Searcharxiv⌕ Search

arXiv subjects

Bruce Woodgate

Publications and source records attributed to Bruce Woodgate.

13 recordsLinked to original sources
arXiv2012

NIMBUS: The Near-Infrared Multi-Band Ultraprecise Spectroimager for SOFIA

We present a new and innovative near-infrared multi-band ultraprecise spectroimager (NIMBUS) for SOFIA. This design is capable of characterizing a large sample of extrasolar planet atmospheres by measuring elemental and molecular abundances during primary transit and occultation. This wide-field spectroimager would also provide new insights into Trans-Neptunian Objects (TNO), Solar System occultations, brown dwarf atmospheres, carbon chemistry in globular clusters, chemical gradients in nearby galaxies, and galaxy photometric redshifts. NIMBUS would be the premier ultraprecise spectroimager by taking advantage of the SOFIA observatory and state of the art infrared technologies. This optical design splits the beam into eight separate spectral bandpasses, centered around key molecular bands from 1 to 4 microns. Each spectral channel has a wide field of view for simultaneous observations of a reference star that can decorrelate time-variable atmospheric and optical assembly effects, allowing the instrument to achieve ultraprecise calibration for imaging and photometry for a wide variety of astrophysical sources. NIMBUS produces the same data products as a low-resolution integral field spectrograph over a large spectral bandpass, but this design obviates many of the problems that preclude high-precision measurements with traditional slit and integral field spectrographs. This instrument concept is currently not funded for development.

astro-ph.IM↗
arXiv2010

PAH Emission Within Lyman Alpha Blobs

We present Spitzer observations of Lya Blobs (LAB) at z=2.38-3.09. The mid-infrared ratios (4.5/8um and 8/24um) indicate that ~60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGN). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (~850um or rest frame far infrared) also indicates a large percentage (~2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with sub-mm detections or meaningful upper limits remains small (~10). We obtained Infrared Spectrograph (IRS) spectra of 6 infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10^11 Mo. There is a weak trend of mass upper limit with the Lya luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs.

astro-ph.CO↗
arXiv2009

Advanced Technology Large-Aperture Space Telescope (ATLAST): A Technology Roadmap for the Next Decade

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of mission concepts for the next generation of UVOIR space observatory with a primary aperture diameter in the 8-m to 16-m range that will allow us to perform some of the most challenging observations to answer some of our most compelling questions, including "Is there life elsewhere in the Galaxy?" We have identified two different telescope architectures, but with similar optical designs, that span the range in viable technologies. The architectures are a telescope with a monolithic primary mirror and two variations of a telescope with a large segmented primary mirror. This approach provides us with several pathways to realizing the mission, which will be narrowed to one as our technology development progresses. The concepts invoke heritage from HST and JWST design, but also take significant departures from these designs to minimize complexity, mass, or both. Our report provides details on the mission concepts, shows the extraordinary scientific progress they would enable, and describes the most important technology development items. These are the mirrors, the detectors, and the high-contrast imaging technologies, whether internal to the observatory, or using an external occulter. Experience with JWST has shown that determined competitors, motivated by the development contracts and flight opportunities of the new observatory, are capable of achieving huge advances in technical and operational performance while keeping construction costs on the same scale as prior great observatories.

astro-ph.IM↗
arXiv2009

Photometric Calibrations for 21st Century Science

The answers to fundamental science questions in astrophysics, ranging from the history of the expansion of the universe to the sizes of nearby stars, hinge on our ability to make precise measurements of diverse astronomical objects. As our knowledge of the underlying physics of objects improves along with advances in detectors and instrumentation, the limits on our capability to extract science from measurements is set, not by our lack of understanding of the nature of these objects, but rather by the most mundane of all issues: the precision with which we can calibrate observations in physical units. We stress the need for a program to improve upon and expand the current networks of spectrophotometrically calibrated stars to provide precise calibration with an accuracy of equal to and better than 1% in the ultraviolet, visible and near-infrared portions of the spectrum, with excellent sky coverage and large dynamic range.

astro-ph.CO↗
arXiv2006

Telescope to Observe Planetary Systems (TOPS): a high throughput 1.2-m visible telescope with a small inner working angle

The Telescope to Observe Planetary Systems (TOPS) is a proposed space mission to image in the visible (0.4-0.9 micron) planetary systems of nearby stars simultaneously in 16 spectral bands (resolution R~20). For the ~10 most favorable stars, it will have the sensitivity to discover 2 R_E rocky planets within habitable zones and characterize their surfaces or atmospheres through spectrophotometry. Many more massive planets and debris discs will be imaged and characterized for the first time. With a 1.2m visible telescope, the proposed mission achieves its power by exploiting the most efficient and robust coronagraphic and wavefront control techniques. The Phase-Induced Amplitude Apodization (PIAA) coronagraph used by TOPS allows planet detection at 2 lambda/d with nearly 100% throughput and preserves the telescope angular resolution. An efficient focal plane wavefront sensing scheme accurately measures wavefront aberrations which are fed back to the telescope active primary mirror. Fine wavefront control is also performed independently in each of 4 spectral channels, resulting in a system that is robust to wavefront chromaticity.

astro-ph↗
arXiv2005

Ultraviolet-Bright, High-Redshift ULIRGS

We present Spitzer Space Telescope observations of the z=2.38 lya-emitter over-density associated with galaxy cluster J2143-4423, the largest known structure (110 Mpc) above z=2. We imaged 22 of the 37 known lya-emitters within the filament-like structure, using the MIPS 24um band. We detected 6 of the lya-emitters, including 3 of the 4 clouds of extended (>50 kpc) lyman alpha emission, also known as Lya Blobs. Conversion from rest-wavelength 7um to total far-infrared luminosity using locally derived correlations suggests all the detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG energies. Lya blobs frequently show evidence for interaction, either in HST imaging, or the proximity of multiple MIPS sources within the Lya cloud. This connection suggests that interaction or even mergers may be related to the production of Lya blobs. A connection to mergers does not in itself help explain the origin of the Lya blobs, as most of the suggested mechanisms for creating Lya blobs (starbursts, AGN, cooling flows) could also be associated with galaxy interactions.

astro-ph↗
arXiv2005

HST STIS spectroscopy of the triple nucleus of M31: two nested disks in Keplerian rotation around a Supermassive Black Hole

We present HST spectroscopy of the nucleus of M31 obtained with STIS. Spectra taken around the CaT lines at 8500 see only the red giants in the double bright- ness peaks P1 and P2. In contrast, spectra taken at 3600-5100 A are sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness red nucleus. P2 has a K-type spectrum, but the embedded blue nucleus has an A-type spectrum with strong Balmer absorption lines. Given the small likelihood for stellar collisions, a 200 Myr old starburst appears to be the most plausible origin of the blue nucleus. In stellar population, size, and velocity dispersion, the blue nucleus is so different from P1 and P2 that we call it P3. The line-of-sight velocity distributions of the red stars in P1+P2 strengthen the support for Tremaine s eccentric disk model. The kinematics of P3 is consistent with a circular stellar disk in Keplerian rotation around a super-massive black hole with M_bh = 1.4 x 10^8 M_sun. The P3 and the P1+P2 disks rotate in the same sense and are almost coplanar. The observed velocity dispersion of P3 is due to blurred rotation and has a maximum value of sigma = 1183+-201 km/s. The observed peak rotation velocity of P3 is V = 618+-81 km/s at radius 0.05" = 0.19 pc corresponding to a circular rotation velocity at this radius of ~1700 km/s. Any dark star cluster alternative to a black hole must have a half-mass radius <= 0.03" = 0.11 pc. We show that this excludes clusters of brown dwarfs or dead stars on astrophysical grounds.

astro-ph↗
arXiv2004

Limits on the Optical Brightness of the Epsilon Eridani Dust Ring

The STIS/CCD camera on the {\em Hubble Space Telescope (HST)} was used to take deep optical images near the K2V main-sequence star $ε$ Eridani in an attempt to find an optical counterpart of the dust ring previously imaged by sub-mm observations. Upper limits for the optical brightness of the dust ring are determined and discussed in the context of the scattered starlight expected from plausible dust models. We find that, even if the dust is smoothly distributed in symmetrical rings, the optical surface brightness of the dust, as measured with the {\em HST}/STIS CCD clear aperture at 55 AU from the star, cannot be brighter than about 25 STMAG/"$^2$. This upper limit excludes some solid grain models for the dust ring that can fit the IR and sub-mm data. Magnitudes and positions for $\approx $59 discrete objects between 12.5" to 58" from $ε$ Eri are reported. Most if not all of these objects are likely to be background stars and galaxies.

astro-ph↗
arXiv2000

Lyman-alpha Imaging of a Very Luminous z=2.3 Starburst Galaxy with WFPC2

We investigate a very luminous Lyman-alpha emitting galaxy, associated with a z=2.3 damped absorption system in the spectrum of the QSO PHL 957. The galaxy was observed with the HST WFPC2, through a narrow filter (F410M) corresponding to rest-frame Lyman -alpha, for 41.2 ksec, with shorter exposures in F555W and F814W. The galaxy is resolved into a close (0.35 arcsec) pair of two components, CFgA and CFgB. The profile of CFgA is consistent with an exponential disk, but CFgB is closer to a bulge galaxy. Fr om the observed colours we estimate rest-frame Lyman-alpha equivalent widths of 151 Angstroms for CFgA and 33 for CFgB. From the F814W and F555W magnitudes we estimate rest-frame blue-band absolute magnitudes of -23.12 for CFgA and -23.24 for CFgB, signi ficantly brighter than local galaxies of the same size. CFgA shows a remarkable 3.9 magnitudes of surface brightness enhancement relative to local spirals, and we speculate that this may be the result of a very luminous starburst, triggered by the merger of the two components. The Lyman-alpha emission could be from a brief phase early in the starburst in which most of these photons can escape. We search for other z=2.3 galaxies with strong Lyman-alpha emission, selecting these by a colour F410M-F555W<-0.2. Eight candidate sources, all fainter than CFgA, are identified. One is a point-source and may be an AGN; the others are irregular a nd of low surface brightness, appearing typical of Lyman break galaxies, but with Lyman-alpha equivalent widths near 100 Angstroms.

astro-ph↗
arXiv1999

STIS Coronagraphic Observations of Beta Pictoris

We present new coronagraphic images of Beta Pictoris obtained with the Space Telescope Imaging Spectrograph (STIS) in September 1997. The high-resolution images (0.1") clearly detect the circumstellar disk as close as 0.75" to the star, corresponding to a projected radius of 15 AU. The images define the warp in the disk with greater precision and at closer radii to Beta Pic than do previous observations. They show that the warp can be modelled by the projection of two components: the main disk, and a fainter component, which is inclined to the main component by 4-5 degrees, and which extends only as far as ~4" from the star. We interpret the main component as arising primarily in the outer disk and the tilted component as defining the inner region of the disk. The observed properties of the warped inner disk are inconsistent with a driving force from stellar radiation. However, warping induced by the gravitational potential of one or more planets is consistent with the data. Using models of planet-warped disks constructed by Larwood and Papaloizou (1997), we derive possible masses of the perturbing object.

astro-ph↗
arXiv1999

Emission-Line Properties of the LMC Bubble N70

We present a spectrophotometric imaging study of the emission bubble N70 (DEM 301) in the Large Magellanic Cloud. N70 is approximately 100 pc in size with a nearly circular shell-like morphology. The nebular emission is powered by an uncertain combination of EUV photons, intense winds, and supernova shock waves from the central population of high-mass stars (the OB association LH 114). We have obtained narrow-band images (FWHM~6A) of N70 in the light of H-alpha (6563A), [N II] (6584A), [S II] (6717,6731A), and [O III] (5007A) along with the corresponding red and green continua. The resulting line fluxes and flux ratios are used to derive ionization rates, nebular densities, volume filling fractions, and excitation indices. Comparison with similar spectrophotometry of the Orion nebula indicates that the outer shell of N70 is especially enhanced in [SII] emission compared to its H-alpha and [N II] emission. The measured intensity ratios in N70 more closely match the range of excitation spanned by giant and supergiant H II shells and even by some of the supernova remnants observed in the LMC. From these spectral diagnostics, we conclude that EUV photons probably contribute most of the inner nebula's ionization, whereas a combination of photoionization plus collisional ionization and excitation of sulfur atoms by low-velocity shocks is driving the emission-line luminosities and intensity ratios observed in the outer shell. Considerations of the radiative and mechanical energetics that are involved may indicate the need for one or two supernova explosions having occurred during the last ~Myr.

astro-ph↗
arXiv1995

A Group of Galaxies at Redshift 2.38

We report the discovery of a group of galaxies at redshift 2.38. We imaged about 10% of a claimed supercluster of QSO absorption-lines at z=2.38 (Francis & Hewett 1993). In this small field (2 arcmin radius) we detect two Ly-alpha emitting galaxies. The discovery of two such galaxies in our tiny field supports Francis & Hewett's interpretation of the absorption-line supercluster as a high redshift "Great Wall". One of the Ly-alpha galaxies lies 22 arcsec from a background QSO, and may be associated with a multi-component Ly-alpha absorption complex seen in the QSO spectrum. This galaxy has an extended (50kpc) lumpy Ly-alpha morphology, surrounding a compact IR-bright nucleus. The nucleus shows a pronounced break in its optical-UV colors at about 4000 A (rest-frame), consistent with a stellar population of mass about 7E11 solar masses, an age of more than 500 Myr, and little on-going star-formation. C IV emission is detected, suggesting that a concealed AGN is present. Extended H-alpha emission is also detected; the ratio of Ly-alpha flux to H-alpha is abnormally low (about 0.7), probable evidence for extended dust. This galaxy is surrounded by a number of very red (B-K>5) objects, some of which have colors suggesting that they too are at z=2.38. We hypothesize that this galaxy, its neighbors and a surrounding lumpy gas cloud may be a giant elliptical galaxy in the act of bottom-up formation.

astro-ph↗