Unveiling the nature of the "Green Pea" galaxies

We review recent results on the oxygen and nitrogen chemical abundances in extremely compact, low-mass starburst galaxies at redshifts between 0.1-0.3 recently named to as "Green Pea" galaxies. These galaxies are genuine metal-poor galaxies ($\sim$ one fifth solar) with N/O ratios unusually high for galaxies of the same metallicity. In combination with their known general properties, i.e., size, stellar mass and star-formation rate, these findings suggest that these objects could be experiencing a short and extreme phase in their evolution. The possible action of both recent and massive inflow of gas, as well as stellar feedback mechanisms are discussed here as main drivers of the starburst activity and their oxygen and nitrogen abundances.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy Formation and Evolution", P. Papaderos, G. Hensler, S. Recchi (eds.). Lisbon, September 2010, Springer Verlag, in pres

Star forming dwarf galaxies

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.Comment: To appear in JENAM Symposium "Dwarf Galaxies: Keys to Galaxy Formation and Evolution", P. Papaderos, G. Hensler, S. Recchi (eds.). Lisbon, September 2010, Springer Verlag, in pres

J-PLUS: The Javalambre Photometric Local Universe Survey

The Javalambre Photometric Local Universe Survey (J-PLUS) is an ongoing 12-band photometric optical survey, observing thousands of square degrees of the Northern Hemisphere from the dedicated JAST/T80 telescope at the Observatorio Astrofisico de Javalambre (OAJ). The T80Cam is a camera with a field of view of 2 deg(2) mounted on a telescope with a diameter of 83 cm, and is equipped with a unique system of filters spanning the entire optical range (3500-10 000 angstrom). This filter system is a combination of broad-, medium-, and narrow-band filters, optimally designed to extract the rest-frame spectral features (the 3700-4000 angstrom Balmer break region, H delta, Ca H+K, the G band, and the Mg b and Ca triplets) that are key to characterizing stellar types and delivering a low-resolution photospectrum for each pixel of the observed sky. With a typical depth of AB similar to 21.25 mag per band, this filter set thus allows for an unbiased and accurate characterization of the stellar population in our Galaxy, it provides an unprecedented 2D photospectral information for all resolved galaxies in the local Universe, as well as accurate photo-z estimates (at the delta z/(1 + z) similar to 0.005-0.03 precision level) for moderately bright (up to r similar to 20 mag) extragalactic sources. While some narrow-band filters are designed for the study of particular emission features ([O II]/lambda 3727, H alpha/lambda 6563) up to z < 0.017, they also provide well-defined windows for the analysis of other emission lines at higher redshifts. As a result, J-PLUS has the potential to contribute to a wide range of fields in Astrophysics, both in the nearby Universe (Milky Way structure, globular clusters, 2D IFU-like studies, stellar populations of nearby and moderate-redshift galaxies, clusters of galaxies) and at high redshifts (emission-line galaxies at z approximate to 0.77, 2.2, and 4.4, quasi-stellar objects, etc.). With this paper, we release the first similar to 1000 deg(2) of J-PLUS data, containing about 4.3 million stars and 3.0 million galaxies at r < 21 mag. With a goal of 8500 deg(2) for the total J-PLUS footprint, these numbers are expected to rise to about 35 million stars and 24 million galaxies by the end of the survey

The spatial clustering of radio sources in NVSS and FIRST; implications for galaxy clustering evolution

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

The clustering of massive galaxies at z similar to 1

We use the angular two-point correlation function to estimate the spatial correlation length of radio sources taken from the large-area 1.4 GHz NVSS radio survey. At the median survey redshift of z similar to 1, r(0) is found to be increasing with flux density. This is consistent with a scenario in which powerful (i.e. FRII) radio galaxies probe significantly more massive spatial structures than less powerful radio galaxies. The large spatial correlation length that we derive for FRIIs is remarkably close to that of extremely red objects (EROs). This implies that powerful radio galaxies and EROs trace equally massive structures at z similar to 1. Moreover, because powerful radio galaxies and EROs are both associated with luminous early-type galaxies we propose that they could be the same objects seen at different evolutionary stages. The correlation length of massive, luminous galaxies at z similar to 1 is comparable to that of bright ellipticals locally, suggesting that r(0) (comoving) of these massive galaxies has changed little from z similar to 1 to z approximate to 0. This is in excellent agreement with current ACDM hierarchical model predictions

A large population of 'Lyman-break' galaxies in a protocluster at redshift <i>z</i> ≈ 4.1

The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density(1-4) relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with 'over-densities' of galaxies that are bright in the Lyman-alpha line of hydrogen(5-7). A powerful technique for detecting high-redshift galaxies is to search for the characteristic 'Lyman break' feature in the galaxy colour, at wavelengths just shortwards of Lyalpha, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate(7-9) protocluster, TNJ1338-1942 at a redshift zapproximate to4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TNJ1338-1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age

Feedback and brightest cluster galaxy formation

We present deep optical imaging of the z 4: 1 radio galaxy TN J1338 - 1942, obtained using the Advanced Camera for Surveys ( ACS) on board the Hubble Space Telescope, as well as ground- based near- infrared imaging data from the European Southern Observatory ( ESO) Very Large Telescope ( VLT). The radio galaxy is known to reside within a large galaxy overdensity ( both in physical extent and density contrast). There is good evidence that this `` protocluster'' region is the progenitor of a present- day rich galaxy cluster. TN J1338 is the dominant galaxy in the protocluster in terms of size and luminosity ( in both the optical and near- infrared) and therefore seems destined to evolve into the brightest cluster galaxy. The high spatial resolution ACS images reveal several kiloparsec- scale features within and around the radio galaxy. The continuum light is aligned with the radio axis and is resolved into two clumps in the i(775) and z(850) bands. These components have luminosities similar to 10(9) L-circle dot and sizes of a few kpc. The estimated nebular continuum, scattered light, synchrotron- and inverse Compton - scattering contributions to the aligned continuum light are only a few percent of the observed total, indicating that the observed flux is likely dominated by forming stars. The estimated star formation rate for the whole radio galaxy is similar to 200M(circle dot) yr(-1). A simple model in which the jet has triggered star formation in these continuum knots is consistent with the available data. A striking, but small, linear feature is evident in the z850 aligned light and may be indicative of a large- scale shock associated with the advance of the radio jet. The rest of the aligned light also seems morphologically consistent with star formation induced by shocks associated with the radio source, as seen in other high- z radio galaxies ( e. g., 4C 41.17). An unusual feature is seen in Ly alpha emission. A wedge- shaped extension emanates from the radio galaxy perpendicularly to the radio axis. This `` wedge'' naturally connects to the surrounding asymmetric, large- scale (similar to 100 kpc) Ly alpha halo. We posit that the wedge is a starburst- driven superwind associated with the first major epoch of formation of the brightest cluster galaxy. The shock and wedge are examples of feedback processes due to both active galactic nucleus and star formation in the earliest stages of massive galaxy formation

A large population of `Lyman-break' galaxies in a protocluster at redshift z ~ 4.1

The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with ‘overdensities’ of galaxies that are bright in the Lyman-α line of hydrogen. A powerful technique for detecting high-redshift galaxies is to search for the characteristic ‘Lyman break’ feature in the galaxy colour, at wavelengths just shortwards of Lyα, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate protocluster, TN J1338–1942 at a redshift z ≈ 4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TN J1338–1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age