T. Richtler

University of Concepción, Concepción, Region del Biobio, Chile

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Publications (223)387.08 Total impact

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    ABSTRACT: The merger remnant NGC 1316 (Fornax A) is one of the most important objects regarding the investigation of merger-related processes. We use kinematical data of globular clusters (GCs) and the diffuse stellar light to investigate the global structure of NGC 1316 and to constrain the dark matter content. We perform multi-object-spectroscopy with VLT/FORS2 and MXU. Out of 562 slits, we extract radial velocities for 177 GCs. Moreover, we measure radial velocities of the integrated galaxy light, using slits with a sufficiently bright "sky". To these data, we add 20 cluster velocities from Goudfrooij et al. (2001). In an appendix, we identify new morphological features of NGC 1316 and its companion galaxy NGC 1317. The GC sample based on radial velocities confirms the colour peaks already found in our photometric study. The bright clusters, which probably have their origin in a 2 Gyr-old starburst and younger star formation events, avoid the systemic velocity. A Gaussian velocity distribution is found only for clusters fainter than about m_R=22 mag. The velocity distribution of clusters shows a pronounced peak at 1600 km/s. These clusters populate a wide area in the south-western region which we suspect to be a disk population. Globular clusters or subsamples of them do not show a clear rotation signal. This is different from the galaxy light, where rotation along the major axis is discernable out to 3 arcmin radius. A simple spherical model like that suggested by dynamical analyses of planetary nebulae reproduces also the velocity dispersions of the faint GCs. The central dark matter density of the present model resembles a giant elliptical galaxy. This contradicts population properties which indicate spiral galaxies as pre-merger components. MOND would provide a solution, but the kinematical complexity of NGC 1316 does not allow a really firm conclusion. (abridged)
    06/2014;
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    ABSTRACT: We present radial velocities (from Gemini/GMOS) of the second sample of ultra-compact dwarfs (UCDs) and bright globular clusters (GCs) in the Antlia cluster. Twenty-three objects are located around the giant elliptical NGC 3268, and one is close to the fainter lenticular NGC 3273. Together with previously found UCDs around NGC 3258 a total of 35 UCDs and bright GCs has been now identified in the Antlia cluster. Their colours and magnitudes are compared with those of the nuclei of dE,N galaxies already confirmed as Antlia members. For a subsample that lie on ACS images and are brighter than M_V = -9 mag, the effective radii (R_eff) have been measured, the maximum radius being approximately 10 pc. In addition to the radial velocity sample, we find 10 objects in the magnitude range corresponding to GCs but with 10 < R_eff < 17 pc, resembling the so-called `extended clusters'. By number and magnitude, the new UCDs fit to the GC luminosity function, supporting their interpretation as bright GCs. Additionally, we use a tracer mass estimator to calculate the mass enclosed up to ~47 kpc from NGC 3268, which results in 2.7 x 10^12 M_o.
    06/2014;
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    ABSTRACT: We present a catalog of point-like sources around NGC 7507, which forms the photometric database for our paper. The sources were obtained from the PSF photometry of MOSAIC images in filters R and C. The catalog contains coordinates, T1 magnitudes with uncertainties, and C-T1 colors and their uncertainties. Magnitudes and colour are corrected by absorption and reddening. (1 data file).
    VizieR Online Data Catalog. 07/2013;
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    ABSTRACT: Context: There is strong evidence that globular cluster systems (GCSs) of massive galaxies are largely assembled by infall/accretion processes. Therefore, we expect the GCSs of isolated elliptical galaxies to be poor. Alhough not completely isolated, NGC 7507 is a massive field elliptical galaxy with an apparently very low dark matter content. Aims: We determine the richness, the colour distribution, and the structural properties of the GCS of NGC 7507. Methods: We perform wide-field Washington photometry with data obtained with the MOSAIC II camera at the 4m-Blanco telescope, CTIO. Results: The GCS is very poor with S_N ~ 0.6. We identify three subpopulations with peaks at (C-T1) colours of 1.21, 1.42, and 1.72. The bluest population may represent the old, metal-poor component. This interpretation is supported by its shallow density profile. The red population is more concentrated, resembling the galaxy light. The intermediate-colour population is strongly peaked in colour and we interpret this population as the signature of a starburst, whose age depends on the metallicity, but should be quite old, since no signatures of a merger are identifiable. In addition, we find a main sequence in the stellar foreground population, which we attribute to the Sagittarius dwarf tidal stream. Conclusions: The extraordinarily poor GCS of NGC 7507, a massive elliptical galaxy, is an illustration of how important the environmental conditions are for producing rich GCSs.
    Astronomy and Astrophysics 05/2013; · 5.08 Impact Factor
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    ABSTRACT: We present the first compact stellar systems with luminosities in the range of ultracompact dwarfs (UCDs), discovered in the Antlia galaxy cluster (-10.5 < MV < -11.6). The magnitude limit between UCDs and globular clusters (CGs) is discussed. By means of imaging from VLT (FORS1), CTIO (MOSAIC) and the Hubble Space Telescope (ACS) archive, 11 UCDs/bright GCs are selected on the basis of photometry and confirmed as Antlia members through radial velocities measured on new Gemini (GMOS) spectra. In addition, nine UCD candidates are identified taking into account properties derived from their surface brightness profiles. All of them, members and candidates, are located in the proximity of NGC 3258, one of the two brightest elliptical galaxies in the cluster core. Antlia UCDs in this sample present absolute magnitudes fainter than MV ˜ -11.6 mag and most of them have colours within the blue GC range, falling only two within the red GC range. Effective radii measured for the ones lying on the ACS field are in the range Reff = 3-11 pc and are similar to equivalent objects in other clusters, obtained from the literature. The UCD sample shares the same behaviour on the size-luminosity plane: a linear relation between Reff and MV is present for UCDs brighter than MV ˜ -10.5 to -11 mag while no trend is detected for fainter ones, that have an approximately constant Reff. The projected spatial distribution of UCDs, GCs and X-ray emission points to an ongoing merger between two Antlia groups, dominated by NGC 3258 and NGC 3268. Nuclei of dwarf elliptical galaxies and blue UCDs share the same locus on the colour-magnitude diagram, supporting the hypothesis that some blue UCDs may be remnants of stripped nucleated dwarfs.
    Monthly Notices of the Royal Astronomical Society 04/2013; 430(2):1088-1101. · 5.52 Impact Factor
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    ABSTRACT: The globular cluster (GC) systems of isolated elliptical galaxies have only recently begun to be studied in detail, and may exhibit morphological connections to the evolutionary histories of their hosts. Here we present the first in a series of wide-field analyses of the GC systems of the isolated ellipticals - Washington C and R photometry of NGC 3585 and NGC 5812 down to ~24 mag. The GC systems are characterised, with each system displaying both the "Universal" blue peak at (C-R)~1.3, and a red peak, but each with differing strengths. The total number of GCs in each system, and their specific frequencies, are estimated. The GC colours and specific frequencies are highly indicative that the host galaxy environment plays a role in shaping its GC system. We produce, and subtract, accurate models of each galaxy, revealing interesting underlying features, including the first definitive evidence that NGC 5812 is interacting with a dwarf companion galaxy. From the galaxy models we also determine surface brightness and colour profiles. Both colour profiles appear quite flat and with (C-R)~1.7 and we discuss the apparent youth of NGC 3585 in the context of this work.
    Astronomy and Astrophysics 12/2012; · 5.08 Impact Factor
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    Tom Richtler
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    ABSTRACT: I review recent and less recent work on globular cluster systems in early-type galaxies. Explaining their properties and possible assembly scenarios, touches on a variety of astrophysical topics from cluster formation itself to galaxy formation and evolution and even details of observational techniques. The spectacular cluster systems of central galaxies in galaxy clusters may owe their richness to a plethora of less spectacular galaxies and their star formation processes. It seems that dwarf galaxies occupy a particularly important role.
    09/2012;
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    ABSTRACT: We present new radial velocities for 289 globular clusters around NGC 4636, the southernmost giant elliptical galaxy of the Virgo cluster. The data were obtained with FORS2/MXU at the Very Large Telescope. Together with data analysed in an earlier study (Schuberth et al. 2006), we now have a sample of 460 globular cluster velocities out to a radius of 12 arcmin (60 kpc) available - one of the largest of its kind. This new data set also provides a much more complete angular coverage. Moreover, we present new kinematical data of the inner stellar population of NGC 4636. We perform an updated Jeans analysis, using both stellar and GC data, to better constrain the dark halo properties. We find a stellar M/L-ratio of 5.8 in the R-band, higher than expected from single stellar population synthesis. We model the dark halo by cored and cuspy analytical halo profiles and consider different anisotropies for the tracer populations. Properties of NFW halos lie well within the expected range of cosmological simulations. Cored halos give central dark matter densities, which are typical for elliptical galaxies of NGC 4636's luminosity. The surface densities of the dark matter halos are higher than those of spiral galaxies. We compare the predictions of Modified Newtonian Dynamics with the derived halo properties and find satisfactory agreement. Therefore NGC 4636 therefore falls onto the baryonic Tully-Fisher relation for spiral galaxies. The comparison with the X-ray mass profile of Johnson et al. (2009) reveals satisfactory agreement only, if the abundance gradient of hot plasma has been taken into account. This might indicate a general bias towards higher masses for X-ray based mass profiles in all systems, including galaxy clusters, with strong abundance gradients.
    Astronomy and Astrophysics 08/2012; 544(A115). · 5.08 Impact Factor
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    ABSTRACT: We present a catalog of point-like sources around NGC 1316, which forms the photometric database for our paper. This catalogue basically is a selection from a larger photometric database. The selection criteria are specified in the paper. The catalog contains coordinates, R magnitudes with uncertainties, C-R colors and their uncertainties as well as "sharp" and "chi" values from DAOPHOT II. The coordinates are for identification purposes only. Depending on the position, deviations of up to 1 arcsec may occur. See the paper for validity limits of the photometric calibration, particularly for very red colors. (1 data file).
    VizieR Online Data Catalog. 07/2012;
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    ABSTRACT: SH2 has been described as an isolated HII-region, located about 6.5 arcmin south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the outskirts of the Fornax cluster of galaxies. We give a first, preliminary description of the stellar content and environment of this remarkable object. We used photometric data in the Washington system and HST photometry from the Hubble Legacy Archive for a morphological description and preliminary aperture photometry. Low-resolution spectroscopy provides radial velocities of the brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not a normal HII-region, ionized by very young stars. It contains a multitude of star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is striking. SH2 seems to be connected to an intermediate-age massive globular cluster with a similar radial velocity, which itself is the main object of a group of fainter clusters. Metallicity estimates from emission lines remain ambiguous. The present data do not yet allow firm conclusions about the nature or origin of SH2. It might be a dwarf galaxy that has experienced a burst of extremely clustered star formation. We may witness how globular clusters are donated to a parent galaxy.
    Astronomy and Astrophysics 03/2012; · 5.08 Impact Factor
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    ABSTRACT: NGC 1316 (Fornax A) is a prominent merger remnant in the outskirts of the Fornax cluster. The cluster system has not yet been studied in its entirety. We therefore present a wide-field study of the globular cluster system of NGC 1316, investigating its properties in relation to the global morphology of NGC 1316. We used the MOSAIC II camera at the 4-m Blanco telescope at CTIO in the filters Washington C and Harris R. We identify globular cluster candidates and study their color distribution and the structural properties of the system. In an appendix, we also make morphological remarks, present color maps, and present new models for the brightness and color profiles of the galaxy. The cluster system is well confined to the optically visible outer contours of NGC 1316. The color distribution of the entire sample is unimodal, but the color distribution of bright subsamples in the bulge shows two peaks that, by comparison with theoretical Washington colors with solar metallicity, correspond to ages of about 2 Gyr and 0.8 Gyr, respectively. We also find a significant population of clusters in the color range 0.8 < C-R < 1.1 which must be populated by clusters younger than 0.8 Gyr, unless they are very metal-poor. The color interval 1.3 < C-R < 1.6 hosts the bulk of intermediate-age clusters which show a surface density profile with a sharp decline at about 4 arcmin. The outer cluster population shows an unimodal color distribution with a peak at C-R=1.1, indicating a larger contribution of old, metal-poor clusters. Their luminosity function does not show the expected turn-over, so the fraction of younger clusters is still significant. Cluster formation in NGC 1316 has continued after an initial burst, presumably related to the main merger. A toy model with two bursts of ages 2 Gyr and 0.8 Gyr is consistent with photometric properties and dynamical M/L-values.
    Astronomy and Astrophysics 03/2012; · 5.08 Impact Factor
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    ABSTRACT: We present an analysis of the structural parameters of the population of dwarf elliptical (dE) galaxies in the Antlia cluster (approx. distance 35 Mpc). The observational data include images of four fields obtained with the CTIO-MOSAIC camera (36'x 36'), as well as GEMINI-GMOS spectra, useful to confirm membership of a fraction of the galaxy sample. In this paper we add 30 dE galaxies located in three fields adjacent to the cluster's central one. The photometric relationships that they follow are in good agreement with those obtained by Smith Castelli et al. (2008), who performed the first systematic study of the color-magnitude and luminosity-effective surface brightness relations followed by early-type galaxies in the central region of Antlia. We study the surface brightness profiles of all dEs present in the four fields (a total of 60 galaxies), by means of fitting Sersic models. The parameters obtained from such fits are similar to those found for other clusters of galaxies (Fornax, Coma, Virgo, Centaurus, etc.). The analysis of the structural parameters of the surface brightness profiles is a tool that allows us to relate observational results with theoretical models that attempt to explain the formation and evolution of galaxies.
    01/2012;
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    ABSTRACT: A sample of confirmed Ultra-Compact Dwarf galaxies and globular clusters around the giant galaxy NGC 3268 in the Antlia cluster is presented, including their Washington photometry. For the Antlia objects discovered so far, the reliability of a common origin with the globular clusters of the galaxies NGC 3258 and NGC 3268 is analyzed.
    01/2012;
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    ABSTRACT: The dark matter (DM) halos of field elliptical galaxies have not been well studied and their properties appear controversial. While some galaxies appear to be nearly devoid of DM, others show clear evidence of its presence. Furthermore, modified Netonian dynamics (MOND), which has been found to have predictive power in the domain of disk galaxies, has not yet been investigated for isolated elliptical galaxies. We study the kinematics of the isolated elliptical NGC 7507, which has been claimed as a clear example of DM presence in early-type galaxies. We obtained major and minor axis long-slit spectroscopy of NGC 7507 using the Gemini South telescope and deep imaging in Kron-Cousins R and Washington C using the CTIO/MOSAIC camera. Mean velocities, velocity dispersion and higher order moments are measured out to ~90 arcsec. The galaxy, although almost circular, has significant rotation along the minor axis and a rapidly declining velocity dispersion along both axes. Jeans models without DM provide an excellent representation of the data with a mass-to-light ratio (M/L) of 3.1 (R-band). The most massive Navarro-Frenk-White (NFW) halo the data allow has a virial mass of only 3.9+3.1-2.1E11 solar masses, although the data are more consistent with models that have a slight radial anisotropy, which implies the galaxy has an even lower DM halo mass of 2.2+2.0-1.2E11 solar masses. Modeling of the h_4 Gauss-Hermite coefficient is inconclusive but seems to be consistent with mild radial anisotropy. A cored logarithmic DM halo with parameters r0 = 7 kpc and v0 = 100 km/s can also reproduce the observed velocity dispersion profile. In conclusion, we cannot easily reproduce the previous findings of a predominance of DM in NGC 7507 within a simple spherical model. DM may be present, but only in conjunction with a strong radial anisotropy, for which there are some indications. (Abridged).
    Astronomy and Astrophysics 11/2011; · 5.08 Impact Factor
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    ABSTRACT: VIMOS allows simultaneous observation of four quadrants in one telescope pointing. Each quadrant is of dimension 7'x8', with a gap of about 2' between the quadrants. For the UCD survey, we placed four multi-object spectroscopy (MOS) pointings around NGC 3311, the central cD galaxy of the Hydra I cluster. (1 data file).
    VizieR Online Data Catalog. 10/2011;
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    ABSTRACT: (Abridge) We present a new analysis of the early-type galaxy population in the central region of the Antlia cluster, focusing on the faint systems like dwarf ellipticals (dE) and dwarf spheroidals (dSph). We confirm 22 early-type galaxies as Antlia members, using GEMINI-GMOS and MAGELLAN-MIKE spectra. Among them, 2 belong to the rare type of compact ellipticals (cE), and 5 are new faint dwarfs that had never been catalogued before. In addition, we present 16 newly identified low surface brightness galaxy candidates, almost half of them displaying morphologies consistent with being Antlia's counterparts of Local Group dSphs, that extend the faint luminosity limit of our study down to MB = -10.1 (BT = 22.6) mag. We built an improved CMR in the Washington photometric system, i.e. integrated T1 magnitudes versus (C - T1) colours, which extends \sim 4 mag faintwards the limit of spectroscopically confirmed Antlia members. When only confirmed early-type members are considered, this relation extends over 10 mag in luminosity with no apparent change in slope or increase in colour dispersion towards its faint end. The intrinsic colour scatter of the relation is compared with those reported for other clusters of galaxies; we argue that it is likely that the large scatter of the CMR, usually reported at faint magnitudes, is mostly due to photometric errors along with an improper membership/morphological classification. The distinct behaviour of the luminosity versus mean effective surface brightness relation at the bright and faint ends is analyzed, while it is confirmed that dE galaxies on the same relation present a very similar effective radius, regardless of their colour. The projected spatial distribution of the member sample confirms the existence of two groups in Antlia, each one dominated by a giant elliptical galaxy and with one cE located close to each giant.
    Monthly Notices of the Royal Astronomical Society 09/2011; · 5.52 Impact Factor
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    ABSTRACT: We study the structure and internal kinematics of the "star pile" in Abell 545 - a low surface brightness structure lying in the center of the cluster.We have obtained deep long-slit spectroscopy of the star pile using VLT/FORS2 and Gemini/GMOS, which is analyzed in conjunction with deep multiband CFHT/MEGACAM imaging. As presented in a previous study the star pile has a flat luminosity profile and its color is consistent with the outer parts of elliptical galaxies. Its velocity map is irregular, with parts being seemingly associated with an embedded nucleus, and others which have significant velocity offsets to the cluster systemic velocity with no clear kinematical connection to any of the surrounding galaxies. This would make the star pile a dynamically defined stellar intra-cluster component. The complicated pattern in velocity and velocity dispersions casts doubts on the adequacy of using the whole star pile as a dynamical test for the innermost dark matter profile of the cluster. This status is fulfilled only by the nucleus and its nearest surroundings which lie at the center of the cluster velocity distribution.
    Astronomy and Astrophysics 04/2011; 528(A61). · 5.08 Impact Factor
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    ABSTRACT: We performed a large spectroscopic survey of compact, unresolved objects in the core of the Hydra I galaxy cluster (Abell 1060), with the aim of identifying ultra-compact dwarf galaxies (UCDs), and investigating the properties of the globular cluster (GC) system around the central cD galaxy NGC 3311. We obtained VIMOS medium resolution spectra of about 1200 candidate objects with apparent magnitudes 18.5 < V < 24.0 mag, covering both the bright end of the GC luminosity function and the luminosity range of all known UCDs. By means of spectroscopic redshift measurements, we identified 118 cluster members, from which 52 are brighter than M_V = -11.0 mag, and can therefore be termed UCDs. The brightest UCD in our sample has an absolute magnitude of M_V = -13.4 mag (corresponding to a mass of > 5 x 10^7 M_sun) and a half-light radius of 25 pc. This places it among the brightest and most massive UCDs ever discovered. Most of the GCs/UCDs are both spatially and dynamically associated to the central cD galaxy. The overall velocity dispersion of the GCs/UCDs is comparable to what is found for the cluster galaxies. However, when splitting the sample into a bright and a faint part, we observe a lower velocity dispersion for the bright UCDs/GCs than for the fainter objects. At a dividing magnitude of M_V = -10.75 mag, the dispersions differ by more than 200 km/s, and up to 300 km/s for objects within 5 arcmin around NGC 3311. We interpret these results in the context of different UCD formation channels, and conclude that interaction driven formation seems to play an important role in the centre of Hydra I.
    Astronomy and Astrophysics 03/2011; 531. · 5.08 Impact Factor
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    ABSTRACT: Two incorrect arguments against MOND in elliptical galaxies could be that the equivalent circular velocity curves tend to become flat at much larger accelerations than in spiral galaxies, and that the Newtonian dark matter halos are more concentrated than in spirals. Here, we compare published scaling relations for the dark halos of elliptical galaxies to the scaling relations expected for MONDian phantom halos. We represent the baryonic content of galaxies by spherical profiles, and their corresponding MONDian phantom halos by logarithmic halos. We then derive the surface densities, central densities, and phase space densities and compare them with published scaling relations. We conclude that it is possible to get flat circular velocity curves at high acceleration in MOND, and that this happens for baryonic distributions described by Jaffe profiles in the region where the circular velocity curve is flat. Moreover, the scaling relations of dark halos of ellipticals are remarkably similar to the scaling relations of phantom halos of MOND.
    Astronomy and Astrophysics 03/2011; 531. · 5.08 Impact Factor
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    ABSTRACT: NGC 3311 is the central cD galaxy of the Hydra I cluster. We use globular clusters around NGC 3311, combined with kinematical data of the galaxy itself, to investigate the dark matter distribution in the central region of Hydra I. Radial velocities of 118 bright globular clusters, based on VLT/VIMOS mask spectroscopy, are used to calculate velocity dispersions which are well defined out to 100 kpc. NGC 3311 is the most distant galaxy for which this kind of study has been performed. We also determine velocity dispersions of the stellar component from long slit spectroscopy out to 20 kpc. Moreover, we present a new photometric model for NGC 3311 in the V-band. We search for a dark halo which in the context of a spherical Jeans model. We also compare the radial velocity distributions of globular clusters and planetary nebulae. The projected stellar velocity dispersion rises from 185 km/s to 350 km/s at a radius of 20 kpc. The globular cluster dispersion rises as well from 500 km/s at 10 kpc to about 800 km/s at 100 kpc, comparable to the velocity dispersion of the cluster galaxies. A dark matter halo with a core reproduces well the velocity dispersions of stars and globular clusters simultaneously under isotropy. The central stellar velocity dispersions predicted by cosmological NFW halos are less good representations, while the globular clusters allow a wide range of halo parameters. A suspected radial anisotropy of the stellar population aggravates the deviations. However, we find discrepancies with previous kinematical data, which we cannot resolve and may indicate a more complicated velocity pattern. Although one cannot conclusively demonstrate that the dark matter halo of NGC 3311 has a core rather than a cusp, a core seems to be preferred by the present data. A more complete velocity field and an analysis of the anisotropy is required to reach firm conclusions.
    Astronomy and Astrophysics 03/2011; 531. · 5.08 Impact Factor

Publication Stats

999 Citations
387.08 Total Impact Points

Institutions

  • 2001–2011
    • University of Concepción
      • • Departamento de Astronomía
      • • Departamento de Física
      Concepción, Region del Biobio, Chile
  • 2007
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
  • 1991–1997
    • University of Bonn
      Bonn, North Rhine-Westphalia, Germany
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
    • Indian Institute of Astrophysics
      Bengalūru, Karnātaka, India
  • 1990
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 1986
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France