In this tutorial paper we summarize how the star formation (SF) history of a galactic region can be derived from the colour-magnitude diagram (CMD) of its resolved stars. The procedures to
build synthetic CMDs and to exploit them to derive the SF histories (SFHs) are described, as well as the corresponding uncertainties. The SFHs of resolved dwarf galaxies of all morphological types, obtained from the application of the synthetic CMD method, are reviewed and discussed. To summarize: (1) only early-type galaxies show evidence of long interruptions in the SF activity; late-type dwarfs present rather continuous, or <i>gasping</i>, SF regimes; (2) a few early-type dwarfs have experienced only one episode of SF activity concentrated at the earliest epochs, whilst many others show extended or recurrent SF activity; (3) no galaxy experiencing now its first SF episode has been found yet; (4) no frequent evidence of strong SF bursts is found; (5) there is no significant difference in the SFH of dwarf irregulars and blue compact dwarfs, except for the current SF rates. Implications of these results on the galaxy formation scenarios are briefly discussed.

Michele Cignoni

Monica Tosi

Star Formation Histories of Dwarf Galaxies from the Colour-Magnitude Diagrams of Their Resolved Stellar Populations

MOND is a phenomenological modification of Newton's law of gravitation which reproduces the dynamics of galaxies, without the need for additional dark matter. This paper reviews the basics of MOND and its application to dwarf galaxies. MOND is generally successful at reproducing stellar velocity dispersions in the Milky Way's classical dwarf ellipticals, for reasonable values of the stellar mass-to-light ratio of the galaxies; two discrepantly high mass-to-light ratios may be explained by tidal effects. Recent observations also show MOND describes tidal dwarf galaxies, which form in complex dynamical environments. The application of MOND to galaxy clusters, where it fails to reproduce observed gas temperatures, is also reviewed. Relativistic theories containing MOND in the non-relativistic limit have now been formulated; they all contain new dynamical fields, which may serve as additional sources of gravitation that could reconcile cluster observations with MOND.
Certain limits of these theories can also give the accelerating expansion of the Universe. The standard dark matter cosmology boasts numerous manifest triumphs; however, alternatives should also be pursued as long as outstanding observational issues remain unresolved, including the empirical successes of MOND on galaxy scales and the phenomenology of dark energy.

Arthur Kosowsky

Dwarf Galaxies, MOND, and Relativistic Gravitation

Dark Matter annihilation holds great potential for directly probing the clumpiness of the Galactic
halo that is one of the key predictions of the Cold Dark Matter paradigm of hierarchical structure
formation. Here we review the <svg style="vertical-align:-2.34499pt;width:8.0625px;" id="M1" height="9.9375" version="1.1" viewBox="0 0 8.0625 9.9375" width="8.0625"  xmlns="http://www.w3.org/2000/svg">
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</svg>-ray signal arising from dark matter annihilation in the centers of Galactic subhalos. We consider both known Galactic dwarf satellite galaxies and dark clumps without a stellar component as potential sources. Utilizing the <i  >Via Lactea II</i> numerical simulation, we estimate fluxes for 18 Galactic dwarf spheroidals with published central densities. The most
promising source is Segue 1, followed by Ursa Major II, Ursa Minor, Draco, and Carina. We show
that if any of the known Galactic satellites can be detected, then at least ten times more subhalos
should be visible, with a significant fraction of them being dark clumps.

Michael Kuhlen

The Dark Matter Annihilation Signal from Dwarf Galaxies and Subhalos

The standard Lambda Cold Dark Matter model is considered to be a triumph of theoretical astrophysics but observations of the Milky Way and its system of satellite galaxies irresistibly signal that theory is incomplete on galactic and subgalactic scales. The Stromlo Missing Satellites (SMS) Survey is a critical endeavor to investigate at what level predictions of
CDM cosmology are consistent with the observed matter distribution in the Milky Way halo. It will be the deepest, most extended search for optically elusive satellite galaxies to date, covering 20 000 square degrees of sky. The international SMS Survey collaboration will exploit 150 TB of CCD images in six filters acquired by the new SkyMapper telescope of the Australian National University over the next five years, expecting on completion photometric limits 0.5–1.0 mag fainter than the Sloan Digital
Sky Survey. The primary objective of the program is to characterise the baryonic and dark matter components of a complete sample of MW satellites in the Southern hemisphere to provide stringent observational constraints for improving our understanding of how the Milky Way formed and what physical processes governed galaxy formation and evolution in general.

Helmut Jerjen

Dwarf Cosmology with the Stromlo Missing Satellites Survey

The dwarf galaxy companions to the Milky Way are unique cosmological laboratories. With luminosities as low as <svg     style="vertical-align:-3.38113pt;width:62.25px;" id="M1" height="19.9125" version="1.1" viewBox="0 0 62.25 19.9125" width="62.25"  xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg">
	
		
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</svg>, they inhabit the lowest mass dark matter halos known to host stars and are presently the most direct tracers of the distribution, mass spectrum, and clustering scale of dark matter. Their resolved stellar populations also facilitate detailed studies of their history and mass content. To fully exploit this potential requires a well-defined census of virtually invisible galaxies to the faintest possible limits and to the largest possible distances. I review the past and present impacts of survey astronomy on the census of Milky Way dwarf galaxy companions and discuss the future of finding ultra-faint dwarf galaxies around the Milky Way and beyond in wide-field survey data.

Beth Willman

In Pursuit of the Least Luminous Galaxies

Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble &#8220;normal&#8221; dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the &#8220;missing baryons,&#8221; known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, &#8220;dark matter&#8221; is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and &#8220;missing baryons&#8221; or &#8220;dark baryons&#8221; is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to &#8220;dark matter&#8221;.

Frederic Bournaud

Tidal Dwarf Galaxies and Missing Baryons

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