Turnover Magnitude Research Articles

Hubble Space TelescopeACS Wide-Field Photometry of the Sombrero Galaxy Globular Cluster System

A detailed imaging analysis of the globular cluster (GC) system of the Sombrero galaxy (NGC 4594) has been accomplished using a six-image mosaic from the Hubble Space Telescope Advanced Camera for Surveys. The quality of the data is such that contamination by foreground stars and background galaxies is negligible for all but the faintest 5% of the GC luminosity function. This enables the study of an effectively pure sample of 659 GCs until ∼2 mag fainter than the turnover magnitude, which occurs at M = -7.60 ± 0.06 for an assumed m - M = 29.77. Two GC metallicity subpopulations are easily distinguishable, with the metal-poor subpopulation exhibiting a smaller intrinsic dispersion in color compared to the metal-rich subpopulation. There are three new discoveries. (1) A metal-poor GC color-magnitude trend has been observed. (2) The fact that the metal-rich GCs are ∼17% smaller than the metal-poor ones for small projected galactocentric radii (less than ∼2') has been confirmed. However, the median half-light radii of the two subpopulations become identical at ∼3' from the center. This is most easily explained if the size difference is the result of projection effects. (3) The brightest (MV < -9.0) members of the GC system show a size-magnitude upturn, where the average GC size increases with increasing luminosity. Evidence is presented that supports an intrinsic origin for this feature rather than being a result of accreted dwarf elliptical nuclei. In addition, the metal-rich GCs show a shallower positive size-magnitude trend, similar to what is found in previous studies of young star clusters.

A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 - I. Observation, data analysis and luminosity function

In this paper and a companion paper, we report on a wide-field imaging survey of the globular cluster (GC) populations around M87 carried out with Suprime-Cam on the 8.2m Subaru telescope. Here we describe the observations, data reduction, and data analysis and present luminosity functions of GC populations around M87 and NGC 4552, another luminous Virgo elliptical in our survey field. The imaging data were taken in the B, V, and I bands with a sky coverage out to 0.5 Mpc from the M87 centre. GC candidates were selected by applying a colour criterion on the B-V and V-I diagram to unresolved objects, which greatly reduces contamination. The data from control fields taken with Subaru/Suprime-Cam were also analyzed for subtraction of contamination in the GC sample. We investigate GC luminosity functions (GCLFs) within 10' (~ 45 kpc) from the host galaxy centre in detail. The V-band turnover magnitude (V_TO) is estimated to be 23.62 +-0.06 mag and 23.56 +- 0.20 mag for the GC population in M87 and NGC 4552, respectively. The GCLF is found to be a function of GC colour; V_TO of the red GC subpopulation (V-I > 1.1) is fainter than that of the blue GC subpopulation (V-I < 1.1) in both M87 and NGC 4552, as expected if the colour differences are primarily due to a metallicity effect and the mass functions of the two subpopulations are similar. The radial dependence of the GCLF is also investigated for the GC population in M87. The GCLF of each subpopulation at 1' < R < 5' is compared with that at 5' < R < 10' but no significant trend with distance is found in the shape of the GCLF. We also estimate GC specific frequencies (S_N) for M87 and NGC 4552. The S_N of the M87 GC population is estimated to be 12.5 +- 0.8 within 25'. The S_N value of the NGC 4552 GC population is estimated to be 5.0 +- 0.6 within 10'.

The old globular cluster system of the dIrr galaxy NGC 1427A in the Fornax cluster

We present a study of the old globular cluster (GC) population of the dwarf irregular galaxy NGC 1427A using multi-wavelength VLT observations in U, B, V, I, H_alpha, J, H, and Ks bands under excellent observing conditions. We applied color and size selection criteria to select old GC candidates and made use of archival ACS images taken with the Hubble Space Telescope to reject contaminating background sources and blended objects from the GC candidates' list. The H_alpha observations were used to check for contamination due to compact, highly reddened young star clusters whose colors and sizes could mimic those of old GCs. After accounting for contamination we obtain a total number of 38+/-8 GC candidates with colors consistent with an old (~10 Gyr) and metal-poor (Z < 0.4xZ_solar) population as judged by simple stellar population models. Our contamination analysis indicates that the density distribution of GCs in the outskirts of the Fornax central cD galaxy NGC1399 may not be spherically symmetric. We derive a present-day specific frequency S_N of 1.6+/-0.23 for NGC 1427A, a value significantly larger than what is observed in the Local Group dwarf irregular galaxies and comparable with the values found for the same galaxy types in the Virgo and Fornax clusters. Assuming a universal globular cluster luminosity function turnover magnitude, we derive a distance modulus to NGC 1427A of 31.01+/-0.21 mag which places it 3.2+/-2.5(statistic)+/-1.6(systematic) Mpc in front of the Fornax central cD galaxy NGC 1399. The implications of this result for the relationship between NGC 1427A and the cluster environment are briefly discussed.

A wide-field photometric study of the globular cluster system of NGC 4636

We investigate the unusually rich cluster system of NGC4636 with wide-field Washington photometry. The globular cluster luminosity function can be followed roughly 1 mag beyond the turn-over magnitude. This corresponds to a distance modulus of m-M=31.24+-0.17, 0.4 mag larger than the distance determined from surface brightness fluctuations. The high specific frequency is confirmed, yet the exact value remains uncertain because of the uncertain distance: it varies between 5.6+-1.2 and 8.9+-1.2. The globular cluster system has a clearly bimodal color distribution. The color peak positions show no radial dependence and are in good agreement with the values found for other galaxies studied in the same filter system. However, a luminosity dependence is found: brighter clusters with an ``intermediate'' color exist. The clusters exhibit a shallow radial distribution within 7'.Within the same radial interval, the galaxy light has a distinctly steeper profile. Because of the difference in the cluster and light distribution the specific frequency increases considerably with radius. At 7' and 9' the density profiles of the red and blue clusters, respectively, change strongly which indicates that we reach the outer rim of the cluster system at approximately 11'. This feature is seen for the first time in a globular cluster system. While the radial distribution of the cluster and field populations are rather different, this is not true for the ellipticity of the system: the elongation as well as the position angle of the cluster system agree well with the galaxy light. We compare the radial distribution of globular clusters with the light profiles for a sample of elliptical galaxies. The difference observed in NGC 4636 is typical of an elliptical galaxy of this luminosity.

Secondary Globular Cluster populations

This study is motivated by two facts: 1. The formation of populous star cluster systems is widely observed to accompany violent star formation episodes in gas-rich galaxies as e.g. those triggered by strong interactions or merging. 2. The Globular Cluster (GC) systems of most but not all early-type galaxies show bimodal optical color distributions with fairly universal blue peaks and somewhat variable red peak colors, yet their Luminosity Functions (LFs) look like simple Gaussians with apparently universal turn-over magnitudes that are used for distance measurements and the determination of . Based on a new set of evolutionary synthesis models for Simple (= single burst) Stellar Populations (SSPs) of various metallicities using the latest Padova isochrones I study the color and luminosity evolution of GC populations over the wavelength range from U through K, providing an extensive grid of models for comparison with observations. I assume the intrinsic widths of the color distributions and LFs to be constant in time at the values observed today for the Milky Way or M 31 halo GC populations. Taking the color distributions and LFs of the Milky Way or M 31 halo GC population as a reference for old metal-poor GC populations in general, I study for which combinations of age and metallicity a secondary GC population formed in some violent star formation event in the history of its parent galaxy may or may not be detected in the observed GC color distributions. I also investigate the effect of these secondary GCs on the LFs of the total GC system. Significant differences are found among the diagnostic efficiencies in various wavelength regions. In particular, we predict the NIR to be able to reveal the presence of GC subpopulations with different age – metallicity combinations that may perfectly hide within one inconspicuous optical color peak. If the entire manifold of possible age – metallicity combinations is admitted for a secondary GC population, we find several cases where the resulting LF of the whole GC system is significantly affected and its turn-over could not serve as a reliable distance indicator. If, on the other hand, we assume some age – metallicity relation for GC populations, the second peak of the LFs vanishes and models indicate single-peak GC LFs even in GC systems with bimodal color distributions. A broad but sufficient age – metallicity relation is, for example, obtained if the secondary GC populations form in mergers of various spiral galaxy types from the ISM pre-enriched over the redshift range from to . As a first illustrative example we apply our models to V- and I-band data presented by Larsen et al. ([CITE]) for blue and red peak GCs in three early-type galaxies. We point out the importance of having multi-band information to independently constrain ages and metallicities of different GC subpopulations and again stress the diagnostic potential of K-band data in addition to optical observations. The models presented here will be used for the interpretation of multi-wavelength data on GC systems in galaxies of various types, luminosities and environments as well as on young star cluster systems in interacting galaxies and mergers. By independently constraining ages and metallicities of individual clusters we expect to shed light on both cluster and galaxy formation scenarios.

Distance to the Centaurus cluster and its subcomponents from surface brightness fluctuations

We present I-band Surface Brightness Fluctuations (SBF) measurements for 15 early type galaxies (3 giants, 12 dwarfs) in the central region of the Centaurus cluster, based on deep photometric data in 7 fields obtained with VLT FORS1 and with very good seeing. From the SBF-distances to our sample galaxies we determine the distance of the Centaurus cluster to be 41.3 ± 2.1 Mpc (33.08 ± 0.11 mag). This places the Centaurus cluster at about the same distance as the “Great Attractor”. We find a distance difference of 0.27 ± 0.34 mag between the two subcomponents Cen 30 and Cen 45, ruling out that both components are separated by their Hubble flow distance. A distance difference of 0.48 ± 0.21 mag is found between the central galaxies NGC 4696 (Cen 30) and NGC 4709 (Cen 45) of both components, supported by the different turn-over magnitudes of their respective globular cluster systems. This suggests that Cen 45 is falling into but has not yet reached Cen 30, supporting the idea of a large scale filament along the line of sight towards Centaurus (Churazov et al. [CITE]). 83.0 ± 8.3 km sMpc-1 is obtained for our Cen 30 sample taking into account the peculiar motion of the Local Group into the direction of the Centaurus cluster. This value of H0 corresponds to a much smaller Hubble flow distortion in the direction of Centaurus than determined by Tonry et al. ([CITE]), implying that the GA mass estimate by Tonry et al. may be too high and/or that the Centaurus cluster falls into the GA almost perpendicularly to the line of sight. As our mean single measurement error is very close to the measured distance scatter of the investigated galaxies, we can only derive an upper limit of ±10 Mpc radial extension for the Centaurus cluster, corresponding to a five times larger radial than tangential extension. No evidence for an infall pattern into the Great Attractor is found within the uncertainties for the 11 galaxies with measured redshifts.

Hubble Space Telescope observations of globular cluster systems along the Hubble sequence of spiral galaxies

We have studied the globular cluster (GC) systems of 7 giant, edge-on spiral galaxies using Hubble Space Telescope imaging in V and I. The galaxy sample covers the Hubble types Sa to Sc, allowing us to study the variation of the properties of GC systems along the Hubble sequence. The photometry reaches ~1.5 mag beyond the turn-over magnitude of the GC luminosity function for each galaxy. Specific frequencies (S_N values) of GCs were evaluated by comparing the numbers of GCs found in our WFPC2 pointings with those in the Milky Way which would be detected in the same metric area. The S_N values of spirals with B/T <= 0.3 (i.e., spirals with a Hubble type later than about Sb) are consistent with a value of S_N = 0.55 +- 0.25. We suggest that this population of GCs represents a `universal', old halo population that is present around each galaxy. Most galaxies in our sample have S_N values that are consistent with a scenario in which GC systems are made up of (i) the aforementioned halo population plus (ii) a population that is associated with bulges, which grows linearly with the mass of the bulge. Such scenarios include the `merger scenario' for the formation of elliptical galaxies as well as the `multi-phase collapse' scenario, but it seems inconsistent with the `secular evolution' scenario of Pfenniger & Norman (1990), in which bulges are formed from disc stars by means of the redistribution of angular momentum through bar instabilities and/or minor perturbations. However, there is one bulge-dominated spiral galaxy in our sample (NGC 7814) with a low S_N value that is consistent with those of the latest-type spirals. Thus, our results suggest that the formation histories of galaxy bulges of early-type spirals can be significantly different from one galaxy to another. (abridged)

Globular Cluster Systems in Four Brightest Cluster Galaxies: A262, A3560, A3565, and A3742

We have used deep I-band (F814W) images from the Space Telescope archive to study the globular cluster systems around the brightest cluster galaxies (BCGs) in A262, A3560, A3565, and A3742. Three of these BCGs have inner dust lanes and peculiar structural features that indicate past histories of low-level interaction and accretion. The deep I-band WFPC2 images have photometric limits that, for all four galaxies, reach near or just beyond the globular cluster luminosity function (GCLF) turnover point. Their specific frequencies are 8.24 ± 1.65, 4.66 ± 0.93, 2.58 ± 0.52, and 2.62 ± 0.52, respectively, all within a factor of 2 of the normal range for giant elliptical galaxies. We obtain new estimates of the GCLF turnover magnitudes, which are shown to be consistent with an adopted constant of H0 70 km s-1 Mpc-1 on the Hubble diagram of GCLF turnover apparent magnitude versus redshift, on a distance scale where the fundamental GCLF calibrator E galaxies (M87 and others) in Virgo are at d = 16 Mpc.

The Globular Cluster System of NGC 1316

We have studied the Globular Cluster System of the merger galaxy NGC 1316 in Fornax, using CCD BV I photometry. Dividing the sample into red (presumably metal-rich) and blue (metal-poor) subpopulations at B - I = 1.75, we find that they follow strikingly different angular distributions. The red clusters show a strong correlation with the galaxy elongation, but the blue ones are circularly distributed. An astonishingly low specific frequency for NGC 1316 of only SN = 0.9±0.2 is derived, which confirms with a larger field a previous finding by Grillmair et al. (1999). Assuming a “normal” SN of ∼ 4 for early-type galaxies, we use stellar population synthesis models to estimate the merger age to about 2 Gyr, if an intermediate-age population were to explain the low SN we observe. By fitting t5 functions to the Globular Cluster Luminosity Function (GCLF), we derive the following turnover magnitudes: and . They support that NGC 1316, in spite of its outlying location, is at the same distance as the core of the Fornax cluster.

The globular cluster system of NGC 1316 (Fornax A)

We have studied the Globular Cluster System of the merger galaxy NGC 1316 in Fornax, using CCD BVI photometry. A clear bimodality is not detected from the broadband colours. However, dividing the sample into red (presumably metal- rich) and blue (metal-poor) subpopulations at B-I=1.75, we find that they follow strikingly different angular distributions. The red clusters show a strong correlation with the galaxy elongation, but the blue ones are circularly distributed. No systematic difference is seen in their radial profile and both are equally concentrated. We derive an astonishingly low Specific Frequency for NGC 1316 of only Sn=0.9, which confirms with a larger field a previous finding by Grillmair et al. (1999). Assuming a normal Sn of ~4 for early-type galaxies, we use stellar population synthesis models to estimate in 2 Gyr the age of this galaxy, if an intermediate-age population were to explain the low Sn we observe. This value agrees with the luminosity-weighted mean age of NGC 1316 derived by Kuntschner & Davies (1998) and Mackie & Fabbiano (1998). By fitting t5 functions to the Globular Cluster Luminosity Function (GCLF), we derived the following turnover magnitudes: B=24.69 +/- 0.15, V=23.87 +/- 0.20 and I=22.72 +/- 0.14. They confirm that NGC 1316, in spite of its outlying location, is at the same distance as the core of the Fornax cluster.

New Insights from [ITAL]HST[/ITAL] Studies of Globular Cluster Systems. I. Colors, Distances, and Specific Frequencies of 28 Elliptical Galaxies

We present an analysis of the globular cluster systems of 28 elliptical galaxies using archival WFPC2 images in the V and I-bands. The V-I color distributions of at least 50% of the galaxies appear to be bimodal {\it at the present level of photometric accuracy}. We argue that this is indicative of multiple epochs of cluster formation early in the history of these galaxies, possibly due to mergers. We also present the first evidence of bimodality in low luminosity galaxies and discuss its implication on formation scenarios. The mean color of the 28 cluster systems studied by us is V-I = 1.04$\pm$0.04 (0.01) mag corresponding to a mean metallicity of Fe/H = -1.0$\pm$0.19 (0.04). We find that the turnover magnitudes of the globular cluster luminosity functions (GCLF) of our sample are in excellent agreement with the distance measurements using other methods and conclude that the accuracy of the GCLF is at least as good as the surface brightness fluctuation method. The absolute magnitude of the turnover luminosity of the GCLF is M$_V^0$ = -7.41 (0.03) in V and M$_I^0$ = -8.46 (0.03) in I. The mean local specific frequency of our sample of elliptical galaxies within the WFPC2 field-of-view is 2.4$\pm$1.8 (0.4), considerably higher than the 1.0$\pm$0.6 (0.1) derived for a comparable sample of S0s in a similar analysis. It shows no obvious correlation with metallicity, host galaxy mass or membership in a galaxy cluster. The median size of clusters in all galaxies appears to be remarkably constant at $\sim$2.4 pc. We suggest that in the future it might be possible to use the sizes of clusters in the inner regions of galaxies as a simple geometrical distance indicator.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of Star Clusters in NGC 1023: Evidence for Three Cluster Populations?

Using Hubble Space Telescope images we have carried out a study of cluster populations in the nearby S0 galaxy NGC 1023. In two WFPC2 pointings we have identified 221 cluster candidates. The small distance (~9 Mpc) combined with deep F555W and F814W images allows us to reach about 2 mag below the expected turnover of the globular cluster luminosity function. NGC 1023 appears to contain at least three identifiable cluster populations: the brighter clusters show a clearly bimodal color distribution with peaks at (V-I)0 = 0.92 and at (V-I)0 = 1.15, and in addition there are a number of fainter, more extended objects with predominantly red colors. Among the brighter clusters, we find that the blue clusters have somewhat larger sizes than the red ones with mean effective radii of Re ~ 2 and Re ~ 1.7 pc, respectively. These clusters have luminosity functions (LFs) and sizes consistent with what is observed for globular clusters in other galaxies. Fitting Gaussians to the LFs of the blue and red compact clusters, we find turnover magnitudes of MTO(blue) = -7.58 and MTO(red) = -7.37 in V and dispersions of σV(blue) = 1.12 and σV(red) = 0.97. The fainter, more extended clusters have effective radii up to Re ~ 10–15 pc, and their LF appears to rise at least down to MV ~ -6, few of them being brighter than MV = -7. We suggest that these fainter objects may have a formation history distinct from that of the brighter GCs.

The Age Difference between the Globular Cluster Subpopulations in NGC 4472

The age difference between the two main globular cluster subpopulations in the Virgo giant elliptical galaxy NGC 4472 (M49) has been determined using Hubble Space Telescope WFPC2 images in the F555W and F814W filters. Accurate photometry has been obtained for several hundred globular clusters in each of the two main subpopulations, down to more than 1 mag below the turnover of their luminosity functions. This allows precise determinations of both the mean colors and the turnover magnitudes of the two main subpopulations. By comparing the data with various population synthesis models, the age-metallicity pairs that fit both the observed colors and magnitudes have been identified. The metal-poor and the metal-rich globular clusters are found to be coeval within the errors (~3 Gyr). If one accepts the validity of our assumptions, these errors are dominated by model uncertainties. A systematic error of up to 4 Gyr could affect this result if the blue and the red clusters have significantly different mass distributions. However, that one subpopulation is half as old as the other is excluded at the 99% confidence level. The different globular cluster populations are assumed to trace the galaxy's major star formation episodes. Consequently, the vast majority of globular clusters (and by implication the majority of stars) in NGC 4472 formed at high redshifts but by two distinct mechanisms or in two episodes. The distance to NGC 4472 is determined to be 15.8 ± 0.8 Mpc, which is in excellent agreement with six of the seven Cepheid distances to Virgo Cluster spiral galaxies. This implies that the spiral and elliptical galaxies in the main body of Virgo are at the same distance.

Globular cluster calibration of the peak brightness of the Type Ia supernova 1992A and the value of H0

We have determined the absolute magnitude at maximum light of SN 1992A by using the turnover magnitude of the globular cluster luminosity function of its parent galaxy, NGC 1380. A recalibration of the peak of the turnover magnitude of the Milky Way clusters using the latest Hipparcos results has been made with an assessment of the complete random and systematic error budget. The following results emerge: a distance to NGC 1380 of 18.6 ± 1.4 Mpc, corresponding to (m − M) 31.35 ± 0.16, and an absolute magnitude of SN 1992A at maximum of MB(max) −18.79 ± 0.16. Taken at face value, SN 1992A seems to be more than half a magnitude fainter than the other SNe Ia for which accurate distances exist. We discuss the implications of this result and present possible explanations. We also discuss the Phillips relationship between rate of decline and the absolute magnitude at maximum, on the basis of nine SNe Ia, the individual distances of which have been obtained with Cepheids and the globular cluster luminosity function. The new calibration of this relationship, applied to the most distant SNe of the Calan–Tololo survey, yields H0 = 62 ± 6 km s−1 Mpc−1.

Globular Cluster Luminosity Functions and the Hubble Constant from WFPC2 Imaging: The Dominant Group Elliptical NGC 5846

view Abstract Citations (24) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Globular Cluster Luminosity Functions and the Hubble Constant from WFPC2 Imaging: The Dominant Group Elliptical NGC 5846 Forbes, Duncan A. ; Brodie, Jean P. ; Huchra, John Abstract The Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) has several advantages over ground-based observations for the study of globular cluster luminosity functions (GCLFs) and distance determination. Here we present WFPC2 data on the globular clusters associated with NGC 5846. This giant elliptical is the dominant galaxy in a small, compact group located ~13 Mpc beyond the Virgo cluster. We have detected over 1200 globular clusters in three (central, north, and south) separate pointings. The luminosity functions in each of these pointings are statistically the same, indicating that the mean luminosity (mass) does not vary between ~3 and 30 kpc from the galaxy center. This suggests that dynamical friction and bulge shocking destruction processes are insignificant. We have fit a Gaussian and t_5_ profile to the GCLF (of the combined pointings) and find that it is well represented by a turnover magnitude of m_V_^0^ = 25.05 +/- 0.10 and a dispersion of σ = 1.34+/-0.06. Our 50% incompleteness level is ~1 mag fainter than the turnover. After applying a metallicity correction to the "universal" GCLF turnover magnitude, we derive a distance modulus of (m-M)=32.32+/-0.23. For a group velocity V_CMB_ = 1883+/-28 km s^-1^, the Hubble constant is H_0_ = 65 +/- 8 km s^-1^ Mpc^-1^. Publication: The Astronomical Journal Pub Date: December 1996 DOI: 10.1086/118194 arXiv: arXiv:astro-ph/9611141 Bibcode: 1996AJ....112.2448F Keywords: GLOBULAR CLUSTERS: GENERAL; GALAXIES: INDIVIDUAL: NGC 5846; DISTANCE SCALE; Astrophysics E-Print: 12 pages, Plate 1 in JPEG format, Latex, full paper also available at http://www.ucolick.org/~forbes/home.html full text sources arXiv | ADS | data products SIMBAD (2) NED (1) MAST (1) ESA (1)

Globular Cluster Luminosity Functions and the Hubble Constant From WFPC Imaging: Galaxies in the Coma I Cloud

view Abstract Citations (16) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Globular Cluster Luminosity Functions and the Hubble Constant From WFPC Imaging: Galaxies in the Coma I Cloud Forbes, Duncan A. Abstract The membership of some galaxies in the nearby (d ~ 12 Mpc) Coma I cloud is uncertain. Here we present globular cluster luminosity functions (GCLFs) from the Hubble Space Telescope for two bright ellipticals which may belong to this group. After fitting the GCLF, we find a turnover magnitude of m_V_^0^ = 23.23 +/- 0.11 for NGC 4278 and m_V_^0^ = 23.07+/- 0.13 for NGC 4494. Our limiting magnitude is about two magnitudes fainter than these values, making this data among the most complete GCLFs published to date. The fitted GCLF dispersions (~1.1^m^) are somewhat smaller than typical values for other ellipticals. Assuming an absolute turnover magnitude of M_V_^0^ = -7.62, and after applying a small metallicity correction, we derive distance modulii of (m-M) = 30.61+/- 0.14 for NGC 4278 and 30.50+/-0.15 for NGC 4494. These distance estimates are compared to other methods, and lie within the published range of values. We conclude that both galaxies lie at the same distance and are both members of the Coma I cloud. Publication: The Astronomical Journal Pub Date: October 1996 DOI: 10.1086/118108 arXiv: arXiv:astro-ph/9611139 Bibcode: 1996AJ....112.1409F Keywords: GLOBULAR CLUSTERS: GENERAL; Astrophysics E-Print: 13 pages, Latex. Full paper also available at http://www.ucolick.org/~forbes/home.html full text sources arXiv | ADS | data products SIMBAD (5) NED (3) MAST (1) ESA (1)

Globular Cluster Luminosity Functions and the Hubble Constant From WFPC2 Imaging: The Giant Elliptical NGC 4365

view Abstract Citations (25) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Globular Cluster Luminosity Functions and the Hubble Constant From WFPC2 Imaging: The Giant Elliptical NGC 4365 Forbes, Duncan A. Abstract The turnover, or peak, magnitude in a galaxy's globular cluster luminosity function (GCLF) may provide a standard candle for an independent distance estimator. Here we examine the GCLF of the giant elliptical NGC 4365 using photometry of ~350 globular clusters from the Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2). The WFPC2 data have several advantages over equivalent ground-based imaging. The membership of NGC 4365 in the Virgo cluster has been the subject of recent debate. We have fit a Gaussian and t_5_ profile to the luminosity function and find that it can be well represented by a turnover magnitude of m^0^_v_ = 24.2+/-03 and a dispersion σ = 1.28+/-0.15. After applying a small metallicity correction to the "universal" globular cluster turnover magnitude, we derive a distance modulus of (m - M) = 31.6+/-0.3 which is in reasonable agreement with that from surface brightness fluctuation measurements. This result places NGC 4365 about 5 Mpc beyond the Virgo cluster core. For a V_CMB_ = 1592+/-24 km s^-1^ the Hubble constant is H_0_ = 72^+10^_-12_ km s^-1^ Mpc^-1^. We also describe our method for estimating a local specific frequency for the GC system within the central 5 h^-1^ kpc which has fewer uncertain corrections than a total estimate. The resulting value of 6.4+/-1.5 indicates that NGC 4365 has a GC richness similar to other early-type galaxies. Publication: The Astronomical Journal Pub Date: September 1996 DOI: 10.1086/118069 arXiv: arXiv:astro-ph/9611140 Bibcode: 1996AJ....112..954F Keywords: GALAXIES: INDIVIDUAL: NGC 4365; GLOBULAR CLUSTERS: GENERAL; DISTANCE SCALE; Astrophysics E-Print: 12 pages, Latex, full paper also available at http://www.ucolick.org/~forbes/home.html full text sources arXiv | ADS | data products SIMBAD (7) NED (4) MAST (1) ESA (1)

Globular Clusters in Fornax: Does [ITAL]M[/ITAL][TSUP]0[/TSUP] Depend on Environment?

We present the V-band globular cluster luminosity functions (GCLFs) of the Fornax Cluster galaxies NGC 1344, NGC 1380, NGC 1399, and NGC 1404. Our observations reach to V = 24.8, roughly 1 mag beyond the GCLF turnover m0V, with ~90% completeness. From the amplitude of the galaxy surface brightness fluctuations, we also estimate the number of globular clusters fainter than this cutoff magnitude. The GCLFs of these galaxies are well fitted by Gaussians; the weighted means of their turnover magnitudes and dispersions are m0V = 23.88 ± 0.10 mag and σ = 1.35 ± 0.07 mag. The assumption of a universal value for the absolute magnitude of the turnover M0V places the Fornax cluster 0.13 ± 0.11 mag more distant than Virgo. However, in light of recent Cepheid and other high-precision distance measurements, as well as ongoing HST observations of GCLFs for the purpose of determining the extragalactic distance scale, we choose to reexamine the universal GCLF hypothesis. Based on data from groups and clusters of galaxies, we find evidence that M0V becomes fainter as the local density of galaxies increases. We speculate on the possible cause of this trend; if it is confirmed, GCLF observations will be less useful for determining distances but may provide important information for constraining theories of star formation in primordial galaxy halos.

Measuring distant globular cluster systems using brightness fluctuations

view Abstract Citations (7) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Measuring Distant Globular Cluster Systems Using Brightness Fluctuations Wing, David L. ; Harris, Gretchen L. H. ; Hanes, David A. ; Harris, William E. Abstract We describe a brightness fluctuation technique to determine the total population of globular clusters around distant galaxies. The method relies on measuring luminosity fluctuations produced by faint unresolved globular clusters in the host galaxy, the amplitude of which depends on both the specific frequency and the luminosity function of the globular cluster system itself. This technique bypasses the need to obtain counts of globular clusters directly which must then be extrapolated past the limiting magnitude to obtain a total cluster population. Brightness fluctuations sample the integrated globular cluster counts up to ~3 mag faintward of the photometric limit and thus provide an improved estimate of total cluster populations over direct counting techniques. This would be especially useful for very distant galaxies where only marginal detections of globular clusters have so far been made and the resulting luminosity function is not well defined even at the bright end. Potentially, this method can provide globular cluster total populations in giant elliptical galaxies out to <~ 100 Mpc. The primary drawback of this approach is that it requires a priori knowledge about the shape and turnover magnitude (M_V_^0^) of the globular cluster luminosity function which, however, is well known empirically. In this paper we explain how to measure globular cluster brightness fluctuations, discuss the limitations of this technique, and demonstrate its feasibility using CCD images of M87 as an example. Publication: The Astronomical Journal Pub Date: January 1995 DOI: 10.1086/117260 Bibcode: 1995AJ....109..121W Keywords: Brightness Discrimination; Faint Objects; Globular Clusters; Luminosity; Astronomical Photometry; Brightness Distribution; Elliptical Galaxies; Statistical Analysis; Astronomy; GLOBULAR CLUSTERS: GENERAL; GALAXIES: DISTANCES AND REDSHIFTS full text sources ADS | data products SIMBAD (9) Related Materials (1) Erratum: 1995AJ....110.1905W

A statistical investigation into the shape of the globular cluster luminosity distribution

view Abstract Citations (88) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A statistical investigation into the shape of the globular cluster luminosity distribution. Secker, Jeff Abstract Recent observations of the globular clusters in the Milky Way and M31 confirm that their luminosities follow a relatively simple distribution, the globular cluster luminosity function (GCLF), that is unimodal and nearly symmetric. Maximum-likelihood methods are used to fit three simple types of analytic functions to the GCLFs in these two galaxies. The analytic function which best describes the GCLFs is found to be the t distribution with a shape parameter of mu about five. The most probable values of the parameters which characterize the Milky Way GCLF are M(V)0 = -7.29 +/- 0.13 for the peak of 'turnover' magnitude, and sigma(t) = 1.1 +/- 0.1 mag for the dispersion parameter. Similarly, the most probable values for the M31 GCLF are V(0) = 17.00 +/- 0.11 and sigma(t) = 0.82 +/- 0.08 for the turnover magnitude and dispersion. For a M31 distance modulus of (m - M)V = 24.51 +/- 0.1, the absolute magnitude of the M31 halo cluster peak is then M(V)0 = -7.51 +/- 0.15. The GCLF for the M31 halo therefore appears to have a slightly higher mean luminosity and smaller sample dispersion than the Milky Way GCLF, though the differences in both parameters are just on the edge of being statistically significant. Publication: The Astronomical Journal Pub Date: October 1992 DOI: 10.1086/116332 Bibcode: 1992AJ....104.1472S Keywords: Globular Clusters; Luminosity; Parameterization; Statistical Analysis; Mass Distribution; Maximum Likelihood Estimates; Milky Way Galaxy; Astrophysics full text sources ADS | data products SIMBAD (99) NED (1)