A SINFONI Integral Field Spectroscopy Survey for Galaxy Counterparts to Damped Lyman-alpha Systems - II. Dynamical Properties of the Galaxies towards Q0302-223 and Q1009-0026

Details of processes through which galaxies convert their gas into stars need to be studied in order to obtain a complete picture of galaxy formation. One way to tackle these phenomena is to relate the HI gas and the stars in galaxies. Here, we present dynamical properties of Damped and sub-Damped Lyman-alpha Systems identified in H-alpha emission with VLT/SINFONI at near infra-red wavelengths. While the DLA towards Q0302-223 is found to be dispersion-dominated, the sub-DLA towards Q1009-0026 shows clear signatures of rotation. We use a proxy to circular velocity to estimate the mass of the halo in which the sub-DLA resides and find M_halo=10^12.6 M_sun. We also derive dynamical masses of these objects, and find M_dyn=10^10.3 M_sun and 10^10.9 M_sun. For one of the two systems (towards Q0302-223), we are able to derive a stellar mass of M_*=10^9.5 M_sun from Spectral Energy Distribution fit. The gas fraction in this object is 1/3rd, comparable to similar objects at these redshifts. Our work illustrates that detailed studies of quasar absorbers can offer entirely new insights into our knowledge of the interaction between stars and the interstellar gas in galaxies.Comment: 6 pages, 2 figures. Accepted for publication in MNRA

The Rising Star-Formation Histories of Distant Galaxies and Implications for Gas Accretion with Time

Distant galaxies show correlations between their current star-formation rates (SFRs) and stellar masses, implying that their star-formation histories (SFHs) are highly similar. Moreover, observations show that the UV luminosities and stellar masses grow from z=8 to 3, implying that the SFRs increase with time. We compare the cosmologically averaged evolution in galaxies at 3 < z < 8 at constant comoving number density, n = 2 x 10^-4 Mpc^-3. This allows us to study the evolution of stellar mass and star formation in the galaxy predecessors and descendants in ways not possible using galaxies selected at constant stellar mass or SFR, quantities that evolve strongly in time. We show that the average SFH of these galaxies increase smoothly from z=8 to 3 as SFR ~ t^alpha with alpha = 1.7 +/- 0.2. This conflicts with assumptions that the SFR is either constant or declines exponentially in time. We show that the stellar mass growth in these galaxies is consistent with this derived SFH. This provides evidence that the slope of the high-mass end of the IMF is approximately Salpeter unless the duty cycle of star formation is much less than unity. We argue that these relations follow from gas accretion (either through accretion or delivered by mergers) coupled with galaxy disk growth under the assumption that the SFR depends on the local gas surface density. This predicts that gas fractions decrease from z=8 to 3 on average as f_gas ~ (1+z)^0.9 for galaxies with this number density. The implied galaxy gas accretion rates at z > 4 are as fast and may even exceed the SFR: this is the "gas accretion epoch". At z < 4 the SFR overtakes the implied gas accretion rate, indicating a period where galaxies consume gas faster than it is acquired. At z < 3, galaxies with this number density depart from these relations implying that star formation and gas accretion are slowed at later times.Comment: Accepted for publication in MNRAS. 13 pages, 7 figures. Comments welcome. Updated with MNRAS-accepted versio

Limits on dust emission from z~5 LBGs and their local environments

We present 1.2mm MAMBO-2 observations of a field which is over-dense in Lyman Break Galaxies (LBGs) at z~5. The field includes seven spectroscopically-confirmed LBGs contained within a narrow (z=4.95+/-0.08) redshift range and an eighth at z=5.2. We do not detect any individual source to a limit of 1.6 mJy/beam (2*rms). When stacking the flux from the positions of all eight galaxies, we obtain a limit to the average 1.2 mm flux of these sources of 0.6mJy/beam. This limit is consistent with FIR imaging in other fields which are over-dense in UV-bright galaxies at z~5. Independently and combined, these limits constrain the FIR luminosity (8-1000 micron) to a typical z~5 LBG of LFIR<~3x10^11 Lsun, implying a dust mass of Mdust<~10^8 Msun (both assuming a grey body at 30K). This LFIR limit is an order of magnitude fainter than the LFIR of lower redshift sub-mm sources (z~1-3). We see no emission from any other sources within the field at the above level. While this is not unexpected given millimetre source counts, the clustered LBGs trace significantly over-dense large scale structure in the field at z = 4.95. The lack of any such detection in either this or the previous work, implies that massive, obscured star-forming galaxies may not always trace the same structures as over-densities of LBGs, at least on the length scale probed here. We briefly discuss the implications of these results for future observations with ALMA.Comment: 10 pages, 6 figures, MNRAS Accepte

A suppressed contribution of low mass galaxies to reionization due to supernova feedback

Motivated by recent observations of the star formation rate density function out to z~7, we describe a simple model for the star formation rate density function at high redshift based on the extended Press-Schechter formalism. This model postulates a starburst following each major merger, lasting for a time t_SF and converting at most f_star of galactic gas into stars. We include a simple physical prescription for supernovae feedback that suppresses star formation in low mass galaxies. Constraining t_SF and f_star to describe the observed star formation rate density at high redshifts, we find that individual starbursts were terminated after a time t_SF~10^7 years. This is comparable to the main-sequence lifetimes of supernova progenitors, indicating that high redshift starbursts are quenched once supernovae feedback had time to develop. High redshift galaxies convert ~10% of their mass into stars for galaxies with star formation rates above ~1 solar mass per year, but a smaller fraction for lower luminosity galaxies. Our best fit model successfully predicts the observed relation between star formation rate and stellar mass at z>~4, while our deduced relation between stellar mass and halo mass is also consistent with data on the dwarf satellites of the Milky Way. We find that supernovae feedback lowers the efficiency of star formation in the lowest mass galaxies and makes their contribution to reionization small. As a result, photo-ionization feedback on low mass galaxy formation does not significantly affect the reionization history. Using a semi-analytic model for the reionization history, we infer that approximately half of the ionizing photons needed to complete reionization have already been observed in star-forming galaxies.Comment: 16 pages, 10 figures. Submitted to MNRA

Estimating Luminosity Function Constraints from High-Redshift Galaxy Surveys

The installation of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) will revolutionize the study of high-redshift galaxy populations. Initial observations of the HST Ultra Deep Field (UDF) have yielded multiple z>~7 dropout candidates. Supplemented by the Great Observatory Origins Deep Survey (GOODS) Early Release Science (ERS) and further UDF pointings, these data will provide crucial information about the most distant known galaxies. However, achieving tight constraints on the z~7 galaxy luminosity function (LF) will require even more ambitious photometric surveys. Using a Fisher matrix approach to fully account for Poisson and cosmic sample variance, as well as covariances in the data, we estimate the uncertainties on LF parameters achieved by surveys of a given area and depth. Applying this method to WFC3 z~7 dropout galaxy samples, we forecast the LF parameter uncertainties for a variety of model surveys. We demonstrate that performing a wide area (~1 deg^2) survey to H_AB~27 depth or increasing the UDF depth to H_AB~30 provides excellent constraints on the high-z LF when combined with the existing UDF GO and GOODS ERS data. We also show that the shape of the matter power spectrum may limit the possible gain of splitting wide area (>~0.5 deg^2) high-redshift surveys into multiple fields to probe statistically independent regions; the increased root-mean-squared density fluctuations in smaller volumes mostly offset the improved variance gained from independent samples.Comment: Version accepted by ApJ

Smoothly-Rising Star Formation Histories During the Reionization Epoch

Cosmological hydrodynamic simulations robustly predict that high-redshift galaxy star formation histories (SFHs) are smoothly-rising and vary with mass only by a scale factor. We use our latest simulations to test whether this scenario can account for recent observations at z>=6 from WFC3/IR, NICMOS, and IRAC. Our simulations broadly reproduce the observed ultraviolet (UV) luminosity functions and stellar mass densities and their evolution at z=6-8, all of which are nontrivial tests of the mean SFH. In agreement with observations, simulated galaxies possess blue UV continua owing to young ages (50-150 Myr), low metallicities (0.1-0.5 Zsun), and low dust columns (E(B-V) <= 0.05). Observations imply a near-unity slope in the stellar mass--star formation rate relation at all z=6-8, confirming the prediction that SFH shapes are invariant. Current surveys detect the majority of galaxies with stellar masses exceeding 10^9 Msun and few galaxies less massive than 10^{8.5} Msun, implying that they probe no more than the brightest 30% of the complete star formation and stellar mass densities at z>=6. Finally, we demonstrate that there is no conflict between smoothly-rising SFHs and recent clustering observations. This is because momentum-driven outflows suppress star formation in low-mass halos, leading to overall occupancies of 0.2-0.4 even though the star formation duty cycle is one. This leads to many interesting predictions at z>=4, among them that (1) optically-selected and UV-selected samples largely overlap; (2) few galaxies exhibit significantly suppressed specific star formation rates; and (3) occupancy is constant or increasing with decreasing luminosity. These predictions are in tentative agreement with current observations, but further analysis of existing and upcoming data sets is required in order to test them more thoroughly. (abridged)Comment: 25 pages, 14 figures, accepted to MNRA

Suboptimal asthma care for immigrant children: results of an audit study

<p>Abstract</p> <p>Background</p> <p>Little is known on the scope and nature of ethnic inequalities in suboptimal asthma care for children. This study aimed to assess (1) ethnic differences in suboptimal asthma care for children with an asthma exacerbation who consulted a physician, and (2) ethnic differences in the nature of suboptimal care.</p> <p>Methods</p> <p>All children aged 6–16 years who during a period of six months consulted the paediatric department of the Academic Medical Centre-University of Amsterdam or one of the six regional primary care centres with an asthma exacerbation were included. Clinical guidelines were systematically converted to review criteria following the strategy as proposed by the Agency for Health Care Policy and Research. Based upon these review criteria and their experience experts of two multidisciplinary panels retrospectively assessed the quality of care and its (possible) failure to prevent the occurrence of asthma exacerbation.</p> <p>Results</p> <p>Only a small number of children (n = 35) were included in the analysis as a result of which the ethnic differences in suboptimal care were not significant. However, the results do indicate immigrant children, in particular 'other non-Western' children (n = 11), more frequently to receive suboptimal care related to the asthma exacerbation when compared to ethnic Dutch children. Furthermore, we found the nature of suboptimal care to differ with under-prescribing in the 'other non-Western' group (n = 11), lack of information exchange between physicians in the Surinamese/Antillean group (n = 12) and lack of education, and counselling of patients and parents in the ethnic Dutch (n = 12) as the most relevant factor.</p> <p>Conclusion</p> <p>Ethnic inequalities in the scope and nature of suboptimal asthma care for children in the Netherlands seem to exist. For the non-western immigrant groups the results indicate the importance of the prescription behaviour of the medical doctor, as well as the supervision by one health care provider.</p

The size-luminosity relation at z=7 in CANDELS and its implication on reionization

The exploration of the relation between galaxy sizes and other physical parameters has provided important clues for understanding galaxy formation. We use the CANDELS Deep+Wide surveys in the GOODS-South, UDS and EGS fields, complemented by data from the HUDF09 program, to address the relation between size and luminosity at z\sim7. We select 153 z-band drop-out galaxies in six different fields characterized by a wide combination of depth and areal coverage, ideally suited to sample without biases the observed size-magnitude plane. Detailed simulations allow us to derive the completeness as a function of size and magnitude and to quantify measurements errors/biases. We find that the half light radius distribution function of z\sim7 galaxies fainter than J=26.6 is peaked at <0.1 arcsec (or equivalently 0.5 kpc proper), while at brighter magnitudes high-z galaxies are typically larger than ~0.15 arcsec. We also find a well defined size-luminosity relation, Rh\simL^1/2. We compute the Luminosity Function in the HUDF and P12HUDF fields, finding large spatial variation on the number density of faint galaxies. Adopting the size distribution and the size-luminosity relation found for faint galaxies at z=7, we derive a mean slope of -1.7\pm0.1 for the luminosity function of LBGs at this redshift. Using this LF, we find that the amount of ionizing photons cannot keep the Universe re-ionized if the IGM is clumpy (C_HII>3) and the Lyman continuum escape fraction of high-z LBGs is relatively low (f_esc<0.3). With future CANDELS data, we can put severe limits to the role of galaxies in the reionization of the Universe.Comment: 21 pages, 15 figures, accepted for publication in A&

Evidence for inhomogeneous reionization in the local Universe from metal-poor globular cluster systems

Exploiting a fundamental characteristic of galaxy assembly in the {\Lambda}CDM paradigm, the observed spatial biasing and kinematics of metal-poor globular star clusters are used to constrain the local reionization epoch around individual galaxies. Selecting three galaxies located in different environments, the first attempt at constraining the environmental propagation of reionization in the local Universe is carried out. The joint constraint from the three galaxies (z_reion = 10.5^{+1.0}_{-0.9}) agrees remarkably well with the latest WMAP constraint on z_reion for a simple instantaneous reionization model. More importantly, the range of z_reion values found here are consistent with the global range of z_reion estimates from other observations. We furthermore find a 1.7{\sigma} indication that reionization completed in low-density environments before the intergalactic medium in high-density environments was reionized. This is consistent with certain theoretical models that predict that reionization was globally prolonged in duration, with neutral hydrogen pockets surviving in high-density environments, even after the surrounding regions were reionized. More generally, this work provides a useful constraint on the formation history of galaxy stellar halos.Comment: MNRAS in pres