The nature of the first galaxies that reionised the universe during the Epoch of Reionisation (EoR) remains unclear. Attempts to directly determine spectral properties of these early galaxies are affected by both limited photometric constraints across the spectrum and by the opacity of the intergalactic medium to the Lyman Continuum (LyC) at high redshift. We approach this by analysing properties of analogous extreme emission line galaxies (EELGs, [OIII]+Hbeta EW $\gt 400$) at $2.5\lt z\lt 4$ from the ZFOURGE survey using the Multi-wavelength Analysis of Galaxy Physical Properties (MAGPHYS) SED fitting code. We compare these to galaxies at $z \gt 5.5$ observed with the James Webb Space Telesope with self-consistent spectral energy distribution fitting methodology. This work focuses on the comparison of their UV slopes (${\unicode{x03B2}}_P$), ionising photon production efficiencies $\xi_{ion}$, star formation rates and dust properties to determine the effectiveness of this analogue selection technique. We report the median ionising photon production efficiencies as log$_{10}(\xi_{ion}/(Hz\ {\rm erg}^{-1}))=$$25.14^{+0.06}_{-0.04}$, $25.16^{+0.06}_{-0.05}$, $25.16^{+0.04}_{-0.05}$, $25.18^{+0.06}_{-0.07}$ for our ZFOURGE control, ZFOURGE EELG, JADES, and CEERS samples, respectively. ZFOURGE EELGs are 0.57 dex lower in stellar mass and have half the dust extinction, compared to their ZFOURGE control counterparts. They also have a similar specific star formation rates and ${\unicode{x03B2}}_P$ to the $z\gt 5.5$ samples. We find that EELGs at low redshift ($2.5\lt z\lt 4$) are analogous to EoR galaxies in their dust attenuation and specific star formation rates. Their extensive photometric coverage and the accessibility of their LyC region opens pathways to infer stellar population properties in the EoR.

Using photometric data available in the literature we want to identify the massive stars members of the metal-poor irregular galaxy IC 10 and the clusters and associations that they form. The census of the clusters and associations of these objects is needed to provide information about age and environment on this galaxy that is apparently going through a starburst phase.

The Herschel/HOBYS key program allows to statistically study the formation of 10−20 M⊙ stars. The IRAM/W43-HERO large program is itself dedicated to the much more extreme W43 molecular complex, which forms stars up to 50 M⊙. Both reveal high-density cloud filaments of several pc3, which are forming clusters of OB-type stars. Given their activity, these so-called mini-starburst cloud ridges could be seen as “miniature and instant models” of starburst galaxies. Both surveys also strongly suggest that high-mass prestellar cores do not exist, in agreement with the dynamical formation of cloud ridges. The HOBYS and W43 surveys are necessary steps towards Galaxy-wide studies of high-mass star formation.

Herschel revealed high-density cloud filaments of several pc3, which are forming clusters of OB-type stars. Counting Herschel protostars gives a direct measure of the mass of stars forming in a period of ~105 yrs, the “instantaneous” star formation activity. Given their activity, these so-called mini-starburst cloud ridges could be seen as “miniature and instant models” of starburst galaxies. Their characteristics could shed light on the origin of massive clusters.

We present the first results from SWAN: “Survey of Water and Ammonia in Nearby galaxies”. Nearby galaxies are conveniently located to probe molecular gas properties on scales of 10 to 200 pc, which are appropriate for the study of Giant Molecular Clouds (GMCs). The resolution of the Very Large Array in D and C configurations corresponds to a few 10s of parsecs in these galaxies. To advance studies of galaxy evolution it is paramount to understand how processes in the molecular Interstellar Medium(ISM) and star formation are linked on these scales. We have observed the metastable transitions of ammonia and the 22GHz water maser line in four nearby galaxies: NGC 253, IC 342, NGC 2146, and NGC 6946 using the VLA. These galaxies were chosen to span an order of magnitude in star formation rate, and a range of galactic ecosystems. We use the ammonia transitions to derive kinetic temperatures, which exposes the heating and cooling balance of the ISM. We then aim to relate these conditions to energetic feedback from star formation as indicated by water masers.

Currently, our analysis is focused on NGC 253. NGC 253 is a barred spiral starburst galaxy with a nucleated star formation rate (SFR) of ≈ 3M⊙ per year. We use a distance of 3.9Mpc for analysis. We have observed ammonia transitions (1,1) to (5,5) and the 22GHz water maser line with a resolution of ≈63pc. We have identified nine regions across the nucleated starburst for study. The ammonia (3,3) line appears to be masing in the centermost 200pc. We have identified two regions of water maser emission. The first region is a minor axis extension, about the center of the galaxy, and is very close to the outflow. By means of these measurements, we gain an understanding of the molecular ISM associated with the nucleated starburst environment in NGC 253.

Submillimetre-selected galaxies are the most luminous, heavily star-forming galaxies in the Universe. While this field has exploded observationally over the past decade and a half, theorists have struggled to develop a concordance model for their origin. Here, I review the major theoretical efforts in this field. I then present a newly developed model for the origin of this enigmatic population of galaxies.

We analyse the correlations between continuum properties and emission line equivalent widths of star-forming and narrow-line active galaxies from SDSS. We show that emission line strengths can be predicted reasonably well from PCA coefficients of the stellar continuum using local multiple linear regression. Since upcoming sky surveys will make broadband observations only, theoretical modelling of spectra will be essential to estimate physical properties of galaxies. Combined with stellar population synthesis models, our technique will help generate more accurate model spectra and mock catalogues of galaxies to be used to fit data from new surveys. We also show that, by combining PCA coefficients from the pure continuum and the emission lines, a plausible distinction can be made between weak AGNs and quiescent star-forming galaxies. Our method uses a support vector machine, and allows a more refined separation of active and star-forming galaxies than the empirical curve of Kauffmann et al. (2003).

Various observational techniques have been used to survey galaxies and AGN, from X-rays to radio frequencies, both photometric and spectroscopic. I will review these techniques aimed at the study of galaxy evolution and of the role of AGNs and star formation as the two main energy production mechanisms. I will then present as a new observational approach the far-IR spectroscopic surveys that could be done with planned astronomical facilities of the next future, such as SPICA from the space and CCAT from the ground.

We selected and studied 180 pairs with d V < 800 km s−1 and Dp < 60 kpc containing Markarian (MRK) galaxies to investigate the dependence of galaxies integral parameters, star-formation (SF) and active galactic nuclei (AGN) properties on kinematics of pairs, their structure and large-scale environments. Projected radial separation Dp and perturbation level P are better measures of interaction strength than dV. The latter correlates with the density of large-scale environment and with the morphologies of galaxies. Both galaxies in a pair are of the same nature, the only difference is that MRK galaxies are usually brighter than their neighbors. Specific star formation rates (SSFR) of galaxies in pairs with smaller Dp or d V is in average 0.5 dex higher than that of galaxies in pairs with larger Dp or d V. Closeness of a neighbor with the same and later morphological type increases the SSFR, while earlier-type neighbors do not increase SSFR. Major interactions/mergers trigger SF and AGN more effectively than minor ones. The fraction of AGNs is higher in more perturbed pairs and pairs with smaller Dp. AGNs typically are in stronger interacting systems than star-forming and passive galaxies. There are correlations of both SSFRs and spectral properties of nuclei between pair members.

We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies.

We present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the η and η' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions.

Understanding the details of how the red sequence is built is a key question in galaxy evolution. What are the relative roles of gas-rich vs. dry mergers, major vs. minor mergers or galaxy mergers vs. gas accretion? In a recent paper (Wild et al. 2009), we compare hydrodynamic simulations with observations to show how gas-rich major mergers result in galaxies with strong post-starburst spectral features, a population of galaxies easily identified in the real Universe using optical spectra. Using spectra from the VVDS deep survey with <z> = 0.7, and a principal component analysis technique to provide indices with high enough SNR, we find that 40% of the mass flux onto the red-sequence could enter through a strong post-starburst phase, and thus through gas-rich major mergers. The deeper samples provided by next generation galaxy redshift surveys will allow us to observe the primary physical processes responsible for the shut-down in starformation and build-up of the red sequence.

Global star formation is the key to understanding galaxy disk formation. This in turn depends on gravitational instability of disks and continuing gas accretion as well as minor merging. A key component is feedback from supernovae. Primary observational constraints on disk galaxy formation and evolution include the Schmidt-Kennicutt law, the Tully-Fisher relation and the galaxy luminosity function. I will review how theory confronts phenomenology, and discuss future prospects for refining our understanding of disk formation.

There are only a few “dark galaxy” candidates discovered to date in the local Universe. One of the most prominent of them is the SW component of a merging system HI 1225+01. On the other hand, the number of known very metal-poor gas-rich dwarfs similar to I Zw 18 and SBS 0335–052 E, W has grown drastically during the last decade, from a dozen and a half to about five dozen. Many of them are very gas-rich, having from ~90 to 99% of all baryons in gas. For some of such objects that have the deep photometry data, no evidences for the light of old stars are found. At least a half of such galaxies with the prominent starbursts have various evidences of interactions, including advanced mergers. This suggests that a fraction of this group objects can be a kind of very stable protogalaxies (or “dark galaxies”), which have recently experienced strong disturbances from nearby massive galaxy-size bodies. Such a collision caused the gas instabilities and its collapse with the subsequent onset of starburst. We briefly discuss the morphology and gas kinematics for the subsample of the most metal-poor dwarfs that illustrate this picture. We discuss also the relation of these rare galaxies to the processes by which “dark galaxies” can occasionally transform to optically visible galaxies.

We present results from new deep HST/ACS photometry of I Zw 18, the most metal-poor blue compact dwarf galaxy in the nearby universe. It has been previously argued that this is a very young system that started forming stars only ≲500 Gyr ago, but other work has hinted that older (≳1 Gyr) red giant branch (RGB) stars may exist in this galaxy. Our deeper data indeed reveal evidence for an RGB. Underlying old (≳1 Gyr) populations are therefore present in even the most metal-poor systems, implying that star formation started at z ≳ 0.1. The RGB tip (TRGB) magnitude and the properties of Cepheid variables identified from our program indicate that I Zw 18 is farther away (D = 19.0 ± 1.8 Mpc) than previously believed.

The stellar mass-metallicity relations of star-forming galaxies at intermediate-z (0.4<z<1) and high-z (z≥2) are compared with the local SDSS galaxies. It shows obvious evolutionary effect, i.e., at a given stellar mass, the intermediate-z galaxies show about 0.3 dex lower metallicity, and the high-z galaxies show about 0.56 dex more metal-deficient than the local ones. These distant galaxies will produce these important parts of their metals during the consequent evolutionary process. A close-box model can explain this evolutionary process generally.

Interaction and merging are the two most important driving forces of galaxy evolution. In contrast to the well studied major mergers of two large gas-rich disk galaxies, which may lead to Ultraluminous Infrared Galaxies (ULIRGs, LFIR>1012 L⊙), mergers between galaxies of unequal mass or a spiral and an elliptical (S+E mergers) are still poorly understood. These moderate luminosity mergers typically have LFIR > 1011 L⊙. Here, we present the results of our multiwavelength study of a sample of such kind of mergers, including interferometric HI and single-dish CO observations, optical and near-infrared imaging as well as optical spectroscopy.

Using a large sample of ~40,000 star-forming galaxies selected from the SDSS, we derive oxygen abundance calibrations from strong-line ratios, such as [N II]/Hα, [O III]/[N II], [N II]/[O II], [N II]/[S II], [S II]/Hα, and [O III]/Hβ. The derived analytic calibrations cover a quite wide range of metallicity, from 12+log(O/H)= 7.1 to 9.3. These calibrations can be used as calibration references for the future studies about metallicities of star-forming galaxies.

Using the Very Large Array (VLA), we have detected the HCO+(1–0) emission line towards the Cloverleaf quasar (z = 2.56; Riechers et al. 2006). This is the first detection of ionized molecular gas emission at high redshift (z>2). HCO+ emission is a star formation indicator similar to HCN, tracing dense molecular hydrogen gas within star-forming molecular clouds. We find a HCO+/CO luminosity ratio of 0.08 and a HCO+/HCN luminosity ratio of 0.8 for the Cloverleaf. These ratios fall within the scatter of the same relationships found for low–z star–forming galaxies. However, a HCO+/HCN luminosity ratio close to unity would not be expected for the Cloverleaf if the recently suggested relation between this ratio and the far–infrared luminosity (Graciá–Carpio et al. 2006) were to hold. We conclude that a ratio between HCO+ and HCN luminosity close to 1 is likely due to the fact that the emission from both lines is optically thick and thermalized and emerges from dense regions of similar volumes. We conclude that HCO+ is potentially a good tracer for dense molecular gas at high redshift.

When falling into a galaxy cluster, the spiral - rich field galaxy population gets transformed into the characteristic E/S0/dE/dSph - rich cluster galaxy population and this already happens at surprisingly large galactocentric radii around $\sim$3R$_{virial}$. A variety of transformation processes are discussed, their respective importance and timescales. Their relations to the cluster properties, however, remain to be explored. Galaxy transformation processes, transition stages, and timescales can very well be explored by a comparison of deep multi-band imaging for a large fraction of the cluster galaxy population (down to M$^{\ast} + 3$ mag out to redshifts ${z \sim 0.5}$) and of spectroscopy of the brighter members with evolutionary synthesis models. SALT's large collecting area and field of view together with its unique $U$-band sensitivity are ideal in this respect.