Self-consistent gas and stellar dynamics of disk galaxies: A problem of dark mass
A. V. Khoperskov, S. S. Khrapov
备注：
7 pages 6 figures, conference: 'Progress in Study of Astrophysical Disks: Collective and Stochastic Phenomena and Computational Tools'
发表信息：
Astrophysics and Space Science Library, 2006, v.337, p.337-344 (In: Astrophysical Disks / Alexei M. Fridman, et al (eds.). Publ. by Springer, Dordrecht, The Netherlands, 2006)
We present results of numerical modeling made for the galactic stellar and stellar-gas disk embedded in the spherical halo and bulge. The stellar disk is simulated by N-body system, the equations of hydrodynamics are solved by TVD-method. We used TREEcode-algorithm for calculation of a self-gravity in stellar and gaseous components. The possibility of bars birth in a hot stellar disk because of gravitational instability of a cold gas component is investigated. The conditions of occurrence lopsided-galaxies from a axisymmetric disk as a result of gravitational instability are explored. The self-consistent models of double bars are constructed and the dynamical stability of these structures is discussed.
The results of photometric decomposition of surface brightness distributions in 85 early-type unbarred galaxies are presented. The SDSS r-images are analysed. Double-tiered exponential disks are found in all galaxies which are studied; the statistics of the disk parameters is derived.
The disk masses of four low surface brightness galaxies (LSB) were estimated using marginal gravitational stability criterion and the stellar velocity dispersion data which were taken from Pizzella et al., 2008 [1]. The constructed mass models appear to be close to the models of maximal disk. The results show that the disks of LSB galaxies may be significantly more massive than it is usually accepted from their brightnesses. In this case their surface densities and masses appear to be rather typical for normal spirals. Otherwise, unlike the disks of many spiral galaxies, the LSB disks are dyna…
A brief overview of several recent disk galaxy scaling relations is presented, along with some historical background. In particular, after introducing the (basic) radial light profiles of disk galaxies, I explain several important `structural' scaling relations and review the latest bulge-(black hole mass) diagrams. I go on to present the typical bulge-to-disk flux ratios of disk galaxies and suggest the use of a grid of bulge-to-disk flux ratio versus disk Hubble type - based on the nature of the spiral arms - to complement the Hubble-Jeans sequence. I then briefly mention pure disk galaxies …
We study star formation rates (SFR) and stellar masses in bulges of nearby disk galaxies, using SFRs and stellar masses derived from Spitzer and GALEX data. At present day SFR the median pseudobulge could have grown the present day stellar mass in 8 Gyr. In almost all galaxies in our sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk, suggesting that almost all galaxies are increasing their B/T through internal star formation. In pseudobulges, SFR density correlates, positvely, with mass density, this is consistent with that stellar mass bein…
From inspection of 30 Hubble Space Telescope ACS images of M31, we provide a catalog of 449 galaxies seen through the spiral disk. Measurements of the positions of the galaxies, their integrated magnitudes in two colors and their sizes, determined from isophotometry, are included in the catalog. We discuss the many difficulties of interpreting these data in terms of the effects of intervening extinction by dust in the disk
We discuss the transitions of galaxy morphologies within the CDM paradigm under the assumption of bulge formation in mergers and disk growth via cooling of gas and subsequent star formation. Based on the relative importance of these two competing processes it is possible to make predictions on the expected morphological mix of galaxies. In particular we here discuss the generation of massive disk galaxies with low bulge-to-total mass ratios. Our results indicate that it is difficult to generate enough massive disk galaxies with B/T $< 0.2$ via major mergers and subsequent disk re-growth, if du…
Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T=3 to T=8. We fitted one-dimensional luminosity profiles with physically motivated functions - the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium - which are likely to yield more accurate results than other functions used in …
By undertaking deep long-slit spectroscopy with the focal reducer SCORPIO of the Russian 6m telescope, we studied stellar population properties and their variation with radius in 15 nearby S0 galaxies sampling a wide range of luminosities and environments. For the large-scale stellar disks of S0s, we have measured SSP-equivalent metallicities ranging from the solar one down to [Z/H]=-0.4 - -0.7, rather high magnesium-to-iron ratios, [Mg/Fe] > +0.2, and mostly old SSP-equivalent ages. Nine of 15 (60%) galaxies have large-scale stellar disks older than 10 Gyr, and among those we find all the gal…
By studying the stellar population properties along the radius in 15 nearby S0 galaxies, I have found that the outer stellar disks are mostly old, with the SSP-equivalent ages of 8-15 Gyr, being often older than the bulges. This fact puts into doubt a currently accepted paradigm that S0 galaxies have formed at z=0.4 by quenching star formation in spiral galaxies.
We study the simulated CO emission from elliptical galaxies formed in the mergers of gas-rich disk galaxies. The cold gas not consumed in the merger-driven starburst quickly resettles into a disk-like configuration. By analyzing a variety of arbitrary merger orbits that produce a range of fast to slow-rotating remnants, we find that molecular disk formation is a fairly common consequence of gas-rich galaxy mergers. Hence, if a molecular disk is observed in an early-type merger remnant, it is likely the result of a "wet merger" rather than a "dry merger". We compare the physical properties from…
We investigate the stellar structure of massive, quiescent galaxies at z~2, based on Hubble Space Telescope/WFC3 imaging from the Early Release Science program. Our sample of 14 galaxies has stellar masses of M* > 10^{10.8} Msol and photometric redshifts of 1.5 < z < 2.5. In agreement with previous work, their half-light radii are <2 kpc, much smaller than equally massive galaxies in the present-day universe. A significant subset of the sample appears highly flattened in projection, which implies, considering viewing angle statistics, that a significant fraction of the galaxies in our sample h…
[Abridged] Due to their large distances, high-z galaxies are observed at a very low spatial resolution. In order to disentangle the evolution of galaxy kinematics from low resolution effects, we have used Fabry-Perot 3D Ha data-cubes of 153 nearby isolated galaxies from the GHASP survey to simulate data-cubes of galaxies at z=1.7. We show that the inner velocity gradient is lowered and is responsible for a peak in the velocity dispersion map. Toy-models of rotating disks have been built to recover the parameters from low resolution data. The poor resolution makes the kinematical inclination un…
A bulge-disk decomposition is made for 737 spiral and lenticular galaxies drawn from a SDSS galaxy sample for which morphological types are estimated. We carry out the bulge-disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast disks are nearly universal, their properties remaining similar among disk galaxies…
We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk galaxies. We successfully measure ages in the outer disk in six systems. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations that are best-fit with star formation histories that decline with time. The observed increase in average stellar ages beyond a profile break is similar to theo…
We present results of the first unbiased search for extended UV (XUV)-disk galaxies undertaken to determine the space density of such galaxies. Our sample contains 561 local (0.001 < z < 0.05) galaxies that lie in the intersection of available GALEX deep imaging (exposure time > 1.5 x 10^4 s) and SDSS DR7 footprints. We explore modifications to the standard classification scheme for our sample that includes both disk- and bulge-dominated galaxies. Visual classification of each galaxy in the sample reveals an XUV-disk frequency of up to 20% for the most nearby portion of our sample. On average …
Star formation is one of the most important processes in galaxy formation. The luminosity of Halpha recombination and [OII] forbidden emissions remain to be most used in measuring formation rate of massive stars in galaxies. Here we report the inclination dependency of continuum-subtracted and aperture-corrected nebular luminosities, including Halpha, Hbeta, Hgamma, [OII], [NII], of disk-dominated galaxies in the local universe. Their luminosities decrease by a factor of three from face-on to edge-on (axis ratio limit = 0.17) orientations. This dependence is deduced to be caused by extinction …
We investigate rest-frame near-infrared (NIR) morphologies of a sample of 139 galaxies with M_{s} >= 1 x 10^{10} M_{sun} at z=0.8-1.2 in the GOODS-North field using our deep NIR imaging data (MOIRCS Deep Survey, MODS). We focus on Luminous Infrared Galaxies (LIRGs), which dominate high star formation rate (SFR) density at z~1, in the sample identified by cross-correlating with the Spitzer/MIPS 24um source catalog. We perform two-dimensional light profile fitting of the z~1 galaxies in the Ks-band (rest-frame J-band) with a single component Sersic model. We find that at z~1, ~90% of LIRGs have …
We have identified 15 XUV disks in a largely field sample of 38 E/S0 galaxies with stellar masses primarily below ~4 x 10^10 M_sun and comparable numbers on the red and blue sequences. We use a new purely quantitative XUV disk definition requiring UV extension relative to a UV-defined star formation threshold radius. The 39(+-9)% XUV-disk frequency for these E/S0s is roughly twice the ~20% reported for late types, possibly indicating that XUV disks are associated with galaxies experiencing weak or inefficient star formation. Consistent with this interpretation, the XUV disks in our sample do n…
The aim of this study is to determine the fractions of different spiral galaxy types, especially bulgeless disks, from a complete and homogeneous sample of 15127 edge-on disk galaxies extracted from the sixth data release from the Sloan Digital Sky Survey. The sample is divided in broad morphological classes and sub types consisting of galaxies with bulges, intermediate types and galaxies which appear bulgeless. A small fraction of disky irregulars is also detected. The morphological separation is based on automated classification criteria which resemble the bulge sizes and the flatness of the…
This review focuses on flat and superthin galaxies. These are edge-on bulgeless galaxies, which are composed of a simple, stellar disk. The properties of these simple disks are at the end of a continuum that extends smoothly from bulge-dominated disk galaxies to the pure disks. On average, simple disks are low-mass galaxies with low surface brightnesses, blue colors, and slow rotational velocities. Widely-accepted cosmological models of galaxy formation and evolution were challenged by a relatively large observed fraction of pure disk galaxies, and only very recent models can explain the exist…
The outskirts of galaxies - especially the very extended HI disks of galaxies - are strongly affected by their local environment. I highlight the giant 2X-HI disks of nearby galaxies (M 83, NGC 3621, and NGC 1512), studied as part of the Local Volume HI Survey (LVHIS), their kinematics and relation to XUV disks, signatures of tidal interactions and accretion events, the MHI - DHI relation as well as the formation of tidal dwarf galaxies. - Using multi-wavelength data, I create 3D visualisations of the gas and stars in galaxies, with the shape of their warped disks obtained through kinematic mo…
The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendi…
We investigate the effects of ram pressure stripping on gas-rich disk galaxies in the cluster environment. Ram pressure stripping principally effects the atomic gas in disk galaxies, stripping away outer disk gas to a truncation radius. We demonstrate that the drag force exerted on truncated gas disks is passed to the stellar disk, and surrounding dark matter through their mutual gravity. Using a toy model of ram pressure stripping, we show that this can drag a stellar disk and dark matter cusp off centre within it's dark matter halo by several kiloparsecs. We present a simple analytical descr…
The nature of vertical heating of disk stars in the inner as well as the outer region of disk galaxies is studied. The galactic bar (which is the strongest non-axisymmetric pattern in the disk) is shown to be a potential source of vertical heating of the disk stars in the inner region. Using a nearly self-consistent high-resolution N-body simulation of disk galaxies, the growth rate of the bar potential is found to be positively correlated with the vertical heating exponent in the inner region of galaxies. We also characterize the vertical heating in the outer region where the disk dynamics is…
We investigate the formation history of massive disk galaxies in hydro-dynamical simulation--the IllustrisTNG, to study why massive disk galaxies survive through cosmic time. 83 galaxies in the simulation are selected with M$_{*,z=0}$ $>8\times10^{10}$ M$_\odot$ and kinematic bulge-to-total ratio less than $0.3$. We find that 8.4 percent of these massive disk galaxies have quiet merger histories and preserve disk morphology since formed. 54.2 percent have a significant increase in bulge components in history, then become disks again till present time. The rest 37.3 percent experience prominent…
In order to determine what processes govern the assembly history of galaxies with rotating disks, we examine the stellar mass Tully-Fisher relation over a wide range in redshift partitioned according to whether or not galaxies contain a prominent bulge. Using our earlier Keck spectroscopic sample, for which bulge/total parameters are available from analyses of HST images, we find that bulgeless disk galaxies with z > 0.8 present a significant offset from the local Tully-Fisher relation whereas, at all redshifts probed, those with significant bulges fall along the local relation. Our results su…
We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 $μ{\rm m}$ images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios…
We have obtained and analyzed long-slit spectral data for the lenticular galaxy IC 719. In this gas-rich S0 galaxy, its large-scale gaseous disk counterrotates the global stellar disk. Moreover in the IC 719 disk we have detected a secondary stellar component corotating the ionized gas. By using emission-line intensity ratios, we have proved the gas excitation by young stars and so are claiming current star formation, most intense in a ring-like zone at the radius of 10" (1.4 kpc). The oxygen abundance of the gas in the starforming ring is about half of the solar abundance. Since the stellar d…
In this paper, we consider the problem of the evolution of the disk subsystem of galaxies in view of the halo. To this end, we have studied the dependence of the evolution of a non-linearly non-radially disk oscillating in its plane depending on the basic parameters of the dark matter halo numerically. The dark matter halo stabilizes the instabilities in the plane of the disk, but destabilizes its vertical oscillations. The global disk structure is dependent strongly on the mass and shape of the of dark matter halo. The evolutionary dependence of the oscillation process of a self-gravitating d…
Counter-rotating galaxies host two components rotating in opposite directions with respect to each other. The kinematic and morphological properties of lenticulars and spirals hosting counter-rotating components are reviewed. Statistics of the counter-rotating galaxies and analysis of their stellar populations provide constraints on the formation scenarios which include both environmental and internal processes.
In order to understand the physical mechanism underlying non-steady stellar spiral arms in disk galaxies we performed a series of N-body simulations with 1.2 and 8 million particles. The initial conditions were chosen to follow Kuijken-Dubinski models. In this work we present the results of a sub-sample of our simulations in which we experiment with different disk central radial velocity dispersion and the disk scale height.
Whether among the myriad tiny proto-galaxies there exists a population with similarities to present day galaxies is an open question. We show, using BlueTides, the first hydrodynamic simulation large enough to resolve the relevant scales, that the first massive galaxies to form are %in fact predicted to have extensive rotationally-supported disks. Although their morphology resembles in some ways Milky-way types seen at much lower redshifts, these high-redshift galaxies are smaller, denser, and richer in gas than their low redshift counterparts. From a kinematic analysis of a statistical sample…
The observations and evolution of clumpy, high-redshift galaxies are reviewed. Models suggest that the clumps form by gravitational instabilities in a gas-rich disk, interact with each other gravitationally, and then merge in the center where they form a bulge. The model requires smooth gas accretion during galaxy growth.
We present a simple theoretical framework for massive galaxies at high redshift, where the main assembly and star formation occurred, and report on the first cosmological simulations that reveal clumpy disks consistent with our analysis. The evolution is governed by the interplay between smooth and clumpy cold streams, disk instability, and bulge formation. Intense, relatively smooth streams maintain an unstable dense gas-rich disk. Instability with high turbulence and giant clumps, each a few percent of the disk mass, is self-regulated by gravitational interactions within the disk. The clumps…
We present results of an analysis of the J, H, and K$_s$ 2MASS images of 139 spiral edge-on galaxies selected from the Revised Flat Galaxies Catalog. The basic structural parameters scalelength (h), scaleheight (z_0), and central surface brightness of the stellar disks (mu_0) are determined for all selected galaxies in the NIR bands. The mean relative ratios of the scaleheights of the thin stellar disks in the J:H:K$_s$ bands are 1.16:1.08:1.00, respectively. Comparing the scaleheights obtained from the NIR bands for the same objects, we estimate the scaleheights of the thin stellar disks corr…
We have studied multi-band surface brightness profiles of a representative sample of 34 nearby dwarf irregular galaxies (dIrrs). Our data include GALEX FUV/NUV, UBV, Hα, and Spitzer 3.6 \mum images. These galaxies constitute the majority of the LITTLE THINGS survey. By modeling the azimuthal averages of the spectral energy distributions with a complete library of star formation (SF) histories, we derived the stellar mass surface density distributions and the SF rate averaged over three different timescales: the recent 0.1 Gyr, 1 Gyr and a Hubble time. We find that, for \sim 80% (27 galaxies) o…
