scholarly journals Substructure in Dwarf Galaxies

2004 ◽  
Vol 21 (4) ◽  
pp. 379-381
Author(s):  
Matthew Coleman
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Large Scale ◽  
Stellar Population ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Tidal Interaction ◽  
Kinematic Evolution ◽  
Dark Material ◽  
Star Formation Histories

AbstractRecent years have seen a series of large-scale photometric surveys with the aim of detecting substructure in nearby dwarf galaxies. Some of these objects display a varying distribution of each stellar population, reflecting their star formation histories. Also, dwarf galaxies are dominated by dark matter, therefore luminous substructure may represent a perturbation in the underlying dark material. Substructure can also be the effect of tidal interaction, such as the disruption of the Sagittarius dSph by the Milky Way. Therefore, substructure in dwarf galaxies manifests the stellar, structural, and kinematic evolution of these objects.

scholarly journals Disk Mass From Large-Scale Dynamics

1998 ◽  
Vol 11 (1) ◽  
pp. 410-411
Author(s):  
J.A. Sellwood
Keyword(s):  
Dark Matter ◽  
Large Scale ◽  
Stellar Population ◽  
Milky Way ◽  
Low Mass Stars ◽  
Rutgers University ◽  
Disk Mass ◽  
Low Mass ◽  
The Individual ◽  
Inner Parts

The radial distribution of mass in a disk galaxy is strongly constrained by its rotation curve. The separate contributions from the individual stellar populations and dark matter (DM) are not easily disentangled, however, especially since there is generally no feature to indicate where the component dominating the central attraction switches from luminous to dark matter. Here I summarize three recent thesis projects at Rutgers University which all suggest that DM has a low density in the inner parts of bright galaxies, and that most of the mass therefore resides in the disk. In addition, I present some preliminary work on the Milky Way. If we are able to determine the M/L of a typical disk stellar population, it should provide a useful constraint on the numbers of low mass stars.

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 Influence of the Void Environment on Chemical Abundances in Dwarf Galaxies and Implications for Connecting Star Formation and Halo Mass

2018 ◽  
Vol 14 (S344) ◽  
pp. 369-372
Author(s):  
Kelly A. Douglass ◽  
Michael S. Vogeley ◽  
Renyue Cen
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Large Scale ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Direct Method ◽  
Dark Matter Halo ◽  
Chemical Abundances ◽  
Abundance Estimates ◽  
Galaxy Populations

AbstractWe study how the void environment affects the chemical evolution of galaxies by comparing the metallicity of dwarf galaxies in voids with dwarf galaxies in denser regions. Using spectroscopic observations from SDSS DR7, we estimate oxygen and nitrogen abundances of 889 void dwarf galaxies and 672 dwarf galaxies in denser regions. A substitute for the [OII] λ3727 doublet is developed, permitting oxygen abundance estimates of SDSS dwarf galaxies at all redshifts with the direct method. We find that void dwarf galaxies have about the same oxygen abundances and slightly lower N/O ratios than dwarf galaxies in denser environments. The lower N/O ratios seen in void dwarf galaxies may indicate both delayed star formation and a dependence of cosmic downsizing on the large-scale environment. Similar oxygen abundances in the two dwarf galaxy populations might be evidence of larger ratios of dark matter halo mass to stellar mass in voids.

scholarly journals Orbits versus Star Formation Histories: A Progress Report

1999 ◽  
Vol 192 ◽  
pp. 447-450 ◽  
Author(s):  
Eva K. Grebel ◽  
Tsafrir Kolatt ◽  
Wolfgang Brandner
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Statistical Approach ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Progress Report ◽  
Polar Plane ◽  
Preliminary Results ◽  
Star Formation Histories

Milky Way dwarf companions and satellites of distant spirals seem to show a preference for polar orbits. We suggest that five out of six M31 dwarf spheroidal companions as well as two dwarf irregulars may also be located near a polar plane.We briefly discuss preliminary results from a statistical approach to study correlations between star formation histories and orbits of Local Group dwarf galaxies, such as a possible correlation between star formation episodes and galaxy separations.

scholarly journals Star formation histories of dwarf galaxies in the FIRE simulations: dependence on mass and Local Group environment

2019 ◽  
Vol 489 (4) ◽  
pp. 4574-4588 ◽  
Author(s):  
Shea Garrison-Kimmel ◽  
Andrew Wetzel ◽  
Philip F Hopkins ◽  
Robyn Sanderson ◽  
Kareem El-Badry ◽  
...  
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Near Field ◽  
Stellar Mass ◽  
Group Environment ◽  
Zoom In ◽  
The Individual ◽  
Star Formation Histories

ABSTRACT We study star formation histories (SFHs) of 500 dwarf galaxies (stellar mass $M_\ast =10^5\!-\!10^9\, \rm {M}_\odot$) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of ‘satellite versus central’ and ‘LG versus individual MW versus isolated dwarf central.’ Around the individual MW-mass hosts, we recover the result expected from environmental quenching: central galaxies in the ‘near field’ have more extended SFHs than their satellite counterparts, with the former more closely resemble isolated (true field) dwarfs (though near-field centrals are still somewhat earlier forming). However, this difference is muted in the LG-like environments, where both near-field centrals and satellites have similar SFHs, which resemble satellites of single MW-mass hosts. This distinction is strongest for M* = 106–$10^7\, \rm {M}_\odot$ but exists at other masses. Our results suggest that the paired halo nature of the LG may regulate star formation in dwarf galaxies even beyond the virial radii of the MW and Andromeda. Caution is needed when comparing zoom-in simulations targeting isolated dwarf galaxies against observed dwarf galaxies in the LG.

scholarly journals No cores in dark matter-dominated dwarf galaxies with bursty star formation histories

2019 ◽  
Vol 486 (4) ◽  
pp. 4790-4804 ◽  
Author(s):  
Sownak Bose ◽  
Carlos S Frenk ◽  
Adrian Jenkins ◽  
Azadeh Fattahi ◽  
Facundo A Gómez ◽  
...  
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Local Environment ◽  
Temporal Variations ◽  
Star Formation History ◽  
Constant Density ◽  
Core Formation ◽  
Star Formation Histories

ABSTRACT Measurements of the rotation curves of dwarf galaxies are often interpreted as requiring a constant density core at the centre, at odds with the ‘cuspy’ inner profiles predicted by N-body simulations of cold dark matter (CDM) haloes. It has been suggested that this conflict could be resolved by fluctuations in the inner gravitational potential caused by the periodic removal of gas following bursts of star formation. Earlier work has suggested that core formation requires a bursty and extended star formation history (SFH). Here we investigate the structure of CDM haloes of dwarf galaxies ($M_{{\rm DM}} \sim 10^9\!-\!5\times 10^{10}\, {\rm M}_\odot$) formed in the apostle (‘A Project of Simulating the Local Environment’) and auriga cosmological hydrodynamic simulations. Our simulations have comparable or better resolution than others that make cores ($M_{{\rm gas}} \sim 10^4\, {\rm M}_\odot$, gravitational softening ∼150 pc). Yet, we do not find evidence of core formation at any mass or any correlation between the inner slope of the DM density profile and temporal variations in the SFH. apostle and auriga dwarfs display a similar diversity in their cumulative SFHs to available data for Local Group dwarfs. Dwarfs in both simulations are DM-dominated on all resolved scales at all times, likely limiting the ability of gas outflows to alter significantly the central density profiles of their haloes. We conclude that recurrent bursts of star formation are not sufficient to cause the formation of cores, and that other conditions must also be met for baryons to be able to modify the central DM cusp.

scholarly journals The Different Environmental Dependencies and Evolutions of Giant and Dwarf Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 202-202
Author(s):  
C.P. Haines ◽  
A. Gargiulo ◽  
A. Mercurio ◽  
P. Merluzzi ◽  
F. La Barbera ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Mass Star ◽  
Massive Galaxies ◽  
Global Properties ◽  
Massive Halos ◽  
Galaxy Populations ◽  
Star Formation Histories

AbstractThe star-formation histories, masses and structural properties of galaxies are strongly dependent on their environment: massive, passively-evolving spheroids dominate cluster cores, while in field regions, galaxies are typically low-mass, star-forming and disk-dominated (e.g Blanton et al. 2005). Equally the global properties of galaxies have been found to be bimodally distributed around a stellar mass of ~3 × 1010 M⊙ (~M*+1) (e.g. Kauffmann et al. 2003). Large-scale spectroscopic surveys have shown that the evolution of massive galaxies is primarily driven by their merger history, rather than through direct interection with the cluster environment, as demonstrated by the finding of massive passively-evolving galaxies in all environments, mild observed environmental trends for their mean stellar ages, and the gradual SF-density relation in which star-formation is still seen to be suppressed in galaxies 3–4 virial radii from the nearest cluster. In contrast, in the dwarf regime (>M*+2) dramatic changes are seen in both the luminosity function and red galaxy fraction between those galaxies in the cores of clusters and those at the virial radius (Mercurio et al. 2006, Haines et al. 2006a).We have examined the origins of the bimodality observed in the global properties of galaxies by comparing the environmental dependencies of star-formation for giant and dwarf galaxy populations. Using SDSS DR4 spectroscopic data to create a volume-limited sample complete to M*+3, we find that the environmental dependences of giant and dwarf galaxies are quite different, implying fundamental differences in their evolution (Haines et al. 2006b). Whereas the star-formation histories of giant galaxies are determined primarily by their merger history, this is not the case for dwarf galaxies. In particular, we find that old or passive dwarf galaxies are ONLY found as satellites within massive halos (clusters, groups or giant galaxies), with none in the lowest density regions. This implies that star-formation in dwarf galaxies must be much more resilient to the effects of mergers, and that the evolution of dwarf galaxies is primarily driven by the mass of their host halo, through effects such as suffocation, ram-pressure stripping or galaxy harassment.

scholarly journals What We Don’t Know About the Universe

1999 ◽  
Vol 171 ◽  
pp. 393-400
Author(s):  
Chris Impey
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Surface Brightness ◽  
Large Scale ◽  
Big Bang ◽  
Low Surface Brightness ◽  
Big Bang Model ◽  
Star Formation Histories ◽  
The Universe ◽  
True Population

AbstractDespite progress on many fronts in cosmology, outstanding questions remain. What is the nature of the dark matter? Is the inflationary big bang model viable? Must we accept a non-zero cosmological constant? Do we know the true population of galaxies? What is the range of star formation histories in the universe? Can gravity alone explain the large scale structure we observe? Studies of the low surface brightness universe may provide the answers to many of these questions.

scholarly journals Reignited star formation in dwarf galaxies that were quenched during reionization

2018 ◽  
Vol 615 ◽  
pp. A64 ◽  
Author(s):  
E. Ledinauskas ◽  
K. Zubovas
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Dwarf Galaxies ◽  
Big Bang ◽  
Baryonic Matter ◽  
Dark Matter Halos ◽  
Stellar Feedback ◽  
Mass Assembly ◽  
Star Formation Histories ◽  
The Big Bang

Context. Irregular dwarf galaxies of the Local Group have very varied properties and star formation histories. Some of them formed the majority of their stars very late compared to others. Extreme examples of this are Leo A and Aquarius, which reached the peak of star formation at z < 1 (more than 6 Gyr after the Big Bang). This fact seemingly challenges the ΛCDM cosmological framework because the dark matter halos of these galaxies on average should assemble the majority of their masses before z ~ 2 (<3 Gyr after the Big Bang). Aims. We investigate whether the delayed star formation histories of some irregular dwarf galaxies might be explained purely by the stochasticity of their mass assembly histories coupled with the effect of cosmic reionization. Methods. We developed a semi-analytic model to follow the accretion of baryonic matter, star formation, and stellar feedback in dark matter halos with present-day virial masses 109 M⊙ < Mdm,0 < 1011 M⊙ and with different stochastic growth histories obtained using the PINOCCHIO code based on Lagrangian perturbation theory. Results. We obtain the distributions of observable parameters and the evolution histories for these galaxies. Accretion of baryonic matter is strongly suppressed after the epoch of reionization in some models, but the galaxies continue to accrete dark matter and eventually reach enough mass for accretion of baryonic matter to begin again. These “reborn” model galaxies show delayed star formation histories that are very similar to those of Leo A and Aquarius. Conclusions. We find that the stochasticity caused by mass assembly histories is enhanced in systems with virial masses ~1010 M⊙ because of their sensitivity to the photoionizing intergalactic radiation field after the epoch of reionization. This results in qualitatively different star formation histories in late- and early-forming galaxies, and it might explain the peculiar star formation histories of irregular dwarf galaxies such as Leo A and Aquarius.

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