scholarly journals Star Formation Histories of Dwarf Galaxies from the Colour-Magnitude Diagrams of Their Resolved Stellar Populations

2010 ◽  
Vol 2010 ◽  
pp. 1-25 ◽  
Author(s):  
Michele Cignoni ◽  
Monica Tosi
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Early Type ◽  
Significant Difference ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Show Evidence ◽  
History Of ◽  
Star Formation Histories

In this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize: (1) only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, orgasping, SF regimes; (2) a few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; (3) no galaxy experiencing now its first SF episode has been found yet; (4) no frequent evidence of strong SF bursts is found; (5) there is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed.

scholarly journals Star Formation History of the Dwarf Galaxies in the Centaurus A Group

2006 ◽  
Vol 2 (S235) ◽  
pp. 320-320
Author(s):  
L. Makarova ◽  
D. Makarov ◽  
A. Dolphin ◽  
I. Karachentsev ◽  
B. Tully ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Hubble Space Telescope ◽  
Star Formation History ◽  
Formation History ◽  
Magnitude Diagram ◽  
History Of ◽  
Advanced Camera For Surveys ◽  
Star Formation Histories ◽  
Centaurus A

We derive quantitative star formation histories (SFH) of the two dwarf spheroidal (KK 197 and ESO 269-066) and one dwarf irregular (ESO 381-018) galaxies in the nearby Centaurus A group. The data are part of our sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope (prog. 9771 & 10235, PI I.Karachentsev). Deep color-magnitude diagram (CMD) of KK 197 is shown in Fig.1.

scholarly journals Pushing back the limits: detailed properties of dwarf galaxies in a ΛCDM universe

2018 ◽  
Vol 616 ◽  
pp. A96 ◽  
Author(s):  
Yves Revaz ◽  
Pascale Jablonka
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Mass Scale ◽  
Dwarf Spheroidal Galaxies ◽  
The Galaxy ◽  
Dynamical Simulations ◽  
Ursa Minor ◽  
Stellar Properties ◽  
Star Formation Histories

We present the results of a set of high-resolution chemo-dynamical simulations of dwarf galaxies in a ΛCDM cosmology. Out of an original (3.4 Mpc/h)3 cosmological box, a sample of 27 systems are re-simulated from z = 70 to z = 0 using a zoom-in technique. Gas and stellar properties are confronted to the observations in the greatest details: in addition to the galaxy global properties, we investigated the model galaxy velocity dispersion profiles, half-light radii, star formation histories, stellar metallicity distributions, and [Mg/Fe] abundance ratios. The formation and sustainability of the metallicity gradients and kinematically distinct stellar populations are also tackled. We show how the properties of six Local Group dwarf galaxies, NGC 6622, Andromeda II, Sculptor, Sextans, Ursa Minor and Draco are reproduced, and how they pertain to three main galaxy build-up modes. Our results indicate that the interaction with a massive central galaxy could be needed for a handful of Local Group dwarf spheroidal galaxies only, the vast majority of the systems and their variety of star formation histories arising naturally from a ΛCDM framework. We find that models fitting well the local Group dwarf galaxies are embedded in dark haloes of mass between 5 × 108 to a few 109 M⊙, without any missing satellite problem. We confirm the failure of the abundance matching approach at the mass scale of dwarf galaxies. Some of the observed faint however gas-rich galaxies with residual star formation, such as Leo T and Leo P, remain challenging. They point out the need of a better understanding of the UV-background heating.

scholarly journals Spatial variations in the star formation history of the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 281-286
Author(s):  
Carme Gallart ◽  
Ingrid Meschin ◽  
Antonio Aparicio ◽  
Peter B. Stetson ◽  
Sebastián L. Hidalgo
Keyword(s):  
Star Formation ◽  
Outer Part ◽  
Large Magellanic Cloud ◽  
Star Formation History ◽  
Wide Field ◽  
Galactocentric Distance ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Star Formation Histories

AbstractBased on the quantitative analysis of a set of wide-field color—magnitude diagrams reaching the old main sequence-turnoffs, we present new LMC star-formation histories, and their variation with galactocentric distance. Some coherent features are found, together with systematic variations of the star-formation history among the three fields analyzed. We find two main episodes of star formation in all three fields, from 1 to 4 and 7 to 13 Gyr ago, with relatively low star formation around ≃ 4–7 Gyr ago. The youngest age in each field gradually increases with galactocentric radius; in the innermost field, LMC 0514–6503, an additional star formation event younger than 1 Gyr is detected, with star formation declining, however, in the last ≃ 200 Myr. The population is found to be older on average toward the outer part of the galaxy, although star formation in all fields seems to have started around 13 Gyr ago.

scholarly journals The history of the Galactic bulge

2016 ◽  
Vol 12 (S323) ◽  
pp. 184-187 ◽  
Author(s):  
A. A. Zijlstra ◽  
K. Gesicki ◽  
M. M. Miller Bertolami
Keyword(s):  
Star Formation ◽  
Planetary Nebulae ◽  
Elliptical Galaxies ◽  
Recent Analysis ◽  
Galactic Bulge ◽  
Luminosity Functions ◽  
New Models ◽  
Show Evidence ◽  
History Of ◽  
Star Formation Histories

AbstractPlanetary nebulae form in stellar populations with ages from 1 to 10 Gyr, and can be used to trace their star formation histories. Here we apply this to the Galactic bulge, where there are indications both for an old origin and for younger stars. We use new stellar models, which have significant different evolutionary speeds during the post-AGB phase. We apply these new models to a sample of 32 planetary nebulae with HST imaging and VLT spectroscopy. The results show evidence for an old starburst, followed by continuous star formation until at least 2Gyr ago. This agrees very well with recent analysis of colour-magnitude diagrams of the bulge. We show that the new models can also explain the [OIII] luminosity functions, and predict the uniform luminosity cut-off both in spiral galaxies and old elliptical galaxies.

scholarly journals R-process enrichment in ultrafaint dwarf galaxies

2020 ◽  
Vol 494 (1) ◽  
pp. 120-128 ◽  
Author(s):  
Yuta Tarumi ◽  
Naoki Yoshida ◽  
Shigeki Inoue
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Galaxy Formation ◽  
Dwarf Galaxies ◽  
Long Distance ◽  
Stellar Feedback ◽  
The Galaxy ◽  
Star Binary ◽  
R Process ◽  
Process Elements

ABSTRACT We study the enrichment and mixing of r-process elements in ultrafaint dwarf galaxies (UFDs). We assume that r-process elements are produced by neutron-star mergers (NSMs), and examine multiple models with different natal kick velocities and explosion energies. To this end, we perform cosmological simulations of galaxy formation to follow mixing of the dispersed r-process elements driven by star formation and the associated stellar feedback in progenitors of UFDs. We show that the observed europium abundance in Reticulum II is reproduced by our inner explosion model where an NSM is triggered at the centre of the galaxy, whereas the relatively low abundance in Tucana III is reproduced if an NSM occurs near the virial radius of the progenitor galaxy. The latter case is realized only if the neutron-star binary has a large natal kick velocity and travels over a long distance of a kiloparsec before merger. In both the inner and outer explosion cases, it is necessary for the progenitor galaxy to sustain prolonged star formation over a few hundred million years after the NSM, so that the dispersed r-process elements are well mixed within the interstellar medium. Short-duration star formation results in inefficient mixing, and then a large variation is imprinted in the stellar europium abundances, which is inconsistent with the observations of Reticulum II and Tucana III.

scholarly journals The role of cold and hot gas flows in feeding early-type galaxy formation

2014 ◽  
Vol 11 (S308) ◽  
pp. 394-397
Author(s):  
Peter H. Johansson
Keyword(s):  
Galaxy Formation ◽  
Gas Flows ◽  
Early Type ◽  
Gas Streams ◽  
Hot Gas ◽  
Stellar Component ◽  
The Galaxy ◽  
History Of ◽  
Gas Accretion ◽  
Low Entropy

AbstractWe study the evolution of the gaseous components in massive simulated galaxies and show that their early formation is fuelled by cold, low entropy gas streams. At lower redshifts of z ≲ 3 the simulated galaxies are massive enough to support stable virial shocks resulting in a transition from cold to hot gas accretion. The gas accretion history of early-type galaxies is directly linked to the formation of their stellar component in the two phased formation scenario, in which the central parts of the galaxy assemble rapidly through in situ star formation and the later assembly is dominated primarily by minor stellar mergers.

scholarly journals Joint Discussion 1: Abundance Ratios in the Oldest Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 45-48
Author(s):  
Beatriz Barbuy ◽  
Michael S. Bessell
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Past History ◽  
Stellar Atmospheres ◽  
Apparent Difference ◽  
Stellar Spectra ◽  
The Galaxy ◽  
Gaseous Flows ◽  
History Of ◽  
Age Of The Universe

Joint Discussion 1 was supported by Division IV (Stars) and Commission 29 (Stellar Spectra), and co-supported by Commissions 28 (Galaxies), 36 (Theory of Stellar Atmospheres) and 37 (Stellar Clusters and Associations). Members of the scientific organizing committee were: N. Arimoto (Japan), B. Barbuy (Brazil), T. Beers (USA), J. Bergeron (Germany), M. Bessell (Australia), R. Cayrel (France), G. Gilmore (UK), B. Gustafsson (Sweden), F. Matteucci (Italy), P. Nissen (Den-mark), and M. Rich (USA). The inspiration for this meeting was the growing overlap and connections between previously separate areas of astrophysical research, namely, studies of stellar abundances, the bulges of galaxies, the gaseous components of nearby galaxies and the clouds (some of which may be primordial) responsible for the narrow absorption lines in quasars. The signature of the early chemical evolution of our Galaxy is imprinted in the abundance ratios of the oldest stars. We recall that element ratios are determined by a mix of the relative rates of different types of supernovae, the stellar IMF, and the relative histories of star formation rates and gaseous flows, and thus encapsulate much of the history of star formation and ISM evolution in galaxies. Hence, abundance ratios in stars are a primary probe for testing theories of galaxy formation and evolution. We do not know how the Galaxy formed: both the Eggen, Lynden-Bell & Sandage (1962) and the Searle & Zinn (1978) scenarios may be accommodated in the recent proposal of van den Bergh (1993) where the inner Galaxy follows ELS, whereas the outer Galaxy formation conforms to the Searle-Zinn proposition. A combination of abundance ratios, ages derived from colour-magnitude diagrams, and kinematical properties, can give us the required information to trace the past history of our Galaxy. We note here, that although stellar evolution and model atmospheres are not discussed in the proceedings both topics are of fundamental underlying importance. Model atmospheres are used to derive temperatures, colors and bolometric corrections of stars that are used not only in abundance analyses but also in deriving the ages of stars by comparing CM diagrams with HR diagrams. This process is under close scrutiny because of the apparent difference between the ages of the oldest stars and the expansion age of the universe.

scholarly journals A predicted correlation between age gradient and star formation history in FIRE dwarf galaxies

2019 ◽  
Vol 490 (1) ◽  
pp. 1186-1201 ◽  
Author(s):  
Andrew S Graus ◽  
James S Bullock ◽  
Alex Fitts ◽  
Michael C Cooper ◽  
Michael Boylan-Kolchin ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Dwarf Galaxies ◽  
Population Studies ◽  
Young Star ◽  
Star Formation History ◽  
Formation History ◽  
The Galaxy ◽  
In Fire ◽  
Star Formation Histories

ABSTRACT We explore the radial variation of star formation histories (SFHs) in dwarf galaxies simulated with Feedback In Realistic Environments (FIRE) physics. The sample contains 26 field dwarf galaxies with Mstar = 105–109 M⊙. We find age gradients are common in our dwarfs, with older stars dominant at large radii. The strength of the gradient correlates with overall galaxy age such that earlier star formation produces a more pronounced gradient. The relation between formation time and strength of the gradient is driven by both mergers and star formation feedback. Mergers can both steepen and flatten the age gradient depending on the timing of the merger and SFHs of the merging galaxy. In galaxies without significant mergers, feedback pushes stars to the outskirts. The strength of the age gradient is determined by the subsequent evolution of the galaxy. Galaxies with weak age gradients constantly grow to z  = 0, meaning that young star formation occurs at a similar radius to which older stars are heated to. In contrast, galaxies with strong age gradients tend to maintain a constant half-mass radius over time. If real galaxies have age gradients as we predict, stellar population studies that rely on sampling a limited fraction of a galaxy can give a biased view of its global SFH. Central fields can be biased young by Gyrs while outer fields are biased old. Fields positioned near the 2D half-light radius will provide the least biased measure of a dwarf galaxy’s global SFH.

scholarly journals The Star Formation History in Nearby Dwarf Galaxies: the Fossil Record in the Color-Magnitude Diagram

1999 ◽  
Vol 192 ◽  
pp. 304-318
Author(s):  
A. Aparicio
Keyword(s):  
Star Formation ◽  
Fossil Record ◽  
Dwarf Galaxies ◽  
Star Formation History ◽  
Major Interest ◽  
Magnitude Diagram ◽  
Critical Issues ◽  
Nearby Galaxies ◽  
Formation And Evolution ◽  
Star Formation Histories

Dwarf galaxies may play a key role in the formation and evolution of bigger systems. This makes knowing how they form and evolve and, in particular, how their star formation histories (SFHs) have proceeded since their birth, a topic of major interest. For nearby galaxies, the color-magnitude diagram (CMD) contains stars formed over all their lifetime. It is hence a fossil record of their SFHs. The analysis with synthetic CMDs provides a powerful tool to retrieve them.In this paper, I discuss the critical issues related to the computation of synthetic CMDs, present a short summary of the currently available results for the SFH extending the full life of galaxies and make a few critical considerations about the powerfulness and draw-backs of the method.

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