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Register a new userThe galaxy luminosity function at z ~ 6 and evidence for rapid evolution in the bright end from z ~ 7 to 5
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We present the results of a search for bright (-22.7 < M_UV < -20.5) Lyman-break galaxies at z ~ 6 within a total of 1.65 square degrees of imaging in the UltraVISTA/COSMOS and UKIDSS UDS/SXDS fields. The deep near-infrared imaging available in the two independent fields, in addition to deep optical (including z-band) data, enables the sample of z ~ 6 star-forming galaxies to be securely detected long-ward of the break (in contrast to several previous studies). We show that the expected contamination rate of our initial sample by cool galactic brown dwarfs is < 3 per cent and demonstrate that they can be effectively removed by fitting brown dwarf spectral templates to the photometry. At z ~ 6 the galaxy surface density in the UltraVISTA field exceeds that in the UDS by a factor of ~ 1.8, indicating strong cosmic variance even between degree-scale fields at z > 5. We calculate the bright end of the rest-frame Ultra-Violet (UV) luminosity function (LF) at z ~ 6. The galaxy number counts are a factor of ~1.7 lower than predicted by the recent LF determination by Bouwens et al.. In comparison to other smaller area studies, we find an evolution in the characteristic magnitude between z ~ 5 and z ~ 7 of dM* ~ 0.4 mag, and show that a double power-law or a Schechter function can equally well describe the LF at z = 6. Furthermore, the bright-end of the LF appears to steepen from z ~ 7 to z ~ 5, which could indicate the onset of mass quenching or the rise of dust obscuration, a conclusion supported by comparing the observed LFs to a range of theoretical model predictions.
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We utilize deep near-infrared survey data from the UltraVISTA fourth data release (DR4) and the VIDEO survey, in combination with overlapping optical and Spitzer data, to search for bright star-forming galaxies at $z gtrsim 7.5$. Using a full photometric redshift fitting analysis applied to the $sim 6,{rm deg}^2$ of imaging searched, we find 27 Lyman-break galaxies (LBGs), including 20 new sources, with best-fitting photometric redshifts in the range $7.4 < z < 9.1$. From this sample we derive the rest-frame UV luminosity function (LF) at $z = 8$ and $z = 9$ out to extremely bright UV magnitudes ($M_{rm UV} simeq -23$) for the first time. We find an excess in the number density of bright galaxies in comparison to the typically assumed Schechter functional form derived from fainter samples. Combined with previous studies at lower redshift, our results show that there is little evolution in the number density of very bright ($M_{rm UV} sim -23$) LBGs between $z simeq 5$ and $zsimeq 9$. The tentative detection of an LBG with best-fit photometric redshift of $z = 10.9 pm 1.0$ in our data is consistent with the derived evolution. We show that a double power-law fit with a brightening characteristic magnitude ($Delta M^*/Delta z simeq -0.5$) and a steadily steepening bright-end slope ($Delta beta/Delta z simeq -0.5$) provides a good description of the $z > 5$ data over a wide range in absolute UV magnitude ($-23 < M_{rm UV} < -17$). We postulate that the observed evolution can be explained by a lack of mass quenching at very high redshifts in combination with increasing dust obscuration within the first $sim 1 ,{rm Gyr}$ of galaxy evolution.
We present the [OII] luminosity function measured in the redshift range 0.1<z<1.65 with unprecedented depth and accuracy. Our measurements are based on medium resolution flux-calibrated spectra of emission line galaxies with the FORS2 instrument at VLT and with the SDSS-III/BOSS spectrograph. The FORS2 spectra and the corresponding catalog containing redshifts and line fluxes are released along with this paper. In this work we use a novel method to combine the aforementioned surveys with GAMA, zCOSMOS and VVDS, which have different target selection, producing a consistent weighting scheme to derive the [OII] luminosity function. The measured luminosity function is in good agreement with previous independent estimates. The comparison with two state-of-the-art semi-analytical models is good, which is encouraging for the production of mock catalogs of [OII] flux limited surveys. We observe the bright end evolution over 8.5 Gyr: we measure the decrease of log L* from 42.4 erg/s at redshift 1.44 to 41.2 at redshift 0.165 and we find that the faint end slope flattens when redshift decreases. This measurement confirms the feasibility of the target selection of future baryonic acoustic oscillation surveys aiming at observing [OII] flux limited samples.
We present the results of a search for the most luminous star-forming galaxies at redshifts z~6 based on CFHT Legacy Survey data. We identify a sample of 40 Lyman break galaxies brighter than magnitude z=25.3 across an area of almost 4 square degrees. Sensitive spectroscopic observations of seven galaxies provide redshifts for four, of which only two have moderate to strong Lyman alpha emission lines. All four have clear continuum breaks in their spectra. Approximately half of the Lyman break galaxies are spatially resolved in 0.7 arcsec seeing images, indicating larger sizes than lower luminosity galaxies discovered with the Hubble Space Telescope, possibly due to on-going mergers. The stacked optical and infrared photometry is consistent with a galaxy model with stellar mass ~ 10^{10} solar masses. There is strong evidence for substantial dust reddening with a best-fit A_V=0.7 and A_V>0.48 at 2 sigma confidence, in contrast to the typical dust-free galaxies of lower luminosity at this epoch. The spatial extent and spectral energy distribution suggest that the most luminous z~6 galaxies are undergoing merger-induced starbursts. The luminosity function of z=5.9 star-forming galaxies is derived. This agrees well with previous work and shows strong evidence for an exponential decline at the bright end, indicating that the feedback processes which govern the shape of the bright end are occurring effectively at this epoch.
We present the results of a new search for bright star-forming galaxies at z ~ 7 within the UltraVISTA DR2 and UKIDSS UDS DR10 data, which together provide 1.65 sq deg of near-infrared imaging with overlapping optical and Spitzer data. Using a full photo-z analysis to identify high-z galaxies and reject contaminants, we have selected a sample of 34 luminous (-22.7 < M_UV < -21.2) galaxies with 6.5 < z < 7.5. Crucially, the deeper imaging provided by UltraVISTA DR2 confirms all of the robust objects previously uncovered by Bowler et al. (2012), validating our selection technique. Our sample includes the most massive galaxies known at z ~ 7, with M_* ~ 10^{10} M_sun, and the majority are resolved, consistent with larger sizes (r_{1/2} ~ 1 - 1.5 kpc) than displayed by less massive galaxies. From our final sample, we determine the form of the bright end of the rest-frame UV galaxy luminosity function (LF) at z ~ 7, providing strong evidence that the bright end of the z = 7 LF does not decline as steeply as predicted by the Schechter function fitted to fainter data. We consider carefully, and exclude the possibility that this is due to either gravitational lensing, or significant contamination of our galaxy sample by AGN. Rather, our results favour a double power-law form for the galaxy LF at high z, or, more interestingly, a LF which simply follows the form of the dark-matter halo mass function at bright magnitudes. This suggests that the physical mechanism which inhibits star-formation activity in massive galaxies (i.e. AGN feedback or some other form of `mass quenching) has yet to impact on the observable galaxy LF at z ~ 7, a conclusion supported by the estimated masses of our brightest galaxies which have only just reached a mass comparable to the critical `quenching mass of M_* = 10 ^{10.2} M_sun derived from studies of the mass function of star-forming galaxies at lower z.
In this paper, we provide updated constraints on the bolometric quasar luminosity function (QLF) from $z=0$ to $z=7$. The constraints are based on an observational compilation that includes observations in the rest-frame IR, B band, UV, soft and hard X-ray in past decades. Our method follows Hopkins et al. 2007 with an updated quasar SED model and bolometric and extinction corrections. The new best-fit bolometric quasar luminosity function behaves qualitatively different from the Hopkins et al. 2007 model at high redshift. Compared with the old model, the number density normalization decreases towards higher redshift and the bright-end slope is steeper at $zgtrsim 2$. Due to the paucity of measurements at the faint end, the faint end slope at $zgtrsim 5$ is quite uncertain. We present two models, one featuring a progressively steeper faint-end slope at higher redshift and the other featuring a shallow faint-end slope at $zgtrsim 5$. Further multi-band observations of the faint-end QLF are needed to distinguish between these models. The evolutionary pattern of the bolometric QLF can be interpreted as an early phase likely dominated by the hierarchical assembly of structures and a late phase likely dominated by the quenching of galaxies. We explore the implications of this model on the ionizing photon production by quasars, the CXB spectrum, the SMBH mass density and mass functions. The predicted hydrogen photoionization rate contributed by quasars is subdominant during the epoch of reionization and only becomes important at $zlesssim 3$. The predicted CXB spectrum, cosmic SMBH mass density and SMBH mass function are generally consistent with existing observations.
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