scholarly journals Ultraviolet spectra of extreme nearby star-forming regions: Evidence for an overabundance of very massive stars

2021 ◽  
Vol 503 (4) ◽  
pp. 6112-6135
Author(s):  
Peter Senchyna ◽  
Daniel P Stark ◽  
Stéphane Charlot ◽  
Jacopo Chevallard ◽  
Gustavo Bruzual ◽  
...  
Keyword(s):  
Stellar Wind ◽  
Massive Stars ◽  
Stellar Populations ◽  
Population Synthesis ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
High Incidence ◽  
Stellar Population Synthesis ◽  
Stellar Masses

ABSTRACT As deep spectroscopic campaigns extend to higher redshifts and lower stellar masses, the interpretation of galaxy spectra depends increasingly upon models for very young stellar populations. Here we present new HST/COS ultraviolet spectroscopy of seven nearby (<120 Mpc) star-forming regions hosting very young stellar populations (∼4–20 Myr) with optical Wolf–Rayet stellar wind signatures, ideal laboratories in which to benchmark these stellar models. We detect nebular C iii] in all seven, but at equivalent widths uniformly <10 Å. This suggests that even for very young stellar populations, the highest equivalent width C iii] emission at ≥15 Å is reserved for inefficiently cooled gas at metallicities at or below that of the SMC. The spectra also reveal strong C iv P-Cygni profiles and broad He ii emission formed in the winds of massive stars, including some of the most prominent He ii stellar wind lines ever detected in integrated spectra. We find that the latest stellar population synthesis prescriptions with improved treatment of massive stars nearly reproduce the entire range of stellar He ii wind strengths observed here. However, we find that these models cannot simultaneously match the strongest wind features alongside the optical nebular line constraints. This discrepancy can be naturally explained by an overabundance of very massive stars produced by a high incidence of binary mass transfer and mergers occurring on short ≲10 Myr time-scales, suggesting these processes may be crucial for understanding systems dominated by young stars both nearby and in the early Universe.

scholarly journals Very Low Mass Stellar Populations in Star-Forming Regions: Near-Infrared Luminosity Functions and Mass Functions

2003 ◽  
Vol 211 ◽  
pp. 91-96 ◽  
Author(s):  
Yumiko Oasa
Keyword(s):  
Near Infrared ◽  
Stellar Populations ◽  
Mass Function ◽  
High Mass ◽  
Star Forming ◽  
Star Forming Regions ◽  
Luminosity Functions ◽  
Low Mass ◽  
Stellar Masses ◽  
Mass Functions

We briefly describe recent studies of the low-mass young stellar populations including substellar objects and of their luminosity functions and mass functions, especially at lower-ends, in different star-forming regions. The mass function is determined by the technique based on the near-infrared photometry for estimating stellar luminosities and then translating them into stellar masses. We compare the local environmental characteristics of regions in which high-mass stars form with those of regions producing only low-mass stars and intermediate stars. We find that there exist numerous very low-mass YSO candidates including young brown dwarfs and young isolated objects with planetary masses in common. Further, the luminosity functions and mass functions in the star-forming regions might not have a uniform shape below the hydrogen-burning limit.

scholarly journals The Tarantula Nebula as a template for extragalactic star forming regions from VLT/MUSE and HST/STIS

2016 ◽  
Vol 12 (S329) ◽  
pp. 292-296
Author(s):  
Paul A. Crowther ◽  
Saida M. Caballero-Nieves ◽  
Norberto Castro ◽  
Christopher J. Evans
Keyword(s):  
Massive Stars ◽  
Central Star ◽  
Population Synthesis ◽  
Uv Spectrum ◽  
Star Forming ◽  
Star Forming Regions ◽  
Integral Field Spectroscopy ◽  
Spatially Extended ◽  
Binary Evolution ◽  
Primary Contribution

AbstractWe present VLT/MUSE observations of NGC 2070, the dominant ionizing nebula of 30 Doradus in the LMC, plus HST/STIS spectroscopy of its central star cluster R136. Integral Field Spectroscopy (MUSE) and pseudo IFS (STIS) together provides a complete census of all massive stars within the central 30×30 parsec2 of the Tarantula. We discuss the integrated far-UV spectrum of R136, of particular interest for UV studies of young extragalactic star clusters. Strong He iiλ1640 emission at very early ages (1–2 Myr) from very massive stars cannot be reproduced by current population synthesis models, even those incorporating binary evolution and very massive stars. A nebular analysis of the integrated MUSE dataset implies an age of ~4.5 Myr for NGC 2070. Wolf-Rayet features provide alternative age diagnostics, with the primary contribution to the integrated Wolf-Rayet bumps arising from R140 rather than the more numerous H-rich WN stars in R136. Caution should be used when interpreting spatially extended observations of extragalactic star-forming regions.

scholarly journals The Formation and Destruction of Molecular Clouds and Galactic Star Formation

2015 ◽  
Vol 11 (S315) ◽  
pp. 61-68
Author(s):  
Shu-ichiro Inutsuka ◽  
Tsuyoshi Inoue ◽  
Kazunari Iwasaki ◽  
Takashi Hosokawa ◽  
Masato I. N. Kobayashi
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Massive Stars ◽  
Age Determination ◽  
Mass Function ◽  
Mass Star ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions

AbstractWe discuss an overall picture of star formation in the Galaxy. Recent high-resolution magneto-hydrodynamical simulations of two-fluid dynamics with cooling/heating and thermal conduction have shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a new scenario of molecular cloud formation through interacting shells or bubbles on galactic scales. We estimate the ensemble-averaged growth rate of individual molecular clouds, and predict the associated cloud mass function. This picture naturally explains the accelerated star formation over many million years that was previously reported by stellar age determination in nearby star forming regions. The recent claim of cloud-cloud collisions as a mechanism for forming massive stars and star clusters can be naturally accommodated in this scenario. This explains why massive stars formed in cloud-cloud collisions follows the power-law slope of the mass function of molecular cloud cores repeatedly found in low-mass star forming regions.

scholarly journals Observations of prestellar cores: Probing the initial conditions for the IMF

2006 ◽  
Vol 2 (S237) ◽  
pp. 132-140
Author(s):  
Philippe André
Keyword(s):  
Main Sequence ◽  
Initial Conditions ◽  
Main Sequence Stars ◽  
Nearby Star ◽  
Star Forming ◽  
Physical Mechanisms ◽  
Star Forming Regions ◽  
Prestellar Cores ◽  
Stellar Masses ◽  
The Imf

AbstractSeveral (sub)millimeter-wave studies of nearby star-forming regions have revealed self-gravitating prestellar condensations that seem to be the direct progenitors of individual stars and whose mass distribution resembles the IMF. In a number of cases, small internal and relative motions have been measured for these condensations, indicating they are much less turbulent than their parent cloud and do not have time to interact before evolving into protostars and pre-main sequence stars. These findings suggest that the IMF is at least partly determined by pre-collapse cloud fragmentation and that one of the keys to understanding the origin of stellar masses lies in the physical mechanisms responsible for the formation and decoupling of prestellar cores within molecular clouds.

scholarly journals The Circumstellar Environment of Embedded Massive Stars

2002 ◽  
Vol 12 ◽  
pp. 143-145 ◽  
Author(s):  
Lee G. Mundy ◽  
Friedrich Wyrowski ◽  
Sarah Watt
Keyword(s):  
Massive Star ◽  
Massive Stars ◽  
Low Mass Stars ◽  
Submillimeter Wavelength ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Circumstellar Environments ◽  
Near Future

Millimeter and submillimeter wavelength images of massive star-forming regions are uncovering the natal material distribution and revealing the complexities of their circumstellar environments on size scales from parsecs to 100’s of AU. Progress in these areas has been slower than for low-mass stars because massive stars are more distant, and because they are gregarious siblings with different evolutionary stages that can co-exist even within a core. Nevertheless, observational goals for the near future include the characterization of an early evolutionary sequence for massive stars, determination if the accretion process and formation sequence for massive stars is similar to that of low-mass stars, and understanding of the role of triggering events in massive star formation.

scholarly journals VLBA DETERMINATION OF THE DISTANCE TO NEARBY STAR-FORMING REGIONS. IV. A PRELIMINARY DISTANCE TO THE PROTO-HERBIG AeBe STAR EC 95 IN THE SERPENS CORE

2010 ◽  
Vol 718 (2) ◽  
pp. 610-619 ◽  
Author(s):  
Sergio Dzib ◽  
Laurent Loinard ◽  
Amy J. Mioduszewski ◽  
Andrew F. Boden ◽  
Luis F. Rodríguez ◽  
...  
Keyword(s):  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions

scholarly journals How Identifying Circumgalactic Gas by Line-of-sight Velocity instead of the Location in 3D Space Affects O vi Measurements

2021 ◽  
Vol 923 (2) ◽  
pp. 137
Author(s):  
Stephanie H. Ho ◽  
Crystal L. Martin ◽  
Joop Schaye
Keyword(s):  
High Resolution ◽  
Density Profile ◽  
Column Density ◽  
Line Of Sight ◽  
Lower Mass ◽  
Star Forming ◽  
3D Space ◽  
High Incidence ◽  
High Incidence Rate ◽  
Stellar Masses

Abstract The high incidence rate of the O vi λλ1032, 1038 absorption around low-redshift, ∼L * star-forming galaxies has generated interest in studies of the circumgalactic medium. We use the high-resolution EAGLE cosmological simulation to analyze the circumgalactic O vi gas around z ≈ 0.3 star-forming galaxies. Motivated by the limitation that observations do not reveal where the gas lies along the line of sight, we compare the O vi measurements produced by gas within fixed distances around galaxies and by gas selected using line-of-sight velocity cuts commonly adopted by observers. We show that gas selected by a velocity cut of ±300 km s−1 or ±500 km s−1 produces a higher O vi column density, a flatter column density profile, and a higher covering fraction compared to gas within 1, 2, or 3 times the virial radius (r vir) of galaxies. The discrepancy increases with impact parameter and worsens for lower-mass galaxies. For example, compared to the gas within 2 r vir, identifying the gas using velocity cuts of 200–500 km s−1 increases the O vi column density by 0.2 dex (0.1 dex) at 1 r vir to over 0.75 dex (0.7 dex) at ≈ 2 r vir for galaxies with stellar masses of 109–109.5 M ⊙ (1010–1010.5 M ⊙). We furthermore estimate that excluding O vi outside r vir decreases the circumgalactic oxygen mass measured by Tumlinson et al. (2011) by over 50%. Our results demonstrate that gas at large line-of-sight separations but selected by conventional velocity windows has significant effects on the O vi measurements and may not be observationally distinguishable from gas near the galaxies.

scholarly journals The formation of discs in clusters

2009 ◽  
Vol 5 (H15) ◽  
pp. 771-771
Author(s):  
Paul C. Clark
Keyword(s):  
Local Density ◽  
Cluster Formation ◽  
Nearby Star ◽  
Single Star ◽  
Star Forming ◽  
Central Object ◽  
Star Forming Regions ◽  
Time Period ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

We review the properties of the discs that form around ‘sink particles’ in smoothed particle hydrodynamics (SPH) simulations of cluster formation, similar to those of Bate et al. (2003) and Bonnell et al. (2004), and compare them to the observed properties of discs in nearby star-forming regions. Contrary to previous suggestions, discs can form and survive in such an environment, despite the chaotic effects of competitive accretion. We find the discs are typically massive, with ratios of disc mass to central object mass of around 0.1, or higher, being typical. Naturally, the evolution of these discs is dominated by gravitational torques, and the more massive examples exhibit strong m=2 spiral modes. We also find that they can continuously grow over a period of 100,000 years, provided the central object is a single sink particle and the local density of sink particles is low. Discs that form around sink particles in the very centres of clusters tend to be shorter lived, but a single star can lose and gain a disc several times during the main accretion phase. However due to the nature of the turbulence in the cluster, the disc orientation can change dramatically over this time period, since disc-sink systems can accrete from counter-rotating envelopes. Since the competitive accretion process brings in material from large distances, the associated angular momentum can be higher than one would expect for an isolated star formation model. As such, we find that the discs are typically several hundred of AUs in extent, with the largest keplerian structures having radii of ~ 2000AU.

scholarly journals Young Stellar Populations in the Collisional Ring Galaxy NGC 922

2009 ◽  
Vol 5 (S262) ◽  
pp. 406-407
Author(s):  
A. Pellerin ◽  
G. R. Meurer ◽  
K. Bekki ◽  
D. M. Elmegreen ◽  
O. I. Wong ◽  
...  
Keyword(s):  
Stellar Populations ◽  
Star Cluster ◽  
Population Synthesis ◽  
Star Forming ◽  
Hα Emission

AbstractWe studied the star cluster population properties in the nearby collisional ring galaxy NGC 922 using HST/WFPC2 photometry and population synthesis modeling. We found that 69% of the detected clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The images also show a tidal plume pointing toward the companion. Its stellar age is consistent with pre-existing stars that were probably stripped off during the passage of the companion. We compared the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS eld. It indicates very similar masses and sizes, suggesting similar origins. Finally, we found clusters that are excellent progenitor candidates for faint fuzzy clusters.

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