C. De Breuck

Intense star formation within resolved compact regions in a galaxy at z = 2.3

Massive galaxies in the early Universe have been shown to be forming stars at surprisingly high rates. Prominent examples are dust-obscured galaxies which are luminous when observed at sub-millimetre wavelengths and which may be forming stars at a rate of 1,000 solar masses (M⊙) per year. These intense bursts of star formation are believed to be driven by mergers between gas-rich galaxies. Probing the properties of individual star-forming regions within these galaxies, however, is beyond the spatial resolution and sensitivity of even the largest telescopes at present. Here we report observations of the sub-millimetre galaxy SMMJ2135-0102 at redshift z = 2.3259, which has been gravitationally magnified by a factor of 32 by a massive foreground galaxy cluster lens. This magnification, when combined with high-resolution sub-millimetre imaging, resolves the star-forming regions at a linear scale of only 100 parsecs. We find that the luminosity densities of these star-forming regions are comparable to the dense cores of giant molecular clouds in the local Universe, but they are about a hundred times larger and 107 times more luminous. Although vigorously star-forming, the underlying physics of the star-formation processes at z ≈ 2 appears to be similar to that seen in local galaxies, although the energetics are unlike anything found in the present-day Universe.

Evidence for powerful AGN winds at high redshift: dynamics of galactic outflows in radio galaxies during the "Quasar Era"

AGN feedback now appears as an attractive mechanism to resolve some of the outstanding problems with the “standard” cosmological models, in particular those related to massive galaxies. At low redshift, evidence is growing that gas cooling and star formation may be efficiently suppressed by mechanical energy input from radio sources. To directly constrain how this may influence the formation of massive galaxies near the peak in the redshift distribution of powerful quasars, z ∼ 2, we present an analysis of the emission-line kinematics of 3 powerful radio galaxies at z ∼ 2−3 (HzRGs) based on rest-frame optical integral-field spectroscopy obtained with SINFONI on the VLT. The host galaxies of powerful radio-loud AGN are among the most massive galaxies, and thus AGN feedback may have a particularly clear signature in these galaxies. We find evidence for bipolar outflows in all HzRGs, with kinetic energies that are equivalent to 0.2% of the rest-mass of the supermassive black hole. Observed total velocity offsets in the outflows are ∼800−1000 km s −1 between the blueshifted and redshifted line emission, and FWHMs ∼ 1000 km s −1 suggest strong turbulence. Line ratios allow to measure electron temperatures, ∼10 4 K from [OIII]λλλ4363, 4959, 5007 at z ∼ 2, electron densities (∼500 cm −3 ) and extinction (AV ∼ 1−4 mag). Ionized gas masses estimated from the Hα luminosity are of order 10 10 M� , similar to the molecular gas content of HzRGs, underlining that these outflows may indicate a significant phase in the evolution of the host galaxy. The total energy release of ∼10 60 erg during a dynamical time of ∼10 7 yrs corresponds to about the binding energy of a massive galaxy, similar to the prescriptions adopted in galaxy evolution models. Geometry, timescales and energy injection rates of order 10% of the kinetic energy flux of the jet suggest that the outflows are most likely driven by the radio source. The global energy density release of ∼10 57 erg s −1 Mpc −3 may also influence the subsequent evolution of the HzRG by enhancing the entropy and pressure in the surrounding halo and facilitating ram-pressure stripping of gas in satellite galaxies that may contribute to the subsequent mass assembly of the HzRG through low-dissipation “dry” mergers.

An ALMA survey of sub-millimetre galaxies in the extended chandra deep field south: The far-infrared properties of SMGs

We exploit Atacama Large Millimeter Array (ALMA) 870 mu m observations of sub-millimetre sources in the Extended Chandra Deep Field South to investigate the far-infrared properties of high-redshift sub-millimetre galaxies (SMGs). Using the precisely located 870 mu m ALMA positions of 99 SMGs, together with 24 mu m and radio imaging, we deblend the Herschel/SPIRE imaging to extract their far-infrared fluxes and colours. The median redshifts for ALMA LESS (ALESS) SMGs which are detected in at least two SPIRE bands increases with wavelength of the peak in their spectral energy distributions (SEDs), with z = 2.3 +/- 0.2, 2.5 +/- 0.3 and 3.5 +/- 0.5 for the 250, 350 and 500 mu m peakers, respectively. 34 ALESS SMGs do not have a >3 sigma counterpart at 250, 350 or 500 mu m. These galaxies have a median photometric redshift derived from the rest-frame UV-mid-infrared SEDs of z = 3.3 +/- 0.5, which is higher than the full ALESS SMG sample; z = 2.5 +/- 0.2. We estimate the far-infrared luminosities and characteristic dust temperature of each SMG, deriving L-IR = (3.0 +/- 0.3) x 10(12) L-circle dot (SFR = 300 +/- 30 M-circle dot yr(-1)) and T-d = 32 +/- 1 K. The characteristic dust temperature of these high-redshift SMGs is Delta T-d = 3-5K lower than comparably luminous galaxies at z = 0, reflecting the more extended star formation in these systems. We show that the contribution of S-870 mu m >= 1 mJy SMGs to the cosmic star formation budget is 20 per cent of the total over the redshift range z similar to 1-4. Adopting an appropriate gas-to-dust ratio, we estimate a typical molecular mass of the ALESS SMGs of M-H2 = (4.2 +/- 0.4) x 10(10) M-circle dot. Finally, we show that SMGs with S-870 mu m > 1 mJy (L-IR greater than or similar to 10(12) L-circle dot) contain similar to 10 per cent of the z similar to 2 volume-averaged H-2 mass density.

An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: high-resolution 870 μm source counts

We report the first counts of faint submillimetre galaxies (SMGs) in the 870-mu m band derived from arcsecond-resolution observations with the Atacama Large Millimeter Array (ALMA). We have used ALMA to map a sample of 122 870-mu m-selected submillimetre sources drawn from the 0 degrees.5x0 degrees.5 the Large Apex BOlometer CAmera (LABOCA) Extended Chandra Deep Field South submillimetre survey (LESS). These ALMA maps have an average depth of sigma 870(mu m) similar to 0.4 mJy, some approximately three times deeper than the original LABOCA survey and critically the angular resolution is more than an order of magnitude higher, FWHM of similar to 1.5 arcsec compared to similar to 19 arcsec for the LABOCA discovery map. This combination of sensitivity and resolution allows us to precisely pinpoint the SMGs contributing to the submillimetre sources from the LABOCA map, free from the effects of confusion. We show that our ALMA-derived SMG counts broadly agree with the submillimetre source counts from previous, lower resolution single-dish surveys, demonstrating that the bulk of the submillimetre sources are not caused by blending of unresolved SMGs. The difficulty which well-constrained theoretical models have in reproducing the high surface densities of SMGs, thus remains. However, our observations do show that all of the very brightest sources in the LESS sample, S-870 (mu m) greater than or similar to 12 mJy, comprise emission from multiple, fainter SMGs, each with 870-mu m fluxes of less than or similar to 9 mJy. This implies a natural limit to the star formation rate in SMGs of less than or similar to 10(3) M-circle dot yr(-1), which in turn suggests that the space densities of z > 1 galaxies with gas masses in excess of similar to 5 x 10(10) M-circle dot is <10(-5) Mpc(-3). We also discuss the influence of this blending on the identification and characterization of the SMG counterparts to these bright submillimetre sources and suggest that it may be responsible for previous claims that they lie at higher redshifts than fainter SMGs.

ALMA REDSHIFTS OF MILLIMETER-SELECTED GALAXIES FROM THE SPT SURVEY: THE REDSHIFT DISTRIBUTION OF DUSTY STAR-FORMING GALAXIES

Using the Atacama Large Millimeter/submillimeter Array, we have conducted a blind redshift survey in the 3 mm atmospheric transmission window for 26 strongly lensed dusty star-forming galaxies (DSFGs) selected with the South Pole Telescope. The sources were selected to have S_(1.4mm) > 20 mJy and a dust-like spectrum and, to remove low-z sources, not have bright radio (S_843MHz) 3. We discuss the effect of gravitational lensing on the redshift distribution and compare our measured redshift distribution to that of models in the literature.

The Most Distant Structure of Galaxies Known: A Protocluster at z = 4.1

Imaging and spectroscopy with the Very Large Telescope have revealed 20 Ly? emitters within a projected distance of 1.3 Mpc and 600 km s-1 of the luminous radio galaxy TN J1338-1942 at z = 4.1. Compared to the field density of Ly? emitters, this implies an overdensity on the order of 15. The structure has a projected size of at least 2.7 ? 1.8 Mpc and a velocity dispersion of 325 km s-1, which makes it the most distant structure known. Using the galaxy overdensity and assuming a bias parameter b = 3-5, the mass is estimated to be ~1015 M?. The radio galaxy itself is surrounded by an uniquely asymmetric Ly? halo. Taken together with our previous data on PKS 1138-262 at z ~ 2.16, these results suggest that luminous radio sources are excellent tracers of high-density regions in the early universe, which evolve into present-day clusters. The statistics of bright radio sources and of concentrations in the Lyman break galaxy population are consistent with the picture that each of those concentrations harbors an active or passive luminous radio source.

A sample of 669 ultra steep spectrum radio sources to find high redshift radio galaxies

Since radio sources with Ultra Steep Spectra (USS; . 1:30;S / ) are ecient tracers of high redshift radio galaxies (HzRGs), we have dened three samples of such USS sources using the recently com- pleted WENSS, TEXAS, MRC, NVSS and PMN radio- surveys. Our combined sample contains 669 sources with S1400 > 10 mJy and covers virtually the entire sky outside the Galactic plane (jbj > 15). For our 2 largest samples, covering > 35, we selected only sources with angu- lar sizes 0: 1J y toS1400 > 2:5 Jy. The identica- tion fraction of our USS sources on the POSS (R. 20) is as low as 15%, independent of spectral index < 1:30. We further show that 85% of the USS sources that can be identied with an X-ray source are probably contained in galaxy clusters, and that < 1:6 sources are excel- lent Galactic pulsar candidates, because the percentage of these sources is four times higher in the Galactic plane. Our sample has been constructed to start an intensive campaign to obtain a large sample of high redshift objects

An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field South: The Redshift Distribution and Evolution of Submillimeter Galaxies

We present the first photometric redshift distribution for a large sample of 870 mu m submillimeter galaxies (SMGs) with robust identifications based on observations with ALMA. In our analysis we consider 96 SMGs in the Extended Chandra Deep Field South, 77 of which have 4-19 band photometry. We model the SEDs for these 77 SMGs, deriving a median photometric redshift of z(phot) = 2.3 +/- 0.1. The remaining 19 SMGs have insufficient photometry to derive photometric redshifts, but a stacking analysis of Herschel observations confirms they are not spurious. Assuming that these SMGs have an absolute H-band magnitude distribution comparable to that of a complete sample of z similar to 1-2 SMGs, we demonstrate that they lie at slightly higher redshifts, raising the median redshift for SMGs to zphot = 2.5 +/- 0.2. Critically we show that the proportion of galaxies undergoing an SMG-like phase at z >= 3 is at most 35% +/- 5% of the total population. We derive a median stellar mass of M star = (8 +/- 1) x 10(10) M circle dot, although there are systematic uncertainties of up to 5 x for individual sources. Assuming that the star formation activity in SMGs has a timescale of similar to 100 Myr, we show that their descendants at z similar to 0 would have a space density and MH distribution that are in good agreement with those of local ellipticals. In addition, the inferred mass-weighted ages of the local ellipticals broadly agree with the look-back times of the SMG events. Taken together, these results are consistent with a simple model that identifies SMGs as events that form most of the stars seen in the majority of luminous elliptical galaxies at the present day.

The properties of the interstellar medium within a star-forming galaxy at z= 2.3

We present an analysis of the molecular and atomic gas emission in the rest-frame far-infrared and submillimetre from the lensedz = 2.3 submillimetre galaxy SMM J2135−0102. We obtain very high signal-to-noise ratio detections of 11 transitions from three species and limits on a further 20 transitions from nine species. We use the 12 CO, [C I] and HCN line strengths to investigate the gas mass, kinematic structure and interstellar medium (ISM) chemistry and find strong evidence for a two-phase medium within this high-redshift starburst galaxy, comprising a hot, dense, luminous component and an underlying extended cool, low-excitation massive component. Employing a suite of photodissociation region models, we show that on average the molecular gas is exposed to an ultraviolet (UV) radiation field that is ∼1000 times more intense than the Milky Way, with star-forming regions having a characteristic density of n ∼ 10 4 cm −3 . Thus, the average ISM density and far-UV radiation field intensity are similar to those found in local ultraluminous infrared galaxies (ULIRGs) and to those found in the central regions of typical starburst galaxies, even though the star formation rate is far higher in this system. The 12 CO spectral line energy distribution and line profiles give strong evidence that the system comprises multiple kinematic components with different conditions, including temperature, and line ratios suggestive of high cosmic-ray flux within clouds, likely as a result of high star formation density. We find tentative evidence of a factor of ∼4 temperature range within the system. We expect that such internal structures are common in high-redshift ULIRGs but are missed due to the poor signal-to-noise ratio of typical observations. We show that, when integrated over the galaxy, the gas and star formation surface densities appear to follow the Kennicutt–Schmidt relation, although by comparing our data to high-resolution submillimetre imaging, our data suggest that this relation breaks down on scales of <100 pc. By virtue of the lens amplification, these observations uncover a wealth of information on the star formation and ISM at z ∼ 2.3 at a level of detail that has only recently become possible at z < 0.1 and show the potential physical properties that will be studied in unlensed galaxies when the Atacama Large Millimeter Array is in full operation.

A submillimetre galaxy at z=4.76 in the LABOCA survey of the Extended Chandra Deep Field South

We report on the identification of the highest redshift submillimetre-selected source currently known LESS J033229.4−275619. This source was detected in the Large Apex Bolometer Camera (LABOCA) Extended Chandra Deep Field-South (ECDF-S) Submillimetre Survey (LESS), a sensitive 870-μm survey (σ_(870 μm)∼ 1.2 mJy) of the full 30 × 30 arcmin_2 ECDF-S with the LABOCA on the Atacama Pathfinder Experiment telescope. The submillimetre emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z= 4.76 . We show that the bolometric emission is dominated by a starburst with a star formation rate of ∼1000 M_⊙ yr^(−1), although we also identify a moderate luminosity active galactic nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z∼ 2 submillimetre galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) quasi-stellar objects at z∼ 5 , but was also occurring in less extreme galaxies at a time when the Universe was less than 10 per cent of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z∼ 3 and that the current estimate of the space density of z > 4 SMGs is only sufficient to produce ≳10 per cent of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z∼ 3 go through an ultraluminous starburst at z≳ 4 then the required volume density of z > 4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.