E. M. Malumuth

NASA, Вашингтон, West Virginia, United States

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Publications (81)106.7 Total impact

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    ABSTRACT: ACCESS, Absolute Color Calibration Experiment for Standard Stars, is a series of rocket-borne sub-orbital missions and ground-based experiments designed to enable improvements in the precision of the astrophysical flux scale through the transfer of absolute laboratory detector standards from the National Institute of Standards and Technology (NIST) to a network of stellar standards with a calibration accuracy of 1% and a spectral resolving power of 500 across the 0.35-1.7 μm bandpass. Establishing improved spectrophotometric standards is important for a broad range of missions and is relevant to many astrophysical problems. Systematic errors associated with problems such as dark energy now compete with the statistical errors and thus limit our ability to answer fundamental questions in astrophysics. The ACCESS payload and ground calibration components currently span a range of readiness levels extending from the design phase, through procurement, fabrication, and component test phases. The strategy for achieving a <1% spectrophotometric calibration accuracy, a description and status of the instrument and the ground calibration system, and the NIST traceability components are discussed.
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    ABSTRACT: We compare mid-infrared emission-line properties, from high-resolution Spitzer spectra of a hard X-ray (14 -- 195 keV) selected sample of nearby (z < 0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89 micron, [Ne II] 12.81 micron, [Ne III] 15.56 micron and [Ne V] 14.32/24.32 micron, and hard X-ray continuum show no differences between Seyfert 1 and Seyfert 2 populations, however six newly discovered BAT AGNs are under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The overall tightness of the mid-infrared correlations and BAT fluxes and luminosities suggests that the emission lines primarily arise in gas ionized by the AGN. We also compare the mid-infrared emission-lines in the BAT AGNs with those from published studies of ULIRGs, PG QSOs, star-forming galaxies and LINERs. We find that the BAT AGN sample fall into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] ratios. These line ratios are lower in sources that have been previously classified in the mid-infrared/optical as AGN than those found for the BAT AGN, suggesting that, in our X-ray selected sample, the AGN represents the main contribution to the observed line emission. These ratios represent a new emission line diagnostic for distinguishing between AGN and star forming galaxies. Comment: 54 pages, 9 Figures. Accepted for publication in The Astrophysical Journal.
    The Astrophysical Journal 04/2010; DOI:10.1088/0004-637X/716/2/1151 · 6.28 Impact Factor
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    ABSTRACT: We compare mid-IR emission-lines properties, from high-resolution Spitzer IRS spectra,of a statistically-complete hard X-ray (14-195 keV) selected sample of nearby (z < 0.05) AGN detected by the Burst Alert Telescope (BAT) aboard Swift. The luminosity distribution for the mid-infrared emission-lines, [O IV] 25.89 mum, [Ne II] 12.81mum , [Ne III] 15.56 mum and [Ne V] mum, and hard X-ray show no differences between Seyfert 1 and Seyfert 2 populations, although six newly discovered BAT AGN are shown to be under-luminous in [O IV], most likely the result of dust extinction in the host galaxy. The correlations between all the mid-infrared emission lines and BAT luminosities are statistically significant. The mid-infrared emission line fluxes are highly correlated, with the worst correlations for [Ne V]-[Ne II] and [O IV]-[Ne II], as a result of enhanced [Ne II] in some sources due to nuclear stellar activity, however the tightness of these mid-infrared correlations suggests that the emission lines primarily arise in gas ionized by the AGN. We also compared the mid-IR emission-lines in the BAT AGNs with those from published studies of star-forming galaxies and LINERs. We found that [Ne III] an [O IV] lines do not unambiguously identify AGNs as stand-along diagnostics, however the BAT AGNs fall into a distinctive region when comparing the [Ne III]/[Ne II] and the [O IV]/[Ne III] quantities. While it is likely that detection of [Ne V] indicates the presence of an AGN, the [Ne V] line is weak compared to [O IV] and may not be detected in weak AGN. We suggest that a composite method using [Ne II], [Ne III], and [O IV] provides a more robust diagnostic.
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    ABSTRACT: We present the full low-resolution (60 < R < 127) and high-resolution (R 600) spectra of five active galactic nuclei (AGN) taken with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The sample was selected from the Swift BAT AGN catalog, derived from a hard X-ray (14-195 keV), all-sky mosaic. This nearly unbiased catalog can detect all but the most Compton thick AGN (NH >1024 cm -2) which will be obscured in this energy regime. The AGN studied are NGC 4395 (z=0.001064), NGC 4102 (z=0.002823), ESO 005 G004 (z=0.006228), UGC 06728 (z=0.006518), and MCG -05-23-016 (z=0.008486) representing the nearest of the 9-month BAT AGN catalog objects with no previous Spitzer IRS observations. We model the continuum IR flux of these objects using XSPEC, a software package primarily used to model X-ray spectra. Our modeling demonstrates a great variety of spectral shapes even in this small sample. Future work will combine our IR data with multi-wavelength photometry in order to isolate the AGN component of the IR flux from the host galaxy light. These five objects are the first of 65 without previous IRS spectra to be analyzed in this ongoing research.
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    ABSTRACT: In ground testing of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3), the CCDs of its UV/visible channel exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. The QEH first manifested itself as an occasionally observed contrast in response across the format of the CCDs, with an amplitude of typically 0.1-0.2% or less at the nominal -83°C operating temperature, but with contrasts of up to 3-5% observed at warmer temperatures. The behavior has been replicated in the laboratory using flight spare detectors and has been found to be related to an initial response deficiency of ~5% amplitude when the CCDs are cooled with no illumination. A visible light flat-field (540nm) with a several times full-well signal level is found to pin the detector response at both optical (600nm) and near-UV (230nm) wavelengths, suppressing the QEH behavior. We have characterized the timescale for the detectors to become unpinned (days for significant response loss at -83°C and have developed a protocol to stabilize the response in flight by flashing the WFC3 CCDs with the instrument's internal calibration system.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2009; DOI:10.1117/12.828439 · 0.20 Impact Factor
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    ABSTRACT: A technique involving ^{55}Fe X-rays provides a straightforward method to measure the response of a detector. The detector's response can lead directly to a calculation of the conversion gain (e^- ADU^{-1}), as well as aid detector design and performance studies. We calibrate the ^{55}Fe X-ray energy response and pair production energy of HgCdTe using 8 HST WFC3 1.7 \micron flight grade detectors. The results show that each K$\alpha$ X-ray generates 2273 \pm 137 electrons, which corresponds to a pair-production energy of 2.61 \pm 0.16 eV. The uncertainties are dominated by our knowledge of the conversion gain. In future studies, we plan to eliminate this uncertainty by directly measuring conversion gain at very low light levels. Comment: 17 pages, 7 Figures, 2 Table. Accepted for publication on PASP
    Proceedings of SPIE - The International Society for Optical Engineering 06/2009; DOI:10.1086/605131 · 0.20 Impact Factor
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    ABSTRACT: We present optical long-slit spectroscopy of the nucleus of the nearby radio galaxy M84 (NGC 4374 = 3C 272.1) obtained with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Our spectra reveal that the nuclear gas disk seen in the Wide Field Planetary Camera 2 imaging by Bower et al. is rotating rapidly. The velocity curve has an S-shape with a peak amplitude of 400 km s−1 at 01 = 8 pc from the nucleus. To model the observed gas kinematics, we construct a thin Keplerian disk model that fits the data well if the rotation axis of the gas disk is aligned with the radio jet axis. These models indicate that the gasdynamics are driven by a nuclear compact mass of 1.5 × 109 M☉ with an uncertainty range of (0.9-2.6) × 109 M☉, and that the inclination of the disk with respect to the plane of the sky is 75°-85°. Of this nuclear mass, only ≤2 × 107 M☉ can possibly be attributed to luminous mass. Thus, we conclude that a dark compact mass (most likely a supermassive black hole) resides in the nucleus of M84.
    The Astrophysical Journal 01/2009; 492(2):L111. DOI:10.1086/311109 · 6.28 Impact Factor
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    ABSTRACT: The installation of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) allows for the first time two-dimensional optical and ultraviolet slitless spectroscopy of faint objects from space. The STIS Parallel Survey (SPS) routinely obtains broadband images and slitless spectra of random fields in parallel with HST observations using other instruments. The SPS is designed to study a wide variety of astrophysical phenomena, including the rate of star formation in galaxies at intermediate to high redshift through the detection of emission-line galaxies. We present the first results of the SPS, which demonstrate the capability of STIS slitless spectroscopy to detect and identify high-redshift galaxies.
    The Astrophysical Journal 01/2009; 492(2):L99. DOI:10.1086/311105 · 6.28 Impact Factor
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    ABSTRACT: The Space Telescope Imaging Spectrograph (STIS) was successfully installed into the Hubble Space Telescope (HST) in 1997 February, during the second HST servicing mission, STS-82. STIS is a versatile spectrograph, covering the 115-1000 nm wavelength range in a variety of spectroscopic and imaging modes that take advantage of the angular resolution, unobstructed wavelength coverage, and dark sky offered by the HST. In the months since launch, a number of performance tests and calibrations have been carried out and are continuing. These tests demonstrate that the instrument is performing very well. We present here a synopsis of the results to date.
    The Astrophysical Journal 01/2009; 492(2):L83. DOI:10.1086/311102 · 6.28 Impact Factor
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    ABSTRACT: We present the first results of a survey of random fields with the slitless G141 (λc = 1.5 μm, Δλ = 0.8 μm) grism on the near-IR camera and multiobject spectrometer (NICMOS) on board the Hubble Space Telescope (HST). Approximately 64 arcmin2 have been observed at intermediate and high Galactic latitudes. The 3 σ limiting line and continuum fluxes in each field vary from 7.5 × 10-17 to 1 × 10-17 ergs cm-2 s-1, and from H = 20 to 22, respectively. Our median and area-weighted 3 σ limiting line fluxes within a 4 pixel aperture are nearly identical at 4.1 × 10-17 ergs cm-2 s-1 and are 60% deeper than the deepest narrowband imaging surveys from the ground. We have identified 33 emission-line objects and derive their observed wavelengths, fluxes, and equivalent widths. We argue that the most likely line identification is Hα and that the redshift range probed is from 0.75 to 1.9. The 2 σ rest-frame equivalent width limits range from 9 to 130 Å, with an average of 40 Å. The survey probes an effective comoving volume of 105 h-350 Mpc3 for q0 = 0.5. Our derived comoving number density of emission-line galaxies in the range 0.7 < z < 1.9 is 3.3 × 10-4 h350 Mpc-3, very similar to that of the bright Lyman break objects at z ~ 3. The objects with detected emission lines have a median F160W magnitude of 20.4 (Vega scale) and a median Hα luminosity of 2.7 × 1042 ergs s-1. The implied star formation rates range from 1 to 324 M☉ yr-1, with an average [N II] λλ6583, 6548 corrected rate of 21 M☉ yr-1 for H0 = 50 km s-1 Mpc and q0 = 0.5 (34 M☉ yr-1 for q0 = 0.1).
    The Astrophysical Journal 01/2009; 520(2):548. DOI:10.1086/307491 · 6.28 Impact Factor
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    ABSTRACT: We present our preliminary results of the analysis of Spitzer observations of the first unbiased AGN sample of the local universe. High column densities of absorbing material along our line of sight can significantly change the observed properties of AGNs. Thus, optical, infrared, and soft X-ray selected samples are hampered by extinction, star formation and absorption, respectively. Therefore an unbiased sample of AGNs is important to investigate the "hidden" nature of the nuclear source. The swift BAT survey in the 14-195 keV band represents a complete sample including Compton thin and previously unknown or non-famous AGNs that were missed from previous X-ray surveys in the 2-10 keV band. Our BAT AGN sample contains 130 objects (z < 0.05 and |b| >15 degrees) that have been observed with the Infrared Spectrograph (IRS) on board Spitzer (Spitzer observer proposal 30745 and 50588; PI: K.A. Weaver). This statistically significant unbiased AGN sample and the richness of the infrared spectrum provides a unique opportunity to test our understanding of AGN unification, classification and evolution in general. Strong polycyclic aromatic hydrocarbon (PAH) emission features at 6.2 and 11.25, and low ionization emission lines such as [Ne II] 12.81 are good indicators of stellar activity. On the other hand, high ionization emission lines such as [O IV] 25.89, [Ne III] 15.51 and [Ne V] 14.32,24.32 can be associated with the AGN. The line ratios between the high- and low-ionization emission lines can be used to measure the relative dominance of the AGN and to investigate the ionization state of the emission-line gas. We present the preliminary infrared spectra of our X-ray selected sample, different correlations and implication to the AGN classification and evolution.
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    ABSTRACT: We present candidate quasars from a multicolor (uBVRI + narrowband) imaging survey of square degree around the Hubble Deep Field-South (HDF-S). We identify 154 candidate quasars with B < 23 using color selection, consistent with previously measured QSO number counts if we assume a 60% selection efficiency. The narrowband filter (NB) was centered at 3958 Å to detect Lyα at the redshift of J2233-6033, the HDF-S QSO. We confirm the presence of Lyα nebulosity extending ~12'' around the HDF-S QSO, reported by Bergeron and coworkers. We detect 10 pointlike objects in emission through the NB filter. Of these, seven satisfy our QSO color selection criteria. One of the emission-line objects is a B ~ 20 radio-quiet quasar at z = 1.56, 67 from the line of sight to the HDF-S QSO and ~12'' from the western edge of the WFPC2 deep field.
    The Astrophysical Journal 12/2008; 541(1):61. DOI:10.1086/309434 · 6.28 Impact Factor
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    ABSTRACT: We have obtained new Hubble Space Telescope observations of M84, a nearby massive elliptical galaxy whose nucleus contains a ≈1.5 × 109 M☉ dark compact object, which presumably is a supermassive black hole. Our Space Telescope Imaging Spectrograph spectrum provides the first clear detection of emission lines in the blue (e.g., [O II] λ3727, Hβ, and [O III] λλ4959, 5007), which arise from a compact region ≈028 across centered on the nucleus. Our Near-Infrared Camera and Multiobject Spectrometer images exhibit the best view through the prominent dust lanes evident at optical wavelengths and provide a more accurate correction for the internal extinction. The relative fluxes of the emission lines we have detected in the blue together with those recently detected in the wavelength range 6295-6867 Å by Bower et al. indicate that the gas at the nucleus is photoionized by a nonstellar process instead of hot stars. Stellar absorption features from cool stars at the nucleus are very weak. We update the spectral energy distribution of the nuclear point source and find that although it is roughly flat in most bands, the optical-to-UV continuum is very red, similar to the spectral energy distribution of BL Lac. Thus, the nuclear point source seen in high-resolution optical images by Bower et al. is not a star cluster but is instead a nonstellar source. Assuming isotropic emission from this source, we estimate that the ratio of bolometric luminosity to Eddington luminosity is ~5 × 10-7. However, this could be underestimated if this source is a misaligned BL Lac object, which is a possibility suggested by the spectral energy distribution and the evidence of optical variability we describe.
    The Astrophysical Journal 12/2008; 534(1):189. DOI:10.1086/308741 · 6.28 Impact Factor
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    ABSTRACT: We present a luminosity function for Hα emission from galaxies at redshifts between 0.7 and 1.9 based on slitless spectroscopy with the near-infrared camera and multiobject spectrometer on the Hubble Space Telescope. The luminosity function is well fit by a Schechter function over the range 6 × 1041 < L41 < 2 × 1043 ergs s-1 with L* = 7 × 1042 ergs s-1 and * = 1.7 × 10-3 Mpc-3 for H0 = 50 km s-1 Mpc-1 and q0 = 0.5. We derive a volume-averaged star formation rate at z = 1.3 ± 0.5 of 0.13 M☉ yr-1 Mpc-3 without correction for extinction. The star formation rate that we derive at ~6500 Å is a factor of 3 higher than that deduced from 2800 Å continua. If this difference is caused entirely by reddening, the extinction correction at 2800 Å is quite significant. The precise magnitude of the total extinction correction at rest-frame UV wavelengths (e.g., 2800 and 1500 Å) is sensitive to the relative spatial distribution of the stars, gas, and dust, as well as to the extinction law. In the extreme case of a homogeneous foreground dust screen and a Milky Way or LMC extinction law, we derive a total extinction at 2800 Å of 2.1 mag, or a factor of 7 correction to the UV luminosity density. If we use the Calzetti reddening curve, which was derived for the model in which stars, gas, and dust are well mixed and nebular gas suffers more extinction than stars, our estimate of A2800 is increased by more than 1 mag.
    The Astrophysical Journal 12/2008; 519(1):L47. DOI:10.1086/312099 · 6.28 Impact Factor
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    ABSTRACT: We present Hubble Space Telescope and ground-based observations of a pair of galaxies at a redshift of 2.38, which are collectively known as 2142-4420 B1. Both galaxies are luminous extremely red objects (EROs) and are separated by 08. They are embedded within a 100 kpc scale diffuse Lyα nebula (or blob) of luminosity ~1044 ergs s-1. The radial profiles and colors of both red objects are most naturally explained if they are young elliptical galaxies, the most distant galaxies of this type found to date. It is not possible, however, to rule out a model in which they are abnormally compact, extremely dusty starbursting disk galaxies. If they are elliptical galaxies, their stellar populations have inferred masses of ~1011 M☉ and ages of ~7 × 108 yr. Both galaxies have color gradients: their centers are significantly bluer than their outer regions. The surface brightness of both galaxies is roughly 1 order of magnitude greater than would be predicted by the Kormendy relation. A chain of diffuse star formation extending 1'' from the galaxies may be evidence that they are interacting or merging. The Lyα nebula surrounding the galaxies shows apparent velocity substructure of amplitude ~700 km s-1. We propose that the Lyα emission from this nebula may be produced by fast shocks that are powered either by a galactic superwind or by the release of gravitational potential energy.
    The Astrophysical Journal 12/2008; 554(2):1001. DOI:10.1086/321417 · 6.28 Impact Factor
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    ABSTRACT: Active galactic nuclei (AGNs) have been a major focus of extragalactic astronomy for decades, but because of obscuration effects, virtually all surveys for AGN based purely on optical, IR, UV or soft X-ray data have been highly biased in their selection (cf. Mushotzky 2004). Thus, to truly understand the intrinsic nature of AGN as a class, it is critical to start with an unbiased hard X-ray survey. This critical, unbiased hard X-ray survey is now available from the SWIFT Burst Alert Telescope (BAT). The BAT detects all bright AGN, whether they are obscured or not, and thus will find famous classical objects as well as previously unknown AGN. In fact, many of the BAT sources are newly discovered AGN, which have been poorly studied, if at all, at other wavelengths. We have found that these 'new' AGN are under-luminous in their IR properties compared to classic AGN and thus IR-selected samples have not been representative. Our IR-weak AGN may be the most heavily obscured ones. Completing the BAT sample is critical to obtain a complete, unbiased sample of AGN properties based on hard X-ray data and to understand this new IR-under-luminous class. These data will become an invaluable addition to the Spitzer archive. Statistical conclusions drawn from classical objects are almost certain to be wrong due to inherent biases in their selection, which exclude this sample of severely absorbed, BAT-detected AGN.
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    ABSTRACT: High-energy particles that induce a glow on the ZnCdTe substrate of the HgCdTe detectors of WFC3 may increase the background noise and reduce the scientific performance of the instrument. To eliminate this problem, a second generation of infrared detectors with substrate removed is under construction. Early tests indicate that the glow problem is eliminated and the quantum efficiency increases dramatically at shorter wavelengths, potentially providing a substantial improvement in the limiting sensitivity of the instrument.
    12/2005: pages 193-198;
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    ABSTRACT: We present the performance of the IR detectors developed for the WFC3 project. These are HgCdTe 1Kx1K devices with cutoff wavelength at 1.7 mum and 150K operating temperature. The two selected flight parts, FPA#64 (prime) and FPA#59 (spare) show quantum efficiency higher than 80% at lambda=1.6 mum and greater than 40% at lambda>1.1mum, readout noise of ~25 e- rms with double correlated sampling, and mean dark current of ~0.04 e/s/pix at 150K. We also report the results obtained at NASA GSFC/DCL on these and other similar devices in what concerns the QE long-term stability, intra-pixel response, and dark current variation following illumination or reset.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2004; DOI:10.1117/12.551807 · 0.20 Impact Factor
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    ABSTRACT: Wide Field Camera 3 is a fourth generation instrument for the Hubble Space Telescope (HST), to be installed during the next HST Servicing Mission 4. For its infrared channel Rockwell Scientific Company has developed a new type of HgCdTe 1Kx1K detector, called WFC3-1R, with cutoff wavelength at 1.7mum and 150K operating temperature. The WFC3-IR detectors are based on HgCdTe MBE grown on a CdZnTe substrate and use a new type of multiplexer, the Hawaii-1R MUX. Two flight detectors, a prime and a spare, have been recently selected on the basis of the measures performed at NASA Goddard Research Center - Detector Characterization Laboratory. These parts show quantum efficiency higher than 80% at lambda=1.6mum and greater than 40% at lambda>1.1mum, readout noise of ~25 e- rms with double correlated sampling, and mean dark current of ~0.04 e/s/pix at 150K. We show that the IR channel of WFC3, equipped with one of these flight detectors, beats the instrument requirements in all configurations and promises to have a discovery efficiency significantly higher than NICMOS. In particular, a two-band wide-area, deep survey made with WFC3 exceeds the discovery efficiency of NICMOS before and after the installation of NCS by a factor of 15 and 10, respectively.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2004; DOI:10.1117/12.507334 · 0.20 Impact Factor
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    ABSTRACT: Detector performance has been characterized for the HST WFC3 IR channel. This will be the first TEC cooled IR instrument on the Hubble Space Telescope (HST), which is made possible because of recent progress in HgCdTe technology. The original detector requirements are compared with the performance of the delivered devices. Achievements in quantum efficiency and dark current are described, as well as difficulties in meeting requirements for noise and dark stability. A special technique developed to illuminate a single pixel, which has demonstrated the excellent spatial resolution of the detectors is described.
    12/2003: pages 175-182;