We use observations of the radial profiles of the mass surface density of total, Sigma_g, and molecular, Sigma_H2, gas, rotation velocity and star formation rate surface density, Sigma_sfr, of the molecular dominated regions of 12 disk galaxies from Leroy et al. to test several star formation laws: a "Kennicutt-Schmidt power law", Sigma_sfr=A_g Sigma_{g,2}^{1.5}$; a "Constant molecular law", Sigma_sfr = A_H2 Sigma_{H2,2}; the "Turbulence-regulated laws" of Krumholz & McKee (KM) and Krumholz, McKee & Tumlinson (KMT), a "Gas-Omega law", Sigma_sfr = B_Omega Sigma_g Omega; and a shear-driven "GMC collisions law", Sigma_sfr = B_CC Sigma_g Omega (1 - 0.7beta), where beta is d ln v_circ / d ln r. We find the constant molecular law, KMT turbulence law and GMC collision law are the most accurate, with an rms error of a factor of 1.5 if the normalization constants are allowed to vary between galaxies. Of these three laws, the GMC collision law does not require a change in physics to account for the full range of star formation activity seen from normal galaxies to circumnuclear starbursts. A single global GMC collision law with B_CC=8.0x10^{-3}, i.e. a gas consumption time of 20 orbital times for beta=0, yields an rms error of a factor of 1.8.
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…
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…
Dark matter (DM) halos of Sc-Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes M_V > -18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention vs. supernova-driven losse…
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…
Dark matter (DM) halos of Sc-Im galaxies satisfy scaling laws analogous to the fundamental plane relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii, higher central densities, and smaller central velocity dispersions. If dwarf spheroidal (dSph) and dwarf Magellanic irregular (dIm) galaxies lie on the extrapolations of these correlations, then we can estimate their baryon loss relative to that of brighter Sc-Im galaxies. We find that, if there had been no such enhanced baryon loss, then typical dSph and dIm galaxies would be brighter in absolute magnitude …
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…
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.
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…
We use observed radial profiles of mass surface densities of total, $Σ_g$, & molecular, $Σ_{\rm H2}$, gas, rotation velocity & star formation rate (SFR) surface density, $Σ_{\rm sfr}$, of the molecular-rich ($Σ_{\rm H2}\geΣ_{\rm HI}/2$) regions of 16 nearby disk galaxies to test several star formation laws: a Kennicutt-Schmidt law, $Σ_{\rm sfr}=A_gΣ_{g,2}^{1.5}$; a Constant Molecular law, $Σ_{\rm sfr}=A_{\rm H2}Σ_{\rm H2,2}$; the turbulence-regulated laws of Krumholz & McKee (KM05) and Krumholz et al. (KMT09), a Gas-$Ω$ law, $Σ_{\rm sfr}=B_ΩΣ_gΩ$; and a shear-driven GMC Collision law, $Σ_{\rm …
Galaxy-wide star formation can be quenched by a number of physical processes such as environmental effects (e.g., ram pressure stripping) and supernova feedback. Using numerical simulations, we here demonstrate that star formation can be severely suppressed in disk galaxies with their gas disks counter-rotating with respect to their stellar disks. This new mechanism of star formation suppression (or quenching) does not depend so strongly on model parameters of disk galaxies, such as bulge-to-disk- ratios and gas mass fractions. Such severe suppression of star formation is due largely to the su…
We investigate the assembly history of massive disk galaxies and describe how they shape their morphology through cosmic time. Using SHARDS and HST data, we modeled the surface brightness distribution of 91 massive galaxies at redshift $0.14<z\leq 1$ in the wavelength range $0.5-1.6$ $μ$m, deriving the uncontaminated spectral energy distributions of their bulges and disks separately. This spectrophotometric decomposition allows us to compare the stellar populations properties of each component in individual galaxies. We find that the majority of massive galaxies ($\sim85\%$) builds inside-out,…
We use the Sloan Digital Sky Survey (SDSS) database to explore the effect of the disk inclination angle on the derived star formation rate (SFR), hence on the slope and width of the Main Sequence (MS) relation for star-forming galaxies. We find that SFRs for nearly edge-on disks are underestimated by factors ranging from $\sim$ 0.2 dex for low mass galaxies up to $\sim$ 0.4 dex for high mass galaxies. This results in a substantially flatter MS relation for high-inclination disks compared to that for less inclined ones, though the global effect over the whole sample of star-forming galaxies is …
We present a method to derive the dynamical mass of face-on galaxy disks using their neutral hydrogen (HI) velocity dispersion. We have applied the method to nearby, gas rich galaxies that have extended HI gas disks and have low inclinations. The galaxy sample includes 4 large disk galaxies; NGC628, NGC6496, NGC3184, NGC4214 and 3 dwarf galaxies DDO46, DDO63 and DDO187. We have used archival data from the THINGS and LITTLE THINGS surveys to derive the HI gas distributions and SPITZER mid-infrared images to determine the stellar disk mass distributions. We examine the disk dynamical and baryoni…
In this paper, we provide a physical model for the origin of variations in the shapes and bump strengths of dust attenuation laws in galaxies by combining a large suite of cosmological "zoom-in" galaxy formation simulations with 3D Monte Carlo dust radiative transfer calculations. We model galaxies over 3 orders of magnitude in stellar mass, ranging from Milky Way like systems through massive galaxies at high-redshift. Critically, for these calculations we employ a constant underlying dust extinction law in all cases, and examine how the role of geometry and radiative transfer effects impact t…
We present a catalog of true edge-on disk galaxies automatically selected from the Seventh Data Release (DR7) of the Sloan Digital Sky Survey. A visual inspection of the $g$, $r$ and $i$ images of about 15000 galaxies allowed us to split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-ons, and 1865 (12.5%) edge-on galaxies not suitable for simple automatic analysis because these objects show signs of interaction, warps, or nearby bright stars project on it. We added more candidate galaxies from RFGC, EFIGI,…
Massive galaxies at higher redshifts ($\emph{z}$ $>$ 2) show different characteristics from their local counterparts: They are compact and most likely have a disk. In this study, we trace the evolution of local massive galaxies by performing a detailed morphological analysis, namely, fitting single Sérsic profiles and performing bulge+disk decompositions. We analyze $\sim$ 250 massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS, GOODS-South and GOODS-North). We confirm that both star-forming and quiescent galaxies increase their sizes significantly from $\emph{z}$ $\approx$ 2.5…
We show, for the first time, that ${\rm H_2}$ formation on dust grains can be enhanced in disk galaxies under strong ram-pressure (RP). We numerically investigate how the time evolution, of ${\rm H}$ {\sc i} and ${\rm H_2}$ components in disk galaxies orbiting a group/cluster of galaxies, can be influenced by hydrodynamical interaction between the gaseous components of the galaxies and the hot intra-cluster medium (ICM). We find that compression of ${\rm H}$ {\sc i} caused by RP increases ${\rm H_2}$ formation in disk galaxies, before RP rapidly strips ${\rm H}$ {\sc i}, cutting off the fuel s…
The outer regions of galactic disks have received increased attention since ultraviolet observations with GALEX demonstrated that nearly 30% of galaxies have UV emission beyond their optical extents, indicating star formation activity. These galaxies have been termed extended UV (XUV) disks. Here, we address whether these observations contradict the gas surface density threshold for star formation inferred from Halpha radial profiles of galaxies. We run smoothed particle hydrodynamics simulations of isolated disk galaxies with fiducial star formation prescriptions and show that over-densities …
We investigate the stellar disk structure of six nearby edge-on spiral galaxies using high-resolution JHKs-band images and 3D radiative transfer models. To explore how mass and environment shape spiral disks, we selected galaxies with rotational velocities between 69 < Vrot < 245 km/sec, and two with unusual morphologies. We find a wide diversity of disk structure. Of the fast-rotating (Vrot > 150 km/sec) galaxies, only NGC 4013 has the super-thin+thin+thick nested disk structure seen in NGC 891 and the Milky Way, albeit with decreased oblateness, while NGC 1055, a disturbed massive spiral gal…
By numerically solving the mass distribution in a rotating disk based on Newton's laws of motion and gravitation, we demonstrate that the observed flat rotation curves for most spiral galaxies correspond to exponentially decreasing mass density from galactic center for the most of the part except within the central core and near periphery edge. Hence, we believe the galaxies described with our model are consistent with that seen through the eyes of Newton. Although Newton's laws and Kepler's laws seem to yield the same results when they are applied to the planets in the solar system, they are …
We present the Waves in Nearby Disk galaxies Survey (WiNDS) consisting of 40 nearby low inclination disk galaxies observed through H$α$ high-resolution Fabry Perot interferometry. WiNDS consists of 12 new galaxy observations and 28 data archived observations obtained from different galaxy surveys. We derive two-dimensional line-of-sight velocity fields that are analyzed to identify the possible presence of vertical velocity flows in the galactic disks of these low-inclination late-type galaxies using velocity residual maps, derived from the subtraction of an axisymmetric rotation model to rota…
The origin of the disk and spheroid of galaxies has been a key open question in understanding their morphology. Using the high-resolution cosmological simulation, New Horizon, we explore kinematically decomposed disk and spheroidal components of 144 field galaxies with masses greater than $\rm 10^9\,M_{\odot}$ at $z=0.7$. The origins of stellar particles are classified according to their birthplace (in situ or ex situ) and their orbits at birth. Before disk settling, stars form mainly through chaotic mergers between proto-galaxies and become part of the spheroidal component. When disk settling…
In this paper we propose a new method for reconstructing the surface density of matter in flat disks of spiral galaxies. The surface density is expressed through observational rotation velocity curves of visible matter in the disks of spiral galaxies. The new method is not based on quadrature of special functions. The found solution is used for processing and analysis of observational data from several spiral galaxies. The new method can be used to more accurately estimate the amount of dark matter in spiral galaxies.
We present photometric models of 532 disk galaxies in 3.6μm images from the Spitzer Survey of Stellar Structure in Galaxies (S$^4$G) using the non-parametric DiskFit algorithm. We first test DiskFit's performance on 400 synthetic S$^4$G-like galaxy images. DiskFit is unreliable in the bulge region, but accurately disentangles exponential disks from Ferrers bars farther out as long as their position angles differ by more than 5${^\circ}$. We then proceed to model the S$^4$G galaxies, successfully fitting 489 of them using an automated approach for initializing DiskFit, optimizing the model and …
We introduce a method to estimate the HI mass within the optical radius of disk galaxies from integrated HI spectra, with an uncertainty of 0.09 dex. We use these estimates to study how inner HI fuels star formation in late-type disk galaxies. We find that star formation rate (SFR) at a given stellar mass ($M_*$) is well correlated with the inner HI surface density ($Σ_{\rm HI,in}$) and inner HI mass-to-stellar mass ratio. For the massive ($M_*>10^{10} M_{\odot}$) disk galaxies, higher SFR at a given stellar mass is also related with higher efficiency of converting inner HI to molecular gas, b…
Massive disk galaxies with high surface brightness plus low surface brightness stellar disks, hosted by massive dark matter halo -- a TNG50 simulation study
Tata Institute of Fundamental Research（塔塔基础研究所）；Inter-University Centre for Astronomy and Astrophysics（大学间天体物理中心）
N-body simulations of galactic collisions are employed to investigate the formation of elliptical rings in disk galaxies. The relative inclination between disk and dwarf galaxies is studied with a fine step of five degrees. It is confirmed that the eccentricity of elliptical ring is linearly proportional to the inclination angle. Deriving from the simulational results, an analytic formula which expresses the eccentricity as a function of time and inclination angle is obtained. This formula shall be useful for the interpretations of the observations of ring systems, and therefore reveals the me…
While spiral and lenticular galaxies have large-scale disks extending beyond their bulges, and most local early-type galaxies with 10^{10} < M_*/M_Sun < 2x10^{11} contain a disk (e.g., ATLAS^3D), the early-type galaxies do possess a range of disk sizes. The edge-on, `intermediate-scale' disk in the `disky elliptical' galaxy NGC 1271 has led to some uncertainty as to what its spheroidal component is. Walsh et al. reported a directly measured black hole mass of 3x10^9 M_Sun for this galaxy; which they remarked was an order of magnitude greater than what they expected based on their derivation of…
We present a UV study of 3 extended UV (XUV) galaxies that we have observed with the UVIT and the GMRT. XUV galaxies show filamentary or diffuse star formation well beyond their optical disks, in regions where the disk surface density lies below the threshold for star formation. GALEX observations found that surprisingly 30% of all the nearby spiral galaxies have XUV disks. The XUV galaxies can be broadly classified as type 1 and type 2 XUV disks. The type 1 XUV disks have star formation that is linked to that in their main disk, and the UV emission appears as extended, filamentary spiral arms…
We have obtained imaging data in two photometric bands, g and r, for a sample of 42 isolated lenticular galaxies with the Las Cumbres Observatory one-meter telescope network. We have analyzed the structure of their large-scale stellar disks. The parameters of surface brightness distributions have been determined including the radial profile shapes and disk thicknesses. After inspecting the radial brightness profiles, all the galaxies have been classified into pure exponential (Type I), truncated (Type II), and antitruncated (Type III) disks. By comparing the derived statistics of the radial pr…
The content of gas in galaxies with an anomalously high relative mass of hydrogen $M_{HI}/M_*$ for a given mass of the stellar population $M_*$ (VHR-galaxies) is considered, using the available samples of such galaxies. It is shown that, within the optical diameter $D_{25}$, the mass of HI in VHR galaxies, as well as in galaxies with "normal" HI content, is limited by a value that depends on the specific angular momentum of the disk. Outer gaseous disks beyond $D_{25}$, which contain the main amount of HI in most of the galaxies we consider, are gravitationally stable, and, as a rule, they ret…
A fraction of early-type dwarf galaxies in the Virgo cluster have a disk component and even possess disk features such as bar, lens, and spiral arms. In this study, we construct 15 galaxy models that resemble VCC856, considered to be an infalling progenitor of disk dwarf galaxies, within observational error ranges, and use $N$-body simulations to study their long-term dynamical evolution in isolation as well as the formation of bar in them. We find that dwarf disk galaxies readily form bars unless they have an excessively concentrated halo or a hot disk. This suggests that infalling dwarf disk…
We present a summary of recent assessments of the mass distribution in disk galaxies. Of issue in order to characterize galaxy formation models is to determine the relative fraction of baryons and dark matter at all radii in galaxies. For disk galaxies, various measurements of the mass distribution in galaxies based on vertical kinematics, strong lensing, residuals of scaling relations, fluid dynamical modeling, bar strength and pattern speed, warps, and others, have called for either a maximal or sub-maximal contribution of the baryons in the inner parts of the disk. We propose a global pictu…
The HI in galaxies often extends past their conventionally defined optical extent. I report results from our team which has been probing low intensity star formation in outer disks using imaging in H-alpha and ultraviolet. Using a sample of hundreds of HI selected galaxies, we confirm that outer disk HII regions and extended UV disks are common. Hence outer disks are not dormant but are dimly forming stars. Although the ultraviolet light in galaxies is more centrally concentrated than the HI, the UV/HI ratio (the Star Formation Efficiency) is nearly constant, with a slight dependency on surfac…
Frequent accretion of external cold gas is thought to play an important role in galaxy assembly. However, almost all known kinematically misaligned galaxies identify only one gas disk that is misaligned with the stellar disk, implying a single gas acquisition event. Here we report a new configuration in two galaxies where both contain two gas disks misaligned with each other and also with the stellar disk. Such systems are not expected to be stable or long-lasting, challenging the traditional picture of gas accretion of galaxies and their angular momentum build-up. The differences in kinematic…
A rare population of massive disk galaxies have been found to invade the red sequence dominated by early-type galaxies. These red/quenched massive disk galaxies have recently gained great interest into their formation and origins. The usually proposed quenching mechanisms, such as bar quenching and environment quenching, seem not suitable for those bulge-less quenched disks in low-density environment. In this paper, we use the IllustrisTNG-300 simulation to investigate the formation of massive quenched central disk galaxies. It is found that these galaxies contain less gas and harbor giant sup…
We explore stellar population properties separately in the bulge and the disk of double-component cluster galaxies to shed light on the formation of lenticular galaxies in dense environments. We study eight low-redshift clusters from the Sydney-AAO Multi-object Integral field (SAMI) Galaxy Survey, using 2D photometric bulge-disk decomposition in the $g$, $r$ and $i$-bands to characterize galaxies. For 192 double-component galaxies with $M_{*}>10^{10~}M_{\odot}$ we estimate the color, age and metallicity of the bulge and the disk. The analysis of the $g-i$ colors reveals that bulges are redder …
It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark-matter-based cosmology. On the contrary, modified gravity offers a promising alternative: the objects in the disks of satellites are tidal dwarf galaxies, that is small galaxies that form from tidal tails of interacting galaxies. After introducing the topic, we review here our work on simulating the formation of the disks of satellites of the Milky Way and An…
A model based on disk-stability criteria to determine the number of spiral arms of a general disk galaxy with an exponential disk, a bulge and a dark halo described by a Hernquist model is presented. The multifold rotational symmetry of the spiral structure can be evaluated analytically once the structural properties of a galaxy, such as the circular speed curve, and the disk surface brightness, are known. By changing the disk mass, these models are aimed at varying the critical length scale parameter of the disk and lead to a different spiral morphology in agreement with prior models. Previou…
Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) program, we compare the integrated Star Formation Rate- Mass relation (SFR-M_ast) relation of 42 cluster galaxies undergoing ram pressure stripping ("stripping galaxies") to that of 32 field and cluster undisturbed galaxies. Theoretical predictions have so far led to contradictory conclusions about whether ram pressure can enhance the star formation in the gas disks and tails or not and until now a statistically significant observed sample of stripping galaxies was lacking. We find that stripping galaxies occupy …
We compare the star-formation history and dynamics of the Milky Way (MW) with the properties of distant disk galaxies. During the first ~4 Gyr of its evolution, the MW formed stars with a high star-formation intensity (SFI), Sigma_SFR~0.6 Msun/yr/kpc2 and as a result, generated outflows and high turbulence in its interstellar medium. This intense phase of star formation corresponds to the formation of the thick disk. The formation of the thick disk is a crucial phase which enables the MW to have formed approximately half of its total stellar mass by z~1 which is similar to "MW progenitor galax…
If advanced extraterrestrial civilizations choose to construct vast numbers of Dyson spheres to harvest radiation energy, this could affect the characteristics of their host galaxies. Potential signatures of such astroengineering projects include reduced optical luminosity, boosted infrared luminosity and morphological anomalies. Here, we apply a technique pioneered by Annis (1999) to search for Kardashev type III civilizations in disk galaxies, based on the predicted offset of these galaxies from the optical Tully-Fisher relation. By analyzing a sample of 1359 disk galaxies, we are able to se…
We suggest and verify a new photometric method enabling derivation of relative thickness of a galactic disk from two-dimensional surface-brightness distribution of the galaxy in the plane of the sky. The method is applied to images of 45 early-type (S0-Sb) galaxies with known radial exponential or double-exponential (with a flatter outer profile) surface-brightness distributions. The data in the r-band have been retrieved from the SDSS archive. Statistics of the estimated relative thicknesses of the stellar disks of early-type disk galaxies shows the following features. The disks of lenticular…
A considerable fraction of the massive quiescent galaxies at \emph{z} $\approx$ 2, which are known to be much more compact than galaxies of comparable mass today, appear to have a disk. How well can we measure the bulge and disk properties of these systems? We simulate two-component model galaxies in order to systematically quantify the effects of non-homology in structures and the methods employed. We employ empirical scaling relations to produce realistic-looking local galaxies with a uniform and wide range of bulge-to-total ratios ($B/T$), and then rescale them to mimic the signal-to-noise …
Spiral structure is the most distinctive feature of disk galaxies and yet debate persists about which theory of spiral structure is the correct one. Many versions of the density wave theory demand that the pitch angle is uniquely determined by the distribution of mass in the bulge and disk of the galaxy. We present evidence that the tangent of the pitch angle of logarithmic spiral arms in disk galaxies correlates strongly with the density of neutral atomic hydrogen in the disk and with the central stellar bulge mass of the galaxy. These three quantities, when plotted against each other, form a…
