scholarly journals The very massive star content of the nuclear star clusters in NGC 5253

2016 ◽  
Vol 12 (S329) ◽  
pp. 327-331
Author(s):  
Linda J. Smith ◽  
Paul A. Crowther ◽  
Daniela Calzetti
Keyword(s):  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Star Clusters ◽  
Population Synthesis ◽  
High Redshift Galaxies ◽  
Far Ultraviolet ◽  
Massive Clusters ◽  
Very High ◽  
Blue Compact Dwarf Galaxy

AbstractThe blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters. Calzetti et al. (2015) find that the two clusters have an age of 1 Myr, in contradiction to the age of 3–5 Myr inferred from the presence of Wolf-Rayet (W-R) spectral features. We use Hubble Space Telescope (HST) far-ultraviolet (FUV) and ground-based optical spectra to show that the cluster stellar features arise from very massive stars (VMS), with masses greater than 100 M⊙, at an age of 1–2 Myr. We discuss the implications of this and show that the very high ionizing flux can only be explained by VMS. We further discuss our findings in the context of VMS contributing to He ii λ1640 emission in high redshift galaxies, and emphasize that population synthesis models with upper mass cut-offs greater than 100 M⊙ are crucial for future studies of young massive clusters.

scholarly journals Hierarchical fragmentation in high redshift galaxies revealed by hydrodynamical simulations

2021 ◽  
Author(s):  
Baptiste Faure ◽  
Frédéric Bournaud ◽  
Jérémy Fensch ◽  
Emanuele Daddi ◽  
Manuel Behrendt ◽  
...  
Keyword(s):  
Gravitational Lensing ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Gas Clusters ◽  
Very High ◽  
Redshift Galaxies

Abstract High-redshift star-forming galaxies have very different morphologies compared to nearby ones. Indeed, they are often dominated by bright star-forming structures of masses up to 108 − 9 M⊙ dubbed «giant clumps». However, recent observations questioned this result by showing only low-mass structures or no structure at all. We use Adaptative Mesh Refinement hydrodynamical simulations of galaxies with parsec-scale resolution to study the formation of structures inside clumpy high-redshift galaxies. We show that in very gas-rich galaxies star formation occurs in small gas clusters with masses below 107 − 8 M⊙ that are themselves located inside giant complexes with masses up to 108 and sometimes 109 M⊙ . Those massive structures are similar in mass and size to the giant clumps observed in imaging surveys, in particular with the Hubble Space Telescope. Using mock observations of simulated galaxies, we show that at very high resolution with instruments like the Atacama Large Millimeter Array or through gravitational lensing, only low-mass structures are likely to be detected, and their gathering into giant complexes might be missed. This leads to the non-detection of the giant clumps and therefore introduces a bias in the detection of these structures. We show that the simulated giant clumps can be gravitationally bound even when undetected in mocks representative for ALMA observations and HST observations of lensed galaxies. We then compare the top-down fragmentation of an initially warm disc and the bottom-up fragmentation of an initially cold disc to show that the process of formation of the clumps does not impact their physical properties.

scholarly journals What can the UV SED tell us about primitive galaxies?

2011 ◽  
Vol 7 (S284) ◽  
pp. 49-52 ◽  
Author(s):  
Sara R. Heap
Keyword(s):  
Dwarf Galaxy ◽  
High Redshift ◽  
High Redshift Galaxies ◽  
Very High ◽  
Redshift Galaxies

AbstractWe use the full SED of a well observed dwarf galaxy, I Zw 18, to evaluate what inferences can be made about very high-redshift galaxies from their UV SED's alone.

scholarly journals The accreted nuclear clusters of the Milky Way

2020 ◽  
Vol 500 (2) ◽  
pp. 2514-2524
Author(s):  
Joel Pfeffer ◽  
Carmela Lardo ◽  
Nate Bastian ◽  
Sara Saracino ◽  
Sebastian Kamann
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Star Clusters ◽  
Host Galaxy ◽  
The Galaxy ◽  
Nuclear Clusters ◽  
The Common ◽  
Massive Clusters ◽  
Peculiar Case

ABSTRACT A number of the massive clusters in the halo, bulge, and disc of the Galaxy are not genuine globular clusters (GCs) but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs and can be readily traced back to their host galaxy (e.g. M54 and the Sagittarius Dwarf galaxy), others have proven more elusive. Here, we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, ω Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken, and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate-mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster–cluster merger.

scholarly journals New methods for identifying Lyman continuum leakers and reionization-epoch analogues

2020 ◽  
Vol 498 (1) ◽  
pp. 164-180 ◽  
Author(s):  
Harley Katz ◽  
Dominika Ďurovčíková ◽  
Taysun Kimm ◽  
Joki Rosdahl ◽  
Jeremy Blaizot ◽  
...  
Keyword(s):  
Emission Line ◽  
Galaxy Formation ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Indirect Methods ◽  
High Redshift Galaxies ◽  
Lyman Continuum ◽  
The Universe ◽  
Ionization Parameter ◽  
Redshift Galaxies

ABSTRACT Identifying low-redshift galaxies that emit Lyman continuum radiation (LyC leakers) is one of the primary, indirect methods of studying galaxy formation in the epoch of reionization. However, not only has it proved challenging to identify such systems, it also remains uncertain whether the low-redshift LyC leakers are truly ‘analogues’ of the sources that reionized the Universe. Here, we use high-resolution cosmological radiation hydrodynamics simulations to examine whether simulated galaxies in the epoch of reionization share similar emission line properties to observed LyC leakers at z ∼ 3 and z ∼ 0. We find that the simulated galaxies with high LyC escape fractions (fesc) often exhibit high O32 and populate the same regions of the R23–O32 plane as z ∼ 3 LyC leakers. However, we show that viewing angle, metallicity, and ionization parameter can all impact where a galaxy resides on the O32–fesc plane. Based on emission line diagnostics and how they correlate with fesc, lower metallicity LyC leakers at z ∼ 3 appear to be good analogues of reionization-era galaxies. In contrast, local [S ii]-deficient galaxies do not overlap with the simulated high-redshift LyC leakers on the S ii Baldwin–Phillips–Terlevich (BPT) diagram; however, this diagnostic may still be useful for identifying leakers. We use our simulated galaxies to develop multiple new diagnostics to identify LyC leakers using infrared and nebular emission lines. We show that our model using only [C ii]158 μm and [O iii]88 μm can identify potential leakers from non-leakers from the local Dwarf Galaxy Survey. Finally, we apply this diagnostic to known high-redshift galaxies and find that MACS 1149_JD1 at z = 9.1 is the most likely galaxy to be actively contributing to the reionization of the Universe.

scholarly journals Constraining VLBI−optical offsets in high redshift galaxies using strong gravitational lensing

2020 ◽  
Vol 494 (2) ◽  
pp. 2312-2326 ◽  
Author(s):  
Cristiana Spingola ◽  
Anna Barnacka
Keyword(s):  
Gravitational Lensing ◽  
Angular Resolution ◽  
Hubble Space Telescope ◽  
High Redshift ◽  
Monte Carlo Sampling ◽  
High Angular Resolution ◽  
Radio Emissions ◽  
High Redshift Galaxies ◽  
Long Baseline ◽  
Redshift Galaxies

ABSTRACT We present a multiwavelength analysis of two highly magnified strong gravitationally lensed galaxies, CLASS B0712+472 and CLASS B1608+656, at redshifts 1.34 and 1.394, respectively, using new VLBI (very long baseline interferometry) and archival Hubble Space Telescope observations. We reconstruct the positions of the radio and optical emissions with their uncertainties using Monte Carlo sampling. We find that in CLASS B0712+472 the optical and radio emissions are co-spatial within 2 ± 5 mas (17 ± 42 pc at redshift of 1.34). But, in CLASS B1608+656, we reconstruct an optical–radio offset of 25 ± 16 mas (214 ± 137 pc at redshift of 1.394), among the smallest offsets measured for an AGN (active galactic nucleus) at such high redshift. The spectral features indicate that CLASS B1608+656 is a post-merger galaxy, which, in combination with the optical–VLBI offset reported here, makes CLASS B1608+656 a promising candidate for a high- z offset–AGN. Furthermore, the milliarcsecond angular resolution of the VLBI observations combined with the precise lens models allow us to spatially locate the radio emission at 0.05 mas precision (0.4 pc) in CLASS B0712+472, and 0.009 mas precision (0.08 pc) in CLASS B1608+656. The search for optical–radio offsets in high redshift galaxies will be eased by the upcoming synoptic all-sky surveys, including Extremely Large Telescope and Square Kilometre Array, which are expected to find ∼105 strongly lensed galaxies, opening an era of large strong lensing samples observed at high angular resolution.

Constraining Galaxy Formation Epoch

2005 ◽  
Vol 201 ◽  
pp. 536-537
Author(s):  
Sukyoung. Yi ◽  
T. Brown ◽  
S. Heap ◽  
I. Hubeny ◽  
W. Landsman ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
High Redshift ◽  
Population Synthesis ◽  
High Redshift Galaxies ◽  
The Galaxy ◽  
The Difference ◽  
Age Estimates ◽  
Good Agreement ◽  
Redshift Galaxies

Pinning down the ages of high redshift galaxies is the most direct way of constraining the galaxy formation epoch. There has been a debate on the age of LBDS 53W091, a red galaxy at z=1.5. The discrepancy in the age estimates of various groups is due to the difference in the population synthesis model. However, there is generally a good agreement among popular models. Polishing the models and assessing their internal uncertainties are crucial in the analysis of high redshift galaxies.

scholarly journals GLACiAR, an Open-Source Python Tool for Simulations of Source Recovery and Completeness in Galaxy Surveys

2018 ◽  
Vol 35 ◽  
Author(s):  
D. Carrasco ◽  
M. Trenti ◽  
S. Mutch ◽  
P. A. Oesch
Keyword(s):  
Hubble Space Telescope ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Software Tool ◽  
Spectral Energy ◽  
High Redshift Galaxies ◽  
Galaxy Surveys ◽  
Modelling Assumptions ◽  
Number Counts ◽  
Cosmic History

AbstractThe luminosity function is a fundamental observable for characterising how galaxies form and evolve throughout the cosmic history. One key ingredient to derive this measurement from the number counts in a survey is the characterisation of the completeness and redshift selection functions for the observations. In this paper, we present GLACiAR, an open python tool available on GitHub to estimate the completeness and selection functions in galaxy surveys. The code is tailored for multiband imaging surveys aimed at searching for high-redshift galaxies through the Lyman-break technique, but it can be applied broadly. The code generates artificial galaxies that follow Sérsic profiles with different indexes and with customisable size, redshift, and spectral energy distribution properties, adds them to input images, and measures the recovery rate. To illustrate this new software tool, we apply it to quantify the completeness and redshift selection functions for J-dropouts sources (redshift z ~ 10 galaxies) in the Hubble Space Telescope Brightest of Reionizing Galaxies Survey. Our comparison with a previous completeness analysis on the same dataset shows overall agreement, but also highlights how different modelling assumptions for the artificial sources can impact completeness estimates.

scholarly journals High-redshift Galaxies and Black Holes Detectable with theJWST: A Population Synthesis Model from Infrared to X-Rays

2017 ◽  
Vol 849 (2) ◽  
pp. 155 ◽  
Author(s):  
Marta Volonteri ◽  
Amy E. Reines ◽  
Hakim Atek ◽  
Daniel P. Stark ◽  
Maxime Trebitsch
Keyword(s):  
Black Holes ◽  
High Redshift ◽  
X Rays ◽  
Population Synthesis ◽  
High Redshift Galaxies ◽  
Redshift Galaxies

scholarly journals On the initial mass-radius relation of stellar clusters

2021 ◽  
Author(s):  
Nick Choksi ◽  
J M Diederik Kruijssen
Keyword(s):  
High Pressure ◽  
Globular Clusters ◽  
High Redshift ◽  
Cluster Formation ◽  
Stellar Clusters ◽  
Population Synthesis ◽  
Star Forming ◽  
Massive Clusters ◽  
Good Agreement ◽  
Environmental Dependence

Abstract Young stellar clusters across nearly five orders of magnitude in mass appear to follow a power-law mass-radius relationship (MRR), $R_{\star }\propto M_{\star }^{\alpha }$, with α ≈ 0.2 − 0.33. We develop a simple analytic model for the cluster mass-radius relation. We consider a galaxy disc in hydrostatic equilibrium, which hosts a population of molecular clouds that fragment into clumps undergoing cluster formation and feedback-driven expansion. The model predicts a mass-radius relation of $R_{\star }\propto M_{\star }^{1/2}$ and a dependence on the kpc-scale gas surface density $R_{\star }\propto \Sigma _{\rm g}^{-1/2}$, which results from the formation of more compact clouds (and cluster-forming clumps within) at higher gas surface densities. This environmental dependence implies that the high-pressure environments in which the most massive clusters can form also induce the formation of clusters with the smallest radii, thereby shallowing the observed MRR at high-masses towards the observed $R_{\star }\propto M_{\star }^{1/3}$. At low cluster masses, relaxation-driven expansion induces a similar shallowing of the MRR. We combine our predicted MRR with a simple population synthesis model and apply it to a variety of star-forming environments, finding good agreement. Our model predicts that the high-pressure formation environments of globular clusters at high redshift naturally led to the formation of clusters that are considerably more compact than those in the local Universe, thereby increasing their resilience to tidal shock-driven disruption and contributing to their survival until the present day.

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