arXiv subjects

S. V. W. Beckwith

Publications and source records attributed to S. V. W. Beckwith.

At least 19 recordsLinked to original sources

arXiv2008

The UDF05 Follow-up of the HUDF: II. Constraints on Reionization from z-dropout Galaxies

[Abridged] We detect three (plus one less certain) z-dropout sources in two separate fields of our UDF05 HST NICMOS images. These z~7 Lyman-Break Galaxy (LBG) candidates allow us to constrain the Luminosity Function (LF) of the star forming galaxy population at those epochs. By assuming a change in only M* and adopting a linear evolution in redshift, anchored to the measured values at z~6, the best fit evolution coefficient is found to be 0.43+-0.19 mag per unit redshift (0.36+-0.18, if including all four candidates), which provides a value of M*(z=7.2)=-19.7+-0.3. This implies a steady evolution for the LBG LF out to z~7, at the same rate that is observed throughout the z~3 to 6 period. This puts a strong constraint on the star-formation histories of z~6 galaxies, whose ensemble star-formation rate density must be lower by a factor 2 at ~170 Myr before the epoch at which they are observed. In particular, a large fraction of stars in the z~6 LBG population must form at redshifts well above z~7. Extrapolating this steady evolution of the LF out to higher redshifts, we estimate that galaxies would be able to reionize the universe by z~6, provided that the faint-end slope of the z>7 LF steepens to alpha~-1.9, and that faint galaxies, with luminosities below the current detection limits, contribute a substantial fraction of the required ionizing photons. This scenario gives however an integrated optical depth to electron scattering that is ~2sigma below the WMAP-5 measurement. Therefore, altogether, our results indicate that, should galaxies be the primary contributors to reionization, either the currently detected evolution of the galaxy population slows down at z>7, or the LF evolution must be compensated by a decrease in metallicity and a corresponding increase in ionization efficiency at these early epochs.

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arXiv2008

SPACE: the SPectroscopic All-sky Cosmic Explorer

We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015-2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0<z<2 down to AB~23 over 3πsr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB~26 and at 2<z<10+. These goals are unreachable with ground-based observations due to the ~500 times higher sky background. To achieve the main science objectives, SPACE will use a 1.5m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices (DMDs) covering a total field of view of 0.4 deg2, and will perform large-multiplexing multi-object spectroscopy (e.g. ~6000 targets per pointing) at a spectral resolution of R~400 as well as diffraction-limited imaging with continuous coverage from 0.8mum to 1.8mum.

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arXiv2007

The UDF05 Follow-up of the HUDF: I. The Faint-End Slope of the Lyman-Break Galaxy Population at z~5

We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP) and NICMOS (F110W, F160W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z~5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V-i, i-z selection criterion, we identify a sample of 101 and 133 candidate z~5 galaxies down to z_{850}=28.5 and 29.25 magnitudes in the NICP12 and in the HUDF fields, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 A LBG LF over the range M_{1400}=[-21.4, -17.1], i.e. down to ~0.04 L* at z~5, and complement it with data from the Subaru Deep Field (SDF) from Yoshida et al. (2006) to extend it to the brighter end (M_{1400}>-22.2). We show that: (i) Different assumptions regarding the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z~5; (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z~5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha ~ -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z~3 and z~6.

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arXiv2005

GEMS Survey Data and Catalog

We describe the data reduction and object cataloging for the GEMS survey, a large-area (800 arcmin^2) two-band (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on HST, centered on the Chandra Deep Field South.

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arXiv2005

GEMS: which galaxies dominate the z~0.7 ultraviolet luminosity density?

We combine high-resolution images from GEMS with redshifts and spectral energy distributions from COMBO-17 to explore the morphological types of galaxies that dominate the z~0.7 UV luminosity density. We analysed rest-frame 280 nm and V-band luminosities of 1483 galaxies with 0.65<z< 0.75, combining these with visual morphological classifications from F850LP images (approximately rest-frame V-band) taken with HST/ACS on the Extended Chandra Deep Field South. We derive UV luminosity functions and j_280 luminosity densities for spheroid-dominated galaxies, spiral galaxies, Magellanic irregulars, and clearly-interacting galaxies with morphologies suggestive of ongoing major mergers. We check the reliability of GEMS morphologies against the deeper GOODS images and quantify an incompleteness of the GEMS merger identification at the faint end. We derive the fractions of the global UV luminosity density j_280 originating from the galaxy types, and find that spiral galaxies and Magellanic irregulars dominate with about 40% each. Interacting and merging galaxies account for roughly 20% of j_280, while the contribution of early types is negligible. These results imply that the strong decline in the UV luminosity density of the Universe observed from z~1 until today is dominated by the decreasing UV luminosities of normal spiral galaxies, accompanied by the migration of UV-luminous star formation in irregular galaxies to systems of progressively lower mass and luminosity. (abridged)

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arXiv2004

The Orion Nebula in the mid-IR

We present two wide-field (5'x5'), diffraction limited, broad-band 10 and 20 micron images of the Orion Nebula, plus six 7-13 micron narrow-band images of BN/KL taken at the 3.8m UKIRT telescope. The wide-field images are mosaics of 35"x35" frames reconstructed using a new restoration method developed for this project. They show the filamentary structure of the dust emission and reveal a new remarkable group of arc-like structures ~1' to the South of the Trapezium. The morphology of the Ney-Allen nebula suggests a complex kinematical status at the center of the Cluster. We find indications that the B0.5V star theta1 Ori-D, is surrounded by a photoevaporated circumstellar disk. Among the four historic Trapezium OB stars, this is the only one without a binary companion, suggesting that stellar multiplicity and the presence of massive circumstellar disks may be mutually exclusive. In the BN/KL complex we detect optically thin silicate emission on top of the deep 10 micron absorption feature. We map the foreground optical depth, color temperature and mid-IR luminosity of the embedded sources. We resolve a conspicuous point source at the location of the IRc2-A knot. The spectral profile of the 10 micron feature is compatible with grain crystallization. We detect several point sources In the OMC-1 South region and discuss their association with the mass loss observed at optical and mm wavelengths. Finally, we list the position and photometry of 177 point sources. With two possible exceptions, all point sources detected at shorter wavelengths display 10 micron emission well above the photospheric level. The model of Robberto et al. (2002, ApJ, 578, 897) provides the simplest explanation for the mid-IR excess.

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arXiv2004

Massive Star Feedback on the IMF

We have obtained the first measures of the mass accretion rates on stars of the Trapezium Cluster. They appear systematically lower than those of similar stars in the Taurus-Auriga association. Together with premature disk evaporation, dramatically revealed by the HST images of the Orion proplyds, this result suggests that low mass stars in a rich cluster may be ``dwarfed'' by the influence of nearby OB stars. This feedback mechanism affects the IMF, producing an excess of low mass stars and brown dwarfs. The observed frequency of low mass objects in Orion vs. Taurus seems to confirm this scenario.

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arXiv2004

Bar Evolution Over the Last Eight Billion Years: A Constant Fraction of Strong Bars in GEMS

One third of present-day spirals host optically visible strong bars that drive their dynamical evolution. However, the fundamental question of how bars evolve over cosmological times has yet to be addressed, and even the frequency of bars at intermediate redshifts remains controversial. We investigate the frequency of bars out to z~1.0 drawing on a sample of 1590 galaxies from the GEMS survey, which provides morphologies from HST ACS two-color images, and highly accurate redshifts from the COMBO-17 survey. We identify spiral galaxies using the Sersic index, concentration parameter, and rest-frame color. We characterize bars and disks by fitting ellipses to F606W and F850LP images, taking advantage of the two bands to minimize bandpass shifting. We exclude highly inclined (i>60 deg) galaxies to ensure reliable morphological classifications, and apply completeness cuts of M_v <= -19.3 and -20.6. More than 40% of the bars that we detect have semi major axes a<0.5" and would be easily missed in earlier surveys without the small PSF of ACS. The bars that we can reliably detect are fairly strong (with ellipticities e>=0.4) and have a in the range ~1.2-13 kpc. We find that the optical fraction of such strong bars remains at ~(30% +- 6%) from the present-day out to look-back times of 2-6 Gyr (z~0.2-0.7) and 6-8 Gyr (z~0.7-1.0); it certainly shows no sign of a drastic decline at z>0.7. Our findings of a large and similar bar fraction at these three epochs favor scenarios in which cold gravitationally unstable disks are already in place by z~1, and where on average bars have a long lifetime (well above 2 Gyr). The distributions of structural bar properties in the two slices are, however, not statistically identical and therefore allow for the possibility that the bar strengths and sizes may evolve over time.

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arXiv2004

Evolution and Impact of Bars over the Last Eight Billion Years: Early Results from GEMS

Bars drive the dynamical evolution of disk galaxies by redistributing mass and angular momentum, and they are ubiquitous in present-day spirals. Early studies of the Hubble Deep Field reported a dramatic decline in the rest-frame optical bar fraction f_opt to below 5% at redshifts z>0.7, implying that disks at these epochs are fundamentally different from present-day spirals. The GEMS bar project, based on ~8300 galaxies with HST-based morphologies and accurate redshifts over the range 0.2-1.1, aims at constraining the evolution and impact of bars over the last 8 Gyr. We present early results indicating that f_opt remains nearly constant at ~30% over the range z=0.2-1.1,corresponding to lookback times of ~2.5-8 Gyr. The bars detected at z>0.6 are primarily strong with ellipticities of 0.4-0.8. Remarkably, the bar fraction and range of bar sizes observed at z>0.6 appear to be comparable to the values measured in the local Universe for bars of corresponding strengths. Implications for bar evolution models are discussed.

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arXiv2004

UV light from young stars in GEMS quasar host galaxies at 1.8<z<2.75

We have performed HST imaging of a sample of 23 high-redshift (1.8<z<2.75) AGN, drawn from the COMBO-17 survey. The sample contains moderately luminous quasars (M_B ~ -23). The data are part of the GEMS imaging survey that provides high resolution optical images obtained with ACS in two bands (F606W and F850LP), sampling the rest-frame UV flux of the targets. To deblend the AGN images into nuclear and resolved (host galaxy) components we use a PSF subtraction technique that is strictly conservative with respect to the flux of the host galaxy. We resolve the host galaxies in both filter bands in 9 of the 23 AGN, whereas the remaining 14 objects are considered non-detections, with upper limits of less than 5% of the nuclear flux. However, when we coadd the unresolved AGN images into a single high signal-to-noise composite image we find again an unambiguously resolved host galaxy. The recovered host galaxies have apparent magnitudes of 23.0<F606W<26.0 and 22.5<F850LP<24.5 with rest-frame UV colours in the range -0.2<(F606W-F850LP)_obs<2.3. The rest-frame absolute magnitudes at 200 nm are -20.0<M_200nm<-22.2. The photometric properties of the composite host are consistent with the individual resolved host galaxies. We find that the UV colors of all host galaxies are substantially bluer than expected from an old population of stars with formation redshift z=5, independent of the assumed metallicities. These UV colours and luminosities range up to the values found for Lyman-break galaxies (LBGs) at z=3. Our results agree with the recent discovery of enhanced blue stellar light in AGN hosts at lower redshifts. [abridged]

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arXiv2004

Colors of AGN host galaxies at 0.5<z<1.1 from GEMS

We present the results from a study of the host galaxies of 15 optically selected AGNs with 0.5<z<1.1 from GEMS. GEMS is a Hubble Space Telescope imaging survey of a ~28"x28" contiguous field centered on the Chandra Deep Field South in the F606W and F850LP filter bands. It incorporates the SEDs and redshifts of ~10000 objects, obtained by the COMBO-17 project. We have detected the host galaxies of all 15 AGNs in the F850LP-band (and 13/15 in the F606W-band), recovering their fluxes, morphologies and structural parameters. We find that 80% of the host galaxies have early-type (bulge-dominated) morphologies, while the rest have structures characteristic of late-type (disk-dominated) galaxies. We find that 25% of the early types, and 30% of the late types, exhibit disturbances consistent with galaxy interactions. The hosts show a wide range of colors, from those of red-sequence galaxies to blue colors consistent with ongoing star formation. Roughly 70% of the morphologically early-type hosts have rest-frame blue colors, a much larger fraction than those typical of non-active morphologically early-type galaxies in this redshift and luminosity range. Yet, we find that the early-type hosts are structurally similar to red-sequence ellipticals, inasmuch as they follow an absolute magnitude versus half-light size correlation that are consistent with the mean relation for early-type galaxies at similar redshifts.

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arXiv2004

The Formation and Evolution of Planetary Systems: First Results from a Spitzer Legacy Science Program

We present 3-160 micron photometry obtained with the IRAC and MIPS instruments for the first five targets from the Spitzer Legacy Science Program "Formation and Evolution of Planetary Systems" and 4-35 micron spectro-photometry obtained with the IRS for two sources. We discuss in detail our observations of the debris disks surrounding HD 105 (G0V, 30 +- 10 Myr) and HD 150706 (G3V, ~ 700 +- 300 Myr). For HD 105, possible interpretations include large bodies clearing the dust inside of 45 AU or a reservoir of gas capable of sculpting the dust distribution. The disk surrounding HD 150706 also exhibits evidence of a large inner hole in its dust distribution. Of the four survey targets without previously detected IR excess, spanning ages 30 Myr to 3 Gyr, the new detection of excess in just one system of intermediate age suggests a variety of initial conditions or divergent evolutionary paths for debris disk systems orbiting solar-type stars.

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arXiv2004

Evolution of optically faint AGN from COMBO-17 and GEMS

We have mapped the AGN luminosity function and its evolution between z=1 and z=5 down to apparent magnitudes of $R<24$. Within the GEMS project we have analysed HST-ACS images of many AGN in the Extended Chandra Deep Field South, enabling us to assess the evolution of AGN host galaxy properties with cosmic time.

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arXiv2004

HST/WFPC2 Study of the Trapezium Cluster: the Influence of Circumstellar Disks on the Initial Mass Function

We have performed the first measures of mass accretion rates in the core of the Orion Nebula Cluster. Four adjacent fields centered on the Trapezium stars have been imaged in the U- and B-bands using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In this paper we focus our attention on a group of 40 stars with known spectral types and complete UBVI WFPC2 photometry. Approximately three quarters of the sources show excess luminosity in the U-band, that we attribute to mass accretion. The known correlation between the U-band excess and the total accretion luminosity allows us to estimate the accretion rates. Overall, mass accretion rates appear lower than those measured by other authors in the Orion flanking fields or in Taurus-Auriga. Mass accretion rates remain low even in the vicinity of the birth line of Palla & Stahler, suggesting that in the core of the Trapezium cluster disk accretion has been recently depressed by an external mechanism. We suggest that the UV radiation generated by the Trapezium OB stars, responsible for the disk evaporation, may also cause the drop of the mass accretion rate. In this scenario, low-mass stars may terminate their pre-main sequence evolution with masses lower than those they would have reached if disk accretion could have proceeded undisturbed until the final disk consumption. In OB associations the low-mass end of the Initial Mass Function may therefore be affected by the rapid evolution of the most massive cluster's stars, causing a surplus "accretion aborted" very low-mass stars and brown dwarfs, and a deficit of intermediate mass stars. This trend is in agreement with recent observations of the IMF in the Trapezium cluster.

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arXiv2002

The Infrared Emission of Circumstellar Envelopes, Dark Silhouettes and Photoionized Disks in HII Regions

We model the IR Spectral Energy Distribution of circumstellar disks embedded in a HII region and photoevaporated by the external UV radiation. The model applies to the photoevaporated disks (proplyds) in Orion Nebula. First we calculate the IR emission of a PMS star surrounded by a dusty globule that is immersed within an HII region. The globule is assumed to be spherical, homogeneous, optically thin in the IR and photoevaporated according to the Dyson (1968) model. Second, we consider the IR emission of a disk directly exposed to the nebular environment. The disk is passive and treated according to the Chiang and Goldreich (1997) model. We improve over the CG97 treatment by tracing the propagation of the various radiative fluxes through the disk superheated atmosphere. Since the opposite disk sides receive different amounts of radiation, the flaring angle and the surface temperature distributions are different, resulting in well distinguished SEDs for the two disk faces. Finally, we combine the globule and disk models to estimate the IR emission of proplyds. The energy input from the central star and the nebular environment increase the disk flaring angle, and therefore also the amount of stellar radiation intercepted by the disk. The relative intensity of the disk vs. envelope emission varies with the tilt angle relative to the directions of th1Ori-C, and of the Earth. We explore the dependence of the SEDs upon the tilt angle with respect to the Earth, the distance from th1Ori-C, the size on the envelope, the inner disk radius and the temperature of the central star. The resulting SEDs are characterized by a broad peak of emission at 30-60micron, and are in general significantly different from those of isolated disks in low-mass star forming regions like Taurus-Auriga.

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arXiv2001

The Formation and Evolution of Planetary Systems: SIRTF Legacy Science in the VLT Era

We will utilize the sensitivity of SIRTF through the Legacy Science Program to carry out spectrophotometric observations of solar-type stars aimed at (1) defining the timescales over which terrestrial and gas giant planets are built, from measurements diagnostic of dust/gas masses and radial distributions; and (2) establishing the diversity of planetary architectures and the frequency of planetesimal collisions as a function of time through observations of circumstellar debris disks. Together, these observations will provide an astronomical context for understanding whether our solar system - and its habitable planet - is a common or a rare circumstance. Achieving our science goals requires measuring precise spectral energy distributions for a statistically robust sample capable of revealing evolutionary trends and the diversity of system outcomes. Our targets have been selected from two carefully assembled databases of solar-like stars: (1) a sample located within 50 pc of the Sun spanning an age range from 100-3000 Myr for which a rich set of ancillary measurements (e.g. metallicity, stellar activity, kinematics) are available; and (2) a selection located between 15 and 180 pc and spanning ages from 3 to 100 Myr. For stars at these distances SIRTF is capable of detecting stellar photospheres with SNR >30 at lambda < 24 microns for our entire sample, as well as achieving SNR >5 at the photospheric limit for over 50% of our sample at lambda=70 microns. Thus we will provide a complete census of stars with excess emission down to the level produced by the dust in our present-day solar system. More information concerning our program can be found at: http://gould.as.arizona.edu/feps

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arXiv2001

The Calar Alto Deep Imaging Survey: K-band Galaxy Number Counts

We present K-band number counts for the faint galaxies in the Calar Alto Deep Imaging Survey (CADIS). We covered 4 CADIS fields, a total area of 0.2deg^2, in the broad band filters B, R and K. We detect about 4000 galaxies in the K-band images, with a completeness limit of K=19.75mag, and derive the K-band galaxy number counts in the range of 14.25 < K < 19.75mag. This is the largest medium deep K-band survey to date in this magnitude range. The B- and R-band number counts are also derived, down to completeness limits of B=24.75mag and R=23.25mag. The K-selected galaxies in this magnitude range are of particular interest, since some medium deep near-infrared surveys have identified breaks of both the slope of the K-band number counts and the mean B-K color at K=17\sim18mag. There is, however, a significant disagreement in the K-band number counts among the existing surveys. Our large near-infrared selected galaxy sample allows us to establish the presence of a clear break in the slope at K=17.0mag from dlogN/dm = 0.64 at brighter magnitudes to dlogN/dm = 0.36 at the fainter end. We construct no-evolution and passive evolution models, and find that the passive evolution model can simultaneously fit the B-, R- and K-band number counts well. The B-K colors show a clear trend to bluer colors for K > 18mag. We also find that most of the K=18-20mag galaxies have a B-K color bluer than the prediction of a no-evolution model for an L_* Sbc galaxy, implying either significant evolution, even for massive galaxies, or the existence of an extra population of small galaxies.

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arXiv2000

Multi-color Classification in the Calar Alto Deep Imaging Survey

We use a multi-color classification method introduced by Wolf, Meisenheimer & Roeser (2000) to reliably identify stars, galaxies and quasars in the up to 16-dimensional color space provided by the filter set of the Calar Alto Deep Imaging Survey (CADIS). The samples of stars, galaxies and quasars obtained this way have been used for dedicated studies published in separate papers. The classification is good enough to detect quasars rather completely and efficiently without confirmative spectroscopy. The multi-color redshifts are accurate enough for most statistical applications, e.g. evolutionary studies of the galaxy luminosity function. We characterize our current dataset on the CADIS 1h-, 9h- and 16h-fields. Using Monte-Carlo simulations we model the classification performance expected for CADIS. We present a summary of the classification results and discuss unclassified objects. More than 99% of the whole catalog sample at R<22 (more than 95% at R<23) are successfully classified matching the expectations derived from the simulations. A small number of peculiar objects challenging the classification are discussed in detail. Spectroscopic observations are used to check the reliability of the multi-color classification (6 mistakes among 151 objects with R<24). We also determine the accuracy of the multi-color redshifts which are rather good for galaxies (sigma_z = 0.03) and useful for quasars. We find the classification performance derived from the simulations to compare well with results from the real survey. Finally, we locate areas for potential improvement of the classification.

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