Are you E. M. Malumuth?

Claim your profile

Publications (115)141.07 Total impact

  • Source
    Sara R. Heap, D. Lindler, E. Malumuth
    [Show abstract] [Hide abstract]
    ABSTRACT: I Zw 18 is one of the most primitive blue, compact dwarf galaxies. The ionized gas in I Zw 18 has a low oxygen abundance (O 1/30 Osun) and nitrogen abundance (N 1/100 Nsun) (Pequignot 2008). We have obtained a far-UV spectrum of the northwest massive star cluster of I Zw 18 using Hubble's Cosmic Origins Spectrograph (COS). The spectrum is compatible with continuous star-formation over the past 10 Myr, and a very low metallicity, log Z/Zsun -1.7, although the stellar surface may be enhanced in carbon. Stellar wind lines are very weak, and the edge velocity of wind lines is very low ( 250 km/s).
    01/2011;
  • [Show abstract] [Hide abstract]
    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.
    07/2010;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Detector Characterization Laboratory at NASA/GSFC has investigated the reciprocity failure characteristics of 1.7mum cut-off HgCdTe devices provided by Teledyne Imaging Sensors to the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) project. The reciprocity failure follows a power law behavior over the range of fluxes tested (0.1-104 photons/second). The slope of the power law varies among detectors, ranging from ~0.3-1%/dex at 1.0mum, which is much smaller than the ~6%/dex effect observed with the HST NICMOS 2.5mum cut-off detectors. In addition, the reciprocity failure exhibits no wavelength dependence, although only a restricted range of wavelengths (0.85-1.0mum) has been explored to date. Despite its relatively small magnitude, reciprocity failure is nevertheless an important effect in the calibration of WFC3 data, as well as in other applications in which there is a large difference in flux between the photometric standards and the scientific sources of interest.
    Proc SPIE 07/2010;
  • Source
    [Show abstract] [Hide abstract]
    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; · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    01/2010;
  • [Show abstract] [Hide abstract]
    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.
    01/2010;
  • Source
    [Show abstract] [Hide abstract]
    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.
    Proc SPIE 08/2009;
  • Source
    [Show abstract] [Hide abstract]
    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
    Proc SPIE 06/2009;
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
    12/2008; 41:239.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have obtained optical long-slit spectroscopy of the nucleus of M32 using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. The stellar rotation velocity and velocity dispersion, as well as the full line-of-sight velocity distribution (LOSVD), were determined as a function of position along the slit using two independent spectral deconvolution algorithms. We see three clear kinematical signatures of the nuclear black hole: a sudden upturn, at ~03 from the center, in the stellar velocity dispersions; a flat or rising rotation curve into the center; and strong, non-Gaussian wings on the central LOSVD. The central velocity dispersion is ~130 km s-1 (Gaussian fit) or 175 km s-1 (corrected for the wings). The central kinematics are consistent with the presence of a supermassive compact object in M32 with a mass in the range × 106 M☉.
    The Astrophysical Journal 12/2008; 550(2):668. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the environment of the nearest Herbig Ae star, HD 104237, with a multiwavelength combination of optical coronagraphic, near-IR, and mid-IR imaging supported by optical, UV, and far-ultraviolet spectroscopy. We confirm the presence of T Tauri stars associated with the Herbig Ae star HD 104237, noted by Feigelson et al. We find that two of the stars within 15'' of HD 104237 have IR excesses, potentially indicating the presence of circumstellar disks, in addition to the Herbig Ae star itself. We derive a new spectral type of A7.5Ve-A8Ve for HD 104237 and find log(L/L☉) = 1.39. With these data, HD 104237 has an age of t ≈ 5 Myr, in agreement with the estimates for the other members of the association. HD 104237 is still actively accreting, with a conspicuous UV/far-UV excess seen down to 1040 Å, and is driving a bipolar microjet termed HH 669. This makes it the second, older Herbig Ae star now known to have a microjet. The presence of the microjet enables us to constrain the circumstellar disk to r ≤ 06 (70 AU) with an inclination angle of i = 18 from pole-on. The absence of a spatially extended continuum and fluorescent H2 emission near Lyα is in agreement with the prediction of shadowed disk models for the IR spectral energy distribution. With the high spatial density of disks in this group of stars, proximity, and minimal reddening, HD 104237 and its companions should serve as ideal laboratories for probing the comparative evolution of planetary systems.
    The Astrophysical Journal 12/2008; 608(2):809. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Spitzer Proposal. 03/2008;