- ID:
- ivo://CDS.VizieR/J/A+A/611/A21
- Title:
- Globular cluster candidates in NGC253
- Short Name:
- J/A+A/611/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters (GCs) are key to our understanding of the Universe, as laboratories of stellar evolution, fossil tracers of the past formation epoch of the host galaxy, and effective distance indicators from local to cosmological scales. We analyze the properties of the sources in the NGC 253 with the aim of defining an up to date catalog of GC candidates in the galaxy. Given the distance of the galaxy, GCs in NGC 253 are ideal targets for resolved color-magnitude diagram studies of extragalactic GCs with next-generation diffraction limited ground-based telescopes. Our analysis is based on the science verification data of two ESO survey telescopes, VST and VISTA. Using ugri photometry from VST and JKs from VISTA, GC candidates were selected using as reference the morpho-photometric and color properties of spectroscopically confirmed GCs available in the literature. The strength of the results was verified against available archival HST/ACS data from the GHOSTS survey: all but two of the selected GC candidates appear as star clusters in HST footprints. The adopted GC selection leads to the definition of a sample of ~350 GC candidates. At visual inspection, we find that 82 objects match all the requirements for selecting GC candidates and 155 are flagged as uncertain GC candidate; however, 110 are unlikely GCs, which are most likely background galaxies. Furthermore, our analysis shows that four of the previously spectroscopically confirmed GCs, i.e., ~20% of the total spectroscopic sample, are more likely either background galaxies or high-velocity Milky Way stars. The radial density profile of the selected best candidates shows the typically observed r^1/4^-law radial profile. The analysis of the color distributions reveals only marginal evidence of the presence of color bimodality, which is normally observed in galaxies of similar luminosity. The GC luminosity function does not show the typical symmetry, mainly because of the lack of bright GCs. Part of the bright GCs missing might be at very large galactocentric distances or along the line of sight of the galaxy dusty disk. As an alternative possibility, we speculate that a fraction of low luminosity GC candidates might instead be metal-rich, intermediate age clusters, but fall in a similar color interval of old, metal-poor GCs. Defining a contaminant-free sample of GCs in extragalactic systems is not a straight forward exercise. Using optical and near-IR photometry we purged the list of GCs with spectroscopic membership and photometric GC candidates in NGC 253. Our results show that the use of either spectroscopic or photometric data only does not generally ensure a contaminant-free sample and a combination of both spectroscopy and photometry is preferred.
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- ID:
- ivo://CDS.VizieR/J/AJ/105/1762
- Title:
- Globular clusters around NGC 1399
- Short Name:
- J/AJ/105/1762
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained integrated Washington photometry (C,M,T1) of globular cluster candidates in the field of NGC 1399. This galaxy, the dominant object in the Fornax cluster, shares with NGC 4486 (M87) the property of possessing one of the largest known specific frequencies of globulars. Conflicting evidence on the presence of a B-V color gradient as a function of galactocentric distance has been reported for this cluster system. Here we investigate the existence of a gradient using the C-T1 index, which is twice as metallicity sensitive as B-V. A small gradient is detected. This color gradient, in the sense that outer clusters are bluer, amounts to approx. 0.1 mag in C-T1 over a galactocentric range from about 0.5 to 3.5 arcmin, corresponding to a difference of approx. 0.2 dex in metallicity. This confirms qualitatively the B-V gradient suggested by Bridges et al. [AJ, 101, 469 (1991)]. Photometry for 420 globular cluster candidates is presented. Metal abundances internally precise to approx. 0.25 dex and accurate to approx. 0.3 dex have been obtained for some 250 of the best candidates, after statistically subtracting a field contamination estimated at 30%. The mean abundance of -0.9 +/- 0.2 confirms previous indications that the NGC 1399 globular cluster system is, on average, significantly more metal rich than that of the Galaxy, as expected from the relative parent galaxy luminosities. Approximately 10% of the clusters exceed solar abundance, similar to the case for NGC 5128. The signature of possible globular cluster formation in mergers, as suggested by Ashman and Zepf [ApJ, 384, 50 (1992)], is found in the distinct peaks in the metallicity distribution function. However, their prediction (based on a simple theory designed only for application to normal elliptical galaxies and not the more complicated cD galaxies represented by NGC 1399) that the color difference between the clusters and the background halo light monotonically increases with radius is not borne out by the observations. The difference decreases with radius from the center to approx. 2 arcmin; beyond this radius, the difference does appear to increase, however. At all radii, the mean globular cluster abundance is some 0.25-0.5 dex more metal poor than that of the background halo.
- ID:
- ivo://CDS.VizieR/J/AJ/106/493
- Title:
- Globular clusters in M87
- Short Name:
- J/AJ/106/493
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep integrated Washington CCD photometry of the extremely populous globular cluster system of NGC 4486 (M87) in Virgo. The metallicities of 407 of the best candidates with T1 < 22 have been estimated from the (C-T1) color. These values are internally precise to ~0.15dex and accurate to ~0.25dex. The mean metallicity of the globular clusters is [Fe/H] = -0.86dex, with a formal standard error of the mean of 0.03dex but a more realistic uncertainty of about 0.2dex. This value is higher than that of the corresponding means of the globular clusters in the Galaxy and M31, but similar to those of the globular clusters in NGC 1399 and NGC 5128, as expected from the relative parent galaxy luminosities. Approximately 10% of the clusters exceed solar abundance, similar to the case for the globular clusters in NGC 1399 and NGC 5128. As found by Couture et al. [ApJS, 73, 671 (1990)], there is a large metallicity dispersion at any radius, with a sigma ~ 0.65dex. However, in contrast to their result and that of previous small-field CCD studies, the globular clusters display a marked gradient in both mean (M-T1) and (C-T1) color with galactocentric distance. The mean metallicity decreases by some 0.6dex over the radial extent of the cluster sample. This result is consistent with the early photographic study by Strom et al. [ApJ, 245, 416 (1981)]. The metallicity distribution function is remarkably similar to that of NGC 1399 found by Ostrov et al. [AJ, 105, 1762 (1993)] using the same technique. The two central cluster ellipticals show significant peaks at very similar metallicities, indicating similar formation and enrichment histories. We also find that this structure in the metallicity distribution function persists to radii where the halo light is dominated by the cD envelope.
- ID:
- ivo://CDS.VizieR/J/ApJS/150/367
- Title:
- Globular clusters in NGC 5128
- Short Name:
- J/ApJS/150/367
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a photometric and spectroscopic survey of the globular cluster (GC) system of NGC 5128 (Centaurus A), a galaxy whose proximity makes it an important target for early-type galaxy studies. We imaged three fields in UBVRI that extend 50 and 30kpc along the major and minor axes, respectively. We used both color and size information to develop efficient selection criteria for differentiating between star clusters and foreground stars. In total, we obtained new velocities for 138 globular clusters, nearly tripling the number of known clusters, and bringing the confirmed total in NGC 5128 to 215. We present a full catalog of all known GCs, with their positions, photometry, and velocities. In addition, we present catalogs of other objects observed, such as foreground stars, background galaxies, three Galactic white dwarfs, seven background QSOs, and 52 optical counterparts to known X-ray point sources. We also report an observation of the cluster [HGH92] G169, in which we confirm the existence of a bright emission line object. This object, however, is unlikely to be a planetary nebula, but may be a supernova remnant.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/123
- Title:
- Globular clusters in NGC 474 from CFHT obs.
- Short Name:
- J/ApJ/835/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters (GCs) are some of the most visible tracers of the merging and accretion histories of galaxy halos. Metal-poor GCs, in particular, are thought to arrive in massive galaxies largely through dry, minor merging events, but it is rare to see a direct connection between GCs and visible stellar streams. NGC 474 is a post-merger early-type galaxy with dramatic fine structures made of concentric shells and radial streams that have been more clearly revealed by deep imaging. We present a study of GCs in NGC 474 to better establish the relationship between merger-induced fine structure and the GC system. We find that many GCs are superimposed on visible streams and shells, and about 35% of GCs outside 3R_e,galaxy_ are located in regions of fine structure. The spatial correlation between GCs and fine structure is significant at the 99.9% level, which shows that this correlation is not coincidental. The colors of GCs on fine structures are mostly blue, and we also find an intermediate-color population that is dominant in the central region and that will likely passively evolve to have colors consistent with a traditional metal-rich GC population. The association of the blue GCs with fine structures is direct confirmation that many metal-poor GCs are accreted onto massive galaxy halos through merging events and that the progenitors of these mergers are sub-L^*^ galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/127/2674
- Title:
- Globular clusters in Sculptor group
- Short Name:
- J/AJ/127/2674
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use CTIO 4m Mosaic II images taken with the Washington CM and Harris R filters to identify candidate globular clusters in the six major galaxies of the Sculptor group: NGC 45, 55, 247, 254, 300, and 7793. From follow-up spectroscopy with Hydra-CTIO, we find 19 new globular clusters in NGC 55, 247, 253, and 300, bringing the total number of known Sculptor group globular clusters to 36. The newly discovered clusters have spectroscopic ages consistent with those of old Milky Way globular clusters, and the majority are metal-poor.
- ID:
- ivo://CDS.VizieR/J/ApJ/559/812
- Title:
- Globular cluster system in M87
- Short Name:
- J/ApJ/559/812
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive database of kinematic, photometric, and positional information for 352 objects in the field of M87 (NGC 4486), the central giant elliptical galaxy in the Virgo Cluster; the majority of the tracers are globular clusters associated with that galaxy. New kinematic information comes from multislit observations with the Multi-Object Spectrograph (MOS) of the Canada-France-Hawaii Telescope (CFHT), an investigation that has added 96 new velocities to and confirmed many of the earlier values in a preexisting data set of 256 velocities published elsewhere. The photometry, consisting of magnitudes and colors in the Washington (T_1_, C-T_1_) system, is based on CCD observations made at the Cerro Tololo Inter-American Observatory (CTIO) and the Kitt Peak National Observatory (KPNO).
- ID:
- ivo://CDS.VizieR/J/other/NewA/17.296
- Title:
- GO Cyg BV light curves
- Short Name:
- J/other/NewA/17.
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study, we present long term photometric variations of the close binary system GO Cyg. Modelling of the system shows that the primary is filling Roche lobe and the secondary of the system is almost filling its Roche lobe. The physical parameters of the system are M_1_=3.0+/-0.2M_{sun}_, M_2_=1.3+/-0.1M_{sun}_, R_1_=2.50+/-0.12R_{sun}_, R_2_=1.75+/-0.09R_{sun}_, L_1_=64+/-9L_{sun}_, L_2_=4.9+/-0.7L_{sun}_, and a=5.5+/-0.3R_{sun}_. Our results show that GO Cyg is the most massive system near contact binary (NCB). Analysis of times of the minima shows a sinusoidal variation with a period of 92.3+/-0.5-years due to a third body whose mass is less than 2.3M_{sun}_. Finally a period variation rate of -1.4x10^-9^d/yr has been determined using all available light curves.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A29
- Title:
- GRB 120327A afterglow colour variations
- Short Name:
- J/A+A/607/A29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive temporal and spectral analysis of the long Swift GRB120327A afterglow data to investigate the possible causes of the observed early time colour variations. We collected data from various instruments/telescopes in X-ray, ultra-violet, optical and near-infrared bands and determined the shapes of the afterglow early-time light curves. We studied the overall temporal behaviour and the spectral energy distributions from early to late times. The ultra-violet, optical, and near-infrared light curves can be modelled with a single power-law component between 200 and 2x10^4^s after the burst event. The X-ray light curve shows a canonical steep-shallow-steep behaviour, typical of long gamma-ray bursts. At early times a colour variation is observed in the ultra-violet/optical bands, while at very late times a hint of a re-brightening is visible. The observed early time colour change can be explained as a variation in the intrinsic optical spectral index, rather than an evolution of the optical extinction.
- ID:
- ivo://CDS.VizieR/J/A+A/568/A75
- Title:
- GRB 130925A GROND light curves
- Short Name:
- J/A+A/568/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Prompt or early optical emission in gamma-ray bursts (GRBs) is notoriously difficult to measure, and observations of the dozen cases show a large variety of properties. Yet, such early emission promises to help us achieve a better understanding of the GRB emission process(es). We performed dedicated observations of the ultra-long duration (T90 about 7000s) Swift GRB 130925A in the optical/near-infrared with the 7-channel Gamma-Ray burst Optical and Near-infrared Detector (GROND) at the 2.2m MPG/ESO telescope. We detect an optical/near-infrared flare with an amplitude of nearly 2mag which is delayed with respect to the keV-MeV prompt emission by about 300-400s. The decay time of this flare is shorter than the duration of the flare (500s) or its delay. While we cannot offer a straightforward explanation, we discuss the implications of the flare properties and suggest ways toward understanding it.
