Globular cluster luminosity function as distance indicator

Globular clusters are among the first objects used to establish the distance scale of the Universe. In the 1970-ies it has been recognized that the differential magnitude distribution of old globular clusters is very similar in different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the so-called Globular Cluster Luminosity Function has been then established as a secondary distance indicator. The intrinsic accuracy of the method has been estimated to be of the order of ~0.2 mag, competitive with other distance determination methods. Lately the study of the Globular Cluster Systems has been used more as a tool for galaxy formation and evolution, and less so for distance determinations. Nevertheless, the collection of homogeneous and large datasets with the ACS on board HST presented new insights on the usefulness of the Globular Cluster Luminosity Function as distance indicator. I discuss here recent results based on observational and theoretical studies, which show that this distance indicator depends on complex physics of the cluster formation and dynamical evolution, and thus can have dependencies on Hubble type, environment and dynamical history of the host galaxy. While the corrections are often relatively small, they can amount to important systematic differences that make the Globular Cluster Luminosity Function a less accurate distance indicator with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review paper based on the invited talk at the conference "The Fundamental Cosmic Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13 pages, 8 figures

A MODEST review

We present an account of the state of the art in the fields explored by the research community invested in 'Modeling and Observing DEnse STellar systems'. For this purpose, we take as a basis the activities of the MODEST-17 conference, which was held at Charles University, Prague, in September 2017. Reviewed topics include recent advances in fundamental stellar dynamics, numerical methods for the solution of the gravitational N-body problem, formation and evolution of young and old star clusters and galactic nuclei, their elusive stellar populations, planetary systems, and exotic compact objects, with timely attention to black holes of different classes of mass and their role as sources of gravitational waves. Such a breadth of topics reflects the growing role played by collisional stellar dynamics in numerous areas of modern astrophysics. Indeed, in the next decade, many revolutionary instruments will enable the derivation of positions and velocities of individual stars in the Milky Way and its satellites and will detect signals from a range of astrophysical sources in different portions of the electromagnetic and gravitational spectrum, with an unprecedented sensitivity. On the one hand, this wealth of data will allow us to address a number of long-standing open questions in star cluster studies; on the other hand, many unexpected properties of these systems will come to light, stimulating further progress of our understanding of their formation and evolution.Comment: 42 pages; accepted for publication in 'Computational Astrophysics and Cosmology'. We are much grateful to the organisers of the MODEST-17 conference (Charles University, Prague, September 2017). We acknowledge the input provided by all MODEST-17 participants, and, more generally, by the members of the MODEST communit

High-resolution morphology and surface photometry of KIG 685 and KIG 895 with ARGOS+LUCI using the Large Binocular Telescope

We aim to refine the sample of isolated early-type galaxies in the Analysis of the interstellar Medium of Isolated Galaxies (AMIGA) catalog via high-resolution imaging. Here, we report the result from a pilot study investigating two candidates, KIG 685 and KIG 895, in K-band with the laser guide star and wavefront sensing facility ARGOS using the Large Binocular Telescope (LBT). Observations, obtained during the commissioning time, achieved a point spread function (PSF) of ≈0.25″. We present the data reduction and the PSF analysis from the best closed-loop exposures to investigate the galaxies' morphological structure, including their nuclear region. We used PROFILER for the decomposition of the azimuthal 1D light distribution and GALFIT for the 2D analysis, accounting for ARGOS's PSF. KIG 685 was found to be a S0 galaxy and has been modeled with two Sérsic components representing a pseudobulge (n = 2.87 ± 0.21, n = 2.29 ± 0.10) and a disk (n = 0.95 ± 0.16, n = 0.78 ± 0.10). Nearly symmetric ring-/shell-like structures emerge after subtracting the GALFIT model from the image. KIG 895 shows a clear irregular arm-like structure, in which the northern outer arm is reminiscent of a tail. The galaxy body is a disk, best fitted by a single Sérsic profile (n = 1.22 ± 0.1; n = 1.32 ± 0.12), that is, KIG 895 is a bulge-less, very late-type spiral. ARGOS high-resolution images clearly showed interaction signatures in KIG 895. We suggest that the ring-/shell-like residuals in KIG 685, a bona fide early-type galaxy, point toward a past accretion event.© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimWe are deeply indebted to the unknown referee for substantial suggestions. We thank Dr. Bogdan Ciambur both for proving us the PROFILER program and for the assistance. We thank Dr. Francesco La Barbera for having provided us the SPIDER K‐band dataset. R.R. thanks dr. Michael Jones for the English revision. R.R. and P.M. acknowledge funding from the INAF PRIN‐SKA 2017 program 1.05.01.88.04. L.V.M. acknowledges support from the grant AYA2015‐65973‐C3‐1‐R (MINECO/FEDER, UE). IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We acknowledge the usage of the HyperLeda database ( http://leda.univ‐lyon1.fr )