scholarly journals From a star cluster ensemble to its formation history

2015 ◽  
Vol 12 (S316) ◽  
pp. 263-264
Author(s):  
Christine Schulz ◽  
Michael Hilker
Keyword(s):  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Galaxy Cluster ◽  
Mass Function ◽  
Star Cluster ◽  
Upper Limit ◽  
Formation History ◽  
Individual Star

AbstractThe present-day sample of ultra-compact dwarf galaxies (UCDs) and globular clusters (GCs) around NGC 1399 is interpreted to be composed of individual star cluster (SC) populations. It is assumed that such an SC population forms at a constant star-formation rate (SFR), and its mass distribution is described by the embedded cluster mass function (ECMF) up to the upper limit Mmax. The GCs and UCDs probably formed in interactions of the progenitor galaxies during the assembly of the central Fornax galaxy cluster which is why we use them as tracers of those events. After some corrections, the overall GC/UCD mass function is decomposed into separate SC populations, each described by an ECMF. Mmax of each ECMF is converted to an SFR according to the SFR-Mmax relation, revealing the SFRs reached during the assembly of galaxies in the central Fornax galaxy cluster.

scholarly journals The systematically varying stellar IMF

2019 ◽  
Vol 14 (S351) ◽  
pp. 117-121 ◽  
Author(s):  
Pavel Kroupa
Keyword(s):  
Globular Clusters ◽  
Massive Star ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Star Formation Rate ◽  
High Redshift ◽  
Formation Rate ◽  
Low Mass Stars ◽  
Dynamical Mass ◽  
Low Mass

AbstractSome ultra-compact dwarf galaxies have large dynamical mass to light (M / L) ratios and also appear to contain an overabundance of LMXB sources, and some Milky Way globular clusters have a low concentration and appear to have a deficit of low-mass stars. These observations can be explained if the stellar IMF becomes increasingly top-heavy with decreasing metallicity and increasing gas density of the forming object. The thus constrained stellar IMF then accounts for the observed trend of metallicity and M / L ratio found amongst M31 globular star clusters. It also accounts for the overall shift of the observationally deduced galaxy-wide IMF from top-light to top-heavy with increasing star formation rate amongst galaxies. If the IMF varies similarly to deduced here, then extremely young very massive star-burst clusters observed at a high redshift would appear quasar-like (Jerabkova et al. 2017).

scholarly journals Do ultracompact dwarf galaxies form monolithically or as merged star cluster complexes?

2021 ◽  
Vol 502 (4) ◽  
pp. 5185-5199
Author(s):  
Hamidreza Mahani ◽  
Akram Hasani Zonoozi ◽  
Hosein Haghi ◽  
Tereza Jeřábková ◽  
Pavel Kroupa ◽  
...  
Keyword(s):  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Mass Function ◽  
Star Cluster ◽  
Initial Mass Function ◽  
Central Mass ◽  
Cluster Complexes ◽  
V Band ◽  
Stellar Masses ◽  
The Imf

ABSTRACT Some ultracompact dwarf galaxies (UCDs) have elevated observed dynamical V-band mass-to-light (M/LV) ratios with respect to what is expected from their stellar populations assuming a canonical initial mass function (IMF). Observations have also revealed the presence of a compact dark object in the centres of several UCDs, having a mass of a few to 15 per cent of the present-day stellar mass of the UCD. This central mass concentration has typically been interpreted as a supermassive black hole, but can in principle also be a subcluster of stellar remnants. We explore the following two formation scenarios of UCDs: (i) monolithic collapse and (ii) mergers of star clusters in cluster complexes as are observed in massively starbursting regions. We explore the physical properties of the UCDs at different evolutionary stages assuming different initial stellar masses of the UCDs and the IMF being either universal or changing systematically with metallicity and density according to the integrated Galactic IMF theory. While the observed elevated M/LV ratios of the UCDs cannot be reproduced if the IMF is invariant and universal, the empirically derived IMF that varies systematically with density and metallicity shows agreement with the observations. Incorporating the UCD-mass-dependent retention fraction of dark remnants improves this agreement. In addition, we apply the results of N-body simulations to young UCDs and show that the same initial conditions describing the observed M/LV ratios reproduce the observed relation between the half-mass radii and the present-day masses of the UCDs. The findings thus suggest that the majority of UCDs that have elevated M/LV ratios could have formed monolithically with significant remnant-mass components that are centrally concentrated, while those with small M/LV values may be merged star cluster complexes.

scholarly journals Testing star formation rate indicators using galaxy merger simulations and radiative transfer

2009 ◽  
Vol 5 (S262) ◽  
pp. 257-260
Author(s):  
Christopher C. Hayward ◽  
Patrik Jonsson ◽  
Kai Noeske ◽  
Stijn Wuyts ◽  
T. J. Cox ◽  
...  
Keyword(s):  
Star Formation ◽  
Radiative Transfer ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Spectral Energy ◽  
Merging Galaxies ◽  
Formation History ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

AbstractWe discuss our ongoing project analyzing N-body/smoothed-particle hydrodynamics simulations of isolated and merging galaxies, performed using GADGET-2 (Springel 2005), with the 3-D adaptive grid, polychromatic Monte Carlo radiative transfer code SUNRISE (Jonsson 2006). We apply commonly used UV, optical, and IR star formation rate (SFR) indicators to the integrated spectral energy distributions (SEDs) of the simulated galaxies in order to determine how well the SFR indicators recover the instantaneous SFR in the simulations. The models underlying each SFR indicator must necessarily make assumptions about physical properties of the galaxies, e.g., the star formation history (SFH), whereas all such properties are known in the simulations. This enables us to test and compare SFR indicators in a way that is complementary to observational studies. We present one preliminary result of interest: even after correcting the Hα luminosity for dust using the Calzetti et al. (2000) attenuation law the SFR is significantly underestimated for simulated galaxies with SFR ≳ 10 M⊙ yr−1.

scholarly journals Hidden infrared star clusters in our Galaxy: follow-up observations

2009 ◽  
Vol 5 (S266) ◽  
pp. 366-366
Author(s):  
Jura Borissova ◽  
Radostin Kurtev ◽  
Margaret M. Hanson ◽  
Leonid Georgiev ◽  
Valentin Ivanov ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Star Cluster ◽  
Open Clusters ◽  
Star Formation History ◽  
Stellar Disk ◽  
Physical Parameters ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Infrared Star

AbstractWe are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to guide models seeking to understand the structure and recent star-formation history of our Galaxy. The immediate goal is to derive accurate cluster physical parameters using precise infrared photometry and spectroscopy. So far, we observed approximately 60 star cluster candidates selected from different infrared catalogs. Their nature, reddening, distance, age and mass are analyzed. Two of them, Mercer 3 and Mercer 5, are new obscured Milky Way globular clusters. Among the newly identified open clusters, the objects [DBS2003] 179, Mercer 23, Mercer 30, Mercer 70, and [DBS2003] 106 are particularly interesting because they contain massive young OB and Wolf–Rayet stars with strong emission lines.

scholarly journals Legacy of star formation in the pre-reionization universe

2019 ◽  
Vol 488 (2) ◽  
pp. 2202-2221 ◽  
Author(s):  
Jason Jaacks ◽  
Steven L Finkelstein ◽  
Volker Bromm
Keyword(s):  
Star Formation ◽  
Luminosity Function ◽  
Star Formation Rate ◽  
Direct Detection ◽  
Formation Rate ◽  
Mass Function ◽  
James Webb Space Telescope ◽  
Current Limiting ◽  
Molecular Cooling ◽  
Low Mass

ABSTRACT We utilize gizmo, coupled with newly developed sub-grid models for Population III (Pop III) and Population II (Pop II), to study the legacy of star formation in the pre-reionization Universe. We find that the Pop II star formation rate density (SFRD), produced in our simulation (${\sim } 10^{-2}\ \mathrm{M}_\odot \, {\rm yr^{-1}\, Mpc^{-3}}$ at z ≃ 10), matches the total SFRD inferred from observations within a factor of <2 at 7 ≲ z ≲ 10. The Pop III SFRD, however, reaches a plateau at ${\sim }10^{-3}\ \mathrm{M}_\odot \, {\rm yr^{-1}\, Mpc^{-3}}$ by z ≈ 10, remaining largely unaffected by the presence of Pop II feedback. At z  = 7.5, ${\sim } 20{{\ \rm per\ cent}}$ of Pop III star formation occurs in isolated haloes that have never experienced any Pop II star formation (i.e. primordial haloes). We predict that Pop III-only galaxies exist at magnitudes MUV ≳ −11, beyond the limits for direct detection with the James Webb Space Telescope. We assess that our stellar mass function (SMF) and UV luminosity function (UVLF) agree well with the observed low mass/faint-end behaviour at z = 8 and 10. However, beyond the current limiting magnitudes, we find that both our SMF and UVLF demonstrate a deviation/turnover from the expected power-law slope (MUV,turn = −13.4 ± 1.1 at z  = 10). This could impact observational estimates of the true SFRD by a factor of 2(10) when integrating to MUV = −12 (−8) at z ∼ 10, depending on integration limits. Our turnover correlates well with the transition from dark matter haloes dominated by molecular cooling to those dominated by atomic cooling, for a mass Mhalo ≈ 108 M⊙ at z ≃ 10.

scholarly journals The 1.4-GHz cosmic star formation history at z < 1.3

2019 ◽  
Vol 36 ◽  
Author(s):  
James E. Upjohn ◽  
Michael J. I. Brown ◽  
Andrew M. Hopkins ◽  
Nicolas J. Bonne
Keyword(s):  
Star Formation ◽  
Luminosity Function ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Radio Continuum ◽  
Star Formation History ◽  
Star Forming ◽  
Formation History ◽  
Radio Measurements ◽  
Radio Luminosity Function

AbstractWe measure the cosmic star formation history out to z = 1.3 using a sample of 918 radio-selected star-forming galaxies within the 2-deg2 COSMOS field. To increase our sample size, we combine 1.4-GHz flux densities from the VLA-COSMOS catalogue with flux densities measured from the VLA-COSMOS radio continuum image at the positions of I &lt; 26.5 galaxies, enabling us to detect 1.4-GHz sources as faint as 40 μJy. We find that radio measurements of the cosmic star formation history are highly dependent on sample completeness and models used to extrapolate the faint end of the radio luminosity function. For our preferred model of the luminosity function, we find the star formation rate density increases from 0.017 M⊙ yr−1 Mpc−3 at z ∼ 0.225 to 0.092 M⊙ yr−1 Mpc−3 at z ∼ 1.1, which agrees to within 40% of recent UV, IR and 3-GHz measurements of the cosmic star formation history.

scholarly journals Binary stars on the galaxy SFH

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
F. Zhang ◽  
L. Li ◽  
Z. Han
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Star Formation History ◽  
Population Synthesis ◽  
Feedback Process ◽  
Formation History ◽  
The Galaxy ◽  
Degeneracy Problem

AbstractUsing the Yunnan-II evolutionary population synthesis models comprising binary stars, we find that the inclusion of binary stars can raise the derived stellar metallicity Z* and/or age t (degeneracy problem), raise the stellar mass M*, lower the gaseous metallicity Zgas and star formation rate (SFR) of galaxies. This means that a few stars form recently in galaxies, while more stars form during the entire evolution process when considering binary stars. If the degeneracy between t and Z* can be broken, its effect on the feedback process and star formation history can be determined.

scholarly journals Globular Clusters, Dwarf Galaxies, and the Assembly of the M87 Halo

2015 ◽  
Vol 11 (S317) ◽  
pp. 153-158
Author(s):  
Eric W. Peng ◽  
Hong-Xin Zhang ◽  
Chengze Liu ◽  
Yiqing Liu
Keyword(s):  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Galaxy Cluster ◽  
Virgo Cluster ◽  
Early Type ◽  
Massive Galaxies ◽  
Low Mass ◽  
Using Data ◽  
The Relationship ◽  
Negative Gradient

AbstractAt the center of the nearest galaxy cluster, the Virgo cluster, lies the massive cD galaxy, M87 (NGC 4486). Using data from the Next Generation Virgo Cluster Survey, we investigate the relationship between M87, its globular clusters (GCs), and satellite dwarf galaxies. We find that the kinematics of GCs and ultra-compact dwarfs (UCDs) are different, indicating that UCDs are not simply massive GCs. We also identify a morphological sequence of envelope fraction around UCDs correlated with cluster-centric distance that suggest UCDs are the result of tidal stripping. Lastly, we find that the [α/Fe] abundance ratios of low-mass early-type galaxies in Virgo exhibit a strong negative gradient within ~ 400 kpc of M87, where the galaxies closest to M87 have the highest values. These satellite galaxies are likely the surviving counterparts of accreted dwarfs that contribute stars to the metal-poor, α-rich stellar halos of massive galaxies. Together, these results describe a dense environment that has had a strong and continuing impact on the evolution of its low-mass neighbors.

scholarly journals THE GAS PHASE MASS METALLICITY RELATION FOR DWARF GALAXIES: DEPENDENCE ON STAR FORMATION RATE AND HI GAS MASS

2015 ◽  
Vol 812 (2) ◽  
pp. 98 ◽  
Author(s):  
Jimmy ◽  
Kim-Vy Tran ◽  
Amélie Saintonge ◽  
Gioacchino Accurso ◽  
Sarah Brough ◽  
...  
Keyword(s):  
Star Formation ◽  
Gas Phase ◽  
Dwarf Galaxies ◽  
Star Formation Rate ◽  
Formation Rate
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