The evolution of giant molecular clouds (GMCs), which are the main sites of star formation, is essential for unraveling how stars form and how galaxies evolve. We analyzed the M33 CO(J = 2–1) data with spatial resolution of 39 pc obtained by ALMA-ACA 7 m array combined with IRAM 30 m. We identified 736 GMCs and classified them into three types; Type I: associated with no Hii regions, Type II: associated with Hii regions with the Hα luminosity L(Hα) < 1037.5 erg s-1, Type III: associated with Hii regions with L(Hα) > 1037.5erg s-1. We found that mass, size, and velocity dispersion of GMCs slightly increase in the order of Type I, II, and III GMCs. Type III GMCs mainly exist in the spiral arm, while many of Type I and Type II GMCs are distributed in the inter-arm. Assuming that the star formation proceeds steadily, we roughly estimated the total GMC lifetime of 30 Myr.

The long-term SAAO survey of Local Group galaxies in the near-infrared (JHKs) has included five dwarf irregulars (dIrr), namely, NGC 6822, IC 1613, WLM, Sgr dIG and NGC 3109. We have found long-period (Mira) variables in all of them. Most of the Miras, which follow a linear LMC period-luminosity (PL) relation well, are carbon-rich. A small group of oxygen-rich Miras are brighter than the linear PL relation predicts, presumably because they are undergoing hot-bottom burning (HBB).

The community of massive stars is working intensively on Local Group dwarf irregular galaxies (dIrr). They are a reservoir of metal-poor massive stars that serve to understand the physics of their higher redshift siblings and population III stars, interpret the farthest, most energetic SNe and GRBs, and compute feedback through Cosmic History. Along the way, we became interested in the recent star-formation history and initial mass-function of the host dIrr’s, their chemical evolution, and gas and dust content. Our team is working to unveil and characterize with spectroscopy the OB-stars in IC 1613, Sextans A and SagDIG, that form a sequence of decreasing metal content. We showcase some results to stimulate synergies between both communities.

We observed a bright H II complex, Hubble V in NGC 6822, using the high-resolution near-infrared spectrograph IGRINS (R = 45,000) attached on the 2.7 m telescope at the McDonald Observatory. We carried out a spectral mapping over a 15″ × 18″ region in the H and K bands using a slit-scanning technique. The emission lines Brγ and He i from ionized regions as well as molecular hydrogen lines from photo-dissociation regions (PDRs), were detected. We show three-dimensional maps of the emission lines and discuss the possibility of an expanding hot bubble structure within which many ionized components are around the central stellar cluster.

The warm ionised medium (WIM), also referred to as diffuse ionised gas (DIG), contains most of the mass of interstellar medium in ionised form, contributing as much as 30% of the total atomic gas mass in the solar neighborhood. The advent of CCDs has enabled unprecedented study of this medium in external galaxies, probing a variety of environments. In particular, we can derive the morphology of the WIM, its distribution across disks, and the correlation with other Population I material. Spectroscopy of the WIM makes it possible to test various ionisation models. I will review here our current understanding of the properties of the WIM in spiral galaxies. A perhaps unexpected result is that the Hα emission from the WIM contributes about 40% of the total observed Hα luminosity from spirals. This places severe constraints on possible sources of ionisation, since only photoionisation by OB stars meets this requirement. Spectroscopic measurements of forbidden line strengths appear in reasonable agreement with photoionisation models. It is not yet clear if the Lyman continuum photons that ionise the WIM are mostly from OB stars located inside traditional HII regions, or from field OB stars.

Molecular gas has still only been detected beyond the R25 radius in a few galaxies. Is this due to the low H2 content or to the difficulty of using Carbon Monoxide (CO) to trace H2? Similarly, star formation (SF) decreases sharply in the outer disks of spirals although HI is often plentiful; is the decrease in SF because there is little H2 or because the SF is very inefficient in the outer disk environment?

Existing observations suggest that while outer disk clouds tend to be smaller (steeper mass function), their CO brightness temperature is only slightly lower than in the inner disk, at least when observed with sufficiently high angular resolution. In near-solar metallicity galaxies (Z ⩾ 0.5Zsol), the CO does not become intrinsically difficult to detect when H2 is present, even in the outer disk. While more observations of CO or other means of tracing H2 in the outer disks are necessary, current data tend to show that the SF rate per unit H2 remains approximately constant with galactocentric distance, indicating that the star formation proceeds normally but the transformation of HI into H2 is very slow in the outer disk.

Of the three kinds of neutral gas found outside the stellar disks of Local Group galaxies, only the products of interaction, like the Magellanic Stream, have a clearly understandable origin. Both the high-velocity clouds and the faint H I between M31 and M33 remain a mystery. New observations of the region between M31 and M33 with the Green Bank Telescope show that the H I there resides in clouds with a size and mass similar to that of dwarf galaxies, but without stars. These clouds might be products of an interaction, or condensations in the hot circumgalactic medium of M31, but both these models have difficulties. The prevalence of clouds like this in the Local Group remains to be determined.

Massive stars play a key role in environments with very different metallicities. To interpret the role of massive stars in these systems we have to know their properties at different metallicities. The Local Group offers an excellent laboratory to this aim.

The identification of the carrier(s) of diffuse interstellar bands (DIBs) is one of the oldest mysteries in stellar spectroscopy. With the advent of 8-10m-class telescopes substantial progress has been made in measuring the properties of DIBs in the optical and near-infrared wavelength domain, not only in the Galaxy, but also in different environments encountered in Local Group galaxies and beyond. Still, the DIB carriers have remained unidentified. The coming decade will witness the development of extremely large telescopes (GMT, TMT and E-ELT) and their instrumentation. In this overview I will highlight the current instrumentation plan of these future observatories, emphasizing their potential role in solving the enigma of the DIBs.

The physical and chemical evolution of galaxies is intimately linked to star formation, We present evidence that molecular gas (H2) is transformed into stars more quickly in smaller and/or subsolar metallicity galaxies than in large spirals – which we consider to be equivalent to a star formation efficiency (SFE). In particular, we show that this is not due to uncertainties in the N(H2)/Ico conversion factor. Several possible reasons for the high SFE in galaxies like the nearby M33 or NGC 6822 are proposed which, separately or together, are the likely cause of the high SFE in this environment. We then try to estimate how much this could contribute to the increase in cosmic star formation rate density from z = 0 to z = 1.

We use the very recently completed high-resolution IRAM CO survey of M33 with the high-resolution HI observations (published by Gratier et al. 2010, A&A, 522, 3) and Herschel Far-IR and submillimeter mapping observations to study how the dust behaves in the molecular and atomic gas phases of the interstellar medium (ISM). M33 is a “young" object in that it is gas-rich with a young stellar population and low metallicity as compared to large spirals like the Milky Way or Andromeda. Nonetheless, it is very clearly a spiral galaxy with a thin and reasonably axisymmetric disk. As such, it can be viewed as a stepping stone towards less evolved objects like magellanic irregulars (including the LMC and SMC) and perhaps distant objects in the early universe. More specifically, we look for radial variations in the dust emission spectrum (β parameter) as well as comparing regions dominated by either H2 or HI. The grey-body emission spectrum flattens (lower β) with galactocentric distance and generally is flatter in the atomic medium as compared to the molecular gas.

A survey has been conducted of Local Group galaxies with the Japanese/South African Infrared Survey Facility at SAAO, Sutherland. A number of Mira variables have been discovered in four dwarf spheroidals, which provides an opportunity to test the usefulness of these stars as distance indicators in galaxies beyond the Magellanic Clouds. These Miras are found to follow the same period-luminosity relation as in the LMC, provided bolometric magnitudes are used.

Star formation appears to be clumped into a hierarchy of structures, from giant molecular clouds down to individual cores and clusters, which are often hierarchical themselves, showing significant substructure. This has been demonstrated for our Galaxy through the application of sophisticated statistical methods, in particular the nearest-neighbour density and the minimum spanning tree (MST), to different star-forming regions. Here we present our analysis of clustered star formation as demonstrated through the detection of structures of young stellar populations in the dwarf star-forming galaxy NGC 6822.

We study the origin and properties of unbound stars in the kinematic samples of dwarf spheroidal galaxies. For this purpose we have run a high resolution N-body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. We create mock kinematic data sets by observing the dwarf in different directions. When the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. However, most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert. We model the velocity dispersion profiles of the cleaned-up kinematic samples using solutions of the Jeans equation. We show that even for such a strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and mass-to-light ratio of the dwarf with accuracy typically better than 25%.

The Ks-band magnitude distribution of carbon-rich and oxygen-rich asymptotic giant branch stars within Local Group galaxies like the Magellanic Clouds, NGC 6822, M33 and SagDIG is easily obtained from ground-based observations. Appropriate stellar evolutionary models covering a range of metallicities and star formation rates are used to produce theoretical distributions that allow us to derive the history of star formation across these galaxies. I will show the result of these studies and discuss the application of this technique to more distant systems as well as deeper observations, like those that VISTA will provide, to improve our understanding of, in particular, the Magellanic Clouds.

How clumpy are galactic halos? Recent observations around both the Milky Way and the Andromeda galaxy (M31) have revealed numerous faint stellar streams and dwarf galaxies, leading to the belief that more of these may yet remain undetected. In this contribution, we present the map produced from the Megacam/CFHT survey that our group has undertaken in the outer halo of M31 and that, for the first time, gives a deep panoramic view of a significant region of the outer halo of a spiral galaxy. This panoramic survey, which covers ∼ 60 sq. deg. of the southern quadrant of the M31 halo, extends the WFC/INT survey of the inner halo (Ferguson et al. 2002) from a projected distance of ∼ 50 to ∼ 150 kpc. It is deep enough to cover three magnitudes below the tip of the red giant branch of stellar populations at the distance of M31. The survey reveals:

• • Three faint dwarf galaxies with absolute magnitudes in the range -7.3 < M_V < -6.4 and the most remote M31 globular cluster at a projected distance of ∼ 120 kpc from M31 (see Martin et al. 2006 for more details).

• • That the giant stream of Ibata et al. (2001) covers a much wider area than previously expected from shallower surveys, has an apocenter at 125±25 kpc from M31 and is probably due to the accretion of a small disk galaxy.

• • A new stellar stream or shell approximately perpendicular to the minor axis of M31 at a projected distance of 120 kpc and with a metallicity of [Fe/H] ∼ -1.5 (assuming it is at the distance of M31).

• • A new stellar stream along the ma jor axis of M31 that extends to at least 100 kpc from M31 with [Fe/H] ∼ -1.3 (once again assuming it is at the distance of M31).

• • Regions void of any stellar structure brighter than 34-35 mag/arcsec2 at a distance of 100 to 130 kpc from M31.

The survey shows that the outer halo of the Andromeda galaxy is very structured, in qualitative agreement with recent cosmological simulations (e.g. Bullock & Johnston, 2005).

The Local Group offers an excellent laboratory for near-field cosmology by permitting us to use the resolved stellar content of its constituent galaxies as probes of galaxy formation and evolution, which in turn is an important means for testing cosmological models of hierarchical structure formation. In this review, we discuss the the least massive, yet most numerous type of galaxy in the Local Group, the dwarf spheroidal galaxies, and compare their properties to cosmological predictions. In particular, we point out problems found with a simple building block scenario and with effects expected from reionization. We show that the star formation histories of dSphs are inconsistent with the predicted cessation of star formation after reionization; instead, extended star formation episodes are observed. The Galactic dSphs contain in part prominent intermediate-age populations, whereas the Galactic halo does not. Conversely, the M31 dSphs are almost entirely old, while the M31 halo contains a substantial intermediate-age population. These differences in the population structure as well as the differences in the modes of star formation inferred from [α/Fe] ratios make dSphs unlikely major contributors to the build-up of the Galactic and M31 halo unless most of the accretion occurred at early epochs. On the other hand, there is clear evidence for ongoing harassment and accretion of a number of dSphs.

We present results from photometric and spectroscopic survey of giant stars in the Leo I dwarf spheroidal galaxy. We find compelling evidence that this galaxy has been tidally disrupted.

With the new discoveries that some dEs are rotationally supported and that dIs may show a large variety in star formation histories, the perceived relationships between these two families of galaxies are changing. There are at least three viable channels for the origin of dwarf elliptical galaxies with strong observational evidence that support their reality. I will discuss the observational evidence for each of these channels and the likely physical processes which determine each channel.