scholarly journals H$_\gamma$ and H$_\delta$ absorption lines and the Initial Mass Function in extragalactic star forming regions

2002 ◽  
Vol 390 (1) ◽  
pp. 47-58
Author(s):  
A. Sinanian ◽  
D. Kunth ◽  
J. Lequeux ◽  
G. Comte ◽  
A. Petrosian
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Absorption Lines ◽  
Initial Mass ◽  
Star Forming ◽  
Star Forming Regions

scholarly journals The Variation of the Initial Mass Function in Clusters

2004 ◽  
Vol 221 ◽  
pp. 237-246
Author(s):  
K. L. Luhman
Keyword(s):  
Star Formation ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Open Clusters ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming ◽  
Star Forming Regions

I review recent measurements of the initial mass function of stars and brown dwarfs in star-forming regions and open clusters and summarize the implications of these data for theories of star formation.

scholarly journals Very Low-Luminosity Objects in Star-Forming Regions

1998 ◽  
Vol 11 (1) ◽  
pp. 423-424
Author(s):  
Motohide Tamura ◽  
Yoichi Itoh ◽  
Yumiko Oasa ◽  
Alan Tokunaga ◽  
Koji Sugitani
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
T Tauri Stars ◽  
Initial Mass Function ◽  
Formation Mechanisms ◽  
Star Forming ◽  
Star Forming Regions ◽  
T Tauri ◽  
Low Mass ◽  
Stellar Sources

Abstract In order to tackle the problems of low-mass end of the initial mass function (IMF) in star-forming regions and the formation mechanisms of brown dwarfs, we have conducted deep infrared surveys of nearby molecular clouds. We have found a significant population of very low-luminosity sources with IR excesses in the Taurus cloud and the Chamaeleon cloud core regions whose extinction corrected J magnitudes are 3 to 8 mag fainter than those of typical T Tauri stars in the same cloud. Some of them are associated with even fainter companions. Follow-up IR spectroscopy has confirmed for the selected sources that their photospheric temperature is around 2000 to 3000 K. Thus, these very low-luminosity young stellar sources are most likely very low-mass T Tauri stars, and some of them might even be young brown dwarfs.

The Initial Mass Function of a Massive Star‐forming Region W51

2000 ◽  
Vol 543 (2) ◽  
pp. 799-821 ◽  
Author(s):  
Shin‐ichiro Okumura ◽  
Atsushi Mori ◽  
Eiji Nishihara ◽  
Etsuji Watanabe ◽  
Takuya Yamashita
Keyword(s):  
Massive Star ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming

scholarly journals Chandra Study of the Cepheus B Star‐forming Region: Stellar Populations and the Initial Mass Function

2006 ◽  
Vol 163 (2) ◽  
pp. 306-334 ◽  
Author(s):  
Konstantin V. Getman ◽  
Eric D. Feigelson ◽  
Leisa Townsley ◽  
Patrick Broos ◽  
Gordon Garmire ◽  
...  
Keyword(s):  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming

scholarly journals The influence of a top-heavy integrated galactic IMF and dust on the chemical evolution of high-redshift starbursts

2020 ◽  
Vol 494 (2) ◽  
pp. 2355-2373 ◽  
Author(s):  
M Palla ◽  
F Calura ◽  
F Matteucci ◽  
X L Fan ◽  
F Vincenzo ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Chemical Elements ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Strong Impact ◽  
Star Forming ◽  
Abundance Patterns

ABSTRACT We study the effects of the integrated galactic initial mass function (IGIMF) and dust evolution on the abundance patterns of high redshift starburst galaxies. In our chemical models, the rapid collapse of gas clouds triggers an intense and rapid star formation episode, which lasts until the onset of a galactic wind, powered by the thermal energy injected by stellar winds and supernova explosions. Our models follow the evolution of several chemical elements (C, N, α-elements, and Fe) both in the gas and dust phases. We test different values of β, the slope of the embedded cluster mass function for the IGIMF, where lower β values imply a more top-heavy initial mass function (IMF). The computed abundances are compared to high-quality abundance measurements obtained in lensed galaxies and from composite spectra in large samples of star-forming galaxies in the redshift range 2 ≲ z ≲ 3. The adoption of the IGIMF causes a sensible increase of the rate of star formation with respect to a standard Salpeter IMF, with a strong impact on chemical evolution. We find that in order to reproduce the observed abundance patterns in these galaxies, either we need a very top-heavy IGIMF (β < 2) or large amounts of dust. In particular, if dust is important, the IGIMF should have β ≥ 2, which means an IMF slightly more top-heavy than the Salpeter one. The evolution of the dust mass with time for galaxies of different mass and IMF is also computed, highlighting that the dust amount increases with a top-heavier IGIMF.

scholarly journals Massive Stars at High Redshifts

2007 ◽  
Vol 3 (S250) ◽  
pp. 415-428
Author(s):  
Max Pettini
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Spectra ◽  
Star Forming ◽  
Star Forming Regions ◽  
Look Ahead ◽  
Low Metallicity ◽  
High Redshift Universe

AbstractThe five years that have passed since the last IAU Symposium devoted to massive stars have seen a veritable explosion of data on the high redshift universe. The tools developed to study massive stars in nearby galaxies are finding increasing application to the analysis of the spectra of star-forming regions at redshifts as high as z = 7. In this brief review, I consider three topics of relevance to this symposium: the determination of the metallicities of galaxies at high redshifts from consideration of their ultraviolet stellar spectra; constraints on the initial mass function of massive stars in galaxies at z = 2 − 3; and new clues to the nucleosynthesis of carbon and nitrogen in massive stars of low metallicity. The review concludes with a look ahead at some of the questions that may occupy us for the next five years (at least!).

scholarly journals Modes of star formation from Herschel

2012 ◽  
Vol 8 (S292) ◽  
pp. 87-90
Author(s):  
L. Testi ◽  
E. Bressert ◽  
S. Longmore
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
Dense Gas ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Massive Cluster

AbstractWe summarize some of the results obtained from Herschel surveys of nearby star forming regions and the Galactic plane. We show that in the nearby star forming regions the starless core spatial surface density distribution is very similar to that of the young stellar objects. This, taken together with the similarity between the core mass function and the initial mass function for stars and the relationship between the amount of dense gas and star formation rate, suggest that the cloud fragmentation process defines the global outcome of star formation. This “simple” view of star formation may not hold on all scales. In particular dynamical interactions are expected to become important at the conditions required to form young massive clusters. We describe the successes of a simple criterion to identify young massive cluster precursors in our Galaxy based on (sub-)millimeter wide area surveys. We further show that in the location of our Galaxy where the best candidate for a precursor of a young massive cluster is found, the “simple” scaling relationship between dense gas and star formation rate appear to break down. We suggest that in regions where the conditions approach those of the central molecular zone of our Galaxy it may be necessary to revise the scaling laws for star formation.

scholarly journals The sub-solar initial mass function in the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 250-255
Author(s):  
Dimitrios A. Gouliermis
Keyword(s):  
Star Formation ◽  
Hubble Space Telescope ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming ◽  
Advanced Camera For Surveys

AbstractThe Magellanic Clouds offer a unique variety of star forming regions seen as bright nebulae of ionized gas, related to bright young stellar associations. Nowadays, observations with the high resolving efficiency of the Hubble Space Telescope allow the detection of the faintest infant stars, and a more complete picture of clustered star formation in our dwarf neighbors has emerged. I present results from our studies of the Magellanic Clouds, with emphasis in the young low-mass pre-main sequence populations. Our data include imaging with the Advanced Camera for Surveys of the association LH 95 in the Large Magellanic Cloud, the deepest observations ever taken with HST of this galaxy. I discuss our findings in terms of the initial mass function, which we constructed with an unprecedented completeness down to the sub-solar regime, as the outcome of star formation in the low-metallicity environment of the LMC.

scholarly journals Impact of metallicity and star formation rate on the time-dependent, galaxy-wide stellar initial mass function

2018 ◽  
Vol 620 ◽  
pp. A39 ◽  
Author(s):  
T. Jeřábková ◽  
A. Hasani Zonoozi ◽  
P. Kroupa ◽  
G. Beccari ◽  
Z. Yan ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Probability Density Distribution ◽  
Star Forming ◽  
The Galaxy ◽  
Stellar Initial Mass Function ◽  
Stellar Masses

The stellar initial mass function (IMF) is commonly assumed to be an invariant probability density distribution function of initial stellar masses. These initial stellar masses are generally represented by the canonical IMF, which is defined as the result of one star formation event in an embedded cluster. As a consequence, the galaxy-wide IMF (gwIMF) should also be invariant and of the same form as the canonical IMF; gwIMF is defined as the sum of the IMFs of all star-forming regions in which embedded clusters form and spawn the galactic field population of the galaxy. Recent observational and theoretical results challenge the hypothesis that the gwIMF is invariant. In order to study the possible reasons for this variation, it is useful to relate the observed IMF to the gwIMF. Starting with the IMF determined in resolved star clusters, we apply the IGIMF-theory to calculate a comprehensive grid of gwIMF models for metallicities, [Fe/H] ∈ (−3, 1), and galaxy-wide star formation rates (SFRs), SFR ∈ (10−5, 105) M⊙ yr−1. For a galaxy with metallicity [Fe/H] < 0 and SFR > 1 M⊙ yr−1, which is a common condition in the early Universe, we find that the gwIMF is both bottom light (relatively fewer low-mass stars) and top heavy (more massive stars), when compared to the canonical IMF. For a SFR < 1 M⊙ yr−1 the gwIMF becomes top light regardless of the metallicity. For metallicities [Fe/H] > 0 the gwIMF can become bottom heavy regardless of the SFR. The IGIMF models predict that massive elliptical galaxies should have formed with a gwIMF that is top heavy within the first few hundred Myr of the life of the galaxy and that it evolves into a bottom heavy gwIMF in the metal-enriched galactic centre. Using the gwIMF grids, we study the SFR−Hα relation and its dependency on metallicity and the SFR. We also study the correction factors to the Kennicutt SFRK − Hα relation and provide new fitting functions. Late-type dwarf galaxies show significantly higher SFRs with respect to Kennicutt SFRs, while star-forming massive galaxies have significantly lower SFRs than hitherto thought. This has implications for gas-consumption timescales and for the main sequence of galaxies. We explicitly discuss Leo P and ultra-faint dwarf galaxies.

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