Browsing by Author "Orsi, Alvaro"

Now showing 1 - 5 of 5
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    Lyα emission-line galaxies at z=3.1 in the extended Chandra Deep Field-South
    (2007) Gronwall, Caryl; Ciardullo, Robin; Hickey, Thomas; Gawiser, Eric; Feldmeier, John J.; van Dokkum, Pieter G.; Urry, C. Megan; Herrera, David; Lehmer, Bret D.; Infante, Leopoldo; Orsi, Alvaro; Marchesini, Danilo; Blanc, Guillermo A.; Francke, Harold; Lira, Paulina; Treister, Ezequiel
    We describe the results of an extremely deep, 0.28 deg(2) survey for z = 3.1 Ly alpha emission-line galaxies in the Extended Chandra Deep Field-South. By using a narrowband 5000 angstrom filter and complementary broadband photometry from the MUSYC survey, we identify a statistically complete sample of 162 galaxies with monochromatic fluxes brighter than 1.5 x10(-17) ergs cm(-2) s(-1) and observer's frame equivalent widths greater than 80 angstrom. We show that the equivalent width distribution of these objects follows an exponential with a rest-frame scale length of w(0) = 76(-8)(+11) angstrom In addition, we show that in the emission line, the luminosity function of Ly alpha galaxies has a faint-end power-law slope of -1.49(-0.34)(+0.45) a bright-end cutoff of log L-* = 42.64(-0.15)(,)(+0.26) and a space density above our detection thresholds of (1.46 +/- 0.12); 10(-3) h(70)(3) galaxies Mpc(-3). Finally, by comparing the emission-line and continuum properties of the Ly alpha emitters, we show that the star formation rates derived from Ly alpha are similar to 3 times lower than those inferred from the rest-frame UV continuum. We use this offset to deduce the existence of a small amount of internal extinction within the host galaxies. This extinction, coupled with the lack of extremely high equivalent width emitters, argues that these galaxies are not primordial Population III objects, although they are young and relatively chemically unevolved.
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    Lyα-emitting galaxies at z=3.1
    (2007) Gawiser, Eric; Francke, Harold; Lai, Kamson; Schawinski, Kevin; Gronwall, Caryl; Ciardullo, Robin; Quadri, Ryan; Orsi, Alvaro; Barrientos, Felipe; Blanc, Guillermo A.; Fazio, Giovanni; Feldmeier, John J.; Huang, Jia-Sheng; Infante, Leopoldo; Lira, Paulina; Padilla, Nelson; Taylor, Edward N.; Treister, Ezequiel; Urry, C. Megan; Van Dokkum, Pieter G.; Virani, Shanil N.
    We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Ly alpha- emitting (LAE) galaxies at z similar or equal to 3: 1 discovered in deep narrowband MUSYC imaging of the Extended Chandra Deep Field-South. LAEs were selected to have observed frame equivalent widths >80 angstrom and emission line fluxes >1.5 x 10(-17) ergs cm(-2) s(-1). Only 1% of our LAE sample appears to host AGNs. The LAEs exhibit a moderate spatial correlation length of r(0) = 3.6(-1.0)(+0.8) Mpc, corresponding to a bias factor b = 1.7(-0.4)(+0.3), which implies median dark matter halo masses of log(10)M(med) = 10.9(-0.9)(+0.5) M-circle dot. Comparing the number density of LAEs, 1.5 +/- 0.3 x 10(-3) Mpc(-3), with the number density of these halos finds a mean halo occupation similar to 1%-10%. The evolution of galaxy bias with redshift implies that most z 3: 1 LAEs evolve into present-day galaxies with L < 2.5L*, whereas other z > 3 galaxy populations typically evolve into more massive galaxies. Halo merger trees show that z 0 descendants occupy halos with a wide range of masses, with a median descendant mass close to that of L*. Only 30% of LAEs have sufficient stellar mass (>similar to 3 x 10(9) M-circle dot) to yield detections in deep Spitzer IRAC imaging. A two-population SED fit to the stacked UBVRIzJK+[3.6, 4.5, 5.6, 8.0] mu m fluxes of the IRAC-undetected objects finds that the typical LAE has low stellar mass (1.0(-0.4)(+0.6) 10(9) M-circle dot), moderate star formation rate (2 +/- 1 M-circle dot yr(-1)), a young component age of 20(-10)(+30) Myr, and little dust (A(V) < 0: 2). The bestfit model has 20% of the mass in the young stellar component, but models without evolved stars are also allowed.
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    The assembly bias of emission-line galaxies
    (2021) Jimenez, Esteban; Padilla, Nelson; Contreras, Sergio; Zehavi, Idit; Baugh, Carlton M.; Orsi, Alvaro
    The next generation of spectroscopic surveys will target emission-line galaxies (ELGs) to produce constraints on cosmological parameters. We study the large-scale structure traced by ELGs using a combination of a semi-analytical model of galaxy formation, a code that computes the nebular emission from H II regions using the properties of the interstellar medium, and a large-volume, high-resolution N-body simulation. We consider fixed number density samples where galaxies are selected by their H alpha, [O III] lambda 5007, or [O II] lambda lambda 3727-3729 emission-line luminosities. We investigate the assembly bias signatures of these samples, and compare them to those of stellar mass- and star formation rate-selected samples. Interestingly, we find that the [O III]- and [O II]-selected samples display scale-dependent bias on large scales and that their assembly bias signatures are also scale dependent. Both these effects are more pronounced for lower number density samples. The [O III] and [O II] emitters that contribute most to the scale dependence tend to have a low gas-phase metallicity and are preferentially found in low-density regions. We also measure the baryon acoustic oscillation (BAO) feature and the beta parameter related to the growth rate of overdensities. We find that the scale of the BAO peak is roughly the same for all selections and that beta is scale dependent at large scales. Our results suggest that ELG samples include environmental effects that should be modelled in order to remove potential systematic errors that could affect the estimation of cosmological parameters.
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    The clustering of Lyα emitters in a ΛCDM Universe
    (2008) Orsi, Alvaro; Lacey, Cedric G.; Baugh, Carlton M.; Infante, Leopoldo
    We combine a semi-analytical model of galaxy formation with a very large simulation which follows the growth of a large-scale structure in a Lambda cold dark matter (Lambda CDM) universe to predict the clustering of Ly alpha emitters. We find that the clustering strength of Ly alpha emitters has only a weak dependence on Ly alpha luminosity but a strong dependence on redshift. With increasing redshift, Ly alpha emitters trace progressively rarer, higher density regions of the universe. Due to the large volume of the simulation, over 100 times bigger than any previously used for this application, we can construct mock catalogues of Ly alpha emitters and study the sample variance of current and forthcoming surveys. We find that the number and clustering of Ly alpha emitters in our mock catalogues are in agreement with measurements from current surveys, but there is a considerable scatter in these quantities. We argue that a proposed survey of emitters at z = 8.8 should be extended significantly in solid angle to allow a robust measurement of Ly alpha emitter clustering.
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    The environments of Ly α blobs - I. Wide-field Ly α imaging of TN J1338-1942, a powerful radio galaxy at z ≃ 4.1 associated with a giant Ly α nebula
    (2015) Saito, Tomoki; Matsuda, Yuichi; Lacey, Cedric G.; Smail, Ian; Orsi, Alvaro; Baugh, Carlton M.; Inoue, Akio K.; Tanaka, Ichi; Yamada, Toru; Ohta, Kouji; De Breuck, Carlos; Kodama, Tadayuki; Taniguchi, Yoshiaki
    We exploit wide-field Ly alpha imaging with Subaru to probe the environment around TN J1338-1942, a powerful radio galaxy with a > 100 kpc Ly alpha halo at z = 4.11. We used a sample of Ly alpha emitters (LAEs) down to log (L-Ly alpha [erg s(-1)]) similar to 42.8 to measure the galaxy density around TN J1338-1942, compared to a control sample from a blank field taken with the same instrument. We found that TN J1338-1942 resides in a region with a peak over-density of delta(LAE) = 2.8 +/- 0.5 on scales of 8 h(-1) Mpc (on the sky) and 112 h(-1) Mpc (line of sight) in comoving coordinates. Adjacent to this overdensity, we found a strong underdensity where virtually no LAEs are detected. We used a semi-analytical model of LAEs derived from the Millennium Simulation to compare our results with theoretical predictions. While the theoretical density distribution is consistent with the blank field, overdense regions such as that around TN J1338-1942 are very rare, with a number density of 6.4 x 10(-8) Mpc(-3) (comoving), corresponding to the densest < 0.4 percentile at z similar or equal to 4.1. We also found that the Ly alpha luminosity function in the TN J1338-1942 field differs from that in the blank field: the number of bright LAEs (log(L-Ly alpha [ergs(-1)]) greater than or similar to 43.3) is enhanced, while the number of fainter LAEs is relatively suppressed. These results suggest that some powerful radio galaxies associated with Ly a nebulae reside in extreme overdensities on similar to 3-6 Mpc scales, where star formation and AGN activity may be enhanced via frequent galaxy mergers or high rates of gas accretion from the surroundings.