Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group

Tolstoy, Eline; Hill, V.; Tosi, M.

doi:10.1146/annurev-astro-082708-101650

Cited by 1,112 publications

(1,255 citation statements)

References 290 publications

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“…Our suggestion is borne out by the discovery of ultrafaint dwarfs with M B as faint as −1 (see Simon & Geha 2007;Tolstoy et al 2009 for reviews and Table 2 for references on galaxies used here). Large surveys such as the Sloan Digital Sky Survey (York et al 2000) have made it possible to detect ever-darker dwarfs via ever-smaller star-count excesses.…”

Section: The Dm Correlations Provide a Waymentioning

confidence: 94%

“…The structural parameters of their visible matter are similar to those of the lowest-luminosity Im galaxies (Kormendy 1985(Kormendy , 1987cBinggeli & Cameron 1991;Ferguson & Binggeli 1994;Kormendy & Bender 2012; see also Figure 9 of this paper). Most of the classical nearby dSph galaxies show evidence of star formation in the past 1 -8 Gyr (e. g., Aaronson & Mould 1985;Mighell 1990;Mighell & Butcher 1992;Lee et al 1993;Beauchamp et al 1995;Weisz 2011;see Da Costa 1994;Mateo 1998, andTolstoy, Hill, &Tosi 2009 for reviews). At the time of their most recent star formation, they would have been classified as irregular galaxies (Kormendy & Bender 1994.…”

Section: Galaxy Selection Criteriamentioning

confidence: 99%

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Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

Kormendy

Freeman

2014

Proc. IAU

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Published mass models fitted to kinematic data are used to study the systematic properties of dark matter (DM) halos in Sc -Im and dwarf spheroidal (dSph) galaxies. Halo parameters are derived for rotationally supported galaxies by decomposing rotation curves V (r) into visible-and dark-matter contributions. The visible matter potential is calculated from the surface brightness assuming that the mass-to-light ratio M/L is constant with radius. "Maximum disk" values of M/L are adjusted to fit as much of the inner rotation curve as possible without making the halo have a hollow core. Rotation curve decomposition is impossible fainter than absolute magnitude M B ≃ −14, where V becomes comparable to the velocity dispersion of the gas. To increase the luminosity range further, we include central densities of dSph and dIm galaxies estimated via the Jeans equation for their stars (dSph) or H I (dIm). Combining these data, we find that DM halos satisfy well defined scaling laws analogous to the "fundamental plane" relations for elliptical galaxies. Halos in less luminous galaxies have smaller core radii r c , higher central densities ρ • , and smaller central velocity dispersions σ. Scaling laws provide new constraints on the nature of DM and on galaxy formation and evolution:1. A continuous sequence of decreasing mass extends from the highest-luminosity Sc I galaxies with M B ≃ −22.4 (H 0 = 70 km s −1 Mpc −1 ) to the lowest-luminosity galaxy with sufficient data (an ultrafaint dSph with M B ≃ −1).2. The high DM densities in dSph galaxies are normal for such tiny galaxies. Because virialized DM density depends on collapse redshift z coll , ρ • ∝ (1 + z coll ) 3 , and because the DM densities in the faintest dwarfs are about 500 times higher than those in the brightest spirals, therefore the collapse redshifts of the faintest dwarfs and the brightest spirals are related by (1 + z dwarf )/(1 + z spiral ) ≃ 8.3. The high DM densities in the dSph companions of our Galaxy imply that they are real galaxies formed from primordial density fluctuations. They are not tidal fragments. Tidal dwarfs cannot retain even the low DM densities of their giant-galaxy progenitors. In contrast, dSph galaxies generally have higher DM densities than those of possible giant-galaxy progenitors.4. We show explicitly that spiral, irregular, and spheroidal galaxies with M V > ∼ −18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that these dS, dIm, and dSph galaxies form a sequence of decreasing baryon retention (caused by supernova-driven winds) or decreasing baryon capture (after cosmological reionization) in smaller galaxies.5. In all structural parameter correlations, dS+Im and dSph galaxies behave similarly; any differences between them are small. We conclude that the difference between z ∼ 0 galaxies that still contain gas (and that still can form stars) and those that do not (and that cannot form stars) is a second-order effect.The primary effect appears to be the physics that control...

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Section: The Dm Correlations Provide a Waymentioning

confidence: 94%

Section: Galaxy Selection Criteriamentioning

confidence: 99%

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

Kormendy

Freeman

2014

Proc. IAU

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“…The sparse population of blue stars above the main turnoff and SGB can plausibly be explained as blue stragglers and their evolved descendants. Moreover, the complete lack of an ancient population (>10 Gyr) would make Crater unlike any known dwarf galaxy, all of which are known to host ancient, metal-poor populations (e.g., Tolstoy et al 2009;Brown et al 2012Brown et al , 2014Weisz et al 2014a). Our finding that Crater is a GC is inline with both Laevens et al (2014) and Kirby et al (2015), who reach the same conclusion using different observations.…”

Section: Dwarf Galaxy or Gc?mentioning

confidence: 99%

A Hubble Space Telescope Study of the Enigmatic Milky Way Halo Globular Cluster Crater*

Weisz

Koposov

Dolphin

et al. 2016

ApJ

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We analyze the resolved stellar populations of the faint stellar system, Crater, based on deep optical imaging taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Crater's color-magnitude diagram (CMD) extends ∼4 mag below the oldest main-sequence (MS) turnoff. Structurally, we find that Crater has a half-light radius of ∼20 pc and no evidence for tidal distortions. We modelCrater's CMD as a simple stellar population (SSP) and alternatively by solving for its full star formation history. In both cases, Crater is welldescribed by an SSP with an age of ∼7.5 Gyr, a metallicity of [M/H]∼−1.65, a total stellar mass of M 1e4  M , anda luminosity of~-M 5.3V , located at a distance of d∼145 kpc, with modest uncertainties due to differences in the underlying stellar evolution models. We argue that the sparse sampling of stars above the turnoff and subgiant branch are likely to be 1.0-1.4  M blue stragglers and their evolved descendants, as opposed to intermediate-age MS stars. We find thatCrater is an unusually young cluster given its location in the Galaxy's outer halo. We discuss scenarios for Crater's origin, including the possibility of being stripped from the SMC or the accretion from lower-mass dwarfs such as Leo I or Carina. Despite uncertainty over its progenitor system, Crater appears to have been incorporated into the Galaxy more recently than z∼1 (8 Gyr ago), providing an important new constraint on the accretion history of the Galaxy.

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“…As is evident from studies of the local sample of SFDGs [e.g 42,148,158,165], the details of the star formation history (SFH) of SFDGs can be very different from individual to individual. Over long time scales it is controlled by feedback processes [111] and environmental influences.…”

Section: Introductionmentioning

confidence: 99%

Star Forming Dwarf Galaxies

Bergvall¹

2011

Astrophysics and Space Science Proceedings

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Star forming dwarf galaxies (SFDGs) have a high gas content and low metallicities, reminiscent of the basic entities in hierarchical galaxy formation scenarios. In the young universe they probably also played a major role in the cosmic reionization. Their abundant presence in the local volume and their youthful character make them ideal objects for detailed studies of the initial stellar mass function (IMF), fundamental star formation processes and its feedback to the interstellar medium. Occasionally we witness SFDGs involved in extreme starbursts, giving rise to strongly elevated production of super star clusters and global superwinds, mechanisms yet to be explored in more detail. SFDGs is the initial state of all dwarf galaxies and the relation to the environment provides us with a key to how different types of dwarf galaxies are emerging. In this review we will put the emphasis on the exotic starburst phase, as it seems less important for present day galaxy evolution but perhaps fundamental in the initial phase of galaxy formation.

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Star-Formation Histories, Abundances, and Kinematics of Dwarf Galaxies in the Local Group

Abstract: Annual Review of Astronomy and Astrophysics, 47, pp. 371-425 (2009)International audienc

Cited by 1,112 publications

References 290 publications

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

Scaling Laws for Dark Matter Halos in Late-Type and Dwarf Spheroidal Galaxies

A Hubble Space Telescope Study of the Enigmatic Milky Way Halo Globular Cluster Crater*

Star Forming Dwarf Galaxies

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