scholarly journals Spatially Resolved Stellar Spectroscopy of the Ultra-diffuse Galaxy Dragonfly 44. III. Evidence for an Unexpected Star Formation History under Conventional Galaxy Evolution Processes

2022 ◽  
Vol 924 (1) ◽  
pp. 32
Author(s):  
Alexa Villaume ◽  
Aaron J. Romanowsky ◽  
Jean Brodie ◽  
Pieter van Dokkum ◽  
Charlie Conroy ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Globular Clusters ◽  
Stellar Population ◽  
Dwarf Galaxies ◽  
Star Formation History ◽  
Population Parameters ◽  
Spatially Resolved ◽  
Formation History ◽  
Field Unit

Abstract We use the Keck Cosmic Web Imager integral field unit spectrograph to (1) measure the global stellar population parameters for the ultra-diffuse galaxy (UDG) Dragonfly 44 (DF44) to much higher precision than previously possible for any UDG and (2) for the first time measure spatially resolved stellar population parameters of a UDG. We find that DF44 falls below the mass–metallicity relation established by canonical dwarf galaxies both in and beyond the Local Group. We measure a flat radial age gradient ( m logage = + 0.01 − 0.08 + 0.08 log Gyr kpc−1) and a flat to positive metallicity gradient ( m [ Fe / H ] = + 0.09 − 0.12 + 0.11 dex kpc−1), which are inconsistent with the gradients measured in similarly pressure-supported dwarf galaxies. We also measure a negative [Mg/Fe] gradient ( m [ Mg / Fe ] = − 0.20 − 0.18 + 0.18 ) dex kpc−1 such that the central 1.5 kpc of DF44 has stellar population parameters comparable to metal-poor globular clusters. Overall, DF44 does not have internal properties similar to other dwarf galaxies and is inconsistent with it having been puffed up through a prolonged, bursty star formation history, as suggested by some simulations. Rather, the evidence indicates that DF44 experienced an intense epoch of “inside-out” star formation and then quenched early and catastrophically, such that star formation was cut off more quickly than in canonical dwarf galaxies.

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 The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. II. The Star-formation History of Andromeda I Derived from Long-period Variables

2021 ◽  
Vol 923 (2) ◽  
pp. 164
Author(s):  
Elham Saremi ◽  
Atefeh Javadi ◽  
Mahdieh Navabi ◽  
Jacco Th. van Loon ◽  
Habib G. Khosroshahi ◽  
...  
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Star Formation History ◽  
Isaac Newton ◽  
Long Period ◽  
Formation History ◽  
Monitoring Survey ◽  
Isaac Newton Telescope

Abstract An optical monitoring survey in the nearby dwarf galaxies was carried out with the 2.5 m Isaac Newton Telescope. 55 dwarf galaxies and four isolated globular clusters in the Local Group were observed with the Wide Field Camera. The main aims of this survey are to identify the most evolved asymptotic giant branch stars and red supergiants at the endpoint of their evolution based on their pulsational instability, use their distribution over luminosity to reconstruct the star-formation history (SFH), quantify the dust production and mass loss from modeling the multiwavelength spectral energy distributions, and relate this to luminosity and radius variations. In this second of a series of papers, we present the methodology used to estimate SFH based on long-period variable (LPV) stars and then derive it for Andromeda I (And I) dwarf galaxy as an example of the survey. Using our identified 59 LPV candidates within two half-light radii of And I and Padova stellar evolution models, we estimated the SFH of this galaxy. A major epoch of star formation occurred in And I peaking around 6.6 Gyr ago, reaching 0.0035 ± 0.0016 M ⊙ yr−1 and only slowly declining until 1–2 Gyr ago. The presence of some dusty LPVs in this galaxy corresponds to a slight increase in recent star formation peaking around 800 Myr ago. We evaluate a quenching time around 4 Gyr ago (z < 0.5), which makes And I a late-quenching dSph. A total stellar mass (16 ± 7) × 106 M ⊙ is calculated within two half-light radii of And I for a constant metallicity Z = 0.0007.

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 Reconstructing the Star Formation History of the Magellanic Clouds

1999 ◽  
Vol 192 ◽  
pp. 72-78
Author(s):  
Jason Harris ◽  
Dennis Zaritsky ◽  
Eva K. Grebel ◽  
Ian Thompson
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Photometric Data ◽  
Star Formation History ◽  
Spatially Resolved ◽  
Formation History ◽  
History Of

We are developing an algorithm to determine the star formation history (SFH) of a mixed stellar population. We will apply the algorithm to hundreds of regions in our Magellanic Clouds Photometric Survey data and reconstruct the spatially resolved star formation history of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). In this paper, we demonstrate the algorithm on a typical region in the LMC, focussing on the obstacles and challenges facing us in attempting to reliably extract the SFH from photometric data.

scholarly journals Recovering the ages and metallicities of stars of a complex stellar population system

2008 ◽  
Vol 4 (S258) ◽  
pp. 245-252
Author(s):  
Sebastian L. Hidalgo ◽  
Antonio Aparicio ◽  
Carme Gallart
Keyword(s):  
Star Formation ◽  
Strong Interaction ◽  
Stellar Population ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Star Formation History ◽  
Host Galaxy ◽  
Population System ◽  
Formation History ◽  
Magnitude Diagram

AbstractWe present a new method to solve for the star-formation history (SFH) of a complex stellar population system from the analysis of the color-magnitude diagram (CMD). The SFH is obtained in four steps: i) computing a synthetic CMD, ii) simulating observational effects, iii) parameterization and sampling of the synthetic and observed CMDs, and iv) solving and averaging the solutions. The consistency and stability of the method have been tested using a mock stellar population.The method has been used to solve the SFH of a set of six isolated Local Group dwarf galaxies observed with HST. The main goal is to probe the effects of cosmological processes, such as reionization in the early star formation, or the ability of SNe feedback to remove gas in small halos, in dwarf galaxies free from environmental effects due to the strong interaction with the host galaxy.

scholarly journals Ground-based & WFPC2 Imaging of Fornax: Spatial Variations in Star Formation History

1999 ◽  
Vol 192 ◽  
pp. 165-169 ◽  
Author(s):  
Eva K. Grebel ◽  
Peter B. Stetson
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Spatial Variations ◽  
Star Formation History ◽  
Apparent Lack ◽  
Formation History

Fornax shows a radial age gradient. The old population is the most extended one similar to what was found in other dwarf galaxies, while younger populations are more centrally concentrated. With ≈ −1.2 dex the dominant intermediate-age population is much more metal-rich than the oldest populations traced by Fornax's globular clusters (≈ −2 dex, 15–11 Gyr). Star formation appears to have proceeded continuously with decreasing rates rather than in distinct episodes. Fornax contains the youngest population ever found in a dwarf spheroidal galaxy, 100–200 Myr, which makes its apparent lack of gas even more puzzling.

scholarly journals Episodic model for star formation history and chemical abundances in giant and dwarf galaxies

2016 ◽  
Vol 462 (4) ◽  
pp. 3739-3750 ◽  
Author(s):  
Suma Debsarma ◽  
Tanuka Chattopadhyay ◽  
Sukanta Das ◽  
Daniel Pfenniger
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Star Formation History ◽  
Chemical Abundances ◽  
Formation History
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