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We present results from a survey for z ∼ 2.85 Lyman-continuum (LyC) emission in the HS1549+1933 field and place constraints on the amount of ionizing radiation escaping from star-forming galaxies. Using a custom narrowband filter (NB3420) tuned to wavelengths just below the Lyman limit at z ⩾ 2.82, we probe the LyC spectral region of 49 Lyman break galaxies (LBGs) and 91 Lyα emitters (LAEs) spectroscopically confirmed at z ⩾ 2.82. Four LBGs and seven LAEs are detected in NB3420. Using V-band data probing the rest-frame nonionizing UV, we observe that many NB3420-detected galaxies exhibit spatial offsets between their LyC and nonionizing UV emission and are characterized by extremely blue NB3420–V colors, corresponding to low ratios of nonionizing to ionizing radiation (FUV/FLyC) that are in tension with current stellar population synthesis models. We measure average values of (FUV/FLyC) for our LBG and LAE samples, correcting for foreground galaxy contamination and H I absorption in the intergalactic medium. We find and . These flux density ratios correspond, respectively, to relative LyC escape fractions of % and %, absolute LyC escape fractions of % and %, and a comoving LyC emissivity from star-forming galaxies of 8.8-15.0 × 1024 erg s–1 Hz–1 Mpc–3. In order to study the differential properties of galaxies with and without LyC detections, we analyze narrowband Lyα imaging and rest-frame near-infrared imaging, finding that while LAEs with LyC detections have lower Lyα equivalent widths on average, there is no substantial difference in the rest-frame near-infrared colors of LBGs or LAEs with and without LyC detections. These preliminary results are consistent with an orientation-dependent model where LyC emission escapes through cleared paths in a patchy interstellar medium. [ABSTRACT FROM AUTHOR]

We study the properties of luminous stellar "clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/FI60W imaging at 1.6µm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ≈5000Å emission, with median of ≈2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~ 1 kpc and ~ 109 M⊙, 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 through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hot 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 Hα-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 toward the central regions. From constraints on a bulge-like component at radii ≼ 1-3 kpc, 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 buildup of stellar bulges and the role of clumps in this process. [ABSTRACT FROM AUTHOR]

We combine Lyman-break colour selection with ultradeep (≳200 ks) Chandra X-ray imaging over a survey area of ∼0.35 deg2 to select high-redshift active galactic nuclei (AGN). Applying careful corrections for both the optical and X-ray selection functions, the data allow us to make the most accurate determination to date of the faint end of the X-ray luminosity function (XLF) at . Our methodology recovers a number density of X-ray sources at this redshift which is at least as high as previous surveys, demonstrating that it is an effective way of selecting high z AGN. Comparing to results at , we find no evidence that the faint slope of the XLF flattens at high z, but we do find significant (factor ∼3.6) negative evolution of the space density of low luminosity AGN. Combining with bright end data from very wide surveys we also see marginal evidence for continued positive evolution of the characteristic break luminosity . Our data therefore support models of luminosity-dependent density evolution between and . A sharp upturn in the the XLF is seen at the very lowest luminosities , most likely due to the contribution of pure X-ray starburst galaxies at very faint fluxes. [ABSTRACT FROM AUTHOR]

We present an estimate of the space density of active galactic nuclei (AGN) at . Combining deep X-ray data with Lyman break galaxy (LBG) colour selection in the rest-frame ultraviolet makes for highly efficient identification of AGN in a narrow redshift range . Using Chandra data from the Groth–Westphal Strip (GWS) and the Hubble Deep Field North (HDF-N), we find a total of 15 X-ray-detected LBGs at , the majority of which are unlikely to have been identified in blanket follow-up surveys of X-ray-detected objects. We find the comoving space density of moderate-luminosity AGN (MLAGN; ) at to be a factor of ∼10 higher than that of the most powerful objects. The available data are consistent with a roughly constant space density of MLAGN from to 3, and they are also consistent with a mild decline in the space density above as predicted by the luminosity-dependent density evolution models of Ueda et al. This strong AGN activity at argues against previous suggestions that the majority of black hole accretion occurs at low redshift. A further implication of our investigation is that, as far as can be determined from current data, the majority of the AGN population at is selected by the LBG dropout technique. Although this is sensitive to AGN with an ultraviolet excess arising from an accretion disc, it predominantly identifies star-forming galaxies. A significant fraction of X-ray sources seem likely to be hosted by these more typical LBGs, further strengthening the starburst–AGN connection at high redshift. [ABSTRACT FROM AUTHOR]

We present an analysis of the X-ray emission from a large sample of ultraviolet (UV) selected, star-forming galaxies within theHubble Deep FieldNorth (HDF-N) region. By excluding all sources with significant detected X-ray emission in the 2-MsChandraobservation we are able to examine the properties of galaxies for which the dominant emission in both UV and X-ray is expected to be predominantly the result of star formation. Stacking the X-ray flux from 216 galaxies in the soft and hard bands produces significant detections (14.9σ and 3.2σ, respectively). The derived mean 2–10 keV rest-frame luminosity is, corresponding to an X-ray derived star formation rate (SFR) of. Comparing the X-ray value with the mean UV derived SFR, uncorrected for attenuation, we find that the average UV attenuation correction factor is∼3. By binning the galaxy sample according to UV magnitude and colour, and stacking the observed frame soft band X-ray flux in each bin, correlations between UV and X-ray emission are examined. We find a strong positive correlation between X-ray emission and rest-frame UV emission, consistent with a strict linear relationship,, at the 90 per cent level. A correlation between the ratio of X-ray-to-UV emission and UV colour is also seen, such thatincreases for redder galaxies. We find no direct relation between X-ray flux and UV colour. Given that X-ray emission offers a view of star formation regions that is relatively unaffected by extinction, results such as these can be used to evaluate the effects of dust on the UV emission from high-zgalaxies. For instance, using the observed correlation between UV colour excess and the ratio of X-ray-to-UV emission (a measure of UV obscuration), we derive a relationship for estimating UV attenuation corrections as a function of colour excess. The observed relation is inconsistent with the Calzetti et al. reddening law, which overpredicts the range in UV attenuation corrections by a factor of∼100 for the UV-selectedz∼ 1 galaxies in this sample. [ABSTRACT FROM AUTHOR]