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Jeremy D. Murphy, Gary J. Hill,
Phillip J. MacQueen,
Trey Taylor,
Ian Soukup,
Walter Moreira,
Mark E. Cornell,
John Good,
Seth Anderson,
Lindsay Fuller,
Hanshin Lee,
Andreas Kelz,
Marc Rafal,
Tom Rafferty,
Sarah Tuttle,
Brian Vattiat
[show abstract]
[hide abstract]
ABSTRACT: We report on extensive testing carried out on the optical fibers for the
VIRUS instrument. The primary result of this work explores how 10+ years of
simulated wear on a VIRUS fiber bundle affects both transmission and focal
ratio degradation (FRD) of the optical fibers. During the accelerated lifetime
tests we continuously monitored the fibers for signs of FRD. We find that
transient FRD events were common during the portions of the tests when motion
was at telescope slew rates, but dropped to negligible levels during rates of
motion typical for science observation. Tests of fiber transmission and FRD
conducted both before and after the lifetime tests reveal that while
transmission values do not change over the 10+ years of simulated wear, a clear
increase in FRD is seen in all 18 fibers tested. This increase in FRD is likely
due to microfractures that develop over time from repeated flexure of the fiber
bundle, and stands in contrast to the transient FRD events that stem from
localized stress and subsequent modal diffusion of light within the fibers.
There was no measurable wavelength dependence on the increase in FRD over 350
nm to 600 nm. We also report on bend radius tests conducted on individual
fibers and find the 266 microns VIRUS fibers to be immune to bending-induced
FRD at bend radii of R > 10cm. Below this bend radius FRD increases slightly
with decreasing radius. Lastly, we give details of a degradation seen in the
fiber bundle currently deployed on the Mitchell Spectrograph (formally VIRUS-P)
at McDonald Observatory. The degradation is shown to be caused by a localized
shear in a select number of optical fibers that leads to an explosive form of
FRD. In a few fibers, the overall transmission loss through the instrument can
exceed 80%.
05/2013;
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Robin Ciardullo,
Caryl Gronwall,
Joshua J. Adams,
Guillermo A. Blanc,
Karl Gebhardt,
Steven L. Finkelstein,
Shardha Jogee, Gary J. Hill,
Niv Drory,
Ulrich Hopp,
Donald P. Schneider,
Gregory R. Zeimann,
Gavin B. Dalton
[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the luminosities and equivalent widths of the 284 z
< 0.56 [O II]-emitting galaxies found in the 169 square arcmin pilot survey for
the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). By combining
emission-line fluxes obtained from the Mitchell spectrograph on the McDonald
2.7-m telescope with deep broadband photometry from archival data, we derive
each galaxy's de-reddened [O II] 3727 luminosity and calculate its total star
formation rate. We show that over the last ~5 Gyr of cosmic time there has been
substantial evolution in the [O II] emission-line luminosity function, with L*
decreasing by ~0.6 +/-0.2 dex in the observed function, and by ~0.9 +/-0.2 dex
in the de-reddened relation. Accompanying this decline is a significant shift
in the distribution of [O II] equivalent widths, with the fraction of high
equivalent-width emitters declining dramatically with time. Overall, the data
imply that the relative intensity of star formation within galaxies has
decreased over the past ~5 Gyr, and that the star formation rate density of the
universe has declined by a factor of ~2.5 between z ~ 0.5 and z ~ 0. These
observations represent the first [O II]-based star formation rate density
measurements in this redshift range, and foreshadow the advancements which will
be generated by the main HETDEX survey.
04/2013;
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[show abstract]
[hide abstract]
ABSTRACT: The upcoming Wide-Field Upgrade (WFU) has ushered in a new era of
instrumentation for the Hobby-Eberly Telescope (HET). Here, we present the
design, construction progress, and lab tests completed to date of the
blue-optimized second generation Low Resolution Spectrograph (LRS2-B). LRS2-B
is a dual-channel, fiber fed instrument that is based on the design of the
Visible Integral Field Replicable Unit Spectrograph (VIRUS), which is the new
flagship instrument for carrying out the HET Dark Energy eXperiment (HETDEX).
LRS2-B utilizes a microlens-coupled integral field unit (IFU) that covers a
7"x12" area on the sky having unity fill-factor with ~300 spatial elements that
subsample the median HET image quality. The fiber feed assembly includes an
optimized dichroic beam splitter that allows LRS2-B to simultaneously observe
370 nm to 470 nm and 460 nm to 700 nm at fixed resolving powers of R \approx
1900 and 1200, respectively. We discuss the departures from the nominal VIRUS
design, which includes the IFU, fiber feed, camera correcting optics, and
volume phase holographic grisms. Additionally, the motivation for the selection
of the wavelength coverage and spectral resolution of the two channels is
briefly discussed. One such motivation is the follow-up study of spectrally and
(or) spatially resolved Lyman-alpha emission from z ~ 2.5 star-forming galaxies
in the HETDEX survey. LRS2-B is planned to be a commissioning instrument for
the HET WFU and should be on-sky during quarter 4 of 2013. Finally, we mention
the current state of LRS2-R, the red optimized sister instrument of LRS2-B.
07/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The Visible Integral Field Replicable Unit Spectrograph (VIRUS) is an array
of at least 150 copies of a simple, fiber-fed integral field spectrograph that
will be deployed on the Hobby-Eberly Telescope (HET) to carry out the HET Dark
Energy Experiment (HETDEX). Each spectrograph contains a volume phase
holographic grating as its dispersing element that is used in first order for
350 nm to 550 nm. We discuss the test methods used to evaluate the performance
of the prototype gratings, which have aided in modifying the fabrication
prescription for achieving the specified batch diffraction efficiency required
for HETDEX. In particular, we discuss tests in which we measure the diffraction
efficiency at the nominal grating angle of incidence in VIRUS for all orders
accessible to our test bench that are allowed by the grating equation. For
select gratings, these tests have allowed us to account for > 90% of the
incident light for wavelengths within the spectral coverage of VIRUS. The
remaining light that is unaccounted for is likely being diffracted into
reflective orders or being absorbed or scattered within the grating layer (for
bluer wavelengths especially, the latter term may dominate the others).
Finally, we discuss an apparatus that will be used to quickly verify the first
order diffraction efficiency specification for the batch of at least 150 VIRUS
production gratings.
07/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We study the mass distribution in the late-type dwarf galaxy NGC 2976 through stellar kinematics obtained with the Visible Integral Field Replicable Unit Spectrograph Prototype and anisotropic Jeans models as a test of cosmological simulations and baryonic processes that putatively alter small-scale structure. Previous measurements of the Hα emission-line kinematics have determined that the dark matter halo of NGC 2976 is most consistent with a cored density profile. We find that the stellar kinematics are best fit with a cuspy halo. Cored dark matter halo fits are only consistent with the stellar kinematics if the stellar mass-to-light ratio is significantly larger than that derived from stellar population synthesis, while the best-fitting cuspy model has no such conflict. The inferred mass distribution from a harmonic decomposition of the gaseous kinematics is inconsistent with that of the stellar kinematics. This difference is likely due to the gas disk not meeting the assumptions that underlie the analysis such as no pressure support, a constant kinematic axis, and planar orbits. By relaxing some of these assumptions, in particular the form of the kinematic axis with radius, the gas-derived solution can be made consistent with the stellar kinematic models. A strong kinematic twist in the gas of NGC 2976's center suggests caution, and we advance the mass model based on the stellar kinematics as more reliable. The analysis of this first galaxy shows promising evidence that dark matter halos in late-type dwarfs may in fact be more consistent with cuspy dark matter distributions than earlier work has claimed.
The Astrophysical Journal 01/2012; 745(1):92. · 6.02 Impact Factor
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Guillermo A. Blanc,
Joshua J. Adams,
Karl Gebhardt, Gary J. Hill,
Niv Drory,
Lei Hao,
Ralf Bender,
Robin Ciardullo,
Steven L. Finkelstein,
Alexander B. Fry, [......],
Caryl Gronwall,
Ulrich Hopp,
Donghui Jeong,
Ralf Kelzenberg,
Eiichiro Komatsu,
Phillip MacQueen,
Jeremy D. Murphy,
Martin M. Roth,
Donald P. Schneider,
and Joseph Tufts
[show abstract]
[hide abstract]
ABSTRACT: We study the escape of Lyα photons from Lyα 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 Lyα luminosity and that predicted by the dust-corrected SFR yields the Lyα escape fraction. We also measure the Lyα luminosity function and luminosity density (ρLyα) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of ρLyα. We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Lyα escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Lyα) > (3-6) × 1042 erg s–1 (0.25-0.5 L*), have a mean E(B – V) = 0.13 ± 0.01, implying an attenuation of ~70% in the UV. They show a median UV uncorrected SFR = 11 M ☉ yr–1, dust-corrected SFR = 34 M ☉ yr–1, and Lyα equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Lyα escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Lyα escape fraction in LAEs correlates with E(B – V) in a way that is expected if Lyα photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Lyα 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 Lyα 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 Lyα escape fraction of LAEs from z ~ 4 to 2. We see hints of a drop in the number density of LAEs from z ~ 4 to 2 in the redshift distribution and the Lyα luminosity function, although larger samples are required to confirm this. The mean Lyα escape fraction of the overall galaxy population decreases significantly from z ~ 6 to z ~ 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 ~ 6 and 2, reducing their Lyα 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 Lyα photons is reached by z ~ 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.
The Astrophysical Journal 06/2011; 736(1):31. · 6.02 Impact Factor
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Steven L. Finkelstein, Gary J. Hill,
Karl Gebhardt,
Joshua Adams,
Guillermo A. Blanc,
Casey Papovich,
Robin Ciardullo,
Niv Drory,
Eric Gawiser,
Caryl Gronwall,
Donald P. Schneider,
and Kim-Vy Tran
[show abstract]
[hide abstract]
ABSTRACT: We present the results of Keck/NIRSPEC spectroscopic observations of three Lyα emitting galaxies (LAEs) at z~ 2.3 discovered with the HETDEX pilot survey. We detect Hα, [O III], and Hβ emission from two galaxies at z= 2.29 and 2.49, designated HPS194 and HPS256, respectively, representing the first detection of multiple rest-frame optical emission lines in galaxies at high redshift selected on the basis of their Lyα emission. We find that the redshifts of the Lyα emission from these galaxies are offset redward of the systemic redshifts (derived from the Hα and [O III] emission) by Δv = 162 ± 37 (photometric) ± 42 (systematic) km s–1 for HPS194 and Δv = 36 ± 35 ± 18 km s–1 for HPS256. An interpretation for HPS194 is that a large-scale outflow may be occurring in its interstellar medium. This outflow is likely powered by star-formation activity, as examining emission line ratios implies that neither LAE hosts an active galactic nucleus. Using the upper limits on the [N II] emission, we place meaningful constraints on the gas-phase metallicities in these two LAEs of Z< 0.17 and < 0.28 Z ☉ (1σ). Measuring the stellar masses of these objects via spectral energy distribution (SED) fitting (~1010 and 6 × 108 M ☉, respectively), we study the nature of LAEs in a mass-metallicity plane. At least one of these two LAEs appears to be more metal poor than continuum-selected star-forming galaxies at the same redshift and stellar mass, implying that objects exhibiting Lyα emission may be systematically less chemically enriched than the general galaxy population. We use the SEDs of these two galaxies to show that neglecting the contribution of the measured emission line fluxes when fitting stellar population models to the observed photometry can result in overestimates of the population age by orders of magnitude and the stellar mass by a factor of ~2. This effect is particularly important at z 7, where similarly strong emission lines may masquerade in the photometry as a 4000 Å break.
The Astrophysical Journal 02/2011; 729(2):140. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present new integral-field spectroscopy in the outskirts of two nearby, edge-on, late-type galaxies to search for the Hα emission that is expected from the exposure of their hydrogen gas to the metagalactic ultraviolet background (UVB). Despite the sensitivity of the VIRUS-P spectrograph on the McDonald 2.7 m telescope to low surface brightness emission and the large field of view, we do not detect Hα to 5σ upper limits of 6.4 × 10–19 erg s–1 cm–2 arcsec–2 in UGC 7321 and of 25 × 10–19 erg s–1 cm–2 arcsec–2 in UGC 1281 in each of the hundreds of independent spatial elements (fibers). We fit gas distribution models from overlapping 21 cm data of H I, extrapolate one scale length beyond the H I data, and estimate predicted Hα surface brightness maps. We analyze three types of limits from the data with stacks formed from increasingly large spatial regions and compare to the model predictions: (1) single fibers, (2) convolution of the fiber grid with a Gaussian, circular kernel (10'' full width at half-maximum), and (3) the co-added spectra from a few hundred fibers over the brightest model regions. None of these methods produce a significant detection (>5σ) with the most stringent constraints on the H I photoionization rate of Γ(z = 0) < 1.7 × 10–14 s–1 in UGC 7321 and Γ(z = 0) < 14 × 10–14 s–1 in UGC 1281. The UGC 7321 limit is below previous measurement limits and also below current theoretical models. Restricting the analysis to the fibers bound by the H I data leads to a comparable limit; the limit is Γ(z = 0) < 2.3 × 10–14 s–1 in UGC 7321. We discuss how a low Lyman limit escape fraction in z ~ 0 redshift star-forming galaxies might explain this lower than predicted UVB strength and the prospects of deeper data to make a direct detection.
The Astrophysical Journal 01/2011; 728(2):107. · 6.02 Impact Factor
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Joshua J. Adams,
Guillermo A. Blanc, Gary J. Hill,
Karl Gebhardt,
Niv Drory,
Lei Hao,
Ralf Bender,
Joyce Byun,
Robin Ciardullo,
Mark E. Cornell, [......],
Andreas Kelz,
Ralf Kelzenberg,
Eiichiro Komatsu,
Phillip J. MacQueen,
Jeremy Murphy,
P. Samuel Odoms,
Martin Roth,
Donald P. Schneider,
Joseph R. Tufts,
and Christopher P. Wilkinson
[show abstract]
[hide abstract]
ABSTRACT: We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment. We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 ' with a 3500-5800 Å bandpass under 5 Å full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4 and 20× 10–17 erg s–1 cm–2 depending on the wavelength, and Lyα luminosities between 3 × 1042 and 6 × 1042 erg s–1 are detectable. This survey method complements narrowband and color-selection techniques in the search of high-redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 105 galaxies via their high-redshift Lyα emission at 1.9 < z < 3.8, and the majority of the remainder objects are low-redshift [O II]3727 emitters at z < 0.56. The classification between low- and high-redshift objects depends on rest-frame equivalent width (EW), as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei fraction among the Lyα emitters is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly significant, resolved objects with FWHM sizes >44 ' which appear to be extended Lyα nebulae. We also find three high-z objects with rest-frame Lyα EW above the level believed to be achievable with normal star formation, EW0>240 Å. Future papers will investigate the physical properties of this sample.
The Astrophysical Journal Supplement Series 12/2010; 192(1):5. · 13.46 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present new integral-field spectroscopy in the outskirts of two nearby, edge-on, late-type galaxies to search for the H-alpha emission that is expected from the exposure of their hydrogen gas to the metagalactic ultraviolet background (UVB). Despite the sensitivity of the VIRUS-P spectrograph on the McDonald 2.7m telescope to low surface brightness emission and the large field-of-view, we do not detect H-alpha to 5 sigma upper limits of 6.4 x 10^(-19) erg/s/cm^2/arcsec^2 in UGC 7321 and of 25 x 10^(-19) erg/s/cm^2/arcsec^2 in UGC 1281 in each of the hundreds of independent spatial elements (fibers). We fit gas distribution models from overlapping 21 cm data of HI, extrapolate one scale length beyond the HI data, and estimate predicted H-alpha surface brightness maps. We analyze three types of limits from the data with stacks formed from increasingly large spatial regions and compare to the model predictions: 1) single fibers, 2) convolution of the fiber grid with a Gaussian, circular kernel (10\arcsec\ full width half maximum), and 3) the coadded spectra from a few hundred fibers over the brightest model regions. None of these methods produce a significant detection (>5 sigma) with the most stringent constraints on the HI photoionization rate of Gamma(z=0)<1.7 x 10^(-14) s^(-1) in UGC 7321 and Gamma(z=0)<14 x 10^(-14) s^(-1) in UGC 1281. The UGC 7321 limit is below previous measurement limits and also below current theoretical models. Restricting the analysis to the fibers bound by the HI data leads to a comparable limit; the limit is Gamma(z=0)<2.3 x 10^(-14) s^(-1) in UGC 7321. We discuss how a low Lyman limit escape fraction in z~0 redshift star forming galaxies might explain this lower than predicted UVB strength and the prospects of deeper data to make a direct detection. Comment: accepted to ApJ; 16 pages, 6 figures, 2 tables
12/2010;
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Steven L. Finkelstein, Gary J. Hill,
Karl Gebhardt,
Joshua Adams,
Guillermo A. Blanc,
Casey Papovich,
Robin Ciardullo,
Niv Drory,
Eric Gawiser,
Caryl Gronwall,
Donald P. Schneider,
Kim-Vy Tran
[show abstract]
[hide abstract]
ABSTRACT: We present Keck/NIRSPEC spectroscopic observations of three Lyman alpha
emitting galaxies (LAEs) at z ~ 2.3 discovered with the HETDEX pilot survey. We
detect Halpha, [OIII], and Hbeta emission from two galaxies at z = 2.29 and
2.49, designated HPS194 and HPS256, respectively, representing the first
detection of multiple rest-frame optical emission lines in galaxies at
high-redshift selected on the basis of their Lyman alpha emission. The
redshifts of the Lyman alpha emission from these galaxies are offset redward of
the systemic redshifts by Delta_v = 162 +/- 37 (photometric) +/- 42
(systematic) km/s for HPS194, and Delta_v = 36 +/- 35 +/- 18 km/s for HPS256.
An interpretation for HPS194 is that a large-scale outflow may be occurring in
its interstellar medium. The emission line ratios imply that neither LAE hosts
an active galactic nucleus. Using the upper limits on the [NII] emission we
place meaningful constraints on the gas-phase metallicities in these two LAEs
of Z < 0.17 and < 0.28 Zsol (1 sigma). Measuring the stellar masses of these
objects via spectral energy distribution (SED) fitting (~ 10^10 and 6 x 10^8
Msol, respectively), we study the nature of LAEs in a mass-metallicity plane.
At least one of these two LAEs appears to be more metal poor than
continuum-selected star-forming galaxies at the same redshift and stellar mass,
implying that objects exhibiting Lyman alpha emission may be systematically
less chemically enriched than the general galaxy population. We use the SEDs of
these two galaxies to show that neglecting the emission lines when fitting
stellar population models to the observed photometry can result in
overestimates of the population age by orders of magnitude, and the stellar
mass by a factor of ~ 2. This effect is particularly important at z > 7, where
similarly strong emission lines may masquerade in the photometry as a 4000 A
break (abridged).
11/2010;
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Joshua J. Adams,
Guillermo A. Blanc, Gary J. Hill,
Karl Gebhardt,
Niv Drory,
Lei Hao,
Ralf Bender,
Joyce Byun,
Robin Ciardullo,
Mark E. Cornell, [......],
Andreas Kelz,
Ralf Kelzenberg,
Eiichiro Komatsu,
Phillip J. MacQueen,
Jeremy Murphy,
P. Samuel Odoms,
Martin Roth,
Donald P. Schneider,
Joseph R. Tufts,
Christopher P. Wilkinson
[show abstract]
[hide abstract]
ABSTRACT: We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 sq.arcmin with a 3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable. This survey method complements narrowband and color-selection techniques in the search for high redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 104 galaxies via their high redshift Ly-alpha emission at 1.9<z<3.8, and the majority of the remainder objects are low redshift [OII]3727 emitters at z<0.56. The classification between low and high redshift objects depends on rest frame equivalent width, as well as other indicators, where available. Based on matches to X-ray catalogs, the active galactic nuclei (AGN) fraction amongst the Ly-alpha emitters (LAEs) is 6%. We also analyze the survey's completeness and contamination properties through simulations. We find five high-z, highly-significant, resolved objects with full-width-half-maximum sizes >44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three high-z objects with rest frame Ly-alpha equivalent widths above the level believed to be achievable with normal star formation, EW(rest)>240 Ang. Comment: 45 pages, 36 figures, 5 tables, submitted to ApJS
11/2010;
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Guillermo A. Blanc,
Joshua Adams,
Karl Gebhardt, Gary J. Hill,
Niv Drory,
Lei Hao,
Ralf Bender,
Robin Ciardullo,
Steven L. Finkelstein,
Eric Gawiser,
Caryl Gronwall,
Ulrich Hopp,
Donghui Jeong,
Ralf Kelzenberg,
Eiichiro Komatsu,
Phillip MacQueen,
Jeremy D. Murphy,
Martin M. Roth,
Donald P. Schneider,
Joseph Tufts
[show abstract]
[hide abstract]
ABSTRACT: 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 HETDEX
Pilot Survey. For 89 LAEs showing counterparts in deep broad-band images we
measure the rest-frame UV luminosity and the UV slope, which we use to estimate
E(B-V) under the assumption of a constant intrinsic UV slope for LAEs. These
two quantities are used to measure the dust-corrected star formation rate
(SFR). A 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. Integration of the luminosity function
provides a measurement of the Ly-alpha luminosity density across our redshift
range. We combine our data with that from other surveys at 0.3<z<7.7 to trace
the evolution of the Ly-alpha luminosity density. We then compare it to that
expected from the star-formation history of the universe in order to
characterize the evolution of the Ly-alpha escape fraction of the overall
galaxy population [abriged]
11/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present deep spectroscopic data for a 24-object subsample of our full 41-object z~0.5 radio galaxy sample in order to investigate the evolution of the Fundamental Plane of radio galaxies. We find that the low-luminosity, FRI-type, radio galaxies in our sample are consistent with the local Fundamental Plane of radio galaxies defined by Bettoni et al. when corrected for simple passive evolution of their stellar populations. However, we find that the higher luminosity, FRII-type radio galaxies are inconsistent with the local Fundamental Plane if only passive evolution is considered, and find evidence for a rotation in the Fundamental Plane at z~0.5 when compared with the local relation. We show that neither passive evolution, nor a mass-dependent evolution in the mass-to-light ratio, nor an evolution in the size of the host galaxies can, by themselves, plausibly explain the observed tilt. However, we suggest that some combination of all three effects, with size evolution as the dominant factor, may be sufficient to explain the difference between the planes. We also find evidence for a correlation between host galaxy velocity dispersion and radio luminosity at the 97% significance level within our sub-sample, although further observations are required in order to determine whether this is different for the FRI and FRII radio sources. Assuming that the M_BH - sigma relation still holds at z~0.5, this implies that radio luminosity scales with black hole mass, in agreement with previous studies. Comment: 19 pages, 10 figures. Accepted for publication in MNRAS
08/2010;
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Richard Savage,
John Booth,
Mark Cornell,
John Good, Gary J. Hill,
Hanshin Lee,
Phillip MacQueen,
Marc Rafal,
Brian Vattiat,
Karl Gebhardt, [......],
Sarah Hinze,
Ian Soukup,
John Jackson,
Jason Mock,
Michael Worthington,
Nicholas Mollison,
Omar Molina,
Brian South,
Douglas Wardell,
Gregory Wedeking
[show abstract]
[hide abstract]
ABSTRACT: The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the McDonald Observatory (MDO). The HET operates with a fixed segmented primary and has a tracker which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A major upgrade of the HET is in progress that will increase the pupil size to 10 meters and the field of view to 22' by replacing the corrector, tracker and prime focus instrument package. In addition to supporting the existing suite of instruments, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). This paper discusses the current status of this upgrade.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
07/2010;
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Brian L. Vattiat, Gary J. Hill,
J. L. Marshall,
D. L. DePoy,
Svend Bauer,
Andreas Kelz,
M. D. Rafal,
Richard Savage,
John Good,
John A. Booth,
M. P. Smith,
Travis Prochaska,
Richard D. Allen
[show abstract]
[hide abstract]
ABSTRACT: The Visible Integral-Field Replicable Unit Spectrograph (VIRUS) is an integral field spectrograph to support observations for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The VIRUS instrument is fed by more than 33,000 optical fibers and consists of 150 spectrographs in 75 individual, identical units. This paper discusses the evolution in mechanical design of the VIRUS unit spectrographs to maximize the cost benefit from volume production. Design features which enable volume manufacture and assembly are discussed. Strategies for reducing part count while enabling precision alignment are detailed. Design considerations for deployment, operation, and maintenance en mass at the Hobby-Eberly Telescope are also made. In addition, several enabling technologies are described including the use of cast aluminum in vacuum housings, use of cast Invar, and processing cast parts for precision tolerances.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
07/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We present the results of our investigation into the stellar populations of 24 radio galaxies at z~0.5 drawn from four complete, low-frequency selected radio surveys. We use the strength of the 4000A break as an indicator of recent star formation, and compare this with radio luminosity, optical spectral classification and morphological classification. We find evidence of different star formation histories for high- and low-luminosity radio sources; our group of low radio luminosity sources (typically FRI-type sources) has systematically older stellar populations than the higher radio luminosity group. Our sample is also fairly well divided by optical spectral classification. We find that galaxies classified as having low excitation spectra (LEGs) possess older stellar populations than high excitation line objects (HEGs), with the HEGs showing evidence for recent star formation. We also investigate the link between radio morphology, as used by Owen & Laing (1989), and the stellar populations. We find that there is a preference for the "fat-double" sources to have older stellar populations than the "classical double" sources, although this is also linked to these sources lying predominantly in the LEG and HEG categories respectively. These results are consistent with the hypothesis that HEGs are powered by accretion of cold gas, which could be supplied, for example, by recent mergers, secular instabilities, or filamentary cold flows. These processes could also trigger star formation in the host galaxy. The host galaxies of the LEGs do not show evidence for recent star formation and an influx of cold gas, and are consistent with being powered by the accretion of the hot phase of the inter-stellar medium. Comment: 7 pages, 4 figures, accepted for publication in MNRAS
04/2010;
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Guillermo A. Blanc,
Karl Gebhardt,
Amanda Heiderman,
Neal J. Evans II,
Shardha Jogee,
Remco van den Bosch,
Irina Marinova,
Tim Weinzirl,
Peter Yoachim,
Niv Drory,
Maximilian Fabricius,
David Fisher,
Lei Hao,
Phillip J. MacQueen,
Juntai Shen, Gary J. Hill,
John Kormendy
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ABSTRACT: VENGA is a large-scale extragalactic IFU survey, which maps the bulges, bars and large parts of the outer disks of 32 nearby normal spiral galaxies. The targets are chosen to span a wide range in Hubble types, star formation activities, morphologies, and inclinations, at the same time of having vast available multi-wavelength coverage from the far-UV to the mid-IR, and available CO and 21cm mapping. The VENGA dataset will provide 2D maps of the SFR, stellar and gas kinematics, chemical abundances, ISM density and ionization states, dust extinction and stellar populations for these 32 galaxies. The uniqueness of the VIRUS-P large field of view permits these large-scale mappings to be performed. VENGA will allow us to correlate all these important quantities throughout the different environments present in galactic disks, allowing the conduction of a large number of studies in star formation, structure assembly, galactic feedback and ISM in galaxies. Comment: 7 pages, 3 figures, proceedings of the "Third Biennial Frank N. Bash Symposium, New Horizons in Astronomy" held in Austin, TX, Oct. 2009. To be published in the Astronomical Society of the Pacific Conference Series, eds. L. Stanford, L. Hao, Y. Mao, J. Green
01/2010;
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Alejo Martínez-Sansigre,
Alexander Karim,
Eva Schinnerer,
Alain Omont,
Daniel J. B. Smith,
Jingwen Wu, Gary J. Hill,
Hans-Rainer Klöckner,
Mark Lacy,
Steve Rawlings,
and Chris J. Willott
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ABSTRACT: We present observations at 1.2 mm with Max-Planck Millimetre Bolometer Array (MAMBO-II) of a sample of z 2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. The typical rms noise achieved by the MAMBO observations is 0.55 mJy beam–1 and five out of 21 sources (24%) are detected at a significance of ≥3σ. Stacking all sources leads to a statistical detection of S 1.2 mm = 0.96 ± 0.11 mJy and stacking only the non-detections also yields a statistical detection, with S 1.2 mm = 0.51 ± 0.13 mJy. At the typical redshift of the sample, z = 2, 1 mJy corresponds to a far-infrared luminosity L FIR~4 × 1012 L ☉. If the far-infrared luminosity is powered entirely by star formation, and not by active galactic nucleus heated dust, then the characteristic inferred star formation rate is ~700 M ☉ yr–1. This far-infrared luminosity implies a dust mass of M d~3 × 108 M ☉, which is expected to be distributed on ~kpc scales. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. Combining our observations at 1.2 mm with mid- and far-infrared data, and additional observations for two objects at 350 μm using SHARC-II, we present dust spectral energy distributions (SEDs) for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. This additional extinction can be consistently achieved by the mass of cool dust responsible for the far-infrared emission, provided the bulk of the dust is within a radius ~2-3 kpc. Comparison of our sample to other samples of z ~ 2 quasars suggests that obscured quasars have, on average, higher far-infrared luminosities than unobscured quasars. There is a hint that the host galaxies of obscured quasars must have higher cool-dust masses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z = 2.767, we detect the CO(3-2) transition, with S COΔν = 630 ± 50 mJy km s–1, corresponding to L CO(3-2) = 3.2 ×107 L ☉, or a brightness-temperature luminosity of L'CO(3-2) = 2.4 × 1010 K km s–1 pc2. For another source at z = 4.17, the lack of detection of the CO(4-3) line suggests the line to have a brightness-temperature luminosity L'CO(4-3) < 1 × 1010 K km s–1 pc2. Under the assumption that in these objects the high-J transitions are thermalized, we can estimate the molecular gas contents to be M ☉ and <8 × 109 M ☉, respectively. The estimated gas depletion timescales are τg = 4 Myr and <16 Myr, and low gas-to-dust mass ratios of M g/M d = 19 and <20 are inferred. These values are at the low end but consistent with those of other high-redshift galaxies.
The Astrophysical Journal 10/2009; 706(1):184. · 6.02 Impact Factor
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Alejo Martinez-Sansigre,
Alexander Karim,
Eva Schinnerer,
Alain Omont,
Daniel J. B. Smith,
Jingwen Wu, Gary J. Hill,
Hans-Rainer Kloeckner,
Mark Lacy,
Steve Rawlings,
Chris J. Willott
[show abstract]
[hide abstract]
ABSTRACT: We present observations at 1.2 mm with MAMBO-II of a sample of z>~2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. Five out of 21 sources (24%) are detected at a significance of >=3sigma. Stacking all sources leads to a statistical detection of = 0.96+-0.11 mJy and stacking only the non-detections also yields a statistical detection, with = 0.51+-0.13 mJy. This corresponds to a typical far-infrared luminosity L_FIR~4x10^12 Lsol. If the far-infrared luminosity is powered entirely by star-formation, and not by AGN-heated dust, then the characteristic inferred star-formation rate is ~700 Msol yr-1. This far-infrared luminosity implies a dust mass of M_dust~3x10^8 Msol. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. We present dust SEDs for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. There is a hint that the host galaxies of obscured quasars must have higher far-infrared luminosities and cool-dust masses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z=2.767, we detect the CO(3-2) transition, with S_CO Delta nu=630+-50 mJy km s-1, corresponding to L_CO(3-2)= 3.2x10^7 Lsol, or L'_CO(3-2)=2.4x10^10 K km s-1 pc2. For another source at z=4.17, the lack of detection of the CO(4-3) line yields a limit of L'_CO(4-3)<1x10^10 K km s-1 pc2. Molecular gas masses, gas depletion timescales and gas-to-dust ratios are estimated (Abridged). Comment: Accepted by ApJ, 25 pages, 11 figures, 4 tables
10/2009;
