Browsing by Subject "formation rate density"
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Item Are Dusty Galaxies Blue? Insights On Uv Attenuation From Dust-Selected Galaxies(2014-12) Casey, C. M.; Scoville, N. Z.; Sanders, D. B.; Lee, N.; Cooray, Asantha; Finkelstein, Steven L.; Capak, P.; Conley, A.; De Zotti, G.; Farrah, D.; Fu, H.; Le Floc'h, E.; Ilbert, O.; Ivison, Rob J.; Takeuchi, T. T.; Finkelstein, Steven L.Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates (SFRs). While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15-500 mu m in the COSMOS field, in particular making use of Herschel imaging, and a rich data set on local galaxies, we find an empirical variation in the relationship between the rest-frame UV slope (beta) and the ratio of infrared-to-ultraviolet emission (L-IR/L-UV = IRX) as a function of infrared luminosity, or total SFR. Both locally and at high-z, galaxies above SFR greater than or similar to 50 M-circle dot yr(-1) deviate from the nominal IRX-beta relation toward bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of << 1% at z less than or similar to 4-10, providing independent verification that contamination from very dusty foreground galaxies is low in Lyman-break galaxy searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g., galaxies with > 50 M-circle dot yr(-1), are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z similar to 2 exhibit steady-Statestar formation in secular disks.Item CANDELS: The Evolution Of Galaxy Rest-Frame Ultraviolet Colors From Z=8 To 4(2012-09) Finkelstein, Steven L.; Papovich, Casey; Salmon, Brett; Finlator, Kristian; Dickinson, Mark; Ferguson, Henry C.; Giavalisco, Mauro; Koekemoer, Anton M.; Reddy, Naveen A.; Bassett, Robert; Conselice, Christopher J.; Dunlop, James S.; Faber, S. M.; Grogin, Norman A.; Hathi, Nimish P.; Kocevski, Dale D.; Lai, Kamson; Lee, Kyoung-Soo; McLure, Ross J.; Mobasher, Bahram; Newman, Jeffrey A.; Finkelstein, Steven L.We study the evolution of galaxy rest-frame ultraviolet (UV) colors in the epoch 4 less than or similar to z less than or similar to 8. We use new wide-field near-infrared data in the Great Observatories Origins Deep Survey-South field from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, Hubble Ultra Deep Field (HUDF) 2009, and Early Release Science programs to select galaxies via photometric redshift measurements. Our sample consists of 2812 candidate galaxies at z greater than or similar to 3.5, including 113 at z similar or equal to 7-8. We fit the observed spectral energy distribution to a suite of synthetic stellar population models and measure the value of the UV spectral slope (beta) from the best-fit model spectrum. We run simulations to show that this measurement technique results in a smaller scatter on beta than other methods, as well as a reduced number of galaxies with catastrophically incorrect beta measurements (i.e.,. Delta beta > 1). We find that the median value of beta evolves significantly from -1.82(-0.04)(+0.00) at z = 4 to -2.37(-0.06)(+0.26) at z = 7. Additionally, we find that faint galaxies at z = 7 have beta = -2.68(-0.24)(+0.39) (similar to-2.4 after correcting for observational bias); this is redder than previous claims in the literature and does not require "exotic" stellar populations (e. g., very low metallicities or top-heavy initial mass functions) to explain their colors. This evolution can be explained by an increase in dust extinction, from low amounts at z = 7 to A(V) similar to 0.5 mag at z = 4. The timescale for this increase is consistent with low-mass asymptotic giant branch stars forming the bulk of the dust. We find no significant (<2 sigma) correlation between beta and M-UV when measuring M-UV at a consistent rest-frame wavelength of 1500 angstrom. This is particularly true at bright magnitudes, though our results do show evidence for a weak correlation at faint magnitudes when galaxies in the HUDF are considered separately, hinting that dynamic range in sample luminosities may play a role. We do find a strong correlation between beta and the stellar mass at all redshifts, in that more massive galaxies exhibit redder colors. The most massive galaxies in our sample have similarly red colors at each redshift, implying that dust can build up quickly in massive galaxies and that feedback is likely removing dust from low-mass galaxies at z >= 7. Thus, the stellar-mass-metallicity relation, previously observed up to z similar to 3, may extend out to z = 7-8.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 New Constraints On Dust Emission And UV Attenuation Of Z=6.5-7.5 Galaxies From Millimeter Observations(2015-02) Schaerer, D.; Boone, F.; Zamojski, M.; Staguhn, J.; Dessauges-Zavadsky, M.; Finkelstein, S.; Combes, F.; Finkelstein, S.Context. Determining the dust properties and UV attenuation of distant star-forming galaxies is of great interest for our understanding of galaxy formation and cosmic star formation in the early Universe. However, few direct measurements exist so far. Aims. To shed new light on these questions, we have targeted two recently discovered Lyman-break galaxies (LBGs) at z approximate to 6.8 and z = 7.508 to search for dust continuum and [C II] 1158 pm line emission. Methods. The strongly lensed z approximate to 6.8 LBG A1703-zD1 behind the galaxy cluster Abell 1703 and the spectroscopically confirmed z = 7.508 LBG z8-GND-5296 in the GOODS-N field were observed with the Plateau de Bure Interferometer (PdBI) at 1.2 mm. These observations were combined with those of three z > 6.5 Ly alpha emitters (HCM6A, Himiko, and IOK-1), for which deep measurements were recently obtained with the PdBI and ALMA. Results. [C II] is undetected in both galaxies, providing a deep upper limit of L-[C II] < 2.8 x 10(7) L for A1703-zD1, comparable to the nondetections of Himiko and IOK-1 with ALMA. Dust continuum emission from A1703-zD1 and z8-GND-5296 is not detected with an rms of 0.12 and 0.16 mJy/beam. From these nondetections and earlier multiwavelength observations we derive upper limits on their IR luminosity and star formation rate, dust mass, and UV attenuation. Thanks to strong gravitational lensing, the achieved limit for A1703-zDI is similar to those achieved with ALMA, probing below the luminous infrared galaxy (LIRG) regime (L-IR < 8.1 x 10(10) L-circle dot) and very low dust masses (M-d < 1.6 x 10(7) M-circle dot). We find that all five galaxies are compatible with the Calzetti IRX-beta relation, their UV attenuation is compatible with several indirect estimates from other methods (the UV slope, extrapolation of the attenuation measured from the IR/UV ratio at lower redshift, and spectral energy distribution fits), and the dust-to-stellar mass ratio is compatible with that of galaxies from z = 0 to 3. From their stellar mass, the high-z galaxies studied here have an attenuation below the one expected from the mean relation of low-redshift (z less than or similar to 1.5) galaxies. Conclusions. More and deeper (sub-)mm data are clearly needed to directly determine the UV attenuation and dust content of the dominant population of high-z star-forming galaxies and to establish their dependence on stellar mass, redshift, and other properties more firmly.