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We analyze the redshift- and luminosity-dependent sizes of dropout galaxy candidates in the redshift range z ∼ 7-12 using deep images from the 2012 Hubble Ultra Deep Field (UDF12) campaign, which offers two advantages over that used in earlier work. First, we utilize the increased signal-to-noise ratio offered by the UDF12 imaging to provide improved measurements for known galaxies at z ≃ 6.5-8 in the HUDF. Second, because the UDF12 data have allowed the construction of the first robust galaxy sample in the HUDF at z > 8, we have been able to extend the measurement of average galaxy size out to higher redshifts. Restricting our measurements to sources detected at >15σ, we confirm earlier indications that the average half-light radii of z ∼ 7-12 galaxies are extremely small, 0.3-0.4 kpc, comparable to the sizes of giant molecular associations in local star-forming galaxies. We also confirm that there is a clear trend of decreasing half-light radius with increasing redshift, and provide the first evidence that this trend continues beyond z ≃ 8. Modeling the evolution of the average half-light radius as a power law, (1 + z)s, we obtain a best-fit index of over z ∼ 4-12. A clear size-luminosity relation is evident in our dropout samples. This relation can be interpreted in terms of a constant surface density of star formation over a range in luminosity of . The average star formation surface density in dropout galaxies is 2-3 orders of magnitude lower than that found in extreme starburst galaxies, but is comparable to that seen today in the centers of normal disk galaxies. © 2013. The American Astronomical Society. All rights reserved.

We investigate the relationship between the quenching of star formation and the structural transformation of massive galaxies, using a large sample of photometrically selected poststarburst galaxies in the UKIDSS Ultra-Deep Survey field. We find that post-starburst galaxies at high redshift (z > 1) show high Sérsic indices, significantly higher than those of active star-forming galaxies, but with a distribution that is indistinguishable from the old quiescent population. We conclude that the morphological transformation occurs before (or during) the quenching of star formation. Recently quenched galaxies are also the most compact; we find evidence that massive post-starburst galaxies (M* > 1010.5M☉) at high redshift (z > 1) are on average smaller than comparable quiescent galaxies at the same epoch. Our findings are consistent with a scenario in which massive passive galaxies are formed from three distinct phases: (1) gas-rich dissipative collapse to very high densities, forming the proto-spheroid, (2) rapid quenching of star formation to create the 'red nugget' with post-starburst features and (3) a gradual growth in size as the population ages, perhaps as a result of minor mergers. [ABSTRACT FROM AUTHOR]

We present the results of a new study of the K-band galaxy luminosity function (KLF) at redshifts z ≤ 3.75, based on a nested combination of the UltraVISTA, Cosmic Assembly Near-infrared Deep Legacy Extragalactic Survey and HUDF surveys. The large dynamic range in luminosity spanned by this new data set (3-4 dex over the full redshift range) is sufficient to clearly demonstrate for the first time that the faint-end slope of the KLF at z ≥ 0.25 is relatively steep (-1.3 ≤ α ≤ -1.5 for a single Schechter function), in good agreement with recent theoretical and phenomenological models. Moreover, based on our new data set, we find that a double Schechter function provides a significantly improved description of the KLF at z ≤ 2. At redshifts z ≥ 0.25, the evolution of the KLF is remarkably smooth, with little or no evolution evident at faint (MK ≥ -20.5) or bright magnitudes (MK ≤ -24.5). Instead, the KLF is seen to evolve rapidly at intermediate magnitudes, with the number density of galaxies at MK ⊧-23 dropping by a factor of ⊧5 over the redshift interval 0.25 ≤ z ≤ 3.75. Motivated by this, we explore a simple description of the evolving KLF based on a double Schechter function with fixed faint-end slopes (α1 = -0.5, α2 = -1.5) and a shared characteristic magnitude (MK*). According to this parametrization, the normalization of the component which dominates the faint end of the KLF remains approximately constant, with ϕ2* decreasing by only a factor of ⊧2 between z ⊧0 and 3.25. In contrast, the component which dominates the bright end of the KLF at low redshifts evolves dramatically, becoming essentially negligible by z ⊧3. Finally, we note that within this parametrization, the observed evolution of MK* between z ⊧0 and 3.25 is entirely consistent with MK* corresponding to a constant stellar mass of M* ⊧5 x 1010 Mࣻ at all redshifts. [ABSTRACT FROM AUTHOR]

We present a new, robust measurement of the evolving rest-frame ultraviolet (UV) galaxy luminosity function (LF) over the key redshift range from z ≃ 2 to z ≃ 4. Our results are based on the high dynamic range provided by combining the Hubble Ultra Deep Field (HUDF), CANDELS/GOODS-South, and UltraVISTA/COSMOS surveys. We utilize the unparalleled multifrequency photometry available in this survey 'wedding cake' to compile complete galaxy samples at z ≃ 2, 3, 4 via photometric redshifts (calibrated against the latest spectroscopy) rather than colour-colour selection, and to determine accurate rest-frame UV absolute magnitudes (M1500) from spectral energy distribution (SED) fitting. Our new determinations of the UV LF extend from M1500 ≃ −22 (AB mag) down to M1500 = −14.5, −15.5 and −16 at z ≃ 2, 3 and 4, respectively (thus, reaching ≃ 3-4 mag fainter than previous blank-field studies at z ≃ 2,3). At z ≃ 2, 3, we find a much shallower faint-end slope (α = −1.32 ± 0.03) than reported in some previous studies (α ≃ −1.7), and demonstrate that this new measurement is robust. By z ≃ 4, the faint-end slope has steepened slightly, to α = −1.43 ± 0.04, and we show that these measurements are consistent with the overall evolutionary trend from z = 0 to 8. Finally, we find that while characteristic number density (ϕ*) drops from z ≃ 2 to z ≃ 4, characteristic luminosity (M*) brightens by ≃ 1 mag. This, combined with the new flatter faint-end slopes, has the consequence that UV luminosity density (and hence unobscured star formation density) peaks at z ≃ 2.5-3, when the Universe was ≃ 2.5 Gyr old. [ABSTRACT FROM AUTHOR]

We present a catalog of high-redshift star-forming galaxies selected to lie within the redshift range z ≃ 7-8 using the Ultra Deep Field 2012 (UDF12), the deepest near-infrared (near-IR) exposures yet taken with the Hubble Space Telescope (HST). As a result of the increased near-IR exposure time compared to previous HST imaging in this field, we probe ~0.65 (0.25) mag fainter in absolute UV magnitude, at z ~ 7 (8), which increases confidence in a measurement of the faint end slope of the galaxy luminosity function. Through a 0.7 mag deeper limit in the key F105W filter that encompasses or lies just longward of the Lyman break, we also achieve a much-refined color-color selection that balances high redshift completeness and a low expected contamination fraction. We improve the number of dropout-selected UDF sources to 47 at z ~ 7 and 27 at z ~ 8. Incorporating brighter archival and ground-based samples, we measure the z ≃ 7 UV luminosity function to an absolute magnitude limit of MUV = -17 and find a faint end Schechter slope of α = -1.87+0.18-0.17. Using a similar color-color selection at z ≃ 8 that takes our newly added imaging in the F140W filter into account, and incorporating archival data from the HIPPIES and BoRG campaigns, we provide a robust estimate of the faint end slope at z ≃ 8, α = -1.94+0.21-0.24. We briefly discuss our results in the context of earlier work and that derived using the same UDF12 data but with an independent photometric redshift technique. [ABSTRACT FROM AUTHOR]

Understanding cosmic reionization requires the identification and characterization of early sources of hydrogenionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign has acquired the deepest infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. The UDF12 campaign thus provides the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize the new UDF12 results with the most recent constraints from CMB observations to infer redshift-dependent ultraviolet (UV) luminosity densities, reionization histories, and electron scattering optical depth evolution consistent with the available data. Under reasonable assumptions about the escape fraction of hydrogen-ionizing photons and the intergalactic medium clumping factor, we find that to fully reionize the universe by redshift z ~ 6 the population of star-forming galaxies at redshifts z ~ 7-9 likely must extend in luminosity below the UDF12 limits to absolute UV magnitudes of MUV ~ -13 or fainter. Moreover, low levels of star formation extending to redshifts z ~ 15-25, as suggested by the normal UV colors of z≃7-8 galaxies and the smooth decline in abundance with redshift observed by UDF12 to z ≃ 10, are additionally likely required to reproduce the optical depth to electron scattering inferred from CMB observations. [ABSTRACT FROM AUTHOR]

We present deep Hubble Space Telescope (HST)/Wide-Field Planetary Camera 2 (WFPC2), rest-frame U images of 17 ∼L⋆ quasars at z ≈ 1 and 2 (V and I bands, respectively), designed to explore the host galaxies. We fit the images with simple axisymmetric galaxy models, including a point source, in order to separate nuclear and host-galaxy emission. We successfully model all of the host galaxies, with luminosities stable to within 0.3 mag. Combining with our earlier Near Infrared Camera and Multi-Object Spectrometer rest-frame optical study of the same sample, we provide the first rest-frame U − V colours for a sample of quasar host galaxies. While the optical luminosities of their host galaxies indicate that they are drawn purely from the most massive (≳L⋆) early-type galaxy population, their colours are systematically bluer than those of comparably massive galaxies at the same redshift. The host galaxies of the radio-loud quasars (RLQs) in our sample are more luminous than their radio-quiet quasar (RQQ) counterparts at each epoch, but have indistinguishable colours, confirming that the RLQs are drawn from only the most massive galaxies (1011–1012 M⊙ even at z ≈ 2), while the RQQs are slightly less massive (∼1011 M⊙). This is consistent with the well-known anticorrelation between radio-loudness and accretion rate. Using simple stellar population ‘frosting’ models, we estimate mean star formation rates of ∼350 M⊙ yr−1 for the RLQs and ∼100 M⊙ yr−1 for the RQQs at z ≈ 2. By z ≈ 1, these rates have fallen to ∼150 M⊙ yr−1 for the RLQs and ∼50 M⊙ yr−1 for the RQQs. We conclude that while the host galaxies are extremely massive, they remain actively star forming at, or close to, the epoch of the quasar. [ABSTRACT FROM AUTHOR]

Using deep Keck spectroscopy of Lyman break galaxies selected from infrared imaging data taken with the Wide Field Camera 3 on board the Hubble Space Telescope, we present new evidence for a reversal in the redshift-dependent fraction of star-forming galaxies with detectable Lyman alpha (Lyα) emission in the redshift range 6.3 < z < 8.8. Our earlier surveys with the DEIMOS spectrograph demonstrated a significant increase with redshift in the fraction of line emitting galaxies over the interval 4 < z < 6, particularly for intrinsically faint systems which dominate the luminosity density. Using the longer wavelength sensitivities of Low Resolution Imaging Spectrometer and NIRSPEC, we have targeted 19 Lyman break galaxies selected using recent WFC3/IR data whose photometric redshifts are in the range 6.3 < z < 8.8 and which span a wide range of intrinsic luminosities. Our spectroscopic exposures typically reach a 5σ sensitivity of <50 Å for the rest-frame equivalent width (EW) of Lyα emission. Despite the high fraction of emitters seen only a few hundred million years later, we find only two convincing and one possible line emitter in our more distant sample. Combining with published data on a further seven sources obtained using FORS2 on the ESO Very Large Telescope, and assuming continuity in the trends found at lower redshift, we discuss the significance of this apparent reversal in the redshift-dependent Lyα fraction in the context of our range in continuum luminosity. Assuming all the targeted sources are at their photometric redshift and our assumptions about the Lyα EW distribution are correct, we would expect to find so few emitters in less than 1% of the realizations drawn from our lower redshift samples. Our new results provide further support for the suggestion that, at the redshifts now being probed spectroscopically, we are entering the era where the intergalactic medium is partially neutral. With the arrival of more sensitive multi-slit infrared spectrographs, the prospects for improving the statistical validity of this result are promising. [ABSTRACT FROM AUTHOR]

We compare Hα, ultraviolet (UV) and infrared (IR) indicators of star formation rate (SFR) for a well-defined sample of emission-line galaxies from the High- z Emission Line Survey (HiZELS). Using emission-line, optical, IR, radio and X-ray diagnostics, we estimate that 5–11 per cent of Hα emitters at this redshift are active galactic nuclei. We detect 35 per cent of the Hα emitters individually at 24 μm, and stack the locations of star-forming emitters on deep 24-μm Spitzer Space Telescope images in order to calculate the typical SFRs of our Hα-emitting galaxies. These are compared to the observed Hα line fluxes in order to estimate the extinction at , and we find a significant increase in dust extinction for galaxies with higher SFRs. We demonstrate that the relationship between SFR and extinction found in the local Universe is also suitable for our high-redshift galaxies, and attribute the overall increase in the typical dust extinction for galaxies to an increase in the average SFR, rather than to a change in dust properties at higher redshift. We calculate the UV extinction, and find a similar dependence on SFR to the Hα results, but no evidence for a 2175 Å UV bump in the dust attenuation law for high-redshift star-forming galaxies. By comparing Hα and UV indicators, we calculate the conversion between the dust attenuation of nebular and stellar radiation, γ, and show that . The extinction/SFR relationship is shown to be applicable to galaxies with a range of morphologies and bulge-to-disc ratios, to both merging and non-merging galaxies, and to galaxies within high- and low-density environments, implying that it is a fundamental property of star-forming regions. In order to allow future studies to easily correct for a SFR-dependent amount of dust extinction, we present an equation to predict the extinction of a galaxy, based solely on its observed Hα luminosity, and use this to recalculate the Hα luminosity function and SFR density at . [ABSTRACT FROM AUTHOR]

We present basic observational data on the 6C** sample. This is a new sample of radio sources drawn from the 151-MHz 6C survey, which was filtered with radio criteria chosen to optimize the chances of finding radio galaxies at . The filtering criteria are a steep-spectral index and a small angular size. The final sample consists of 68 sources from a region of sky covering 0.421 sr. We present Very Large Array radio maps, and the results of K-band imaging and optical spectroscopy. Near-infrared counterparts are identified for 66 of the 68 sources, down to a 3σ limiting magnitude of K∼ 22 mag in a 3-arcsec aperture. Eight of these identifications are spatially compact, implying an unresolved nuclear source. The K-magnitude distribution peaks at a median K≈ 18.7 mag, and is found to be statistically indistinguishable from that of the similarly selected 6C* sample, implying that the redshift distribution could extend to z≳ 4. Redshifts determined from spectroscopy are available for 22 (32 per cent) of the sources, over the range of 0.2 ≲ z≲ 3.3. We measure 15 of these, whereas the other seven were previously known. Six sources are at . Four sources show broad emission lines in their spectra and are classified as quasars. Three of these show also an unresolved K-band identification. 11 sources fail to show any distinctive emission and/or absorption features in their spectra. We suggest that these could be (i) in the so-called ‘redshift desert’ region of or (ii) at a greater redshift, but feature weak emission-line spectra. [ABSTRACT FROM AUTHOR]

We present the results of a deepHubble Space Telescope(HST)/Wide Field and Planetary Camera 2 imaging study of 17 quasars at, designed to determine the properties of their host galaxies. The sample consists of quasars with absolute magnitudes in the range, allowing us to investigate host galaxy properties across a decade in quasar luminosity, but at a single redshift. Our previous imaging studies of active galactic nuclei hosts have focused primarily on quasars of moderate luminosity, but the most powerful objects in the current sample have powers comparable to the most luminous quasars found at high redshifts.We find that the host galaxies of all the radio-loud quasars, and all the radio-quiet quasars in our sample with nuclear luminosities, are massive bulge-dominated galaxies, confirming and extending the trends deduced from our previous studies. From the best-fitting model host galaxies we have estimated spheroid and hence black hole (BH) masses, and the efficiency (with respect to the Eddington luminosity) with which each quasar emits radiation. The largest inferred black hole mass in our sample is, comparable to the mass of the black holes at the centres of M87 and Cygnus A. We find no evidence for super-Eddington accretion rates in even the most luminous objects.We investigate the role of scatter in the black hole–spheroid mass relation in determining the ratio of quasar to host-galaxy luminosity, by generating simulated populations of quasars lying in hosts with a Schechter mass function. Within the subsample of the highest-luminosity quasars, the observed variation in nuclear-host luminosity ratio is consistent with being the result of the scatter in the black hole–spheroid relation. Quasars with high nuclear-host luminosity ratios can be explained in terms of sub-Eddington accretion rates on to black holes in the high-mass tail of the black hole–spheroid relation. Our results imply that, owing to the Schechter function cut-off, host mass should not continue to increase linearly with quasar luminosity, at the very highest luminosities. Any quasars more luminous thanshould be found in massive elliptical hosts, which at the present day would have. [ABSTRACT FROM AUTHOR]

We present the first results from a major Hubble Space Telescope programme designed to investigate the cosmological evolution of quasar host galaxies from to the present day. Here we describe J and H-band NICMOS imaging of two quasar samples at redshifts of 0.9 and 1.9 respectively. Each sample contains equal numbers of radio-loud and radio-quiet quasars, selected to lie within the same narrow range of optical absolute magnitude . Filter and target selection were designed to ensure that at each redshift the images sample the same part of the object's rest-frame spectrum, longwards of 4000 Å, where starlight from the host galaxy is relatively prominent, but avoiding potential contamination by [O iii]λ5007 and Hα emission lines. At we have been able to establish host-galaxy luminosities and scalelengths with sufficient accuracy to demonstrate that the hosts of both radio-loud and radio-quiet quasars lie on the same Kormendy relation described by 3CR radio galaxies at comparable redshift . Taken at face value the gap between the host luminosities of radio-loud and radio-quiet objects appears to have widened from only ≃ 0.4 mag at to ≃ 1 mag at , a difference that cannot be a result of emission-line contamination, given the design of our study. However, within current uncertainties, simple passive stellar evolution is sufficient to link these galaxies with the elliptical hosts of low-redshift quasars of comparable nuclear output, implying that the hosts are virtually fully assembled by . At the hosts have proved harder to characterize accurately, and for only two of the nine quasars observed has it proved possible to properly constrain the scalelength of the host galaxy. However, the data are of sufficient quality to yield host-galaxy luminosities accurate to within a factor of ≃ 2. At this redshift the luminosity gap between radio-loud and radio-quiet quasars appears to have widened further to ≃ 1.5 mag. Thus while the hosts of radio-loud quasars remain consistent with a formation epoch of , allowing for passive evolution implies that the hosts of radio-quiet quasars are times less massive at than at . If the relationship between black hole and spheroid mass is unchanged out to redshift , then our results rule out any model of quasar evolution which involves a substantial component of luminosity evolution . Rather, this study indicates that at there is a substantial increase in the number density of active black holes, along with a moderate increase in the fuelling efficiency of a typical observed quasar. The fact that this latter effect is not displayed by the radio-loud objects in our sample might be explained by a selection effect arising from the fact that powerful radio sources are only produced by the most massive black holes . [ABSTRACT FROM AUTHOR]

In this paper, the third and final of a series, we present complete K-band imaging and some complementary I-band imaging of the filtered 6C* sample. We find no systematic differences between the K–z relation of 6C* radio galaxies and those from complete samples, so the near-infrared properties of luminous radio galaxies are not obviously biased by the additional 6C* radio selection criteria (steep spectral index and small angular size). The 6C*K–z data significantly improve delineation of the K–z relation for radio galaxies at high redshift (z>2). Accounting for non-stellar contamination, and for correlations between radio luminosity and stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z>2. In a particular spatially flat universe with a cosmological constant (Ω[sub M]=0.3 and Ω[sub Λ]=0.7), the most luminous radio sources appear to be associated with galaxies with a luminosity distribution with a high mean (≈5 L*), and a low dispersion (σ∼0.5 mag) which formed their stars at epochs corresponding to z&gsim;2.5. This result is in line with recent submillimetre studies of high-redshift radio galaxies and the inferred ages of extremely red objects from faint radio samples. [ABSTRACT FROM AUTHOR]

We have exploited the new, deep, near-infrared Y,J,H,Ks UltraVISTA imaging of the COSMOS field, in tandem with deep optical and mid-infrared imaging, to conduct a new search for luminous galaxies at redshifts z ≃ 7. We have utilised this unique multi-wavelength dataset to select galaxy candidates at redshifts z > 6.5 by searching first for Y+J-detected objects which are undetected in the CFHT and HST optical data. This sample was then refined using a photometric redshift fitting code, enabling the rejection of lower-redshift galaxy contaminants and cool galactic M, L, T dwarf stars. The final result of this process is a small sample of (at most) ten credible galaxy candidates at z > 6.5 (from over 200,000 galaxies detected in the year-one UltraVISTA data). The new z ≃ 7 galaxies reported here are the first credible z ≃ 7 Lyman-break galaxies discovered in the COSMOS field and, as the most UV-luminous discovered to date at these redshifts, are prime targets for deep follow-up spectroscopy. We explore their physical properties, and briefly consider the implications of their inferred number density for the form of the galaxy luminosity function at z ≃ 7. [ABSTRACT FROM PUBLISHER]