G. J. Stacey

University of Lethbridge, Lethbridge, Alberta, Canada

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Publications (222)336.83 Total impact

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    ABSTRACT: Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg2 in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities 1024 cm-2 and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg-2 detected in the infrared in the Chandra/SWIRE field, of which ~40% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only ~33% of all Compton-thick AGNs are detected in the X-rays at our depth [F(0.3-8 keV) > 10-15 ergs cm-2 s-1]. We report the discovery of two sources in our sample of Compton-thick AGNs, SWIRE J104409.95+585224.8 (z = 2.54) and SWIRE J104406.30+583954.1 (z = 2.43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.
    The Astrophysical Journal 12/2008; 642(2):673. · 6.28 Impact Factor
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    ABSTRACT: We report the first detection of the 205 μm 3P1 P0 [N II] line from a ground-based observatory using a direct detection spectrometer. The line was detected from the Carina star formation region using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) on the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at the South Pole. The [N II] 205 μm line strength indicates a low-density (n ~ 32 cm-3) ionized medium, similar to the low-density ionized halo previously reported in its [O III] 52 and 88 μm line emission. When compared with the Infrared Space Observatory [C II] observations of this region, we find that 27% of the [C II] line emission arises from this low-density ionized gas, but the large majority (~73%) of the observed [C II] line emission arises from the neutral interstellar medium. This result supports and underpins prior conclusions that most of the observed [C II] 158 μm line emission from Galactic and extragalactic sources arises from the warm, dense photodissociated surfaces of molecular clouds. The detection of the [N II] line demonstrates the utility of Antarctic sites for THz spectroscopy.
    The Astrophysical Journal 12/2008; 652(2):L125. · 6.28 Impact Factor
  • Thomas Nikola, Gordon J. Stacey, C. Matt Bradford
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    ABSTRACT: We present a trade study for a submillimeter direct-detection spectrometer operating at the background limit for the Cornell Caltech Atacama Telescope (CCAT). In this study we compare the classical echelle spectrometer ZEUS with the waveguide grating spectrometer Z-Spec. The science driver for this instrument is spectroscopic investigation of high redshift galaxies as their far-IR fine structure line emission is redshifted into the telluric submillimeter windows. The baseline detector consists of SQUID multiplexed TES bolometers and the ideal spectrometer to detect weak lines from distant extragalactic sources is a grating with a resolution of ~103 and a large bandwidth, covering an entire telluric submillimeter window instantaneously. Since the density of high-z sources on the sky is ~100 within a 10'×10' field of view and a redshift range of Deltaz~0.2 we also explore multi-object (~50 objects) capability, including articulated mirrors and flexible waveguide fibers.
    Proceedings of SPIE - The International Society for Optical Engineering 08/2008; · 0.20 Impact Factor
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    ABSTRACT: We propose to accurately trace molecular gas excitation and mass along the plane of the two nearby nearby edge-on spiral galaxies, NGC 4905 and 5907 through deep IRS spectroscopy of four pure rotational lines (S(3), S(2), S(1), and S(0)) of H2. Our primary goal is to investigate the physical state, mass, and heating processes in the molecular ISM in these galaxies, and compare them with our on-going study of the edge-on galaxy NGC 891. Prior modeling of the S(1) and S(0) emission from NCG 891 suggests an enormous amount of cool (T< 90K) H2 (5 to 15 times the atomic mass) for this galaxy if the ortho to para H2 ratio is 3. However, these models are hampered by the degeneracy between gas excitation and the (assumed) o/p ratio. Including the S(3) and S(2) lines in the analysis breaks the degeneracy, enabling independent determination of gas excitation for the ortho and para species, and a measure of the o/p ratio. Using three lines (S(2), S(1), and S(0)) for NGC 891, we find gas excitation near 220 K, with an o/p ratio near unity, resulting in greatly reduced molecular gas mass. We were awarded time in Cycle 4 to verify this model through deeper integrations of the S(0), S(1), and S(2) lines, and observations of the S(3) line in NGC 891. {These observations have not yet been scheduled}. Here we propose to extend our study by mapping all four lines in the disks of galaxies with different gas contents than NGC 891: the early type Sb NGC 4565 and the late type Sc NGC 5907. We are particularly intrigued with the regions outside of the CO emitting disk where the gas is likely not heated in a PDR scenario but rather by modest velocity cloud-cloud collisions in the outer galaxy. The proposed observations address the heating source as the ortho and para ratio depends on the formation temperature: a larger ratio indicates a larger formation temperature. Did H2 form in a relatively warm far-UV bathed environment near stars, or in a cold environment devoid of young stars?
    Spitzer Proposal. 03/2008;
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    ABSTRACT: We report the first detection of a mid-J isotopic CO line from an external galaxy. We detected the 13CO (6-5) line from the starburst nucleus of NGC 253. The line is suprisingly bright with an integrated intensity 7% of the 12CO (6-5) line, indicating optical depth in the 12CO line. Our LVG modeling shows that a single warm (T ~ 120 K), dense (n ~ 104 cm-3) component emits most of the 12CO and 13CO line emission from J = 2-1 through J = 7-6. The CO(1-0) line comes from an additional lower excitation envelope. About 60% of the total molecular gas mass within 70 pc of the nucleus is in the warm, dense component. We show that stellar far-UV photons or X-ray photons from a nuclear source are unlikely to be the primary sources of the gas heating. The most likely sources of heat are cosmic rays from the nuclear starburst or microturbulence within molecular clouds.
    EAS Publications Series 01/2008; 31:151-154.
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    ABSTRACT: We report the detection of the 158 mum [CII] line from the LIR ˜ 1014 L&sun; galaxy FSC 10026+4949 at z = 1.12. This is the first detection of [CII] from the z = 1-3 epoch of enhanced starformation. The L[CII]/LFIR ratio is 1.3 × 10-3, larger than the ratio typically seen in local ULIRGs, but similar to that measured in normal and starburst galaxies. This high ratio implies that the UV fields powering the far-infrared emission are of only modest intensity, and that FSC 10026+4949 may be undergoing a galaxy-wide starburst.
    EAS Publications Series 01/2008; 31:159-162.
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    ABSTRACT: We report the detection of 13CO J=6-->5 emission from the nucleus of the starburst galaxy NGC 253 with the redshift (z) and Early Universe Spectrometer (ZEUS), a new submillimeter grating spectrometer. This is the first extragalactic detection of the 13CO J=6-->5 transition, which traces warm, dense molecular gas. We employ a multiline LVG analysis and find ~35%-60% of the molecular interstellar medium is both warm (T~110 K) and dense (nH2~104 cm-3). We analyze the potential heat sources and conclude that ultraviolet and X-ray photons are unlikely to be energetically important. Instead, the molecular gas is most likely heated by an elevated density of cosmic rays or by the decay of supersonic turbulence through shocks. If the cosmic rays and turbulence are created by stellar feedback within the starburst, then our analysis suggests the starburst may be self-limiting.
    The Astrophysical Journal 01/2008; 689. · 6.28 Impact Factor
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    ABSTRACT: The fine structure line of [CI] at 370 μm, and the CO (7→6) rotational line at 371 μm are important coolants which can be used to probe the temperature and density of the warm gas component in regions of enhanced star formation. These lines can be used to provide key constrains on the physical properties of the warm molecular gas component and to deduce the excitation mechanism that heats the molecular gas. We have used the Cornell submillimeter spectrometer, SPIFI, on the JCMT to map the [CI] and CO (7→6) line emission from the nuclear regions of the nearby galaxies NGC 253 and M82, and from the overlap region of NGC4038/9. In both NGC 253 and NGC 4038/9 the [CI] emission appears fairly constant, while the CO (7→6) emission peaks at the nucleus and the most active star-forming region, respectively. The observations of NGC 253 suggest that the majority of the nuclear molecular gas is most likely heated by cosmic rays. The spatial distribution of the line emission in the overlap region of NGC 4038/9 is suggestive of a PDR, with a decrease in density from the most active region to the outside. In contrast, in M82 both the CO (7→6) and [CI] line intensities vary over the mapped region, with the line ratios remaining fairly constant. This suggests a change in the beam filling factor of PDRs with a higher PDR number density in the most active regions.
    12/2007: pages 225-230;
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    ABSTRACT: We discuss optical associations, spectral energy distributions (SEDs), and photometric redshifts for Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey sources in the European Large-Area ISO Survey (ELAIS) N1 area and the Lockman Validation Field (VF). The band-merged Infrared Array Camera (IRAC) (3.6, 4.5, 5.8, and 8.0 mum) and Multiband Imaging Photometer for Spitzer (24, 70, and 160 mum) data have been associated with optical UgriZ data from the Isaac Newton Telescope Wide Field Survey in ELAIS N1 and with our own optical Ugri data in Lockman-VF. Criteria for eliminating spurious infrared sources and for carrying out star-quasar-galaxy separation are discussed, and statistics of the identification rate are given. Thirty-two percent of sources in the ELAIS N1 field are found to be optically blank (to r=23.5) and 16% in Lockman-VF (to r=25). The SEDs of selected ELAIS sources in N1 detected by SWIRE, most with spectroscopic redshifts, are modeled in terms of a simple set of galaxy and quasar templates in the optical and near-infrared (NIR), and with a set of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and active galactic nucleus [AGN] dust torus) in the mid-infrared. The optical data, together with the IRAC 3.6 and 4.5 mum data, have been used to determine photometric redshifts. For galaxies with known spectroscopic redshifts, there is a notable improvement in the photometric redshift when the IRAC data are used, with a reduction in the rms scatter from 10% in (1+z) to 7%. Although further spectroscopic data are needed to confirm this result, the prospect of determining good photometric redshifts for much of the SWIRE survey, expected to yield over 2 million extragalactic objects, is excellent. Some modifications to the optical templates were required in the previously uninvestigated wavelength region 2-5 mum. The photometric redshifts are used to derive the 3.6 and 24 mum redshift distribution and to compare this with the predictions of models. For those sources with a clear mid-infrared excess, relative to the galaxy starlight model used for the optical and NIR, the mid- and far-infrared data are modeled in terms of the same dust emission templates (cirrus, M82, Arp 220, and AGN dust torus). The proportions found of each template type are cirrus, 31%; M82, 29%; Arp 220, 10%; and AGN dust tori, 29%. The distribution of the different infrared SED types in the LIR/Lopt versus LIR plane, where LIR and Lopt are the infrared and optical bolometric luminosities, respectively, is discussed. There is an interesting population of luminous cool cirrus galaxies with LIR>Lopt, implying a substantial dust optical depth. Galaxies with Arp 220-like SEDs, of which there are a surprising preponderance compared with preexisting source count models, tend to have high ratios of infrared to optical bolometric luminosity, consistent with having very high extinction. There is also a high proportion of galaxies whose mid-infrared SEDs are fitted by an AGN dust torus template (29%). Of these only 8% of these are type 1 AGNs according to the optical-NIR template fitting, whereas 25% are fitted with galaxy templates in the optical-NIR and have LIR>Lopt and so have to be type 2 AGN. The remainder have LIR<Lopt and so can be Seyfert galaxies, in which the optical AGN fails to be detected against the light of the host galaxy. The implied dust covering factor, >=75%, is much higher than that inferred for bright optically selected quasars.
    The Astronomical Journal 12/2007; · 4.97 Impact Factor
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    ABSTRACT: We present mid-infrared maps and preliminary analysis for 61 galaxies observed with the ISOCAM instrument aboard the Infrared Space Observatory. Many of the general features of galaxies observed at optical wavelengths—spiral arms, disks, rings, and bright knots of emission—are also seen in the mid-infrared, except the prominent optical bulges are absent at 6.75 and 15 μm. In addition, the maps are quite similar at 6.75 and 15 μm, except for a few cases where a central starburst leads to lower Iν(6.75 μm)/Iν(15 μm) ratios in the inner region. We also present infrared flux densities and mid-infrared sizes for these galaxies. The mid-infrared color Iν(6.75 μm)/Iν(15 μm) shows a distinct trend with the far-infrared color Iν(60 μm)/Iν(100 μm). The quiescent galaxies in our sample [Iν(60 μm)/Iν(100 μm) 0.6] show Iν(6.75 μm)/Iν(15 μm) near unity, whereas this ratio drops significantly for galaxies with higher global heating intensity levels. Azimuthally averaged surface brightness profiles indicate the extent to which the mid-infrared flux is centrally concentrated, and provide information on the radial dependence of mid-infrared colors. The galaxies are mostly well resolved in these maps: almost half of them have <10% of their flux in the central resolution element. A comparison of optical and mid-infrared isophotal profiles indicates that the flux at 4400 Å near the optical outskirts of the galaxies is approximately 8 (7) times that at 6.75 μm (15 μm), comparable to observations of the diffuse quiescent regions of the Milky Way.
    The Astronomical Journal 12/2007; 120(2):583. · 4.97 Impact Factor
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    ABSTRACT: We present the analysis of Infrared Space Observatory long-wavelength spectrometer (LWS) observations of the two nearby late-type galaxies NGC 1313 and NGC 6946. Both galaxies have been fully mapped in the [C II] far-infrared fine-structure line at 158 μm, and some regions have been observed also in the [O I] 63 μm and [N II] 122 μm lines. We use these observations to derive the physical properties of the atomic interstellar medium, to establish how they relate to other interstellar medium components (gas and dust), and to establish how they vary with different galaxy components such as nucleus, spiral arms, and disk. The [C II] line is the main cooling line of the atomic medium. In NGC 6946 and NGC 1313, its emission represents 0.8% of the infrared emission. Moreover, the [C II] emission can be spatially associated with three components: the nucleus, the star-forming regions in spiral arms, and the diffuse galaxy disk. This last component contributes 40% in NGC 6946 and ~30% in NGC 1313 to the total emission. We apply the photodissociation region (PDR) model by Kaufman et al. to derive PDR physical parameters responsible for the neutral atomic gas emission (G0, n, and Ts). The results do not significantly differ from what Malhotra et al. recently found by modeling the integrated emission of a sample of 60 normal galaxies. This suggests that the emission in each region under the LWS beam in NGC 6946 and NGC 1313 (corresponding to a linear size of ~1.5 kpc) is likely to arise from a mixture of components similar to the mixture producing the integrated emission of normal galaxies. However, some regions in NGC 6946 have a G0/n ratio ~2–3 times smaller than the mean value found for the normal galaxy sample (1.3), suggesting that the beam-averaged contribution of a less active component in these regions is higher than its contribution in the integrated emission of normal galaxies or, conversely, that the bulk of the integrated emission of the normal galaxies is dominated by a few active regions probably located in their nuclei. CO(1–0) and [C II] in NGC 6946 are well correlated, and the mean [C II]/CO ratio agrees with the mean integrated ratios of the normal galaxies sample. This value (~500) is a factor of ~2 less than the mean ratio found for a sample of normal galaxies observed with the Kupier Airborne Observatory (KAO) by Stacey et al. This difference is probably due to the fact that the KAO beam (55'') is smaller than the LWS beam (75''), such that the Stacey et al. KAO observations are likely to be more biased toward the nucleus of the galaxies and therefore toward more active regions. In NGC 1313 only four LWS regions have been observed in CO(1–0), and three of them were detected. The [C II]/CO(1–0) seems to systematically increase from the northeast to the south, along the S-shaped spiral arm, indicating that the interstellar medium conditions in NGC 1313 are much more inhomogeneous than the conditions in NGC 6946. H I and [C II] in NGC 6946 are completely uncorrelated, probably because they arise from different gas components: [C II] arises principally in dense and warm PDR and H I from diffuse (n 3 × 103 cm-3) gas. On the other hand, in NGC 1313 we successfully detect two distinct gas components: a cirrus-like component, for which H I and [C II] are weakly correlated as observed in our Galaxy, and a component associated with dense PDRs completely uncorrelated from H I as observed in NGC 6946. Finally, we find that the H I residing in dense gas surrounding the star-forming regions and presumably recently photodissociated constitutes a few percent of the total H I. In turn, this dense gas component produces most of the [C II] emission emitted by the atomic neutral medium, even if its contribution is lower in NGC 1313 than in NGC 6946. On the other hand, the [C II] emission arising from ionized gas is higher in NGC 1313 than in NGC 6946.
    The Astronomical Journal 12/2007; 124(2):751. · 4.97 Impact Factor
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    ABSTRACT: The far-infrared and submillimeter regimes harbor significant numbers of strong lines useful as diagnostics of processes in the interstellar medium, regions of intense star formation, and AGN activity. Covering a decade or more in wavelength, many of them are emitted or redshifted to wavelengths where they are obscured by atmospheric absorption, and so airborne and space-based instruments must be used. Capable, sensitive detector arrays are needed for this; we have been developing such arrays based on multiplexed superconducting bolometers. At the present level of maturity, we have fielded a submillimeter spectrometer containing around ten detectors of the requisite sensitivity. In the coming months, new instruments will demonstrate up to of order 100 bolometers (e.g., 8× 16). We are working to implement over a thousand pixels in a single detector package. One application for such large arrays is the 100 μ m-655 μ m spectrometer SAFIRE on SOFIA. Future directions will be for space-based observatories such as SAFIR.
    09/2007; 375:217.
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    ABSTRACT: We propose to obtain deep IRS spectra of the outer disk of the nearby edge on spiral galaxy NGC 891. Our primary goal is to investigate the physical state, mass, and heating processes in the molecular ISM through investigations of four pure rotational lines of H2. Pioneering work in the S(0) and S(1) lines with ISO indicate large quantities of warm (T ~ 120 K) molecular clouds along the disk of the galaxy ? fully half of the cold H2 component traced in CO. Furthermore, the ISO results suggest vast quantities of cool (T 12 kpc) for cool molecular gas by deep integrations in the S(1) and S(0) lines. Finally, we plan a sparse map of most of the disk to detect the S(3) line using the Short-Lo spectrometer. The S(0), S(2), and S(1) and S(3) transitions constrain the excitation of para and ortho H2 respectively, and together yield the o/p ratio. The four lines will therefore solidly establish the mass of warm and cool molecular gas in NGC 891. Are there massive quantities of cool gas in the outer disks of galaxies?
    Spitzer Proposal. 05/2007;
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    ABSTRACT: We have obtained large scale, 1' resolution maps of the edge-on spiral galaxy NGC 891 in the 158 micron [CII] and CO(1 - 0) lines. The [CII] distribution largely follows the optical image, but is significantly asymmetric - there is a pronounced ridge of emission to the north. The CO(1 - 0) and 2.8 cm radio continuum are similarly asymmetric suggesting that the [CII] emission arises from both the UV exposed surfaces of giant molecular clouds and from the diffuse ionized medium. For low density media, we estimate 25% of the observed [CII] emission arises from ionized gas clouds. The HI 21 cm line emission bears little resemblance to the other tracers, along the major axis. Assuming "standard" atomic cloud parameters, only 15% of the observed [CII] intensity along the plane comes from the atomic medium. The remainder (60%) of the [CII] emission is associated with dense photodissociation regions (PDRs) on the surfaces of molecular clouds. The [CII]/CO(1 - 0) line intensity ratio for these regions is similar to Galactic molecular clouds, providing an important link between the molecular clouds in NGC 891 and the Milky Way. For the outer regions (r > 4 kpc) of NGC 891, most of the [CII] emission arises from atomic clouds with Galactic parameters (T 100 K, n 30 cm-3). The enhanced [CII] to FIR continuum ratio in these outer regions is a reflection of the increased efficiency for photoelectic heating in low UV field environments. Integrated over the galaxy about 25% of the observed [CII] emission arises from atomic clouds. The [CII] emission may be marginally resolved in the z direction with our 55" beam - indicating a scale height larger than that of CO. This extraplanar [CII] may be associated with the "filaments" observed in the optical recombination lines.
    04/2007: pages 90-91;
  • Thomas Nikola, Gordon J. Stacey, Terry Herter
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    ABSTRACT: We present a concept for a far-IR integral field spectrograph for SOFIA, the Cornell Mapping Spectrometer (CMS). CMS takes advantage of the next generation of large bolometer arrays to deliver moderate resolution spectroscopy in the wavelength range between 40 mum and 220 mum over a large field of view. Two separate wavelength channels with each employing six SCUBA-2-like bolometer arrays will provide 64 element spectra over a 10 × 12 spatial pixel footprint. By matching the pixel size to the beam size the field of view obtained is 190" × 160" at the important [CII] line in the long-lambda channel and 77" × 64" at the [OI] line in the short-lambda channel. The sliced image is fed into an R2 echelle spectrometer of modest resolving power (R ≈ 2000). The grating will operate in 4th order at 158 mum in the long-lambda channel and 4th order at 63 mum in the short-lambda channel. This results in nearly matching orders for other important fine-structure lines of [NII] and [OIII]. Filterwheels are placed right in front of the detector arrays to separate the orders. By subdividing the detector assemblies and appropriately placing the 3 × 1 detector sub-assemblies it is possible to observe four fine-structure lines simultaneously. CMS combines the advantages of a FIFI-LS design (instantaneous spatial and spectral coverage) with the sensitivity advantage of bolometers over photo-conductors. This will make CMS the instrument of choice for deep spectroscopic integrations of extended regions in galaxies.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2007; · 0.20 Impact Factor
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    ABSTRACT: We report results of a recently-completed pre-formulation phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25–400 μm. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1′ field of view to accomplish three primary scientific objectives: (1) learn how planetary systems form from protostellar disks, and how they acquire their inhomogeneous composition; (2) characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets of different types form; and (3) learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously.
    Advances in Space Research. 01/2007;
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    ABSTRACT: Understanding galaxy formation is at the foundation of extragalactic astronomy. Galaxies are thought to be assembled via mergers of small dwarf-like systems at high redshift. One of the best ways of providing observational constraints to the models is through a better understanding of local examples of these "building blocks", star forming dwarf galaxies. We have exploited the SWIRE legacy database to perform an unbiased search for extreme star forming PAH-rich dwarf galaxies. We wish to observe a complete and flux-limited 8 um selected sample of 27 PAH-rich dwarf galaxies in the ELAIS N1 field with the Infrared Spectrograph. This proposal is part of a much larger study of the PAH-rich dwarf galaxy population. However, the Spitzer observations are critical for our project as this is a mid-infrared selected sample and we need to compare the mid-infrared properties with Spitzer surveys of known galaxy type. Only Spitzer enables us to measure the PAH features; directly observe the low-J rotational molecular hydrogen lines; and the fine structure lines in a practically extinction-free wavelength range. These observations will characterize the physical properties of the star-forming regions, e.g., star formation rate, excitation, electron density, warm molecular gas mass. Please note that this is a COMPLETE SURVEY OF 27 PAH-RICH DWARVES. The SPITZER TIME request is SPLIT between this GTO proposal (SJH_PDGT), which has my total GTO time allocation of 6.6 hrs for 4 sources AND a GO proposal (SJH_PDGO) to observe the remaining 23 SOURCES in 37.9 hrs.
    Spitzer Proposal. 05/2006;
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    ABSTRACT: We propose to investigate the nature of a sample of high luminosity infrared bright galaxies in the redshift range of 0.6 to 3 through complete IRS high resolution spectroscopy. Our sample focuses on systems that we will observe in March 2006 in their 158 micron [CII] line emission using Cornell's submm grating spectrometer, ZEUS on the CSO. The combined [CII] and Spitzer IRS spectroscopy will comprise the thesis work of Cornell student Steven Hailey-Dunsheath. The combined data sets will (1) Determine the hardness of the ambient interstellar radiation fields thereby tracing the most massive stars on the main sequence, or revealing the presence of an AGN. (2) Determine the total ionizing flux from stars, hence the relative importance of starformation to accretion in creating the IR luminosity of these sources. (3) Determine the strength of the ambient far-UV radiation fields, hence the physical sizes of the starforming regions. The sources proposed here are among the most distant, and most luminous sources known in the Universe. As such, they are heavily studied by many research groups. We propose deep IRS high resolution spectroscopy for these sources, for which we have built a scientific case coupled to research going on in our group at Cornell. It is clear that the spectra that we obtain will be invaluable for many other science programs including future programs involving Herschel, and JWST. We therefore welcome and encourage collaborations.
    Spitzer Proposal. 05/2006;
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    ABSTRACT: We present a first cut instrument design package for the proposed 25 meter Cornell-Caltech Atacama Telescope (CCAT). The primary science for CCAT can be achieved through wide field photometric imaging in the short submillimeter through millimeter (200 mum to 2 mm) telluric windows. We present strawman designs for two cameras: a 32,000 pixel short submillimeter (200 to 650 mum) camera using transition edge sensed bare bolometer arrays that Nyquist samples (@ 350 mum) a 5'×5' field of view (FoV), and a 45,000 pixel long wavelength camera (850 mum to 2 mm) that uses slot dipole antennae coupled bolometer arrays with wavelength dependent sampling that covers up to a 20' square FoV. These are our first light instruments. We also anticipate "borrowed" instruments such as direct detection and heterodyne detection spectrometers will be available at, or nearly at first light.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2006; 6275. · 0.20 Impact Factor
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    ABSTRACT: We present an 11 arcsec resolution map of the central two parsecs of the Galaxy in the CO J =7->6 rotational transition. The CO emission shows rotation about Sgr A*, but also evidence for non-circular turbulent motion and a clumpy morphology. We combine our dataset with available CO measurements to model the physical conditions in the disk. We find that the molecular gas in the region is both warm and dense, with T~200-300 K, n_H2~50,000-70,000 cm^-3. The mass of warm molecular gas we measure in the central two parsecs is at least 2000 M_solar, about 20 times the UV-excited atomic gas mass, ruling out an UV heating scenario for the molecular material. We compare the available spectral tracers with theoretical models and conclude that molecular gas is heated with magneto-hydrodynamic shocks with v~10-20 kms and B~0.3-0.5 mG. Using the conditions derived with the CO analysis, we include the other important coolants--neutral oxygen and molecular hydrogen--to estimate the total cooling budget of the molecular material. We derive a mass to luminosity ratio of 2-3 M_solar/ L_solar, which is consistent with the total power dissipated via turbulent decay in 0.1 pc cells with v_rms~15 kms. These size and velocity scales are comparable to the observed clumping scale and the velocity dispersion. At this rate, the material near Sgr A* its dissipating its orbital energy on an orbital timescale, and cannot last for more than a few orbits. Our conclusions support a scenario in which the features near Sgr A* such as the CND and northern arm are generated by infalling clouds with low specific angular momentum. Comment: 31 pages, including 5 figures, accepted for publication in ApJ
    The Astrophysical Journal 01/2005; · 6.28 Impact Factor

Publication Stats

2k Citations
336.83 Total Impact Points

Institutions

  • 2014
    • University of Lethbridge
      Lethbridge, Alberta, Canada
  • 1992–2012
    • Cornell University
      • Department of Astronomy
      Ithaca, New York, United States
  • 1991–2009
    • University of California, Berkeley
      • Department of Physics
      Berkeley, CA, United States
  • 2005
    • California Institute of Technology
      Pasadena, California, United States