skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Intermediate-age globular clusters in four galaxy merger remnants

Abstract

We present the results of combining Hubble Space Telescope optical photometry with ground-based K{sub s} -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIK{sub s} GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ∼1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies.

Authors:
 [1];  [2];  [3];  [4];  [5]
  1. Giant Magellan Telescope Organization, 251 South Lake Avenue, Pasadena, CA 91101 (United States)
  2. Gemini Observatory, Casilla 603, La Serena (Chile)
  3. Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
  4. The University of Adelaide, South Australia 5005 (Australia)
  5. Monash University, Clayton, Victoria 3800 (Australia)
Publication Date:
OSTI Identifier:
22365484
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; FINE STRUCTURE; GALAXIES; INTERACTIONS; K ABSORPTION; METALLICITY; PHOTOMETRY; SPACE; STAR CLUSTERS; TELESCOPES

Citation Formats

Trancho, Gelys, Miller, Bryan W., Schweizer, François, Burdett, Daniel P., and Palamara, David, E-mail: gtrancho@gmto.org. Intermediate-age globular clusters in four galaxy merger remnants. United States: N. p., 2014. Web. doi:10.1088/0004-637X/790/2/122.
Trancho, Gelys, Miller, Bryan W., Schweizer, François, Burdett, Daniel P., & Palamara, David, E-mail: gtrancho@gmto.org. Intermediate-age globular clusters in four galaxy merger remnants. United States. doi:10.1088/0004-637X/790/2/122.
Trancho, Gelys, Miller, Bryan W., Schweizer, François, Burdett, Daniel P., and Palamara, David, E-mail: gtrancho@gmto.org. 2014. "Intermediate-age globular clusters in four galaxy merger remnants". United States. doi:10.1088/0004-637X/790/2/122.
@article{osti_22365484,
title = {Intermediate-age globular clusters in four galaxy merger remnants},
author = {Trancho, Gelys and Miller, Bryan W. and Schweizer, François and Burdett, Daniel P. and Palamara, David, E-mail: gtrancho@gmto.org},
abstractNote = {We present the results of combining Hubble Space Telescope optical photometry with ground-based K{sub s} -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIK{sub s} GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ∼1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies.},
doi = {10.1088/0004-637X/790/2/122},
journal = {Astrophysical Journal},
number = 2,
volume = 790,
place = {United States},
year = 2014,
month = 8
}
  • We study mass functions of globular clusters derived from Hubble Space Telescope/Advanced Camera for Surveys images of the early-type merger remnant galaxy NGC 1316, which hosts a significant population of metal-rich globular clusters of intermediate age ({approx}3 Gyr). For the old, metal-poor ({sup b}lue{sup )} clusters, the peak mass of the mass function M{sub p} increases with internal half-mass density {rho}{sub h} as M{sub p}{proportional_to}{rho}{sub h}{sup 0.44}, whereas it stays approximately constant with galactocentric distance R{sub gal}. The mass functions of these clusters are consistent with a simple scenario in which they formed with a Schechter initial mass function andmore » evolved subsequently by internal two-body relaxation. For the intermediate-age population of metal-rich ({sup r}ed{sup )} clusters, the faint end of the previously reported power-law luminosity function of the clusters with R{sub gal} > 9 kpc is due to many of those clusters having radii larger than the theoretical maximum value imposed by the tidal field of NGC 1316 at their R{sub gal}. This renders disruption by two-body relaxation ineffective. Only a few such diffuse clusters are found in the inner regions of NGC 1316. Completeness tests indicate that this is a physical effect. Using comparisons with star clusters in other galaxies and cluster disruption calculations using published models, we hypothesize that most red clusters in the low-{rho}{sub h} tail of the initial distribution have already been destroyed in the inner regions of NGC 1316 by tidal shocking, and that several remaining low-{rho}{sub h} clusters will evolve dynamically to become similar to 'faint fuzzies' that exist in several lenticular galaxies. Finally, we discuss the nature of diffuse red clusters in early-type galaxies.« less
  • We use observations from the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) study of Galactic globular clusters to investigate the spatial distribution of the inner regions of the disrupting Sagittarius dwarf spheroidal galaxy (Sgr). We combine previously published analyses of four Sgr member clusters located near or in the Sgr core (M54, Arp 2, Terzan 7, and Terzan 8) with a new analysis of diffuse Sgr material identified in the background of five low-latitude Galactic bulge clusters (NGC 6624, 6637, 6652, 6681, and 6809) observed as part of the ACS survey. By comparing the bulge cluster color-magnitude diagrams tomore » our previous analysis of the M54/Sgr core, we estimate distances to these background features. The combined data from four Sgr member clusters and five Sgr background features provide nine independent measures of the Sgr distance and, as a group, provide uniformly measured and calibrated probes of different parts of the inner regions of Sgr spanning 20 Degree-Sign over the face of the disrupting dwarf. This allows us, for the first time, to constrain the three-dimensional orientation of Sgr's disrupting core and globular cluster system and compare that orientation to the predictions of an N-body model of tidal disruption. The density and distance of Sgr debris are consistent with models that favor a relatively high Sgr core mass and a slightly greater distance (28-30 kpc, with a mean of 29.4 kpc). Our analysis also suggests that M54 is in the foreground of Sgr by {approx}2 kpc, projected on the center of the Sgr dSph. While this would imply a remarkable alignment of the cluster and the Sgr nucleus along the line of sight, we cannot identify any systematic effect in our analysis that would falsely create the measured 2 kpc separation. Finally, we find that the cluster Terzan 7 has the most discrepant distance (25 kpc) among the four Sgr core clusters, which may suggest a different dynamical history than the other Sgr core clusters.« less
  • From a photoelectric and photographic investigation in the UBV system of the very compact, low galactic latitude, southern globular cluster NGC 6441, characteristics in the C-M diagram that are in accord with observations of the most metal-rich globular clusters in the Galaxy have been found. After an extensive discussion of the problem of isolating the cluster stars from the field stars, and of the problem of determining E (B--V), E (B--V) =0.46+-0.15 mag is adopted. If M/subV/,=+0.9 mag, then (m-M)$sub 0$=14.7+-0.3 mag. This makes NGC 6441, one of the intrinsically brightest globular clusters in the Galaxy, consistent with the largemore » mass determined recently by Illingworth. However, no unusual features were detected in its C-M diagram that might account for its appearing within the error box of the 3U 1746--37 X-ray source, except possibly the anomalous position of V6 in the diagram. It is also found that NGC 6441 has a normal M/L ratio, and that, if our adopted reddening is correct, it is at perigalacticon. (AIP)« less
  • Photoelectric photometry of the integrand light of globular clusters in selected filter passbands has been used to derive estimates of their interstellar reddenings and metal abundances (i.e., (Fe/H)). The uncertainties in these estimates average +- 0.03 in E (B--V) and +- 0.10 in (Fe/H), which are not much larger than the uncertainties in the estimates derived from the best methods that rely on observations of individual stars in the clusters. Seventy-nine globular clusters have been observed with our technique, which brings to 84 the total number of globular clusters with precise estimates of metal abundance.