggested that extended gas in the vicinity of galaxies produces the QSO absorption lines. 24 references.

Material in the Vicinity of Galaxies

It is increasingly certain that the principal concentrations of neutral hydrogen gas are in spiral and irregular galaxies. The intergalactic medium (IGM) appears to be either a near-void with <ρ> ≲ 1.5 × 10−11 cm−3 from the 3C9 measurements of Gunn and Peterson (1965) or at best a hot, highly ionized gas with very little neutral hydrogen present (Field and Perrenod, 1977). In clusters of galaxies, the intracluster medium (ICM) also appears to be mostly hot and ionized, as suggested by X-ray observations (Jones et al. 1977) and by observations of head-tail radio galaxies. Even if most of the IGM and ICM were ionized, however, one might imagine that there exist high-density concentrations where the cooling rate is sufficient to allow recombination, particularly in the vicinity of galaxies. One might expect such condensations to be revealed either by 21-cm emission, or by absorption against a bright background continuum source.

Single radio sources in the vicinity of galaxies

Single radio sources in the vicinity of galaxies