scholarly journals A spatially-resolved study of initial mass function in the outer Galaxy

2016 ◽  
Vol 11 (S321) ◽  
pp. 34-36
Author(s):  
Chikako Yasui ◽  
Natsuko Izumi ◽  
Masao Saito ◽  
Naoto Kobayashi
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
High Mass ◽  
Initial Mass ◽  
Mass Detection ◽  
Spatially Resolved ◽  
Luminosity Functions ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies

AbstractOutskirts of spiral galaxies, including our own, and dwarf irregular galaxies are known to have a different environment from the solar neighborhood, e.g., low metallicities ( ~ − 1 dex). Among them, the outer Galaxy is the closest and hence is so far the only site suitable for population studies of resolved stars on the same basis as solar neighborhood. We have obtained NIR images of young clusters in the outer Galaxy, using the Subaru 8.2-m telescope, and clearly resolved cluster members with mass detection limits of ~ 0.1 M⊙. Based on the fitting of K-band luminosity functions (KLFs) for four clusters, we found that the initial mass function (IMF) in the outer Galaxy is consistent with that in the solar neighborhood in terms of the high-mass slope and IMF peak. Upcoming observations with a higher spatial resolution and sensitivity, using JWST, TMT, etc., will allow us to extend spatially-resolved studies of the IMF to Local Group galaxies.

scholarly journals The Star Formation History and IMF in the LMC and SMC from Deep HST Imaging

1999 ◽  
Vol 190 ◽  
pp. 351-353
Author(s):  
J. Holtzman ◽  
J. R. Mould ◽  
J. S. Gallagher
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
Star Formation History ◽  
Initial Mass ◽  
Luminosity Functions ◽  
Formation History

We present deep photometry to V ~ 27.5 obtained with the HST in several fields in the LMC and the SMC. We derive luminosity functions for the faintest stars which are consistent with an initial mass function similar to that of the solar neighborhood, although moderate variations are not excluded. We discuss implications of these observations for the star formation history in these regions of the LMC and SMC.

scholarly journals THE HIGH-MASS STELLAR INITIAL MASS FUNCTION IN M31 CLUSTERS

2015 ◽  
Vol 806 (2) ◽  
pp. 198 ◽  
Author(s):  
Daniel R. Weisz ◽  
L. Clifton Johnson ◽  
Daniel Foreman-Mackey ◽  
Andrew E. Dolphin ◽  
Lori C. Beerman ◽  
...  
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Stellar Initial Mass Function

scholarly journals Bimodal Star Formation and Remnant-Dominated Galactic Models

1987 ◽  
Vol 117 ◽  
pp. 413-413
Author(s):  
Richard B. Larson
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Mass Function ◽  
Current Data ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
Gas Content ◽  
High Mass ◽  
Stellar Content ◽  
Stellar Initial Mass Function

Current data on the luminosity function of nearby stars allow the possibility that the stellar initial mass function (IMF) is double-peaked and that the star formation rate (SFR) has decreased substantially with time. It is then possible to account for all of the unseen mass in the solar vicinity as stellar remnants. A model for the solar neighborhood has been constructed in which the IMF is bimodal, the SFR is constant for the low-mass mode and strongly decreasing for the high-mass mode, and the mass in remnants is equal to the column density of unseen matter; this model is found to be consistent with all of the available constraints on the evolution and stellar content of the solar neighborhood. In particular, the observed chemical evolution is satisfactorily reproduced without infall. The total SFR in the model decreases roughly with the 1.4 power of the gas content, which is more plausible than the nearly constant SFR required by models with a monotonic IMF.

scholarly journals Formation of Stellar Clusters and the Importance of Thermodynamics for Fragmentation

2007 ◽  
Vol 3 (S246) ◽  
pp. 3-12
Author(s):  
Ralf S. Klessen ◽  
Paul C. Clark ◽  
Simon C. O. Glover
Keyword(s):  
Star Formation ◽  
Dynamic Properties ◽  
Mass Function ◽  
Mass Scale ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
High Mass ◽  
Mass Star ◽  
Heating Regime ◽  
Effective Equation

AbstractWe discuss results from numerical simulations of star cluster formation in the turbulent interstellar medium (ISM). The thermodynamic behavior of the star-forming gas plays a crucial role in fragmentation and determines the stellar mass function as well as the dynamic properties of the nascent stellar cluster. This holds for star formation in molecular clouds in the solar neighborhood as well as for the formation of the very first stars in the early universe. The thermodynamic state of the ISM is a result of the balance between heating and cooling processes, which in turn are determined by atomic and molecular physics and by chemical abundances. Features in the effective equation of state of the gas, such as a transition from a cooling to a heating regime, define a characteristic mass scale for fragmentation and so set the peak of the initial mass function of stars (IMF). As it is based on fundamental physical quantities and constants, this is an attractive approach to explain the apparent universality of the IMF in the solar neighborhood as well as the transition from purely primordial high-mass star formation to the more normal low-mass mode observed today.

Synergies between Massive Stars and Metal-poor Dwarf Irregular Galaxies

2018 ◽  
Vol 14 (S344) ◽  
pp. 178-181
Author(s):  
Miriam Garcia ◽  
Artemio Herrero ◽  
Francisco Najarro ◽  
Norberto Castro ◽  
Inés Camacho
Keyword(s):  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Ob Stars ◽  
Irregular Galaxies ◽  
Formation History ◽  
Population Iii Stars ◽  
Dwarf Irregular Galaxies ◽  
Cosmic History

AbstractThe community of massive stars is working intensively on Local Group dwarf irregular galaxies (dIrr). They are a reservoir of metal-poor massive stars that serve to understand the physics of their higher redshift siblings and population III stars, interpret the farthest, most energetic SNe and GRBs, and compute feedback through Cosmic History. Along the way, we became interested in the recent star-formation history and initial mass-function of the host dIrr’s, their chemical evolution, and gas and dust content. Our team is working to unveil and characterize with spectroscopy the OB-stars in IC 1613, Sextans A and SagDIG, that form a sequence of decreasing metal content. We showcase some results to stimulate synergies between both communities.

scholarly journals Star formation histories in dwarf irregular galaxies in the Local Group

1991 ◽  
Vol 148 ◽  
pp. 343-344
Author(s):  
L. Greggio ◽  
G. Marconi ◽  
P. Focardi ◽  
M. Tosi
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Mass Function ◽  
Initial Mass Function ◽  
Main Sequence Stars ◽  
Star Formation Activity ◽  
Irregular Galaxies ◽  
Ccd Observations ◽  
Star Formation Histories ◽  
Dwarf Irregular Galaxies

The process of star formation (SF) and the modalities with which it occurs in galaxies of different sizes are still poorly understood. On the other hand, interpretation of the chemical and photometric properties of galaxies requires the adoption of adequate laws for the SF rate and Initial Mass Function (IMF) in model computations. Dwarf irregular galaxies in the Local Group offer the chance to study their SF history through analysis of their HR diagrams, which can be derived down to V 25, corresponding to MV0, i.e. to main sequence stars of 2 M⊙. Therefore, for these galaxies, we can derive information on the star formation activity which has occurred over the last 1 Gyr approximately. In this framework, we have undertaken CCD observations of Dwarf irregular galaxies in the Local Group with ESO telescopes and briefly present here the results obtained for DDO 210, Sextans B and NGC 3109.

scholarly journals System initial mass function of the 25 Ori group from planetary-mass objects to intermediate/high-mass stars

2019 ◽  
Vol 486 (2) ◽  
pp. 1718-1740 ◽  
Author(s):  
Genaro Suárez ◽  
Juan José Downes ◽  
Carlos Román-Zúñiga ◽  
Miguel Cerviño ◽  
César Briceño ◽  
...  
Keyword(s):  
Power Law ◽  
Near Infrared ◽  
Mass Range ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Formation Mechanisms ◽  
Stellar Association ◽  
Planetary Mass

Abstract The stellar initial mass function (IMF) is an essential input for many astrophysical studies but only in a few cases has it been determined over the whole cluster mass range, limiting the conclusions about its nature. The 25 Orionis group (25 Ori) is an excellent laboratory for investigating the IMF across the entire mass range of the population, from planetary-mass objects to intermediate/high-mass stars. We combine new deep optical photometry with optical and near-infrared data from the literature to select 1687 member candidates covering a 1.1° radius area in 25 Ori. With this sample we derived the 25 Ori system IMF from 0.012 to 13.1 M⊙. This system IMF is well described by a two-segment power law with Γ = −0.74 ± 0.04 for m < 0.4 M⊙ and Γ = 1.50 ± 0.11 for m ≥ 0.4 M⊙. It is also well described over the whole mass range by a tapered power-law function with Γ = 1.10 ± 0.09, mp = 0.31 ± 0.03 and β = 2.11 ± 0.09. The best lognormal representation of the system IMF has mc = 0.31 ± 0.04 and σ = 0.46 ± 0.05 for m < 1 M⊙. This system IMF does not present significant variations with the radii. We compared the resultant system IMF as well as the brown dwarf/star ratio of 0.16 ± 0.03 that we estimated for 25 Ori with that of other stellar regions with diverse conditions and found no significant discrepancies. These results support the idea that general star-formation mechanisms are probably not strongly dependent on environmental conditions. We found that the substellar and stellar objects in 25 Ori do not have any preferential spatial distributions and confirmed that 25 Ori is a gravitationally unbound stellar association.

scholarly journals Stellar velocity dispersion and initial mass function gradients in dissipationless galaxy mergers

2020 ◽  
Vol 499 (1) ◽  
pp. 559-572
Author(s):  
Carlo Nipoti ◽  
Carlo Cannarozzo ◽  
Francesco Calura ◽  
Alessandro Sonnenfeld ◽  
Tommaso Treu
Keyword(s):  
Velocity Dispersion ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Galaxy Mergers ◽  
Orbital Parameters ◽  
Spatially Resolved ◽  
Stellar Velocity ◽  
Stellar Initial Mass Function ◽  
The Imf

ABSTRACT The stellar initial mass function (IMF) is believed to be non-universal among early-type galaxies (ETGs). Parametrizing the IMF with the so-called IMF mismatch parameter αIMF, which is a measure of the stellar mass-to-light ratio of an ensemble of stars and thus of the ‘heaviness’ of its IMF, one finds that for ETGs αe (i.e. αIMF integrated within the effective radius Re) increases with σe (the line-of-sight velocity dispersion σlos integrated within Re) and that, within the same ETG, αIMF tends to decrease outwards. We study the effect of dissipationless (dry) mergers on the distribution of the IMF mismatch parameter αIMF in ETGs using the results of binary major and minor merging simulations. We find that dry mergers tend to make the αIMF profiles of ETGs shallower, but do not alter significantly the shape of the distributions in the spatially resolved σlos–αIMF space. Individual galaxies undergoing dry mergers tend to decrease their αe, due to erosion of αIMF gradients and mixing with stellar populations with lighter IMF. Their σe can either decrease or increase, depending on the merging orbital parameters and mass ratio, but tends to decrease for cosmologically motivated merging histories. The αe–σe relation can vary with redshift as a consequence of the evolution of individual ETGs: based on a simple dry-merging model, ETGs of given σe are expected to have higher αe at higher redshift, unless the accreted satellites are so diffuse that they contribute negligibly to the inner stellar distribution of the merger remnant.

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