Breaking the Curve with CANDELS: A Bayesian Approach to Reveal the Non-Universality of the Dust-Attenuation Law at High Redshift

Dust attenuation affects nearly all observational aspects of galaxy evolution, yet very little is known about the form of the dust-attenuation law in the distant Universe. Here, we model the spectral energy distributions (SEDs) of galaxies at z = 1.5--3 from CANDELS with rest-frame UV to near-IR imaging under different assumptions about the dust law, and compare the amount of inferred attenuated light with the observed infrared (IR) luminosities. Some individual galaxies show strong Bayesian evidence in preference of one dust law over another, and this preference agrees with their observed location on the plane of infrared excess (IRX, $L_{\text{TIR}}/L_{\text{UV}}$) and UV slope ($\beta$). We generalize the shape of the dust law with an empirical model, $A_{\lambda,\delta}=E(B-V)\ k_\lambda\ (\lambda/\lambda_V)^\delta$ where $k_\lambda$ is the dust law of Calzetti et al. (2000), and show that there exists a correlation between the color excess ${E(B-V)}$ and tilt $\delta$ with ${\delta=(0.62\pm0.05)\log(E(B-V))}$+ ${(0.26~\pm~0.02)}$. Galaxies with high color excess have a shallower, starburst-like law, and those with low color excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample show no correlation between the shape of the dust law and stellar mass, star-formation rate, or $\beta$. The change in the dust law with color excess is consistent with a model where attenuation is caused by by scattering, a mixed star-dust geometry, and/or trends with stellar population age, metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows potential to constrain the dust law at even higher ($z>3$) redshifts.Comment: 20 pages, 18 figures, resubmitted to Ap

Properties of Submillimeter Galaxies in a Semi-analytic Model using the "Count Matching" Approach: Application to the ECDF-S

We present a new technique for modeling submillimeter galaxies (SMGs): the "Count Matching" approach. Using lightcones drawn from a semi-analytic model of galaxy formation, we choose physical galaxy properties given by the model as proxies for their submillimeter luminosities, assuming a monotonic relationship. As recent interferometric observations of the Extended Chandra Deep Field South show that the brightest sources detected by single-dish telescopes are comprised by emission from multiple fainter sources, we assign the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA observed number counts for this field are reproduced. After turning the model catalogs given by the proxies into submillimeter maps, we perform a source extraction to include the effects of the observational process on the recovered counts and galaxy properties. We find that for all proxies, there are lines of sight giving counts consistent with those derived from LABOCA observations, even for input sources with randomized positions in the simulated map. Comparing the recovered redshift, stellar mass and host halo mass distributions for model SMGs with observational data, we find that the best among the proposed proxies is that in which the submillimeter luminosity increases monotonically with the product between dust mass and SFR. This proxy naturally reproduces a positive trend between SFR and bolometric IR luminosity. The majority of components of blended sources are spatially unassociated.Comment: 21 pages, 20 figures, 5 tables. Accepted for publication in MNRA

Spectra of GRB 970228 from the Transient Gamma-Ray Spectrometer

Visible afterglow counterparts have now been detected for two GRBs (970228 and 970508) but are absent, with $L_{opt}/L_{\gamma}$ ratios at least two orders of magnitude lower, for other GRBs, e.g., 970828. The causes of this variation are unknown. Any correspondence which could be discovered between the gamma-ray properties of a GRB and its $L_{opt}/L_{\gamma}$ would be useful, both in determining the GRB mechanisms, and in allocating resources for counterpart searches and studies. This paper presents the gamma-ray spectra of GRB 970228 as measured by the Transient Gamma-Ray Spectrometer and comments on characteristics of this GRB compared to others that do and do not have observable counterparts.Comment: To appear in "Gamma-Ray Bursts", Proceedings of the 4th Huntsville Symposium, 1997, eds. C. Meegan, R. Preece, and T. Koshut, 5 pages, LaTeX (aipproc.sty incl.), 3 figs. (epsfig.sty

Physical Properties of Sub-galactic Clumps at 0.5 ≤ Z ≤ 1.5 in the UVUDF

We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 05 ≤ 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

Physical Properties of Sub-galactic Clumps at 0.5 ≤ Z ≤ 1.5 in the UVUDF

We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 05 ≤ 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

The Herschel Stripe 82 Survey (HerS): maps and early catalog

We present the first set of maps and band-merged catalog from the Herschel Stripe 82 Survey (HerS). Observations at 250, 350, and 500μm were taken with the Spectral and Photometric Imaging Receiver instrument aboard the Herschel Space Observatory. HerS covers 79deg 2 along the SDSS Stripe 82 to an average depth of 13.0, 12.9, and 14.8mJybeam −1 (including confusion) at 250, 350, and 500μm, respectively. HerS was designed to measure correlations with external tracers of the dark matter density field—either point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e., clusters and gravitational lensing)—in order to measure the bias and redshift distribution of intensities of infrared-emitting dusty star-forming galaxies and active galactic nuclei. By locating HerS in Stripe 82, we maximize the overlap with available and upcoming cosmological surveys. The band-merged catalog contains 3.3 × 10 4 sources detected at a significance of ?3σ (including confusion noise). The maps and catalog are available at http://www.astro.caltech.edu/hers/

UVUDF: Ultraviolet Imaging of the Hubble Ultradeep Field with Wide-field Camera 3

We present an overview of a 90-orbit Hubble Space Telescope treasury program to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters. This survey is designed to: (i) Investigate the episode of peak star formation activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability of photometric redshift estimates; and (v) Measure the star formation rate efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview paper, we describe the survey details and data reduction challenges, including both the necessity of specialized calibrations and the effects of charge transfer inefficiency. We provide a stark demonstration of the effects of charge transfer inefficiency on resultant data products, which when uncorrected, result in uncertain photometry, elongation of morphology in the readout direction, and loss of faint sources far from the readout. We agree with the STScI recommendation that future UVIS observations that require very sensitive measurements use the instrument's capability to add background light through a "post-flash". Preliminary results on number counts of UV-selected galaxies and morphology of galaxies at z~1 are presented. We find that the number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely consistent with the number predicted by published luminosity functions. We also confirm that the image mosaics have sufficient sensitivity and resolution to support the analysis of the evolution of star-forming clumps, reaching 28-29th magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on filter and observing epoch.Comment: Accepted A

UVUDF: UV Luminosity Functions at the Cosmic High Noon

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 ~ 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_(UV) = -15.9, -16.3, -16.8 and fit a faint-end slope of α = -1.20^(+0.10)_(-0.13), -1.32^(+0.10)_(-0.14), -1.39^(+0.08)_(-0.12) 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 ~ 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-β 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_∗ ≾ 5 x 10^9 M_⊙). We conclude that this could be due to a larger contribution from starbursting galaxies compared to the high-mass end

Properties of submillimetre galaxies in a semi-analytic model using the ‘Count Matching’ approach: application to the ECDF-S

We present a new technique for modelling submillimetre galaxies (SMGs): the 'Count Matching' approach. Using light cones drawn from a semi-analytic model of galaxy formation, we choose physical galaxy properties given by the model as proxies for their submillimetre luminosities, assuming a monotonic relationship. As recent interferometric observations of the Extended Chandra Deep Field-South show that the brightest sources detected by single-dish telescopes are comprised by emission from multiple fainter sources, we assign the submillimetre fluxes so that the combined Large APEX BOlometer CAmera (LABOCA) plus bright-end Atacama Large Millimeter/submillimeter Array observed number counts for this field are reproduced. After turning the model catalogues given by the proxies into submillimetre maps, we perform a source extraction to include the effects of the observational process on the recovered counts and galaxy properties. We find that for all proxies, there are lines of sight giving counts consistent with those derived from LABOCA observations, even for input sources with randomized positions in the simulated map. Comparing the recovered redshift, stellar mass and host halo mass distributions for model SMGs with observational data, we find that the best among the proposed proxies is that in which the submillimetre luminosity increases monotonically with the product between dust mass and star formation rate (SFR). This proxy naturally reproduces a positive trend between SFR and bolometric IR luminosity. The majority of components of blended sources are spatially unassociated.Instituto de Astrofísica de La Plat