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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Interacting galaxies in the IllustrisTNG simulations - I: Triggered star formation in a cosmological context

ABSTRACT We use the IllustrisTNG cosmological hydrodynamical simulations to investigate how the specific star formation rates (sSFRs) of massive galaxies (M* > 1010 M⊙) depend on the distance to their closest companions. We estimate sSFR enhancements by comparing with control samples that are matched in redshift, stellar mass, local density, and isolation, and we restrict our analysis to pairs with stellar mass ratios of 0.1 to 10. At small separations (∼15 kpc), the mean sSFR is enhanced by a factor of 2.0 ± 0.1 in the flagship (110.7 Mpc)3 simulation (TNG100-1). Statistically significant enhancements extend out to 3D separations of 280 kpc in the (302.6 Mpc)3 simulation (TNG300-1). We find similar trends in the EAGLE and Illustris simulations, although their sSFR enhancements are lower than those in TNG100-1 by about a factor of two. Enhancements in IllustrisTNG galaxies are seen throughout the redshift range explored (0 ≤ $z$ < 1), with the strength of the enhancements decreasing with increasing redshift for galaxies with close companions. In order to more closely compare with observational results, we separately consider 2D projected distances between galaxies in IllustrisTNG. We detect significant sSFR enhancements out to projected separations of 260 kpc in TNG300-1, with projection effects diluting the size of the enhancements by about 20 per cent below 50 kpc. We find similar sSFR enhancements in TNG100-1 and Sloan Digital Sky Survey galaxies, with enhancements extending out to projected separations of about 150 kpc for star-forming galaxies at $z$ < 0.2. Finally, by summing over all separations, we estimate that the presence of closest companions boosts the average sSFR of massive galaxies in TNG100-1 by 14.5 per cent.

Patton, David R.↗
DOE OSTI2023

Long-slit spectral study of the unusual post-interacting galaxy Arp 263

ABSTRACT Arp 263 is a single irregularly shaped galaxy with intense star formation. Its short tidal features of low brightness visible in both optics and the H i line, as well as the strong non-circular motion of atomic gas in the outskirts, give pieces of evidence of a recent merging with some intruder, non-observed directly. We carried out spectral observations of this galaxy at the 6 m telescope of the Special Astrophysical Observatory. The spectra for three positions of the spectral slit were obtained: two of them cross the central region of the galaxy and the third one runs along the nearly straight narrow chain of clumps of emission gas with a length of 4–5 kpc. We derived the profiles of velocity, fluxes, and oxygen abundances (O/H) along the slits. We confirm that within the radius of several kpc the galaxy rotates regularly. The maximal value of the rotational velocity allows us to conclude that the dark mass of the galaxy prevails over the mass of its visible components. The observed velocity profile along the peripheral star-forming chain gives pieces of evidence that it is located outside of the plane of the disc, and the gas that formed the chain is probably falling back on to the disc after being ejected from the galaxy. We discuss that the observed chain of clumps is the result of gravitational instability of the gaseous filament.

Astronomy & Astrophysics↗
NASA NTRS1989

An infrared study of starbursts in the interacting galaxy pair Arp 299 (NGC 3690+IC 694)

Extensive infrared observations have been obtained of the three active regions in Arp 299. Multiaperture JHK photometry reveals that the colors of the three regions are totally different from each other, and that there are very red nuclei smaller than 4 arcsec in two of them. Multiaperture spectroscopy of the Br-gamma and the shock-excited H2 lines shows that both the atomic and molecular lines are spatially extended, indicating that Arp 299 is undergoing an active episode of star formation not only in its nuclei but also well outside of them. Although there is some evidence that suggests the presence of a compact, active galactic nucleus, a simple starburst model can explain the bolometric luminosities, production rates of ionizing photons, and H24 line luminosities of each active region in Arp 299. However, each starburst cannot last longer than 10 to the 8th yr.

Nakagawa, Takao↗
NASA NTRS1990

Are bars essential for starbursts in non-interacting galaxies

Analyzed here are the 1.6 and 2.2 micron images of a sample of galaxies that are classified as unbarred by the Revised Shapley-Ames Catalog. These galaxies have characteristic properties of nuclear starbursts and are examined through near infrared imaging in a search for hidden bars. Researchers selected a sample of 36 galaxies from the Revised Shapley-Ames Catalog that have far infrared luminosities greater than 10(exp 10) solar luminosity and hot Infrared Astronomy Satellite (IRAS) colors between 60 and 100 microns, indicative of nuclear starbursts, but are not classified as Seyfert 1 or 2. Their determination of the presence of a bar relies primarily on an analysis of the 2 micron image using the Galaxy Surface Photometry (GASP) package (Cawson, 1983). The GASP analysis programs determine the galaxy surface brightness and ellipticity profiles as well as the position angle and the center coordinates of the ellipses. To test the way that GASP will characterize the surface brightness of barred galaxies, two galaxies with known bars, NGC 1068 and NGC 2523, were imaged with the 2 micron camera and analyzed with GASP. Fifteen of the sample that are not clearly barred from optical data and are isolated were imaged at 1.6 and 2.2 microns; 9 of these do not appear to have bars. Strong bars therefore do not appear to be an absolute requirement for high infrared luminosity in isolated galaxies.

Pompea, Stephen M.↗
NASA NTRS1990

Star formation in infrared bright and infrared faint starburst interacting galaxies

Short wavelength IUE spectra of Arp 248b and UGC 8315N are combined with optical spectra and interpreted using a combination of spectrum synthesis and spectral diagnostics to place constraints on the massive star populations of the central regions of these galaxies and to deduce information about the star formation histories in the last 10(exp 8) years. The authors find that both galaxies have substantial fractions of their optical light coming from massive stars and that Arp 248b may be dominated in the UV by WR stars. The UV spectra are dominated by radiation from evolved massive stars and the authors place and age on the burst in Arp 248b of a few tens of millions of years.

Lamb, Susan A.↗
NASA NTRS1990

Simulations of gas clouds in interacting galaxies

A companion can induce a variety of morphological changes in a galaxy. The author uses N-body simulations to study the effects of different kinds of perturbations on the dynamics of a disk galaxy. The model is two-dimensional, with a disk consisting of about 60,000 particles. Most of the particles (80%) represent the old stellar population with a high velocity dispersion, while the rest (20%) represent gas clouds with a low velocity dispersion. Initially, the velocity dispersion corresponds to Q = 1 for the star particles, and Q = O for the gas particles, where Q is Toomre's (1964) stability parameter. The gas clouds can collide inelastically. The disk is stabilized by a rigid halo potential, and by the random motions of the old star particles. To simulate the effect of an encounter on the disk, a companion galaxy, modelled as a point mass, can move in a co-planar orbit around the disk. A complete description of the N-body code is found in Thomasson (1989). The spiral structures caused by a companion in first a direct and then a retrograde (with respect to the rotation of the disk) parabolic orbit are presented. The associated velocity fields suggest a way to observationally distinguish between leading and trailing spiral arms. The stability of the gas component in a disk in which tidally triggered infall of gas to the center occurs is studied. Finally, the author shows how a ring of gas can form in a disk as a result of a co-planar encounter with another galaxy.

Thomasson, Magnus↗
NASA NTRS1994

Soft X-ray observations of the interacting galaxies NGC 1808 and NGC 1792

The soft X-ray emission from both galaxies NGC 1808 and NGC 1792, which we investigated using the ROSAT HRI and Position Sensitive Proportional Counter (PSPC), comes most probably from X-ray binaries and/or from hot ionized gas in powerful supernovae and supernova remnants. The distribution of the soft X-ray emission in NGC 1808, which is very well correlated with the distribution of 'radio knots' in the central starburst, suggests that hot gas dominates the emission in the ROSAT band. This is consistent with the results of PSPC observations by Junkes et al. The total soft X-ray luminosity in the ROSAT band of NGC 1808 of 1.2 x 10(exp 41) ergs/s is relatively high compared with other nearby starburst galaxies. Soft X-ray emission of diffuse hot ionized gas that is associated with the outflow traced by the conspicuous dust filaments protruding from the plane has been detected. Its luminosity in the ROSAT band is greater than or equal to 3 x 10(exp 39) ergs/s, i.e., several percent of the total soft X-ray luminosity. Thus, NGC 1808 is another example for a 'superwind' galaxy. The soft X-ray radiation from NGC 1792 is more likely to be dominated by a population of high-mass X-ray binaries or young powerful supernovae which are associated with the high-level star formation going on in the very prominent H II regions along its spiral arms, with possibly an additional contribution of diffuse hot ionized gas. The soft X-ray luminosities of individual sources lie in the range of 5 x 10(exp 38) to 2.7 x 10(exp 39) ergs/s, thus exceeding by far the Eddington luminosity of an accreting neutron star. The peaks of some of these soft X-ray luminous sources are offset with respect to the H II regions by a few hundred parsecs. Accordingly, if the soft X-ray sources should originate from the H II regions, their relative velocities with respect to the ambient medium have to be as high as approximately 100 km/s.

Dahlem, Michael↗
NASA NTRS2001

HST Observations of Star Formation in Interacting Galaxies: NGC 4194, the "Medusa"

Ultraviolet and visible imaging of the blue compact galaxy NGC4194 was obtained to survey the star-forming knots in the center of this galaxy. Photometry and image analysis were performed on these regions. Comparison with evolutionary tracks indicates many of the knots are reddened with a typical E(B-V)approx.0.3. The knot ages range from 10(exp 6-10(exp 8)years. Some of the knots may have masses 3-5x10(exp 5) solar mass. The FUV fluxes correspond to the flux from 60-3.8x10(exp 3) O5V stars.

Weistrop, D.↗
NASA NTRS1993

The Galaxy activity-interaction connection. II - Radio observations

VLA results are presented for southern interacting galaxies at 6 and 20 cm, with a view to the detection and classification of the nature of radio emission in a set of advanced-interaction disk galaxies. Maps of radio emission are given for the 42 interacting systems in the sample, as well as 10 control systems, and radio properties are compared with optical and IR properties; the radio in all of the present interacting galaxies are attributable to properties associated with a burst of star formation due to galaxy interaction.

Smith, Eric P.↗
DOE OSTI2023

Pre- and post-processing of cluster galaxies out to 5 × R 200: the extreme case of A2670

ABSTRACT We study galaxy interactions in the large-scale environment around A2670, a massive (M200 = $8.5 \pm 1.2~\times 10^{14} \, \mathrm{{M}_{\odot }}$) and interacting galaxy cluster at z = 0.0763. We first characterize the environment of the cluster out to 5× R200 and find a wealth of substructures, including the main cluster core, a large infalling group, and several other substructures. To study the impact of these substructures (pre-processing) and their accretion into the main cluster (post-processing) on the member galaxies, we visually examined optical images to look for signatures indicative of gravitational or hydrodynamical interactions. We find that ∼21 per cent of the cluster galaxies have clear signs of disturbances, with most of those (∼60 per cent) likely being disturbed by ram pressure. The number of ram-pressure stripping candidates found (101) in A2670 is the largest to date for a single system, and while they are more common in the cluster core, they can be found even at >4 × R200, confirming cluster influence out to large radii. In support of a pre-processing scenario, most of the disturbed galaxies follow the substructures found, with the richest structures having more disturbed galaxies. Post-processing also seems plausible, as many galaxy–galaxy mergers are seen near the cluster core, which is not expected in relaxed clusters. In addition, there is a comparable fraction of disturbed galaxies in and outside substructures. Overall, our results highlight the complex interplay of gas stripping and gravitational interactions in actively assembling clusters up to 5 × R200, motivating wide-area studies in larger cluster samples.

Astronomy & Astrophysics↗
NASA NTRS1976

The dynamical interaction between galaxies and intracluster gas in clusters of galaxies

The interaction between the hot gas inferred to exist in clusters of galaxies and the interstellar medium of a spherical galaxy has been studied by means of time-dependent numerical hydrodynamics. Galaxies moving at transonic speeds with respect to the ambient medium lose 80% to 90% of their interstellar gas before a crossing time has elapsed. The amount of gas remaining is consistent with current observational limits to the gas content of elliptical galaxies. Negligible heating of the intracluster gas results from this process. Implications of these results for spiral galaxies with halos, radio sources in clusters of galaxies, and globular clusters in galactic halos are discussed.

Lea, S. M.↗
NASA NTRS1991

The galaxy activity-interaction connection. I - Optical observations

As part of an investigation into the triggering of nuclear radio emission in interacting galaxies, new multicolor, broadband data are presented from a subset of Arp-Madore Catalog galaxies selected on the basis of their optical morphology - systems with loops and/or tails. The CTIO 4 m is used to obtain images in B, V, R, and I for the purpose of performing synthetic aperture photometry. Isophotal ellipse fitting to the more regular objects in the sample is also performed to quantify their isophotal deviation from purely elliptical morphologies. Color index maps for the galaxies are constructed, and the optical morphologies, broadband colors, and detailed photometric properties as well as the IRAS fluxes for the galaxies are discussed. These data are used to obtain a rough measure of the level of activity present in these systems.

Smith, Eric P.↗
NASA NTRS1990

Two-dimensional caustics in disturbed galaxy disks

Interacting galaxies show a variety of exotic morphologies besides the well-known rings, spirals, and bars. It is proposed that many of these can be identified with nonlinear, caustic structures that are known from singularity theory to be generic in collisionless dynamics. A simple kinematical model for stellar orbits is used to study the development of caustic waveforms in galaxy disks following impulsive, nonaxially symmetric (collisional) disturbances. It appears that all of the caustics known from singularity theory to be generic in two dimensions develop as transient forms in at least some moderately off-center collisions. The more complex, higher-order caustics appear most prominently in the more off-center and larger amplitude disturbances. It is further suggested that the highly nonlinear caustic waves may play an important role in interaction-induced star formation.

Struck-Marcell, Curtis↗
NASA NTRS1990

Global effects of interactions on galaxy evolution

Recent observations of the evolutionary properties of paired and interacting galaxies are reviewed, with special emphasis on their global emission properties and star formation rates. Data at several wavelengths provide strong confirmation of the hypothesis, proposed originally by Larson and Tinsley, that interactions trigger global bursts of star formation in galaxies. The nature and properties of the starbursts, and their overall role in galactic evolution are also discussed.

Kennicutt, Robert C., Jr.↗
NASA NTRS1992

Bar-spheroid interaction in galaxies

N-body simulation and linear analysis is employed to investigate the secular evolution of barred galaxies, with emphasis on the interaction between bars and spheroidal components of galaxies. This interaction is argued to drive secular transfer of angular momentum from bars to spheroids, primarily through resonant coupling. A moderately strong bar, having mass within corotation about 0.3 times the enclosed spheroid mass, is predicted to shed all its angular momentum typically in less than about 10 exp 9 yr. Even shorter depletion time scales are found for relatively more massive bars. It is suggested either that spheroids around barred galaxies are structured so as to inhibit strong coupling with bars, or that bars can form by unknown processes long after disks are established. The present models reinforce the notion that bars can drive secular evolution in galaxies.

Hernquist, Lars↗