scholarly journals The stellar populations of high-redshift dwarf galaxies

2020 ◽  
Vol 498 (3) ◽  
pp. 4134-4149
Author(s):  
V Gelli ◽  
S Salvadori ◽  
A Pallottini ◽  
A Ferrara
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Formation Rate ◽  
Stellar Populations ◽  
High Mass ◽  
Evolutionary Patterns ◽  
Chemical Enrichment ◽  
Stellar Feedback

ABSTRACT We use high-resolution (≈10 pc), zoom-in simulations of a typical (stellar mass $M_\star \simeq 10^{10}\, {\rm M}_{\odot }$) Lyman Break Galaxy (LBG) at z ≃ 6 to investigate the stellar populations of its six dwarf galaxy satellites, whose stellar [gas] masses are in the range log (M⋆/M⊙) ≃ 6−9 [log (Mgas/M⊙) ≃ 4.3−7.75]. The properties and evolution of satellites show no dependence on the distance from the central massive LBG (<11.5 kpc). Instead, their star formation and chemical enrichment histories are tightly connected to their stellar (and sub-halo) mass. High-mass dwarf galaxies ($M_\star \gtrsim 5\times 10^8 \, {\rm M}_{\odot }$) experience a long history of star formation, characterized by many merger events. Lower mass systems go through a series of short star formation episodes, with no signs of mergers; their star formation activity starts relatively late (z ≈ 7), and it is rapidly quenched by internal stellar feedback. In spite of the different evolutionary patterns, all satellites show a spherical morphology, with ancient and more metal-poor stars located towards the inner regions. All six dwarf satellites experienced high star formation rate ($\rm \gt 5\, {\rm M}_{\odot }\, {\rm yr}^{-1}$) bursts, which can be detected by James Webb Space Telescope while targeting high-z LBGs.

Dwarf galaxies at low and high redshift

2018 ◽  
Vol 14 (S344) ◽  
pp. 437-445
Author(s):  
Xu Kong ◽  
Jianhui Lian ◽  
Yulong Gao ◽  
Zuyi Chen ◽  
Guangwen Chen ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Near Infrared ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Formation Rate ◽  
Mass Star ◽  
Chemical Enrichment ◽  
Galaxy Sample

AbstractThe overwhelming majority of galaxies in the Universe are dwarf galaxies. But although they are important components in understanding galaxy evolution, these systems are typically too faint to be observed at high redshifts. However, we are able to obtain an unobscured view of early star formation and chemical enrichment in these galaxies at low redshift and low-redshift analogs at high redshift. In this talk, I will review the mass-metallicity relation, the mass-star formation rate relation of galaxies, the classifications of dwarf galaxies, and the importance of dwarf galaxies for both astronomy and physics. Then I will introduce some work in our group on connections among between different types of dwarf galaxies,the mass-metallicity relations and the main sequence relations of dwarf galaxies, using the deep optical and near infrared images and spectra of large dwarf galaxy sample. At the end, I will talk about some projects of dwarf galaxies we are working on, including the spectroscopic survey for compact dwarf galaxies using the LAMOST.

scholarly journals Exploration of the high-redshift universe enabled by THESEUS

2021 ◽  
Author(s):  
N. R. Tanvir ◽  
E. Le Floc’h ◽  
L. Christensen ◽  
J. Caruana ◽  
R. Salvaterra ◽  
...  
Keyword(s):  
Star Formation ◽  
Gamma Ray ◽  
High Redshift ◽  
Formation Rate ◽  
Star Forming ◽  
Chemical Enrichment ◽  
Long Duration ◽  
Absorption Studies ◽  
Population Iii Stars ◽  
High Redshift Universe

AbstractAt peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer of star formation and star-forming galaxies over the whole of cosmic history. Their bright power-law afterglows provide ideal backlights for absorption studies of the interstellar and intergalactic medium back to the reionization era. The proposed THESEUS mission is designed to detect large samples of GRBs at z > 6 in the 2030s, at a time when supporting observations with major next generation facilities will be possible, thus enabling a range of transformative science. THESEUS will allow us to explore the faint end of the luminosity function of galaxies and the star formation rate density to high redshifts; constrain the progress of re-ionisation beyond $z\gtrsim 6$ z ≳ 6 ; study in detail early chemical enrichment from stellar explosions, including signatures of Population III stars; and potentially characterize the dark energy equation of state at the highest redshifts.

scholarly journals Observations of the Lyman-α Universe

2020 ◽  
Vol 58 (1) ◽  
pp. 617-659
Author(s):  
Masami Ouchi ◽  
Yoshiaki Ono ◽  
Takatoshi Shibuya
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
High Redshift ◽  
Formation Rate ◽  
Neutral Hydrogen ◽  
Resonant Scattering ◽  
Dark Matter Halo ◽  
Emission Data ◽  
Star Forming ◽  
High Redshift Universe

Hydrogen Lyman-α (Lyα) emission has been one of the major observational probes for the high-redshift Universe since the first discoveries of high- z Lyα-emitting galaxies in the late 1990s. Due to the strong Lyα emission originated by resonant scattering and recombination of the most abundant element, Lyα observations witness not only Hii regions of star formation and active galactic nuclei (AGNs) but also diffuse Hi gas in the circumgalactic medium (CGM) and the intergalactic medium (IGM). Here, we review Lyα sources and present theoretical interpretations reached to date. We conclude the following: ▪  A typical Lyα emitter (LAE) at z ≳ 2 with a L* Lyα luminosity is a high- z counterpart of a local dwarf galaxy, a compact metal-poor star-forming galaxy (SFG) with an approximate stellar (dark matter halo) mass and star-formation rate of 108−9M⊙ (1010−11M⊙) and 1–10 M⊙ year−1, respectively. ▪  High- z SFGs ubiquitously have a diffuse Lyα-emitting halo in the CGM extending to the halo virial radius and beyond. ▪  Remaining neutral hydrogen at the epoch of cosmic reionization makes a strong dimming of Lyα emission for galaxies at z > 6 that suggests the late reionization history. The next-generation large-telescope projects will combine Lyα emission data with Hi Lyα absorptions and 21-cm radio data that map out the majority of hydrogen (Hi+Hii) gas, uncovering the exchanges of ( a) matter by outflow and inflow and ( b) radiation, relevant to cosmic reionization, between galaxies and the CGM/IGM.

scholarly journals Testing the Relationship between Bursty Star Formation and Size Fluctuations of Local Dwarf Galaxies

2021 ◽  
Vol 922 (2) ◽  
pp. 217
Author(s):  
Najmeh Emami ◽  
Brian Siana ◽  
Kareem El-Badry ◽  
David Cook ◽  
Xiangcheng Ma ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Formation Rate ◽  
Critical Role ◽  
Space Telescopes ◽  
Large Space ◽  
Stellar Feedback ◽  
Band Size ◽  
Low Mass ◽  
Stellar Masses

Abstract Stellar feedback in dwarf galaxies plays a critical role in regulating star formation via galaxy-scale winds. Recent hydrodynamical zoom-in simulations of dwarf galaxies predict that the periodic outward flow of gas can change the gravitational potential sufficiently to cause radial migration of stars. To test the effect of bursty star formation on stellar migration, we examine star formation observables and sizes of 86 local dwarf galaxies. We find a correlation between the R-band half-light radius (R e ) and far-UV luminosity (L FUV) for stellar masses below 108 M ⊙ and a weak correlation between the R e and Hα luminosity (L Hα ). We produce mock observations of eight low-mass galaxies from the FIRE-2 cosmological simulations and measure the similarity of the time sequences of R e and a number of star formation indicators with different timescales. Major episodes of R e time sequence align very well with the major episodes of star formation, with a delay of ∼50 Myr. This correlation decreases toward star formation rate indicators of shorter timescales such that R e is weakly correlated with L FUV (10–100 Myr timescale) and is completely uncorrelated with L Hα (a few Myr timescale), in agreement with the observations. Our findings based on FIRE-2 suggest that the R-band size of a galaxy reacts to star formation variations on a ∼50 Myr timescale. With the advent of a new generation of large space telescopes (e.g., JWST), this effect can be examined explicitly in galaxies at higher redshifts, where bursty star formation is more prominent.

scholarly journals Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM

2019 ◽  
Vol 490 (4) ◽  
pp. 5538-5550 ◽  
Author(s):  
Saundra M Albers ◽  
Daniel R Weisz ◽  
Andrew A Cole ◽  
Andrew E Dolphin ◽  
Evan D Skillman ◽  
...  
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Optimal Path ◽  
Stellar Mass ◽  
Star Formation History ◽  
Stellar Feedback ◽  
Formation History

ABSTRACT We present the star formation history (SFH) of the isolated (D ∼ 970 kpc) Local Group dwarf galaxy Wolf–Lundmark–Melotte (WLM) measured from colour–magnitude diagrams (CMDs) constructed from deep Hubble Space Telescope imaging. Our observations include a central ($0.5 \, r_h$) and outer field ($0.7 \, r_h$) that reach below the oldest main-sequence turn-off. WLM has no early dominant episode of star formation: 20 per cent of its stellar mass formed by ∼12.5 Gyr ago ($z$ ∼ 5). It also has an SFR that rises to the present with 50 per cent of the stellar mass within the most recent 5 Gyr ($z$ < 0.7). There is evidence of a strong age gradient: the mean age of the outer field is 5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models suggest such steep gradients are associated with strong stellar feedback and dark-matter core creation. The SFHs of real isolated dwarf galaxies and those from the Feedback in Realistic Environment suite are in good agreement for M⋆($z$ = 0) ∼ 107–109M⊙, but in worse agreement at lower masses ($M_{\star }(z=0) \sim 10^5\!-\!10^7 \, \mathrm{M}_{\odot }$). These differences may be explainable by systematics in the models (e.g. reionization model) and/or observations (HST field placement). We suggest that a coordinated effort to get deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo coverage) is the optimal path for measuring global SFHs of isolated dwarf galaxies.

scholarly journals Forming early-type galaxies without AGN feedback: a combination of merger-driven outflows and inefficient star formation

2019 ◽  
Vol 492 (1) ◽  
pp. 1385-1398 ◽  
Author(s):  
Michael Kretschmer ◽  
Romain Teyssier
Keyword(s):  
Star Formation ◽  
Numerical Models ◽  
High Redshift ◽  
Formation Rate ◽  
Small Scale ◽  
Molecular Gas ◽  
Early Type ◽  
Perfect Agreement ◽  
Stellar Feedback ◽  
Major Merger

ABSTRACT Regulating the available gas mass inside galaxies proceeds through a delicate balance between inflows and outflows, but also through the internal depletion of gas due to star formation. At the same time, stellar feedback is the internal engine that powers the strong outflows. Since star formation and stellar feedback are both small-scale phenomena, we need a realistic and predictive subgrid model for both. We describe the implementation of supernova momentum feedback and star formation based on the turbulence of the gas in the ramses code. For star formation, we adopt the so-called multifreefall model. The resulting star formation efficiencies can be significantly smaller or bigger than the traditionally chosen value of $1\, {\rm per\, cent}$. We apply these new numerical models to a prototype cosmological simulation of a massive halo that features a major merger which results in the formation of an early-type galaxy without using AGN feedback. We find that the feedback model provides the first-order mechanism for regulating the stellar and baryonic content in our simulated galaxy. At high redshift, the merger event pushes gas to large densities and large turbulent velocity dispersions, such that efficiencies come close to $10\, {\rm per\, cent}$, resulting in large star formation rate (SFR). We find small molecular gas depletion time during the starburst, in perfect agreement with observations. Furthermore, at late times, the galaxy becomes quiescent with efficiencies significantly smaller than $1\, {\rm per\, cent}$, resulting in small SFR and long molecular gas depletion time.

scholarly journals The sensitivity of stellar feedback to IMF averaging versus IMF sampling in galaxy formation simulations

2021 ◽  
Vol 502 (4) ◽  
pp. 5417-5437
Author(s):  
Matthew C Smith
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
H Ii Regions ◽  
Stellar Feedback ◽  
Stellar Masses ◽  
The Imf

ABSTRACT Galaxy formation simulations frequently use initial mass function (IMF) averaged feedback prescriptions, where star particles are assumed to represent single stellar populations that fully sample the IMF. This approximation breaks down at high mass resolution, where stochastic variations in stellar populations become important. We discuss various schemes to populate star particles with stellar masses explicitly sampled from the IMF. We use Monte Carlo numerical experiments to examine the ability of the schemes to reproduce an input IMF in an unbiased manner while conserving mass. We present our preferred scheme which can easily be added to pre-existing star formation prescriptions. We then carry out a series of high-resolution isolated simulations of dwarf galaxies with supernovae (SNe), photoionization, and photoelectric heating to compare the differences between using IMF averaged feedback and explicitly sampling the IMF. We find that if SNe are the only form of feedback, triggering individual SNe from IMF averaged rates gives identical results to IMF sampling. However, we find that photoionization is more effective at regulating star formation when IMF averaged rates are used, creating more, smaller H ii regions than the rare, bright sources produced by IMF sampling. We note that the increased efficiency of the IMF averaged feedback versus IMF sampling is not necessarily a general trend and may be reversed depending on feedback channel, resolution and other details. However, IMF sampling is always the more physically motivated approach. We conservatively suggest that it should be used for star particles less massive than $\sim 500\, \mathrm{M_\odot }$.

scholarly journals The Local Group Dwarf Galaxies. The Star Formation Histories derived using the Long Period Variable Stars

2018 ◽  
Vol 14 (S344) ◽  
pp. 125-129
Author(s):  
Elham Saremi ◽  
Atefeh Javadi ◽  
Jacco Th. van Loon ◽  
Habib Khosroshahi ◽  
Sara Rezaei kh ◽  
...  
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Variable Stars ◽  
Star Formation History ◽  
Long Period ◽  
Period Variable ◽  
Monitoring Survey

AbstractDwarf galaxies in the Local Group (LG) represent a distinct as well as diverse family of tracers of the earliest phases of galaxy assembly and the processing resulting from galactic harrassment. Their stellar populations can be resolved and used as probes of the evolution of their host galaxy. In this regard, we present the first reconstruction of the star formation history (SFH) of them using the most evolved AGB stars that are long period variable (LPV). LPV stars trace stellar populations as young as ∼ 30 Myr to as old as the oldest globular clusters. For the nearby, relatively massive and interacting gas-rich dwarf galaxies, the Magellanic Clouds, we found that the bulk of the stars formed ∼ 10 Gyr ago for the LMC, while the strongest episode of star formation in the SMC occurred a few Gyr later. A peak in star formation around 0.7 Gyr ago in both Clouds is likely linked to their recent interaction. The Andromeda satellite pair NGC147/185 show different histories; the main epoch of star formation for NGC 185 occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate (SFR). In the case of NGC 147, the SFR peaked only 6.9 Gyr ago, staying intense until ∼ 3 Gyr ago. Star formation in the isolated gas-rich dwarf galaxy IC 1613 has proceeded at a steady rate over the past 5 Gyr, without any particular dominant epoch. Due to lack of sufficient data, we have conducted an optical monitoring survey at the Isaac Newton Telescope (INT) of 55 dwarf galaxies in the LG to reconstruct the SFH of them uniformly. The observations are made over ten epochs, spaced approximately three months apart, as the luminosity of LPV stars varies on timescales of months to years. The system of galactic satellites of the large Andromeda spiral galaxy (M31) forms one of the key targets of our monitoring survey. We present the first results in the And I dwarf galaxy, where we discovered 116 LPVs among over 10,000 stars.

scholarly journals Lyman-alpha opacities at z=4-6 require low mass, radiatively-suppressed galaxies to drive cosmic reionization

2021 ◽  
Author(s):  
Pierre Ocvirk ◽  
Joseph S W Lewis ◽  
Nicolas Gillet ◽  
Jonathan Chardin ◽  
Dominique Aubert ◽  
...  
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
High Redshift ◽  
Formation Rate ◽  
High Mass ◽  
Lyman Alpha ◽  
Low Mass ◽  
Halo Population ◽  
Fully Coupled ◽  
Two Populations

Abstract The high redshift Lyman-α forest, in particular the Gunn-Peterson trough, is the most unambiguous signature of the neutral to ionized transition of the intergalactic medium (IGM) taking place during the Epoch of Reionization (EoR). Recent studies have shown that reproducing the observed Lyman-α opacity distributions after overlap required a non-monotonous evolution of cosmic emissivity: rising, peaking at z∼6, and then decreasing onwards to z=4. Such an evolution is puzzling considering galaxy buildup and the cosmic star formation rate are still continously on the rise at these epochs. Here, we use new RAMSES-CUDATON simulations to show that such a peaked evolution may occur naturally in a fully coupled radiation-hydrodynamical framework. In our fiducial run, cosmic emissivity at z>6 is dominated by a low mass (${\rm M_{DM}}<2 \times 10^9 \rm M_{\odot }$), high escape fraction halo population, driving reionization, up to overlap. Approaching z=6, this population is radiatively suppressed due to the rising ionizing UV background, and its emissivity drops. In the meantime, the high mass halo population builds up and its emissivity rises, but not fast enough to compensate the dimming of the low mass haloes, because of low escape fractions. The combined ionizing emissivity of these two populations therefore naturally results in a rise and fall of the cosmic emissivity, from z=12 to z=4, with a peak at z∼6. An alternative run, which features higher escape fractions for the high mass haloes and later suppression at low mass, leads to overshooting the ionizing rate, over-ionizing the IGM and therefore too low Lyman-α opacities.

scholarly journals The gas, metal, and dust evolution in low-metallicity local and high-redshift galaxies

2020 ◽  
Vol 641 ◽  
pp. A168 ◽  
Author(s):  
A. Nanni ◽  
D. Burgarella ◽  
P. Theulé ◽  
B. Côté ◽  
H. Hirashita
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Massive Stars ◽  
High Redshift ◽  
Stellar Mass ◽  
Type Ii ◽  
Chemical Enrichment ◽  
Dust Mass ◽  
Low Metallicity ◽  
Dust Evolution

Context. The chemical enrichment in the interstellar medium (ISM) of galaxies is regulated by several physical processes: star birth and death, grain formation and destruction, and galactic inflows and outflows. Understanding such processes and their relative importance is essential to following galaxy evolution and the chemical enrichment through the cosmic epochs, and to interpreting current and future observations. Despite the importance of such topics, the contribution of different stellar sources to the chemical enrichment of galaxies, for example massive stars exploding as Type II supernovae (SNe) and low-mass stars, as well as the mechanisms driving the evolution of dust grains, such as for example grain growth in the ISM and destruction by SN shocks, remain controversial from both observational and theoretical viewpoints. Aims. In this work, we revise the current description of metal and dust evolution in the ISM of local low-metallicity dwarf galaxies and develop a new description of Lyman-break galaxies (LBGs) which are considered to be their high-redshift counterparts in terms of star formation, stellar mass, and metallicity. Our goal is to reproduce the observed properties of such galaxies, in particular (i) the peak in dust mass over total stellar mass (sMdust) observed within a few hundred million years; and (ii) the decrease in sMdust at a later time. Methods. We fitted spectral energy distribution of dwarf galaxies and LBGs with the “Code Investigating GALaxies Emission”, through which the total stellar mass, dust mass, and star formation rate are estimated. For some of the dwarf galaxies considered, the metal and gas content are available from the literature. We computed different prescriptions for metal and dust evolution in these systems (e.g. different initial mass functions for stars, dust condensation fractions, SN destruction, dust accretion in the ISM, and inflow and outflow efficiency), and we fitted the properties of the observed galaxies through the predictions of the models. Results. Only some combinations of models are able to reproduce the observed trend and simultaneously fit the observed properties of the galaxies considered. In particular, we show that (i) a top-heavy initial mass function that favours the formation of massive stars and a dust condensation fraction for Type II SNe of around 50% or more help to reproduce the peak of sMdust observed after ≈100 Myr from the beginning of the baryon cycle for both dwarf galaxies and LBGs; (ii) galactic outflows play a crucial role in reproducing the observed decline in sMdust with age and are more efficient than grain destruction from Type II SNe both in local galaxies and at high-redshift; (iii) a star formation efficiency (mass of gas converted into stars) of a few percent is required to explain the observed metallicity of local dwarf galaxies; and (iv) dust growth in the ISM is not necessary in order to reproduce the values of sMdust derived for the galaxies under study, and, if present, the effect of this process would be erased by galactic outflows.

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