Main Disk Research Articles

SDSS. IV. MaNGA: The Impact of the Acquisition of Gas with Opposite Angular Momentum on the Evolution of Galaxies

A gaseous counterrotating galaxy is a galaxy containing a gas component with opposite angular momentum to the main stellar disk. The counterrotating gas provides direct evidence for the accretion of external material, a key aspect in hierarchical galaxy evolution. We identified 303 gaseous counterrotators out of 9992 galaxies in MaNGA. The majority of the counterrotators are early types. This implies their formation is highly correlated with early-type galaxies, although it is still difficult to know if one leads to the other. To disentangle which of the galaxy characteristics within a morphological class were changed by the accretion of counterrotating gas, we carefully selected a comparison sample with similar fundamental galactic properties but corotation in gas. This comparison shows that gaseous counterrotation correlates with weak rotation in the stellar component, the high central concentration of star-forming regions, if present, and a higher fraction of central low ionization emission regions (cLIER) galaxies. The light distributions of the stellar components, dust and H i content (both low), and overall suppressed star formation rates are similar for both samples and seem typical for the morphological class. We claim that elliptical and about half of the lenticular counterrotators, those with weak rotation in the stellar component in the outskirts and central regions, likely have a major merger origin for the gas acquisition, and the other half of lenticulars, with stronger stellar rotation, may have a minor merger or pure gas accretion origin.

An Imaging and Spectroscopic Exploration of the Dusty Compact Obscured Nucleus Galaxy Zw 049.057* *Based in part on observations obtained with the Southern African Large Telescope (SALT).

Zw 049.057 is a moderate-mass, dusty, early-type galaxy that hosts a powerful compact obscured nucleus (CON, L FIR,CON ≥ 1011 L ⊙). The resolution of the Hubble Space Telescope enabled measurements of the stellar light distribution and characterization of dust features. Zw 049.057 is inclined with a prominent three-zone disk; the R ≈ 1 kpc star-forming inner dusty disk contains molecular gas, a main disk with less dust and an older stellar population, and a newly detected outer stellar region at R > 6 kpc with circular isophotes. Previously unknown polar dust lanes are signatures of a past minor merger that could have warped the outer disk to near face-on. Dust transmission measurements provide lower limit gas mass estimates for dust features. An extended region with moderate optical depth and M ≥ 2 × 108 M ⊙ obscures the central 2 kpc. Optical spectra show strong interstellar Na D absorption with a constant velocity across the main disk, likely arising in this extraplanar medium. Opacity measurements of the two linear dust features, pillars, give a total mass of ≥106 M ⊙, flow rates of ≥2 M ⊙ yr−1, and few Myr flow times. Dust pillars are associated with the CON and are visible signs of its role in driving large-scale feedback. Our assessments of feedback processes suggest gas recycling sustains the CON. However, radiation pressure driven mass loss and efficient star formation must be avoided for the active galactic nucleus to retain sufficient gas over its lifespan to produce substantial mass growth of the central black hole.

Cold Water Emission Cannot Be Used to Infer Depletion of Bulk Elemental Oxygen [O/H] in Disks

We reexamine the constraints provided by Herschel Space Observatory data regarding cold water emission from protoplanetary disks. Previous disk models that were used to interpret observed water emission concluded that oxygen (O/H) is depleted by at least 2 orders of magnitude if a standard, interstellar gas/dust mass ratio is assumed in the disk. In this work, we use model results from a recent disk parameter survey and show that most of the Herschel constraints obtained for cold water (i.e., for transitions with an upper energy level E up < 200 K, where the bulk of the disk water lies) can be explained with disk models adopting interstellar medium-like oxygen elemental abundance (i.e., O/H = 3.2 × 10−4) and the canonical gas/dust mass ratio of 100. We show that cold water vapor is mainly formed by photodesorption of water ice at the interface between the molecular layer and the midplane, and that its emission is relatively independent of the main disk properties like the disk gas mass and gas/dust mass ratio. We find that the abundance of water vapor in the outer disk is set by photoprocesses and depends on the (constant) vertical column density of water ice needed to attenuate the far-ultraviolet photon flux, resulting in roughly constant emission for the parameters (gas mass, dust mass, disk radius) varied in our survey. Importantly, water line emission is found to be optically thick and hence sensitive to temperature more than abundance, possibly driving previous inferences of large-scale oxygen depletion.

Possible origins of anomalous H I gas around MHONGOOSE galaxy, NGC 5068

The existing reservoirs of neutral atomic hydrogen gas (H I) in galaxies are insufficient to have maintained the observed levels of star formation without some kind of replenishment. This refuelling of the H I reservoirs is likely to occur at column densities an order of magnitude lower than previous observational limits (NH I, limit ∼ 1019 cm−2 at a 30″ resolution over a linewidth of 20 km s−1). In this paper, we present recent deep H I observations of NGC 5068, a nearby isolated star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. With these new data, we were able to detect low column density H I around NGC 5068 with a 3σ detection limit of NH I = 6.4 × 1017 cm−2 at a 90″ resolution over a 20 km s−1 linewidth. The high sensitivity and resolution of the MeerKAT data reveal a complex morphology of the H I in this galaxy – a regularly rotating inner disk coincident with the main star-forming disk of the galaxy, a warped outer disk of low column density gas (NH I &lt; 9 × 1019 cm−2), in addition to clumps of gas on the north-western side of the galaxy. We employed a simple two disk model that described the inner and outer disks, which enabled us to identify anomalous gas that deviates from the rotation of the main galaxy. The morphology and the kinematics of the anomalous gas suggest a possible extra-galactic origin. We explore a number of possible origin scenarios that may explain the anomalous gas, and conclude that fresh accretion is the most likely scenario.

A Dynamic Galaxy: Stellar Age Patterns across the Disk of M101

Using deep, narrowband imaging of the nearby spiral galaxy M101, we present stellar age information across the full extent of the disk of M101. Our narrowband filters measure age-sensitive absorption features such as the Balmer lines and the slope of the continuum between the Balmer break and 4000 Å break. We interpret these features in the context of inside-out galaxy formation theories and dynamical models of spiral structure. We confirm the galaxy’s radial age gradient, with the mean stellar age decreasing with radius. In the relatively undisturbed main disk, we find that stellar ages get progressively older with distance across a spiral arm, consistent with the large-scale shock scenario in a quasi-steady spiral wave pattern. Unexpectedly, we find the same pattern across spiral arms in the outer disk as well, beyond the corotation radius of the main spiral pattern. We suggest that M101 has a dynamic, or transient, spiral pattern with multiple pattern speeds joined together via mode coupling to form coherent spiral structure. This scenario connects the radial age gradient inherent to inside-out galaxy formation with the across-arm age gradients predicted by dynamic spiral arm theories across the full radial extent of the galaxy.

A plausible link between dynamically unsettled molecular gas and the radio jet in NGC 6328

We report the detection of outflowing molecular gas at the center of the nearby radio galaxy NGC6328 (z = 0.014), which has a gigahertz-peaked spectrum radio core and a compact (2 pc) young double radio lobe tracing jet. Utilizing Atacama Large Millimeter/submillimeter Array (ALMA) CO(3 − 2) and CO(2 − 1) observations, as well as a novel code developed to fit the 3D gas distribution and kinematics, to study the molecular gas kinematics, we find that the bulk of the gas is situated within a highly warped disk structure, most likely the result of a past merger event. Our analysis further uncovers, within the inner regions of the gas distribution (R &lt; 300 pc) and at a position angle aligning with that of the radio jet (150°), the existence of two anti-diametric molecular gas structures kinematically detached from the main disk. These structures most likely trace a jet-induced cold gas outflow with a total lower limit mass of 2 × 106 M⊙ mass, corresponding to an outflow rate of 2 M⊙ yr−1 and a kinetic power of 2.7 × 1040 erg s−1. The energy required to maintain such a molecular outflow is aligned with the mechanical power of the jet.

Deriving the intrinsic properties of M51 with radiative transfer models

ABSTRACT A quantitative derivation of the intrinsic properties of galaxies related to their fundamental building blocks, gas, dust, and stars is essential for our understanding of galaxy evolution. A fully self-consistent derivation of these properties can be achieved with radiative transfer (RT) methods that are constrained by panchromatic imaging observations. Here, we present an axi-symmetric RT model of the UV-optical-FIR/submm spectral and spatial energy distribution of the face-on spiral galaxy M51. The model reproduces reasonably well the azimuthally averaged radial profiles derived from the imaging data available for this galaxy, from GALEX, Sloan Digital Sky Survey, 2MASS, Spitzer, and Herschel. We model the galaxy with three distinct morphological components: a bulge, an inner disc, and a main disc. We derive the length parameters of the stellar emissivity and of the dust distribution. We also derive the intrinsic global and spatially resolved parameters of M51. We find a faint ‘outer disc’ bridging M51 with its companion galaxy M51b. Finally, we present and discuss an alternative model, with dust properties that change within the galaxy.

Experimental investigation on the impact force of the oblique water entry of a slender projectile with spring buffer

On water impact, a projectile experiences impact forces that can threaten its structural safety and the stability of its trajectory. In the engineering applications, the underwater vehicle may need to entry and exit of water several times. The elastic buffer can be used repeatedly, which meet the requirement of the scene. To mitigate the effects of a strong impact, a projectile with a spring buffer connecting its main body and disk is designed in this work. The impact force of the main body during water entry is studied experimentally. The experimental equipment and the force measurement system are newly developed by the authors. The main focus is the cavity evolution and the axial force of the main body. The cavity of the projectile with a buffer is slightly elongated and thickened compared with that without a buffer. A special necking phenomenon of the cavity is observed as the spring buffer is compacted. The effects of the spring stiffness, the disk mass, and the impact velocity on the axial force and impulse are extensively discussed. Compared with the case without a buffer, the axial force of the main body is only mitigated within a small range of stiffness values. When the stiffness increases, the axial force begins to fluctuate with a larger peak and a narrow pulse. The peak force is nearly twice that in the case without a buffer. However, the impulse is always smaller, although some fluctuations occur in the larger stiffness cases. Additionally, an increased disk mass can also mitigate the force peak and the impulse of the main body, but fluctuations also occur in cases with larger masses. The coefficients of the axial force and the impulse of the main body decrease with increasing impact velocities. The result indicates that the elastic buffer only in a narrow stiffness can effectively reduce the impact load of the water entry projectile. This study can provide references for the load reduction design of the projectile with an elastic buffer during water entry or exit.

NGC 3314a/b and NGC 3312: Ram pressure stripping in Hydra I cluster substructure

Cluster substructure and ram pressure stripping in individual galaxies are among the primary pieces of evidence for the ongoing growth of galaxy clusters as they accrete galaxies and groups from their surroundings. We present a multiwavelength study of the center of the Hydra I galaxy cluster, including exquisite new MeerKAT H I and DECam Hα imaging which reveal conclusive evidence for ram pressure stripping in NGC 3312, NGC 3314a, and NGC 3314b through compressed H I contours, well-defined H I tails, and ongoing star formation in the stripped gas. In particular, we quantify the stripped material in NGC 3312, and NGC 3314a, which makes up between 8% and 35% of the gas still in the disk, is forming stars at ∼0.5 M⊙ yr−1, and extends ∼30−60 kpc from the main disk. The estimated stellar mass in the tails is an order of magnitude less than the H I mass. A fourth “ring” galaxy at the same velocity does not show signs of ram pressure in H I. In addition, we used the H I and stellar morphologies, combined with a Beta model of the hot intracluster medium, to constrain the real distances of the galaxies to the cluster center, and we used the chance alignment of NGC 3314b behind NGC 3314a to break the degeneracy between whether the galaxies are in front or in back of the cluster. The drag seen in the H I tails supports our preferred scenario that NGC 3312 and NGC 3314a are moving toward us as part of a foreground substructure which has already passed its pericenter and is on “out fall” from the cluster. The high surviving H I content of the galaxies may suggest that the substructure or intragroup medium can protect them from the harshest effects of ram pressure, or that the galaxies are in fact on more tangential orbits.

Chemical Cartography with APOGEE: Mapping Disk Populations with a 2-process Model and Residual Abundances

We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] versus [Mg/H] with a 2-process model, which decomposes abundance patterns into a “prompt” component tracing core-collapse supernovae and a “delayed” component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals Δ[X/H] from this two-parameter fit. The rms residuals range from ∼0.01–0.03 dex for the most precisely measured APOGEE abundances to ∼0.1 dex for Na, V, and Ce. The correlations of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow for the comparison of populations controlled for differences in metallicity and [α/Fe]. Relative to the main disk (R = 3–13 kpc), we find nearly identical abundance patterns in the outer disk (R = 15–17 kpc), 0.05–0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4–1 dex) of multiple elements in ω Cen. The residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.

NOEMA Observations of CO Emission in Arp 142 and Arp 238

Abstract Previous studies have shown significant differences in the enhancement of the star formation rate (SFR) and star formation efficiency (SFE = SFR/M mol) between spiral–spiral and spiral–elliptical mergers. In order to shed light on the physical mechanism of these differences, we present NOEMA observations of the molecular gas distribution and kinematics (linear resolutions of ∼2 kpc) in two representative close major-merger star-forming pairs: the spiral–elliptical pair Arp 142 and the spiral–spiral pair Arp 238. The CO in Arp 142 is widely distributed over a highly distorted disk without any nuclear concentration, and an off-center ringlike structure is discovered in channel maps. The SFE varies significantly within Arp 142, with a starburst region (region 1) near the eastern tip of the distorted disk showing an SFE ∼ 0.3 dex above the mean of the control sample of isolated galaxies and the SFE of the main disk (region 4) 0.43 dex lower than the mean of the control sample. In contrast, the CO emission in Arp 238 is detected only in two compact sources at the galactic centers. Compared to the control sample, Arp 238-E shows an SFE enhancement of more than 1 dex, whereas Arp 238-W has an enhancement of ∼0.7 dex. We suggest that the extended CO distribution and large SFE variation in Arp 142 are due to an expanding large-scale ring triggered by a recent high-speed head-on collision between the spiral galaxy and the elliptical galaxy, and the compact CO sources with high SFEs in Arp 238 are associated with nuclear starbursts induced by gravitational tidal torques in a low-speed coplanar interaction.

The curious case of NGC 5068 and its neutral hydrogen fingers

AbstractHow galaxies replenish their gas supply in order to sustain star formation, is a research topic of many of the new and upcoming neutral atomic hydrogen (Hi) surveys on the SKA precursor instruments. This replenishment, or accretion, of gas in the form of Hi is likely to occur at column densities one or two orders of magnitude below previous observational limits and it has, so far, not been unambiguously detected. We present recent deep Hi observations of NGC 5068, an isolated nearby star-forming galaxy observed by MeerKAT as part of the MHONGOOSE survey. This survey is the deepest Hi survey of nearby galaxies until the advent of the SKA and is reaching column densities of resolution. The combination of the resolution and sensitivity of the MeerKAT HI data have revealed “fingers” of low column density gas extending out from the main Hi disk of the galaxy. While the origin of these fingers remains a mystery for now, the dynamics of the main galaxy disk and the outer disk in which the fingers are located, as well as the morphology of the fingers, does not seem to suggest a previous merger event.

Extended neutral hydrogen filamentary network in NGC 2403

AbstractWe present new neutral hydrogen (Hi) observations of the nearby galaxy NGC 2403 to determine the nature of a low-column density cloud that was detected earlier by the Green Bank Telescope.We find that this cloud is the tip of a complex of filaments of extraplanar gas that is coincident with the main disk. The total Hi mass of the complex is 2 × 107 M⊙ or 0.6% of the total Hi mass of the galaxy. The main structure, previously referred to as the 8-kpc filament, is now seen to be even more extended, along a 20 kpc stream.

CAPOS: The bulge Cluster APOgee Survey

Context.Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools.Aims.CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, [α/Fe], and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs.Methods.CAPOS uses the APOGEE-2S spectrograph observing in theHband to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline.Results.We derive mean [Fe/H] values of −0.85 ± 0.04 (Terzan 2), −1.40 ± 0.05 (Terzan 4), −1.20 ± 0.10 (HP 1), −1.40 ± 0.07 (Terzan 9), −1.07 ± 0.09 (Djorg 2), −1.06 ± 0.06 (NGC 6540), and −1.11 ± 0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean [α/Fe] and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have [Si/Fe] abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances of the iron-peak elements Mn and Ni and compare their trends with field populations.Conclusions.CAPOS is proving to be an unprecedented resource for greatly improving our knowledge of the formation and evolution of BGCs and the bulge itself.

A comparison of the UV and HI properties of the extended UV (XUV) disk galaxies NGC 2541, NGC 5832 and ESO406-042

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. The UV luminosity is associated with compact star forming regions along the extended spiral arms. The star formation is probably driven by slow gas accretion from nearby galaxies or the intergalactic medium (IGM). But the type 2 XUV disks have star formation associated with an outer low luminosity stellar disk that is often truncated near the optical radius of the galaxy. The nature of the stellar disks in type 2 XUV disks are similar to that of the diffuse stellar disks of low surface brightness galaxies. The star formation in type 2 XUV disks is thought to be due to rapid gas accretion or gas infall from nearby high velocity clouds (HVCs), interacting galaxies or the IGM. In this paper we investigate the star formation properties of the XUV regions of two type 2 galaxies and one mixed XUV type galaxy and compare them with the neutral hydrogen (HI) emission in their disks. We present preliminary results of our UVIT (FUV and NUV) observations of NGC 2541, NGC 5832 and ESO406-042, as well as GMRT observations of their HI emission. We describe the UV emission morphology, estimate the star formation rates and compare it with the HI distribution in these type 2 and mixed XUV galaxies.

Working bodies of a moldboard plow for combined soil processing with a turnover of a layer

The paper shows the issues of moldboard tillage with simultaneous additional cutting of a wrapped layer with disk working bodies. An overview of the main disk working bodies used in agriculture is given. The technical solution of a combined arable unit is proposed and the technological process of its operation is presented. A brief description of the laboratory and field installation is also presented.

A novel formulation and analysis for heat transfer in von Kármán flow involving viscoelastic fluid: OHAM solutions

This research concentrates on the von Karman flow of viscoelastic fluid obeying second grade model over a heated permeable disk. Our interest is to explore how fluid motion triggered around the disk is affected by the existence of both elasticity and viscous dissipation effects. It is found that the problem exhibits self-similar solution only when a prescribed wall temperature distribution is considered. Series solutions are worked out by using an easy to implement yet reliable routine BVPh 2.0 of MATHEMATICA based on the homotopy analysis method. The total squared residual of the system is evaluated which illustrates that the approximate solution accurately matches the exact solution at sufficiently higher order of approximation. The influence of parameters on the disk pumping efficiency and resisting torque is also deliberated. Graphical results reveal a marked formation of momentum/thermal boundary layer provided that the viscoelastic fluid parameter is sufficiently large. An important outcome is that the elastic effects of fluid tend to reduce the torque required to main disk rotation. Moreover, flow behavior near the disk is substantially altered by wall suction effect. Entrained flow is predicted to accelerate whenever elastic effects are present.

Dynamical Properties of Molecular-forming Gas Clumps in Galaxies at the Epoch of Reionization

Abstract We study the properties of molecular-forming gas clumps (MGCs) at the epoch of reionization using cosmological zoom-in simulations. We identify MGCs in a prototypical galaxy (“Althæa”) using an H2 density-based clump finder. We compare their mass, size, velocity dispersion, gas surface density, and virial parameter ( ) to observations. In Althæa, the typical MGC mass and size are M ⊙ and pc, which are comparable to those found in nearby spirals and starburst galaxies. MGCs are highly supersonic and supported by turbulence, with rms velocity dispersions of 20–100 km s−1 and pressure of (i.e., with respect to the Milky Way), similar to those found in nearby and z ∼ 2 gas-rich starburst galaxies. In addition, we perform stability analysis to understand the origin and dynamical properties of MGCs. We find that MGCs are globally stable in the main disk of Althæa. Densest regions where star formation is expected to take place in clouds and cores on even smaller scales instead have lower and Toomre Q values. Detailed studies of the star-forming gas dynamics at the epoch of reionization thus require a spatial resolution of ≲40 pc (≃ ), which is within reach with the Atacama Large (sub-)Millimeter Array and the Next Generation Very Large Array.

GMC Collisions as Triggers of Star Formation. VII. The Effect of Magnetic Field Strength on Star Formation

Abstract We investigate the formation of stars within giant molecular clouds (GMCs) evolving in environments of different global magnetic field strength and large-scale dynamics. Building upon a series of magnetohydrodynamic simulations of noncolliding and colliding GMCs, we employ density- and magnetically regulated star formation subgrid models in clouds that range from moderately magnetically supercritical to near critical. We examine gas and star cluster morphologies, magnetic field strengths and relative orientations, prestellar core densities, temperatures, mass-to-flux ratios and velocities, star formation rates and efficiencies over time, spatial clustering of stars, and kinematics of the stars and natal gas. The large-scale magnetic criticality of the region greatly affects the overall gas evolution and star formation properties. GMC collisions enhance star formation rates and efficiencies in magnetically supercritical conditions, but may actually inhibit them in the magnetically critical case. This may have implications for star formation in different Galactic environments such as the Galactic Center and the main Galactic disk.

A study of microprocessor systems using RAMD approach

The aim of the present study is to offer results of reliability, availability, maintainability and dependability analysis of a microprocessor system. A microprocessor is designed with the help of seven subsystems including input, terminal, processor, main memory disk, addressing modes, disk controller and disk drives. Reliability, availability, maintainability and dependability analysis has been performed for all the subsystems. For analysis purpose, state transition diagram has been designed for all subsystems and using Markov birth–death process governing equations has been derived. All random variables are exponentially distributed, i.e., follows constant failure rate. Mean time between failures, mean time to repair, availability, reliability, maintainability and dependability ratio parameters for all the subsystems are computed. The reliability and maintainability are estimated at various time instants.