scholarly journals Stars and gas in the most metal-poor galaxies – I. COS and MUSE observations of SBS 0335−052E

2020 ◽  
Vol 500 (3) ◽  
pp. 2908-2927
Author(s):  
Aida Wofford ◽  
Alba Vidal-García ◽  
Anna Feltre ◽  
Jacopo Chevallard ◽  
Stéphane Charlot ◽  
...  
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Spectral Synthesis ◽  
Optical Emission ◽  
Rotating Stars ◽  
Test Models ◽  
The Galaxy ◽  
Low Metallicity ◽  
Super Star Clusters ◽  
Shock Precursor

ABSTRACT Among the nearest most metal-poor starburst-dwarf galaxies known, SBS 0335−052E is the most luminous in integrated nebular He ii λ4686 emission. This makes it a unique target to test spectral synthesis models and spectral interpretation tools of the kind that will be used to interpret future rest-frame UV observations of primeval galaxies. Previous attempts to reproduce its He ii λ4686 luminosity found that X-ray sources, shocks, and single Wolf–Rayet stars are not main contributors to the He ii-ionizing budget; and that only metal-free single rotating stars or binary stars with a top-heavy IMF and an unphysically low metallicity can reproduce it. We present new UV (COS) and optical (MUSE) spectra that integrate the light of four super star clusters in SBS 0335−052E. Nebular He ii, [C iii], C iii], C iv, and O iii] UV emission lines with equivalent widths between 1.7 and 5 Å and a C iv λλ1548, 1551 P-Cygni like profile are detected. Recent extremely metal-poor shock + precursor models and binary models fail to reproduce the observed optical emission-line ratios. We use different sets of UV and optical observables to test models of constant star formation with single non-rotating stars that account for very massive stars as blueshifted O v λ1371 absorption is present. Simultaneously fitting the fluxes of all high-ionization UV lines requires an unphysically low metallicity. Fitting the P-Cygni like + nebular components of C iv λλ1548, 1551 does not constrain the stellar metallicity and time since the beginning of star formation. We obtain 12+log(O/H)$\, = 7.45\pm 0.04$ and log(C/O)$\, = -0.45^{+0.03}_{-0.04}$ for the galaxy. Model testing would benefit from higher spatial resolution UV and optical spectroscopy of the galaxy.

scholarly journals The Herschel Dwarf Galaxy Survey

2019 ◽  
Vol 626 ◽  
pp. A23 ◽  
Author(s):  
D. Cormier ◽  
N. P. Abel ◽  
S. Hony ◽  
V. Lebouteiller ◽  
S. C. Madden ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Spectral Synthesis ◽  
Line Emission ◽  
Ionized Gas ◽  
Star Forming ◽  
Gas Phases ◽  
Physical Conditions ◽  
Radiation Fields ◽  
Low Metallicity

The sensitive infrared telescopes, Spitzer and Herschel, have been used to target low-metallicity star-forming galaxies, allowing us to investigate the properties of their interstellar medium (ISM) in unprecedented detail. Interpretation of the observations in physical terms relies on careful modeling of those properties. We have employed a multiphase approach to model the ISM phases (H II region and photodissociation region) with the spectral synthesis code Cloudy. Our goal is to characterize the physical conditions (gas densities, radiation fields, etc.) in the ISM of the galaxies from the Herschel Dwarf Galaxy Survey. We are particularly interested in correlations between those physical conditions and metallicity or star-formation activity. Other key issues we have addressed are the contribution of different ISM phases to the total line emission, especially of the [C II]157 μm line, and the characterization of the porosity of the ISM. We find that the lower-metallicity galaxies of our sample tend to have higher ionization parameters and galaxies with higher specific star-formation rates have higher gas densities. The [C II] emission arises mainly from PDRs and the contribution from the ionized gas phases is small, typically less than 30% of the observed emission. We also find a correlation – though with scatter – between metallicity and both the PDR covering factor and the fraction of [C II] from the ionized gas. Overall, the low metal abundances appear to be driving most of the changes in the ISM structure and conditions of these galaxies, and not the high specific star-formation rates. These results demonstrate in a quantitative way the increase of ISM porosity at low metallicity. Such porosity may be typical of galaxies in the young Universe.

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 The star formation history of galaxies in 3D: CALIFA perspective

2014 ◽  
Vol 10 (S309) ◽  
pp. 99-104
Author(s):  
R. M. González Delgado ◽  
R. Cid Fernandes ◽  
R. García-Benito ◽  
E. Pérez ◽  
A. L. de Amorim ◽  
...  
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Spectral Synthesis ◽  
Stellar Mass ◽  
Star Formation History ◽  
Chemical Enrichment ◽  
Radial Profiles ◽  
Formation History ◽  
The Galaxy ◽  
History Of

AbstractWe resolve spatially the star formation history of 300 nearby galaxies from the CALIFA integral field survey to investigate: a) the radial structure and gradients of the present stellar populations properties as a function of the Hubble type; and b) the role that plays the galaxy stellar mass and stellar mass surface density in governing the star formation history and metallicity enrichment of spheroids and the disks of galaxies. We apply the fossil record method based on spectral synthesis techniques to recover spatially and temporally resolved maps of stellar population properties of spheroids and spirals with galaxy mass from 109 to 7×1011 M⊙. The individual radial profiles of the stellar mass surface density (μ⋆), stellar extinction (AV), luminosity weighted ages (〈logage〉L), and mass weighted metallicity (〈log Z/Z⊙〉M) are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc and Sd). All these properties show negative gradients as a sight of the inside-out growth of massive galaxies. However, the gradients depend on the Hubble type in different ways. For the same galaxy mass, E and S0 galaxies show the largest inner gradients in μ⋆; and Andromeda-like galaxies (Sb with log M⋆ (M⊙) ∼ 11) show the largest inner age and metallicity gradients. In average, spiral galaxies have a stellar metallicity gradient ∼ −0.1 dex per half-light radius, in agreement with the value estimated for the ionized gas oxygen abundance gradient by CALIFA. A global (M⋆-driven) and local (μ⋆-driven) stellar metallicity relation are derived. We find that in disks, the stellar mass surface density regulates the stellar metallicity; in spheroids, the galaxy stellar mass dominates the physics of star formation and chemical enrichment.

scholarly journals Cosmic archaeology with massive stellar black hole binaries

2020 ◽  
Vol 495 (1) ◽  
pp. L81-L85 ◽  
Author(s):  
L Graziani ◽  
R Schneider ◽  
S Marassi ◽  
W Del Pozzo ◽  
M Mapelli ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Gravitational Wave ◽  
Galaxy Formation ◽  
Population Synthesis ◽  
Formation Model ◽  
Black Hole Binaries ◽  
The Galaxy ◽  
Low Metallicity ◽  
Black Hole Masses

ABSTRACT The existence of massive stellar black hole binaries (MBHBs), with primary black hole masses $\ge 31 \, \mathrm{ M}_\odot$, was proven by the detection of the gravitational wave (GW) event GW150914 during the first LIGO/Virgo observing run (O1), and successively confirmed by seven additional GW signals discovered in the O1 and O2 data. By adopting the galaxy formation model gamesh coupled with binary population synthesis (BPS) calculations, here we investigate the origin of these MBHBs by selecting simulated binaries compatible in mass and coalescence redshifts. We find that their cosmic birth rates peak in the redshift range 6.5 ≤ z ≤ 10, regardless of the adopted BPS. These MBHBs are then old systems forming in low-metallicity ($Z \sim [0.01\!-\!0.1] \, Z_{\odot }$), low-stellar-mass galaxies, before the end of cosmic reionization, i.e. significantly beyond the peak of cosmic star formation. GW signals generated by coalescing MBHBs open up new possibilities to probe the nature of stellar populations in remote galaxies, at present too faint to be detected by available electromagnetic facilities.

An H I Mosaic of the Small Magellanic Cloud

1995 ◽  
Vol 12 (1) ◽  
pp. 13-19 ◽  
Author(s):  
L. Staveley-Smith ◽  
R. J. Sault ◽  
D. McConnell ◽  
M. J. Kesteven ◽  
D. Hatzidimitriou ◽  
...  
Keyword(s):  
Star Formation ◽  
Neutral Hydrogen ◽  
Optical Emission ◽  
Magellanic Cloud ◽  
Molecular Gas ◽  
Small Magellanic Cloud ◽  
High Brightness ◽  
First Results ◽  
Low Metallicity ◽  
High Column

AbstractThis paper describes the first results from a 20 deg2 mosaic of the Small Magellanic Cloud (SMC) in the λ21-cm line of neutral hydrogen. The mosaic consists of 320 separate pointings with the 375-m array of the Australia Telescope Compact Array. The angular resolution is 1′· 5 (26 pc, for a distance of 60 kpc) and the velocity resolution is l·6kms−1. The images reveal a structure of remarkable complexity, with much of the spatial power contained in high-brightness temperature compact knots and filaments. Numerous wind-blown ‘bubbles’ and ‘supershells’ are evident in the data, both inside and outside the stellar confines of the SMC. Some high-density H I regions are seen to correlate with Hα regions, indicating sites of current star formation. However, many high-column-density H I regions are devoid of optical emission and may represent regions of future star formation. These regions may be under-abundant in diffuse molecular gas due to the high radiation field and low metallicity of the SMC.

scholarly journals Stars and Gas in the Large Interacting Galaxy NGC 6872

2004 ◽  
Vol 217 ◽  
pp. 422-423 ◽  
Author(s):  
Cathy Horellou ◽  
Bärbel Koribalski
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Spiral Galaxies ◽  
The Other ◽  
Dark Matter Halo ◽  
Stellar Clusters ◽  
Test Models ◽  
The Galaxy ◽  
Tidal Perturbations ◽  
Tidal Tails

The luminous barred galaxy NGC 6872 is one of the largest spiral galaxies known. Star formation occurs all along the arms, which extend over more than 100 kpc. The galaxy experiences tidal perturbations from the nearby companion IC 4970 passing by on a low-inclination, prograde orbit. We have mapped the large-scale distribution and kinematics of the atomic gas (HI) in the NGC 6872/IC 4970 system and carried out N-body simulations with stars and gas. HI is absent from the central region; on the other hand, large gas concentrations are found at the tip of the tidal arms, spatially coincident with the blue stellar clusters and with the peaks of the Hα distribution. We use that remarkable system to investigate the evolution of gas and stars in a close prograde encounter, examine the influence of a dark matter halo on the length of the tidal tails, and test models of collisionally induced star formation.

scholarly journals Star Formation in Tadpole Galaxies

2014 ◽  
Vol 1 (1) ◽  
pp. 96-102 ◽  
Author(s):  
Casiana Muñoz-Tuñon ◽  
Jorge Sanchez Almeida ◽  
Debra M. Elmegreen ◽  
Bruce G. Elmegreen
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
High Redshift ◽  
Star Forming ◽  
Spatially Resolved ◽  
Test Models ◽  
The Galaxy ◽  
Galaxy Disk ◽  
Tail Structure ◽  
Remarkable Result

Tadpole Galaxies look like a star forming head with a tail structure to the side. They are also named cometaries. In a series of recent works we have discovered a number of issues that lead us to consider them extremely interesting targets. First, from images, they are disks with a lopsided starburst. This result is rmly  established with long slit spectroscopy in a nearby representative sample. They rotate with the head following the rotation pattern but displaced from the rotation center. Moreover, in a search for extremely metal poor (XMP) galaxies, we identied tadpoles as the dominant shapes in the sample - nearly 80% of the local XMP galaxies have a tadpole morphology. In addition, the spatially resolved analysis of the metallicity shows the remarkable result that there is a metallicity drop right at the position of the head. This is contrary to what intuition would say and dicult to explain if star formation has happened from gas processed in the disk. The result could however be understood if the star formation is driven by pristine gas falling into the galaxy disk. If conrmed, we could be unveiling, for the rst time, cool  ows in action in our nearby world. The tadpole class is relatively frequent at high redshift - 10% of resolvable galaxies in the Hubble UDF but less than 1% in the local Universe. They are systems that could track cool ows and test models of galaxy formation.

scholarly journals Super star clusters in Hii galaxies

2009 ◽  
Vol 5 (S266) ◽  
pp. 447-450
Author(s):  
Patricio Lagos ◽  
Eduardo Telles ◽  
E. R. Carrasco
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Massive Star ◽  
Star Clusters ◽  
Dominant Mode ◽  
Star Cluster ◽  
The Galaxy ◽  
Super Star Clusters ◽  
Field Unit ◽  
The Masses

AbstractWe summarize our results based on observations with the NIRI camera on the Gemini North telescope of three Hii galaxies (Mrk 36, UM 408 and UM 461), obtained to identify and determine the ages and masses of the elementary components (the star cluster population) of the starburst regions in compact Hii galaxies. Our preliminary results indicate that the masses of the stellar clusters in these galaxies range from ~104 to ~106 M⊙, with associated ages of a few Myr. The most massive star clusters fall in the so-called super star cluster category. The identification of these clusters suggests that the formation and evolution of massive star clusters is the dominant mode of star formation in these galaxies. Their spatial distribution and ages seem to indicate that star formation is simultaneous over these timescales in some of our objects. We also review our recent description of the spatial distribution of physical conditions in the Hii galaxy UM 408 using the GMOS integral-field unit on Gemini South. The spatial distribution of the oxygen abundance does not show any significant variation or gradient across the galaxy on scales of hundreds of parsecs, within our observational uncertainties, confirming that this compact Hii galaxy, like other previously studied dwarf irregular galaxies, is chemically homogeneous.

scholarly journals A VLT/MUSE analysis of HeIIλ1640 emitters at z = 2 – 4

2019 ◽  
Vol 15 (S352) ◽  
pp. 78-78
Author(s):  
Themiya Nanayakkara
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Stellar Population ◽  
Population Models ◽  
X Ray ◽  
Uv Emission ◽  
Low Metallicity ◽  
Star Formation Histories ◽  
X Ray Binaries ◽  
The Universe

AbstractIn the quest to study early star-formation physics in the universe, one of the most sought after tracers is HeIIλ1640, with its presence in the lack of other metal emission/absorption lines generally being interpreted as evidence for metal-poor stellar populations. HeII ionizing photons are produced via sources of hard ionizing radiation and requires photons with energies ⩾ 54.4eV, however, traditional stellar population models lack sufficient ionising photons to match with current observations. Our analysis of z = 2 – 4 HeIIλ1640 emitters from deep 10-30h pointings from MUSE has shown that ISM properties inferred from multiple rest-UV diagnostics are not compatible with requirements necessary to reproduce HeIIλ1640 equivalent-widths. Thus, we have used latest generation of single, rotational, and binary stellar population models with realistic dust physics to explore rest-UV emission line diagnostics and link with H and He+ ionisation photon production efficiencies (ξion (H,He+)) in a variety of stellar/gas metallicities and star-formation histories. I will discus our latest results and show that including ‘exotic’ stellar phenomena such as extreme low-metallicity binary stars, X-ray binaries, and dust dissociation physics may be necessary to lessen the tension between models and observations.

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