scholarly journals Mapping the stellar age of the Milky Way bulge with the VVV

2020 ◽  
Vol 644 ◽  
pp. A140 ◽  
Author(s):  
F. Surot ◽  
E. Valenti ◽  
O. A. Gonzalez ◽  
M. Zoccali ◽  
E. Sökmen ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Interstellar Extinction ◽  
Star Formation History ◽  
Galactic Bulge ◽  
Formation History ◽  
Color Excess ◽  
Infrared Surveys ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

Context. A detailed study of the Galactic bulge stellar population necessarily requires an accurate representation of the interstellar extinction, particularly toward the Galactic plane and center, where severe and differential reddening is expected to vary on sub-arcmin scales. Although recent infrared surveys have addressed this problem by providing extinction maps across the whole Galactic bulge area, dereddened color-magnitude diagrams near the plane and center appear systematically undercorrected, prompting the need for higher resolution. These undercorrections affect any stellar study sensitive to color (e.g., star formation history analyses via color-magnitude diagram fitting), either making them inaccurate or limiting them to small and relatively stable extinction windows where this value is low and better constrained. Aims. This study is aimed at providing a high-resolution (2 arcmin to ∼10 arcsec) color excess map for the VVV bulge area in J − Ks color. Methods. We used the MW-BULGE-PSFPHOT catalogs, sampling ∼300 deg2 across the Galactic bulge (|l| < 10° and −10° < b <  5°) to isolate a sample of red clump and red giant branch stars, for which we calculated the average J − Ks color in a fine spatial grid in (l, b) space. Results. We obtained an E(J − Ks) map spanning the VVV bulge area of roughly 300 deg2, with the equivalent of a resolution between ∼1 arcmin for bulge outskirts (l <  6°) to below 20 arcsec within the central |l| < 1°, and below 10 arcsec for the innermost area (|l| < 1° and |b| < 3°).

scholarly journals Star formation history and metallicity in the Galactic inner bulge revealed by the red giant branch bump

2018 ◽  
Vol 620 ◽  
pp. A83 ◽  
Author(s):  
F. Nogueras-Lara ◽  
R. Schödel ◽  
H. Dong ◽  
F. Najarro ◽  
A. T. Gallego-Calvente ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Angular Resolution ◽  
Interstellar Extinction ◽  
Star Formation History ◽  
Galactic Centre ◽  
Luminosity Functions ◽  
Formation History ◽  
Red Giant ◽  
The One

Context. The study of the inner region of the Milky Way bulge is hampered by high interstellar extinction and extreme source crowding. Sensitive high angular resolution near-infrared imaging is needed to study stellar populations and their characteristics in such a dense and complex environment. Aims. We aim at investigating the stellar population in the innermost Galactic bulge, to study the star formation history in this region of the Galaxy. Methods. We used the 0.2″ angular resolution JHKs data from the GALACTICNUCLEUS survey to study the stellar population within two 8.0′×3.4′ fields, about 0.6° and 0.4° to the Galactic north of the Milky Way centre and to compare it with the one in the immediate surroundings of Sagittarius A*. We also characterise the absolute extinction and the extinction curve of the two fields. Results. The average interstellar extinction to the outer and the inner field is AKs ∼ 1.20 ± 0.08 mag and ∼1.48 ± 0.10 mag, respectively. We present Ks luminosity functions that are complete down to at least two magnitudes below the red clump (RC). We detect a feature in the luminosity functions that is fainter than the RC by 0.80 ± 0.03 and 0.79 ± 0.02 mag, respectively, in the Ks band. It runs parallel to the reddening vector. We identify the feature as the red giant branch bump. Fitting α-enhanced BaSTI luminosity functions to our data, we find that a single old stellar population of ∼12.8 ± 0.6 Gyr and Z = 0.040 ± 0.003 provides the best fit. Our findings thus show that the stellar population in the innermost bulge is old, similar to the one at larger distances from the Galactic plane, and that its metallicity is about twice solar at distances as short as about 60 pc from the centre of the Milky Way, similar to what is observed at about 500 pc from the Galactic Centre. Comparing the obtained metallicity with previous known values at larger latitudes (|b| > 2°), our results favour a flattening of the gradient at |b| < 2°. As a secondary result we obtain that the extinction index in the studied regions agrees within the uncertainties with our previous value of α = 2.30 ± 0.08 that was derived for the very Galactic centre.

scholarly journals Strömgren Photometry of Field Red Giants in the LMC

1999 ◽  
Vol 190 ◽  
pp. 368-369
Author(s):  
Andrew A. Cole ◽  
John S. Gallagher ◽  
Tammy A. Smecker-Hane
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Red Giants ◽  
Strong Constraint ◽  
Preliminary Results ◽  
Field Star ◽  
Abundance Estimates ◽  
Formation History ◽  
Red Clump ◽  
Red Giant

We present here preliminary results of our program to obtain rough abundance estimates for > 104 red giant branch and red clump stars in four fields of the LMC. The derived abundance distributions will be a strong constraint on models of the LMC's star-formation history based on field star color-magnitude diagrams.

Variations in Star Formation History and the Red Giant Branch Tip

2004 ◽  
Vol 606 (2) ◽  
pp. 869-893 ◽  
Author(s):  
Michael K. Barker ◽  
Ata Sarajedini ◽  
Jason Harris
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Formation History ◽  
Red Giant

scholarly journals Non-parametric density reconstruction of the Galactic bulge area using red clump stars in the VVV survey

2020 ◽  
Vol 499 (2) ◽  
pp. 1937-1947
Author(s):  
Dylan Paterson ◽  
Brendan Coleman ◽  
Chris Gordon
Keyword(s):  
Parametric Method ◽  
Major Axis ◽  
Galactic Bulge ◽  
Buckling Instability ◽  
Giant Stars ◽  
Red Clump ◽  
Red Giant ◽  
High Resolution Reconstruction ◽  
Spiral Arm ◽  
Non Parametric

ABSTRACT Studies of the red clump giant population in the inner Milky Way suggest the Galactic bulge/bar has a boxy/peanut/X-shaped structure as predicted by its formation via a disc buckling instability. We used a non-parametric method of estimating the Galactic bulge morphology that is based on maximum entropy regularization. This enabled us to extract the 3D distribution of the red giant stars in the bulge from deep photometric catalogues of the VISTA Variables in the Via Lactea survey. Our high-resolution reconstruction confirms the well-known boxy/peanut/X-shaped structure of the bulge. We also find spiral arm structures that extend to around 3 kpc in front of and behind the bulge and are on different sides of the bulge major axis. We show that the detection of these structures is robust to the uncertainties in the luminosity function.

scholarly journals The Magellanic Edges Survey I: Description and first results

2020 ◽  
Vol 497 (3) ◽  
pp. 3055-3075
Author(s):  
L R Cullinane ◽  
A D Mackey ◽  
G S Da Costa ◽  
S E Koposov ◽  
V Belokurov ◽  
...  
Keyword(s):  
Target Selection ◽  
Radial Distance ◽  
Large Magellanic Cloud ◽  
Disc Model ◽  
Observation Strategy ◽  
First Results ◽  
Mass Estimate ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

ABSTRACT We present an overview of, and first science results from, the Magellanic Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of red clump and red giant branch stars in the highly substructured periphery of the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a sample of ~7000 stars with individual 3D velocities that probes larger galactocentric radii than most previous studies. We outline our target selection, observation strategy, data reduction, and analysis procedures, and present results for two fields in the northern outskirts (&gt;10° on-sky from the centre) of the Large Magellanic Cloud (LMC). One field, located in the vicinity of an arm-like overdensity, displays apparent signatures of perturbation away from an equilibrium disc model. This includes a large radial velocity dispersion in the LMC disc plane, and an asymmetric line-of-sight velocity distribution indicative of motions vertically out of the disc plane for some stars. The second field reveals 3D kinematics consistent with an equilibrium disc, and yields Vcirc = 87.7 ± 8.0 km s−1 at a radial distance of ~10.5 kpc from the LMC centre. This leads to an enclosed mass estimate for the LMC at this radius of (1.8 ± 0.3) × 1010 M⊙.

Star formation history and dynamical evolution of the solar neighbourhood

2017 ◽  
Vol 13 (S334) ◽  
pp. 310-311
Author(s):  
Andreas Just ◽  
Kseniia Sysoliatina
Keyword(s):  
Star Formation ◽  
Galactic Plane ◽  
Dynamical Evolution ◽  
Star Formation History ◽  
Solar Neighbourhood ◽  
Data Set ◽  
Disc Model ◽  
Formation History ◽  
Number Counts ◽  
Good Agreement

AbstractWe used our detailed analytic local disc model to compare predictions in number counts, colour distribuitons and kinematics with a data set extracted from a combination of TGAS and RAVE catalogues. We find generally a very good agreement with some deviations close to the Galactic plane.

scholarly journals Cosmology with Nearby Dwarf Galaxies: The View from HST

1998 ◽  
Vol 11 (1) ◽  
pp. 127-130
Author(s):  
Eline Tolstoy
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Direct Evidence ◽  
Global Scale ◽  
Star Formation History ◽  
Monte Carlo Techniques ◽  
Formation History ◽  
Magnitude Diagram ◽  
Red Giant ◽  
Sophisticated Analysis

Stellar Evolution theory is based upon well understood physics and provides clear predictions as to how a Colour-Magnitude Diagram (CMD) will change due to effects of age and metallicity. The theory has been tested by looking at nearby coeval star clusters. The power of applying CMD analysis to galaxies has been demonstrated in studies of the Carina dSph (Smecker-Hane et al. 1996). In Carina the observation of separate, distinct Main Sequence (MS) Turnoffs has forced us to believe that this small, nearby companion of our Galaxy has had a very complex star formation history. No similar direct evidence for “bursting” behaviour on a global scale has been seen indisputably in larger systems. Partly this is due to the greater distances of larger systems, but also to the complications in distinguishing old star formation events (> 1 Gyr old) in systems which are currently forming stars. Where we lack MS turnoffs we have to resort to statistical modeling of the CMD. This has been applied using a a number of different approaches, but all generally based on Monte-Carlo techniques (e.g. Tosi et al. 1992; Bertelli et al. 1992; Tolstoy &; Saha 1996). However, even using these more sophisticated analysis techniques, it is difficult to find unique solutions. This is mostly due to the age-metallicity degeneracy on the Red Giant Branch (RGB). The RGB is usually the most populated, easiest to observe phase of stellar evolution. The Carina CMD reveals the dangers of blindly interpreting the RGB, because from the RGB alone it is impossible to extract the information revealed by the MS Turnoffs.

Breaking the age–metallicity degeneracy: The metallicity distribution and star formation history of the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 263-268 ◽  
Author(s):  
Andrew A. Cole ◽  
Aaron J. Grocholski ◽  
Doug Geisler ◽  
Ata Sarajedini ◽  
Verne V. Smith ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Large Magellanic Cloud ◽  
Star Formation History ◽  
Red Giants ◽  
Formation History ◽  
History Of ◽  
Red Giant ◽  
Metallicity Distribution ◽  
Modelling Process

AbstractWe have obtained metallicities from near-infrared calcium triplet spectroscopy for nearly a thousand red giants in 28 fields spanning a range of radial distances from the center of the bar to near the tidal radius. We have used these data to investigate the radius-metallicity and age-metallicity relations. A powerful application of these data is in conjunction with the analysis of deep HST color–magnitude diagrams (CMDs). Most of the power in determining a robust star-formation history from a CMD comes from the main-sequence turnoff and subgiant branches. The age-metallicity degeneracy that results is largely broken by the red giant branch color, but theoretical model RGB colors remain uncertain. By incorporating the observed metallicity distribution function into the modelling process, a star-formation history with massively increased precision and accuracy can be derived. We incorporate the observed metallicity distribution of the LMC bar into a maximum-likelihood analysis of the bar CMD, and present a new star formation history and age–metallicity relation for the bar. The bar is certainly younger than the disk as a whole, and the most reliable estimates of its age are in the 5–6 Gyr range, when the mean gas abundance of the LMC had already increased to [Fe/H] ≳ −0.6. There is no obvious metallicity gradient among the old stars in the LMC disk out to a distance of 8–10 kpc, but the bar is more metal-rich than the disk by ≈0.1–0.2 dex. This is likely to be the result of the bar's younger average age. In both disk and bar, 95% of the red giants are more metal-rich than [Fe/H] = −1.2.

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