Dwarf galaxies are generally faint. To derive their age and metallicity distributions, it is critical to optimize the use of any collected photon. Koleva et al., using full spectrum fitting, have found strong population gradients in some dwarf elliptical galaxies. Here, we show that the population profiles derived with this method are consistent and more precise with those obtained with spectrophotometric indices. This allows studying fainter objects in less telescope time.

To determine the star formation histories of dwarf galaxies we use fossil methods. Compared to the color-magnitude diagrams analyzes, which are well tested and widely accepted, the studies of integrated spectra are still young. In order to assess their capabilities and limitations, we compare the results of three publicly available star formation recovery programs (StarLight, STECKMAP and ULySS).

We summarize our results on the photometric metallicities and on the presence of metallicity gradients for nine M 81 group dSphs. The majority of our studied dSphs contains a significant fraction of intermediate–age stellar populations, which we consider as a function of the deprojected distance from the dominant galaxy of the group.

The fate of metals after they are released in starburst episodes is still unclear. What phases of the interstellar medium are involved, and in which timescales? Evidence has grown over the past few years that the neutral phase of blue compact dwarf (BCD) galaxies may be metal-deficient as compared to the ionized gas of their H ii regions. These results have strong implications for our understanding of the chemical evolution of galaxies. We review here the main results and the main caveats in the metal abundance determination from far-UV absorption-lines. We also discuss possible scenarios concerning the journey of metals into the interstellar medium.

It has been claimed in the past that in low-metallicity Blue Compact Dwarf (BCDs) galaxies, the N/O value is independent of metallicity (O/H ratio), implying the need to invoke a primary production of nitrogen in intermediate-mass stars, in addition to the secondary nitrogen produced from the CNO cycle in high-mass stars. In order to better understand this controversial issue we undertook an integral field spectroscopic study of the nebular gas within a sample of BCDs previously thought to have anomalously high N/O values. Here we present the results of this study for 3 BCDs: two with anomalous N/O values (Mrk 996 and UM 420) and one with more normal N/O values (UM 462). We describe in detail how we derived the physical conditions (Te, Ne) as a function of position within the galaxy, and as a consequence, how this revealed both revised metallicities and normal N/O ratios and uncovered one of the first clear evidences of nitrogen self-enrichment of an H ii  region from WR stars.

Polar ring galaxies are systems with nearly orthogonally rotated components. We have found the gas on polar (or strongly inclined) orbits in two BCD galaxies using ionized gas velocity fields taken with a Fabry-Perot interferometer of the SAO RAS 6-m telescope. Our analysis shows that all ionized gas in Mrk 33 is concentrated in a compact disk (3 kpc in diameter) which rotates in the polar plane relative to the main stellar body. The gaseous disk in Mrk 370 has a more complex structure with a heavily warped innermost part. The presence of polar gaseous structures supports an idea that current the burst of star formation in these galaxies is due to the external gas accretion or merging. A possible fraction of polar structures among BCD galaxies seems to be very large (up to 10–15%).

Observing the HI Lyα line in absorption and emission with deep spectroscopic surveys we can study dwarf galaxies at high redshift. We describe how these observations tell us about typical (i.e., low mass, faint) star-forming galaxies, and how the various observational manifestations, damped Lyα systems, faint Lyα emitters, and continuum sources, fit together in a hierarchical universe.

Blue compact dwarf galaxies take up the low end of the distribution of metallicity as derived using collisional emission lines in ionized gaseous nebulae. In fact, the most metal poor objects in the Local Universe belong to this category. Nevertheless, the abundance discrepancy factor (ADF) found in some local HII regions whose metallicity have been derived by means of recombination lines and the offset claimed by some authors in relation to the predictions of some photoionization models question the real chemical status of these objects. In this contribution, we summarize the results of Pérez-Montero  (2010, MNRAS, 404, 2037) and we show how tailor-made models of a subsample of HII galaxies with a good determination of the thermal inner structure can be used to shed some light on this issue, helping also to study their star formation history and the properties of their ionizing stellar clusters.

We present a mass-metallicity (M–Z) relation of 412 blue compact dwarf galaxies at z = 0.2 ~ 0.5 using the Sloan Digital Sky Survey (SDSS) DR7 spectroscopic data. We found a variation of mass-metallicity relations depending on the redshift in which metallicity evolution of low mass galaxies appear to be stronger than that of high mass galaxies. The specific star formation rate (SSFR) shows tight correlation with galaxy mass in the sense that low mass galaxies have substantially high SSFR. We also discuss environmental effect in the SSFR vs galaxy mass relation. At a given mass, merging system shows systematically higher SSFR than isolated one.

Resolved observations of nearby galaxies help us to understand the relationship between gas and star formation in dwarf galaxies. The star formation histories recovered from their fossil records place constraints on how much gas dwarf galaxies could have acquired at early times. Are dwarf galaxies able to accrete a significant amount of gas at later times, or is the bulk of the gas in place once the dwarf galaxy establishes its gravitational identity? In the current epoch, we have a wealth of observations which allow us to study the process of star formation. Spatially resolved, recent star formation histories allow us to ask fundamental questions such as: What conditions are required for star formation? What is the impact of the star formation on the structure of the ISM? Does star formation heat the ISM and consequently suppress future star formation, or does it compress the ISM and lead to more star formation? Does understanding star formation at z = 0 help us to understand star formation at higher redshifts?

The Herschel Dwarf Galaxy Survey investigates the metal enrichment of the dust and gas in galaxies through observations of the local universe dwarf galaxies via the new far-infrared (FIR) and submillimetre imaging spectroscopic and photometric observations from the recently launched Herschel Space Observatory. The dust spectral energy distributions can now be constrained out to submm wavelengths and often show a submm excess in the low metallicity galaxies, which, if tracing very cold dust, could highlight large dust masses, sometimes not easily reconciled with their low-metallicity and observed gas mass. Additionally, Herschel observations of the FIR fine-structure lines probe the low density ionised gas, the HII regions and photodissociation regions. L[CII]/LCO is remarkably high in dwarf galaxies – typically an order of magnitude larger than more metal-rich starburst galaxies, pointing to a potentially significant reservoir of H2 not traced by CO but shielded in the C+-emitting envelopes. Thus a more accurate estimate of the molecular gas mass in low metallicity galaxies will be via the (CO + [CII]) to H2 conversion factor. The 88 μm [OIII] line is the brightest of all FIR lines in low-metallicity galaxies, sometimes 1.5 to 2 time brighter than the 158 μm [CII] line which is usually the dominate FIR coolant in normal spiral and starburst galaxies. The 88 μm [OIII] line may become the workhorse diagnostic for the high-redshift low-metallicity galaxies which will be targets for future submm observatories, such as ALMA. Further observations from The Herschel Dwarf Galaxy survey will provide a more complete picture of the nature of the dust and gas in low metallicity galaxies and thus a more comprehensive view of the chemical evolution of galaxies.

We report the results of an analysis of the emission spectra of HII-regions in IC 10 ionized by star clusters and WR stars based on observations made with the 6-m telescope SAO RAS using MPFS field spectrograph and SCORPIO focal reducer operating in the slit spectrograph mode. We determine the masses and ages of ionizing star clusters in the violent star-forming region of the galaxy in terms of the new evolutionary models of emission-line spectra of HII-regions developed by Martin-Manjon et al. (2010). We estimate the amount of stars needed to ionize the brightest HII-region HL 111.

We have confirmed 19 new dwarf members in five nearby (z ≤ 0.014) groups of galaxies, measured their photometric characteristics and compared the photometric scaling relations of the late-type dwarf galaxies in the field, group and cluster environments. We found no clear evidence for the structure-environment relations but some hints for the colour-environment dependencies.

Using an optically-unbiased selection process based on the HIPASS neutral hydrogen survey, we have identified a sample of over 170 spatially isolated, gas-rich dwarf galaxies in the southern hemisphere with cz between 350 and 1500 km s−1, with R-band luminosities and HI masses less than the Small Magellanic Cloud, most of which lack spectroscopic data. This paper summarises our survey criteria and procedures and nebular abundance measurements using the WiFeS IFU on the ANU 2.3 m telescope. (See longer version on astro.ph.)

Star formation in the low mass and low metallicity environments of dwarf galaxies provides important clues about how star formation proceeded in the early universe. To measure the properties of youngest star forming regions – those closest to stellar birth conditions – one needs to use an extinction-free tracer of thermal emission, such as free-free continuum emission in the radio, to penetrate the dust surrounding these regions. We present high sensitivity and high resolution observations of the radio continuum emission in the low metallicity dwarf galaxy II Zw 40 and combine it with HST ACS data and single dish CO(1–0) to gain a more complete picture of star formation in this galaxy.

The metallicity of galaxies and its evolution with redshift is of paramount importance for understanding galaxy formation. Abundances in the interstellar medium (ISM) are typically determined using emission-line spectroscopy of H ii  regions. However, since H ii  regions are associated with recent SF they may not have abundances typical for the galaxy as a whole. This is true in particular for star-forming galaxies (SFGs), in which the bulk of the metals may be contained in the neutral gas. It is therefore important to directly probe the metal abundances in the neutral gas. This can be done using absorption lines in the Far UV. We have developed techniques to do this in SFGs, where the absorption is measured for sightlines toward bright SF regions within the galaxy itself. We have successfully applied this technique to a sample of galaxies observed with FUSE. The results have been very promising, suggesting in I Zw18 that abundances in the neutral gas may be up to 0.5 dex lower than in the ionized gas. However, the interpretation of the FUSE data is complicated by the very large FUSE aperture (30 arcsec), the modest S/N, and the limited selection of species available in the FUSE bandpass. The advent of COS on HST now allows a significant advance in all of these areas. We will therefore obtain absorption line spectroscopy with G130M (~1150–1450 Å) in the same sample for which we already have crude constraints from FUSE. The results will provide important new insights into the metallicities of galaxies, and into outstanding problems at high redshift such as the observed offset between the metallicities of Lyman Break Galaxies and Damped Lyman Alpha systems.

We present observations of multiple system of dwarf galaxies at the Russian 6-m telescope and the GMRT (Giant Metrewave Radio Telescope). The optical observations are a part of the programme Study of Groups of Dwarf Galaxies in the Local Supercluster. The group of galaxies under consideration looks like filament of 5 dwarfs. Two faint galaxies show peculiar structure. Long slit spectrum reveals inner motions about 150 km s−1 in one of them. It suggests that the galaxy is on stage of ongoing interaction. Probably, we see the group in moment of its formation.

We present recent results on the oxygen and nitrogen chemical abundances in the extremely compact, low-mass starburst galaxies at redshifts 0.1–0.3 usually referred to as “green pea” galaxies. We show that they are metal-poor galaxies (~1/5 solar) with lower oxygen abundances than star-forming galaxies of similar mass and N/O ratios unusually high for galaxies of the same metallicity. Recent, rapid, and massive inflows of cold gas, possibly coupled with enriched outflows from supernova winds, are used to explain the results. This is consistent with the known “pea” galaxy properties and suggest that these rare objects are experiencing a short and extreme phase in their evolution.

In this work, based on Integral Field Unit spectroscopy observations on the Gemini South telescope, we study the spatial distribution of the He II λ4686 emission line and its relationship with the properties of the interstellar medium in two compact H II galaxies (Tol 0104-388 and Tol 2146-391). We explore the possible mechanisms responsible for this high-ionization emission line. Our preliminary results indicate that this emission line and its spatial distribution is associated with a mix of sources, where most of the emission is likely due to the ionizing radiation from radiative shocks originates by the presence of a myriad of unresolved star clusters in the central regions. Wolf-Rayet stars can be excluded as the primary source producing the observed morphology of the He II λ4686 emission line.

We present a preliminary large-scale, neutral Hydrogen emission map of structure around dwarf irregular (dIm) galaxy NGC 1569. These data were taken earlier this year with the Robert C. Byrd Green Bank Telescope (GBT). Our primary objective was to search for HI structure potentially connecting NGC 1569 with IC 342 as an explanation for the starburst and peculiar kinematics prevalent in NGC 1569.