scholarly journals Super Star Cluster Luminosity Functions in Interacting Luminous Infrared Galaxies

2010 ◽  
Vol 6 (S277) ◽  
pp. 37-40
Author(s):  
Zara Randriamanakoto ◽  
Petri Väisänen
Keyword(s):  
Star Formation ◽  
Adaptive Optics ◽  
Power Law ◽  
Mass Function ◽  
Initial Mass Function ◽  
Infrared Galaxies ◽  
Data Set ◽  
Luminous Infrared Galaxies ◽  
Luminosity Functions ◽  
Super Star Clusters

AbstractYoung and massive super star clusters (SSCs) are found whenever very active star formation is going on, such as that in interacting Luminous Infrared Galaxies (LIRGs). From a deep NIR adaptive optics imaging survey, we present thus far the first K-band SSC luminosity functions (LFs) in these types of galaxies, and also a relation between the brightest SSC and the global SFR of the galaxy. Based on the derived LFs, one can constrain the cluster initial mass function (CIMF) and study the formation and evolution of SSCs. Our preliminary results are in disagreement with theoretical expectations which suggest that the SSC LF should be well fitted by a single power-law with an index of −2. We find power-law indexes of ~−1.5, shallower than the expected ones. Taken at face value, our results appear to support the concept that the CIMF is mass-dependent, not universal, which will be studied in more detail by mass-modelling of the SSCs. The data-set will also allow us to estimate the fraction of total star formation originating in the SSCs over a range of galaxy types.

scholarly journals Spatially-Resolved View of High-Redshift Starbursts: the case of Sub-mm Galaxies

2012 ◽  
Vol 8 (S295) ◽  
pp. 92-92
Author(s):  
Karín Menéndez-Delmestre ◽  
Andrew W. Blain ◽  
Mark Swinbank ◽  
Ian Smail ◽  
Rob J. Ivison ◽  
...  
Keyword(s):  
Star Formation ◽  
Adaptive Optics ◽  
Spatial Scales ◽  
Large Fraction ◽  
Spectroscopic Techniques ◽  
Infrared Galaxies ◽  
Star Forming ◽  
Luminous Infrared Galaxies ◽  
Disk Structure ◽  
Hα Emission

AbstractUltra-luminous infrared galaxies (LIR > 1012 L⊙) are locally rare, but appear to dominate the co-moving energy density at higher redshifts (z>2). Many of these are optically-faint, dust-obscured galaxies that have been identified by the detection of their thermal dust emission at sub-mm wavelengths. Multi-wavelength spectroscopic follow-up observations of these sub-mm galaxies (SMGs) have shown that they are massive (Mstellar ~ 1011 M⊙) objects undergoing intense star-formation (SFRs ~ 102−103 M⊙ yr−1) with a mean redshift of z ~ 2, coinciding with the epoch of peak quasar activity. The large fraction of AGNs in SMGs and the derived SMBH masses (M• < 108 M⊙) in these galaxies suggest that the submm phase may play an important role in the rapid growth of SMBHs. When both AGN and star-formation activity are present, long-slit spectroscopic techniques face difficulties in disentangling their contributions and may result in SFR and mass overestimates. We present an integral field view of the Hα emission in a sample of 3 SMGs at z~1.4–2.4 with the IFU instrument OSIRIS on Keck. Designed to be used with Laser Guide Star Adaptive Optics, OSIRIS allows a spatial resolution of up to 10× higher than what has been possible in previous seeing-limited studies of the ionized gas in these galaxies. Our main results are the following: (1) We detect multiple galactic-scale sub-components: the compact, broad Hα emission (FWHM >1000 km s−1) likely associated with an AGN, the more extended narrow-line Hα emission (FWHM ≲500 km s−1) of star-forming regions; the latter are dominated by multiple 1–2 kpc sized Hα-bright clumps, each contributing 1-25% of the total clump-integrated Hα emission. (2) We derive clump dynamical masses ~1–10×109M⊙, 1–2 orders of magnitude larger than the kpc-scaled stellar clumps uncovered in optically-selected z ~ 2 star-forming galaxies. (3) We determine high star-formation rate surface densities (ΣSFR~1–50 M⊙yr−1 kpc−2, after extinction correction), similar to local starbursts and luminous infrared galaxies. In contrast to these local environments, SMGs undergo such intense activity on significantly larger spatial scales as revealed by extended Hα emission over 4–16 kpc. (4) We find no evidence of ordered global motion as it would be found in a disk, but rather large velocity offsets (~ few × 100 km s−1) between the distinct stellar clumps. The merger interpretation is likely the most accurate scenario for the SMGs in our sample. However, the final test of whether an underlying disk structure is present will come from studies of the cold gas at the high spatial resolutions possible with ALMA.We refer the reader to Menéndez-Delmestre et al. (2012) for more details.

scholarly journals Star formation history of the solar neighbourhood as told by Gaia

2020 ◽  
Vol 501 (1) ◽  
pp. 302-328
Author(s):  
Jairo A Alzate ◽  
Gustavo Bruzual ◽  
Daniel J Díaz-González
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Solar Neighbourhood ◽  
Data Set ◽  
Formation History ◽  
Solar Metallicity ◽  
History Of

ABSTRACT The Gaia data release 2 (DR2) catalogue is the best source of stellar astrometric and photometric data available today. The history of the Milky Way galaxy is written in stone in this data set. Parallaxes and photometry tell us where the stars are today, when were they formed, and with what chemical content, that is, their star formation history (SFH). We develop a Bayesian hierarchical model suited to reconstruct the SFH of a resolved stellar population. We study the stars brighter than $G\, =\, 15$ within 100 pc of the Sun in Gaia DR2 and derive an SFH of the solar neighbourhood in agreement with previous determinations and improving upon them because we detect chemical enrichment. Our results show a maximum of star formation activity about 10 Gyr ago, producing large numbers of stars with slightly below solar metallicity (Z  =  0.014), followed by a decrease in star formation up to a minimum level occurring around 8 Gyr ago. After a quiet period, star formation rises to a maximum at about 5 Gyr ago, forming stars of solar metallicity (Z  =  0.017). Finally, star formation has been decreasing until the present, forming stars of Z  =  0.03 at a residual level. We test the effects introduced in the inferred SFH by ignoring the presence of unresolved binary stars in the sample, reducing the apparent limiting magnitude, and modifying the stellar initial mass function.

scholarly journals Galactic consequences of clustered star formation

2009 ◽  
Vol 5 (S266) ◽  
pp. 417-420
Author(s):  
M. R. Haas ◽  
P. Anders
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Sampling Method ◽  
Mass Function ◽  
Star Cluster ◽  
Initial Mass Function ◽  
High Mass ◽  
Power Law Distribution ◽  
Chemical Enrichment ◽  
Low Mass

AbstractIf all stars form in clusters and both stars and clusters follow a power-law distribution which favours the creation of low-mass objects, the numerous low-mass clusters will be deficient in high-mass stars. Therefore, the stellar mass function integrated over the entire galaxy (the integrated galactic initial mass function; IGIMF) will be steeper at the high-mass end than the underlying stellar IMF. We show how the steepness of the IGIMF depends on the sampling method and on the assumptions made regarding the star cluster mass function. We also investigate the O-star content, integrated photometry and chemical enrichment of galaxies that result from several IGIMFs compared to more standard IMFs.

scholarly journals Comment on “An excess of massive stars in the local 30 Doradus starburst”

Science ◽  
2018 ◽  
Vol 361 (6400) ◽  
pp. eaat6506 ◽  
Author(s):  
Will M. Farr ◽  
Ilya Mandel
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Ad Hoc ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Formation History ◽  
Power Law Exponent ◽  
Stellar Initial Mass Function

Schneider et al. (Reports, 5 January 2018, p. 69) used an ad hoc statistical method in their calculation of the stellar initial mass function. Adopting an improved approach, we reanalyze their data and determine a power-law exponent of 2.05−0.13+0.14. Alternative assumptions regarding dataset completeness and the star formation history model can shift the inferred exponent to 2.11−0.17+0.19 and 2.15−0.13+0.13, respectively.

scholarly journals Simulating star clusters across cosmic time – I. Initial mass function, star formation rates, and efficiencies

2019 ◽  
Vol 489 (2) ◽  
pp. 1880-1898 ◽  
Author(s):  
Chong-Chong He ◽  
Massimo Ricotti ◽  
Sam Geen
Keyword(s):  
Star Formation ◽  
Power Law ◽  
High Redshift ◽  
Star Clusters ◽  
Cosmic Time ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Initial Mass ◽  
Solar Metallicity

ABSTRACT We present radiation-magneto-hydrodynamic simulations of star formation in self-gravitating, turbulent molecular clouds, modelling the formation of individual massive stars, including their UV radiation feedback. The set of simulations have cloud masses between mgas = 103 M⊙ and 3 × 105 M⊙ and gas densities typical of clouds in the local Universe ($\overline{n}_{\rm gas} \sim 1.8\times 10^2$ cm−3) and 10× and 100× denser, expected to exist in high-redshift galaxies. The main results are as follows. (i) The observed Salpeter power-law slope and normalization of the stellar initial mass function at the high-mass end can be reproduced if we assume that each star-forming gas clump (sink particle) fragments into stars producing on average a maximum stellar mass about $40{{\ \rm per\ cent}}$ of the mass of the sink particle, while the remaining $60{{\ \rm per\ cent}}$ is distributed into smaller mass stars. Assuming that the sinks fragment according to a power-law mass function flatter than Salpeter, with log-slope 0.8, satisfy this empirical prescription. (ii) The star formation law that best describes our set of simulation is ${\rm d}\rho _*/{\rm d}t \propto \rho _{\rm gas}^{1.5}$ if $\overline{n}_{\rm gas}\lt n_{\rm cri}\approx 10^3$ cm−3, and ${\rm d}\rho _*/{\rm d}t \propto \rho _{\rm gas}^{2.5}$ otherwise. The duration of the star formation episode is roughly six cloud’s sound crossing times (with cs = 10 km s−1). (iii) The total star formation efficiency in the cloud is $f_*=2{{\ \rm per\ cent}} (m_{\rm gas}/10^4~\mathrm{M}_\odot)^{0.4}(1+\overline{n}_{\rm gas}/n_{\rm cri})^{0.91}$, for gas at solar metallicity, while for metallicity Z &lt; 0.1 Z⊙, based on our limited sample, f* is reduced by a factor of ∼5. (iv) The most compact and massive clouds appear to form globular cluster progenitors, in the sense that star clusters remain gravitationally bound after the gas has been expelled.

scholarly journals Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?

2019 ◽  
Vol 485 (4) ◽  
pp. 4852-4862 ◽  
Author(s):  
Dávid Guszejnov ◽  
Philip F Hopkins ◽  
Andrew S Graus
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Milky Way ◽  
Extreme Environments ◽  
Mass Function ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Arbitrary Power ◽  
Power Law Function ◽  
The Imf

Abstract One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky Way and neighbouring galaxies. But recent observations of early-type galaxies can be interpreted to imply a ‘bottom-heavy’ IMF, while others of ultrafaint dwarfs could imply a ‘top-heavy’ IMF. This would impose powerful constraints on star formation models. We explore what sort of ‘cloud-scale’ IMF models could possibly satisfy these constraints. We utilize simulated galaxies that reproduce (broadly) the observed galaxy properties, while they also provide the detailed star formation history and properties of each progenitor star-forming cloud. We then consider generic models where the characteristic mass of the IMF is some arbitrary power-law function of progenitor cloud properties, along with well-known literature IMF models which scale with Jeans mass, ‘turbulent Bonnor–Ebert mass’, temperature, the opacity limit, metallicity, or the ‘protostellar heating mass’. We show that no IMF models currently in the literature – nor any model where the turnover mass is an arbitrary power-law function of a combination of cloud temperature/density/size/metallicity/velocity dispersion/magnetic field – can reproduce the claimed IMF variation in ellipticals or dwarfs without severely violating observational constraints in the Milky Way. Specifically, they predict too much variation in the ‘extreme’ environments of the Galaxy compared to that observed. Either the IMF varies in a more complicated manner, or alternative interpretations of the extragalactic observations must be explored.

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 Fragmentation and the Initial Mass Function

1989 ◽  
Vol 120 ◽  
pp. 44-55
Author(s):  
Richard B. Larson
Keyword(s):  
Star Formation ◽  
Power Law ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Solar Mass ◽  
Universal Feature ◽  
Basic Features ◽  
The Imf

A central problem in the theory of star formation is to understand the spectrum of masses, or Initial Mass Function, with which stars are formed. The fundamental role of the IMF in galactic evolution has been described by Tinsley (1980), and an extensive review of evidence concerning the IMF and its possible variability has been presented by Scalo (1986). Although the IMF derived from the observations is subject to many uncertainties, two basic features seem reasonably well established. One is that the typical stellar mass, defined such that equal amounts of matter condense into stars above and below this mass, is within a factor of 3 of one solar mass. A theory of star formation should therefore be able to explain why most stars are formed with masses of order one solar mass. The second apparently universal feature is that the IMF for relatively massive stars can be approximated by a power law with a slope not greatly different from that originally proposed by Salpeter (1955). Thus we also need to understand why the IMF always has a similar power-law tail toward higher masses.

scholarly journals The K-band luminosity functions of super star clusters in luminous infrared galaxies, their slopes and the effects of blending

2013 ◽  
Vol 431 (1) ◽  
pp. 554-569 ◽  
Author(s):  
Z. Randriamanakoto ◽  
P. Väisänen ◽  
S. Ryder ◽  
E. Kankare ◽  
J. Kotilainen ◽  
...  
Keyword(s):  
Star Clusters ◽  
Infrared Galaxies ◽  
Luminous Infrared Galaxies ◽  
Luminosity Functions ◽  
Super Star Clusters ◽  
K Band
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