Search

We present the design, rationale, properties and catalogs of the MusE Gas FLOw and Wind survey (MEGAFLOW), a survey of the cool gaseous halos of $z\sim1$ galaxies using low-ionization MgII absorption systems. The survey consists of 22 quasar fields selected from the Sloan Digital Sky Survey (SDSS) having multiple ($\geq3$) strong MgII absorption lines over the redshift range $0.31$, i.e. more than 60 galaxies per arcmin$^{2}$. They were identified using a dual detection algorithm based on both continuum and emission line objects. The achieved [OII] 50\%\ completeness is 3.7$\times 10^{-18}$ erg/s/cm$^2$ (corresponding to SFR$>0.01$ M$_\odot$ yr$^{-1}$ at $z=1$) using realistic mock [OII] emitters and the 50\%\ completeness is $m_{F775W}\approx26$ AB magnitudes for continuum sources. We find that (i) the fraction of [OII] emitting galaxies which have no continuum is $\sim15$\%; (ii) the success rate in identifying at least one galaxy within 500 km/s and 100 kpc is $\approx90$\%\ for MgII absorptions with $W_r^{2796}\gtrsim0.5$~\AA; (iii) the mean number of galaxies per MgII absorption is $2.9\pm1.6$ within the MUSE field-of-view; (iv) of the 80 MgII systems at $0.310^9$ M$_\odot$, and star-formation rates $>1$ M$_\odot$ yr$^{-1}$., Comment: 23 pages; 16 figures; accepted for publication in A&A

We quantify the stellar rotation of galaxies by computing the $\lambda_{R}$ parameter, a proxy for the stellar angular momentum in a sample of 106 galaxies with redshift 0.1 $<$ z $<$ 0.8 and stellar masses from $\sim$10$^{7.5}$ to 10$^{11.8}$ M$_{\odot}$. The sample is located in the CANDELS/GOODS-S and COSMOS fields, and it was observed by various MUSE surveys. We create stellar velocity and velocity dispersion maps using a full-spectrum fitting technique, covering spatially $\sim$2$R_{e}$ for the galaxies. We study the impact of the atmospheric seeing on the spin parameter and apply corrections when pertinent. Through the analysis of the $\lambda_{R}-\epsilon$ diagram, we notice that the fraction of round and massive galaxies increases with redshift. We lack galaxies with $\lambda_{R}$ < 0.1 in the sample and we find only one potential, but uncertain, low-mass slow rotator at z $\sim0.3$. Moreover, we do not see an evident evolution or trend in the stellar angular momentum with redshift. We characterize the sample environment using two indicators: a local estimator based on the Voronoi tesselation method, and a global estimator derived by the use of the Friends-of-Friends algorithm. We find no correlation between the environment and $\lambda_{R}$ given that we are not probing dense regions or massive galaxy structures. We also analyze the kinematic maps of the sample finding that about 40$\%$ of galaxies are consistent with being regular rotators, having rotating stellar discs with flat velocity dispersion maps, while $\sim20\%$ of galaxies have complex velocity maps and can be identified as non-regular rotators in spite of their $\lambda_{R}$ values. For the remaining galaxies the classification is uncertain. As we lack galaxies with $\lambda_{R}$< 0.1, we are not able to identify when galaxies become slow rotators within the surveyed environments, area and redshift range., Comment: 26 pages, 18 figures, full abstract on the paper

We introduce the MUSE gAlaxy Groups in COSMOS (MAGIC) survey, which was built to study the impact of environment on galaxy evolution over the last 8 Gyr. It consists of 17 MUSE fields targeting 14 massive structures at intermediate redshift ($0.321.5$. The spectroscopic redshift completeness is high: in the redshift range of [OII] emitters ($0.25 \le z < 1.5$), where most of the groups are found, it globally reaches a maximum of 80% down to $z_{app}^{++}=25.9$, and locally decreases from $\sim 100$% to $\sim50$% in magnitude bins from $z_{app}^{++}=23-24$ to $z_{app}^{++}=25.5$. We find that the fraction of quiescent galaxies increases with local density and with the time spent in groups. A morphological dichotomy is also found between bulge-dominated quiescent and disk-dominated star-forming galaxies. As environment gets denser, the peak of the stellar mass distribution shifts towards $M_*>10^{10}~M_\odot$, and the fraction of galaxies with $M_*<10^9~M_\odot$ decreases significantly, even for star-forming galaxies. We also highlight peculiar features such as close groups, extended nebulae, and a gravitational arc. Our results suggest that galaxies are preprocessed in groups of increasing mass before entering rich groups and clusters. We publicly release two catalogs containing the properties of galaxies and groups, respectively., Comment: 27 pages, 22 figures, accepted for publication in A&A

The chemical composition of gas in galaxies can be measured in detail from absorption spectroscopy. By studying gas in galaxies in this way, it is possible to investigate the small and faint galaxies, which are the most numerous in the universe. In particular, the chemical distribution of gas in absorbing systems gives us insight into cycles of gas in and around galaxies. Here we study chemical enrichment within 64 Damped Lyman-alpha Absorption (DLA) systems between $1.7 < z < 4.2$. We use high-resolution spectra from VLT/UVES to infer dust depletion from relative abundances of several metals. We perform a component-by-component analysis within DLAs, and characterise variations in their chemical enrichment. Unlike hydrogen, the metal columns can be characterised for individual components. We use them to derive the dust depletion ([Zn/Fe]fit), as an indicator for chemical enrichment. We find that some DLAs are chemically diverse within themselves, with [Zn/Fe]fit ranging up to 0.62 dex within a single system. This suggests that absorbing gas within these galaxies is chemically diverse. Although we do not find a clear trend of decreasing dust depletion with redshift, we do see that the most chemically enriched systems are at lower redshifts. We also observe evidence for dust-poor components at all redshifts, which may be due to the accretion of pristine gas onto galaxies. We combine the chemical and kinematic properties of the individual gas components and observe potential signatures of infalling gas, with low depletion at velocities below $\sim$100km/s, and outflows, with high depletion and velocities of $\sim$600km/s. We find over-abundances of alpha-elements (an enhancement of $\sim$0.3dex) and under-abundances of Mn in several components, which is likely a signature of core-collapse SNe nucleosythesis in the ISM. We observe these effects mostly at lower levels of chemical enrichment., Comment: 56 pages, 99 figures, Accepted for publication in A&A, Abstract abridged for arXiv

We study the link between gas flow events and key galaxy scaling relations: the relations between star formation rate (SFR) and stellar mass (the main sequence, MS), gas metallicity and stellar mass (the mass-metallicity relation, MZR) and gas metallicity, stellar mass and SFR (the fundamental metallicity relation, FMR). Using all star-forming galaxies (SFGs) in the 22 MUSE fields of the MusE GAs FLOw and Wind (MEGAFLOW) survey, we derive the MS, MZR and FMR scaling relations for 385 SFGs with $M = 10^8 - 10^{11.5}$ $M_\odot$ at redshifts 0.35 < z < 0.85. Using the MUSE data and complementary X-Shooter spectra at 0.85 < z < 1.4, we determine the locations of 21 SFGs associated with inflowing or outflowing circumgalactic gas (i.e. with strong MgII absorption in background quasar spectra) relative to these scaling relations. Compared to a control sample of galaxies without gas flows (i.e., without MgII absorption within 70 kpc of the quasar), SFGs with inflow events (i.e., MgII absorption along the major axis) are preferentially located above the MS, while SFGs with ouflow events (i.e., MgII absorption along the minor axis) are preferentially more metal rich. Our observations support the scenario in which gas accretion increases the SFR while diluting the metal content and where circumgalactic outflows are found in more metal-rich galaxies., Comment: 13 pages, 8 figures

The evolution of galaxies is influenced by many physical processes which may vary depending on their environment. We combine Hubble Space Telescope (HST) and Multi-Unit Spectroscopic Explorer (MUSE) data of galaxies at 0.25

It is still a challenge to assess the merger fraction of galaxies at different cosmic epochs in order to probe the evolution of their mass assembly. Using the Illustris cosmological simulations, we investigate the relation between the separation of galaxies in a pair, both in velocity and projected spatial separation space, and the probability that these interacting galaxies will merge in the future. From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction. We then probe the evolution of the major and minor merger fraction using the latest MUSE deep observations over the HUDF, HDFS, COSMOS-Gr30 and Abell 2744 regions. From a parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366 close pairs spread over a large range of redshifts ($0.2

The well-known quasar SDSS J095253.83+011421.9 (J0952+0114) at z=3.02 has one of the most peculiar spectra discovered so far, showing the presence of narrow Ly$\alpha$ and broad metal emission lines. Although recent studies have suggested that a Proximate Damped Ly$\alpha$ system (PDLA) causes this peculiar spectrum, the origin of the gas associated with the PDLA is unknown. Here we report the results of MUSE observations that reveal a new giant ($\approx$ 100 physical kpc) Lyman $\alpha$ nebula. The detailed analysis of the Ly$\alpha$ velocity, velocity dispersion, and surface brightness profiles suggests that the J0952+0114 Ly$\alpha$ nebula shares similar properties of other QSO nebulae previously detected with MUSE, implying that the PDLA in J0952+0144 is covering only a small fraction of the QSO emission solid angle. We also detected bright and spectrally narrow CIV$\lambda$1550 and HeII$\lambda$1640 extended emission around J0952+0114 with velocity centroids similar to the peak of the extended and central narrow Ly$\alpha$ emission. The presence of a peculiarly bright, unresolved, and relatively broad HeII$\lambda$1640 emission in the central region at exactly the same PDLA redshift hints at the possibility that the PDLA originates in a clumpy outflow with a bulk velocity of about 500 km/s. The smaller velocity dispersion of the large scale Ly$\alpha$ emission suggests that the high-speed outflow is confined to the central region. Lastly, the derived spatially resolved HeII/Ly$\alpha$ and CIV/Ly$\alpha$ maps show a positive gradient with the distance to the QSO hinting at a non-homogeneous ionization parameter distribution., Comment: 17 pages, 13 figures and 2 tables; Accepted for publication in ApJ

Following the success of the Plateau de Bure high-z Blue Sequence Survey (PHIBSS), we present the PHIBSS2 legacy program, a survey of the molecular gas properties of star-forming galaxies on and around the star formation main sequence (MS) at different redshifts using NOEMA. This survey significantly extends the existing sample of star-forming galaxies with CO molecular gas measurements, probing the peak epoch of star formation (z=1-1.6) as well as its building-up (z=2-3) and winding-down (z=0.5-0.8) phases. The targets are drawn from the GOODS, COSMOS, and AEGIS deep fields and uniformly sample the MS in the stellar mass (M*) - star formation rate (SFR) plane with log(M*/Msun) = 10-11.8. We describe the survey strategy and sample selection before focusing on the results obtained at z=0.5-0.8, where we report 60 CO(2-1) detections out of 61 targets. We determine their molecular gas masses and separately obtain disc sizes and bulge-to-total (B/T) luminosity ratios from HST I-band images. The median molecular gas-to-stellar mass ratio, gas fraction, and depletion time as well as their dependence with M* and offset from the MS follow published scaling relations for a much larger sample of galaxies spanning a wider range of redshifts. The galaxy-averaged Kennicutt-Schmidt (KS) relation between molecular gas and SFR surface densities is strikingly linear, pointing towards similar star formation timescales within galaxies at any given epoch. In terms of morphology, the molecular gas content, the SFR, the disc stellar mass, and the disc molecular gas fraction do not seem to correlate with B/T and the stellar surface density, which suggests an ongoing supply of fresh molecular gas to compensate for the build-up of the bulge. Our measurements do not yield any significant variation of the depletion time with B/T and hence no strong evidence for morphological quenching within the scatter of the MS., Comment: Accepted for publication in A&A (28 pages, 9 figures, 4 tables)

Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, fed by inflows from the intergalactic medium and by outflows due to galactic winds. Absorption-line measurements along the sightlines to bright and rare background quasars indicate that this circumgalactic medium pervades far beyond the extent of starlight in galaxies, but very little is known about the spatial distribution of this gas. A new window into circumgalactic environments was recently opened with the discovery of ubiquitous extended Lyman-alpha emission from hydrogen around high-redshift galaxies, facilitated by the extraordinary sensitivity of the MUSE instrument at the ESO Very Large Telescope. Due to the faintness of this emission, such measurements were previously limited to especially favourable systems or to massive statistical averaging. Here we demonstrate that low surface brightness Lyman-alpha emission surrounding faint galaxies at redshifts between 3 and 6 adds up to a projected sky coverage of nearly 100%. The corresponding rate of incidence (the mean number of Lyman-alpha emitters penetrated by any arbitrary line of sight) is well above unity and similar to the incidence rate of high column density absorbers frequently detected in the spectra of distant quasars. This similarity suggests that most circumgalactic atomic hydrogen at these redshifts has now been detected also in emission., Comment: published in Nature, online on 01 Oct 2018, in print on 11 Oct 2018. This is the Authors' version, for the published version see https://www.nature.com/articles/s41586-018-0564-6 ; free viewing access via https://rdcu.be/8eCx

The Lyman alpha (lya) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km/s compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics and correlations with quasar absorption lines when only lya is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the lya line profile. We use spectroscopic observations of Lyman-Alpha Emitters (LAEs) for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z~3 and z~6 as part of various Multi Unit Spectroscopic Explorer (MUSE) Guaranteed Time Observations (GTO). We also include a compilation of spectroscopic lya data from the literature spanning a wide redshift range (z~0-8). First, restricting our analysis to double-peaked lya spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, Vpeak, and the separation of the peaks. Secondly, we find a correlation between Vpeak and the full width at half maximum of the lya line. Fitting formulas, to estimate systemic redshifts of galaxies with an accuracy of +-100 km/s when only the lya emission line is available, are given for the two methods., Comment: letter, accepted for publication in MNRAS

We analyse a sample of 8 highly magnified galaxies at redshift 0.6

We present the "SINS/zC-SINF AO survey" of 35 star-forming galaxies, the largest sample with deep adaptive optics-assisted (AO) near-infrared integral field spectroscopy at z~2. The observations, taken with SINFONI at the Very Large Telescope, resolve the Ha and [NII] line emission and kinematics on scales of ~1.5 kpc. In stellar mass, star formation rate, rest-optical colors and size, the AO sample is representative of its parent seeing-limited sample and probes the massive (M* ~ 2x10^9 - 3x10^11 Msun), actively star-forming (SFR ~ 10-600 Msun/yr) part of the z~2 galaxy population over a wide range in colors ((U-V)_rest ~ 0.15-1.5 mag) and half-light radii (R_e,H ~ 1-8.5 kpc). The sample overlaps largely with the "main sequence" of star-forming galaxies in the same redshift range to a similar K_AB = 23 magnitude limit; it has ~0.3 dex higher median specific SFR, ~0.1 mag bluer median (U-V)_rest color, and ~10% larger median rest-optical size. We describe the observations, data reduction, and extraction of basic flux and kinematic properties. With typically 3-4 times higher resolution and 4-5 times longer integrations (up to 23hr) than the seeing-limited datasets of the same objects, the AO data reveal much more detail in morphology and kinematics. The now complete AO observations confirm the majority of kinematically-classified disks and the typically elevated disk velocity dispersions previously reported based on subsets of the data. We derive typically flat or slightly negative radial [NII]/Ha gradients, with no significant trend with global galaxy properties, kinematic nature, or the presence of an AGN. Azimuthal variations in [NII]/Ha are seen in several sources and are associated with ionized gas outflows, and possible more metal-poor star-forming clumps or small companions. [Abridged], Comment: Submitted to the Astrophysical Journal Supplement Series. 64 pages, 36 figures. The reduced data sets will be made available once the paper is accepted for publication. A version with full resolution Figures is available at http://www.mpe.mpg.de/~forster/FS18_AOsurvey_ApJSsubm.html

We provide, for the first time, robust observational constraints on the galaxy major merger fraction up to $z\approx 6$ using spectroscopic close pair counts. Deep Multi Unit Spectroscopic Explorer (MUSE) observations in the Hubble Ultra Deep Field (HUDF) and Hubble Deep Field South (HDF-S) are used to identify 113 secure close pairs of galaxies among a parent sample of 1801 galaxies spread over a large redshift range ($0.2

We tested the performance of photometric redshifts for galaxies in the Hubble Ultra Deep field down to 30th magnitude. We compared photometric redshift estimates from three spectral fitting codes from the literature (EAZY, BPZ and BEAGLE) to high quality redshifts for 1227 galaxies from the MUSE integral field spectrograph. All these codes can return photometric redshifts with bias |Dzn|=|z-z_phot|/(1+z)<0.05 down to F775W=30 and spectroscopic incompleteness is unlikely to strongly modify this statement. We have, however, identified clear systematic biases in the determination of photometric redshifts: in the 0.43 they are systematically biased high by up to Dzn = 0.05, an offset that can in part be explained by adjusting the amount of intergalactic absorption applied. In agreement with previous studies we find little difference in the performance of the different codes, but in contrast to those we find that adding extensive ground-based and IRAC photometry actually can worsen photo-z performance for faint galaxies. We find an outlier fraction, defined through |Dzn|>0.15, of 8% for BPZ and 10% for EAZY and BEAGLE, and show explicitly that this is a strong function of magnitude. While this outlier fraction is high relative to numbers presented in the literature for brighter galaxies, they are very comparable to literature results when the depth of the data is taken into account. Finally, we demonstrate that while a redshift might be of high confidence, the association of a spectrum to the photometric object can be very uncertain and lead to a contamination of a few percent in spectroscopic training samples that do not show up as catastrophic outliers, a problem that must be tackled in order to have sufficiently accurate photometric redshifts for future cosmological surveys., Comment: 24 pages and 25 figures, accepted for A&A

We have conducted a two-layered spectroscopic survey (1'x1' ultra deep and 3'x3' deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for HST continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z>3 and to HST/F775W magnitudes as faint as ~30 mag (AB, 1-sigma). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [OII] at z<1.5 (473 objects) and Lya at 2.9~20% up to 28-29 mag and ~27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ~80% of the targeted z~2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ~20-40%. We empirically redefine the selection boundaries to make an attempt to improve them to ~60%. The revised boundaries allow bluer colors that capture Lya emitters with high Lya equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog., Comment: 26 pages, 26 figures, 4 tables, accepted for publication in A&A (MUSE UDF Series Paper II), the redshift catalogs will be available at the CDS

This paper provides an update of our previous scaling relations (Genzel et al.2015) between galaxy integrated molecular gas masses, stellar masses and star formation rates, in the framework of the star formation main-sequence (MS), with the main goal to test for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ~1mm dust photometry, in a large sample of 1444 star forming galaxies (SFGs) between z=0 and 4. The sample covers the stellar mass range log(M*/M_solar)=9.0-11.8, and star formation rates relative to that on the MS, delta_MS=SFR/SFR(MS), from 10^{-1.3} to 10^{2.2}. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t_depl, defined as the ratio of molecular gas mass to star formation rate, scales as (1+z)^{-0.6}x(delta_MS)^{-0.44}, and is only weakly dependent on stellar mass. The ratio of molecular-to-stellar mass mu_gas depends on (1+z)^{2.5}x (delta_MS)^{0.52}x(M*)^{-0.36}, which tracks the evolution of the specific star formation rate. The redshift dependence of mu_gas requires a curvature term, as may the mass-dependences of t_depl and mu_gas. We find no or only weak correlations of t_depl and mu_gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high-z., Comment: Now accepted by ApJ; Figures and tables have been updated, and an appendix has been added

We use a background quasar to detect the presence of circum-galactic gas around a $z=0.91$ low-mass star forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the VLT show that the host galaxy has a dust-corrected star-formation rate (SFR) of 4.7$\pm$0.2 Msun/yr, with no companion down to 0.22 Msun/yr (5 $\sigma$) within 240 kpc (30"). Using a high-resolution spectrum (UVES) of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle $\alpha$ of only $15^\circ$), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a "cold flow disk" extending at least 12 kpc ($3\times R_{1/2}$). We estimate the mass accretion rate $\dot M_{\rm in}$ to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the HI column density of $\log N_{\rm HI} \simeq 20.4$ obtained from a {\it HST}/COS NUV spectrum. From a detailed analysis of the low-ionization lines (e.g. ZnII, CrII, TiII, MnII, SiII), the accreting material appears to be enriched to about 0.4 $Z_\odot$ (albeit with large uncertainties: $\log Z/Z_\odot=-0.4~\pm~0.4$), which is comparable to the galaxy metallicity ($12+\log \rm O/H=8.7\pm0.2$), implying a large recycling fraction from past outflows. Blue-shifted MgII and FeII absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The MgII and FeII doublet ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent FeII* emission., Comment: 17 pages, 11 figures, in press (ApJ), minor edits after the proofs. Data available at http://muse-vlt.eu/science/j1422/

(Abridged) We make use of the deepest VLT/MUSE observations performed so far on the Hubble Deep Field South (HDFS) to characterize the low-mass (< $10^{10}$M$_\odot$) galaxy population at intermediate redshift. We identify a sample of 28 spatially-resolved emission-line galaxies in the deep (27h integration time) MUSE data cube, spread over a redshift interval of 0.2 < z < 1.4. The public HST images and multi-band photometry over the HDFS are used to constrain the stellar mass and star formation rate (SFR) of the galaxies and to perform a morphological analysis. We derive the resolved ionized gas properties of these galaxies from the MUSE data and model the disk (both in 2D and with GalPaK$^{\rm 3D}$) to retrieve their intrinsic gas kinematics. We build a sample of resolved emission-line galaxies of much lower stellar mass and SFR (by $\sim$1-2 orders of magnitude) than previous 3D spectroscopic surveys. Most of the spatially-resolved MUSE-HDFS galaxies have gas kinematics consistent with disk-like rotation, but about 20% have velocity dispersions larger than the rotation velocities, and 30% are part of a close pair and/or show clear signs of recent gravitational interactions. In the high-mass regime, the MUSE-HDFS galaxies follow the Tully-Fisher relation defined from previous surveys in a similar redshift range. This scaling relation extends also to lower masses/velocities but with a higher dispersion. The MUSE-HDFS galaxies follow the scaling relations defined in the local universe between the specific angular momentum and the stellar mass. However, we find that intermediate-redshift star-forming galaxies fill a continuum transition from the spiral to elliptical local scaling relations, according to the dynamical state of the gas. This indicates that some galaxies may lose their angular momentum and become dispersion-dominated prior to becoming passive., Comment: 26 pages. Published in A&A

We report the detection of extended Ly alpha emission around individual star-forming galaxies at redshifts z = 3-6 in an ultradeep exposure of the Hubble Deep Field South obtained with MUSE on the ESO-VLT. The data reach a limiting surface brightness (1sigma) of ~1 x 10^-19 erg s^-1 cm^-2 arcsec^-2 in azimuthally averaged radial profiles, an order of magnitude improvement over previous narrowband imaging. Our sample consists of 26 spectroscopically confirmed Ly alpha-emitting, but mostly continuum-faint (m_AB >~ 27) galaxies. In most objects the Ly alpha emission is considerably more extended than the UV continuum light. While 5 of the faintest galaxies in the sample show no significantly detected Ly alpha haloes, the derived upper limits suggest that this is just due to insufficient S/N. Ly alpha haloes therefore appear to be (nearly) ubiquitous even for low-mass (~10^8-10^9 M_sun) star-forming galaxies at z>3. We decompose the Ly alpha emission of each object into a compact `continuum-like' and an extended halo component, and infer sizes and luminosities of the haloes. The extended Ly alpha emission approximately follows an exponential surface brightness distribution with a scale length of a few kpc. While these haloes are thus quite modest in terms of their absolute sizes, they are larger by a factor of 5-15 than the corresponding rest-frame UV continuum sources as seen by HST. They are also much more extended, by a factor ~5, than Ly alpha haloes around low-redshift star-forming galaxies. Between ~40% and >90% of the observed Ly alpha flux comes from the extended halo component, with no obvious correlation of this fraction with either the absolute or the relative size of the Ly alpha halo. Our observations provide direct insights into the spatial distribution of at least partly neutral gas residing in the circumgalactic medium of low to intermediate mass galaxies at z > 3., Comment: accepted by Astronomy & Astrophysics

We present the results of a survey for intervening HI 21-cm absorbers at intermediate and low redshift (0180 K. A subset of our systems were also searched for OH absorption, but no detections were made., Comment: Accepted for publication in MNRAS, 13 pages with 10 figures

We present Karl G. Jansky Very Large Array observations of the CO J=1-0 transition in a sample of four $z\sim2$ main sequence galaxies. These galaxies are in the blue sequence of star-forming galaxies at their redshift, and are part of the IRAM Plateau de Bure HIgh-$z$ Blue Sequence Survey (PHIBSS) which imaged them in CO J=3-2. Two galaxies are imaged here at high signal-to-noise, allowing determinations of their disk sizes, line profiles, molecular surface densities, and excitation. Using these and published measurements, we show that the CO and optical disks have similar sizes in main-sequence galaxies, and in the galaxy where we can compare CO J=1-0 and J=3-2 sizes we find these are also very similar. Assuming a Galactic CO-to-H$_2$ conversion, we measure surface densities of $\Sigma_{mol}\sim1200$ M$_\odot$pc$^{-2}$ in projection and estimate $\Sigma_{mol}\sim500-900$ M$_\odot$pc$^{-2}$ deprojected. Finally, our data yields velocity-integrated Rayleigh-Jeans brightness temperature line ratios $r_{31}$ that are approximately unity. In addition to the similar disk sizes, the very similar line profiles in J=1-0 and J=3-2 indicate that both transitions sample the same kinematics, implying that their emission is coextensive. We conclude that in these two main sequence galaxies there is no evidence for significant excitation gradients or a large molecular reservoir that is diffuse or cold and not involved in active star-formation. We suggest that $r_{31}$ in very actively star-forming galaxies is likely an indicator of how well mixed the star formation activity and the molecular reservoir are., Comment: To appear in ApJ

We present a method to constrain galaxy parameters directly from three-dimensional data cubes. The algorithm compares directly the data with a parametric model mapped in $x,y,\lambda$ coordinates. It uses the spectral lines-spread function (LSF) and the spatial point-spread function (PSF) to generate a three-dimensional kernel whose characteristics are instrument specific or user generated. The algorithm returns the intrinsic modeled properties along with both an `intrinsic' model data cube and the modeled galaxy convolved with the 3D-kernel. The algorithm uses a Markov Chain Monte Carlo (MCMC) approach with a nontraditional proposal distribution in order to efficiently probe the parameter space. We demonstrate the robustness of the algorithm using 1728 mock galaxies and galaxies generated from hydrodynamical simulations in various seeing conditions from 0.6" to 1.2". We find that the algorithm can recover the morphological parameters (inclination, position angle) to within 10% and the kinematic parameters (maximum rotation velocity) to within 20%, irrespectively of the PSF in seeing (up to 1.2") provided that the maximum signal-to-noise ratio (SNR) is greater than $\sim3$ pixel$^{-1}$ and that the ratio of the galaxy half-light radius to seeing radius is greater than about 1.5. One can use such an algorithm to constrain simultaneously the kinematics and morphological parameters of (nonmerging) galaxies observed in nonoptimal seeing conditions. The algorithm can also be used on adaptive-optics (AO) data or on high-quality, high-SNR data to look for nonaxisymmetric structures in the residuals., Comment: 16 pages, 10 figures, accepted to publication in AJ, revised version after proofs corrections. Algorithm available at http://galpak.irap.omp.eu

We observed the Hubble Deep Field South with the new panoramic integral field spectrograph MUSE that we built and just commissioned at the VLT. The data cube resulting from 27 hours of integration covers one arcmin^2 field of view at an unprecedented depth with a 1 sigma emission line surface brightness limit of 1x$10^{-19}$ erg/s/cm$^2$/arcsec$^2$ and contains ~90,000 spectra. We present the combined and calibrated data cube, and we perform a first-pass analysis of the sources detected in the HDF-S imaging. We measured the redshifts of 189 sources up to a magnitude F814W = 29.5, increasing by more than an order of magnitude the number of known spectroscopic redshifts in this field. We also discovered 26 Lya emitting galaxies which are not detected in the HST WFPC2 deep broad band images. The intermediate spectral resolution of 2.3{\AA} allows us to separate resolved asymmetric Lya emitters, [O II] emitters, and C III] emitters and the large instantaneous wavelength range of 4500{\AA} helps to identify single emission lines. We also show how the three dimensional information of MUSE helps to resolve sources which are confused at ground-based image quality. Overall, secure identifications are provided for 83% of the 227 emission line sources detected in the MUSE data cube and for 32% of the 586 sources identified in the HST catalog of Casertano et al 2000. The overall redshift distribution is fairly flat to z=6.3, with a reduction between z=1.5 to 2.9, in the well-known redshift desert. The field of view of MUSE also allowed us to detect 17 groups within the field. We checked that the number counts of [O II] and Ly-a emitters are roughly consistent with predictions from the literature. Using two examples we demonstrate that MUSE is able to provide exquisite spatially resolved spectroscopic information on intermediate redshift galaxies present in the field., Comment: 21 pages, 20 figures. Note that the catalogues, data cube and associated spectra will be released upon acceptance of the paper

We combine molecular gas masses inferred from CO emission in 500 star forming galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other surveys, with gas masses derived from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion time scale (tdepl) and gas to stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence with redshift, specific star formation rate (sSFR) and stellar mass (M*). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO-H2 mass conversion factor varies little within 0.6dex of the main sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M* are driven by the flattening of the SFR-M* relation. Throughout the redshift range probed a larger sSFR at constant M* is due to a combination of an increasing gas fraction and a decreasing depletion time scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine Mmolgas with an accuracy of 0.1dex in relative terms, and 0.2dex including systematic uncertainties., Comment: ApJ accepted

Over the past 18 months we have revisited the science requirements for a multi-object spectrograph (MOS) for the European Extremely Large Telescope (E-ELT). These efforts span the full range of E-ELT science and include input from a broad cross-section of astronomers across the ESO partner countries. In this contribution we summarise the key cases relating to studies of high-redshift galaxies, galaxy evolution, and stellar populations, with a more expansive presentation of a new case relating to detection of exoplanets in stellar clusters. A general requirement is the need for two observational modes to best exploit the large (>40 sq. arcmin) patrol field of the E-ELT. The first mode ('high multiplex') requires integrated-light (or coarsely resolved) optical/near-IR spectroscopy of >100 objects simultaneously. The second ('high definition'), enabled by wide-field adaptive optics, requires spatially-resolved, near-IR of >10 objects/sub-fields. Within the context of the conceptual study for an ELT-MOS called MOSAIC, we summarise the top-level requirements from each case and introduce the next steps in the design process., Comment: 17 pages, to be published in Proc SPIE 9147: Ground-based & Airborne Instrumentation for Astronomy V

Galaxies are thought to be fed by the continuous accretion of intergalactic gas, but direct observational evidence has been elusive. The accreted gas is expected to orbit about the galaxy's halo, delivering not just fuel for star-formation but also angular momentum to the galaxy, leading to distinct kinematic signatures. Here we report observations showing these distinct signatures near a typical distant star-forming galaxy where the gas is detected using a background quasar passing 26 kpc from the host. Our observations indicate that gas accretion plays a major role in galaxy growth since the estimated accretion rate is comparable to the star-formation rate., Comment: 33 pages, 8 figures, version matching the proofed text

Background quasars are potentially sensitive probes of galactic outflows provided that one can determine the origin of the absorbing material since both gaseous disks and strong bipolar outflows can contribute to the absorption cross-section. Using a dozen quasars passing near spectroscopically identified galaxies at $z\sim0.1$, we find that the azimuthal orientation of the quasar sight-lines with strong MgII absorption (with EW>0.3 \AA) is bi-modal: about half the MgII sight-lines are aligned with the major axis and the other half are within 30deg. of the minor axis, showing that bipolar outflows contribute significantly to the MgII cross-section. This bi-modality is also present in the instantaneous star-formation rates (SFRs) of the hosts. For the sight-lines aligned along the minor axis, a simple bi-conical wind model is able to reproduce the observed MgII kinematics and the MgII dependence with impact parameter b, (EW $\propto b^{-1}$). Using our wind model, we can directly extract key wind properties such as the de-projected outflow speed $V_{out}$ of the cool material traced by MgII and the outflow rates. The outflow speeds are found to be 150-300 \kms, i.e. of the order of the circular velocity, and smaller than the escape velocity by a factor of ~2. The outflow rates are typically two to three times the instantaneous SFRs. Our results demonstrates how background quasars can be used to measure wind properties with high precision., Comment: 16pages, 15 figures, accepted to MNRAS, accepted version

The kinematics of distant galaxies, from z=0.1 to z>2, play a key role in our understanding of galaxy evolution from early times to the present. One of the important parameters is the intrinsic, or local, velocity dispersion of a galaxy, which allows one to quantify the degree of non-circular motions such as pressure support. However, this is difficult to measure because the observed dispersion includes the effects of (often severe) beam smearing on the velocity gradient. Here we investigate four methods of measuring the dispersion that have been used in the literature, to assess their effectiveness at recovering the intrinsic dispersion. We discuss the biasses inherent in each method, and apply them to model disk galaxies in order to determine which methods yield meaningful quantities, and under what conditions. All the mean weighted dispersion estimators are affected by (residual) beam smearing. In contrast, the dispersion recovered by fitting a spatially and spectrally convolved disk model to the data is unbiassed by the beam smearing it is trying to compensate. Because of this, and because the bias it does exhibit depends only on the signal-to-noise, it can be considered reliable. However, at very low signal-to-noise, all methods should be used with caution., Comment: accepted by ApJ

[Abridged] In order to understand which process (e.g. galactic winds, cold accretion) is responsible for the cool (T~10^4 K) halo gas around galaxies, we embarked on a program to study the star-formation properties of galaxies selected by their MgII absorption signature in quasar spectra. Specifically, we searched for the H-alpha line emission from galaxies near very strong z=2 MgII absorbers (with rest-frame equivalent width EW>2 \AA) because these could be the sign-posts of outflows or inflows. Surprisingly, we detect H-alpha from only 4 hosts out of 20 sight-lines (and 2 out of the 19 HI-selected sight-lines), despite reaching a star-formation rate (SFR) sensitivity limit of 2.9 M/yr (5-sigma) for a Chabrier initial mass function. This low success rate is in contrast with our z=1 survey where we detected 66%\ (14/21) of the MgII hosts. Taking into account the difference in sensitivity between the two surveys, we should have been able to detect >11.4 of the 20 z=2 hosts whereas we found only 4 galaxies. Interestingly, all the z=2 detected hosts have observed SFR greater than 9 M/yr, well above our sensitivity limit, while at z=1 they all have SFR less than 9 M/yr, an evolution that is in good agreement with the evolution of the SFR main sequence. Moreover, we show that the z=2 undetected hosts are not hidden under the quasar continuum after stacking our data and that they also cannot be outside our surveyed area. Hence, strong MgII absorbers could trace star-formation driven winds in low-mass halos (Mhalo < 10^{10.6} Msun). Alternatively, our results imply that z=2 galaxies traced by strong MgII absorbers do not form stars at a rate expected (3--10 M/yr) for their (halo or stellar) masses, supporting the existence of a transition in accretion efficiency at Mhalo ~ 10^{11} Msun. This scenario can explain both the detections and the non-detections., Comment: 14 pages, 4 fig.; MNRAS in press, minor corrections to match proofs

We use the first systematic samples of CO millimeter emission in z>1 'main-sequence' star forming galaxies (SFGs) to study the metallicity dependence of the conversion factor {\alpha}CO, from CO line luminosity to molecular gas mass. The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is ~1 Gyr-1 for near-solar metallicity galaxies with stellar masses above M_S~1e11 M_sun. In this regime the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density, or redshift between z~0 and 2. Below M_S the depletion rate increases rapidly with decreasing metallicity. We argue that this trend is not caused by starburst events, by changes in the physical parameters of the molecular clouds, or by the impact of the fundamental metallicity-SFR-stellar mass relation. A more probable explanation is that the conversion factor is metallicity dependent and that star formation can occur in 'CO-dark' gas. The trend is also expected theoretically from the effect of enhanced photodissociation of CO by ultraviolet radiation at low metallicity. From the available z~0 and z~1-3 samples we constrain the slope of the log({\alpha}CO) -log (metallicity) relation to range between -1 and -2, fairly insensitive to the assumed slope of the gas-star formation rate relation. Because of the lower metallicities near the peak of the galaxy formation activity at z~1-2 compared to z~0, we suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below M_S., Comment: ApJ in press

We study the properties of luminous stellar clumps identified in deep, high resolution HST/NIC2 F160W imaging at 1.6um of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ~5000A emission, with median of about 2%; the total contribution of clump light ranges from 10%-25%. The median intrinsic clump size and stellar mass are ~1kpc and log(Mstar[Msun])~9, in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation via gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with ACS/F814W imaging available for one source, and AO-assisted SINFONI Halpha data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or Halpha-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material towards the central regions. From constraints on a bulge-like component at radii <1-3kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the build-up of stellar bulges and the role of clumps in this process., Comment: 29 pages, 11 figures. Revised version accepted for publication in the Astrophysical Journal

We have studied the properties of giant star forming clumps in five z~2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad H{\alpha}/[NII] line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10-40 km/s/kpc, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized, or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps., Comment: accepted Astrophys. Journal, February 9, 2011

We present deep and high-resolution HST/NIC2 F160W imaging at 1.6micron of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sersic index n<1), with median effective radii of ~5kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), Multiplicity (Psi), and M_20 coefficients. The strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and Halpha emission reveal no significant differences, suggesting similar global distributions of the on-going star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z~2 galaxy types indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z~2 galaxy population, with correspondingly large effective radii, low Sersic indices, low G, and high Psi and M_20. The combined NIC2 and SINFONI dataset yields insights of unprecedented detail into the nature of mass accretion at high redshift. [Abridged], Comment: 44 pages, 19 figures. Revised version accepted for publication in the Astrophysical Journal

We have measured redshifts for 243 z ~3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Lya forest and 1020 Lyman-break galaxies at z ~3. We find an increase in neutral hydrogen absorption within 5 h^-1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Lya-LBG cross-correlation can be described by a power-law on scales larger than 3 h^-1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (<2 h^-1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We find that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Lya absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 CIV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h^-1 Mpc consistent with the relation measured at ~Mpc scales., Comment: 33 pages, 16 figures, accepted by MNRAS

We present the initial imaging and spectroscopic data acquired as part of the VLT VIMOS Lyman-break galaxy Survey. UBR (or UBVI) imaging covers five 36'x36' fields centred on bright z>3 QSOs, allowing ~21,000 22 LBGs and 10 z>2 QSOs from a total of 19 VIMOS pointings. From the galaxy spectra, we observe a 625+-510 km/s velocity offset between the ISM absorption and Ly-alpha emission line redshifts. Using the photometric and spectroscopic catalogues, we have analysed the galaxy clustering at z~3. In the photometric case, the angular correlation function, w(theta), is well fit by a double power-law with clustering scale-length, r_0 = 3.19+0.32-0.54 Mpc/h for r < 1 Mpc/h and r_0 = 4.59+0.31-0.33 Mpc/h at larger scales. Using the redshift sample we estimate the semi-projected correlation function, w_p(sigma) and find r_0 = 3.67+0.23-0.24 Mpc/h for the VLT sample and r_0 = 3.98+0.14-0.15 Mpc/h for a combined VLT+Keck sample. From the z-space correlation functions and assuming the above xi(r) models, we find that the combined VLT and Keck surveys require a galaxy velocity dispersion, ^1/2 ~ 700 km/s, higher than the ~400 km/s found by previous authors. We also measure a value for the gravitational growth rate parameter of beta(z=3) = 0.48+-0.17, implying a low value for the bias of b = 2.06+1.1-0.5. This value is consistent with the galaxy clustering amplitude which gives b = 2.22+-0.16, assuming the standard cosmology, implying that the evolution of the gravitational growth rate is also consistent with Einstein gravity. We have compared our LBG clustering amplitudes with lower redshift measurements and find that the clustering strength is not inconsistent with that of low-redshift L* spirals for simple 'long-lived' galaxy models., Comment: 27 pages, 25 figures, accepted in MNRAS

We use the first systematic data sets of CO molecular line emission in z~1-3 normal star forming galaxies for a comparison of the dependence of galaxy-averaged star formation rates on molecular gas masses at low and high redshifts, and in different galactic environments. Although the current high-z samples are still small and biased toward the luminous and massive tail of the actively star-forming 'main-sequence', a fairly clear picture is emerging. Independent of whether galaxy integrated quantities or surface densities are considered, low- and high-z SFG galaxy populations appear to follow similar molecular gas-star formation relations with slopes 1.1 to 1.2. The gas-depletion time scale in these SFGs grows from 0.5 Gyrs at z~2 to 1.5 Gyrs at z~0. Because star formation depletion times are significantly smaller than the Hubble time at all redshifts sampled, star formation rates and gas fractions are set by the balance between gas accretion from the halo and stellar feedback. In contrast, very luminous gas rich major mergers at both low-z and high-z produce on average 4 to10 times more far-infrared luminosity per unit gas mass. Only some fraction of this difference can be explained by uncertainties in gas-mass or luminosity estimators; much of it must be intrinsic. The most likely interpretation is that the star formation relation is driven by global dynamical effects. For a given mass, the more compact merger systems produce stars more rapidly because their gas clouds are more compressed with shorter dynamical times, so that they churn more quickly through the available gas reservoir than the typical normal disk galaxies. When the dependence on galactic dynamical time scale is explicitly included, disk galaxies and mergers appear to follow similar gas to star-formation relations. The mergers may be forming stars at slightly higher efficiencies than the disks., Comment: accepted for publication in MNRAS

Stars form from cold molecular interstellar gas. Since this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more gas rich. Molecular gas observations in the distant Universe have so far been largely restricted to very luminous, rare objects, including mergers and quasars. Here we report the results of a systematic survey of molecular gas in samples of typical massive star forming galaxies at ~1.2 and 2.3, when the Universe was 40% and 24% of its current age. Our measurements provide empirical evidence that distant star forming galaxies indeed were gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z= 2.3 and z=1.2 is ~44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z~2 and 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies., Comment: To Appear in Nature Feb 11, 2010; Supplementary Information included here

Using the cosmological baryonic accretion rate and normal star formation efficiencies, we present a very simple model for star-forming galaxies (SFGs) that accounts for the mass and redshift dependencies of the SFR-Mass and Tully-Fisher relations from z=2 to the present. The time evolution follows from the fact that each modelled galaxy approaches a steady state where the SFR follows the (net) cold gas accretion rate. The key feature of the model is a halo mass floor M_{min}~10^{11} below which accretion is quenched in order to simultaneously account for the observed slopes of the SFR-Mass and Tully-Fischer relations. The same successes cannot be achieved via a star-formation threshold (or delay) nor by varying the SF efficiency or the feedback efficiency. Combined with the mass ceiling for cold accretion due to virial shock heating, the mass floor M_{min} explains galaxy "downsizing", where more massive galaxies formed earlier and over a shorter period of time. It turns out that the model also accounts for the observed galactic baryon and gas fractions as a function of mass and time, and the cosmic SFR density from z~6 to z=0, which are all resulting from the mass floor M_{min}. The model helps to understand that it is the cosmological decline of accretion rate that drives the decrease of cosmic SFR density between z~2 and z=0 and the rise of the cosmic SFR density allows us to put a constraint on our main parameter M_{min}~10^{11} solar masses. Among the physical mechanisms that could be responsible for the mass floor, we view that photo-ionization feedback (from first in-situ hot stars) lowering the cooling efficiency is likely to play a large role., Comment: 19pages, 14 figures, accepted to ApJ, updated references

We used the large binocular camera (LBC) mounted on the large binocular telescope (LBT) to observe the Lockman Hole in the U, B, and V bands. Our observations cover an area of 925 sq.arcmin. We reached depths of 26.7, 26.3, and 26.3 mag(AB) in the three bands, respectively, in terms of 50% source detection efficiency, making this survey the deepest U-band survey and one of the deepest B and V band surveys with respect to its covered area. We extracted a large number of sources (~89000), detected in all three bands and examined their surface density, comparing it with models of galaxy evolution. We find good agreement with previous claims of a steep faint-end slope of the luminosity functions, caused by late-type and irregular galaxies at z>1.5. A population of dwarf star-forming galaxies at 1.5

The structure of a sample of high-redshift (z=2), rotating galaxies with high star formation rates and turbulent gas velocities of sigma=40-80 km/s is investigated. Fitting the observed disk rotational velocities and radii with a Mo, Mao, White (1998) (MMW) model requires unusually large disk spin parameters lambda_d>0.1 and disk-to-dark halo mass fraction m_d=0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1200 km/s, vmax/sigma>3 and rd=4-8 kpc. For the dispersion-dominated sample, radial pressure gradients partly compensate the gravitational force, reducing the rotational velocities. Including this pressure effect in the MMW model, dispersion-dominated galaxies can be fitted well with spin parameters lf lambda_d=0.03-0.05 for high disk mass fractions of m_d=0.2 and with lambda_d=0.01-0.03 for m_d=0.05. These values are in good agreement with cosmological expectations. For the rotation-dominated sample however pressure effects are small and better agreement with theoretically expected disk spin parameters can only be achieved if the dark halo mass contribution in the visible disk regime (2-3*rd) is smaller than predicted by the MMW model. We argue that these galaxies can still be embedded in standard cold dark matter halos if the halos did not contract adiabatically in response to disk formation. It is shown that the observed high turbulent gas motions of the galaxies are consistent with a Toomre instability parameter Q=1 which is equal to the critical value, expected for gravitational disk instability to be the major driver of turbulence. The dominant energy source of turbulence is then the potential energy of the gas in the disk., Comment: 23 pages, 4 figures, ApJ, in press

We present the SINS survey with SINFONI of high redshift galaxies. With 80 objects observed and 63 detected, SINS is the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z~1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the "SINS Halpha sample" of 62 rest-UV/optically-selected sources at 1.3~10 star-forming galaxies at z~1.5-2.5, with some bias towards bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans two orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values of approximately log(M*/Msun) = 10.5, 70 Msun/yr, and 3/Gyr. The ionized gas distribution and kinematics are spatially resolved on scales ranging from 1.5 kpc for adaptive optics assisted observations to typically 4-5 kpc for seeing-limited data. The Halpha morphologies tend to be irregular and/or clumpy. About one-third are rotation-dominated yet turbulent disks, another third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Halpha luminosities and equivalent widths suggest on average roughly twice higher dust attenuation towards the HII regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates. [Abridged], Comment: 81 pages, 34 figures. Revised version accepted for publication in the Astrophysical Journal

We present the modeling of SINFONI integral field dynamics of 18 star forming galaxies at z ~ 2 from Halpha line emission. The galaxies are selected from the larger sample of the SINS survey, based on the prominence of ordered rotational motions with respect to more complex merger induced dynamics. The quality of the data allows us to carefully select systems with kinematics dominated by rotation, and to model the gas dynamics across the whole galaxy using suitable exponential disk models. We obtain a good correlation between the dynamical mass and the stellar mass, finding that large gas fractions Mgas~M*) are required to explain the difference between the two quantities. We use the derived stellar mass and maximum rotational velocity Vmax from the modeling to construct for the first time the stellar mass Tully-Fisher relation at z ~ 2.2. The relation obtained shows a slope similar to what is observed at lower redshift, but we detect an evolution of the zero point. We find that at z ~ 2.2 there is an offset in log(M*) for a given rotational velocity of 0.41+-0.11 with respect to the local Universe. This result is consistent with the predictions of the latest N-body/hydrodynamical simulations of disk formation and evolution, which invoke gas accretion onto the forming disk in filaments and cooling flows. This scenario is in agreement with other dynamical evidence from SINS, where gas accretion from the halo is required to reproduce the observed properties of a large fraction of the z ~ 2 galaxies., Comment: 10 pages, 6 figures, submitted to ApJ

We developed a new method to extract halo merger rates from the Millennium Simulation. First, by removing superfluous mergers that are artifacts of the FOF halo finder, we find a lower merger rate compared to previous work. The reductions are more significant at lower redshifts, lower halo masses, and minor mergers. Our approach agrees better with predictions from the EPS model. Second, we find that the FOF halo finder overestimates the halo mass by up to 50% for halos that are about to merge, which leads to an additional ~20% overestimate of the merger rate. Therefore, we define halo masses by including only gravitationally bound particles. We provide new best-fitting parameters for a global formula to account for these improvements. In addition, we extract the merger rate per progenitor halo, as well as per descendant halo. The former is the quantity that is related to observed galaxy merger fractions when they are measured via pair counting. At low mass/redshift the merger rate increases with mass and redshift. At high mass/redshift (for halos with masses a few times the "knee" of the mass function) these trends break down, and the merger rate per progenitor halo decreases with mass and increases only moderately with redshift. Defining the merger rate per progenitor halo also allows us to quantify the rate at which halos are being accreted onto larger halos. We provide an analytic formula to convert given merger rates per descendant halo into merger rates per progenitor halo. Finally, we perform a comparison between observed merger fractions and the fraction of halos that have undergone a major merger during the recent dynamical friction time, and find a fair agreement, within the large uncertainties of the observations. Our new halo merger trees are available at http://www.mpe.mpg.de/ir/MillenniumMergerTrees/., Comment: 16 pages, 13 figures. Accepted for publication in The Astrophysical Journal