scholarly journals The star formation history in 12 SMC fields

2008 ◽  
Vol 4 (S256) ◽  
pp. 269-274
Author(s):  
Noelia E. D. Noël ◽  
Antonio Aparicio ◽  
Carme Gallart ◽  
Sebastián L. Hidalgo ◽  
Edgardo Costa ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Star Formation ◽  
Main Sequence ◽  
Milky Way ◽  
Stellar Populations ◽  
Star Formation History ◽  
Theoretical Studies ◽  
Formation History ◽  
Stellar Halo ◽  
Hubble Time

AbstractWe present a quantitative analysis of the star formation history (SFH) of 12 fields in the Small Magellanic Cloud (SMC) based on unprecedented deep [(B–R),R] color—magnitude diagrams (CMDs) from Noël et al. (2007). Our fields reach down to the oldest main sequence (MS) turnoff with high photometric accuracy, which is vital for obtaining accurate SFHs. We use the IAC-pop code (Aparicio & Hidalgo 2009) to obtain the SFH, using a single CMD generated using IAC-star (Aparicio & Gallart 2004). We find that there are three main periods of enhancement of star formation: a young one peaked at ~0.2–0.5 Gyr old, only present in the eastern and in the central-most fields; one at intermediate ages, peaked at ~4–5 Gyr old in all fields; and an old one, peaked at ~10 Gyr in all the fields but the western ones, in which this old enhancement splits into two, peaked at ~8 Gyr old and at ~12 Gyr old. This “two-enhancement” zone seems to be a robust feature since it is unaffected when using different stellar evolutionary libraries, implying that stars in the SMC take a Hubble time or more to mix. This indicates that there was a global enhancement in ψ(t) at ~4–5 Gyr ago in the SMC. We also find that the age of the old population is similar at all radii and at all azimuth and we constrain the age of this oldest population to be older than ~11.5 Gyr old. The intermediate-age population, in turn, presents variations with both, radii and azimuth. Theoretical studies based on results from larger spatial areas are needed to understand the origin of the young gradient. This young component is highly affected by interactions between Milky Way/LMC/SMC. We do not find yet a region dominated by an old, Milky Way-like, halo at 4.5 kpc from the SMC center, indicating either that this old stellar halo does not exist in the SMC or that its contribution to the stellar populations, at the galactocentric distances of our outermost field, is negligible.

scholarly journals The Controversial Star-Formation History and Helium Enrichment of the Milky Way Bulge

2016 ◽  
Vol 33 ◽  
Author(s):  
David M. Nataf
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Milky Way ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Asymptotic Giant Branch Stars ◽  
Rr Lyrae ◽  
Formation History ◽  
Solar Metallicity

AbstractThe stellar population of the Milky Way bulge is thoroughly studied, with a plethora of measurements from virtually the full suite of instruments available to astronomers. It is thus perhaps surprising that alongside well-established results lies some substantial uncertainty in its star-formation history. Cosmological models predict the bulge to host the Galaxy's oldest stars for [Fe/H] ≲ −1, and this is demonstrated by RR Lyrae stars and globular cluster observations. There is consensus that bulge stars with [Fe/H] ≲ 0 are older than t ≈ 10 Gyr. However, at super-solar metallicity, there is a substantial unresolved discrepancy. Data from spectroscopic measurements of the main-sequence turnoff and subgiant branch, the abundances of asymptotic giant branch stars, the period distribution of Mira variables, the chemistry and central-star masses of planetary nebulae, all suggest a substantial intermediate-age population (t ≈ 3 Gyr). This is in conflict with predictions from cosmologically motivated chemical evolution models and photometric studies of the main-sequence turnoff region, which both suggest virtually no stars younger than t ≈ 8 Gyr. A possible resolution to this conflict is enhanced helium-enrichment, as this would shift nearly all of the age estimates in the direction of decreasing discrepancy.

scholarly journals SMC in space and time: a project to study the evolution of the prototype interacting late-type dwarf galaxy

2008 ◽  
Vol 4 (S255) ◽  
pp. 381-386 ◽  
Author(s):  
M. Tosi ◽  
J. Gallagher ◽  
E. Sabbi ◽  
K. Glatt ◽  
E. K. Grebel ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Variable Stars ◽  
Star Formation History ◽  
Space And Time ◽  
Deep Well ◽  
Formation History ◽  
Central Regions ◽  
Stellar Halo ◽  
Hubble Time

AbstractWe introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams (CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time.

scholarly journals Star Formation History in the Fornax Dwarf Galaxy from HST data

1999 ◽  
Vol 192 ◽  
pp. 174-178 ◽  
Author(s):  
G. Marconi ◽  
R. Buonanno ◽  
M. Castellani ◽  
C. E. Corsi ◽  
R. Zinn
Keyword(s):  
Star Formation ◽  
Globular Cluster ◽  
Main Sequence ◽  
Dwarf Galaxy ◽  
Hubble Space Telescope ◽  
Global Analysis ◽  
Stellar Populations ◽  
Star Formation History ◽  
A Value ◽  
Formation History

Using observations from the Hubble Space Telescope archive, color-magnitude diagrams have been constructed for globular Cluster 4 in the Fornax dSph galaxy and its surrounding field. These diagrams extend below the main-sequence turnoffs and have yielded measurements of the ages of the populations. In particular, from our analysis Cluster 4 shows [Fe/H] ≃ 2.0, a value significantly lower than that derived for the Fornax field ([Fe/H] ≃ −1.40). Putting our results in the frame of the findings of Buonanno et al. (1998) for the Fornax clusters 1, 2, 3 and 5, a global analysis of the properties of Fornax stellar populations has been performed.

scholarly journals High-speed stars: Galactic hitchhikers

2020 ◽  
Vol 638 ◽  
pp. A122 ◽  
Author(s):  
E. Caffau ◽  
L. Monaco ◽  
P. Bonifacio ◽  
L. Sbordone ◽  
M. Haywood ◽  
...  
Keyword(s):  
Star Formation ◽  
High Speed ◽  
Milky Way ◽  
Star Formation History ◽  
Proper Motions ◽  
Orbital Parameters ◽  
Blue Stragglers ◽  
Formation History ◽  
Cool Stars ◽  
Age Estimates

Context. The search for stars born in the very early stages of the Milky Way star formation history is of paramount importance in the study of the early Universe since their chemistry carries irreplaceable information on the conditions in which early star formation and galaxy buildup took place. The search for these objects has generally taken the form of expensive surveys for faint extremely metal-poor stars, the most obvious but not the only candidates to a very early formation. Aims. Thanks to Gaia DR2 radial velocities and proper motions, we identified 72 bright cool stars displaying heliocentric transverse velocities in excess of 500 km s−1. These objects are most likely members of extreme outer-halo populations, either formed in the early Milky Way build-up or accreted from since-destroyed self-gravitating stellar systems. Methods. We analysed low-resolution FORS spectra of the 72 stars in the sample and derived the abundances of a few elements. Despite the large uncertainties on the radial velocity determination, we derived reliable orbital parameters for these objects. Results. The stars analysed are mainly slightly metal poor, with a few very metal-poor stars. Their chemical composition is much more homogeneous than expected. All the stars have very eccentric halo orbits, some extending well beyond the expected dimension of the Milky Way. Conclusions. These stars can be the result of a disrupted small galaxy or they could have been globular cluster members. Age estimates suggest that some of them are evolved blue stragglers, now on the subgiant or asymptotic giant branches.

scholarly journals Recovering the Star Formation History of IC1613 Dwarf Galaxy Using Evolved Stars

2018 ◽  
Vol 14 (S344) ◽  
pp. 77-80
Author(s):  
Seyed Azim Hashemi ◽  
Atefeh Javadi ◽  
Jacco Th. van Loon
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Evolved Stars ◽  
Formation History ◽  
The Galaxy ◽  
Red Supergiants ◽  
Period Variable

AbstractDetermining the star formation history (SFH) is key to understand the formation and evolution of dwarf galaxies. Recovering the SFH in resolved galaxies is mostly based on deep colour–magnitude diagrams (CMDs), which trace the signatures of multiple evolutionary stages of their stellar populations. In distant and unresolved galaxies, the integrated light of the galaxy can be decomposed, albeit made difficult by an age–metallicity degeneracy. Another solution to determine the SFH of resolved galaxies is based on evolved stars; these luminous stars are the most accessible tracers of the underlying stellar populations and can trace the entire SFH. Here we present a novel method based on long period variable (LPV) evolved asymptotic giant branch (AGB) stars and red supergiants (RSGs). We applied this method to reconstruct the SFH for IC1613, an irregular dwarf galaxy at a distance of 750 kpc. Our results provide an independent confirmation that no major episode of star formation occurred in IC1613 over the past 5 Gyr.

scholarly journals The hierarchical evolution of Brightest Cluster Galaxies: red galaxies in a young universe

2012 ◽  
Vol 8 (S295) ◽  
pp. 200-203
Author(s):  
Chiara Tonini
Keyword(s):  
Star Formation ◽  
Stellar Populations ◽  
Star Formation History ◽  
Analytic Model ◽  
Cluster Galaxies ◽  
Star Formation Activity ◽  
Brightest Cluster Galaxies ◽  
Formation History ◽  
Red Galaxies ◽  
Analytic Models

AbstractWe investigate the evolution of Brightest Cluster Galaxies (BCGs) from redshift z ~ 1.6 to z = 0. We upgrade the hierarchical semi-analytic model of Croton et al. (2006) with a new spectro-photometric model that produces realistic galaxy spectra, making use of the Maraston (2005) stellar populations and a new recipe for the dust extinction. We compare the model predictions of the K-band luminosity evolution and the J-K, V-I and I-K colour evolution with a series of datasets, including Collins et al. (Nature, 2009) who argued that semi-analytic models based on the Millennium simulation cannot reproduce the red colours and high luminosity of BCGs at z > 1. We show instead that the model is well in range of the observed luminosity and correctly reproduces the colour evolution of BCGs in the whole redshift range up to z ~ 1.6. We argue that the success of the semi-analytic model is in large part due to the implementation of a more sophisticated spectro-photometric model. An analysis of the model BCGs shows an increase in mass by a factor 2-3 since z ~ 1, and star formation activity down to low redshifts. While the consensus regarding BCGs is that they are passively evolving, we argue that this conclusion is affected by the degeneracy between star formation history and stellar population models used in SED-fitting, and by the inefficacy of toy-models of passive evolution to capture the complexity of real galaxies, especially those with rich merger histories like BCGs. Following this argument, we also show that in the semi-analytic model, the BCGs show a realistic mix of stellar populations, and that these stellar populations are mostly old. In addition, the age-redshift relation of the model BCGs follows that of the Universe, meaning that given their merger history and star formation history, the ageing of BCGs is always dominated by the ageing of their stellar populations. In a ΛCDM Universe, we define such evolution as ‘passive in the hierarchical sense’.

scholarly journals Dissecting the Formation Histories of Galaxies with Stellar Populations Models

2009 ◽  
Vol 5 (S262) ◽  
pp. 153-163
Author(s):  
Ivo Labbé
Keyword(s):  
Star Formation ◽  
Current Knowledge ◽  
High Redshift ◽  
Local Environment ◽  
Stellar Populations ◽  
Current Data ◽  
Star Formation History ◽  
Spectral Energy ◽  
Formation History ◽  
History Of

AbstractHow did galaxies evolve from primordial fluctuations to the well-ordered but diverse population of disk and elliptical galaxies that we observe today? Stellar populations synthesis models have become a crucial tool in addressing this question by helping us to interpret the spectral energy distributions of present-day galaxies and their high redshift progenitors in terms of fundamental characteristics such as stellar mass and age. I will review our current knowledge on the evolution of stellar populations in early- and late type galaxies at z < 1 and the tantalizing – but incomplete – view of the stellar populations in galaxies at 1 < z < 3, during the global peak of star formation. Despite great progress, many fundamental questions remain: what processes trigger episodes of galaxy-scale star formation and what quenches them? To what degree does the star formation history of galaxies depend on the merger history, (halo) mass, or local environment? I will discuss some of the challenges posed in interpreting current data and what improved results might be expected from new observational facilities in the near- and more distant future.

Sign in / Sign up

Export Citation Format

Share Document