scholarly journals The Initial Mass Function of Massive Stars in Galaxies: Empirical Evidence

1986 ◽  
Vol 116 ◽  
pp. 451-466 ◽  
Author(s):  
John M. Scalo
Keyword(s):  
Formation Rate ◽  
Mass Function ◽  
Convincing Evidence ◽  
Initial Mass Function ◽  
Solar Neighborhood ◽  
High Mass ◽  
Mass Limit ◽  
Nearby Galaxies ◽  
Evolution Modeling ◽  
Excitation Conditions

Observational constraints on the form of the high-mass stellar IMF are reviewed. The evidence includes star counts in the solar neighborhood, individual and composite star clusters, and nearby galaxies, and arguments based on integrated light and chemical evolution modeling. There is no convincing evidence for any systematic variations of the shape of the high-mass IMF. However, the various determinations are very uncertain, and do not allow any firm estimate of the logarithmic slope of the upper IMF; the appropriate value is somewhere between −1.3 and −2.3, with region-to-region variations smaller than about ±0.5. A number of lines of evidence suggest that the lower mass limit or mode mass of the IMF increases with increasing star formation rate, reaching perhaps 10–15 m⊙ in some starburst galaxies. It is also possible that the upper mass limit depends on metallicity, based on variations in excitation conditions of HII regions.

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 THE ADF AND THE t2 FORMALISM IN H II REGIONS BASED ON THE UPPER MASS LIMIT OF THE IMF FOR THE MW

2020 ◽  
Vol 56 (2) ◽  
pp. 235-244
Author(s):  
L. Carigi ◽  
A. Peimbert ◽  
M. Peimbert ◽  
G. Delgado-Inglada
Keyword(s):  
Milky Way ◽  
Spiral Galaxies ◽  
Star Formation Rate ◽  
Direct Method ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
H Ii Regions ◽  
Mass Limit ◽  
Better Than

We study in depth the abundance discrepancy problem in H II regions, this time from a different perspective than the usual one: by studying the effect of the upper mass limit (Mup) of the initial mass function (IMF) on the O, C, and He predicted by chemical evolution models for the Milky Way. We use abundances determined with the direct method (DM) and with the temperature independent method (TIM). We compare the predicted abundances at the present time with observations of Orion, M17, and M8 to determine the Mup value of the galactic IMF. From the DM abundances, the models predict an Mup = 25 − 45 M⨀, while from the TIM, CEMs derive an Mup = 70 − 110 M⨀. Spiral galaxies with the stellar mass and star formation rate of the MW are predicted to have an Mup ≈ 100 M⨀. These results support that abundances derived from the TIM are better than those derived from the DM.

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.

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 Implications of a density dependent IMF for the statistics of progenitors of gravitational wave sources

2018 ◽  
Vol 14 (S346) ◽  
pp. 464-467
Author(s):  
Indulekha Kavila ◽  
Megha Viswambharan
Keyword(s):  
Globular Clusters ◽  
Formation Rate ◽  
Compact Object ◽  
Mass Function ◽  
Initial Distribution ◽  
Initial Mass Function ◽  
High Mass ◽  
Mass Star ◽  
Stellar Masses ◽  
The Impact

AbstractObservations of mergers of multi-compact object systems offer insights to the formation processes of massive stars in globular clusters. Simulations of stellar clusters, may be used to understand and interpret observations. Simulations generally adopt an Initial Mass Function (IMF) with a Salpeter slope at the high mass end, for the initial distribution of stellar masses. However, observations of the nearest high mass star forming regions point to the IMF at the high mass end being flatter than Salpeter, in regions where the stellar densities are high. We explore the impact of this on the formation rate of potential GW sources, estimated from standard considerations. Globular clusters being significant contributors to the ionization history of the universe, the results have implications for the same. It impacts our ability to explore the putative mass gap, between the upper limit for neutron star masses and the lower limit for black hole masses, also.

scholarly journals The initial mass function in the extended ultraviolet disc of M83

2019 ◽  
Vol 491 (2) ◽  
pp. 2366-2390 ◽  
Author(s):  
S M Bruzzese ◽  
David A Thilker ◽  
G R Meurer ◽  
Luciana Bianchi ◽  
A B Watts ◽  
...  
Keyword(s):  
Main Sequence ◽  
Hubble Space Telescope ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Main Sequence Stars ◽  
Red Giant ◽  
The Imf

ABSTRACT Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disc (XUV disc) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper end of the initial mass function (IMF) in the outer disc using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power-law slope α = −2.35 ± 0.3 and an upper mass limit $M_{\rm u}=25_{-3}^{+17} \, \mathrm{M}_\odot$. This IMF is consistent with the observed H $\rm \alpha$ emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV discs are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.

scholarly journals Star Formation and Galactic Evolution: From Protogalaxies to Starbursts

1987 ◽  
Vol 115 ◽  
pp. 663-689 ◽  
Author(s):  
Joseph Silk
Keyword(s):  
Star Formation ◽  
Physical Mechanism ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
Galactic Evolution ◽  
Solar Neighborhood ◽  
Formation Theory ◽  
Formation Efficiency

Three topics in star formation theory are reviewed: the initial mass function, the star formation efficiency, and the star formation rate. A physical mechanism for bimodal star formation is developed. Applications are made to the solar neighborhood, to the inner galaxy, to starburst galaxies, and to past star formation in protodisks and in protoellipticals. Implications are drawn for galactic morphology, for chemical evolution, and for the present density of stellar remnants.

scholarly journals CO Multi-line Imaging of Nearby Galaxies (COMING). VI. Radial variations in star formation efficiency

2019 ◽  
Vol 71 (Supplement_1) ◽  
Author(s):  
Kazuyuki Muraoka ◽  
Kazuo Sorai ◽  
Yusuke Miyamoto ◽  
Moe Yoda ◽  
Kana Morokuma-Matsui ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
Molecular Gas ◽  
Spiral Arms ◽  
Nearby Galaxies ◽  
The Difference ◽  
Line Imaging ◽  
Formation Efficiency

Abstract We examined radial variations in molecular-gas based star formation efficiency (SFE), which is defined as star formation rate per unit molecular gas mass, for 80 galaxies selected from the CO Multi-line Imaging of Nearby Galaxies project (Sorai et al. 2019, PASJ, 71, S14). The radial variations in SFE for individual galaxies are typically a factor of 2–3, which suggests that SFE is nearly constant along the galactocentric radius. We found an averaged SFE in 80 galaxies of (1.69 ± 1.1) × 10−9 yr−1, which is consistent with Leroy et al. (2008, AJ, 136, 2782) if we consider the contribution of helium to the molecular gas mass evaluation and the difference in the assumed initial mass function between the two studies. We compared SFE among different morphological (i.e., SA, SAB, and SB) types, and found that SFE within the inner radii (r/r25 < 0.3, where r25 is the B-band isophotal radius at 25 mag arcsec−2) of SB galaxies is slightly higher than that of SA and SAB galaxies. This trend can be partly explained by the dependence of SFE on global stellar mass, which probably relates to the CO-to-H2 conversion factor through the metallicity. For two representative SB galaxies in our sample, NGC 3367 and NGC 7479, the ellipse of r/r25 = 0.3 seems to cover not only the central region but also the inner part of the disk, mainly the bar. These two galaxies show higher SFE in the bar than in the spiral arms. However, we found an opposite trend in NGC 4303; SFE is lower in the bar than in the spiral arms, which is consistent with earlier studies (e.g., Momose et al. 2010, ApJ, 721, 383). These results suggest a diversity of star formation activities in the bar.

Recovering the star formation history of galaxies through spectral fitting: Current challenges

2019 ◽  
Vol 15 (S359) ◽  
pp. 386-390
Author(s):  
Lucimara P. Martins
Keyword(s):  
Star Formation ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Stellar Spectra ◽  
Spectral Fitting ◽  
Formation History ◽  
History Of ◽  
Nearby Galaxies ◽  
Extract Information

AbstractWith the exception of some nearby galaxies, we cannot resolve stars individually. To recover the galaxies star formation history (SFH), the challenge is to extract information from their integrated spectrum. A widely used tool is the full spectral fitting technique. This consists of combining simple stellar populations (SSPs) of different ages and metallicities to match the integrated spectrum. This technique works well for optical spectra, for metallicities near solar and chemical histories not much different from our Galaxy. For everything else there is room for improvement. With telescopes being able to explore further and further away, and beyond the optical, the improvement of this type of tool is crucial. SSPs use as ingredients isochrones, an initial mass function, and a library of stellar spectra. My focus are the stellar libraries, key ingredient for SSPs. Here I talk about the latest developments of stellar libraries, how they influence the SSPs and how to improve them.

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