arXiv subjects

Markus Kissler-Patig

Publications and source records attributed to Markus Kissler-Patig.

At least 55 records · Page 3Linked to original sources

arXiv2004

Extragalactic Globular Clusters in the Near Infrared: IV. Quantifying the Age Structure using Monte-Carlo Simulations

In previous papers of the series we used a combination of optical and near-infrared colours to derive constraints on the relative age structure in globular cluster systems. Here, we present the details, strength and limitations of our method based on Monte-Carlo simulations of colour-colour diagrams and cumulative age distributions. The simulations are based on general informations about the globular cluster systems (e.g. colour-ranges, the number ratios between sub-populations) and the different single stellar population models (SSP's) which are used to derive relative ages. For both the modeled systems and the observed globular cluster systems we derive the cumulative age distribution and introduce two parameters to define it, the so-called 50 % age and the result of the reduced $χ$$^2$test of the comparison between models and observations. The method was tested successfully on several systems and allowed to reveal significant intermediate age populations in two of them.

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arXiv2003

Keck Spectroscopy and Imaging of Globular Clusters in the Lenticular Galaxy NGC 524

We have obtained Keck LRIS imaging and spectra for 29 globular clusters associated with the lenticular galaxy NGC 524. Using the empirical calibration of Brodie & Huchra we find that our spectroscopic sample spans a metallicity range of --2.0 < [Fe/H] < 0. We have compared the composite spectrum of the metal-poor ([Fe/H] < --1) and metal-rich clusters with stellar population models and conclude that the clusters are generally old and coeval at the 2 sigma confidence level. To determine the mean [alpha/Fe] ratios of the globular clusters, we have employed the Milone et al. 'alpha-enhanced' stellar population models. We verified the reliability of these models by comparing them with high S/N Galactic globular cluster data. We observe a weak trend of decreasing [alpha/Fe] with increasing metallicity in the NGC 524 clusters. Analysis of the cluster system kinematics reveals that the full sample exhibits a rotation of 114+/-60 km/s around a position angle of 22+/-27 deg, and a velocity dispersion of 186+/-29 km/s at a mean radius of 89 arcsec from the galaxy centre. Subdividing the clusters into metal-poor and metal-rich subcomponents we find that the metal-poor (17) clusters and metal-rich (11) clusters have similar velocity dispersions (197+/-40 km/s and 169+/-47 km/s respectively). The metal-poor clusters dominate the rotation in our sample with 147+/-75 km/s, whilst the metal-rich clusters show no significant rotation (68+/-84 km/s). We derive a virial and projected mass estimation for NGC 524 of between 4 and 13 x 10^11 Msun (depending on the assumed orbital distribution) interior to 2 effective radii of this galaxy.

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arXiv2003

Extragalactic Globular Clusters in the Near Infrared: III. NGC 5846 and NGC 7192

In this third paper of our series on near-IR and optical photometry of globular cluster systems in early-type galaxies we concentrate on the photometric results for NGC 5846 and NGC 7192, two group ellipticals, and on a first comparison between the globular cluster systems investigated so far. In NGC 5846 the colour-colour diagram shows clear bi-modality in (V-K), which is confirmed by a KMM test. The mean colour of both peaks were estimated to be (V-K) =2.57+/-0.06 (blue) and (V-K)=3.18+/-0.06 (red). The situation in NGC 7192 is different, in that the colour-colour diagram gives no evidence for a distinct second population of globular clusters. Using simulated colour distributions of globular cluster systems, we make a first step in quantifying the cumulative age distribution in globular cluster systems. Also here the result for NGC 5846 leads us to the conclusion that its metal-rich globular cluster population contains two globular cluster populations which differ in age by several Gyr. The age structure for NGC 7192 shows instead strong similarity with a single-age population.

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arXiv2003

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)

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arXiv2002

Integrated Spectroscopy of Bulge Globular Clusters and Fields I. The Data Base and Comparison of Individual Lick Indices in Clusters and Bulge

We present a comprehensive spectroscopic study of the integrated light of metal-rich Galactic globular clusters and the stellar population in the Galactic bulge. We measure line indices which are defined by the Lick standard system and compare index strengths of the clusters and Galactic bulge. Both metal-rich globular clusters and the bulge are similar in most of the indices, except for the CN index. We find a significant enhancement in the CN/ index ratio in metal-rich globular clusters compared with the Galactic bulge. The mean iron index of the two metal-rich globular clusters NGC 6528 and NGC 6553 is comparable with the mean iron index of the bulge. Index ratios such as Mgb/ , Mg2/ , Ca4227/ , and TiO/ , are comparable in both stellar population indicating similar enhancements in individual elements which are traced by the indices. From the globular cluster data we fully empirically calibrate several metallicity-sensitive indices as a function of [Fe/H] and find tightest correlations for the Mg2 index and the composite [MgFe] index. We find that all indices show a similar behavior with galactocentric radius, except for the Balmer series, which show a large scatter at all radii. However, the scatter is entirely consistent with the cluster-to-cluster variations in the horizontal branch morphology.

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arXiv2002

Extragalactic Globular Clusters in the Near Infrared I: A comparison between M87 and NGC 4478

We compare optical and near infrared colours of globular clusters in M87, the central giant elliptical in Virgo, and NGC 4478, an intermediate luminosity galaxy in Virgo, close in projection to M87. Combining V and I photometry obtained with the WFPC2 on HST and Ks photometry obtained with the NIRC on Keck 1, we find the broad range in colour and previously detected bi-modality in M87. We confirm that NGC 4478 only hosts a blue sub-population of globular clusters and now show that these clusters' V-I and V-K colours are very similar to those of the halo globular clusters in Milky Way and M31. Most likely, a metal-rich sub-population never formed around this galaxy (rather than having formed and been destroyed later), probably because its metal-rich gas was stripped during its passage through the centre of the Virgo cluster. The V-I, V-K colours are close to the predicted colours from SSP models for old populations. However, M87 hosts a few red clusters that are best explained by intermediate ages (a few Gyr). Generally, there is evidence that the red, metal-rich sub-population has a complex colour structure and is itself composed of clusters spanning a large metallicity and, potentially, age range. This contrasts with the blue, metal-poor population which appears very homogeneous in all galaxies observed so far.

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arXiv2002

Extragalactic Globular Clusters in the Near-Infrared II. The Globular Clusters Systems of NGC 3115 and NGC 4365

We combine near-infrared photometry obtained with the VLT/ISAAC instrument and archival HST/WFPC2 optical images to determine VIK magnitudes and colours of globular clusters in two early-type galaxies, NGC 3115 and NGC 4365. The combination of near-IR and optical photometry provides a way to lift the age-metallicity degeneracy. For NGC 3115, the globular cluster colours reveal two major sub-populations, consistent with previous studies. By comparing the V-I, V-K colours of the NGC 3115 globular clusters with SSP models, we find that the colour difference between the two >10 Gyr old major sub-populations is primarily due to a difference in metallicity. We find Δ[Fe/H] = 1.0 +/- 0.3 dex and the blue and red globular cluster sub-populations being coeval within 3 Gyr. In contrast to the NGC 3115 globular clusters, the globular cluster system in NGC 4365 exhibits a more complex age and metallicity structure. We find a significant population of intermediate-age very metal-rich globular clusters along with an old population of both metal-rich and metal-poor clusters. Specifically, we observe a large population of globular clusters with V-K and V-I colours, for which all current SSP models give ages and metallicities in the range ~2-8 Gyr and ~0.5-3 Z_solar, respectively. After 10 Gyr of passive evolution, the intermediate-age globular clusters in NGC 4365 will have colours which are consistent with the very metal-rich population of globular clusters in giant elliptical galaxies, such as M87. Our results for both globular cluster systems are consistent with previous age and metallicity studies of the diffuse galactic light. In addition to the major globular cluster populations in NGC 3115 and NGC 4365 we report on the detection of objects with extremely red colours.

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arXiv2001

From old Globular Clusters to early Structures in the Universe: the Formation of old, metal-poor Halos around early-type Galaxies

Old, metal-poor globular clusters trace the formation and evolution of early-type galaxies. Their are the best probes, at low redshift, of the building-up of galaxy halos at high redshift. Their properties constrain the characteristics of their progenitors. Recent results suggest that DLAs at z>3 are the likely hosts for their formation. Finally, they shed light on the old, metal-poor halos probably present around all early-type galaxies.

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arXiv2001

Age Estimates for Globular Clusters in NGC 1399

We present high signal-to-noise Keck spectra for 10 globular clusters associated with the giant Fornax elliptical NGC 1399, and compare measured line indices with current stellar population models. Our data convincingly demonstrate, for the first time, that at least some of the clusters in a giant elliptical galaxy have super-solar abundance ratios, similar to the host galaxy. From Hbeta line-strengths the majority of clusters have ages of ~11 Gyrs (within 2sigma), which is similar to the luminosity-weighted stellar age of NGC 1399. Two of the clusters (which also reveal enhanced abundance ratios) show significantly higher Hbeta values than the others. It remains unclear whether this is due to young (~2 Gyr) ages, or extremely old (> 15 Gyr) ages with a warm blue horizontal branch. However a conflict with current cosmological parameters is avoided if the young age is favored. Either alternative indicates a complicated age distribution among the metal-rich clusters and sets interesting constraints on their chemical enrichment at late epochs.

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arXiv2001

Spectroscopy of Globular Clusters in M81

We present moderate-resolution spectroscopy of globular clusters (GCs) around the Sa/Sb spiral galaxy M81 (NGC 3031). Sixteen candidate clusters were observed with the Low Resolution Imaging Spectrograph on the Keck I telescope. All are confirmed as bona fide GCs, although one of the clusters appears to have been undergoing a transient event during our observations. In general, the M81 globular cluster system (GCS) is found to be very similar to the Milky Way (MW) and M31 systems, both chemically and kinematically. A kinematic analysis of the velocities of 44 M81 GCS, (the 16 presented here and 28 from previous work) strongly suggests that the red, metal-rich clusters are rotating in the same sense as the gas in the disk of M81. The blue, metal-poor clusters have halo-like kinematics, showing no evidence for rotation. The kinematics of clusters whose projected galactocentric radii lie between 4 and 8 kpc suggest that they are rotating much more than those which lie outside these bounds. We suggest that these rotating, intermediate-distance clusters are analogous to the kinematic sub-population in the metal-rich, disk GCs observed in the MW and we present evidence for the existence of a similar sub-population in the metal-rich clusters of M31. With one exception, all of the M81 clusters in our sample have ages that are consistent with MW and M31 GCs. One cluster may be as young as a few Gyrs. The correlations between absorption-line indices established for MW and M31 GCs also hold in the M81 cluster system, at least at the upper end of the metallicity distribution (which our sample probes). On the whole, the mean metallicity of the M81 GCS is similar to the metallicity of the MW and M31 GCSs. The projected mass of M81 is similar to the masses of the MW and M31. Its mass profile indicates the presence of a dark matter halo.

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arXiv2001

Metal-rich and metal-poor globular clusters in ellipticals: Did we learn anything? or Constraints on galaxy formation and evolution from globular cluster sub-populations

A brief review on globular cluster sub-populations in galaxies, and their constraints on galaxy formation and evolution is given. The metal-poor and metal-rich sub-populations are put in a historical context, and their properties, as known to date, are summarized. We review why the study of these sub-populations is extremely useful for the study of galaxy formation and evolution, but highlight a few caveats with the current interpretations. We re-visit the current globular cluster system formation scenarios and show how they boil down to a single scenario for the metal-poor clusters (namely the formation in ``universal'', small fragments at high $z$) and that a hierarchical formation seems favored for the metal-rich clusters.

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arXiv2001

Globular cluster systems II: On the formation of old globular clusters and their sites of formation

We studied the metal-poor globular cluster (GC) populations of a large variety of galaxies (47 galaxies spanning about 10mag in absolute brightness) and compared their mean [Fe/H] with the properties of the host galaxies. The mean [Fe/H] of the systems lie in the -1.65<[Fe/H]<-1.20 range (74% of the population). Using only GC systems with more than 6 objects detected, 85% of the population lie within -1.65<[Fe/H]<-1.20. The relation between the mean [Fe/H] of the metal-poor GC systems and the Mv of their host galaxies presents a very low slope which includes zero. An analysis of the correlation of the mean [Fe/H] with other galaxy properties also leads to the conclusion that no strong correlation exists. The lack of correlation suggests a formation of all metal-poor GC in similar gas fragments. A weak correlation might exist between mean [Fe/H] of the metal-poor GC and host galaxy metallicity. This would imply that some fragments in which metal-poor GC formed were already embedded in the larger dark matter halo of the final galaxy (as oppose to being independent satellites that were accreted later). Our result suggests a homogeneous formation of metal-poor GC in all galaxies, in typical fragments of masses around 10^9-10^10 solar masses with very similar metallicities, compatible with hierarchical formation scenarios for galaxies. We compared the mean [Fe/H] of the metal-poor GC populations with the typical metallicities of high-z objects. If we add the constraint that GC need a high column density of gas to form, DLAs are the most likely sites for the formation of metal-poor GC populations.

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arXiv2000

Kinematics, ages, and metallicities of star clusters in NGC 1316: A 3 Gyr old merger remnant

We report on multi-object spectroscopy of 37 candidate star clusters around the giant early-type radio galaxy NGC 1316 (Fornax A), the brightest galaxy in the Fornax cluster. For the star clusters in this sample, we measure a mean radial velocity of 1698 +/- 46 km/s, a rotation velocity of 175 +/- 70 km/s, and a velocity dispersion of 227 +/- 33 km/s within a galactocentric radius of 24 kpc. Using the projected mass estimator and assuming isotropic orbits, the estimated total mass is (6.6 +/- 1.7) E+11 solar masses within a radius of 24 kpc. The mass is uncertain by about a factor of two, depending on the orbital assumptions. The implied M/L_B ratio is in the range 3-6. Four star clusters in our sample are exceptionally luminous (M_V < -12.3). This means that (1) at least this many clusters in NGC 1316 are up to an order of magnitude more luminous than the most luminous star cluster in our Galaxy or M31, and (2) that the S/N ratio of their spectra allows us to measure line strengths with good accuracy. By comparing the colours and equivalent widths of H-alpha and the Ca II triplet absorption lines for those bright star clusters in our sample with those of single-burst population models, we find that they are coeval with an age of 3.0 +/- 0.5 Gyr. Their metallicities are found to be solar to within 0.15 dex. These results show once again that globular clusters with near-solar metallicity do form during galactic mergers, and, moreover, that they can survive disruption processes taking place during the merger (e.g., dynamical friction, tidal disruption), as well as evaporation. In this respect, NGC 1316 provides a hitherto "missing" evolutionary link between young merger remnants of age ~0.5 Gyr such as NGC 3597, NGC 3921 and NGC 7252 on one side, and older giant ellipticals featuring bimodal colour distributions on the other side.

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arXiv2000

A new look at globular cluster colors in NGC 3311 and the case for exclusively metal-rich globular cluster systems

NGC 3311, the central cD galaxy in the Hydra cluster, was previously thought to host the most metal-rich globular cluster system known. Ground-based Washington photometry had indicated the almost complete absence of the population of globular clusters near [Fe/H] ~ -1 dex, normally dominant in the metallicity distribution functions of giant elliptical galaxies. Lacking the normal metal-poor globular cluster population, NGC 3311 was an outstanding exception among galaxies, not easily understood under any of the current globular cluster formation scenarios. Our HST/WFPC2 data yield normal globular cluster colors and hence metallicities for this galaxy. We find a bi-modal color distribution with peaks at (V-I)=0.91 +/- 0.03 and 1.09 +/- 0.03, corresponding to [Fe/H] ~ -1.5 and -0.75 dex (somewhat dependent on the choice of the conversion relation between color and metallicity). We review the evidence for exclusively metal-rich globular cluster systems in other galaxies and briefly discuss the implications for our understanding of globular cluster and galaxy formation.

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arXiv2000

Globular Clusters in the dE,N galaxy NGC 3115 DW1: New Insights from Spectroscopy and HST Photometry

The properties of globular clusters in dwarf galaxies are key to understanding the formation of globular cluster systems, and in particular in verifying scenarios in which globular cluster systems of larger galaxies formed (at least partly) from the accretion of dwarf galaxies. Here, we revisit the globular cluster system of the dE,N galaxy NGC 3115 DW1 - a companion of the nearby S0 galaxy NGC 3115 - adding Keck/LRIS spectroscopy and HST/WFPC2 imaging to previous ground-based photometry. Spectra for seven globular clusters reveal normal abundance ratios with respect to the Milky Way and M31 clusters, as well as a relatively high mean metallicity ([Fe/H] = -1.0+/-0.1 dex). Crude kinematics indicate a high velocity dispersion within 10 kpc which could either be caused by dark matter dominated outer regions, or by the stripping of outer globular clusters by the nearby giant galaxy NGC 3115. The total galaxy mass out to 3 and 10 kpc lies between 10^10 and 10^11 solar masses and 2*10^10 and 4*10^11 solar masses, respectively, depending on the mass estimator used and the assumptions on cluster orbits and systemic velocity. The HST imaging allows measurement of sizes for two clusters, returning core radii around 2.0 pc, similar to the sizes observed in other galaxies. Spectroscopy allows an estimate of the degree of contamination by foreground stars or background galaxies for the previous ground-based photometry, but does not require a revision of previous results: NGC 3115 DW1 hosts around 60+/-20 clusters which corresponds to a specific frequency of 4.9+/-1.9, on the high end for massive dEs. Given its absolute magnitude (M_V=-17.7 mag) and the properties of its cluster system, NGC 3115 DW1 appears to be a transition between a luminous dE and low-luminosity E galaxy.

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arXiv2000

Imaging of the protoelliptical NGC 1700 and its globular cluster system

An excellent candidate for a young elliptical, or `protoelliptical' galaxy is NGC 1700. Here we present new B, V and I band imaging using the Keck telescope and reanalyse existing V and I band images from the Hubble Space Telescope. After subtracting a model of the galaxy from the Keck images NGC 1700 reveals two symmetric tidal tail-like structures. If this interpretation is correct, it suggests a past merger event involving two spiral galaxies. These tails are largely responsible for the `boxiness' of the galaxy isophotes observed at a radius of about 13 kpc. We also show that the B-I colour distribution of the globular cluster system is bimodal. The mean colour of the blue population is consistent with those of old Galactic globular clusters. Relative to this old, metal poor population, we find that the red population is younger and more metal rich. This young population has a similar age and metallicity as that inferred for the central stars, suggesting that they are both associated with an episode of star formation triggered by the merger that may have formed the galaxy. Although possessing large errors, we find that the majority of the age estimates of NGC 1700 are reasonably consistent and we adopt a `best estimate' for the age of 3.0 +/-1.0 Gyr. This relatively young age places NGC 1700 within the age range where there is a notable lack of obvious candidates for protoellipticals. The total globular cluster specific frequency is rather low for a typical elliptical, even after taking into account fading of the galaxy over the next 10 Gyr. We speculate that NGC 1700 will eventually form a relatively `globular cluster poor' elliptical galaxy.

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arXiv2000

Extragalactic Globular Cluster Systems: A new Perspective on Galaxy Formation and Evolution

We present an overview of observational progress in the study of extragalactic globular cluster systems. Globular clusters turn out to be excellent tracers not only for the star-formation histories in galaxies, but also for kinematics at large galactocentric radii. Their properties can be used to efficiently constrain galaxy formation and evolution. After a brief introduction of the current methods and futures perspectives, we summarize the knowledge gained in various areas of galaxy research through the study of globular clusters. In particular, we address the star-formation histories of early-type galaxies; globular cluster population in late-type galaxies and their link to early-type galaxies; star and cluster formation during mergers and violent interactions; and the kinematics at large radii in early-type galaxies. The different points are reviewed within the context of galaxy formation and evolution. Finally, we revisit the globular cluster luminosity function as a distance indicator. Despite its low popularity in the literature, we demonstrate that it ranks among one of the most precise distance indicators to early-type galaxies, provided that it is applied properly.

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arXiv2000

The Formation of Galaxies, the Formation of Old Globular Clusters and the Link with High-Redshift Objects

In this paper, we are exploring the properties of old, metal-poor globular clusters in galaxies. We investigate whether their properties are related to the properties of their host galaxies, and whether we can constrain their formation. The main result is that the mean metallicities of old GC systems are found to lie in a narrow range -1.7 < [Fe/H] < -1.1 (80 % of the population). Moreover, no correlations are found between the mean metallicities and other galaxy properties which implies a GC formation independent of the host galaxies. Further, we try to identify the sites of old, metal-poor GC formation, with any currently known high redshift objects. We find that the metalicities of damped Ly$α$ systems in the redshift range 1.6 < z < 4 are consistent with our GC metalicities, which suggests that these high-density neutral gas objects may be the progenitors of the old, metal-poor globular clusters.

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