scholarly journals The Ophiuchus stream progenitor: a new type of globular cluster and its possible Sagittarius connection

2020 ◽  
Vol 492 (3) ◽  
pp. 4164-4174 ◽  
Author(s):  
James M M Lane ◽  
Julio F Navarro ◽  
Azadeh Fattahi ◽  
Kyle A Oman ◽  
Jo Bovy
Keyword(s):  
Globular Cluster ◽  
Surface Brightness ◽  
Lower Surface ◽  
Galactic Centre ◽  
Proper Motions ◽  
Weakly Bound ◽  
The Galaxy ◽  
Length Width ◽  
New Type ◽  
Short Arc

ABSTRACT The Ophiuchus stream is a short arc-like stellar feature of uncertain origin located ∼5 kpc North of the Galactic centre. New proper motions from the second Gaia data release reconcile the direction of motion of stream members with the stream arc, resolving a puzzling mismatch reported in earlier work. We use N-body simulations to show that the stream is likely only on its second pericentric passage, and thus was formed recently. The simulations suggest that most of the disrupted progenitor is visible in the observed stream today, and that little further tidal debris is expected to lie beyond the ends of the stream. The luminosity, length, width, and velocity dispersion of the stream suggest a globular cluster (GC) progenitor substantially fainter and of lower surface brightness than estimated in previous work, and unlike any other known globulars in the Galaxy. This result suggests the existence of clusters that would extend the known GC population to fainter and more weakly bound systems than hitherto known. How such a weakly bound cluster of old stars survived until it was disrupted so recently, however, remains a mystery. Integrating backwards in time, we find that the orbits of Sagittarius and Ophiuchus passed within ∼5 kpc of each other about ∼100 Myr ago, an interaction that might help resolve this puzzle.

scholarly journals The disruption of the low-mass globular cluster E 3

2020 ◽  
Vol 499 (2) ◽  
pp. 2157-2161
Author(s):  
Julio A Carballo-Bello ◽  
Ricardo Salinas ◽  
Andrés E Piatti
Keyword(s):  
Globular Cluster ◽  
Surface Brightness ◽  
Galactic Centre ◽  
Proper Motions ◽  
Tidal Disruption ◽  
Low Surface Brightness ◽  
Low Mass ◽  
Important Amount ◽  
Tidal Tails ◽  
Gaia Dr2

ABSTRACT We use Gaia DR2 photometry and proper motions to search for the hypothetical tidal tails of the Galactic globular cluster E 3. Using a modified version of a classical decontamination procedure, we are able to identify the presence of an extended structure emerging from the cluster up to r ∼ 1 deg from its centre, thus suggesting that this poorly studied cluster is undergoing a tidal disruption process. These low surface brightness structures are aligned with the direction to the Galactic centre, as expected for a cluster close to its perigalacticon. Different scenarios to explain the important amount of mass lost by this cluster are discussed.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

scholarly journals Field/isolated lenticular galaxies with high SN values: the case of NGC 4546 and its globular cluster system

2020 ◽  
Vol 493 (2) ◽  
pp. 2253-2270 ◽  
Author(s):  
Carlos G Escudero ◽  
Favio R Faifer ◽  
Analía V Smith Castelli ◽  
Mark A Norris ◽  
Juan C Forte
Keyword(s):  
Globular Cluster ◽  
Gaussian Mixture ◽  
Brightness Distribution ◽  
Galactic Centre ◽  
Distance Modulus ◽  
Lenticular Galaxies ◽  
Additional Group ◽  
The Galaxy ◽  
Colour Distribution ◽  
Specific Frequency

ABSTRACT We present a photometric study of the field lenticular galaxy NGC 4546 using Gemini/GMOS imaging in g′r′i′z′. We perform a 2D image decomposition of the surface brightness distribution of the galaxy using galfit, finding that four components adequately describe it. The subtraction of this model from our images and the construction of a colour map allow us to examine in great detail the asymmetric dust structures around the galactic centre. In addition, we perform a detailed analysis of the globular cluster (GC) system of NGC 4546. Using a Gaussian Mixture Model algorithm in the colour–colour plane, we detected hints of multiple groups of GC candidates: the classic blue and red subpopulations, a group with intermediate colours that present a concentrated spatial distribution towards the galaxy, and an additional group towards the red end of the colour distribution. We estimate a total GC population for NGC 4546 of 390 ± 60 members and specific frequency SN = 3.3 ± 0.7, which is relatively high compared to the typical value for galaxies of similar masses and environment. We suggest that the unusual GC population substructures were possibly formed during the interaction that led to the formation of the young ultra-compact dwarf (NGC 4546-UCD1) found in this system. Finally, we estimate the distance modulus of NGC 4546 by analysing its luminosity function, resulting in (m − M) = 30.75 ± 0.12 mag (14.1 Mpc).

scholarly journals Structure and Kinematical Properties of the Galaxy at Intermediate Galactic Latitudes

1998 ◽  
Vol 179 ◽  
pp. 221-222
Author(s):  
D. K. Ojha ◽  
O. Bienaymé ◽  
A. C. Robin
Keyword(s):  
Vertical Structure ◽  
Local Density ◽  
Thick Disk ◽  
Sample Survey ◽  
Galactic Centre ◽  
Proper Motions ◽  
Perfect Agreement ◽  
The Galaxy ◽  
Centre Region ◽  
Disk Component

We have carried out a sample survey in UBVR photometry and proper motions in various directions in the Galaxy. Three fields in the direction of galactic anticentre, centre, and antirotation have been surveyed. Using our new data together with wide-area surveys in other fields available to date, we discuss the radial and vertical structure of the Galaxy. Our results confirm that the thick disk population is distinct from other populations based on their kinematical and spatial distribution. The most probable value of scale height for the thick disk component is determined to be hz≃760±50 pc and a local density of ≃7.4+2.5−1.5% relative to the thin disk. The ratio of the number of thick disk stars in our galactic centre region to that in anticentre region yield hR≃3±1 kpc for the scale length of thick disk. These values are in perfect agreement with the recent determination given by Robin et al. (1996).

scholarly journals Planetary nebulae in the central region of the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 41-45 ◽  
Author(s):  
L. Perek
Keyword(s):  
Central Region ◽  
Surface Brightness ◽  
Large Scale ◽  
Direct Determination ◽  
Planetary Nebulae ◽  
Galactic Centre ◽  
Large Numbers ◽  
The Galaxy ◽  
Objective Prism

Planetary nebulae are convenient objects for studying the large-scale structure of the Galaxy. Firstly, they are easily recognized up to considerable distances on plates taken through an objective prism, and secondly, methods have been devised by various authors to determine their distances from two observable quantities: angular diameter and surface brightness. The importance of the subsystem of planetary nebulae has been accentuated especially by the discoveries by Minkowski and Haro of large numbers of planetaries in the direction of the galactic centre. The distribution of planetaries on the sphere suggests that they are connected with the galactic nucleus, but no direct determination of their distances, which would either confirm or contradict this statement, is available. The most serious obstacle in studying the subsystem of planetaries is the lack of observing data. The aim of the reported paper (Perek 1963) is to give a tentative outline of the distribution of planetaries in space based on extensive new observing material.

scholarly journals Mass and shape of the Milky Way’s dark matter halo with globular clusters from Gaia and Hubble

2019 ◽  
Vol 621 ◽  
pp. A56 ◽  
Author(s):  
Lorenzo Posti ◽  
Amina Helmi
Keyword(s):  
Dark Matter ◽  
Phase Space ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Cluster System ◽  
Dark Matter Halo ◽  
Proper Motions ◽  
Axis Ratio ◽  
The Galaxy ◽  
Globular Cluster System

Aims. We estimate the mass of the inner (< 20 kpc) Milky Way and the axis ratio of its inner dark matter halo using globular clusters as tracers. At the same time, we constrain the distribution in phase-space of the globular cluster system around the Galaxy. Methods. We use the Gaia Data Release 2 catalogue of 75 globular clusters’ proper motions and recent measurements of the proper motions of another 20 distant clusters obtained with the Hubble Space Telescope. We describe the globular cluster system with a distribution function (DF) with two components: a flat, rotating disc-like one and a rounder, more extended halo-like one. While fixing the Milky Way’s disc and bulge, we let the mass and shape of the dark matter halo and we fit these two parameters, together with six others describing the DF, with a Bayesian method. Results. We find the mass of the Galaxy within 20 kpc to be M(<20 kpc) = 1.91−0.17+0.18×1011 M⊙, of which MDM(<20 kpc) = 1.37−0.17+0.18×1011 M⊙ is in dark matter, and the density axis ratio of the dark matter halo to be q = 1.30 ± 0.25. Assuming a concentration-mass relation, this implies a virial mass Mvir = 1.3±0.3×1012 M⊙. Our analysis rules out oblate (q <  0.8) and strongly prolate halos (q >  1.9) with 99% probability. Our preferred model reproduces well the observed phase-space distribution of globular clusters and has a disc component that closely resembles that of the Galactic thick disc. The halo component follows a power-law density profile ρ ∝ r−3.3, has a mean rotational velocity of Vrot ≃ −14km s−1 at 20 kpc, and has a mildly radially biased velocity distribution (β ≃ 0.2 ± 0.07, which varies significantly with radius only within the inner 15 kpc). We also find that our distinction between disc and halo clusters resembles, although not fully, the observed distinction in metal-rich ([Fe/H] > −0.8) and metal-poor ([Fe/H] ≤ −0.8) cluster populations.

Extra-tidal features using Gaia DR2

2019 ◽  
Vol 14 (S351) ◽  
pp. 420-421
Author(s):  
Julio A. Carballo-Bello
Keyword(s):  
Mass Distribution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Space Mission ◽  
Cluster Center ◽  
Proper Motions ◽  
The Galaxy ◽  
Tidal Tails ◽  
Gaia Dr2

AbstractIn recent years, we have gathered enough evidence showing that most of the Galactic globular clusters extend well beyond their King tidal radii and fill their Jacobi radii in the form of “extended stellar haloes”. In some cases, because of the interaction with the Milky Way, stars are able to exceed the Jacobi radius, generating tidal tails which may be used to trace the mass distribution in the Galaxy. In this work, we use the precious information provided by the space mission Gaia (photometry, parallaxes and proper motions) to analyze NGC 362 in the search for member stars in its surroundings. Our preliminar results suggest that it is possible to identify member stars and tidal features up to distances of a few degrees from the globular cluster center.

scholarly journals The Globular Cluster Specific Frequency in NGC 1399 and 4486: A Comparative Study

2002 ◽  
Vol 207 ◽  
pp. 251-255 ◽  
Author(s):  
Juan C. Forte ◽  
Doug Geisler ◽  
E. Kim ◽  
Myung Gyoon Lee ◽  
Pablo Ostrov
Keyword(s):  
Comparative Study ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Surface Brightness ◽  
Two Systems ◽  
The Galaxy ◽  
Long Time ◽  
Specific Frequency

A two color CCD survey for globular clusters in the galactocentric range from 2 to 7 arcmin from the galaxy centers is presented for NGC 1399 and NGC 4486 (M87), two systems that, for a long time, have been considered as class archetypes of the so called “high specific frequency phenomenon”. The new results, combined with previously published HST data for the inner 2 arcmin, and with a re-discussion of the surface brightness profiles, allow a new estimate of the globular cluster specific frequencies. The resulting SN values cannot be considered as anomalously large and, rather, they are consistent with values obtained for other galaxies with similar morphologies.

scholarly journals The Globular Cluster System of M 87

1988 ◽  
Vol 126 ◽  
pp. 605-606
Author(s):  
Judith G. Cohen
Keyword(s):  
Globular Cluster ◽  
Surface Brightness ◽  
Position Angle ◽  
Cluster System ◽  
Point Sources ◽  
Ellipse Fitting ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Color Gradients

Long exposures with the 4-Shooter at the Cassegrain focus of the 200-inch telescope at Palomar Observatory have been obtained for M87 (and two other giant ellipticals in Virgo). Ellipse fitting with a code specially developed to reject point sources has been carried out to determine the surface brightness in various bandpasses of the underlying galaxy. The color gradients in the galaxy are quite small over the entire regime between 2 and 350 arc-sec from the nucleus of M87. Also I find that there is no difference between the ellipse parameters (position angle and eccentricity) derived in the various colors, i.e. the isochromes and the isophotes coincide. Details of the study of the halo of M87 are described in a paper submitted to the Astronomical Journal.

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