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Title: NEW CONSTRAINTS ON A COMPLEX RELATION BETWEEN GLOBULAR CLUSTER COLORS AND ENVIRONMENT

Abstract

We present an analysis of high-quality photometry for globular clusters (GCs) in the Virgo cluster core region, based on data from the Next Generation Virgo Cluster Survey (NGVS) pilot field, and in the Milky Way (MW), based on Very Large Telescope/X-Shooter spectrophotometry. We find significant discrepancies in color–color diagrams between sub-samples from different environments, confirming that the environment has a strong influence on the integrated colors of GCs. GC color distributions along a single color are not sufficient to capture the differences we observe in color–color space. While the average photometric colors become bluer with increasing radial distance to the cD galaxy M87, we also find a relation between the environment and the slope and intercept of the color–color relations. A denser environment seems to produce a larger dynamic range in certain color indices. We argue that these results are not due solely to differential extinction, Initial Mass Function variations, calibration uncertainties, or overall age/metallicity variations. We therefore suggest that the relation between the environment and GC colors is, at least in part, due to chemical abundance variations, which affect stellar spectra and stellar evolution tracks. Our results demonstrate that stellar population diagnostics derived from model predictions which are calibratedmore » on one particular sample of GCs may not be appropriate for all extragalactic GCs. These results advocate a more complex model of the assembly history of GC systems in massive galaxies that goes beyond the simple bimodality found in previous decades.« less

Authors:
;  [1]; ; ;  [2]; ;  [3]; ;  [4]; ; ; ;  [5]; ;  [6];  [7];  [8];  [9];
  1. Observatoire Astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, F-67000 Strasbourg (France)
  2. Institute of Astrophysics, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago (Chile)
  3. Department of Astronomy, Peking University, Beijing 100871 (China)
  4. Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg (Germany)
  5. Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada)
  6. AIM Paris Saclay, CNRS/INSU, CEA/Irfu, Université Paris Diderot, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France)
  7. Department of Physics and Astronomy, Youngstown State University, One University Plaza, Youngstown, OH 44555 (United States)
  8. UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States)
  9. European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany)
Publication Date:
OSTI Identifier:
22654220
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 829; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CALIBRATION; COLOR; DISTRIBUTION; FORECASTING; GALAXY CLUSTERS; LIMITING VALUES; MASS; METALLICITY; MILKY WAY; PARTICLE TRACKS; PHOTOMETRY; SPACE; SPECTRA; SPECTROPHOTOMETRY; STAR CLUSTERS; STAR EVOLUTION; STARS; TELESCOPES

Citation Formats

Powalka, Mathieu, Lançon, Ariane, Puzia, Thomas H., Alamo-Martínez, Karla, Ángel, Simón, Peng, Eric W., Lim, Sungsoon, Schönebeck, Frederik, Grebel, Eva K., Blakeslee, John P., Côté, Patrick, Ferrarese, Laura, Gwyn, S. D. J., Cuillandre, Jean-Charles, Duc, Pierre-Alain, Durrell, Patrick, Guhathakurta, Puragra, Kuntschner, Harald, E-mail: mathieu.powalka@astro.unistra.fr, and and others. NEW CONSTRAINTS ON A COMPLEX RELATION BETWEEN GLOBULAR CLUSTER COLORS AND ENVIRONMENT. United States: N. p., 2016. Web. doi:10.3847/2041-8205/829/1/L5.
Powalka, Mathieu, Lançon, Ariane, Puzia, Thomas H., Alamo-Martínez, Karla, Ángel, Simón, Peng, Eric W., Lim, Sungsoon, Schönebeck, Frederik, Grebel, Eva K., Blakeslee, John P., Côté, Patrick, Ferrarese, Laura, Gwyn, S. D. J., Cuillandre, Jean-Charles, Duc, Pierre-Alain, Durrell, Patrick, Guhathakurta, Puragra, Kuntschner, Harald, E-mail: mathieu.powalka@astro.unistra.fr, & and others. NEW CONSTRAINTS ON A COMPLEX RELATION BETWEEN GLOBULAR CLUSTER COLORS AND ENVIRONMENT. United States. doi:10.3847/2041-8205/829/1/L5.
Powalka, Mathieu, Lançon, Ariane, Puzia, Thomas H., Alamo-Martínez, Karla, Ángel, Simón, Peng, Eric W., Lim, Sungsoon, Schönebeck, Frederik, Grebel, Eva K., Blakeslee, John P., Côté, Patrick, Ferrarese, Laura, Gwyn, S. D. J., Cuillandre, Jean-Charles, Duc, Pierre-Alain, Durrell, Patrick, Guhathakurta, Puragra, Kuntschner, Harald, E-mail: mathieu.powalka@astro.unistra.fr, and and others. Tue . "NEW CONSTRAINTS ON A COMPLEX RELATION BETWEEN GLOBULAR CLUSTER COLORS AND ENVIRONMENT". United States. doi:10.3847/2041-8205/829/1/L5.
@article{osti_22654220,
title = {NEW CONSTRAINTS ON A COMPLEX RELATION BETWEEN GLOBULAR CLUSTER COLORS AND ENVIRONMENT},
author = {Powalka, Mathieu and Lançon, Ariane and Puzia, Thomas H. and Alamo-Martínez, Karla and Ángel, Simón and Peng, Eric W. and Lim, Sungsoon and Schönebeck, Frederik and Grebel, Eva K. and Blakeslee, John P. and Côté, Patrick and Ferrarese, Laura and Gwyn, S. D. J. and Cuillandre, Jean-Charles and Duc, Pierre-Alain and Durrell, Patrick and Guhathakurta, Puragra and Kuntschner, Harald, E-mail: mathieu.powalka@astro.unistra.fr and and others},
abstractNote = {We present an analysis of high-quality photometry for globular clusters (GCs) in the Virgo cluster core region, based on data from the Next Generation Virgo Cluster Survey (NGVS) pilot field, and in the Milky Way (MW), based on Very Large Telescope/X-Shooter spectrophotometry. We find significant discrepancies in color–color diagrams between sub-samples from different environments, confirming that the environment has a strong influence on the integrated colors of GCs. GC color distributions along a single color are not sufficient to capture the differences we observe in color–color space. While the average photometric colors become bluer with increasing radial distance to the cD galaxy M87, we also find a relation between the environment and the slope and intercept of the color–color relations. A denser environment seems to produce a larger dynamic range in certain color indices. We argue that these results are not due solely to differential extinction, Initial Mass Function variations, calibration uncertainties, or overall age/metallicity variations. We therefore suggest that the relation between the environment and GC colors is, at least in part, due to chemical abundance variations, which affect stellar spectra and stellar evolution tracks. Our results demonstrate that stellar population diagnostics derived from model predictions which are calibrated on one particular sample of GCs may not be appropriate for all extragalactic GCs. These results advocate a more complex model of the assembly history of GC systems in massive galaxies that goes beyond the simple bimodality found in previous decades.},
doi = {10.3847/2041-8205/829/1/L5},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 829,
place = {United States},
year = {Tue Sep 20 00:00:00 EDT 2016},
month = {Tue Sep 20 00:00:00 EDT 2016}
}
  • Color-magnitude diagrams (CMDs) derived from Hubble Space Telescope (HST) Advanced Camera for Surveys F606W, F814W photometry of six globular clusters (GCs) are presented. The six GCs form two loose groupings in Galactocentric distance (R{sub GC}): IC 4499, NGC 6426, and Ruprecht 106 at {approx}15-20 kpc and NGC 7006, Palomar 15, and Pyxis at {approx}40 kpc. The CMDs allow the ages to be estimated from the main-sequence turnoff in every case. In addition, the age of Palomar 5 (R{sub GC} {approx} 18 kpc) is estimated using archival HST Wide Field Planetary Camera 2 V, I photometry. The age analysis reveals themore » following: IC 4499, Ruprecht 106, and Pyxis are 1-2 Gyr younger than inner halo GCs with similar metallicities; NGC 7006 and Palomar 5 are marginally younger than their inner halo counterparts; NGC 6426 and Palomar 15, the two most metal-poor GCs in the sample, are coeval with all the other metal-poor GCs within the uncertainties. Combined with our previous efforts, the current sample provides strong evidence that the Galactic GC age-metallicity relation consists of two distinct branches. One suggests a rapid chemical enrichment in the inner Galaxy while the other suggests prolonged GC formation in the outer halo. The latter is consistent with the outer halo GCs forming in dwarf galaxies and later being accreted by the Milky Way.« less
  • Magnitudes for the seven RR Lyr variables and one red variable in NGC 5897 have been derived from 213 B plates taken from 1939 through 1987 and from 38 V plates taken from 1956 through 1987. Blue light curves have been constructed for all the periodic variables and visual light curves for all but one star (V4) with a badly blended image. The period distribution of the RR Lyr stars is rather unusual, with three periods from 0.797 to 0.856 day, two at 0.420 and 0.454 day, and two more at 0.342 and 0.349 day. No variation to within +more » or - 0.1 mag can be seen for SK 120, a star which appears to be a cluster member lying within the instability strip. 26 refs.« less
  • Several population synthesis models now predict integrated colors of simple stellar populations in the mid-infrared bands. To date, the models have not been extensively tested in this wavelength range. In a comparison of the predictions of several recent population synthesis models, the integrated colors are found to cover approximately the same range but to disagree in detail, for example, on the effects of metallicity. To test against observational data, globular clusters (GCs) are used as the closest objects to idealized groups of stars with a single age and single metallicity. Using recent mass estimates, we have compiled a sample ofmore » massive, old GCs in M31 which contain enough stars to guard against the stochastic effects of small-number statistics, and measured their integrated colors in the Spitzer/IRAC bands. Comparison of the cluster photometry in the IRAC bands with the model predictions shows that the models reproduce the cluster colors reasonably well, except for a small (not statistically significant) offset in [4.5] - [5.8]. In this color, models without circumstellar dust emission predict bluer values than are observed. Model predictions of colors formed from the V band and the IRAC 3.6 and 4.5 {mu}m bands are redder than the observed data at high metallicities and we discuss several possible explanations. In agreement with model predictions, V - [3.6] and V - [4.5] colors are found to have metallicity sensitivity similar to or slightly better than V - K{sub s}.« less
  • We present a study of the spatial and color distributions of four early-type galaxies and their globular cluster (GC) systems observed as part of our ongoing wide-field imaging survey. We use BVR KPNO 4 m+MOSAIC imaging data to characterize the galaxies' GC populations, perform surface photometry of the galaxies, and compare the projected two-dimensional shape of the host galaxy light to that of the GC population. The GC systems of the ellipticals NGC 4406 and NGC 5813 both show an elliptical distribution consistent with that of the host galaxy light. Our analysis suggests a similar result for the giant ellipticalmore » NGC 4472, but a smaller GC candidate sample precludes a definite conclusion. For the S0 galaxy NGC 4594, the GCs have a circular projected distribution, in contrast to the host galaxy light, which is flattened in the inner regions. For NGC 4406 and NGC 5813, we also examine the projected shapes of the metal-poor and metal-rich GC subpopulations and find that both subpopulations have elliptical shapes that are consistent with those of the host galaxy light. Lastly, we use integrated colors and color profiles to compare the stellar populations of the galaxies to their GC systems. For each galaxy, we explore the possibility of color gradients in the individual metal-rich and metal-poor GC subpopulations. We find statistically significant color gradients in both GC subpopulations of NGC 4594 over the inner ∼5 effective radii (∼20 kpc). We compare our results to scenarios for the formation and evolution of giant galaxies and their GC systems.« less