Browsing by Subject "yale-chile musyc"
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Item The HETDEX Pilot Survey. II. The Evolution Of The Ly Alpha Escape Fraction From The Ultraviolet Slope And Luminosity Function Of 1.9 < Z < 3.8 Laes(2011-07) Blanc, Guillermo A.; Adams, Joshua J.; Gebhardt, Karl; Hill, Gary J.; Drory, Niv; Hao, Lei; Bender, Ralf; Ciardullo, Robin; Finkelstein, Steven L.; Fry, Alexander B.; Gawiser, Eric; Gronwall, Caryl; Hopp, Ulrich; Jeong, Donghui; Kelzenberg, Ralf; Komatsu, Eiichiro; MacQueen, Phillip; Murphy, Jeremy D.; Roth, Martin M.; Schneider, Donald P.; Tufts, Joseph; Blanc, Guillermo A.; Adams, Joshua J.; Gebhardt, Karl; Hill, Gary J.; Fry, Alexander B.; |Jeong, Donghui; Komatsu, Eiichiro; Murphy, Jeremy D.We study the escape of Ly alpha photons from Ly alpha emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by The Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. For 89 LAEs with broadband counterparts we measure ultraviolet (UV) luminosities and UV slopes, and estimate E(B - V) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SFRs). Comparison between the observed Ly alpha luminosity and that predicted by the dust-corrected SFR yields the Ly alpha escape fraction. We also measure the Ly alpha luminosity function and luminosity density (rho(Ly alpha)) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of rho(Ly alpha). We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Ly alpha escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Ly alpha) > (3-6) x 10(42) erg s(-1) (0.25-0.5 L*), have a mean < E(B - V)> = 0.13 +/- 0.01, implying an attenuation of similar to 70% in the UV. They show a median UV uncorrected SFR = 11 M-circle dot yr(-1), dust-corrected SFR = 34 M-circle dot yr(-1), and Ly alpha equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Ly alpha escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Ly alpha escape fraction in LAEs correlates with E(B - V) in a way that is expected if Ly alpha photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Ly alpha EW with dust, due to a clumpy multi-phase interstellar medium (ISM), is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Ly alpha can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Ly alpha escape fraction of LAEs from z similar to 4 to 2. We see hints of a drop in the number density of LAEs from z similar to 4 to 2 in the redshift distribution and the Ly alpha luminosity function, although larger samples are required to confirm this. The mean Ly alpha escape fraction of the overall galaxy population decreases significantly from z similar to 6 to z similar to 2, in agreement with recent results. Our results point toward a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z similar to 6 and 2, reducing their Ly alpha escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Ly alpha photons is reached by z similar to 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.Item Ly Alpha-Emitting Galaxies At Z=2.1 In ECDF-S: Building Blocks Of Typical Present-Day Galaxies?(2010-05) Guaita, Lucia; Gawiser, Eric; Padilla, Nelson; Francke, Harold; Bond, Nicholas A.; Gronwall, Caryl; Ciardullo, Robin; Feldmeier, John J.; Sinawa, Shawn; Blanc, Guillermo A.; Virani, Shanil; Blanc, Guillermo A.We discovered a sample of 250 Ly alpha emitting (LAE) galaxies at z similar or equal to 2.1 in an ultra-deep 3727 angstrom narrow-band MUSYC image of the Extended Chandra Deep Field-South. The LAEs were selected to have rest-frame equivalent widths (EWs) > 20 angstrom and emission-line fluxes F(Ly alpha) > 2.0 x 10(-17) erg cm(-2) s(-1), after carefully subtracting the continuum contributions from narrow-band photometry. The median emission-line flux of our sample is F(Ly alpha) = 4.2 x 10(-17) erg cm(-2) s(-1), corresponding to a median Ly alpha luminosity L(Ly alpha) = 1.3 x 10(42) erg s(-1) at z similar or equal to 2.1. At this flux, our sample is >= 90% complete. Approximately 4% of the original NB-selected candidates were detected in X-rays by Chandra, and 7% were detected in the rest-frame far-UV by the Galaxy Evolution Explorer; these objects were eliminated to minimize contamination by active galactic nuclei and low-redshift galaxies. At L(Ly alpha) >= 1.3 x 10(42) erg s(-1), the EW distribution is unbiased and is represented by an exponential with scale-length 83 +/- 10 angstrom. Above this same luminosity threshold, we find a number density of 1.5 +/- 0.5 x 10(-3) Mpc(-3). Neither the number density of LAEs nor the scale-length of their EW distribution show significant evolution from z similar or equal to 3 to z similar or equal to 2. We used the rest-frame UV luminosity to estimate a median star formation rate of 4 M(circle dot) yr(-1). The median rest-frame UV slope, parameterized by the color B - R, is typical of dust-free, 0.5-1 Gyr old or moderately dusty, 300-500 Myr old population. Approximately 30% of our sample is consistent with being very young (age < 100 Myr) galaxies without dust. Approximately 40% of the sample occupies the z similar to 2 star-forming galaxy locus in the UVR two-color diagram, but the true percentage could be significantly higher taking into account photometric errors. Clustering analysis reveals that LAEs at z similar or equal to 2.1 have r(0) = 4.8 +/- 0.9 Mpc, corresponding to a bias factor b = 1.8 +/- 0.3. This implies that z similar or equal to 2.1 LAEs reside in dark matter halos with median masses log(M/M(circle dot)) = 11.5(-0.5)(+0.4), which are among the lowest mass halos yet probed at this redshift. We used the Sheth and Tormen conditional mass function to study the descendants of these LAEs and found that their typical present-day descendants are local galaxies with L* properties, like the Milky Way.Item Panchromatic Estimation Of Star Formation Rates In Bzk Galaxies At 1 < Z < 3(2012-05) Kurczynski, Peter; Gawiser, Eric; Huynh, Minh; Ivison, Rob J.; Treister, Ezequiel; Smail, Ian; Blanc, Guillermo A.; Cardamone, Carolin N.; Greve, Thomas R.; Schinnerer, Eva; Urry, Meg; van der Werf, Paul; Blanc, Guillermo A.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 mu m, UV, radio, and X-ray wavebands. We find consistency with our best estimator, SFRIR+UV, to within errors for the preferred radio SFR calibration. Our results imply that 24 mu m 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 SFRIR+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-circle dot yr(-1), respectively, with additional systematic uncertainty of a factor of similar to 2.