[en] Stacking analysis is a means of detecting faint sources using a priori position information to estimate an aggregate signal from individually undetected objects. Confusion severely limits the effectiveness of stacking in deep surveys with limited angular resolution, particularly at far-infrared to submillimeter wavelengths, and causes a bias in stacking results. Deblending corrects measured fluxes for confusion from adjacent sources; however, we find that standard deblending methods only reduce the bias by roughly a factor of 2 while tripling the variance. We present an improved algorithm for simultaneous stacking and deblending that greatly reduces bias in the flux estimate with nearly minimum variance. When confusion from neighboring sources is the dominant error, our method improves upon rms error by at least a factor of 3 and as much as an order of magnitude compared to other algorithms. This improvement will be useful for Herschel and other telescopes working in a source confused, low signal-to-noise regime.

[en] Star formation histories (SFHs) reveal physical processes that influence how galaxies form their stellar mass. We compare the SFHs of a sample of 36 nearby (D ⪅ 4 Mpc) dwarf galaxies from the ACS Nearby Galaxy Survey Treasury (ANGST), inferred from the color–magnitude diagrams (CMDs) of individually resolved stars in these galaxies, with those reconstructed by broadband spectral energy distribution (SED) fitting using the dense basis SED-fitting code. When comparing individual SFHs, we introduce metrics for evaluating SFH reconstruction techniques. For both the SED and CMD methods, the median normalized SFH of galaxies in the sample shows a period of quiescence at lookback times of 3–6 Gyr followed by rejuvenated star formation over the past 3 Gyr that remains active until the present day. To determine if these represent special epochs of star formation in the D <4 Mpc portion of the Local Volume, we break this ANGST dwarf galaxy sample into subsets based on specific star formation rate and spatial location. Modulo offsets between the methods of about 1 Gyr, all subsets show significant decreases and increases in their median normalized SFHs at the same epochs, and the majority of the individual galaxy SFHs are consistent with these trends. These results motivate further study of potential synchronized star formation quiescence and rejuvenation in the Local Volume as well as development of a hybrid method of SFH reconstruction that combines CMDs and SEDs, which have complementary systematics.

[en] We study the physical properties of 216 z ≅ 2.1 Lyα-emitting galaxies (LAEs) discovered in an ultra-deep narrow- MUSYC image of the ECDF-S. We fit their stacked spectral energy distribution (SED) using Charlot and Bruzual templates. We consider star formation histories (SFHs) parameterized by the e-folding time parameter τ, allowing for exponentially decreasing (τ > 0), exponentially increasing (τ < 0), and constant star formation rates (SFRs). We estimated the average flux at 5015 A of our LAE sample, finding a non-detection, which translates into negligible He II line emission at z ≅ 2.1. In addition to this, the lack of high equivalent width (EW) Lyα line objects ruled out the hypothesis of a top-heavy initial mass function in LAEs. The typical LAEs of our sample are characterized by best-fit parameters and 68% confidence intervals of log(M_*/M_sun) = 8.6[8.4-9.1], E(B - V) = 0.22[0.00-0.31], τ = -0.02[(- 4)-18] Gyr, and age_SF = 0.018[0.009-3] Gyr. Thus, we obtain robust measurements of low stellar mass and dust content, but we cannot place meaningful constraints on the age or SFH of the LAEs. We also calculate the instantaneous SFR to be 35[0.003-170] M_sun yr^-1, with its average over the last 100 Myr before observation giving (SFR)₁₀₀ = 4[2-30] M_sun yr^-1. When we compare the results for the same SFH, typical LAEs at z ≅ 2.1 appear dustier and show higher instantaneous SFRs than z ≅ 3.1 LAEs, while the observed stellar masses of the two samples seem consistent. Because the majority are low-mass galaxies, our typical LAEs appear to occupy the low-mass end of the distribution of star-forming galaxies at z ∼ 2. We perform SED fitting on several sub-samples selected based on photometric properties and find that LAE sub-samples at z ≅ 2.1 exhibit heterogeneous properties. The typical IRAC-bright, UV-bright, and red LAEs have the largest stellar mass and dust reddening. The typical UV-faint, IRAC-faint, and high EW LAE sub-samples appear less massive (<10⁹ M_sun) and less dusty, with E(B - V) consistent with zero.

[en] We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at $0.5⩽<!--\; ???\; -->z⩽<!--\; ???\; -->1.5$ in the rest-frame far-ultraviolet (FUV) using Hubble Space Telescope Wide Field Camera 3 broadband imaging in F225W, F275W, and F336W. An analysis of 1404 galaxies yields 209 galaxies that host 403 kpc scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps and determine the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of ∼4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from lower than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher SFRs, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.

[en] We search for evidence of diffuse Lyα emission from extended neutral hydrogen surrounding Lyα emitting galaxies (LAEs) using deep narrow-band images of the Extended Chandra Deep Field South. By stacking the profiles of 187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and carefully performing low-surface brightness photometry, we obtain mean surface brightness maps that reach 9.9, 8.7, and 6.2 × 10^–19 erg cm^–2 s^–1 arcsec^–2 in the emission line. We undertake a thorough investigation of systematic uncertainties in our surface brightness measurements and find that our limits are 5-10 times larger than would be expected from Poisson background fluctuations; these uncertainties are often underestimated in the literature. At z ∼ 3.1, we find evidence for extended halos with small-scale lengths of 5-8 kpc in some but not all of our sub-samples. We demonstrate that sub-samples of LAEs with low equivalent widths and brighter continuum magnitudes are more likely to possess such halos. At z ∼ 2.1, we find no evidence of extended Lyα emission down to our detection limits. Through Monte-Carlo simulations, we also show that we would have detected large diffuse LAE halos if they were present in our data sets. We compare these findings to other measurements in the literature and discuss possible instrumental and astrophysical reasons for the discrepancies

[en] We present the rest-1500 Å UV luminosity functions (LF) for star-forming galaxies during the cosmic high noon—the peak of cosmic star formation rate at $1.5<<!--\; <\; -->z<<!--\; <\; -->3$. We use deep NUV imaging data obtained as part of the Hubble Ultra-Violet Ultra Deep Field (UVUDF) program, along with existing deep optical and NIR coverage on the HUDF. We select F225W, F275W, and F336W dropout samples using the Lyman break technique, along with samples in the corresponding redshift ranges selected using photometric redshifts, and measure the rest-frame UV LF at $z\sim <!--\; ???\; -->1.7,2.2,3.0$, respectively, using the modified maximum likelihood estimator. We perform simulations to quantify the survey and sample incompleteness for the UVUDF samples to correct the effective volume calculations for the LF. We select galaxies down to $M_{\mathrm{U}\mathrm{V}}=-<!--\; ???\; -->15.9,-<!--\; ???\; -->16.3,-<!--\; ???\; -->16.8$ and fit a faint-end slope of $\mathrm{\alpha <!--\; ??\; -->}=-<!--\; ???\; -->{1.20}_{-<!--\; ???\; -->0.13}^{+0.10},-<!--\; ???\; -->{1.32}_{-<!--\; ???\; -->0.14}^{+0.10},-<!--\; ???\; -->{1.39}_{-<!--\; ???\; -->0.12}^{+0.08}$ at $1.4<<!--\; <\; -->z<<!--\; <\; -->1.9$, $1.8<<!--\; <\; -->z<<!--\; <\; -->2.6$, and $2.4<<!--\; <\; -->z<<!--\; <\; -->3.6$, respectively. We compare the star formation properties of $z\sim <!--\; ???\; -->2$ galaxies from these UV observations with results from Hα and UV+IR observations. We find a lack of high-SFR sources in the UV LF compared to the Hα and UV+IR, likely due to dusty SFGs not being properly accounted for by the generic $IRX\text{--}\mathrm{\beta <!--\; ??\; -->}$ relation used to correct for dust. We compute a volume-averaged UV-to-Hα ratio by abundance matching the rest-frame UV LF and Hα LF. We find an increasing UV-to-Hα ratio toward low-mass galaxies ($M_{\star <!--\; ???\; -->}\lesssim <!--\; ???\; -->5\times <!--\; ??\; -->{10}^9{M}_{\odot <!--\; ???\; -->}$). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end.

[en] We determine star formation rates (SFRs) in a sample of color-selected, star-forming (sBzK) galaxies (K_AB < 21.8) in the Extended Chandra Deep Field-South. To identify and avoid active galactic nuclei, we use X-ray, IRAC color, and IR/radio flux ratio selection methods. Photometric redshift-binned, average flux densities are measured with stacking analyses in Spitzer-MIPS IR, BLAST and APEX/LABOCA submillimeter, VLA and GMRT radio, and Chandra X-ray data. We include averages of aperture fluxes in MUSYC UBVRIz'JHK images to determine UV-through-radio spectral energy distributions. We determine the total IR luminosities and compare SFR calibrations from FIR, 24 μm, UV, radio, and X-ray wavebands. We find consistency with our best estimator, SFR_IR+UV, to within errors for the preferred radio SFR calibration. Our results imply that 24 μm only and X-ray SFR estimates should be applied to high-redshift galaxies with caution. Average IR luminosities are consistent with luminous infrared galaxies. We find SFR_IR+UV for our stacked sBzKs at median redshifts 1.4, 1.8, and 2.2 to be 55 ± 6 (random error), 74 ± 8, and 154 ± 17 M_☉ yr^–1, respectively, with additional systematic uncertainty of a factor of ∼2.

[en] We present photometry and derived redshifts from up to eleven bandpasses for 9927 galaxies in the Hubble Ultra Deep field (UDF), covering an observed wavelength range from the near-ultraviolet (NUV) to the near-infrared (NIR) with Hubble Space Telescope observations. Our Wide Field Camera 3 (WFC3)/UV F225W, F275W, and F336W image mosaics from the ultra-violet UDF (UVUDF) imaging campaign are newly calibrated to correct for charge transfer inefficiency, and use new dark calibrations to minimize background gradients and pattern noise. Our NIR WFC3/IR image mosaics combine the imaging from the UDF09 and UDF12 campaigns with CANDELS data to provide NIR coverage for the entire UDF field of view. We use aperture-matched point-spread function corrected photometry to measure photometric redshifts in the UDF, sampling both the Lyman break and Balmer break of galaxies at $z\sim <!--\; ???\; -->0.8$–$3.4$, and one of the breaks over the rest of the redshift range. Our comparison of these results with a compilation of robust spectroscopic redshifts shows an improvement in the galaxy photometric redshifts by a factor of two in scatter and a factor three in outlier fraction (OLF) over previous UDF catalogs. The inclusion of the new NUV data is responsible for a factor of two decrease in the OLF compared to redshifts determined from only the optical and NIR data, and improves the scatter at $z<<!--\; <\; -->0.5$ and at $z><!--\; >\; -->2$. The panchromatic coverage of the UDF from the NUV through the NIR yields robust photometric redshifts of the UDF, with the lowest OLF available.

[en] We use the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) GOODS-S multi-wavelength catalog to identify counterparts for 20 Lyα emitting (LAE) galaxies at z = 2.1. We build several types of stacked spectral energy distributions (SEDs) of these objects. We combine photometry to form average and median flux-stacked SEDs, and postage-stamp images to form average and median image-stacked SEDs. We also introduce scaled flux stacks that eliminate the influence of variation in overall brightness. We use the SED fitting code SpeedyMC to constrain the physical properties of individual objects and stacks. Our LAEs at z = 2.1 have stellar masses ranging from 2 × 10⁷ M _☉ to 8 × 10⁹ M _☉ (median = 3 × 10⁸ M _☉), ages ranging from 4 Myr to 500 Myr (median = 100 Myr), and E(B – V) between 0.02 and 0.24 (median = 0.12). Although still low, this represents significantly more dust reddening than has been reported for LAEs at higher redshifts. We do not observe strong correlations between Lyα equivalent width (EW) and age or E(B – V). The Lyα radiative transfer (q) factors of our sample are predominantly close to one and do not correlate strongly with EW or E(B – V). The absence of strong correlations with EW or q implies that Lyα radiative transfer is highly anisotropic and/or prevents Lyα photons from scattering in dusty regions. The SED parameters of the flux stacks match the average and median values of the individual objects, with the flux-scaled median SED performing best with uncertainties reduced by a factor of two. Median image-stacked SEDs provide a poor representation of the median individual object, and none of the stacking methods capture the large dispersion of LAE properties.

[en] We estimate the UV continuum slope, β, for 923 galaxies in the range 1 < z < 8 in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at 1 < z < 2 down to an absolute magnitude M_UV=−14(∼0.006 L_z=1^∗;0.02 L_z=0^∗), comparable to dwarf galaxies in the local universe. We combine deep HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data from HST/WFC3/IR (HUDF12). Galaxies in the range 1 < z < 2 are significantly bluer than local dwarf galaxies. We find their mean (median) values <β > = – 1.382(– 1.830) ± 0.002 (random) ± 0.1 (systematic). We find comparable scatter in β (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than z > 2 galaxies. We study the trends of β with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, dβ/dM = –0.11 ± 0.01, and no evolution in dβ/dM with redshift. A modest increase in dust reddening with redshift and luminosity, ΔE(B – V) ∼ 0.1, and a comparable increase in the dispersion of dust reddening at z < 2, appears likely to explain the observed trends. At z > 2, we find trends that are consistent with previous works; combining our data with the literature in the range 1 < z < 8, we find a color evolution with redshift, dβ/dz = –0.09 ± 0.01 for low luminosity (0.05 L_z=3^∗), and dβ/dz = –0.06 ± 0.01 for medium luminosity (0.25 L_z=3^∗) galaxies