L. Trouille

Publications (12)12.05 Total impact

• Article: Testing for a large local void by investigating the Near-Infrared Galaxy Luminosity Function

  R. C. Keenan, A. J. Barger, L. L. Cowie, W. -H. Wang, I. Wold, L. Trouille
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  ABSTRACT: Recent cosmological modeling efforts have shown that a local underdensity on scales of a few hundred Mpc (out to z ~ 0.1), could produce the apparent acceleration of the expansion of the universe observed via type Ia supernovae. Several studies of galaxy counts in the near-infrared (NIR) have found that the local universe appears under-dense by ~25-50% compared with regions a few hundred Mpc distant. Galaxy counts at low redshifts sample primarily L ~ L* galaxies. Thus, if the local universe is under-dense, then the normalization of the NIR galaxy luminosity function (LF) at z>0.1 should be higher than that measured for z<0.1. Here we present a highly complete (> 90%) spectroscopic sample of 1436 galaxies selected in the H-band to study the normalization of the NIR LF at 0.1<z<0.3 and address the question of whether or not we reside in a large local underdensity. We find that for the combination of our six fields, the product phi* L* at 0.1 < z < 0.3 is ~ 30% higher than that measured at lower redshifts. While our statistical errors in this measurement are on the ~10% level, we find the systematics due to cosmic variance may be larger still. We investigate the effects of cosmic variance on our measurement using the COSMOS cone mock catalogs from the Millennium simulation and recent empirical estimates. We find that our survey is subject to systematic uncertainties due to cosmic variance at the 15% level ($1 sigma), representing an improvement by a factor of ~ 2 over previous studies in this redshift range. We conclude that observations cannot yet rule out the possibility that the local universe is under-dense at z<0.1.
  07/2012;
• Article: The OPTX Project. V. Identifying Distant Active Galactic Nuclei

  L. Trouille, A. J. Barger, and C. Tremonti
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  ABSTRACT: The Baldwin, Phillips, and Terlevich emission-line ratio diagnostic ([O III]/Hβ versus [N II]/Hα, hereafter BPT diagram) efficiently separates galaxies whose signal is dominated by star formation (BPT-SF) from those dominated by active galactic nucleus (AGN) activity (BPT-AGN). Yet this BPT diagram is limited to z < 0.5, the redshift at which [N II]λ6584 leaves the optical spectral window. Using the Sloan Digital Sky Survey (SDSS), we construct a new diagnostic, or TBT diagram, that is based on rest-frame g – z color, [Ne III]λ3869, and [O II]λλ3726 + 3729 and can be used for galaxies out to z < 1.4. The TBT diagram identifies 98.7% of the SDSS BPT-AGN as TBT-AGN and 97% of the SDSS BPT-SF as TBT-SF. Furthermore, it identifies 97% of the OPTX Chandra X-ray-selected AGNs as TBT-AGN. This is in contrast to the BPT diagram, which misidentifies 20% of X-ray-selected AGNs as BPT-SF. We use the Great Observatories Origins Deep Survey North and Lockman Hole galaxy samples, with their accompanying deep Chandra imaging, to perform X-ray and infrared stacking analyses to further validate our TBT-AGN and TBT-SF selections; that is, we verify the dominance of AGN activity in the former and star formation activity in the latter. Finally, we address the inclusion of the majority of the BPT-comp (sources lying between the BPT-SF and BPT-AGN regimes) in our TBT-AGN regime. We find that the stacked BPT-comp source is X-ray hard (Γeff = 1.0+0.4 –0.4) and has a high X-ray luminosity to total infrared luminosity ratio. This suggests that, on average, the X-ray signal in BPT-comp is dominated by obscured or low accretion rate AGN activity rather than by star formation, supporting their inclusion in the TBT-AGN regime.
  The Astrophysical Journal 11/2011; 742(1):46. · 6.02 Impact Factor
• Source

  Available from: ArXiv

  Article: The OPTX Project V: Identifying Distant AGNs

  L. Trouille, A. J. Barger, C. Tremonti
  [show abstract] [hide abstract]
  ABSTRACT: The Baldwin, Phillips, and Terlevich emission-line ratio diagnostic ([OIII]/H{\beta} versus [NII]/H{\alpha}, hereafter BPT diagram) efficiently separates galaxies whose signal is dominated by star formation from those dominated by AGN activity (BPT-AGN). Yet this BPT diagram is limited to z < 0.5, the redshift at which [NII]{\lambda}6584 leaves the optical spectral window. Using the Sloan Digital Sky Survey (SDSS), we construct a new diagnostic, or TBT diagram, that is based on rest-frame g-z color, [NeIII]{\lambda}3869, and [OII]{\lambda}{\lambda}3726 + 3729 and can be used for galaxies out to z < 1.4. The TBT diagram identifies 98.7% of the SDSS BPT-AGN as TBT-AGN and 97% of the SDSS BPT-SF as TBT-SF. Furthermore, it identifies 97% of the OPTX Chandra X-ray selected AGNs as TBT-AGN. This is in contrast to the BPT diagram, which misidentifies 20% of X-ray selected AGNs as BPT-SF. We use the GOODS-N and Lockman Hole galaxy samples, with their accompanying deep Chandra imaging, to perform X-ray and infrared stacking analyses to further validate our TBT-AGN and TBT-SF selections; that is, we verify the dominance of AGN activity in the former and star formation activity in the latter. Finally, we address the inclusion of the majority of the BPT-comp (sources lying between the BPT-SF and BPT-AGN regimes) in our TBT-AGN regime. We find that the stacked BPT-comp source is X-ray hard (<{\Gamma}eff> = 1.0 +/-0.4) and has a high X-ray luminosity to total infrared luminosity ratio. This suggests that, on average, the X-ray signal in BPT-comp is dominated by obscured or low accretion rate AGN activity rather than by star formation, supporting their inclusion in the TBT-AGN regime.
  09/2011;
• Source

  Available from: Peter L. Capak

  Article: An Atlas of z=5.7 and z=6.5 Ly alpha Emitters

  E. M. Hu, L. L. Cowie, A. J. Barger, P. Capak, Y. Kakazu, L. Trouille
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  ABSTRACT: We present an atlas of 88 z~5.7 and 30 z~6.5 Ly alpha emitters obtained from a wide-field narrowband survey. We combined deep narrowband imaging in 120A bandpass filters centered at 8150A and 9140A with deep BVRIz broadband imaging to select high-redshift galaxy candidates over an area of 4180 square arcmin. The goal was to obtain a uniform selection of comparable depth over the 7 targeted fields in the two filters. For the GOODS-N region of the HDF-N field, we also selected candidates using a 120A filter centered at 9210A. We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of Ly alpha emitters. At the 3.3A resolution of the DEIMOS observations the asymmetric profile for Ly alpha emission with its steep blue fall-off can be clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for many of the galaxies and that the composite spectral profiles are nearly identical at z=5.7 and z=6.5. We analyze the distributions of line widths and Ly alpha equivalent widths and find that the lines are marginally narrower at the higher redshift, with median values of 0.77A at z=6.5 and 0.92A at z=5.7. The line widths have a dependence on the Ly alpha luminosity of the form L(L alpha)^(0.3). We compare the surface densities and the luminosity functions at the two redshifts and find that there is a multiplicative factor of 2 decrease in the number density of bright Ly alpha emitters from z=5.7 to z=6.5, while the characteristic luminosity is unchanged. Comment: Accepted for publication in the Astrophysical Journal
  09/2010;
• Source

  Available from: ArXiv

  Article: The OPTX Project IV: How Reliable is [OIII] as a Measure of AGN Activity?

  L. Trouille, A. J. Barger
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  ABSTRACT: We compare optical and hard X-ray identifications of AGNs using a uniformly selected (above a flux limit of f_2-8 keV = 3.5e-15 erg/cm2/s) and highly optically spectroscopically complete ( > 80% for f_2-8 keV > 1e-14 erg/cm2/s and > 60% below) 2-8 keV sample observed in three Chandra fields (CLANS, CLASXS, and the CDF-N). We find that empirical emission-line ratio diagnostic diagrams misidentify 20-50% of the X-ray selected AGNs that can be put on these diagrams as star formers, depending on which division is used. We confirm that there is a large (2 orders in magnitude) dispersion in the log ratio of the [OIII]5007A to hard X-ray luminosities for the non-broad line AGNs, even after applying reddening corrections to the [OIII] luminosities. We find that the dispersion is similar for the broad-line AGNs, where there is not expected to be much X-ray absorption from an obscuring torus around the AGN nor much obscuration from the galaxy along the line-of-sight if the AGN is aligned with the galaxy. We postulate that the X-ray selected AGNs that are misidentified by the diagnostic diagrams have low [OIII] luminosities due to the complexity of the structure of the narrow-line region, which causes many ionizing photons from the AGN not to be absorbed. This would mean that the [OIII] luminosity can only be used to predict the X-ray luminosity to within a factor of ~3 (one sigma). Despite selection effects, we show that the shapes and normalizations of the [OIII] and transformed hard X-ray luminosity functions show reasonable agreement, suggesting that the [OIII] samples are not finding substantially more AGNs at low redshifts than hard X-ray samples. Comment: Accepted for publication in the Astrophysical Journal. 11 pages, 10 figures
  08/2010;
• Source

  Available from: ArXiv

  Article: An Extremely Deep Wide-Field Near-Infrared Survey: Bright Galaxy Counts and Local Large Scale Structure

  R. C. Keenan, L. Trouille, A. J. Barger, L. L. Cowie, W H Wang
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  ABSTRACT: We present a deep, wide-field near-infrared (NIR) survey over five widely separated fields at high Galactic latitude covering a total of ~ 3 deg^2 in J, H, and Ks. The deepest areas of the data (~ 0.25 deg^2) extend to a 5 sigma limiting magnitude of JHKs > 24 in the AB magnitude system. Although depth and area vary from field to field, the overall depth and large area of this dataset make it one of the deepest wide-field NIR imaging surveys to date. This paper discusses the observations, data reduction, and bright galaxy counts in these fields. We compare the slope of the bright galaxy counts with the Two Micron All Sky Survey (2MASS) and other counts from the literature and explore the relationship between slope and supergalactic latitude. The slope near the supergalactic equator is sub- Euclidean on average pointing to the possibility of a decreasing average space density of galaxies by ~ 10-15% over scales of ~ 250-350 Mpc. On the contrary, the slope at high supergalactic latitudes is strongly super-Euclidean on average suggesting an increase in the space density of galaxies as one moves from the voids just above and below the supergalactic plane out to distances of ~ 250-350 Mpc. These results suggest that local large scale structure could be responsible for large discrepancies in the measured slope between different studies in the past. In addition, the local universe away from the supergalactic plane appears to be underdense by ~ 25-100% relative to the space densities of a few hundred megaparsecs distant. Subject headings: cosmology: observations and large scale structure of universe-galaxies: fundamental parameters (counts)-infrared: galaxies Comment: Accepted to ApJS, 18 Pages, 14 Figures, 8 Tables
  12/2009;
• Article: The OPTX Project. III. X-ray Versus Optical Spectral Type for Active Galactic Nuclei

  L. Trouille, A. J. Barger, L. L. Cowie, Y. Yang, and R. F. Mushotzky
  [show abstract] [hide abstract]
  ABSTRACT: We compare the optical spectral types with the X-ray spectral properties for a uniformly selected (sources with fluxes greater than the 3σ level and above a flux limit of f 2-8 keV > 3.5 × 10–15 erg cm–2 s–1), highly spectroscopically complete (>80% for f 2-8 keV > 10–14 erg cm–2 s–1 and >60% below) 2-8 keV X-ray sample observed in three Chandra fields (CLANS, CLASXS, and the CDF-N) that cover ~1.2 deg2. For our sample of 645 spectroscopically observed sources, we confirm that there is significant overlap of the X-ray spectral properties, as determined by the effective photon indices, Γeff, obtained from the ratios of the 0.5-2 keV to 2-8 keV counts, for the different optical spectral types. For example, broad-line active galactic nuclei (AGNs) are expected to be unobscured and hence X-ray soft (Γeff ≥ 1.2), yet we find 20%± 3% have Γeff <1.2. Non-broad-line AGNs are expected to be obscured and hence X-ray hard (Γeff < 1.2), yet we find 33% ± 4% have Γeff ≥ 1.2. Thus, one cannot use the X-ray spectral classifications and the optical spectral classifications equivalently. Since it is not understood how X-ray and optical classifications relate to the obscuration of the central engine, we strongly advise against a mixed classification scheme, as it can only complicate the interpretation of X-ray AGN samples. We confirm the dependence of optical spectral type on X-ray luminosity, and for z < 1, we find a similar luminosity dependence of Γeff. However, this dependence breaks down at higher redshifts due to the highly redshift-dependent nature of Γeff. We therefore also caution that any classification scheme which depends on Γeff is likely to suffer from serious redshift bias.
  The Astrophysical Journal 09/2009; 703(2):2160. · 6.02 Impact Factor
• Source

  Available from: ArXiv

  Article: The OPTX Project III: X-ray versus Optical Spectral Type for AGNs

  L. Trouille, A. J. Barger, L. L. Cowie, Y Yang, R. F. Mushotzky
  [show abstract] [hide abstract]
  ABSTRACT: We compare the optical spectral types with the X-ray spectral properties for a uniformly selected (sources with fluxes greater than the 3 sigma level and above a flux limit of f_2-8 keV > 3.5x10^-15 erg/cm2/s), highly spectroscopically complete (>80% for f_2-8 keV > 10^-14 erg/cm2/s and >60% below) 2-8 keV X-ray sample observed in three Chandra fields (CLANS, CLASXS, and the CDF-N) that cover ~1.2 deg^2. For our sample of 645 spectroscopically observed sources, we confirm that there is significant overlap of the X-ray spectral properties, as determined by the effective photon indices, Geff, obtained from the ratios of the 0.5-2 keV to 2-8 keV counts, for the different optical spectral types. For example, of the broad-line AGNs (non-broad-line AGNs), 20% +/- 3% (33% +/- 4%) have Geff<1.2 (Geff > 1.2). Thus, one cannot use the X-ray spectral classifications and the optical spectral classifications equivalently. Since it is not understood how X-ray and optical classifications relate to the obscuration of the central engine, we strongly advise against a mixed classification scheme, as it can only complicate the interpretation of X-ray AGN samples. We confirm the dependence of optical spectral type on X-ray luminosity, and for z<1, we find a similar luminosity dependence of Geff. However, this dependence breaks down at higher redshifts due to the highly redshift-dependent nature of Geff. We therefore also caution that any classification scheme which depends on Geff is likely to suffer from serious redshift bias. Comment: Accepted for publication in The Astrophysical Journal. 11 pages, 8 figures, 4 tables
  07/2009;
• Source

  Available from: ArXiv

  Article: The OPTX Project II: Hard X-ray Luminosity Functions of Active Galactic Nuclei for z<5

  B. Yencho, A. J. Barger, L. Trouille, L. M. Winter
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  ABSTRACT: We use the largest, most uniform, and most spectroscopically complete to faint X-ray flux limits Chandra sample to date to construct hard 2-8 keV rest-frame X-ray luminosity functions (HXLFs) of spectroscopically identified active galactic nuclei (AGNs) to z~5. In addition, we use a new 2-8 keV local sample selected by the very hard (14-195 keV) SWIFT 9-month Burst Alert Telescope (BAT) survey to construct the local 2-8 keV HXLF. We do maximum likelihood fits of the combined distant plus local sample (as well as of the distant sample alone) over the redshift intervals 0<z<1.2, 0<z<3, and 0<z<5 using a variety of analytic forms, which we compare with the HXLFs. We recommend using our luminosity dependent density evolution (LDDE) model fits of the combined distant plus local sample over 0<z<3 for all the spectroscopically identified sources and for the broad-line AGNs.
  03/2009;
• Source

  Available from: ArXiv

  Article: The OPTX Project I: The Flux and Redshift Catalogs for the CLANS, CLASXS, and CDF-N fields

  L. Trouille, A. J. Barger, L. L. Cowie, Y Yang, R. F. Mushotzky
  [show abstract] [hide abstract]
  ABSTRACT: We present the redshift catalogs for the X-ray sources detected in the Chandra Deep Field North (CDF-N), the Chandra Large Area Synoptic X-ray Survey (CLASXS), and the Chandra Lockman Area North Survey (CLANS). The catalogs for the CDF-N and CLASXS fields include redshifts from previous work, while the redshifts for the CLANS field are all new. For fluxes above 10^-14 ergs cm^-2 s^-1 (2-8 keV) we have redshifts for 76% of the sources. We extend the redshift information for the full sample using photometric redshifts. The goal of the OPTX Project is to use these three surveys, which are among the most spectroscopically complete surveys to date, to analyze the effect of spectral type on the shape and evolution of the X-ray luminosity functions and to compare the optical spectral types with the X-ray spectral properties. We also present the CLANS X-ray catalog. The nine ACIS-I fields cover a solid angle of ~0.6 square degrees and reach fluxes of 7x10^-16 ergs cm^-2 s^-1 (0.5-2 keV) and 3.5x10^-15 ergs cm^-2 s^-1 (2-8 keV). We find a total of 761 X-ray point sources. Additionally, we present the optical and infrared photometric catalog for the CLANS X-ray sources, as well as updated optical and infrared photometric catalogs for the X-ray sources in the CLASXS and CDF-N fields. The CLANS and CLASXS surveys bridge the gap between the ultradeep pencil-beam surveys, such as the CDFs, and the shallower, very large-area surveys. As a result, they probe the X-ray sources that contribute the bulk of the 2-8 keV X-ray background and cover the flux range of the observed break in the logN-logS distribution. We construct differential number counts for each individual field and for the full sample.
  12/2008;
• Source

  Available from: ArXiv

  Article: Measuring the Sources of the Intergalactic Ionizing Flux

  L. L. Cowie, A. J. Barger, L. Trouille
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  ABSTRACT: We use a wide-field (0.9 square degree) X-ray sample with optical and GALEX ultraviolet observations to measure the contribution of Active Galactic Nuclei (AGNs) to the ionizing flux as a function of redshift. Our analysis shows that the AGN contribution to the metagalactic ionizing background peaks around z=2. The measured values of the ionizing background from the AGNs are lower than previous estimates and confirm that ionization from AGNs is insufficient to maintain the observed ionization of the intergalactic medium (IGM) at z>3. We show that only sources with broad lines in their optical spectra have detectable ionizing flux and that the ionizing flux seen in an AGN is not correlated with its X-ray color. We also use the GALEX observations of the GOODS-N region to place a 2-sigma upper limit of 0.008 on the average ionization fraction fnu(700 A)/fnu(1500 A) for 626 UV selected galaxies in the redshift range z=0.9-1.4. We then use this limit to estimate an upper bound to the galaxy contribution in the redshift range z=0-5. If the z~1.15 ionization fraction is appropriate for higher redshift galaxies, then contributions from the galaxy population are also too low to account for the IGM ionization at the highest redshifts (z>4).
  11/2008;
• Article: An atlas of z = 5.7 and z = 6.5 Lyα emitters

  E. M. Hu, L. L. Cowie, A. J. Barger, P. Capak, Y. Kakazu, L. Trouille
  [show abstract] [hide abstract]
  ABSTRACT: We present an atlas of 88 z ~ 5.7 and 30 z ~ 6.5 Lyα emitters obtained from a wide-field narrowband survey. We combined deep narrowband imaging in 120 Å bandpass filters centered at 8150 Å and 9140 Å with deep B V R I z broadband imaging to select high-redshift galaxy candidates over an area of 4180 arcmin^2. The goal was to obtain a uniform selection of comparable depth over the seven targeted fields in the two filters. For the GOODS-North region of the Hubble Deep Field-North field, we also selected candidates using a 120 Å filter centered at 9210 Å. We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of Lyα emitters. At the 3.3 Å resolution of the DEIMOS observations the asymmetric profile for Lyα emission can be clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for many of the galaxies and that the composite spectral profiles are nearly identical at z = 5.7 and z = 6.5.We analyze the distributions of line widths and Lyα equivalent widths and find that the lines are marginally narrower at the higher redshift, with median values of 0.77 Å at z = 6.5 and 0.92 Å at z = 5.7. The line widths have a dependence on the Lyα luminosity of the form ~L^(0.3)_α . We compare the surface densities and the luminosity functions at the two redshifts and find that there is a multiplicative factor of two decrease in the number density of bright Lyα emitters from z = 5.7 to z = 6.5, while the characteristic luminosity is unchanged.