48 results on '"Konstantopoulos, I."'
Search Results
2. NEOWISE OBSERVATIONS OF NEAR-EARTH OBJECTS: PRELIMINARY RESULTS
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Mainzer, A, Grav, T, Bauer, J, Masiero, J, McMillan, RS, Cutri, RM, Walker, R, Wright, E, Eisenhardt, P, Tholen, DJ, Spahr, T, Jedicke, R, Denneau, L, DeBaun, E, Elsbury, D, Gautier, T, Gomillion, S, Hand, E, Mo, W, Watkins, J, Wilkins, A, Bryngelson, GL, Del Pino Molina, A, Desai, S, Camus, M Gómez, Hidalgo, SL, Konstantopoulos, I, Larsen, JA, Maleszewski, C, Malkan, MA, Mauduit, J-C, Mullan, BL, Olszewski, EW, Pforr, J, Saro, A, Scotti, JV, and Wasserman, LH
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infrared: planetary systems ,minor planets ,asteroids: general ,planets and satellites: general ,surveys ,astro-ph.EP ,Astronomical and Space Sciences ,Atomic ,Molecular ,Nuclear ,Particle and Plasma Physics ,Physical Chemistry (incl. Structural) ,Astronomy & Astrophysics - Abstract
With the NEOWISE portion of the Wide-field Infrared Survey Explorer (WISE) project, we have carried out a highly uniform survey of the near-Earth object (NEO) population at thermal infrared wavelengths ranging from 3 to 22 μm, allowing us to refine estimates of their numbers, sizes, and albedos. The NEOWISE survey detected NEOs the same way whether they were previously known or not, subject to the availability of ground-based follow-up observations, resulting in the discovery of more than 130 new NEOs. The survey's uniform sensitivity, observing cadence, and image quality have permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by NEOWISE during the fully cryogenic portion of the WISEmission to the larger population. We find that there are 981 19 NEAs larger than 1km and 20,500 3000 NEAs larger than 100m. We show that the Spaceguard goal of detecting 90% of all 1km NEAs has been met, and that the cumulative size distribution is best represented by a broken power law with a slope of 1.32 0.14 below 1.5km. This power-law slope produces 13, 200 1900 NEAs with D > 140m. Although previous studies predict another break in the cumulative size distribution below D 50-100m, resulting in an increase in the number of NEOs in this size range and smaller, we did not detect enough objects to comment on this increase. The overall number for the NEA population between 100 and 1000m is lower than previous estimates. The numbers of near-Earth comets and potentially hazardous NEOs will be the subject of future work. © 2011. The American Astronomical Society. All rights reserved.
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- 2011
3. Nonsingular dislocation and crack fields: implications to small volumes
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Kioseoglou, J., Konstantopoulos, I., Ribarik, G., Dimitrakopulos, G. P., and Aifantis, E. C.
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- 2009
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4. Early signs of left ventricular dysfunction in adolescents with Type 1 diabetes mellitus: The importance of impaired circadian modulation of blood pressure and heart rate
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Karavanaki, K., Kazianis, G., Konstantopoulos, I., Tsouvalas, E., and Karayianni, C.
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- 2008
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5. QT interval prolongation in association with impaired circadian variation of blood pressure and heart rate in adolescents with Type 1 diabetes
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Karavanaki, K., Kazianis, G., Kakleas, K., Konstantopoulos, I., and Karayianni, C.
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- 2007
6. Modeling the response of ER damper: phenomenology and emulation
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Burton, Scott A., Makris, Nicos, Konstantopoulos, I., and Antsaklis, P.J.
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Electrorheological fluids -- Models ,Damping (Mechanics) -- Models ,Science and technology - Abstract
In this paper physically motivated and nonparametric models are investigated that predict within some tolerance the response of a semiactive electrorheological (ER) damper that was designed, constructed, and tested. The electrorheological damper is a hydraulic device that was designed for applications in vibration control of civil structures. The simplest possible physically motivated phenomenological models are first considered to predict the damper response without and with the presence of electric field. Subsequently, the performance of a multilayer neural network constructed and trained by an efficient algorithm known as the dependence identification algorithm is examined to predict the response of the ER damper. The performance of the neural network is compared to that of the phenomenological models and some conclusions are provided.
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- 1996
7. Erratum to: Nonsingular dislocation and crack fields: implications to small volumes
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Kioseoglou, J., Konstantopoulos, I., Ribarik, G., Dimitrakopulos, G. P., and Aifantis, E. C.
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- 2009
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8. SAMI Galaxy Survey: observing the environmental quenching of star formation in GAMA groups.
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Schaefer, A L, Croom, S M, Scott, N, Brough, S, Allen, J T, Bekki, K, Bland-Hawthorn, J, Bloom, J V, Bryant, J J, Cortese, L, Davies, L J M, Federrath, C, Fogarty, L M R, Green, A W, Groves, B, Hopkins, A M, Konstantopoulos, I S, López-Sánchez, A R, Lawrence, J S, and McElroy, R E
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STAR formation ,GALACTIC evolution ,STELLAR mass ,RADIAL distribution function ,DENSITY of stars - Abstract
We explore the radial distribution of star formation in galaxies in the SAMI Galaxy Survey as a function of their Local Group environment. Using a sample of galaxies in groups (with halo masses less than |$\simeq 10^{14} \, \mathrm{M_{\odot }}$|) from the Galaxy And Mass Assembly Survey, we find signatures of environmental quenching in high-mass groups (|$M_{\mathrm{ G}}\, \gt\, 10^{12.5} \, \mathrm{M_{\odot }}$|). The mean integrated specific star formation rate (sSFR) of star-forming galaxies in high-mass groups is lower than for galaxies in low-mass groups or those that are ungrouped, with |$\Delta \log (\mathrm{ sSFR}/\mathrm{yr^{-1}}) \,=\, 0.45 \pm 0.07$|. This difference is seen at all galaxy stellar masses. In high-mass groups, star-forming galaxies more massive than |$M_{*} \sim 10^{10} \, \mathrm{M_{\odot }}$| have centrally concentrated star formation. These galaxies also lie below the star formation main sequence, which suggests they may be undergoing outside-in quenching. Lower mass galaxies in high-mass groups do not show evidence of concentrated star formation. In groups less massive than |$M_{\mathrm{ G}} = 10^{12.5} \, \mathrm{M_{\odot }}$|, we do not observe these trends. In this regime, we find a modest correlation between centrally concentrated star formation and an enhancement in the total star formation rate, consistent with triggered star formation in these galaxies. [ABSTRACT FROM AUTHOR]
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- 2019
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9. The SAMI Galaxy Survey: stellar and gas misalignments and the origin of gas in nearby galaxies.
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Bryant, J J, Croom, S M, van de Sande, J, Scott, N, Fogarty, L M R, Bland-Hawthorn, J, Bloom, J V, Taylor, E N, Brough, S, Robotham, A, Cortese, L, Couch, W, Owers, M S, Medling, A M, Federrath, C, Bekki, K, Richards, S N, Lawrence, J S, and Konstantopoulos, I S
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GALACTIC evolution ,EVOLUTIONARY theories ,SPECTRAL imaging ,SPECTROGRAPHS ,GALACTIC dynamics ,KINEMATICS - Abstract
Misalignment of gas and stellar rotation in galaxies can give clues to the origin and processing of accreted gas. Integral field spectroscopic observations of 1213 galaxies from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey show that 11 per cent of galaxies with fitted gas and stellar rotation are misaligned by more than 30° in both field/group and cluster environments. Using SAMI morphological classifications and Sérsic indices, the misalignment fraction is 45 ± 6 per cent in early-type galaxies (ETGs), but only 5 ± 1 per cent in late-type galaxies (LTGs). The distribution of position angle offsets is used to test the physical drivers of this difference. Slower dynamical settling time of the gas in elliptical stellar mass distributions accounts for a small increase in misalignment in early-type galaxies. However, gravitational dynamical settling time is insufficient to fully explain the observed differences between ETGs and LTGs in the distributions of the gas/stellar position angle offsets. LTGs have primarily accreted gas close to aligned rather than settled from misaligned based on analysis of the skewed distribution of PA offsets compared to a dynamical settling model. Local environment density is less important in setting the misalignment fractions than morphology, suggesting that mergers are not the main source of accreted gas in these discs. Cluster environments are found to have gas misalignment driven primarily by cluster processes not by gas accretion. [ABSTRACT FROM AUTHOR]
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- 2019
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10. The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry.
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Bloom, J. V., Croom, S. M., Bryant, J. J., Schaefer, A. L., Bland-Hawthorn, J., Brough, S., Callingham, J., Cortese, L., Federrath, C., Scott, N., van de Sande, J., D'Eugenio, F., Sweet, S., Tonini, C., Allen, J. T., Goodwin, M., Green, A. W., Konstantopoulos, I. S., Lawrence, J., and Lorente, N.
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DWARF galaxies ,INTEGRAL field spectroscopy ,ASYMMETRY (Chemistry) ,KINEMATICS ,STELLAR mass ,FLOW velocity - Abstract
In order to determine the causes of kinematic asymmetry in the Hα gas in the SAMI (Sydney- AAO Multi-object IFS) Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxies on perturbation. We use spatially resolved Hα velocity fields from the SAMI Galaxy Survey to quantify kinematic asymmetry (...) in nearby galaxies and environmental and stellar mass data from the Galaxy And Mass Assembly survey. We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with log (M
* /M⊙ ) > 10.0, but there is no significant correlation for galaxies with log (M* /M⊙ ) < 10.0. Moreover, lowmass galaxies [log (M* /M⊙ ) < 9.0] have greater kinematic asymmetry at all separations, suggesting a different physical source of asymmetry is important in low-mass galaxies. We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetry in low-mass galaxies. High gas fraction is linked to high σm /V (where σm is Hα velocity dispersion and V the rotation velocity), which is strongly correlated with ..., and galaxies with log (M* /M⊙ ) < 9.0 have offset ... from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with log (M* /M⊙ ) < 9.0. Gas mass and asymmetry are also inversely correlated in our sample. We propose that low gas masses in dwarf galaxies may lead to asymmetric distribution of gas clouds, leading to increased relative turbulence. [ABSTRACT FROM AUTHOR]- Published
- 2018
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11. The SAMI Galaxy Survey: the low-redshift stellar mass Tully-Fisher relation.
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Bloom, J. V., Croom, S. M., Bryant, J. J., Callingham, J. R., Schaefer, A. L., Cortese, L., Hopkins, A. M., D'Eugenio, F., Scott, N., Glazebrook, K., Tonini, C., McElroy, R. E., Clark, H. A., Catinella, B., Allen, J. T., Bland-Hawthorn, J., Goodwin, M., Green, A. W., Konstantopoulos, I. S., and Lawrence, J.
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GALACTIC evolution ,GALACTIC redshift ,STELLAR mass ,SPECTRAL imaging ,INTEGRAL field spectroscopy - Abstract
We investigate the Tully-Fisher relation (TFR) for a morphologically and kinematically diverse sample of galaxies from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey using two-dimensional spatially resolved Hα velocity maps and find a welldefined relation across the stellar mass range of 8.0 < log (M
* /M☉ ) < 11.5. We use an adaptation of kinemetry to parametrize the kinematic Hα asymmetry of all galaxies in the sample, and find a correlation between scatter (i.e. residuals off the TFR) and asymmetry. This effect is pronounced at low stellar mass, corresponding to the inverse relationship between stellar mass and kinematic asymmetry found in previous work. For galaxies with log (M* /M☉ ) < 9.5, 25 ± 3 per cent are scattered below the root mean square (RMS) of the TFR, whereas for galaxies with log (M* /M☉ ) > 9.5 the fraction is 10 ± 1 per cent. We use 'simulated slits' to directly compare our results with those from long slit spectroscopy and find that aligning slits with the photometric, rather than the kinematic, position angle, increases global scatter below the TFR. Further, kinematic asymmetry is correlated with misalignment between the photometric and kinematic position angles. This work demonstrates the value of 2D spatially resolved kinematics for accurate TFR studies; integral field spectroscopy reduces the underestimation of rotation velocity that can occur from slit positioning off the kinematic axis. [ABSTRACT FROM AUTHOR]- Published
- 2017
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12. The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies.
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Foster, C., van de Sande, J., D'Eugenio, F., Cortese, L., McDermid, R. M., Bland-Hawthorn, J., Brough, S., Bryant, J., Croom, S. M., Goodwin, M., Konstantopoulos, I. S., Lawrence, J., López-Sánchez, Á. R., Medling, A. M., Owers, M. S., Richards, S. N., Scott, N., Taranu, D. S., Tonini, C., and Zafar, T.
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KINEMATICS ,INTEGRAL field spectroscopy ,AXIAL flow ,GALACTIC dynamics ,GRAVITATIONAL potential - Abstract
Using the stellar kinematic maps and ancillary imaging data from the Sydney AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of kinematically selected samples of galaxies is inferred. We implement an efficient and optimized algorithm to fit the intrinsic shape of galaxies using an established method to simultaneously invert the distributions of apparent ellipticities and kinematic misalignments. The algorithm output compares favourably with previous studies of the intrinsic shape of galaxies based on imaging alone and our reanalysis of the ATLAS
3D data. Our results indicate that most galaxies are oblate axisymmetric. We show empirically that the intrinsic shape of galaxies varies as a function of their rotational support as measured by the 'spin' parameter proxy λRe . In particular, low-spin systems have a higher occurrence of triaxiality, while high-spin systems are more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies is linked to their formation and merger histories. Galaxies with high-spin values have intrinsic shapes consistent with dissipational minor mergers, while the intrinsic shape of low-spin systems is consistent with dissipationless multimerger assembly histories. This range in assembly histories inferred from intrinsic shapes is broadly consistent with expectations from cosmological simulations. [ABSTRACT FROM AUTHOR]- Published
- 2017
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13. The SAMI Galaxy Survey: kinematics of dusty early-type galaxies.
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Bassett, R., Bekki, K., Cortese, L., Driver, S. P., Davies, L. J. M., Wong, O. I., Couch, W. J., Foster, C., Brough, S., Goodwin, M., Lawrence, J. S., Bryant, J. J., Richards, S. N., Owers, M. S., Konstantopoulos, I. S., Sansom, A. E., van de Sande, J., Bland-Hawthorn, J., Croom, S. M., and Sweet, S. M.
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INTERSTELLAR reddening ,KINEMATICS ,COSMIC dust ,IONIZED gases - Abstract
Recently, large samples of visually classified early-type galaxies (ETGs) containing dust have been identified using space-based infrared observations with the Herschel Space Telescope. The presence of large quantities of dust in massive ETGs is peculiar as X-ray haloes of these galaxies are expected to destroy dust in ~10
7 yr (or less). This has sparked a debate regarding the origin of the dust: Is it internally produced by asymptotic giant branch stars, or is it accreted externally through mergers? We examine the 2D stellar and ionized gas kinematics of dusty ETGs using integral field spectroscopy observations from the SAMI Galaxy Survey, and integrated star formation rates, stellar masses and dust masses from the GAMA survey. Only 8 per cent (4/49) of visually classified ETGs are kinematically consistent with being dispersion-supported systems. These 'dispersion-dominated galaxies' exhibit discrepancies between stellar and ionized gas kinematics, either offsets in the kinematic position angle or large differences in the rotational velocity, and are outliers in star formation rate at a fixed dust mass compared to normal star-forming galaxies. These properties are suggestive of recent merger activity. The remaining ~90 per cent of dusty ETGs have low velocity dispersions and/or large circular velocities, typical of 'rotation-dominated galaxies'. These results, along with the general evidence of published works on X-ray emission in ETGs, suggest that they are unlikely to host hot, X-ray gas consistent with their low M* when compared to dispersion-dominated galaxies. This means that dust will be long-lived and thus these galaxies do not require external scenarios for the origin of their dust content. [ABSTRACT FROM AUTHOR]- Published
- 2017
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14. Galaxy and Mass Assembly (GAMA): probing the merger histories of massive galaxies via stellar populations.
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Ferreras, I., Hopkins, A. M., Gunawardhana, M. L. P., Sansom, A. E., Owers, M. S., Driver, S., Davies, L., Robotham, A., Taylor, E. N., Konstantopoulos, I., Brough, S., Norberg, P., Croom, S., Loveday, J., Wang, L., and Bremer, M.
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GALAXIES ,DARK matter ,SATELLITE radio services ,GALACTIC evolution - Abstract
The merging history of galaxies can be traced with studies of dynamically close pairs. These consist of a massive primary galaxy and a less massive secondary (or satellite) galaxy. The study of the stellar populations of secondary (lower mass) galaxies in close pairs provides a way to understand galaxy growth by mergers. Here we focus on systems involving at least one massive galaxy - with stellar mass above 10
11 M☉ in the highly complete Galaxy and Mass Assembly (GAMA) survey. Our working sample comprises 2692 satellite galaxy spectra (0.1 ≤ z ≤ 0.3). These spectra are combined into high S/N stacks, and binned according to both an 'internal' parameter, the stellar mass of the satellite galaxy (i.e. the secondary), and an 'external' parameter, selecting either the mass of the primary in the pair, or the mass of the corresponding dark matter halo. We find significant variations in the age of the populations with respect to environment. At fixed mass, satellites around the most massive galaxies are older and possibly more metal-rich, with age differences ~1-2 Gyr within the subset of lower mass satellites (~1010 M☉ ). These variations are similar when stacking with respect to the halo mass of the group where the pair is embedded. The population trends in the lower mass satellites are consistent with the old stellar ages found in the outer regions of massive galaxies. [ABSTRACT FROM AUTHOR]- Published
- 2017
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15. The SAMI Galaxy Survey: the link between angular momentum and optical morphology.
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Cortese, L., R. Fogarty, L. M., Bekki, K., van de Sande, J., Couch, W., Catinella, B., Colless, M., Obreschkow, D., Taranu, D., Tescari, E., Barat, D., Bland-Hawthorn, J., Bloom, J., Bryant, J. J., Cluver, M., Croom, S. M., Drinkwater, M. J., d’Eugenio, F., Konstantopoulos, I. S., and Lopez-Sanchez, A.
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INTEGRAL field spectroscopy ,ANGULAR momentum (Mechanics) ,STELLAR mass ,GALACTIC evolution ,KINEMATICS ,ASTRONOMICAL research - Abstract
We investigate the relationship between stellar and gas specific angular momentum j, stellar mass M
* and optical morphology for a sample of 488 galaxies extracted from the Sydney-AAO Multi-object Integral field Galaxy Survey. We find that j, measured within one effective radius, monotonically increases with M* and that, for M* > 109.5 M⊙ , the scatter in this relation strongly correlates with optical morphology (i.e. visual classification and Sérsic index). These findings confirm that massive galaxies of all types lie on a plane relating mass, angular momentum and stellar-light distribution, and suggest that the large-scale morphology of a galaxy is regulated by its mass and dynamical state. We show that the significant scatter in the M* -j relation is accounted for by the fact that, at fixed stellar mass, the contribution of ordered motions to the dynamical support of galaxies varies by at least a factor of 3. Indeed, the stellar spin parameter (quantified via λR ) correlates strongly with Sérsic and concentration indices. This correlation is particularly strong once slow rotators are removed from the sample, showing that late-type galaxies and early-type fast rotators form a continuous class of objects in terms of their kinematic properties. [ABSTRACT FROM AUTHOR]- Published
- 2016
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16. The SAMI Galaxy Survey: gas streaming and dynamical M/L in rotationally supported systems.
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Cecil, G., Fogarty, L. M. R., Richards, S., Bland-Hawthorn, J., Lange, R., Moffett, A., Catinella, B., Cortese, L., Ho, I.-T., Taylor, E. N., Bryant, J. J., Allen, J. T., Sweet, S. M., Croom, S. M., Driver, S. P., Goodwin, M., Kelvin, L., Green, A. W., Konstantopoulos, I. S., and Owers, M. S.
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GALACTIC dynamics ,ASTRONOMICAL surveys ,DARK matter ,ASTRONOMICAL photometry ,SPECTRAL energy distribution - Abstract
Line-of-sight velocities of gas and stars can constrain dark matter (DM) within rotationally supported galaxies if they trace circular orbits extensively. Photometric asymmetries may signify non-circular motions, requiring spectra with dense spatial coverage. Our integral-field spectroscopy of 178 galaxies spanned the mass range of the Sydney-AAO Multi-object integral field spectrograph (SAMI) Galaxy Survey. We derived circular speed curves (CSCs) of gas and stars from non-parametric fits out to r ~ 2r
e . For 12/14 with measured HI profiles, ionized gas and HI maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies by approximating the radial light profile as nested, very flattened mass homeoids viewed as a Sérsic form. Fitting broad-band spectral energy distributions to Sloan Digital Sky Survey images gave median stellar mass/light 1.7 assuming a Kroupa initial mass function (IMF) versus 2.6 dynamically. Two-thirds of the dynamical mass/light measures were consistent with star+remnant IMFs. One-fifth required upscaled starlight to fit, hence comparable mass of unobserved baryons and/or DM distributed like starlight across the SAMI aperture that came to dominate motions as the starlight CSCs declined rapidly. The rest had mass distributed differently from light. Subtracting fits of Sérsic radial profiles to 13 VIKING Z-band images revealed residual weak bars. Near the bar major axis, we assessed m = 2 streaming velocities, and found deviations usually <30 km s-1 from the CSC; three showed no deviation. Thus, asymmetries rarely influenced the CSC despite colocated shock-indicating, emission-line flux ratios in more than 2/3 of our sample. [ABSTRACT FROM AUTHOR]- Published
- 2016
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17. The SAMI Galaxy Survey: can we trust aperture corrections to predict star formation?
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Richards, S. N., Bryant, J. J., Croom, S. M., Hopkins, A. M., Schaefer, A. L., Bland-Hawthorn, J., Allen, J. T., Brough, S., Cecil, G., Cortese, L., Fogarty, L. M. R., Gunawardhana, M. L. P., Goodwin, M., Green, A. W., Ho, I. -T., Kewley, L. J., Konstantopoulos, I. S., Lawrence, J. S., Lorente, N. P. F., and Medling, A. M.
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REDSHIFT ,GALAXIES ,SPECTRUM analysis ,ASTRONOMY ,ASTROPHYSICS - Abstract
In the low-redshift Universe (z < 0.3), our view of galaxy evolution is primarily based on fibre optic spectroscopy surveys. Elaborate methods have been developed to address aperture effects when fixed aperture sizes only probe the inner regions for galaxies of ever decreasing redshift or increasing physical size. These aperture corrections rely on assumptions about the physical properties of galaxies. The adequacy of these aperture corrections can be tested with integralfield spectroscopic data. We use integral-field spectra drawn from 1212 galaxies observed as part of the SAMI Galaxy Survey to investigate the validity of two aperture correction methods that attempt to estimate a galaxy's total instantaneous star formation rate.We show that biases arise when assuming that instantaneous star formation is traced by broad-band imaging, and when the aperture correction is built only from spectra of the nuclear region of galaxies. These biases may be significant depending on the selection criteria of a survey sample. Understanding the sensitivities of these aperture corrections is essential for correct handling of systematic errors in galaxy evolution studies. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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18. Sizes and shapes of young star cluster light profiles in M83.
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Ryon, J. E., Bastian, N., Adamo, A., Konstantopoulos, I. S., Gallagher III, J. S., Larsen, S., Hollyhead, K., Silva-Villa, E., and Smith, L. J.
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STAR clusters ,POWER law (Mathematics) ,LOGNORMAL distribution ,STELLAR evolution ,MOLECULAR clouds - Abstract
We measure the radii and two-dimensional light profiles of a large sample of young, massive star clusters in M83 using archival HST/Wide Field Camera 3 (WFC3) imaging of seven adjacent fields. We use GALFIT to fit the two-dimensional light profiles of the clusters, from which we find effective (half-light) radii, core radii, and slopes of the power-law (EFF) profile (η).We find lognormal distributions of effective radius and core radius, with medians of ≈ 2.5 and ≈ 1.3 pc, respectively. Our results provide strong evidence for a characteristic size of young, massive clusters. The average effective radius and core radius increase somewhat with cluster age. Little to no change in effective radius is observed with increasing galactocentric distance, except perhaps for clusters younger than 100 Myr. We find a shallow correlation between effective radius and mass for the full cluster sample, but a stronger correlation is present for clusters 200-300 Myr in age. Finally, the majority of the clusters are best fit by an EFF model with index η≤ 3.0. There is no strong evidence for change in η with cluster age, mass, or galactocentric distance. Our results suggest that clusters emerge from early evolution with similar radii and are not strongly affected by the tidal field of M83. Mass-loss due to stellar evolution and/or giant molecular cloud interactions appear to dominate cluster expansion in the age range we study. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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19. Galaxy And Mass Assembly (GAMA): the effect of close interactions on star formation in galaxies.
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Davies, L. J. M., Robotham, A. S. G., Driver, S. P., Alpaslan, M., Baldry, I. K., Bland-Hawthorn, J., Brough, S., Brown, M. J. I., Cluver, M. E., Drinkwater, M. J., Foster, C., Grootes, M. W., Konstantopoulos, I. S., Lara-López, M. A., López-Sánchez, A. R., Loveday, J., Meyer, M. J., Moffett, A. J., Norberg, P., and Owers, M. S.
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STELLAR evolution ,TURBULENCE ,FLUID dynamics ,ASTRONOMICAL observations - Abstract
The modification of star formation (SF) in galaxy interactions is a complex process, with SF observed to be both enhanced in major mergers and suppressed in minor pair interactions. Such changes likely to arise on short time-scales and be directly related to the galaxy-galaxy interaction time. Here we investigate the link between dynamical phase and direct measures of SF on different time-scales for pair galaxies, targeting numerous star-formation rate (SFR) indicators and comparing to pair separation, individual galaxy mass and pair mass ratio. We split our sample into the higher (primary) and lower (secondary) mass galaxies in each pair and find that SF is indeed enhanced in all primary galaxies but suppressed in secondaries of minor mergers. We find that changes in SF of primaries are consistent in both major and minor mergers, suggesting that SF in the more massive galaxy is agnostic to pair mass ratio. We also find that SF is enhanced/suppressed more strongly for short-duration SFR indicators (e.g. Ha), highlighting recent changes to SF in these galaxies, which are likely to be induced by the interaction. We propose a scenario where the lower mass galaxy has its SF suppressed by gas heating or stripping, while the higher mass galaxy has its SF enhanced, potentially by tidal gas turbulence and shocks. This is consistent with the seemingly contradictory observations for both SF suppression and enhancement in close pairs. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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20. A comprehensive HST BVI catalogue of star clusters in five Hickson compact groups of galaxies.
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Fedotov, K., Gallagher, S. C., Durrell, P. R., Bastian, N., Konstantopoulos, I. S., Charlton, J., Johnson, K. E., and Chandar, R.
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STAR clusters ,COMPACT groups ,GALAXY clusters ,STELLAR populations - Abstract
We present a photometric catalogue of star cluster candidates in Hickson compact groups (HCGs) 7, 31, 42, 59, and 92, based on observations with the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope. The catalogue contains precise cluster positions (right ascension and declination), magnitudes, and colours in the BVI filters. The number of detected sources ranges from 2200 to 5600 per group, from which we construct the high-confidence sample by applying a number of criteria designed to reduce foreground and background contaminants. Furthermore, the high-confidence cluster candidates for each of the 16 galaxies in our sample are split into two subpopulations: one that may contain young star clusters and one that is dominated by globular older clusters. The ratio of young star cluster to globular cluster candidates varies from group to group, from equal numbers to the extreme of HCG 31 which has a ratio of 8 to 1, due to a recent starburst induced by interactions in the group. We find that the number of blue clusters with M
V < -9 correlates well with the current star formation rate in an individual galaxy, while the number of globular cluster candidates with MV < -7.8 correlates well (though with large scatter) with the stellar mass. Analyses of the high-confidence sample presented in this paper show that star clusters can be successfully used to infer the gross star formation history of the host groups and therefore determine their placement in a proposed evolutionary sequence for compact galaxy groups. [ABSTRACT FROM AUTHOR]- Published
- 2015
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21. The SAMI Galaxy Survey: Early Data Release.
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Allen, J. T., Croom, S. M., Konstantopoulos, I. S., Bryant, J. J., Sharp, R., Cecil, G. N., Fogarty, L. M. R., Foster, C., Green, A. W., Ho, I.-T., Owers, M. S., Schaefer, A. L., Scott, N., Bauer, A. E., Baldry, I., Barnes, L. A., Bland-Hawthorn, J., Bloom, J. V., Brough, S., and Colless, M.
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GALAXIES ,COMPRESSED sensing ,INTEGRAL field spectroscopy ,FIBER optical sensors ,ASTRONOMICAL observations ,ASTRONOMICAL observatories - Abstract
We present the Early Data Release of the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The SAMI Galaxy Survey is an ongoing integral field spectroscopic survey of 3400 low-redshift (z < 0.12) galaxies, covering galaxies in the field and in groups within the Galaxy And Mass Assembly (GAMA) survey regions, and a sample of galaxies in clusters. In the Early Data Release, we publicly release the fully calibrated data cubes for a representative selection of 107 galaxies drawn from the GAMA regions, along with information about these galaxies from the GAMA catalogues. All data cubes for the Early Data Release galaxies can be downloaded individually or as a set from the SAMI Galaxy Survey website. In this paper we also assess the quality of the pipeline used to reduce the SAMI data, giving metrics that quantify its performance at all stages in processing the raw data into calibrated data cubes. The pipeline gives excellent results throughout, with typical sky subtraction residuals in the continuum of 0.9-1.2 per cent, a relative flux calibration uncertainty of 4.1 per cent (systematic) plus 4.3 per cent (statistical), and atmospheric dispersion removed with an accuracy of 0.09 arcsec, less than a fifth of a spaxel. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
22. The SAMI Galaxy Survey: the discovery of a luminous, low-metallicity HII complex in the dwarf galaxy GAMA J141103.98-003242.3.
- Author
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Richards, S. N., Schaefer, A. L., López-Sánchez, Á. R., Croom, S. M., Bryant, J. J., Sweet, S. M., Konstantopoulos, I. S., Allen, J. T., Bland-Hawthorn, J., Bloom, J. V., Brough, S., Fogarty, L. M. R., Goodwin, M., Green, A. W., Ho, I. -T., Kewley, L. J., Koribalski, B. S., Lawrence, J. S., Owers, M. S., and Sadler, E. M.
- Subjects
DWARF galaxies ,GALAXY formation ,INTEGRAL field spectroscopy ,STELLAR luminosity function ,STELLAR activity - Abstract
We present the discovery of a luminous unresolved H II complex on the edge of dwarf galaxy GAMA J141103.98-003242.3 using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. This dwarf galaxy is situated at a distance of ∼100 Mpc and contains an unresolved region of H II emission that contributes ∼70 per cent of the galaxy's Hα luminosity, located at the top end of established H II region luminosity functions. For the H II complex, we measure a star formation rate of 0.147 ± 0.041 M
⊙ yr-1 and a metal licity of 12+log(O/H) = 8.01 ± 0.05 that is lower than the rest of the galaxy by ∼0.2 dex. Data from the H I Parkes All-Sky Survey (HIPASS) indicate the likely presence of neutral hydrogen in the galaxy to potentially fuel ongoing and future star-forming events. We discuss various triggering mechanisms for the intense star formation activity of this H II complex, where the kinematics of the ionized gas are well described by a rotating disc and do not show any features indicative of interactions. We show that SAMI is an ideal instrument to identify similar systems to GAMA J141103.98-003242.3, and the SAMI Galaxy Survey is likely to find many more of these systems to aid in the understanding of their formation and evolution. [ABSTRACT FROM AUTHOR]- Published
- 2014
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23. SHOCK-ENHANCED C+ EMISSION AND THE DETECTION OF H2O FROM THE STEPHAN'S QUINTET GROUP-WIDE SHOCK USING HERSCHEL Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
- Author
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Appleton, P. N., Guillard, P., Boulanger, F., Cluver, M. E., Ogle, P., Falgarone, E., Forêts, G. Pineau des, O'Sullivan, E., Duc, P.-A., Gallagher, S., Gao, Y., Jarrett, T., Konstantopoulos, I., Lisenfeld, U., Lord, S., Lu, N., Peterson, B. W., Struck, C., Sturm, E., and Tuffs, R.
- Subjects
GALAXIES ,CONSTELLATIONS ,INTERSTELLAR medium ,STAR formation ,ASTROPHYSICS research - Abstract
We present the first Herschel spectroscopic detections of the [O I] 63 μm and [C II] 158 μm fine-structure transitions, and a single para-H
2 O line from the 35 × 15 kpc2 shocked intergalactic filament in Stephan's Quintet. The filament is believed to have been formed when a high-speed intruder to the group collided with a clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (>1000 km s–1 ) luminous [C II] line profiles, as well as fainter [O I] 63 μm emission. SPIRE FTS observations reveal water emission from the p-H2 O (111 -000 ) transition at several positions in the filament, but no other molecular lines. The H2 O line is narrow and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [C II]/PAHtot and [C II]/FIR ratios are too large to be explained by normal photo-electric heating in photodissociation regions. H II region excitation or X-ray/cosmic-ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [C II], [O I], and warm H2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the intergalactic medium is dissipated to small scales and low velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [C II]/[O I] ratio, and the relatively high [C II]/H2 ratios observed. The discovery that [C II] emission can be enhanced, in large-scale turbulent regions in collisional environments, has implications for the interpretation of [C II] emission in high-z galaxies. [ABSTRACT FROM AUTHOR]- Published
- 2013
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- View/download PDF
24. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES.
- Author
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KONSTANTOPOULOS, I. S., MAYBHATE, A., CHARLTON, J. C., FEDOTOV, K., DURRELL, P. R., MULCHAEY, J. S., ENGLISH, J., DESJARDINS, T. D., GALLAGHER, S. C., WALKER, L. M., JOHNSON, K. E., TZANAVARIS, P., and GRONWALL, C.
- Subjects
- *
STELLAR populations , *WAVELENGTHS , *STAR clusters , *DWARF galaxies , *INTERSTELLAR medium - Abstract
We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy.We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 "associates" (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
25. UNDER PRESSURE: STAR CLUSTERS AND THE NEUTRAL HYDROGEN MEDIUM OF TIDAL TAILS.
- Author
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MULLAN, B., KEPLEY, A. A., MAYBHATE, A., ENGLISH, J., KNIERMAN, K., HIBBARD, J. E., BASTIAN, N., CHARLTON, J. C., DURRELL, P. R., GRONWALL, C., ELMEGREEN, D., and KONSTANTOPOULOS, I. S.
- Subjects
STAR clusters ,RADIAL velocity of galaxies ,KINETIC energy ,DISPERSION (Atmospheric chemistry) ,ENERGY density ,MECHANICAL energy - Abstract
Using archival data from ATCA, WHISP, and the Very Large Array, we have analyzed the HI emission of 22 tidal tail regions of the Mullan et al. sample of pairwise interacting galaxies. We have measured the column densities, line-of-sight velocity dispersions, and kinetic energy densities on ~kpc scales. We also constructed a tracer of the line-of-sight velocity gradient over ~10 kpc scales. We compared the distributions of these properties between regions that do and do not contain massive star cluster candidates (MV < -8.5; ~10
4 -106 M☉ as observed in Hubble Space Telescope WFPC2 VI data). In agreement with Maybhate et al., we find that a local, ~kpc-scale column density of log NHI ≳ 20.6 cm-2 is frequently required for detecting clustered star formation. This HI gas also tends to be turbulent, with line-of-sight velocity dispersions σlos ≈ 10-75 km s-1 , implying high kinetic energy densities (log ΣKE > 46 erg pc-2 ). Thus, high HI densities and pressures, partly determined by the tail dynamical age and other interaction characteristics, are connected to large-scale cluster formation in tidal tails overall. Last, we find that the high mechanical energy densities of the gas are likely not generally due to feedback from star formation. Rather, these properties are more likely to be a cause of star formation than a result. [ABSTRACT FROM AUTHOR]- Published
- 2013
- Full Text
- View/download PDF
26. THE SNAPSHOT HUBBLE U-BAND CLUSTER SURVEY (SHUCS). I. SURVEY DESCRIPTION AND FIRST APPLICATION TO THE MIXED STAR CLUSTER POPULATION OF NGC 4041.
- Author
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KONSTANTOPOULOS, I. S., SMITH, L. J., ADAMO, A., SILVA-VILLA, E., GALLAGHER, J. S., BASTIAN, N., RYON, J. E., WESTMOQUETTE, M. S., ZACKRISSON, E., LARSEN, S. S., WEISZ, D. R., and CHARLTON, J. C.
- Published
- 2013
- Full Text
- View/download PDF
27. Revealing a ring-like cluster complex in a tidal tail of the starburst galaxy NGC 2146 Revealing a ring-like cluster complex in a tidal tail of the starburst galaxy NGC 2146.
- Author
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Adamo, A., Smith, L. J., Gallagher, J. S., Bastian, N., Ryon, J., Westmoquette, M. S., Konstantopoulos, I. S., Zackrisson, E., Larsen, S. S., Silva-Villa, E., Charlton, J. C., and Weisz, D. R.
- Subjects
GALAXY clusters ,STARBURSTS ,DISTRIBUTION of stars ,STAR clusters ,STATISTICAL correlation ,STAR formation ,FIELD emission - Abstract
ABSTRACT We report the discovery of a ring-like cluster complex in the starburst galaxy NGC 2146. The Ruby Ring, so named due to its appearance, shows a clear ring-like distribution of star clusters around a central object. It is located in one of the tidal streams that surround the galaxy. NGC 2146 is part of the Snapshot Hubble U-band Cluster Survey (SHUCS). The WFC3/ F336 W data have added critical information to the available archival Hubble Space Telescope imaging set of NGC 2146, allowing us to determine ages, masses and extinctions of the clusters in the Ruby Ring. These properties have then been used to investigate the formation of this extraordinary system. We find evidence of a spatial and temporal correlation between the central cluster and the clusters in the ring. The latter are about 4 Myr younger than the central cluster, which has an age of 7 Myr. This result is supported by the Hα emission which is strongly coincident with the ring, and weaker at the position of the central cluster. From the derived total Hα luminosity of the system, we constrain the star formation rate density to be quite high (Σ
SFR = 0.47 M⊙ yr−1 kpc−2 ). The Ruby Ring is the product of an intense and localized burst of star formation, similar to the extended cluster complexes observed in M 51 and the Antennae, but more impressive because it is quite isolated. The central cluster contains only 5 per cent of the total stellar mass in the clusters that are determined within the complex. The ring-like morphology, the age spread and the mass ratio support a triggering formation scenario for this complex. We discuss the formation of the Ruby Ring in a 'collect and collapse' framework. The predictions made by this model agree quite well with the estimated bubble radius and expansion velocity produced by the feedback from the central cluster, making the Ruby Ring an interesting case of triggered star formation. [ABSTRACT FROM AUTHOR]- Published
- 2012
- Full Text
- View/download PDF
28. Spectroscopic constraints on the form of the stellar cluster mass function (Research Note).
- Author
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Bastian, N., Konstantopoulos, I. S., Trancho, G., Weisz, D. R., Larsen, S. S., Fouesneau, M., Kaschinski, C. B., and Gieles, M.
- Subjects
- *
STAR clusters , *MASS (Physics) , *SPECTRUM analysis , *STATISTICS , *SPIRAL galaxies - Abstract
This contribution addresses the question of whether the initial cluster mass function (ICMF) has a fundamental limit (or truncation) at high masses. The shape of the ICMF at high masses can be studied using the most massive young (<10 Myr) clusters, however this has proven difficult due to low-number statistics. In this contribution we use an alternative method based on the luminosities of the brightest clusters, combined with their ages. The advantages are that more clusters can be used and that the ICMF leaves a distinct pattern on the global relation between the cluster luminosity and median age within a population. If a truncation is present, a generic prediction (nearly independent of the cluster disruption law adopted) is that the median age of bright clusters should be younger than that of fainter clusters. In the case of an non-truncated ICMF, the median age should be independent of cluster luminosity. Here, we present optical spectroscopy of twelve young stellar clusters in the face-on spiral galaxy NGC 2997. The spectra are used to estimate the age of each cluster, and the brightness of the clusters is taken from the literature. The observations are compared with the model expectations of Larsen (2009, A&A, 494, 539) for various ICMF forms and both mass dependent and mass independent cluster disruption. While there exists some degeneracy between the truncation mass and the amount of mass independent disruption, the observations favour a truncated ICMF. For low or modest amounts of mass independent disruption, a truncation mass of 5-6 × 105 M☉ is estimated, consistent with previous determinations. Additionally, we investigate possible truncations in the ICMF in the spiral galaxy M 83, the interacting Antennae galaxies, and the collection of spiral and dwarf galaxies present in Larsen (2009, A&A, 494, 539) based on photometric catalogues taken from the literature, and find that all catalogues are consistent with having a truncation in the cluster mass functions. However for the case of the Antennae, we find a truncation mass of a few ×106 M☉, suggesting a dependence on the environment, as has been previously suggested. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
29. THE MERGER HISTORY, ACTIVE GALACTIC NUCLEUS, AND DWARF GALAXIES OF HICKSON COMPACT GROUP 59.
- Author
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Konstantopoulos, I. S., Gallagher, S. C., Fedotov, K., Durell, P. R., Tzanavaris, P., Hill, A. R., Zabludoff, A. I., Maier, M. L., Elmegreen, D. M., Charlton, J. C., Johnson, K. E., Brandt, W. N., Walker, L. M., Eracleous, M., Maybhate, A., Gronwall, C., English, J., Hornschemeier, A. E., and Mulchaey, J. S.
- Subjects
- *
GALAXIES , *PHOTOMETRY , *DWARF galaxies , *STAR clusters , *GALACTIC nuclei - Abstract
Compact group galaxies often appear unaffected by their unusually dense environment. Closer examination can, however, reveal the subtle, cumulative effects of multiple galaxy interactions. Hickson Compact Group (HCG) 59 is an excellent example of this situation. We present a photometric study of this group in the optical (Hubble Space Telescope), infrared (Spitzer), and X-ray (Chandra) regimes aimed at characterizing the star formation and nuclear activity in its constituent galaxies and intra-group medium. We associate five dwarf galaxies with the group and update the velocity dispersion, leading to an increase in the dynamical mass of the group of up to a factor of 10 (to 2.8 x 1013 Mʘ), and a subsequent revision of its evolutionary stage. Star formation is proceeding at a level consistent with the morphological types of the four main galaxies, of which two are star-forming and the other are two quiescent. Unlike in some other compact groups, star-forming complexes across HCG 59 closely follow mass-radius scaling relations typical of nearby galaxies. In contrast, the ancient globular cluster populations in galaxies FICG 59A and B show intriguing irregularities, and two extragalactic H II regions are found just west of B We age-date a faint stellar stream in the intra-group medium at ~1 Gyr to examine recent interactions. We detect a likely low-luminosity active galactic nucleus in HCG 59A by its ~ 1040 erg s-1 X-ray emission; the active nucleus rather than star formation can account for the UV+IR spectral energy distribution. We discuss the implications of our findings in the context of galaxy evolution in dense environments. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
30. Stellar clusters in M83: formation, evolution, disruption and the influence of the environment.
- Author
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Bastian, N., Adamo, A., Gieles, M., Silva-Villa, E., Lamers, H. J. G. L. M, Larsen, S. S., Smith, L. J., Konstantopoulos, I. S., and Zackrisson, E.
- Subjects
STAR clusters ,STAR formation ,STELLAR evolution ,STELLAR populations ,WAVELENGTHS ,IMAGING systems in astronomy ,STAR catalogs ,LOGNORMAL distribution - Abstract
ABSTRACT We study the stellar cluster population in two adjacent fields in the nearby, face-on spiral galaxy M83 using multiwavelength Wide Field Camera 3/ Hubble Space Telescope imaging. After automatic detection procedures, the clusters are selected through visual inspection to be centrally concentrated, symmetric, and resolved on the images, which allows us to differentiate between clusters and likely unbound associations. We compare our sample with previous studies and show that the differences between the catalogues are largely due to the inclusion of a large numbers of diffuse associations within previous catalogues as well as the inclusion of the central starburst region, where the completeness limit is significantly worse than in the surrounding regions. We derive the size distribution of the clusters, which is well described by a lognormal distribution with a peak at ∼2.5 pc, and find evidence for an expansion in the half-light radius of clusters with age. The luminosity function of the clusters is well approximated by a power law with an index of −2 over most of the observed range; however, a steepening is seen at M
V =−9.3 and −8.8 in the inner and outer fields, respectively. Additionally, we show that the cluster population is inconsistent with a pure power-law mass distribution, but instead exhibits a truncation at the high-mass end. If described as a Schechter function, the characteristic mass is 1.6 × 105 and 0.5 × 105 M⊙ for the inner and outer fields, respectively, in agreement with previous estimates of other cluster populations in spiral galaxies. Comparing the predictions of the mass-independent disruption (MID) and mass-dependent disruption (MDD) scenarios with the observed distributions, we find that both models can accurately fit the data. However, for the MID case, the fraction of clusters destroyed (or mass lost) per decade in age is dependent on the environment; hence, the age and mass distributions of clusters are not universal. In the MDD case, the disruption time-scale scales with galactocentric distance (being longer in the outer regions of the galaxy) in agreement with analytic and numerical predictions. Finally, we discuss the implications of our results on other extragalactic surveys, focusing on the fraction of stars that form in clusters and the need (or lack thereof) for infant mortality. [ABSTRACT FROM AUTHOR]- Published
- 2012
- Full Text
- View/download PDF
31. Evidence for environmentally dependent cluster disruption in M83.
- Author
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Bastian, N., Adamo, A., Gieles, M., Lamers, H. J. G. L. M., Larsen, S. S., Silva-Villa, E., Smith, L. J., Kotulla, R., Konstantopoulos, I. S., Trancho, G., and Zackrisson, E.
- Subjects
WAVELENGTHS ,STAR observations ,GALAXY clusters ,ALGORITHMS ,STELLAR mass ,STELLAR populations - Abstract
ABSTRACT Using multiwavelength imaging from the Wide Field Camera 3 on the Hubble Space Telescope we study the stellar cluster populations of two adjacent fields in the nearby face-on spiral galaxy, M83. The observations cover the galactic centre and reach out to ∼6 kpc, thereby spanning a large range of environmental conditions, ideal for testing empirical laws of cluster disruption. The clusters are selected by visual inspection to be centrally concentrated, symmetric and resolved on the images. We find that a large fraction of objects detected by automated algorithms (e.g. SE xtractor or daofind) are not clusters, but rather are associations. These are likely to disperse into the field on time-scales of tens of Myr due to their lower stellar densities and not due to gas expulsion (i.e. they were never gravitationally bound). We split the sample into two discrete fields (inner and outer regions of the galaxy) and search for evidence of environmentally dependent cluster disruption. Colour-colour diagrams of the clusters, when compared to simple stellar population models, already indicate that a much larger fraction of the clusters in the outer field are older by tens of Myr than in the inner field. This impression is quantified by estimating each cluster's properties (age, mass and extinction) and comparing the age/mass distributions between the two fields. Our results are inconsistent with 'universal' age and mass distributions of clusters, and instead show that the ambient environment strongly affects the observed populations. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
32. STAR CLUSTERS IN THE TIDAL TAILS OF INTERACTING GALAXIES: CLUSTER POPULATIONS ACROSS A VARIETY OF TAIL ENVIRONMENTS.
- Author
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Mullan, B., Konstantopoulos, I. S., Kepley, A. A., Lee, K. H., Charlton, J. C., Knierman, K., Bastian, N., Chandar, R., Durrell, P. R., Elmegreen, D., English, J., Gallagher, S. C., Gronwall, C., Hibbard, J. E., Hunsberger, S., Johnson, K. E., Maybhate, A., Palma, C., Trancho, G., and Vacca, W. D.
- Published
- 2011
- Full Text
- View/download PDF
33. GALAXY EVOLUTION IN A COMPLEX ENVIRONMENT: A MULTI-WAVELENGTH STUDY OF HCG 7Based on observations made with the NASA/ESA Hubble Space Telescope.
- Author
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Konstantopoulos, I. S., Gallagher, S. C., Fedotov, K., Durrell, P. R., Heiderman, A., Elmegreen, D. M., Charlton, J. C., Hibbard, J. E., Tzanavaris, P., Chandar, R., Johnson, K. E., Maybhate, A., Zabludoff, A. E., Gronwall, C., Szathmary, D., Hornschemeier, A. E., English, J., Whitmore, B., Oliveira, C. Mendes de, and Mulchaey, J. S.
- Published
- 2010
- Full Text
- View/download PDF
34. Constraining star cluster disruption mechanisms.
- Author
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Konstantopoulos, I. S., Bastian, N., Gieles, M., and Lamers, H. J. G. L. M.
- Abstract
Star clusters are found in all sorts of environments, and their formation and evolution is inextricably linked to the star-formation process. Their eventual destruction can result from a number of factors at different times, but the process can be investigated as a whole through the study of cluster age distributions. Observations of populous cluster samples reveal a distribution following a power law of index approximately −1. In this work, we use M33 as a test case to examine the age distribution of an archetypal cluster population and show that it is, in fact, the evolving shape of the mass detection limit that defines this trend. That is to say, any magnitude-limited sample will appear to follow a dN/dτ = τ−1 relation, while cutting the sample according to mass gives rise to a composite structure, perhaps implying a dependence of the cluster disruption process on mass. In the context of this framework, we examine different models of cluster disruption from both theoretical and observational perspectives. [ABSTRACT FROM PUBLISHER]
- Published
- 2009
- Full Text
- View/download PDF
35. The early expansion of cluster cores.
- Author
-
Bastian, N., Gieles, M., Goodwin, S. P., Trancho, G., Smith, L. J., Konstantopoulos, I., and Efremov, Yu.
- Subjects
STAR clusters ,ASTRONOMY ,SPECTRUM analysis ,STELLAR luminosity function ,METAPHYSICAL cosmology - Abstract
The observed properties of young star clusters, such as the core radius and luminosity profile, change rapidly during the early evolution of the clusters. Here we present observations of six young clusters in M51 where we derive their sizes using Hubble Space Telescope ( HST) imaging and ages using deep Gemini-North spectroscopy. We find evidence for a rapid expansion of the cluster cores during the first 20 Myr of their evolution. We confirm this trend by including data from the literature of both Galactic and extragalactic embedded and young clusters, and possible mechanisms (rapid gas removal, stellar evolutionary mass loss and internal dynamical heating) are discussed. We explore the implications of this result, focussing on the fact that clusters were more concentrated in the past, implying that their stellar densities were much higher and relaxation times ( t
relax ) correspondingly shorter. Thus, when estimating if a particular cluster is dynamically relaxed (i.e. when determining if a cluster's mass segregation is due to primordial or dynamical processes), the current relaxation time is only an upper limit, with trelax likely being significantly shorter in the past. [ABSTRACT FROM AUTHOR]- Published
- 2008
- Full Text
- View/download PDF
36. The Young Cluster Population of M82 Region BBased on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. These observations are associated with program 10853.
- Author
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Smith, L. J., Bastian, N., Konstantopoulos, I. S., III, J. S. Gallagher, Gieles, M., Grijs, R. de, Larsen, S. S., O’Connell, R. W., and Westmoquette, M. S.
- Published
- 2007
- Full Text
- View/download PDF
37. A detailed study of the enigmatic cluster M82F.
- Author
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Bastian, N., Konstantopoulos, I., Smith, L. J., Trancho, G., Westmoquette, M. S., and Gallagher III, J. S.
- Subjects
- *
SPECTRUM analysis , *STAR clusters , *ELECTROMAGNETIC measurements , *STARBURSTS , *NEAR infrared spectroscopy - Abstract
We present a detailed study of the stellar cluster M82F, using multiband high-resolution Hubble Space Telescope ( HST) imaging and deep ground-based optical slit and integral field spectroscopy. Using the imaging, we create colour maps of the cluster and surrounding region in order to search for substructure. We find a large amount of substructure, which we interpret as the result of differential extinction across the projected face of the cluster. With this interpretation, we are able to construct a spatially resolved extinction map across the cluster which is used to derive the intrinsic flux distribution. Fitting cluster profiles (King and Elson, Fall & Freeman) to the intrinsic images, we find that the cluster is 15–30 per cent larger than previous estimates, and that no strong evidence of mass segregation in this cluster exists. Using the optical spectra, we find that the age of M82F is 60–80 Myr and from its velocity conclude that the cluster is not physically associated with a large H ii region that it is projected upon, both in agreement with previous studies. The reconstructed integral field maps show that that majority of the line emission comes from a nearby H ii region. The spatial dependence of the line widths (implying the presence of multiple components) measured corresponds to the extinction map derived from photometry, indicating that the gas/dust clouds responsible for the extinction are also partially ionized. Even with the wealth of observations presented here, we do not find a conclusive solution to the problem of the high light-to-mass ratio previously found for this cluster and its possible top-heavy stellar initial mass function. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
38. THE SNAPSHOT HUBBLE U-BAND CLUSTER SURVEY (SHUCS). II. THE STAR CLUSTER POPULATION OF NGC 2997.
- Author
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Ryon, J. E., Adamo, A., Bastian, N., Smith, L. J., Gallagher, III J. S., Konstantopoulos, I. S., Larsen, S., Silva-Villa, E., and Zackrisson, E.
- Published
- 2014
- Full Text
- View/download PDF
39. SHOCKS AND STAR FORMATION IN STEPHAN'S QUINTET. I. GEMINI SPECTROSCOPY OF Hα-BRIGHT KNOTS.
- Author
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Konstantopoulos, I. S., Appleton, P. N., Guillard, P., Trancho, G., Cluver, M. E., Bastian, N., Charlton, J. C., Fedotov, K., Gallagher, S. C., Smith, L. J., and Struck, C. J.
- Subjects
- *
GALAXIES , *STAR formation , *SHOCK waves , *SUPERNOVAE , *COMETS , *RADIATION - Abstract
We present a Gemini-GMOS spectroscopic study of Hubble Space Telescope(HST)-selected Hα-emitting regions in Stephan's Quintet (HCG 92), a nearby compact galaxy group, with the aim of disentangling the processes of shock-induced heating and star formation in its intra-group medium. The ≈40 sources are distributed across the system, but most densely concentrated in the ∼kiloparsec-long shock region. Their spectra neatly divide them into narrow- and broad-line emitters, and we decompose the latter into three or more emission peaks corresponding to spatial elements discernible in HST imaging. The emission-line ratios of the two populations of Hα-emitters confirm their nature as H II regions (90% of the sample) or molecular gas heated by a shock front propagating at ≲300 km s–1. Their redshift distribution reveals interesting three-dimensional structure with respect to gas-phase baryons, with no H II regions associated with shocked gas, no shocked regions in the intruder galaxy NGC 7318B, and a sharp boundary between shocks and star formation. We conclude that star formation is inhibited substantially, if not entirely, in the shock region. Attributing those H II regions projected against the shock to the intruder, we find a lopsided distribution of star formation in this galaxy, reminiscent of pileup regions in models of interacting galaxies. The Hα luminosities imply mass outputs, star formation rates, and efficiencies similar to nearby star-forming regions. Two large knots are an exception to this, being comparable in stellar output to the prolific 30 Doradus region. We also examine Stephan's Quintet in the context of compact galaxy group evolution, as a paradigm for intermittent star formation histories in the presence of a rich, X-ray-emitting intra-group medium. All spectra are provided as supplemental materials. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
40. THE OPTICAL STRUCTURE OF THE STARBURST GALAXY M82. II. NEBULAR PROPERTIES OF THE DISK AND INNER WIND.
- Author
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Westmoquette, M. S., Gallagher, J. S., Smith, L. J., Trancho, G., Bastian, N., and Konstantopoulos, I. S.
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- 2009
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41. A SPECTROSCOPIC CENSUS OF THE M82 STELLAR CLUSTER POPULATION ,.
- Author
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Konstantopoulos, I. S., Bastian, N., Smith, L. J., Westmoquette, M. S., Trancho, G., and Gallagher III, J. S.
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- 2009
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42. THE OPTICAL STRUCTURE OF THE STARBURST GALAXY M82. I. DYNAMICS OF THE DISK AND INNER-WIND.
- Author
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Westmoquette, M. S., Smith, L. J., Gallagher III, J. S., Trancho, G., Bastian, N., and Konstantopoulos, I. S.
- Published
- 2009
- Full Text
- View/download PDF
43. Sustainable metropolitan areas perspectives through assessment of the existing waste management strategies.
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Vardopoulos I, Konstantopoulos I, Zorpas AA, Limousy L, Bennici S, Inglezakis VJ, and Voukkali I
- Subjects
- Cities, Greece, Humans, Solid Waste analysis, Refuse Disposal, Waste Management
- Abstract
Human activities are considered among the main producers of any kind of pollution. This paper, through a Driver-Pressure-State-Impact-Response (DPSIR) model analyses, focuses on the evaluation and assessment of the existing practices, procedures, and results obtained in order to determine whether the municipal solid waste (MSW) management implemented in three major Greek municipalities in the greater urban area of Attica, namely the municipalities of Nea Smirni, Vyronas, and Piraeus, could be considered viable and sustainable. The evaluation indicated that MSW in Greek cities have reduced over the last years, also suggesting a steady downward trend, which could be considered consistent with that of the per capita incomes in Greece due to the extended economic austerity, while at the same time the recycling indicator seems to optimize. The results are very useful for policymakers and local authorities towards taking actions related to the targets set from the circular economy strategies as well as the targets set from United Nation Development Program and the European Green Deal Strategy.
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- 2021
- Full Text
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44. Fatigue-Induced Inter-Limb Asymmetries in Strength of the Hip Stabilizers, Postural Control and Gait Following a Unilateral Countermovement Vertical Jump Protocol.
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Konstantopoulos I, Kafetzakis I, Chatziilias V, and Mandalidis D
- Abstract
It is generally accepted that neuromuscular overload and fatigue of one lower limb can affect the functional ability of the ipsilateral limb, and possibly the contralateral limb, increasing the likelihood of injury. The purpose of the current study was to examine the effect of a unilateral countermovement vertical jump (UCVJ) fatigue protocol on the neuromuscular function of the ipsilateral as well as the contralateral lower limb. The isometric strength of the hip stabilizers, postural control via posturographic analysis during the Y-Balance-Test (YBT), and the stance-phase-of-gait were assessed in 24 healthy physical active males and females before and after execution of a UCVJ fatigue protocol. The fatigue protocol included 5 sets of 20 maximum UCVJs performed on the supportive leg, with a 30-s break between sets. Following a 16.8% decline in vertical jump performance and an associated 2.3-fold increase in perceived exertion, our findings revealed significant post-fatigue inter-limb differences regarding postural control. The post-fatigue inter-limb differences regarding the isometric strength of the hip stabilizers and the stance-phase-of-gait parameters were not significant. Our findings showed that a 100 UCVJs session is likely to induce significant inter-limb differences in postural control, possibly increasing the risk of lower limb injury.
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- 2021
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45. Re-affirming the necessity of sending even minor surgical specimens for histopathology: a case of inverted papilloma of the adenoids.
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Vlastarakos PV, Georgiadis T, Boutsi S, and Konstantopoulos I
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- Child, Female, Human papillomavirus 16, Humans, Papilloma, Inverted pathology, Papilloma, Inverted virology, Papillomavirus Infections diagnosis, Papillomavirus Infections pathology, Papillomavirus Infections virology, Respiratory Tract Neoplasms pathology, Respiratory Tract Neoplasms virology, Adenoids pathology, Papilloma, Inverted diagnosis, Respiratory Tract Neoplasms diagnosis
- Published
- 2016
46. Cytokine response to diabetic ketoacidosis (DKA) in children with type 1 diabetes (T1DM).
- Author
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Karavanaki K, Karanika E, Georga S, Bartzeliotou A, Tsouvalas M, Konstantopoulos I, Fotinou A, Papassotiriou I, and Karayianni C
- Subjects
- Adolescent, C-Reactive Protein metabolism, Child, Child, Preschool, Diabetes Mellitus, Type 1 therapy, Female, Humans, Interleukin-10 blood, Interleukin-1beta blood, Interleukin-2 blood, Interleukin-6 blood, Interleukin-8 blood, Leukocyte Count, Male, Tumor Necrosis Factor-alpha metabolism, Cytokines blood, Diabetes Mellitus, Type 1 blood, Diabetic Ketoacidosis blood
- Abstract
It has been suggested that cytokine release during DKA may result in capillary perturbation and thus may contribute to the development of its acute clinical complications (i.e.cerebral or pulmonary edema). We studied in 38 newly diagnosed T1DM children with DKA, aged 7.68±3.07 years, plasma levels of cytokines IL-1β (interleukin-1β), IL-2, IL-6, IL-8, IL-10, TNF-α (tumour necrosis factor-α) and also WBC (white blood cell count), hs-CRP (high sensitivity C-reactive protein), GH (growth hormone) and cortisol, prior to, during and 120h after DKA management, with the aim to monitor their levels at different time-points and in different degrees of DKA severity. Prior to DKA management the levels of IL-6, IL-8, IL-10, WBC and cortisol were elevated, but were all reduced within 120 h after DKA management. Then the patients were divided into two groups: a. moderate/severe: pH≤7.2, b. mild DKA: pH>7.2. In the group with moderate/severe DKA (ph≤7.2), IL-10 levels were the highest of all cytokines, but were significantly decreased after 6h (91.76 vs 18.04 pg/mL, p=0.008), with no further change, while IL-6 levels were decreased at 120 h (28.32 vs 11.9 pg/mL, p=0.003). The above were not observed in the group with mild DKA. In conclusion, in the children with DKA of our study, in the group with moderate/severe DKA the IL-10 levels were prematurely reduced at 6 hours, while the IL-6 levels remained high and were reduced at 120 hours after the DKA management. These changes may be responsible for increased capillary perturbation, which could lead to the subsequent development of acute DKA complications.
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- 2011
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47. Screening for associated autoimmunity in children and adolescents with type 1 diabetes mellitus (T1DM).
- Author
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Karavanaki K, Kakleas K, Paschali E, Kefalas N, Konstantopoulos I, Petrou V, Kanariou M, and Karayianni C
- Subjects
- Adolescent, Autoimmune Diseases immunology, Child, Diabetes Mellitus, Type 1 complications, Female, Glutamate Decarboxylase immunology, Humans, Insulin-Secreting Cells immunology, Logistic Models, Male, Mass Screening, Prevalence, Stomach immunology, Thyroid Gland immunology, Thyroiditis, Autoimmune immunology, Autoantibodies immunology, Autoimmune Diseases diagnosis, Autoimmunity immunology, Diabetes Mellitus, Type 1 immunology
- Abstract
Background/aims: Type 1 diabetes (T1DM) is associated with autoimmune thyroid, celiac, autoimmune gastric and Addison's disease. Our aim was to investigate the prevalence of associated autoantibodies in relation to the demographic and beta-cell autoantibody status (anti-GAD)., Methods: Antibodies against thyroid peroxidase (anti-TPO), thyroglobulin (anti-Tg), tissue transglutaminase (anti-tTG IgA), parietal cells (APCA) and adrenal tissue (AAA) were measured in 144 children with T1DM with a mean +/- SD age of 12.3 +/- 4.6 years and a diabetes duration of 4.6 +/- 3.8 years., Results: The prevalence of antibody positivity among our patients was: anti-GAD 53.2%, anti-thyroid (anti-TPO 17.4%, anti-Tg 11.1%); anti-tTG IgA 7.6%, APCA 4.0%, and AAA 0%. Among the children with positive anti-thyroid antibodies, 60% developed autoimmune thyroiditis, while among those anti-tTG IgA positive, 62.5% developed biopsy-confirmed celiac disease. Female gender was more frequent among anti-tTG IgA-positive patients (OR 4.47, p = 0.068), while increasing age was associated with anti-Tg positivity (OR 22.9, p = 0.041). The presence of anti-thyroid antibodies was associated with the presence of anti-GAD (OR 1.45, p = 0.01) and parietal cell antibodies (OR 4.98, p = 0.09)., Conclusion: Among T1DM patients, the prevalence rates of anti-thyroid and parietal cell antibodies increased with age and diabetes duration. As the presence of anti-GAD was associated with gastric and thyroid autoimmunity, it could serve as marker for the development of additional autoimmunity in adolescents with diabetes., (2009 S. Karger AG, Basel.)
- Published
- 2009
- Full Text
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48. Prevalence of allergic symptoms among children with diabetes mellitus type 1 of different socioeconomic status.
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Karavanaki K, Tsoka E, Karayianni C, Petrou V, Pippidou E, Brisimitzi M, Mavrikiou M, Kakleas K, Konstantopoulos I, Manoussakis M, and Dacou-Voutetakis C
- Subjects
- Breast Feeding, Child, Diabetes Mellitus, Type 1 complications, Female, Humans, Hypersensitivity complications, Infections, Male, Prevalence, Surveys and Questionnaires, Vaccination, Diabetes Mellitus, Type 1 epidemiology, Hypersensitivity epidemiology, Social Class
- Abstract
The aim of the study was to assess the possible associations between allergies and type 1 diabetes mellitus (DM1), stratified by social class. We studied 127 children with DM1 with a median age of 10.8 yr and 150 controls of comparable age and sex distribution. The parents completed questionnaires on their education and occupation and on their children's history of allergic symptoms, breast-feeding, viral infections, and measles-mumps-rubella (MMR) vaccination. Lower family's social class was more frequently encountered among the DM1 families than in the controls (OR = 0.56, 95% CI: 0.35-0.92). The occurrence of any allergic symptoms among children with DM1 (35.45%) was not significantly different from the controls (38.78%), neither in the total group (OR = 0.87, 95% CI: 0.52-1.45) nor in the stratified analysis by social class. Similar findings were observed regarding the different types of allergic symptoms. In the univariate analysis, breast-feeding, the experience of viral infections, and MMR vaccination were found to be protective of DM1 presentation in both upper and lower social classes. In the multiple logistic regression analysis, the experience of more than 2 infections/yr (OR = 0.12, 95% CI: 0.04-0.34), the origin from middle and upper social classes (OR = 0.42, 95% CI: 0.22-0.80) and breast-feeding (OR = 0.58, 95% CI: 0.31-1.07) were protective of DM1 occurrence. In children with DM1, the presence of allergic symptoms was not associated with the development of DM1. Among the environmental factors, the origin from middle or upper social classes, breast-feeding, the experience of viral infections, and MMR vaccination were found to have a protective effect on DM1 presentation.
- Published
- 2008
- Full Text
- View/download PDF
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