A precise analytical approximation for the deprojection of the Sérsic profile

The Sérsic model shows a close fit to the surface brightness (or surface density) profiles of elliptical galaxies and galaxy bulges, and possibly also those of dwarf spheroidal galaxies and globular clusters. The deprojected density and mass profiles are important for many astrophysical applications, in particular for mass-orbit modeling of these systems. However, the exact deprojection formula for the Sérsic model employs special functions that are not available in most computer languages. We show that all previous analytical approximations to the 3D density profile are imprecise at low Sérsic index (n ≲ 1.5). We derived a more precise analytical approximation to the deprojected Sérsic density and mass profiles by fitting two-dimensional tenth-order polynomials to the residuals of the analytical approximations by Lima Neto et al. (1999, MNRAS, 309, 481; LGM) for these profiles, relative to the numerical estimates. Our LGM-based polynomial fits have typical relative precision better than 0.2% for both density and mass profiles, for Sérsic indices 0.5 ≤ n ≤ 10 and radii 0.001 < r/Re < 1000. Our approximation is much more precise than previously published approximations (except, in some models, for a few discrete values of the index). An appendix compares the deprojected Sérsic profiles with those of other popular simple models.

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Population gradients in dwarf spheroidal galaxies KKs 3 and ESO 269-66

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318005550 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 420-421

Author(s):

M. E. Sharina ◽

L. N. Makarova ◽

D. I. Makarov

Keyword(s):

Surface Density ◽

Globular Clusters ◽

Stellar Populations ◽

Density Profiles ◽

Dwarf Spheroidal Galaxies ◽

Star Forming ◽

Central Regions ◽

Low Metallicity ◽

High Metallicity ◽

Spheroidal Galaxies

AbstractWe compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.

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Effects of initial density profiles on massive star cluster formation in giant molecular clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab491 ◽

2021 ◽

Author(s):

Yingtian Chen ◽

Hui Li ◽

Mark Vogelsberger

Keyword(s):

Angular Momentum ◽

Star Formation ◽

Molecular Clouds ◽

Globular Clusters ◽

Cluster Formation ◽

Initial Density ◽

Giant Molecular Clouds ◽

Density Profiles ◽

Stellar Feedback ◽

Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

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Dynamical Evolution of Globular Clusters After Core Collapse

Symposium - International Astronomical Union ◽

10.1017/s0074180900147357 ◽

1985 ◽

Vol 113 ◽

pp. 139-160 ◽

Cited By ~ 4

Author(s):

Douglas C. Heggie

Keyword(s):

Surface Density ◽

Globular Clusters ◽

Stellar System ◽

Dynamical Evolution ◽

Theoretical Models ◽

Numerical Calculations ◽

Core Collapse ◽

Density Profiles ◽

The Core ◽

Fokker Planck

This review describes work on the evolution of a stellar system during the phase which starts at the end of core collapse. It begins with an account of the models of Hénon, Goodman, and Inagaki and Lynden-Bell, as well as evaporative models, and modifications to these models which are needed in the core. Next, these models are related to more detailed numerical calculations of gaseous models, Fokker-Planck models, N-body calculations, etc., and some problems for further work in these directions are outlined. The review concludes with a discussion of the relation between theoretical models and observations of the surface density profiles and statistics of actual globular clusters.

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Globular clusters and dwarf spheroidal galaxies of the outer galactic halo: On the putative scenario of their formation

Astronomical and Astrophysical Transactions ◽

10.1080/10556790108208191 ◽

2001 ◽

Vol 20 (1) ◽

pp. 89-92

Author(s):

V. V. Kravtsov

Keyword(s):

Globular Clusters ◽

Galactic Halo ◽

Dwarf Spheroidal Galaxies ◽

Spheroidal Galaxies

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Variable Stars in Dwarf Spheroidal Galaxies

International Astronomical Union Colloquium ◽

10.1017/s0252921100033315 ◽

1973 ◽

Vol 21 ◽

pp. 35-48

Author(s):

Steven Van Agt

Keyword(s):

Globular Clusters ◽

Local Group ◽

Elliptical Galaxies ◽

Variable Stars ◽

Dwarf Spheroidal Galaxies ◽

Theoretical Predictions ◽

History Of ◽

Set Up ◽

Theoretical Considerations ◽

Spheroidal Galaxies

Interest in dwarf spheroidal galaxies is motivated by a number of reasons; an important one on the occasion of this colloquium is the abundance of variable stars. The theory of stellar evolution and stellar pulsations is now able to predict from theoretical considerations characteristic properties of variable stars in the colour-magnitude diagram (Iben, 1971). By observing the variable stars in the field, and in as wide a selection of objects as possible, more insight can be obtained into the history of the oldest members of our Galaxy (the globular clusters) and of the dwarf spheroidal galaxies in the Local Group. It is worthwhile to explore the spheroidal galaxies as observational tests for the theoretical predictions of conditions in space away from our Galaxy. The numbers of variable stars in the dwarf spheroidal galaxies are such that we may expect well-defined relations to emerge once reliable magnitude sequences have been set up, the variable stars found, and their periods determined. Six dwarf spheroidal galaxies are presently known in the Local Group within a distance of 250 kpc. In Table I, which lists members of the Local Group, they are at the low-luminosity end of the sequence of elliptical galaxies (van den Bergh, 1968).

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New mass bound on fermionic dark matter from a combined analysis of classical dSphs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1573 ◽

2019 ◽

Vol 487 (4) ◽

pp. 5711-5720 ◽

Cited By ~ 7

Author(s):

D Savchenko ◽

A Rudakovskyi

Keyword(s):

Dark Matter ◽

Lower Bound ◽

Cold Dark Matter ◽

Pauli Exclusion Principle ◽

Dark Matter Halo ◽

Exclusion Principle ◽

Fermion Mass ◽

Density Profiles ◽

Combined Analysis ◽

Dwarf Spheroidal Galaxies

ABSTRACTDwarf spheroidal galaxies (dSphs) are the most compact dark-matter-dominated objects observed so far. The Pauli exclusion principle limits the number of fermionic dark matter particles that can compose a dSph halo. This results in a well-known lower bound on their particle mass. So far, such bounds were obtained from the analysis of individual dSphs. In this paper, we model dark matter halo density profiles via the semi-analytical approach and analyse the data from eight ‘classical’ dSphs assuming the same mass of dark matter fermion in each object. First, we find out that modelling of Carina dSph results in a much worse fitting quality compared to the other seven objects. From the combined analysis of the kinematic data of the remaining seven ‘classical’ dSphs, we obtain a new 2σ lower bound of m ≳ 190 eV on the dark matter fermion mass. In addition, by combining a sub-sample of four dSphs – Draco, Fornax, Leo I, and Sculptor – we conclude that 220 eV fermionic dark matter appears to be preferred over the standard cold dark matter at about the 2σ level. However, this result becomes insignificant if all seven objects are included in the analysis. Future improvement of the obtained bound requires more detailed data, both from ‘classical’ and ultra-faint dSphs.

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The Chemical Abundances of the Halo Clusters of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900145504 ◽

1978 ◽

Vol 80 ◽

pp. 177-182

Author(s):

R. Canterna ◽

R. A. Schommer

Keyword(s):

Globular Clusters ◽

Broad Band ◽

Mean Value ◽

Red Giants ◽

Galactocentric Distance ◽

Chemical Abundances ◽

Dwarf Spheroidal Galaxies ◽

The Galaxy ◽

Ursa Minor ◽

Metal Abundances

Photometric metal abundances of individual red giants in eight extremely distant halo globular clusters and the Draco and Ursa Minor dwarf spheroidal galaxies have been obtained using the Washington broad-band system, C, M, T1, T2(Canterna 1976). Observations were made at the KPNO 2.1-m and CTIO 1.5-m telescopes. In Table I we list for each system the mean value of [Fe/H], the number of stars observed in each system, n, the Galactocentric distance, RGC, the intrinsic color of the giant branch at the level of the horizontal branch (HB), (B-V)o,g, and the fraction of HB stars bluer than the RR Lyrae gap, fB. Sources for unpublished color-magnitude diagram (CMD) data are: Pal 11 (Canterna and Schommer), Pal 12 (Canterna and Harris), and Ursa Minor (Schommer, Olszewski and Kunkel).

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Twins born in different environments? Nuclei of two dSphs: isolated galaxy KKS3 and E269-66, a close neighbor of NGC5128

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316008693 ◽

2015 ◽

Vol 12 (S316) ◽

pp. 349-350

Author(s):

Margarita Sharina ◽

Alexei Kniazev ◽

Igor Karachentsev

Keyword(s):

Globular Clusters ◽

Massive Star ◽

Stellar Population ◽

Central Star ◽

Close Neighbor ◽

Dwarf Spheroidal Galaxies ◽

Star Forming ◽

Star Formation Histories ◽

Massive Clusters ◽

Centaurus A

AbstractWe present the results of age, metallicity and radial velocity determination for central massive globular clusters (GCs) in dwarf spheroidal galaxies: KKs3 and ESO269-66. KKS3 is a unique isolated galaxy. ESO269-66 is a close neighbor of the giant S0 Centaurus A. The results contribute to the knowledge about the origin of massive star clusters and their host dSphs. The structure and star formation histories of the two dwarf galaxies look rather similar. Both of them have experienced several star-forming events. The most recent ones occurred 1-2 Gyr ago, and most powerful bursts happened 12-14 Gyrs ago. Our analysis has shown that both GCs appear to be 1-2 Gyr younger and 0.1-0.3 dex more metal-rich than the most ancient metal-poor stars in the host dSphs. We examine signatures of multiple stellar population in the GCs using our data. Since central star-forming bursts were extended in time, the massive clusters might be considered as nuclei of the galaxies.

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