Recent observations have suggested that the C III] lambda 1907/1909 emission lines could be alternative diagnostic lines for galaxies in the reionization epoch. We use the F128N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to search for C III] emission in a sample of five galaxies at z = 5.7 in the Subaru Deep Field and the Subaru/XMM-Newton Deep Field. Using the F128N narrowband imaging, together with the broadband imaging, we do not detect C III] emission for the five galaxies with JAB ranging from 24.10 to 27.00 in our sample. For the brightest galaxy J132416.13+274411.6 in our sample (z = 5.70, J(AB) = 24.10), which has a significantly higher signal to noise, we report a C III] flux of 3.34 +/- 1.81 x 10(-18) erg s(-1)cm(-2), which places a stringent 3 sigma upper limit of 5.43 x 10(-18) erg s(-1)cm(-2) on C III] flux and 6.57 angstrom on the C III] equivalent width. Using the stacked image, we put a 3 sigma upper limit on the mean C III] flux of 2.55 x 10(-18) erg s(-1) cm(-2) and a 3 sigma upper limit on the mean C III] equivalent width of 4.20 angstrom for this sample of galaxies at z = 5.70. Combined with strong C III] detection reported among high-z galaxies in the literature, our observations suggest that the equivalent widths of C III] from galaxies at z > 5.70 exhibit a wide range of distribution. Our strong limits on C III] emission could be used as a guide for future observations in the reionization epoch.

In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.5. <. z. <. 2.5 selected from 3D-HST. We confirm that star-forming galaxies are larger than quiescent galaxies at fixed stellar mass (M*). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27. +/-. 0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed M. takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/M., whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/M. at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of > 0.5 dex in the central density threshold correlated with quiescence from z.similar to. 0.7-2.0. Neither a compact size nor high-n are sufficient to assess the likelihood of quiescence for the average galaxy; instead, the combination of these two parameters together with M* results in a unique quenching threshold in central density/velocity.

We present a robust measurement of the rest-frame UV luminosity function (LF) and its evolution during the peak epoch of cosmic star formation at 1 < z < 3. We use our deep near-ultraviolet imaging from WFC3/UVIS on the Hubble Space Telescope and existing Advanced Camera for Surveys (ACS)/WFC and WFC3/IR imaging of three lensing galaxy clusters, Abell 2744 and MACS J0717 from the Hubble Frontier Field survey and Abell 1689. Combining deep UV imaging and high magnification from strong gravitational lensing, we use photometric redshifts to identify 780 ultra-faint galaxies with M-UV < -12.5 AB mag at 1 < z < 3. From these samples, we identified five new, faint, multiply imaged systems in A1689. We run a Monte Carlo simulation to estimate the completeness correction and effective volume for each cluster using the latest published lensing models. We compute the rest-frame UV LF and find the best-fit faint-end slopes of alpha = -1.56 +/- 0.04, alpha = -1.72 +/- 0.04, and alpha = -1.94 +/- 0.06 at 1.0 < z < 1.6, 1.6 < z < 2.2, and 2.2 < z < 3.0, respectively. Our results demonstrate that the UV LF becomes steeper from z similar to 1.3 to z similar to 2.6 with no sign of a turnover down to MUV = -14 AB mag. We further derive the UV LFs using the Lyman break "dropout" selection and confirm the robustness of our conclusions against different selection methodologies. Because the sample sizes are so large and extend to such faint luminosities, the statistical uncertainties are quite small, and systematic uncertainties (due to the assumed size distribution, for example) likely dominate. If we restrict our analysis to galaxies and volumes above >50% completeness in order to minimize these systematics, we still find that the faint-end slope is steep and getting steeper with redshift, though with slightly shallower (less negative) values (alpha = -1.55 +/- 0.06, -1.69 +/- 0.07, and -1.79 +/- 0.08 for z similar to 1.3, 1.9, and 2.6, respectively). Finally, we conclude that the faint star-forming galaxies with UV magnitudes of -18.5 < M-UV < -12.5 covered in this study produce the majority (55%-60%) of the unobscured UV luminosity density at 1 < z < 3.

In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.5. <. z. <. 2.5 selected from 3D-HST. We confirm that star-forming galaxies are larger than quiescent galaxies at fixed stellar mass (M*). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27. +/-. 0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed M. takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/M., whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/M. at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of > 0.5 dex in the central density threshold correlated with quiescence from z.similar to. 0.7-2.0. Neither a compact size nor high-n are sufficient to assess the likelihood of quiescence for the average galaxy; instead, the combination of these two parameters together with M* results in a unique quenching threshold in central density/velocity.

In this paper we use ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field in band. 3 and band. 6, to place blind constraints on the CO luminosity function and the evolution of the cosmic molecular gas density as a function of redshift up to z similar to 4.5. This study is based on galaxies that have been selected solely through their CO emission and not through any other property. In all of the redshift bins the ASPECS measurements reach the predicted "knee" of the CO luminosity function (around 5 x 10(9) K km s(-1) pc(2)). We find clear evidence of an evolution in the CO luminosity function with respect to z similar to 0, with more CO-luminous galaxies present at z similar to 2. The observed galaxies at z similar to 2 also appear more gas-rich than predicted by recent semi-analytical models. The comoving cosmic molecular gas density within galaxies as a function of redshift shows a drop by a factor of 3-10 from z similar to 2 to z similar to 0 (with significant error bars), and possibly a decline at z > 3. This trend is similar to the observed evolution of the cosmic star formation rate density. The latter therefore appears to be at least partly driven by the increased availability of molecular gas reservoirs at the peak of cosmic star formation (z similar to 2).

We present; 0 4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z. =. 1.3-3.0. These galaxies are selected from sensitive blank-field surveys of the 2 x 2' Hubble Ultra-Deep Field at gimel = 5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z similar to 2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z similar to 2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2 similar to 1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected main-sequence SFGs. The typical galactic-average SFR surface density is 2.5Me circle dot yr(-1) kpc(-2), sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinctionindependent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3-8 times larger, providing a constraint on the characteristic SFR (similar to 300Me yr(-1)) above which a significant population of more compact SFGs appears to emerge.

The determination of galaxy redshifts in the James Webb Space Telescope's (JWST) blank-field surveys will mostly rely on photometric estimates, based on the data provided by JWST's Near-Infrared Camera (NIRCam) at 0.6-5.0 mu m and Mid Infrared Instrument (MIRI) at lambda > 5.0 mm. In this work we analyze the impact of choosing different combinations of NIRCam and MIRI broadband filters (F070W to F770W), as well as having ancillary data at lambda < 0.6 mu m, on the derived photometric redshifts (z(phot)) of a total of 5921 real and simulated galaxies, with known input redshifts z = 0-10. We found that observations at lambda < 0.6 mm are necessary to control the contamination of high-z samples by low-z interlopers. Adding MIRI (F560W and F770W) photometry to the NIRCam data mitigates the absence of ancillary observations at l < 0.6 mm and improves the redshift estimation. At z = 7-10, accurate zphot can be obtained with the NIRCam broadbands alone when S/N >= 10, but the z(phot) quality significantly degrades atb S/N <= 5. Adding MIRI photometry with 1 mag brighter depth than the NIRCam depth allows for a redshift recovery of 83%-99%, depending on spectral energy distribution type, and its effect is particularly noteworthy for galaxies with nebular emission. The vast majority of NIRCam galaxies with [F150W] = 29. AB mag at z =7-10 will be detected with MIRI at [F560W, F770W] < 28 mag if these sources are at least mildly evolved or have spectra with emission lines boosting the mid-infrared fluxes.

We present a study of photometric redshift accuracy in the 3D-HST photometric catalogs, using 3D-HST grism redshifts to quantify and dissect trends in redshift accuracy for galaxies brighter than JH(IR) > 24 with an unprecedented and representative high-redshift galaxy sample. We find an average scatter of 0.0197 +/- 0.0003(1 + z) in the Skelton et al. photometric redshifts. Photometric redshift accuracy decreases with magnitude and redshift, but does not vary monotonically with color or stellar mass. The 1 sigma scatter lies between 0.01 and 0.03 (1 + z) for galaxies of all masses and colors below z. <. 2.5 (for JH(IR) < 24), with the exception of a population of very red (U - V > 2), dusty star-forming galaxies for which the scatter increases to similar to 0.1 (1+ z). We find that photometric redshifts depend significantly on galaxy size; the largest galaxies at fixed magnitude have photo-zs with up to similar to 30% more scatter and similar to 5 times the outlier rate. Although the overall photometric redshift accuracy for quiescent galaxies is better than that for star-forming galaxies, scatter depends more strongly on magnitude and redshift than on galaxy type. We verify these trends using the redshift distributions of close pairs and extend the analysis to fainter objects, where photometric redshift errors further increase to similar to 0.046 (1 + z) at H-F160W = 26. We demonstrate that photometric redshift accuracy is strongly filter dependent and quantify the contribution of multiple filter combinations. We evaluate the widths of redshift probability distribution functions and find that error estimates are underestimated by a factor of similar to 1.1 - 1.6, but that uniformly broadening the distribution does not adequately account for fitting outliers. Finally, we suggest possible applications of these data in planning for current and future surveys and simulate photometric redshift performance in the Large Synoptic Survey Telescope, Dark Energy Survey (DES), and combined DES and Vista Hemisphere surveys.

The slope of the ultraviolet continuum emissions from a galaxy between 1250 and 2600 Å provides insights about several facets of the galaxy. Mainly, it is well-correlated with the amount of dust. This work presents a search for objects whose UV-continuum slopes are excessively steep, as well as suggestions for follow-up. The method used is looking through existing data sets, and proposing follow-up of the outliers in the distribution of slopes. Close to fifteen objects with slopes beyond what is easily explained by theory are presented. Since these lie beyond the realm of current theories, confirmations of these may hint at more extreme stellar populations than those currently known. This may include excessively metal-poor stars such as population III stars, or stellar populations where the initial mass function (IMF) for some reason may be biased towards massive stars. Steeper slopes are in general indicative of a lack of dust and an abundance of hot, blue stars; this is due to the reddening caused by dust, and emissions from cooler stars being peaked at longer wavelengths.

We statistically study the physical properties of a sample of narrow absorption line (NAL) systems looking for empirical evidences to distinguish between intrinsic and intervening NALs without taking into account any a priori definition or velocity cut-off. We analyse the spectra of 100 quasars with 3.5 < z(em) < 4.5, observed with X-shooter/Very Large Telescope in the context of the XQ-100 Legacy Survey. We detect an similar to 8 sigma excess in the CIV number density within 10 000 km s(-1) of the quasar emission redshift with respect to the random occurrence of NALs. This excess does not show a dependence on the quasar bolometric luminosity and it is not due to the redshift evolution of NALs. It extends far beyond the standard 5000 km s(-1) cutoff traditionally defined for associated absorption lines. We propose to modify this definition, extending the threshold to 10 000 km s(-1) when weak absorbers (equivalent width < 0.2 angstrom) are also considered. We infer NV is the ion that better traces the effects of the quasar ionization field, offering the best statistical tool to identify intrinsic systems. Following this criterion, we estimate that the fraction of quasars in our sample hosting an intrinsic NAL system is 33 per cent. Lastly, we compare the properties of the material along the quasar line of sight, derived from our sample, with results based on close quasar pairs investigating the transverse direction. We find a deficiency of cool gas (traced by C II) along the line of sight connected to the quasar host galaxy, in contrast with what is observed in the transverse direction.