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Karachentsev, Igor D., Valentina E. Karachentseva, Walter K. Huchtmeier, Dmitry I. Makarov, and Serafim S. Kaisin. "Probe of Dark Galaxies via Disturbed/Lopsided Isolated Galaxies." Proceedings of the International Astronomical Union 3, S244 (2007): 235–46. http://dx.doi.org/10.1017/s1743921307014044.
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AbstractSearching for lopsided/interacting objects among 1500 isolated galaxies yields only eight strongly disturbed galaxies which may be explained as a result of their interaction with massive dark objects. We present results of spectral and photometric observations of these galaxies performed with the 6-m telescope that lead to significant restriction on cosmic abundance of dark galaxies.
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Struck, Curtis. "Star formation in mergers and interacting galaxies: gathering the fuel." Proceedings of the International Astronomical Union 2, S237 (2006): 317–22. http://dx.doi.org/10.1017/s1743921307001664.
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AbstractSelected results from recent studies of star formation in galaxies at different stages of interaction are reviewed. Recent results from the Spitzer Space Telescope are highlighted. Ideas on how large-scale driving of star formation in interacting galaxies might mesh with our understanding of star formation in isolated galaxies and small scale mechanisms within galaxies are considered. In particular, there is evidence that on small scales star formation is determined by the same thermal and turbulent processes in cool compressed clouds as in isolated galaxies. If so, this affirms the notion that the primary role of large-scale dynamics is to gather and compress the gas fuel. In gas-rich interactions this is generally done with increasing efficiency through the merger process.
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Athanassoula, E. "Isolated and Interacting Galaxies: Simulations with GRAPE." Symposium - International Astronomical Union 208 (2003): 177–88. http://dx.doi.org/10.1017/s0074180900207134.
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I present N-body simulations of isolated and interacting galaxies, made on GRAPE machines. In particular I discuss the formation and evolution of N-body bars and compare their properties to those of bars in early-type and late-type galactic discs. I argue that the halo can help the bar grow, contrary to previous beliefs, by taking positive angular momentum from it via its resonant stars. I then focus on the interaction and subsequent merging of a barred disc galaxy with a spheroidal satellite. The evolution depends strongly on the mass (density) of the satellite and may lead to its destruction or to the destruction of the bar.
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Zaragoza-Cardiel, J., J. E. Beckman, J. Font, A. Camps-Fariña, B. García-Lorenzo, and S. Erroz-Ferrer. "Star formation enhancement characteristics in interacting galaxies." Proceedings of the International Astronomical Union 10, S309 (2014): 354. http://dx.doi.org/10.1017/s174392131401045x.
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AbstractWe have observed 12 interacting galaxies using the Fabry-Perot interferometer GHαFaS (Galaxy Hα Fabry-Perot system) on the 4.2m William Herschel Telescope (La Palma). We have extracted the physical properties (sizes, Hα luminosity and velocity dispersion) of 236 HII regions for the full sample of interacting galaxies. We have derived the physical properties of 664 HII regions for a sample of 28 isolated galaxies observed with the same instrument in order to compare both populations of HII regions, finding that there are brighter and denser star forming regions in the interacting galaxies compared with the isolated galaxies sample.
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Fernández, María, Fangting Yuan, Shiyin Shen, Jun Yin, Ruixiang Chang, and Shuai Feng. "Isolated Galaxies versus Interacting Pairs with MaNGA." Galaxies 3, no. 4 (2015): 156–63. http://dx.doi.org/10.3390/galaxies3040156.
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Young, J. S. "Molecular Gas and Star Formation in Interacting and Isolated Galaxies." Symposium - International Astronomical Union 186 (1999): 217–26. http://dx.doi.org/10.1017/s0074180900112665.
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The results of the FCRAO Extragalactic CO Survey are used to examine the trends regarding the molecular gas distribution, the star formation efficiency, and the global gas surface densities (HI and H2) in galaxies as a function of environment. Relative to a sample of isolated Sbc-Scd galaxies, the strongly interacting galaxies have more compact gas distributions, a higher mean value for the global star formation efficiency, and a larger fraction of gas in molecular form. Not only is the molecular gas redistributed during interactions, but evidence is presented for an enhanced conversion of atomic to molecular gas as well.
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Kronberger, T., W. Kapferer, S. Schindler, A. Böhm, E. Kutdemir, and B. L. Ziegler. "Internal Kinematics of Modelled Isolated and Interacting Disc Galaxies." Proceedings of the International Astronomical Union 2, S235 (2006): 216. http://dx.doi.org/10.1017/s1743921306006223.
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AbstractWe present a systematic investigation of the velocity fields of both isolated and interacting spiral galaxies in combined N-body/hydrodynamical simulations. Closely mimicking the procedures applied in observations of distant, small, and faint galaxies we extract rotation curves (RCs) and compare the results of the simulation directly to observations. Irregularities in the velocity field reflect disturbances in the gravitational potential of the galaxy. They can be used to trace the recent interaction history of a galaxy and give possible clues to the type of the respective interaction. In addition, identifying disturbances in the RCs is important for Tully-Fisher studies in order to accurately derive the maximum rotation velocity.
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Kaneko, Hiroyuki, Nario Kuno, Daisuke Iono, et al. "Properties of molecular gas in galaxies in early and mid stages of Interaction. III. Resolved Kennicutt–Schmidt law." Publications of the Astronomical Society of Japan 74, no. 2 (2022): 343–63. http://dx.doi.org/10.1093/pasj/psab129.
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Abstract We study properties of the interstellar medium, an ingredient of stars, and star formation activity, in four nearby galaxy pairs in the early and mid stages of interaction for both a galaxy scale and a kpc scale. The galaxy-scale Kennicutt–Schmidt law shows that seven of eight interacting galaxies have a star formation rate within a factor of three compared with the best fit of the isolated galaxies, although we have shown that molecular hydrogen gas is efficiently produced from atomic hydrogen during the interaction in the previous paper (Kaneko et al. 2017 PASJ, 69, 66). The galaxy-scale specific star formation rate (sSFR) and star formation efficiency (SFE) in interacting galaxies are comparable to those in isolated galaxies. We also investigate SFE and the Kennicutt–Schmidt law on a kpc scale. The spatial distributions of SFE reveal that SFE is locally enhanced, and the enhanced regions take place asymmetrically or at off-centre regions. The local enhancement of SFE could be induced by shock. We find that the index of the Kennicutt–Schmidt law for the interacting galaxies in the early stage is 1.30 ± 0.04, which is consistent with that of the isolated galaxies. Since CO emission, which is used in the Kennicutt–Schmidt law, is a tracer of the amount of molecular gas, this fact suggests that dense gas, which is more directly connected to star formation, is not changed at the early stage of interaction.
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Garay-Solis, Yeny, Jorge K. Barrera-Ballesteros, Dario Colombo, et al. "Exploring the Impact of Galactic Interactions and Mergers on the Central Star Formation of APEX/EDGE–CALIFA Galaxies." Astrophysical Journal 952, no. 2 (2023): 122. http://dx.doi.org/10.3847/1538-4357/acd781.
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Abstract Galactic interactions and subsequent mergers are a paramount channel for galaxy evolution. In this work, we use the data from 236 star-forming CALIFA galaxies with integrated molecular gas observations in their central region (approximately within an effective radius)—from the APEX millimeter telescope and the CARMA millimeter telescope array. This sample includes isolated (126 galaxies) and interacting galaxies in different merging stages (110 galaxies; from pairs, merging, and postmerger galaxies). We show that the impact of interactions and mergers in the center of galaxies is revealed as an increase in the fraction of molecular gas (compared to isolated galaxies). Furthermore, our results suggest that the change in star formation efficiency is the main driver for both an enhancement and/or suppression of the central star formation—except in merging galaxies where the enhanced star formation appears to be driven by an increase of molecular gas. We suggest that gravitational torques due to the interaction and subsequent merger transport cold molecular gas inwards, increasing the gas fraction without necessarily increasing star formation.
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Lisenfeld, U., L. Verdes-Montenegro, J. Sulentic, et al. "The Far-Infrared Properties of the Most Isolated Galaxies." Proceedings of the International Astronomical Union 2, S235 (2006): 219. http://dx.doi.org/10.1017/s1743921306006259.
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AbstractWe describe the mid- (MIR) and far- (FIR) infrared properties of a large (~1000) sample of the most isolated galaxies in the local Universe. This sample is intended as a “nurture-free” zero point against which more environmentally influenced samples can be compared. We reprocess IRAS MIR/FIR survey data using the ADDSCAN/SCANPI utility for 1030 out of 1050 galaxies from the Catalogue of Isolated Galaxies (CIG) as part of the AMIGA project. We focus on diagnostics (FIR luminosity LFIR, R = log(LFIR/LB) and IRAS colours) thought to be sensitive to effects of environment or interaction. The distribution of log(LFIR) is sharply peaked from 9.0–10.5 with very few (<2%) galaxies above 10.5. Review of available optical images of the most FIR luminous galaxies finds the majority to be, likely, interacting systems missed in our earlier morphological reevaluation. The optically normalised luminosity diagnostic R = log(LFIR/LB) shows a distribution sharply peaked between 0.0 and −1.0. These results were compared to the magnitude limited CfA sample that was selected without environmental discrimination. This modestly (e.g. compared to cluster, binary galaxy and compact group samples) environmentally affected sample shows significantly higher mean log(LFIR) and R, whereas the mean log(LB) is the same. Our sample shows a strong LFIR vs. LB correlation, with a slope steeper than one (LFIR ∝ L1.41B). Interacting galaxies were found above this correlation, showing an enhancement in LFIR. With respect to the IRAS colours, we found higher F60/F100 value for ellipticals and late-type galaxies than for spirals, indicating a higher dust temperature. The mean value of F60/F100 was found to be lower than for interacting samples from the literature. The results indicate that the FIR emission is a variable enhanced by interaction, and that our sample probably shows the lowest possible mean value. This attests to the utility of our sample for defining a nurture-free zero point. More details can be found in the paper (The AMIGA sample of isolated galaxies, III. IRAS data and infrared diagnositics, U. Lisenfeld et al.) which is accepted for publication in Astronomy & Astrophysics.
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Bergvall, Nils, Eija Laurikainen, Susanne Aalto, and Lennart Johansson. "Star Formation in a Magnitude Limited Sample of Interacting Galaxies." Symposium - International Astronomical Union 171 (1996): 344. http://dx.doi.org/10.1017/s0074180900232634.
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We report on optical/near-IR spectroscopy and photometry of a magnitude limited sample of interacting pairs and merging galaxies and a control sample of apparently isolated galaxies (1,2). All observations were carried out at ESO, La Silla. When compared to the control sample, the interacting galaxies show only a moderate increase of star formation activity, in the central area typically a factor 2-3. Starburst activity seems to be very rare. Ongoing CO observations (Aalto, Horellou, Booth, Wiklind, Bergvall) indicate that these objects are not particularly rich in molecular gas. The interacting/merging galaxies have relatively high optical luminosities and high FIR luminosities and temperatures but these parameters are not correlated with other star formation signatures. We conclude that the interacting and merging galaxies in this sample, from the global star formation aspect, do not differ dramatically from scaled up versions of normal, isolated galaxies. This could suggest that many of the most lumino components in interacting pairs could originate from multiple ‘quiet’ mergers.
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Donoso, L., M. V. Alonso, D. García Lambas, G. Coldwell, E. O. Schmidt, and G. A. Oio. "Analysis of interacting and isolated quasars." Astronomy & Astrophysics 615 (July 2018): A11. http://dx.doi.org/10.1051/0004-6361/201629407.
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Aims. The main goal of this study was to determine the effects on equivalent widths (EWs) of some spectral lines produced in the quasars by the presence of surrounding galaxies. To carry this out, a sample of 4663 quasars (QSOs) in the redshift range of 0.20 to 0.40 from the Sloan Digital Sky Survey data release 7 was analyzed. Methods. Three QSO sub-samples were defined, taking into account the projected separations and radial velocity differences with neighboring galaxies. In this way, we utilized two sub-samples of QSOs with strong and weak galaxy interactions, with projected separations smaller than 70 kpc, and between 70 and 140 kpc, respectively, and with radial velocity differences less than 5000 km s−1. These sub-samples were compared with isolated QSOs defined as having greater projected separations and radial velocity differences to the galaxies. Results. From a statistical study of the EWs of relevant spectral lines in the QSOs, we show an increment of the EWs of about 20% in the [OIII]λλ4959, 5007 lines and 7% in Hα for QSOs with stronger galaxy interactions relative to the isolated QSOs. These increments were also observed restricting the sub-samples to velocity differences of 3000 km s−1. These results indicate that some line EWs of QSOs could be marginally influenced by the environment and that they are not affected by the emission of the host galaxy, which was estimated to be around 10% of the total emission. Furthermore, in order to gain a better understanding of the origin of the Hα emission line, we performed broad and narrow line decomposition in 100 QSOs in the restricted Sint sub-sample and also 100 randomly selected QSOs in the Iso sub-sample. When these QSOs were compared, the narrow component remained constant whereas the broad component was incremented. Our results, which reveal slight differences in EWs of some emission lines, suggest that galaxy interactions with QSOs may affect the QSO activity.
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Zasov, Anatoli V. "The HI Content of Non-Isolated Galaxies." International Astronomical Union Colloquium 124 (1990): 175–82. http://dx.doi.org/10.1017/s0252921100005066.
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It seems obvious that the evolution of star formation rate and hence of gas content in galaxies strongly depends on their environment. It reveals itself in particular in enhanced star formation or even in a strong burst of activity of massive stars often observed in an interacting galaxies. Nevertheless it should be noted that the time scale for the gas to be exhausted in these galaxies is unknown even approximately. To clarify a role of surroundings in the evolution of disk galaxies we should compare the HI content of isolated and non-isolated galaxies otherwise similar by their properties.
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Menon, T. K. "Radio Diagnostics of Galaxy Interactions." Symposium - International Astronomical Union 186 (1999): 383–86. http://dx.doi.org/10.1017/s0074180900113154.
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The Hickson Compact Groups (Hickson 1982) are relatively isolated systems of galaxies with projected separations comparable to the diameters of the galaxies themselves and are an ideal laboratory for the study of the effects of interactions on the various properties of galaxies. Roughly one third of the galaxies in HCG show clear signs of interaction such as tidal distortion, truncation, and peculiar rotation curves. Galaxies that are not now interacting may have suffered past interactions or mergers. My study is based on a VLA survey of galaxies of different morphologies in 65 Compact Groups from Hickson's (1982, 1993) catalogue and only groups with minimum of 4 accordant velocities were included in the study. This final sample consisted of 298 galaxies (80E, 92S0, 126S). The observations were carried out using the VLA in various configurations at wavelengths of 20cm and 6cm over a period of several years. The angular resolutions ranged from 20″ to 0.3″ and non-detection sensitivities ranged from 1 mJy to 0.3 mJy for different observations. A total of 86 galaxies were detected as radio sources (32ES0, 54S).
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Xu, Cong, and Jack W. Sulentic. "Quantifying the Fir Interaction Enhancement in Paired Galaxies." International Astronomical Union Colloquium 124 (1990): 297–301. http://dx.doi.org/10.1017/s025292110000525x.
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We study the “Catalogue of Isolated Pairs of Galaxies in the Northern Hemisphere” (CPG hereafter) by Karachentsev (1972), and a well matched comparison sample taken from the “Catalog of Isolated Galaxies” (Karachentseva 1973, CIG hereafter), in order to quantify the enhanced FIR emission properties of interacting galaxies (see Sulentic 1989 for details of the samples). The isolation criterion used in compiling the CPG and the CIG means that both the pairs and single galaxies have been Httle influenced by their environment for a long time (t ≳ 109 yrs: Stocke et al 1978).
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Combes, F. "Extended Gas in Interacting Systems." Symposium - International Astronomical Union 186 (1999): 89–96. http://dx.doi.org/10.1017/s0074180900112318.
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HI observations have revealed large gaseous extensions in interacting and merging systems. The interstellar gas is obviously dragged out in tidal tails during an encounter, and the percentage of HI in the tails increases with the merging stage. However, the opposite is true for the molecular gas, which is observed highly concentrated towards the nuclei of interacting galaxies, amounting to a significant fraction of the dynamical mass. Statistically, there appears to be more gas observed in interacting galaxies than in normal, isolated ones. As N-body simulations show, the gas is driven inwards in the interaction process by the strong gravity torques, before being consumed through star formation in the triggered starbursts. We review here all observations that could bring more knowledge about the state of the gas in the outer parts of galaxies, and about accretion processes. The link with the observations of the Lyα absorbers at low and high redshifts is discussed.
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Fuentes-Carrera, Isaura, Nelli Cárdenas-Martínez, Martín Nava-Callejas, and Margarita Rosado. "Gas dynamics and star formation in “isolated” and interacting galaxies using FP observations." Proceedings of the International Astronomical Union 14, S353 (2019): 264–65. http://dx.doi.org/10.1017/s1743921319008238.
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AbstractWe present scanning Fabry-Perot observations of different types of star-forming galaxies from apparently isolated LIRGs to equal mass interacting galaxies. We analyze the ionized gas kinematics, its relation with the morphology of each system and the location of SF regions for different systems.
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Athanassoula, E. "Evolution of Bars in Isolated and in Interacting Disk Galaxies." International Astronomical Union Colloquium 157 (1996): 309–20. http://dx.doi.org/10.1017/s0252921100049940.
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AbstractI use N-body simulations to follow the evolution of bars in both isolated and interacting disk galaxies. The pattern speeds of bars evolving in isolated galaxies decline gradually with time, due to transfer of angular momentum from the bar to other components in the galaxy. Both the form and amount of this decline depend on the model used. The fate of a bar in an interacting disk galaxy depends on the mass, central concentration and orbit of the perturber. The pattern speed, form and amplitude of the bar may change, the bar can become off-centered, or, more drastically, it can disappear altogether. Finally I propose a scenario for the evolution of NGC 7217, which could, if proven correct, explain the formation of the rings in that galaxy and also, at least qualitatively, the existence of a retrograde population.
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Mickaelian, A. M., M. P. Véron-Cetty, and P. Véron. "What is the Maximun IR Luminosity of a Single Spiral Galaxy?" Symposium - International Astronomical Union 205 (2001): 232–33. http://dx.doi.org/10.1017/s0074180900221062.
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A new sample of IRAS galaxies at high galactic latitudes has been built by optically identifying IRAS point sources.In no more than about 100 cases, an apparently interacting system of galaxies is located near the IR source. The large majority are unambiguously identified with a single, relatively isolated galaxy. This confirms that, although galaxy interaction may trigger starburst activity, the IR luminosity in most objects is due to normal star formation in the disc.
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Craig, Peter, Sukanya Chakrabarti, Heidi Newberg, and Alice Quillen. "Dynamically produced moving groups in interacting simulations." Monthly Notices of the Royal Astronomical Society 505, no. 2 (2021): 2561–74. http://dx.doi.org/10.1093/mnras/stab1431.
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ABSTRACT We show that smoothed particle hydrodynamics (SPH) simulations of dwarf galaxies interacting with a Milky Way-like disc produce moving groups in the simulated stellar disc. We analyse three different simulations: one that includes dwarf galaxies that mimic the Large Magellanic Cloud, Small Magellanic Cloud, and the Sagittarius dwarf spheroidal; another with a dwarf galaxy that orbits nearly in the plane of the Milky Way disc; and a null case that does not include a dwarf galaxy interaction. We present a new algorithm to find large moving groups in the VR, Vϕ plane in an automated fashion that allows us to compare velocity substructure in different simulations, at different locations, and at different times. We find that there are significantly more moving groups formed in the interacting simulations than in the isolated simulation. A number of dwarf galaxies are known to orbit the Milky Way, with at least one known to have had a close pericentre approach. Our analysis of simulations here indicates that dwarf galaxies like those orbiting our Galaxy produce large moving groups in the disc. Our analysis also suggests that some of the moving groups in the Milky Way may have formed due to dynamical interactions with perturbing dwarf satellites. The groups identified in the simulations by our algorithm have similar properties to those found in the Milky Way, including similar fractions of the total stellar population included in the groups, as well as similar average velocities and velocity dispersions.
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Quintana, H. "Dynamics of Groups around Interacting Double Ellipticals: Measuring Dark Matter Haloes." International Astronomical Union Colloquium 124 (1990): 37–41. http://dx.doi.org/10.1017/s025292110000484x.
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Binary galaxies, as binary stars, are important to measure masses, as suggested by Page (1952). Because three orbit parameters are measurable for galaxies at one instant of time, severe uncertainties remain in the orbit and mass determinations. These uncertainties can partly be overcome by statistical studies of selected samples and/or n-body simulations. Close double galaxies (and isolated galaxies) could also be useful to estimate dynamical masses if we can find test particles around them.Interacting elliptical pairs or dumb-bell galaxies are found with a large range, between 0-1200 km s-1, of relative radial velocities. Standard 2-body orbit calculations, highly uncertain due to projection factors, suggest for the largest velocity differences very large galaxy masses, if the systems are bound and stationary. However, recent n-body simulations model these binaries as galaxies captured from hyperbolic orbits, requiring masses of order a few times 1011M⊙) (Borne et al. 1988), but producing systems that are short lived.
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Armus, Lee, Timothy M. Heckman, and George K. Miley. "The Nature of the Emission-line Nebulae in Powerful Far-infrared Galaxies." International Astronomical Union Colloquium 124 (1990): 409–13. http://dx.doi.org/10.1017/s025292110000542x.
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AbstractWe discuss our program of narrow-band (Hα + [Nil]) imaging of a sample of 30 powerful far-infrared galaxies (FIRG’s) chosen to have far-infrared spectral energy distributions similar to the prototype FIRG’s Arp 220, NGC 3690, NGC 6240, and M82. The emission-line nebulae of these IR color-selected sample (ICSS) galaxies as a class are both impressively large (mean half light radius, r ~1.3 Kpc, and mean diameter, D ~16 Kpc) and luminous (LTOT ~108 Lo; uncorrected for internal extinction). The mean total Hα + [Nil] luminosity of the FIRG’s is comparable to that found for pairs of optically selected interacting galaxies (Bushouse, Lamb, and Werner 1988), but is a factor of ~5 greater than that of isolated spirals (Kennicutt and Kent 1983). Only ~25% of the nearby (z ≤ 0.10) FIRG’s have morphologies suggesting that large HII~regions contribuí significantly to their emission-line appearance. The broad-band morphologies of our IR color-selected galaxies fall into three major categories. Nearly 75% are single galaxy systems, with the remaining FIRG’s being either multiple nuclei systems, or members of interacting pairs. Since we see few (10%) currently interacting FIRG’s, yet many (80%) with highly distorted continuum morphologies, our IR color criteria may be preferentially selecting galaxies that have undergone highly inelastic, rapidly merging interactions.
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Koribalski, Bärbel S. "H I Tidal Tails, Bridges and Clouds." Symposium - International Astronomical Union 217 (2004): 34–40. http://dx.doi.org/10.1017/s0074180900197074.
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There is plenty of intergalactic HI gas without any obvious stellar content ranging from (1) extended gas envelopes around some normal and peculiar galaxies, (2) tidal tails/bridges in interacting or merging galaxy systems, (3) large-scale rings around early type galaxies, and (4) detached clouds at varying distances from associated galaxies, but there are few or no isolated HI clouds.The HIPASS Bright Galaxy Catalog, which covers the whole southern sky, contains only one definite extragalactic HI cloud which is located close to the galaxy NGC 2442 whereas it is sensitive to isolated HI clouds with MHI > 106 x D2 M⊙. The space density of HI clouds is therefore about 1/1000th that of galaxies with the same MHI.
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Camps-Fariña, A., J. Beckman, J. Zaragoza-Cardiel, et al. "Kinematic properties of superbubbles in the Antennae, M83 and Arp 270." Proceedings of the International Astronomical Union 10, S309 (2014): 304. http://dx.doi.org/10.1017/s174392131401000x.
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AbstractSuperbubbles and large scale expansion in galaxies are important indicators of activity in galaxies: they are formed in starbursts and around active nuclei. Superbubbles can be used to give information about the star-forming region which produced them. We present in-depth results of our study of kinematically detected superbubbles using a method based on Fabry-Perot spectroscopy, which allows us to map regions of expansion across the entire disk of a galaxy. Three objects have been selected for this poster based on the interest of the results they show: two interacting galaxies, the Antennae and Arp270, at different stages of galaxy interaction, and the more isolated galaxy M83. We present the kinematic expansion maps, as well as a census of detected superbubbles and a dynamical study of their properties.
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Conidis, George J. "Spin Alignment in Analogues of The Local Sheet." Proceedings of the International Astronomical Union 11, S308 (2014): 443–48. http://dx.doi.org/10.1017/s1743921316010334.
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AbstractTidal torque theory and simulations of large scale structure predict spin vectors of massive galaxies should be coplanar with sheets in the cosmic web. Recently demonstrated, the giants (Ks⩽ -22.5 mag) in the Local Volume beyond the Local Sheet have spin vectors directed close to the plane of the Local Supercluster, supporting the predictions of Tidal Torque Theory. However, the giants in the Local Sheet encircling the Local Group display a distinctly different arrangement, suggesting that the mass asymmetry of the Local Group or its progenitor torqued them from their primordial spin directions. To investigate the origin of the spin alignment of giants locally, analogues of the Local Sheet were identified in the SDSS DR9. Similar to the Local Sheet, analogues have an interacting pair of disk galaxies isolated from the remaining sheet members. Modified sheets in which there is no interacting pair of disk galaxies were identified as a control sample.Galaxies in face-on control sheets do not display axis ratios predominantly weighted toward low values, contrary to the expectation of tidal torque theory. For face-on and edge-on sheets, the distribution of axis ratios for galaxies in analogues is distinct from that in controls with a confidence of 97.6% & 96.9%, respectively. This corroborates the hypothesis that an interacting pair can affect spin directions of neighbouring galaxies.
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Sánchez-Alarcón, P. M., J. Román, J. H. Knapen, L. Verdes-Montenegro, and S. Comerón. "Break type and interactions from ultra-deep optical imaging of isolated galaxies." Proceedings of the International Astronomical Union 17, S373 (2021): 275–77. http://dx.doi.org/10.1017/s1743921322004732.
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AbstractIn the standard cosmological model of galaxy evolution, mergers and interactions play a fundamental role in shaping galaxies. Galaxies that are currently isolated are thus interesting, allowing us to identify how internal or external processes impact galactic structure. However, current observational limits may be obscuring crucial information in the low-mass or low-brightness regime. We use the AMIGA catalog of isolated galaxies to explore the impact of different factors on the structure of these galaxies. In particular, we study the type of disk break based on the degree of isolation and the presence of interactions which are only detectable in the ultra-low surface brightness regime. We present the first results of an extensive observational campaign of ultra-deep optical imaging targeting a sample of 25 low-redshift (z < 0.035) isolated galaxies. The nominal surface brightness limits achieved are comparable to those to be obtained in the 10-year LSST coadds ( mag arcsec−2; 3σ ; 10” × 10”). We find that isolated galaxies have a considerably higher fraction of purely exponential disk profiles and a lower presence of up-bending breaks than field or cluster galaxies. Our extreme imaging depth allows us to detect the presence of previously unreported interactions with minor companions in some of the galaxies in our sample (∼40% of the galaxies show signs of interaction). The results of our work fit with the general framework of galactic structure in which up-bending breaks (Type III) would be produced by mergers and down-bending breaks (Type II) due to a threshold in star formation that would tend to become single exponential disk (Type I) in case of cessation or decrease of star formation.
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Lane, Richard R., Tom Richtler, and Ricardo Salinas. "What can isolated elliptical galaxies tell us about Cold Dark Matter?" Proceedings of the International Astronomical Union 11, S317 (2015): 326–27. http://dx.doi.org/10.1017/s1743921315008789.
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AbstractDue to their environment isolated elliptical galaxies (IEs) should not be undergoing extant evolutionary processes yet many IEs have interacting dwarf companions, and where no merger remnants are visible IEs are often dynamically young. Furthermore, some IEs do not require dark matter to explain their dynamics. However, according to Cold Dark Matter (CDM) simulations all elliptical galaxies should be dark matter dominated, even if isolated, and IEs are much rarer in nature than predicted by CDM. Moreover, merging at the ~107 M⊙ level was recently discovered in the M31 system, showing that hierarchical merging may indeed be scale-free, as predicted by CDM. It seems a natural question to ask: what can IEs tell us about CDM? Here we analyse several IEs as probes of CDM. Our results spawn many new questions.
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Jones, M. G., D. Espada, L. Verdes-Montenegro, et al. "The AMIGA sample of isolated galaxies." Astronomy & Astrophysics 609 (December 22, 2017): A17. http://dx.doi.org/10.1051/0004-6361/201731448.
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Context. We present the largest catalogue of HI single dish observations of isolated galaxies to date, as part of the multi-wavelength compilation being performed by the AMIGA project (Analysis of the interstellar Medium in Isolated GAlaxies). Despite numerous studies of the HI content of galaxies, no revision focused on the HI scaling relations of the most isolated L∗ galaxies has been made since Haynes & Giovanelli (1984, AJ, 89, 758). Aims. The AMIGA sample has been demonstrated to be almost “nurture free”, therefore, by creating scaling relations for the HI content of these galaxies we will define a metric of HI normalcy in the absence of interactions. Methods. The catalogue comprises of our own HI observations with Arecibo, Effelsberg, Nançay and GBT, and spectra collected from the literature. In total we have measurements or constraints on the HI masses of 844 galaxies from the Catalogue of Isolated Galaxies (CIG). The multi-wavelength AMIGA dataset includes a revision of the B-band luminosities (LB), optical diameters (D25), morphologies, and isolation. Due to the large size of the catalogue, these revisions permit cuts to be made to ensure isolation and a high level of completeness, which was not previously possible. With this refined dataset we fit HI scaling relations based on luminosity, optical diameter and morphology. Our regression model incorporates all the data, including upper limits, and accounts for uncertainties in both variables, as well as distance uncertainties. Results. The scaling relation of HI mass with D25 is in good agreement with that of Haynes & Giovanelli (1984), but our relation with LB is considerably steeper. This disagreement is attributed to the large uncertainties in the luminosities, which introduce a bias when fitting with ordinary least squares regression (as was done in previous works), and the different morphology distributions of the samples. We find that the main effect of morphology on the D25-relation is to increase the intercept towards later types, while for the LB-relation it is to flatten the slope. These trends were not evident in previous works due to the small number of detected early-type galaxies. Applying our relations to HI detected galaxies in the Virgo cluster we find that although the typical HI-deficiency is only ~0.3 dex, the tail of the distribution extends over an order of magnitude beyond that of the AMIGA sample. These results are in general agreement with previous studies of HI-deficiency in the Virgo cluster. Conclusions. The HI scaling relations of the AMIGA sample define an up-to-date metric of the HI content of almost “nurture free” galaxies. These relations allow the expected HI mass, in the absence of interactions, of an individual galaxy to be predicted to within 0.25 dex (for typical measurement uncertainties). These relations are thus suitable for use as statistical measures of the impact of interactions on the neutral gas content of galaxies.
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Rampazzo, R., A. Omizzolo, M. Uslenghi, et al. "Morphology and surface photometry of a sample of isolated early-type galaxies from deep imaging." Astronomy & Astrophysics 640 (August 2020): A38. http://dx.doi.org/10.1051/0004-6361/202038156.
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Context. Isolated early-type galaxies are evolving in unusually poor environments for this morphological family, which is typical of cluster inhabitants. We investigate the mechanisms driving the evolution of these galaxies. Aims. Several studies indicate that interactions, accretions, and merging episodes leave their signature on the galaxy structure, from the nucleus down to the faint outskirts. We focus on revealing such signatures, if any, in a sample of isolated early-type galaxies, and we quantitatively revise their galaxy classification. Methods. We observed 20 (out of 104) isolated early-type galaxies, selected from the AMIGA catalog, with the 4KCCD camera at the Vatican Advanced Technology Telescope in the Sloan Digital Sky Survey g and r bands. These are the deepest observations of a sample of isolated early-type galaxies so far: on average, the light profiles reach μg ≈ 28.11 ± 0.70 mag arcsec−2 and μr ≈ 27.36 ± 0.68 mag arcsec−2. The analysis was performed using the AIDA package, providing point spread function-corrected 2D surface photometry up to the galaxy outskirts. The package provides a model of the 2D galaxy light distribution, which after model subtraction enhances the fine and peculiar structures in the residual image of the galaxies. Results. Our re-classification suggests that the sample is composed of bona fide early-type galaxies spanning from ellipticals to late-S0s galaxies. Most of the surface brightness profiles are best fitted with a bulge plus disc model, suggesting the presence of an underlying disc structure. The residuals obtained after the model subtraction show the nearly ubiquitous presence of fine structures, such as shells, stellar fans, rings, and tails. Shell systems are revealed in about 60% of these galaxies. Conclusions. Because interaction, accretion, and merging events are widely interpreted as the origin of the fans, ripples, shells and tails in galaxies, we suggest that most of these isolated early-type galaxies have experienced such events. Because they are isolated (after 2–3 Gyr), these galaxies are the cleanest environment in which to study phenomena connected with events like these.
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Bootz, Vitor, Marina Trevisan, Trinh Thuan, Yuri Izotov, Angela Krabbe, and Oli Dors. "Isolated groups of extremely blue dwarf galaxies." Proceedings of the International Astronomical Union 15, S359 (2020): 168–69. http://dx.doi.org/10.1017/s1743921320001830.
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AbstractInteractions and mergers between dwarf galaxies are mostly gas-rich and should be marked by an intense star formation activity. But these processes, which are expected to be common at earlier times, are very difficult to observe at low redshifts. To investigate that, we look in the Sloan Digital Sky Survey (SDSS) for compact groups that contain one luminous compact galaxy (LCG) with very high specific star formation rate (sSFR) and at least two other blue galaxies. We found 24 groups that satisfy these criteria, among which 12 groups have SDSS spectroscopic data for at least 2 member galaxies. Here we want to investigate, using the tidal strength estimator Q, how interactions between neighbouring galaxies affect the sSFR and concentration of each LCG. Statistical tests reveal a correlation between Q and their sSFR, indicating that tidal forces between neighbouring galaxies might be inducing bursts of star formation in the LCGs.
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Ryan-Weber, E. V., M. E. Putman, K. C. Freeman, G. R. Meurer, and R. L. Webster. "Discovery of Intergalactic H II Regions." Symposium - International Astronomical Union 217 (2004): 492–97. http://dx.doi.org/10.1017/s0074180900198250.
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We have discovered a number of very small isolated H II regions 20-30 kpc from their nearest galaxy. The H II regions appear as tiny emission line dots (ELdots) in narrow band images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We have spectroscopic confirmation of 5 isolated H II regions in 3 systems. The Hα luminosities of the H II regions are equivalent to the ionizing flux of only 1 large or a few small OB stars each. These stars appear to have formed in situ and represent atypical star formation in the low density environment of galaxy outskirts. In situ star formation in the intergalactic medium offers an alternative to galactic wind models to explain metal enrichment. In interacting systems (2 out of 3), isolated H II regions could be a starting point for tidal dwarf galaxies.
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Ramírez-Moreta, P., L. Verdes-Montenegro, S. Leon, J. Blasco-Herrera, M. Fernández-Lorenzo, and M. Yun. "Faint features in the isolated galaxy CIG96." Proceedings of the International Astronomical Union 11, S321 (2016): 292. http://dx.doi.org/10.1017/s1743921316008826.
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The AMIGA project carries out a multiwavelength study of the largest catalogue of isolated galaxies from the Local Universe (CIG, Karachentseva 1973). Compared to any other sample —field galaxies included— and using highly strict isolation criteria (unperturbed for at least ~3 Gyr, Verdes-Montenegro et al. 2005), all the results show that these galaxies have the lowest values of the physical magnitudes expected to be enhanced by interactions. This strongly supports isolated galaxies as ideal laboratories for the study of galaxy formation and evolution. Despite CIG galaxies show the lowest HI integrated profile asymmetry level when compared to any other sample, some cases present up to 50% HI asymmetry (Espada et al. 2011b). We aim to shed light over the causes and sources of such asymmetries with our deep radiointerferometric and optical observations of CIG targets. Since major mergers are ruled out by the isolation criteria, in this work we are addressing whether minor mergers, internal processes or primordial gas accretion are responsible for such asymmetries.
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van Driel, Wim, and Bert van den Broek. "Barred Extreme IRAS Galaxies." International Astronomical Union Colloquium 157 (1996): 256–58. http://dx.doi.org/10.1017/s0252921100049897.
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AbstractWe studied a statistically complete sample of 57 southern socalled extreme IRAS galaxies, i.e., objects with a high far-infrared/blue luminosity ratio, LFIR/LB>3, using optical (imaging and spectra), radio continuum, and CO(1–0) line observations. The sample can be divided into three distinct categories: dwarfs (20%), barred spirals (35%), and interacting systems (35%). The barred galaxies are generally morphologically undisturbed, isolated systems, with average star formation rates (4 M⊙ yr–1) and efficiencies (LFIR/MH2 = 16 L⊙/M⊙) for galaxies in our sample. An enhanced massive star formation rate is the cause of the infrared brightness in 93% of all galaxies in the sample. The nuclear region is the most important star formation locus, generally unresolved at 1" resolution, i.e., less than 0.2-0.6 kpc size (H0=75 km s–1 Mpc–1), though 2 kpc size in three cases. In about two-thirds of the extreme IRAS SB’s, fainter, diffuse (2.5-10 kpc size) massive star formation is seen in the bar as well.
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Cutri, Roc M. "Nuclear and Extended Infrared Emission in Paired and Isolated Galaxies." International Astronomical Union Colloquium 124 (1990): 415–19. http://dx.doi.org/10.1017/s0252921100005431.
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The empirical connection between gravitational and collisional interactions among galaxies and enhanced activity has been well-documented. However, the physical mechanisms which are responsible for triggering the various forms of activity have not been determined. We present the preliminary results of a study of the nuclear and integrated infrared properties of galaxies chosen from the Catalog of Isolated Pairs of Galaxies in the Northern Hemisphere (Karachentsev 1972; hereafter CPG) and the Catalog of Isolated Galaxies (Karachentseva 1973; hereafter KI). Observations of these large, unbiased samples of paired and isolated galaxies are analyzed with the hope of identifying which aspects of galaxy encounters are most closely coupled to the presence of activity.
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Márquez, I. "Environmental Effects on the Properties of Spiral Galaxies: Isolated Pairs of Spirals." Symposium - International Astronomical Union 171 (1996): 410. http://dx.doi.org/10.1017/s0074180900233299.
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We characterized isolated spiral galaxies as a reference for the properties of interacting ones: we selected all the spirals in CfA catalog with mB ≤ 13.0,δ ≥ 0, a≤ 4′ and 73° > i > 32°. The isolated ones were those having no companions in ΔD≤0.5Mpc and ΔV≤500 km/s and no satellites galaxies in their neighborhood (from Nilson catalog and Palomar charts). To select the isolated pairs of spirals we used Karachentsev's catalog applying similar conditions for mB, δ, a, i and the same isolation criteria. We used broad band CCD images (Johnson B,V e I), narrow band CCD images (Hα) and long slit spectra in Ha region. The BVI images analysis consisted on applying sharp-divided methods, obtaining simulated images (from bulge/disk decomposition and galaxy orientation in the sky) and Fourier analysis. From Hα images we determined total emission, size, distribution and flux of HII regions. We also obtained the rotation curves.
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Deng, Xin-Fa. "A comparison of the star formation rate and the specific star formation rate distributions between paired galaxies and isolated ones." Canadian Journal of Physics 91, no. 4 (2013): 337–42. http://dx.doi.org/10.1139/cjp-2012-0487.
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From each of two volume-limited main galaxy samples of the Sloan Digital Sky Survey data release 7, a paired galaxy sample and an isolated galaxy sample are constructed and comparative studies between the star formation of galaxies in pairs and isolated are performed to explore influences of galaxy interactions on star formation. It is found that isolated galaxies have an enhancement of the star formation rate and the specific star formation rate, which suggests that interactions between galaxies are not the trigger of enhanced star formation.
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Koopmann, Rebecca A., and Jeffrey D. P. Kenney. "Star Formation Along the Bars of Virgo Cluster and Isolated Spiral Galaxies." International Astronomical Union Colloquium 157 (1996): 105–7. http://dx.doi.org/10.1017/s025292110004954x.
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Star formation along the bar is common in late-type barred galaxies (Phillips and Garcia-Barreto et al., these proceedings), which tend to have weak stellar bars. It is rarer in strongly barred galaxies, e.g., early-type spiral galaxies. Abundance gradient measurements (Martin & Roy 1995) and simulations (Friedli & Benz 1995) suggest that star formation along the bar of strongly barred galaxies may indicate a young bar. Since bars can be created in tidal interactions and mergers (Noguchi 1987), it is of interest to investigate the star formation properties of barred galaxies in different environments. We use Hα images to compare the star formation properties in the bar region of a sample of barred galaxies in the Virgo Cluster and a control sample of isolated galaxies. We focus on the three galaxies with the strongest star formation along the bar, including NGC 4424, a possible merger remnant.
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Mazzei, P., R. Rampazzo, A. Marino, G. Trinchieri, M. Uslenghi, and A. Wolter. "Insights into the Evolution of Five Isolated Galaxies." Astrophysical Journal 927, no. 1 (2022): 124. http://dx.doi.org/10.3847/1538-4357/ac4808.
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Abstract Galaxy evolution is believed to be conditioned by the environment. Isolated galaxies or galaxies in poor groups are an excellent laboratory to study evolutionary mechanisms where effects of the environment are minimal. We present new Swift-UVOT data in six filters, three in the ultraviolet (UV), of five isolated galaxies aiming at shedding light into their evolution. For all of our targets, we present new UV integrated fluxes, and for some of them also new UBV magnitudes. Our observations allow us to improve their multiwavelength spectral energy distributions, extending them over about three orders of magnitude in wavelength. We exploit our smooth particle hydrodynamical simulations with chemo-photometric implementation anchored, a posteriori, to the global multiwavelength properties of our targets, to give insight into their evolution. Then we compare their evolutionary properties with those previously derived for several galaxies in groups. The evolution of our targets is driven by a merger that occurred several gigayears ago, in the redshift range 0.5 ≤ z ≤ 4.5, not unlike what we have already found for galaxies in groups. The merger shapes the potential well where the gas is accreting, driving the star formation rate and the galaxy evolution. Isolated galaxies should not have suffered from interactions for at least 3 Gyr. However, the initial merger is still leaving its signature on the properties of our targets. Several rejuvenation episodes, triggered by in situ accretion, are highlighted. Moreover, jellyfish morphologies appear as these galaxies achieve their maximum star formation rate, before their quenching phase.
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Steffen, Joshua L., Hai Fu, Joel R. Brownstein, et al. "SDSS-IV MaNGA: How Galaxy Interactions Influence Active Galactic Nuclei." Astrophysical Journal 942, no. 2 (2023): 107. http://dx.doi.org/10.3847/1538-4357/aca768.
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Abstract We present a comparative study of active galactic nuclei (AGN) between galaxy pairs and isolated galaxies with the final data release of the MaNGA integral field spectroscopic survey. We build a sample of 391 kinematic galaxy pairs within the footprint of the survey and select AGN using the survey's spectra. We use the comoving volume densities of the AGN samples to quantify the effects that tidal interactions have on the triggering of nuclear accretion. Our hypothesis is that the pair sample contains AGN that are triggered by not only stochastic accretion but also tidally induced accretion and correlated accretion. With the level of stochastically triggered AGN fixed by the control sample, we model the strength of tidally induced accretion and correlated accretion as a function of projected separation (r p ) and compare the model expectations with the observed volume densities of dual AGN and offset AGN (single AGN in a pair). At r p ∼ 10 kpc, we find that tidal interactions induce ∼30% more AGN than stochastic fueling and cause ∼12% of the offset AGN to become dual AGN because of correlations. The strength of both these effects decreases with increasing r p . We also find that the [O iii] luminosities of the AGN in galaxy pairs are consistent with those found in isolated galaxies, likely because stochastically fed AGN dominate even among close pairs. Our results illustrate that while we can detect tidally induced effects statistically, it is challenging to separate tidally induced AGN and stochastically triggered AGN in interacting galaxies.
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Repetto, P., M. Rosado, R. Gabbasov, and I. Fuentes-Carrera. "KPG 390: A pair of trailing spirals." Proceedings of the International Astronomical Union 6, S271 (2010): 127–34. http://dx.doi.org/10.1017/s1743921311017534.
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AbstractIn this study we present scanning Fabry-Perot Hα observations of the isolated interacting galaxy pair NGC 5278/79. We derived velocity fields, various kinematic parameters and rotation curves for both galaxies. These kinematical results together with the fact that dust lanes have been detected in both galaxies, as well as the analysis of surface brightness profiles along the minor axis, allowed us to determine univocally that both components of the interacting pair are trailing spirals. We have also estimated the mass of NGC 5278 fitting its rotation curve with a disk-halo component. We have tested three different types of halo (pseudo-isothermal, Hernquist and Navarro Frenk White) and we have obtained that the rotation curve can be fitted either with a pseudo-isothermal, an Hernquist halo or a Navarro Frenk White halo component, although in the first case the amount of dark matter required is about ten times smaller than for the other two halo distributions.
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Pfefferkorn, F., Th Boller, and P. Rafanelli. "Soft X-ray properties of a spectroscopically selected sample of interacting and isolated Seyfert galaxies." Astronomy & Astrophysics 368, no. 3 (2001): 797–816. http://dx.doi.org/10.1051/0004-6361:20010055.
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Argudo-Fernández, M., I. Lacerna, and S. Duarte Puertas. "The dependence of mass and environment on the secular processes of AGNs in terms of morphology, colour, and specific star-formation rate." Astronomy & Astrophysics 620 (December 2018): A113. http://dx.doi.org/10.1051/0004-6361/201833328.
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Context. Galaxy mass and environment play a major role in the evolution of galaxies. In the transition from star-forming to quenched galaxies, active galactic nuclei (AGNs) also have a principal action therein. However, the connections between these three actors are still uncertain. Aims. In this work we investigate the effects of stellar mass and the large-scale structure (LSS) environment on the fraction of optical nuclear activity in a population of isolated galaxies, where AGN would not be triggered by recent galaxy interactions or mergers. Methods. As a continuation of a previous work, we focus on isolated galaxies to study the effect of stellar mass and the LSS in terms of morphology (early- and late-type), colour (red and blue), and specific star-formation rate (quenched and star-forming). To explore where AGN activity is affected by the LSS, we separate galaxies into two groups, of low- and high mass, respectively, and use the tidal strength parameter to quantify the effects. Results. We found that AGN is strongly affected by stellar mass in “active” galaxies (namely late-type, blue, and star-forming), but that mass has no influence on “quiescent” galaxies (namely early-type, red, and quenched), at least for masses down to 1010 M⊙. In relation to the LSS, we found an increase in the fraction of star-forming nuclei galaxies with denser LSS in low-mass star-forming and red isolated galaxies. Regarding AGN, we find a clear increase in the fraction of AGNs with denser environment in quenched and red isolated galaxies, independently of the stellar mass. Conclusions. Active galactic nuclei activity appears to be “mass triggered” in active isolated galaxies. This means that AGN activity is independent of the intrinsic properties of the galaxies, but is dependent on their stellar mass. On the other hand, AGN activity appears to be “environment triggered” in quiescent isolated galaxies, where the fraction of AGNs as a function of specific star formation rate and colour increases from void regions to denser LSS, independently of stellar mass.
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Kopenhafer, Claire, Brian W. O’Shea, and G. Mark Voit. "Seeking Self-regulating Simulations of Idealized Milky Way–like Galaxies." Astrophysical Journal 951, no. 2 (2023): 107. http://dx.doi.org/10.3847/1538-4357/accbb7.
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Abstract Precipitation is potentially a mechanism through which the circumgalactic medium (CGM) can regulate a galaxy’s star formation. Here, we present idealized simulations of isolated Milky Way–like galaxies intended to examine the ability of galaxies to self-regulate their star formation, in particular via precipitation. We also examine the impact of rotation in the CGM. Using six simulations, we explore variations in the initial CGM t cool/t ff ratio and rotation profile. Those variations affect the amount of gas accretion and star formation within the galactic disk. To encourage this accretion and better study its dependence on CGM structure, we gradually increase the efficiency of stellar feedback during the first half of our simulations. Yet despite this gradual increase, the resulting outflows quickly evacuate large, hot cavities within the CGM and even beyond r 200. Some of the CGM gas avoids interacting with the cavities and is able to feed the disk along its midplane, but the cooling of feedback-heated gas far from the midplane is too slow to supply the disk with additional gas. Our simulations illustrate the importance of physical mechanisms in the outer CGM and IGM for star formation regulation in Milky Way–scale halos.
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Verheijen, Marc, and Brent Tully. "A dichotomy between HSB and LSB galaxies." International Astronomical Union Colloquium 171 (1999): 92–101. http://dx.doi.org/10.1017/s0252921100054166.
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AbstractA complete sample of spiral galaxies in the Ursa Major cluster is imaged at various optical wavelengths and in the Near-Infrared K′-band. HI rotation curves were obtained for all gas rich systems. The Near-Infrared surface brightness distribution of disk galaxies turns out to be bimodal; galaxies avoid a domain around mag/arcsec2. This bimodality is particularly striking when only the more isolated, non-interacting systems are considered. The Luminosity Function of the HSB family of galaxies is truncated well above the completion limit while the Luminosity Function of the LSB family is still sharply rising at our limiting magnitude. Near-Infrared mass-to-light ratios suggest that HSB galaxies are close to a kinematic maximum-disk situation while LSB galaxies are dark matter dominated at all radii. Assuming equal Near-Infrared mass-to-light ratios for both HSB and LSB systems, we find that the gap in the surface brightness distribution corresponds to a situation in which the baryonic mass is marginally self-gravitating. We finally conclude that the luminosity-line width relation is a fundamental correlation between the amount and distribution of dark matter mass and the total luminosity, regardless of how the luminous mass is distributed within the dark mater halo.
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Kenney, Jeffrey, and Rebecca Koopmann. "Environmental Extremists in the Virgo Cluster." Symposium - International Astronomical Union 186 (1999): 387–92. http://dx.doi.org/10.1017/s0074180900113166.
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Many types of galaxy interactions have been posited to occur in clusters, although it remains unclear which processes actually occur, and which ones might help explain the tendency for early type galaxies to inhabit high density environments, or cause the rapid evolution of cluster galaxies (e.g., Dressler et al. 1997). With these questions in mind, we have been conducting an environmental inventory of galaxies in the Virgo Cluster. Our approach is to combine surveys of spirals and S0s with detailed studies of the most interesting and peculiar galaxies. In this paper, we describe two main points. 1.) There is a population of spiral galaxies in the Virgo cluster with the small central light concentrations (bulge-to-disk ratios, or B/D's) characteristic of isolated Sb and Sc galaxies, but global star formation rates lower than those of isolated spirals of any Hubble class (Sa-Sc). These Virgo galaxies are generally classified as “early type” (e.g. Sa), and thus contribute to the morphology-density relationship. 2.) There are several types of environmental interactions occurring in Virgo, including low velocity tidal interactions and mergers, high velocity tidal interactions and collisions, HI accretion, and ICM-ISM stripping. We discuss examples of some of these interactions.
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Tissera, P. B., M. S. Alonso, D. G. Lambas, and G. Coldwell. "Triggering Star Formation by Galaxy-Galaxy Interactions." Symposium - International Astronomical Union 217 (2004): 434–35. http://dx.doi.org/10.1017/s0074180900198146.
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We analyzed the effects of having a close companion on the star formation activity of galaxies in the 8K galaxy pair catalog selected from the 2dFGRS. We found that, statistically, galaxies with rp < 25h−1 kpc and ΔV < 100km s−1 have enhanced star formation with respect to isolated galaxies with the same luminosity and redshift distribution. Our results suggest that the physical processes at work during tidal interactions can overcome the effects of environment, except in dense regions.
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Oosterloo, Tom, Raffaella Morganti, Elaine M. Sadler, Annette Ferguson, Thijs van der Hulst, and Helmut Jerjen. "Tidal Remnants and Intergalactic H II Regions." Symposium - International Astronomical Union 217 (2004): 486–91. http://dx.doi.org/10.1017/s0074180900198249.
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We report the discovery of two small intergalactic H II regions in the loose group of galaxies around the field elliptical NGC 1490. The H II regions are located at least 100 kpc from any optical galaxy but are associated with a number of large H I clouds that are lying along an arc 500 kpc in length and that have no optical counterpart on the Digital Sky Survey. The sum of the H I masses of the clouds is almost 1010M⊙ and the largest H I cloud is about 100 kpc in size. Deep optical imaging reveals a very low surface brightness counterpart to this largest H I cloud, making this one of the H I richest optical galaxies known (MHI/LV ~ 200). Spectroscopy of the H II regions indicates that the abundance in these H II regions is only slightly sub-solar, excluding a primordial origin of the H I clouds. The H I clouds are perhaps remnants resulting from the tidal disruption of a reasonably sized galaxy, probably quite some time ago, by the loose group to which NGC 1490 belongs. Alternatively, they are remnants of the merger that created the field elliptical NGC 1490. The isolated H II regions show that star formation on a very small scale can occur in intergalactic space in gas drawn from galaxies by tidal interactions. Many such intergalactic small star formation regions may exist near tidally interacting galaxies.
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Shah, Ekta A., Jeyhan S. Kartaltepe, Christina T. Magagnoli, et al. "Investigating the Effect of Galaxy Interactions on Star Formation at 0.5 < z < 3.0." Astrophysical Journal 940, no. 1 (2022): 4. http://dx.doi.org/10.3847/1538-4357/ac96eb.
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Abstract Observations and simulations of interacting galaxies and mergers in the local universe have shown that interactions can significantly enhance the star formation rates (SFRs) and fueling of active galactic nuclei (AGN). However, at higher redshift, some simulations suggest that the level of star formation enhancement induced by interactions is lower due to the higher gas fractions and already increased SFRs in these galaxies. To test this, we measure the SFR enhancement in a total of 2351 (1327) massive (M * > 1010 M ⊙) major (1 < M 1/M 2 < 4) spectroscopic galaxy pairs at 0.5 < z < 3.0 with ΔV < 5000 km s−1 (1000 km s−1) and projected separation <150 kpc selected from the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find that the highest level of SFR enhancement is a factor of 1.23 − 0.09 + 0.08 in the closest projected separation bin (<25 kpc) relative to a stellar mass-, redshift-, and environment-matched control sample of isolated galaxies. We find that the level of SFR enhancement is a factor of ∼1.5 higher at 0.5 < z < 1 than at 1 < z < 3 in the closest projected separation bin. Among a sample of visually identified mergers, we find an enhancement of a factor of 1.86 − 0.18 + 0.29 (∼3σ) for coalesced systems. For this visually identified sample, we see a clear trend of increased SFR enhancement with decreasing projected separation (2.40 − 0.37 + 0.62 versus 1.58 − 0.20 + 0.29 for 0.5 < z < 1.6 and 1.6 < z < 3.0, respectively). The SFR enhancements seen in our interactions and mergers are all lower than the level seen in local samples at the same separation, suggesting that the level of interaction-induced star formation evolves significantly over this time period.
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Wirth, Gregory, and Paola Belloni. "Morphology of E+A Galaxies in CL0016+16 (z=0.54)." Symposium - International Astronomical Union 171 (1996): 469. http://dx.doi.org/10.1017/s0074180900233871.
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We present new results on the morphology of member galaxies in the distant cluster C10016+16 from HST images (WFCl). Based on narrow multiband ground-based photometry and spectra obtained with the Keck 10 m telescope we identify 7 new cluster members which appear to have strong Balmer absorption features but no detectable emission lines, doubling the number of such galaxies previously observed with HST in this cluster. These candidate E+A galaxies have been identified in other distant clusters, but the morphology of this population has appeared bulge-like in AC114 (Couch et al., 1994, ApJ 430, 107) and disk-like or irregular and interacting in C10939+47 and C10016+16 (Wirth et al., 1994 ApJ 435, L105). By means of the image concentration index as a quantitative measure of morphology we show that our enlarged sample of E+A objects in C10016+16 now contains some galaxies resembling bulge systems as well as the previously-identified disk-like objects. The observed heterogeneity suggests that both galaxy mergers (rapidly resulting in an r1/4 profile) and ram-pressure stripping of isolated late-type systems may originate E+A objects.
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McConnachie, Alan W., Clare R. Higgs, Guillaume F. Thomas, et al. "Solo dwarfs – III. Exploring the orbital origins of isolated Local Group galaxies with Gaia Data Release 2." Monthly Notices of the Royal Astronomical Society 501, no. 2 (2020): 2363–77. http://dx.doi.org/10.1093/mnras/staa3740.
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ABSTRACT We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star-forming, dwarf galaxies in the Local Group, taken as part of the Solo survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613, and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2, and Phoenix) are close enough that their proper motions have already been derived using red giant branch stars. Systematic errors in Gaia DR2 are significant for NGC 6822, IC 1613, and WLM. We explore the orbits for these galaxies, and conclude that Phoenix, Leo A, and WLM are unlikely to have interacted with the Milky Way or M31, unless these large galaxies are very massive (${\gtrsim}1.6 \times 10^{12}\, \mathrm{M}_\odot$). We rule out a past interaction of NGC 6822 with M31 at ${\sim}99.99{{\ \rm per\ cent}}$ confidence, and find there is a &lt;10 per cent chance that NGC 6822 has had an interaction with the Milky Way. We examine the likely origins of NGC 6822 in the periphery of the young Local Group, and note that a future interaction of NGC 6822 with the Milky Way or M31 in the next 4 Gyr is essentially ruled out. Our measurements indicate that future Gaia data releases will provide good constraints on the interaction history for the majority of these galaxies.