scholarly journals The Milky Way’s bulge star formation history as constrained from its bimodal chemical abundance distribution

2020 ◽  
Vol 497 (3) ◽  
pp. 3557-3570 ◽  
Author(s):  
Jianhui Lian ◽  
Gail Zasowski ◽  
Sten Hasselquist ◽  
David M Nataf ◽  
Daniel Thomas ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Critical Role ◽  
Bimodal Distribution ◽  
Distribution Functions ◽  
Star Formation History ◽  
Chemical Abundance ◽  
Secular Evolution ◽  
Formation History ◽  
Quenching Process

ABSTRACT We conduct a quantitative analysis of the star formation history (SFH) of the Milky Way’s (MW) bulge by exploiting the constraining power of its stellar [Fe/H] and [Mg/Fe] distribution functions. Using Apache Point Observatory Galactic Evolution Experiment survey data, we confirm the previously established bimodal [Mg/Fe]–[Fe/H] distribution within 3 kpc of the inner Galaxy. To fit the chemical bimodal distribution, we use a simple but flexible star formation framework, which assumes two distinct stages of gas accretion and star formation, and systematically evaluate a wide multidimensional parameter space. We find that the data favour a three-phase SFH that consists of an initial starburst, followed by a rapid star formation quenching episode, and a lengthy, quiescent secular evolution phase. The metal-poor, high-α bulge stars ([Fe/H] < 0.0 and [Mg/Fe] > 0.15) are formed rapidly (<2 Gyr) during the early starburst. The density gap between the high- and low-α sequences is due to the quenching process. The metal-rich, low-α population ([Fe/H] > 0.0 and [Mg/Fe] < 0.15) then accumulates gradually through inefficient star formation during the secular phase. This is qualitatively consistent with the early SFH of the inner disc. Given this scenario, a notable fraction of young stars (age <5 Gyr) is expected to persist in the bulge. Combined with extragalactic observations, these results suggest that a rapid star formation quenching process is responsible for bimodal distributions in both the MW’s stellar populations and in the general galaxy population and thus plays a critical role in galaxy evolution.

scholarly journals The chemical properties of the Milky Way’s on-bar and off-bar regions: evidence for inhomogeneous star formation history in the bulge

2020 ◽  
Vol 500 (1) ◽  
pp. 282-290
Author(s):  
Jianhui Lian ◽  
Gail Zasowski ◽  
Sten Hasselquist ◽  
Justus Neumann ◽  
Steven R Majewski ◽  
...  
Keyword(s):  
Star Formation ◽  
Chemical Properties ◽  
Distribution Functions ◽  
Star Formation History ◽  
Chemical Abundance ◽  
Independent Information ◽  
Formation History ◽  
Vertical Variations ◽  
Bar Buckling ◽  
Gas Accretion

ABSTRACT Numerous studies of integrated starlight, stellar counts, and kinematics have confirmed that the Milky Way is a barred galaxy. However, far fewer studies have investigated the bar’s stellar population properties, which carry valuable independent information regarding the bar’s formation history. Here, we conduct a detailed analysis of chemical abundance distributions ([Fe/H] and [Mg/Fe]) in the on-bar and off-bar regions to study the azimuthal variation of star formation history (SFH) in the inner Galaxy. We find that the on-bar and off-bar stars at Galactocentric radii 3 kpc < rGC < 5 kpc have remarkably consistent [Fe/H] and [Mg/Fe] distribution functions and [Mg/Fe]–[Fe/H] relation, suggesting a common SFH shared by the long bar and the disc. In contrast, the bar and disc at smaller radii (2 kpc < rGC < 3 kpc) show noticeable differences, with relatively more very metal-rich ($\rm [Fe/H] \sim 0.4$) stars but fewer solar abundance stars in the bar. Given the three-phase star formation history proposed for the inner Galaxy in Lian et al., these differences could be explained by the off-bar disc having experienced either a faster early quenching process or recent metal-poor gas accretion. Vertical variations of the abundance distributions at small rGC suggest a wider vertical distribution of low-α stars in the bar, which may serve as chemical evidence for vertical heating through the bar buckling process. The lack of such vertical variations outside the bulge may then suggest a lack of vertical heating in the long bar.

scholarly journals Star-Forming Galaxies at Cosmic Noon

2020 ◽  
Vol 58 (1) ◽  
pp. 661-725 ◽  
Author(s):  
Natascha M. Förster Schreiber ◽  
Stijn Wuyts
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Star Formation History ◽  
Massive Galaxies ◽  
Star Forming ◽  
Dense Cores ◽  
Gravitational Instabilities ◽  
James Webb Space Telescope ◽  
Formation History ◽  
Large Telescopes

Ever deeper and wider look-back surveys have led to a fairly robust outline of the cosmic star-formation history, which culminated around [Formula: see text]; this period is often nicknamed “cosmic noon.” Our knowledge about star-forming galaxies at these epochs has dramatically advanced from increasingly complete population censuses and detailed views of individual galaxies. We highlight some of the key observational insights that influenced our current understanding of galaxy evolution in the equilibrium growth picture: ▪  Scaling relations between galaxy properties are fairly well established among massive galaxies at least out to [Formula: see text], pointing to regulating mechanisms already acting on galaxy growth. ▪  Resolved views reveal that gravitational instabilities and efficient secular processes within the gas- and baryon-rich galaxies at [Formula: see text] play an important role in the early buildup of galactic structure. ▪  Ever more sensitive observations of kinematics at [Formula: see text] are probing the baryon and dark matter budget on galactic scales and the links between star-forming galaxies and their likely descendants. ▪  Toward higher masses, massive bulges, dense cores, and powerful AGNs and AGN-driven outflows are more prevalent and likely play a role in quenching star formation. We outline emerging questions and exciting prospects for the next decade with upcoming instrumentation, including the James Webb Space Telescope and the next generation of extremely large telescopes.

scholarly journals The age–chemical abundance structure of the Galactic disc – II. α-dichotomy and thick disc formation

2020 ◽  
Vol 497 (2) ◽  
pp. 2371-2384 ◽  
Author(s):  
Jianhui Lian ◽  
Daniel Thomas ◽  
Claudia Maraston ◽  
Timothy C Beers ◽  
Christian Moni Bidin ◽  
...  
Keyword(s):  
Star Formation ◽  
Cosmic Time ◽  
Theoretical Models ◽  
Bimodal Distribution ◽  
Chemical Abundance ◽  
Secular Evolution ◽  
Thick Disc ◽  
Star Formation Activity ◽  
Gas Accretion ◽  
Disc Formation

ABSTRACT We extend our previous work on the age–chemical abundance structure of the Galactic outer disc to the inner disc (4 < r < 8  kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]–[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multiphase inner disc formation scenario that matches the observed bimodal [Mg/Fe]–[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes $6\,$Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times ($t\sim 1\,$ Gyr) and the second one $6\,$ Gyr later at a cosmic time of $t\sim 7\,$ Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-α sequence, and the second starburst leads to the formation of the metal-poor low-α sequence. The metal-rich low-α stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the α-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z >1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively.

scholarly journals A Photometric Survey of Field Stars in the Large Magellanic Cloud: Probing its Star-Formation History

1999 ◽  
Vol 190 ◽  
pp. 343-344 ◽  
Author(s):  
T. A. Smecker-Hane ◽  
J. S. Gallagher ◽  
Andrew Cole ◽  
P. B. Stetson ◽  
E. Tolstoy
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Stellar Population ◽  
Formation Rate ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Star Formation History ◽  
Wide Field ◽  
Formation History ◽  
Magnitude Diagram

The Large Magellanic Cloud (LMC) is unique among galaxies in the Local Group in that it is the most massive non-spiral, is relatively gas-rich, and is actively forming stars. Determining its star-formation rate (SFR) as a function of time will be a cornerstone in our understanding of galaxy evolution. The best method of deriving a galaxy's past SFR is to compare the densities of stars in a color-magnitude diagram (CMD), a Hess diagram, with model Hess diagrams. The LMC has a complex stellar population with ages ranging from 0 to ~ 14 Gyr and metallicities from −2 ≲ [Fe/H] ≲ −0.4, and deriving its SFR and simultaneously constraining model input parameters (distance, age-metallicity relation, reddening, and stellar models) requires well-populated CMDs that span the magnitude range 15 ≤ V ≤ 24. Although existing CMDs of field stars in the LMC show tantalizing evidence for a significant burst of star formation that occurred ~ 3 Gyr ago (for examples, see Westerlund et al. 1995; Vallenari et al. 1996; Elson, et al. 1997; Gallagher et al. 1999, and references therein), estimates of the enhancement in the SFR vary from factors of 3 to 50. This uncertainty is caused by the relatively large photometric errors that plague crowded ground-based images, and the small number statistics that plague CMDs created from single Wide Field Planetary Camera 2 (WFPC2) images.

scholarly journals The star formation history of the Fornax dwarf spheroidal galaxy

2009 ◽  
Vol 5 (S262) ◽  
pp. 353-354
Author(s):  
Enrico V. Held ◽  
Eline Tolstoy ◽  
Luca Rizzi ◽  
Mary Cesetti ◽  
Andrew A. Cole ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Stellar Population ◽  
Main Sequence ◽  
Dwarf Galaxy ◽  
Star Formation History ◽  
Stellar Content ◽  
Formation History ◽  
First Results ◽  
History Of

AbstractWe present the first results of a comprehensive HST study of the star-formation history of Fornax dSph, based on WFPC2 imaging of 7 Fornax fields. Our observations reach the oldest main-sequence turnoffs, allowing us to address fundamental questions of dwarf galaxy evolution, such as the spatial variations in the stellar content, and whether the old stellar population is made up of stars formed in a very early burst or the result of a more continuous star formation.

scholarly journals CALIFA survey: The spatially resolved star formation history of massive galaxies

2012 ◽  
Vol 8 (S295) ◽  
pp. 300-303
Author(s):  
Rosa González Delgado ◽  
Enrique Pérez ◽  
Roberto Cid Fernandes ◽  
Rubén García-Benito ◽  
André de Amorim ◽  
...  
Keyword(s):  
Growth Rate ◽  
Star Formation ◽  
Galaxy Evolution ◽  
Local Density ◽  
Spectral Synthesis ◽  
Mass Density ◽  
Stellar Mass ◽  
Star Formation History ◽  
Formation History ◽  
History Of

AbstractThe Calar Alto Legacy Integral Field Area (CALIFA) project is an ongoing 3D spectroscopic survey of 600 nearby galaxies of all kinds. This pioneer survey is providing valuable clues on how galaxies form and evolve. Processed through spectral synthesis techniques, CALIFA datacubes allow us to, for the first time, spatially resolve the star formation history of galaxies spread across the color-magnitude diagram. The richness of this approach is already evident from the results obtained for the first ~ 1/6 of the sample. Here we show how the different galactic spatial sub-components (“bulge” and “disk”) grow their stellar mass over time. We explore the results stacking galaxies in mass bins, finding that, except at the lowest masses, galaxies grow inside-out, and that the growth rate depends on a galaxy's mass. The growth rate of inner and outer regions differ maximally at intermediate masses. We also find a good correlation between the age radial gradient and the stellar mass density, suggesting that the local density is a main driver of galaxy evolution.

scholarly journals Molecular Gas in Galaxies at all Redshifts

2010 ◽  
Vol 6 (S277) ◽  
pp. 47-54
Author(s):  
Françoise Combes
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Star Formation History ◽  
Gas Content ◽  
Continuum Emission ◽  
Massive Galaxies ◽  
Normal Galaxies ◽  
Galaxy Type ◽  
Formation History ◽  
Formation Efficiency

AbstractI review some recent results about the molecular content of galaxies, obtained essentially from the CO lines, but also dense tracers, or the dust continuum emission. New results have been obtained on molecular cloud physics, and their efficiency to form stars, shedding light on the Kennicutt-Schmidt law as a function of surface density and galaxy type. Large progress has been made on galaxy at moderate and high redshifts, allowing to interprete the star formation history and star formation efficiency as a function of gas content, or galaxy evolution. In massive galaxies, the gas fraction was higher in the past, and galaxy disks were more unstable and more turbulent. ALMA observations will allow the study of more normal galaxies at high z with higher spatial resolution and sensitivity.

scholarly journals Initial Model Catalogue for Galaxy Evolution

2004 ◽  
Vol 21 (2) ◽  
pp. 171-174 ◽  
Author(s):  
Naohito Nakasato
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Milky Way ◽  
High Redshift ◽  
Random Number Generator ◽  
Star Formation History ◽  
Initial Model ◽  
Model Galaxy ◽  
Formation History ◽  
Type Ia

AbstractWe have computed full hydrochemodynamical evolution for 150 initial models of protogalaxies with our chemodynamical SPH code named GENSO. Various parameters for all models are identical except for a seed for a random number generator. In other words, all models have similar global properties but have the different merging history that leads to a different evolution in each model. Results of the series of computations have two main applications. Firstly, we have an initial model catalogue for subsequent modelling of galaxy evolution. Since the resulting evolution depends strongly on the initial phase of the particle distribution, it is crucial to find a suitable initial model when we model a specific real galaxy in the Universe, notably the Milky Way in our case. We will make a precise chemical and dynamical model of the Milky Way out of 150 models in our initial model catalogue. Secondly, we can obtain a large variety of global histories of physical values such as star formation, metallicity in the ISM and stellar components, and Type II and Ia supernova rates. For example, the resulting total star formation history shows the peak at a high redshift z ∼ 6 and the peak value is ∼280 M⊙ yr–1 Mpc–3. Also, the Type Ia rate obtained has a peak at z ∼ 3.5. All of our results and model catalogue are publicly available from our website for those who wish to model galaxy evolution.

scholarly journals Multi-Color Surface Photometry of Nearby Galaxies

1998 ◽  
Vol 179 ◽  
pp. 285-286
Author(s):  
T. Ichikawa ◽  
N. Itoh ◽  
K. Yanagisawa
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Spiral Galaxies ◽  
Stellar Structure ◽  
Star Formation History ◽  
Optical Observations ◽  
Wide Field ◽  
Formation History

Near-infrared (NIR) emission in galaxies is mainly radiated by old population low temperature stars, which construct the basic stellar structure and keep the trails of past galaxy evolution. On the other hand, optical observations show recent star formation activity, especially in spiral galaxies. Therefore multi-color observations from optical to near-infrared wavelengths are very important to understand the past and recent star-formation history. Nearby large galaxies are well studied not only in optical but also in mid- and far-infrared by IRAS, CO and HI radio observations. However, the study in the near-infrared is still limited because large format arrays are not common. Here we show a wide-field, near-infrared imaging of nearby elliptical and spiral galaxies and discuss their star-formation history.

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