Moire K. M. Prescott

National Optical Astronomy Observatory, Tucson, Arizona, United States

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Publications (25)80.41 Total impact

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    ABSTRACT: We present IRAM Plateau de Bure Interferometer observations of the CO(3-2) and CO(5-4) line transitions from an Lyα blob at z ~ 2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emissions are detected at the location of a strong MIPS source that is offset by ~1.''5 from the Lyα peak. Neither of these emission components is resolved with the 1.''7 beam, showing that the gas and dust are confined to within ~7 kpc from this galaxy. No millimeter source is found at the location of the Lyα peak, ruling out a central compact source of star formation as the power source for the Lyα emission. Combined with a spatially resolved spectrum of Lyα and He II, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Lyα profile is symmetric, and its line center agrees with that of the CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Lyα emission. In the region near the Lyα peak, the gas is slowly receding (~100 km s–1) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, I CO(5-4)/I CO(3-2) = 0.97 ± 0.21. This line ratio is lower than the average values found in high-z submillimeter galaxies and QSOs but is consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity.
    The Astrophysical Journal 03/2014; 784(2):171. · 6.73 Impact Factor
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    ABSTRACT: We present IRAM PdBI observations of the CO(3-2) and CO(5-4) line transitions from a Ly-alpha blob at z~2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emission are detected at the location of a strong MIPS source that is offset by ~1.5" from the Ly-alpha peak. Neither of these emission components is resolved with the 1.7" beam, showing that the gas and dust are confined to within ~7kpc from this galaxy. No millimeter source is found at the location of the Ly-alpha peak, ruling out a central compact source of star formation as the power source for the Ly-alpha emission. Combined with a spatially-resolved spectrum of Ly-alpha and HeII, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Ly-alpha profile is symmetric and its line center agrees with that of CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Ly-alpha emission. In the region near the Ly-alpha peak, the gas is slowly receding (~100km/s) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, I_CO(5-4)/I_CO(3-2)=0.97+/-0.21. This line ratio is lower than the average values found in high-z SMGs and QSOs, but consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity.
    02/2014;
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    Sungryong Hong, Arjun Dey, Moire K. M. Prescott
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    ABSTRACT: Modern spectroscopic surveys produce large spectroscopic databases, generally with sizes well beyond the scope of manual investigation. The need arises, therefore, for an automated line detection method with objective indicators for detection significance. In this paper, we present an automated and objective method for emission line detection in spectroscopic surveys and apply this technique to 1574 spectra, obtained with the Hectospec spectrograph on the MMT Observatory (MMTO), to detect Lyman alpha emitters near z ~ 2.7. The basic idea is to generate on-source (signal plus noise) and off-source (noise only) mock observations using Monte Carlo simulations, and calculate completeness and reliability values, (C, R), for each simulated signal. By comparing the detections from real data with the Monte Carlo results, we assign the completeness and reliability values to each real detection. From 1574 spectra, we obtain 881 raw detections and, by removing low reliability detections, we finalize 649 detections from an automated pipeline. Most of high completeness and reliability detections, (C, R) ~ (1.0, 1.0), are robust detections when visually inspected; the low C and R detections are also marginal on visual inspection. This method at detecting faint sources is dependent on the accuracy of the sky subtraction.
    11/2013;
  • Moire K. M. Prescott, Arjun Dey, Buell T. Jannuzi
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    ABSTRACT: Using a systematic broadband search technique, we have carried out a survey for large Lyα nebulae (or Lyα "blobs") at 2 z 3 within 8.5 deg2 of the NOAO Deep Wide-Field Survey Boötes field, corresponding to a total survey comoving volume of 108h –370 Mpc3. Here, we present our spectroscopic observations of candidate giant Lyα nebulae. Of 26 candidates targeted, 5 were confirmed to have Lyα emission at 1.7 z 2.7, 4 of which were new discoveries. The confirmed Lyα nebulae span a range of Lyα equivalent widths, colors, sizes, and line ratios, and most show spatially extended continuum emission. The remaining candidates did not reveal any strong emission lines, but instead exhibit featureless, diffuse, blue continuum spectra. Their nature remains mysterious, but we speculate that some of these might be Lyα nebulae lying within the redshift desert (i.e., 1.2 z 1.6). Our spectroscopic follow-up confirms the power of using deep broadband imaging to search for the bright end of the Lyα nebula population across enormous comoving volumes.
    The Astrophysical Journal 12/2012; 762(1):38. · 6.73 Impact Factor
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    Moire K. M. Prescott, Arjun Dey, Buell T. Jannuzi
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    ABSTRACT: Using a systematic broad-band search technique, we have carried out a survey for large Lya nebulae (or Lya "blobs") at 2<z<3 within 8.5 square degrees of the NOAO Deep Wide-Field Survey (NDWFS) Bootes field, corresponding to a total survey comoving volume of ~10^8 h_70^-3 Mpc^3. Here, we present our spectroscopic observations of candidate giant Lya nebulae. Of 26 candidates targeted, 5 were confirmed to have Lya emission at 1.7<z<2.7, four of which were new discoveries. The confirmed Lya nebulae span a range of Lya equivalent widths, colors, sizes, and line ratios, and most show spatially-extended continuum emission. The remaining candidates did not reveal any strong emission lines, but instead exhibit featureless, diffuse, blue continuum spectra. Their nature remains mysterious, but we speculate that some of these might be Lya nebulae lying within the redshift desert (i.e., 1.2<z<1.6). Our spectroscopic follow-up confirms the power of using deep broad-band imaging to search for the bright end of the Lya nebula population across enormous comoving volumes.
    11/2012;
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    ABSTRACT: This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. With the addition of an open (publicly funded) community access component, the scientific impact of BigBOSS can be extended to many important astrophysical questions related to the origin and evolution of galaxies, stars, and the IGM. Massive spectroscopy is the critical missing ingredient in numerous ongoing and planned ground- and space-based surveys, and BigBOSS is unique in its ability to provide this to the US community. BigBOSS data from community-led projects will play a vital role in the education and training of students and in maintaining US leadership in these fields of astrophysics. We urge the NSF-AST division to support community science with the BigBOSS multi-object spectrograph through the period of the BigBOSS survey in order to ensure public access to the extraordinary spectroscopic capability.
    11/2012;
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    ABSTRACT: In order to constrain the bolometric luminosities, dust properties, and molecular gas content of giant Lyα nebulae, the so-called Lyα blobs, we have carried out a study of dust continuum and CO line emission in two well-studied representatives of this population at z ~ 3: an Lyα blob discovered by its strong Spitzer Multiband Infrared Photometer 24 μm detection (LABd05) and the Steidel blob 1 (SSA22-LAB01). We find that the spectral energy distribution of LABd05 is well described by an active-galactic-nucleus-starburst composite template with L FIR = (4.0 ± 0.5) × 1012 L ☉, comparable to high-z submillimeter galaxies and ultraluminous infrared galaxies. New Large APEX Bolometer Camera 870 μm measurements rule out the reported Submillimeter Common-User Bolometer Array detection of the SSA22-LAB01 (S 850 μm = 16.8 mJy) at the >4σ level. Consistent with this, ultradeep Plateau de Bure Interferometer observations with ~2'' spatial resolution also fail to detect any 1.2 mm continuum source down to 0.45 mJy beam–1 (3σ). Combined with the existing (sub)millimeter observations in the literature, we conclude that the FIR luminosity of SSA22-LAB01 remains uncertain. No CO line is detected in either case down to integrated flux limits of S νΔV 0.25-1.0 Jy km s–1, indicating a modest molecular gas reservoir, M(H2) < (1-3) × 1010 M ☉. The non-detections exclude, with high significance (12σ), the previous tentative detection of a CO J = 4-3 line in the SSA22-LAB01. The increased sensitivity afforded by the Atacama Large Millimeter/submillimeter Array will be critical in studying molecular gas and dust in these interesting systems.
    The Astrophysical Journal 12/2011; 744(2):178. · 6.73 Impact Factor
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    Moire K. M. Prescott, Arjun Dey, Buell T. Jannuzi
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    ABSTRACT: Giant Lya nebulae (or Lya "blobs") are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionization mechanisms, and space density. Systematic narrow-band Lya nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys and pose a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lya nebulae at 2<z<3 within deep broad-band imaging and have carried out a survey of the 9.4 square degree NOAO Deep Wide-Field Survey (NDWFS) Bootes field. With a total survey comoving volume of ~10^8 h^-3_70 Mpc^3, this is the largest volume survey for Lya nebulae ever undertaken. In this first paper in the series, we present the details of the survey design and a systematically-selected sample of 79 candidates, which includes one previously discovered Lya nebula.
    The Astrophysical Journal 11/2011; 748(2). · 6.73 Impact Factor
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    ABSTRACT: Detailed analysis of the substructure of Lya nebulae can put important constraints on the physical mechanisms at work and the properties of galaxies forming within them. Using high resolution HST imaging of a Lya nebula at z~2.656, we have taken a census of the compact galaxies in the vicinity, used optical/near-infrared colors to select system members, and put constraints on the morphology of the spatially-extended emission. The system is characterized by (a) a population of compact, low luminosity (~0.1 L*) sources --- 17 primarily young, small (Re~1-2 kpc), disky galaxies including an obscured AGN --- that are all substantially offset (>20 kpc) from the line-emitting nebula; (b) the lack of a central galaxy at or near the peak of the Lya emission; and (c) several nearly coincident, spatially extended emission components --- Lya, HeII, and UV continuum --- that are extremely smooth. These morphological findings are difficult to reconcile with theoretical models that invoke outflows, cold flows, or resonant scattering, suggesting that while all of these physical phenomena may be occurring, they are not sufficient to explain the powering and large extent of Lya nebulae. In addition, although the compact galaxies within the system are irrelevant as power sources, the region is significantly overdense relative to the field galaxy population (by at least a factor of 4). These observations provide the first estimate of the luminosity function of galaxies within an individual Lya nebula system, and suggest that large Lya nebulae may be the seeds of galaxy groups or low-mass clusters.
    The Astrophysical Journal 11/2011; 752(2). · 6.73 Impact Factor
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    ABSTRACT: In order to constrain the bolometric luminosities, dust properties and molecular gas content of giant Lyman alpha nebulae, the so-called Lyman alpha blobs, we have carried out a study of dust continuum and CO line emission in two well-studied representatives of this population at z ~ 3: a Lya blob discovered by its strong Spitzer MIPS 24um detection (LABd05; Dey et al. 2005) and the Steidel blob 1 (SSA22-LAB01; Steidel et al. 2000). We find that the spectral energy distribution of LABd05 is well described by an AGN-starburst composite template with L(FIR) = (4.0 +/- 0.5) x 10^12 Lsun, comparable to high-z sub-millimeter galaxies and ultraluminous infrared galaxies. New APEX/LABOCA 870um measurements rule out the reported SCUBA detection of the SSA22-LAB01 (S[850um] = 16.8 mJy) at the > 4sigma level. Consistent with this, ultra-deep Plateau de Bure Interferometer (PdBI) observations with ~2arcsec spatial resolution also fail to detect any 1.2mm continuum source down to ~0.45mJy per beam (3sigma). Combined with the existing (sub)mm observations in the literature, we conclude that the FIR luminosity of SSA22-LAB01 remains uncertain. No CO line is detected in either case down to integrated flux limits of (Snu dV) < 0.25--1.0 Jy km/s, indicating a modest molecular gas reservoir, M(H_2) < 1--3 x 10^10 Msun. The non-detections exclude, with high significance (12 sigma), the previous tentative detection of a CO(4-3) line in the SSA22-LAB01. The increased sensitivity afforded by ALMA will be critical in studying molecular gas and dust in these interesting systems.
    10/2011;
  • 07/2011;
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    Moire K. M. Prescott, Paul S. Smith, Gary D. Schmidt, Arjun Dey
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    ABSTRACT: Recent theoretical work has suggested that Lyalpha nebulae could be substantially polarized in the Lyalpha emission line, depending on the geometry, kinematics, and powering mechanism at work. Polarization observations can therefore provide a useful constraint on the source of ionization in these systems. In this Letter, we present the first Lyalpha polarization measurements for a giant Lyalpha nebula at z&ap; 2.656. We do not detect any significant linear polarization of the Lyalpha emission: P Lyalpha = 2.6% ± 2.8% (corrected for statistical bias) within a single large aperture. The current data also do not show evidence for the radial polarization gradient predicted by some theoretical models. These results rule out singly scattered Lyalpha (e.g., from the nearby active galactic nucleus, AGN) and may be inconsistent with some models of backscattering in a spherical outflow. However, the effects of seeing, diminished signal-to-noise ratio, and angle averaging within radial bins make it difficult to put strong constraints on the radial polarization profile. The current constraints may be consistent with higher density outflow models, spherically symmetric infall models, photoionization by star formation within the nebula or the nearby AGN, resonant scattering, or non-spherically symmetric cold accretion (i.e., along filaments). Higher signal-to-noise ratio data probing to higher spatial resolution will allow us to harness the full diagnostic power of polarization observations in distinguishing between theoretical models of giant Lyalpha nebulae.
    The Astrophysical Journal Letters 01/2011; 730(2). · 6.35 Impact Factor
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    ABSTRACT: Low luminosity galaxies contribute significantly to the mass and star-formation density of the universe at early epochs. Ly(alpha) emitting galaxies (LAEs) are powerful probes of the low-luminosity end of the luminosity function, and are also used to place constraints on the reionization epoch and the early mass assembly of galaxies. Most LAE studies have focused primarily on high redshifts (z~3-7) where the physical nature and large-scale context of LAEs remain largely unconstrained. In order to remedy this situation, we have begun a survey for LAEs at 1.8<z<2.0, the lowest redshifts feasible from the ground. We have successfully identified large samples of LAEs, and spectroscopically confirmed our selection method. Here, we propose to extend our spectroscopic study to the UDS field, which has existing deep Spitzer imaging, and is targeted for deep near-IR imaging by the Hubble Multi-Cycle Treasury Program. The near- and mid-IR data coupled with spectroscopic redshifts are essential for determining the age and mass distributions of the LAEs. Our study will create the largest sample (~100) of spectroscopically confirmed LAEs with existing deep near- and mid-IR imaging, and will thus provide robust measurements of the stellar masses, ages, and reddening of LAEs, enabling us to directly determine their significance in the z~1.9 universe.
    NOAO Proposal. 08/2010;
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    Moire K M Prescott, Arjun Dey, Buell T Jannuzi
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    ABSTRACT: We have discovered a ≈45 kpc Lyα nebula (or Lyα "blob") at z ≈ 1.67 which exhibits strong, spatially-extended He ii emission and very weak C iv and C iii] emission. This is the first spatially-extended Lyα+He ii emitter observed and the lowest redshift Lyα blob yet found. Strong Lyα and He iiλ1640 emission in the absence of metal lines has been proposed as a unique observational signature of primordial galaxy formation (e.g., from gravitational cooling radiation or Population III star formation), but no convincing examples of spatially-extended Lyα+He ii emitters have surfaced either in Lyα-emitting galaxy surveys at high redshifts (z > 4) or in studies of Lyα nebulae at lower redshifts. From comparisons with photoionization models, we find that the observed line ratios in this nebula are consistent with low metallicity gas (Z 10 −2 − 10 −3 Z ⊙), but that this conclusion depends on the unknown ionization parameter of the system. The large He ii equivalent width (≈37±1 A) and the large He ii/Lyα ratio (0.12±0.04) suggest that the cloud is being illuminated by a hard ionizing continuum, either an AGN or very low metallicity stars, or perhaps powered by gravitational cooling radiation. Thus far there is no obvious sign of a powerful AGN in or near the system, so in order to power the nebula while remaining hidden from view even in the mid-infrared, the AGN would need to be heavily obscured. Despite the strong Lyα+He ii emission, it is not yet clear what is the dominant power source for this nebula. The system therefore serves as an instructive example of how the complexities of true astrophysical sources will complicate matters when attempting to use a strong Lyα+He ii signature as a unique tracer of primordial galaxy formation.
    The Astrophysical Journal 07/2009; 702(1). · 6.73 Impact Factor
  • Naveen Reddy, Mark Brodwin, Arjun Dey, Moire Prescott
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    ABSTRACT: We propose to obtain deep IRAC 3.6 micron imaging of fields where we have conducted a survey of low redshift (z~1.9) Lyman-alpha emitters (LAEs), in order to measure directly their individual stellar masses. The targeted sample includes ~25 spectroscopically-confirmed LAEs at zD1.7-2.1 and roughly twice as many candidates, for a total sample size of ~75 objects. This would constitute perhaps the largest sample of homogeneously selected LAEs with individual measurements of their masses, allowing for a unique opportunity to correlate such measurements with other galaxy properties. In particular, the proposed imaging enables us to quantify the actual stellar mass distribution in of LAEs (as opposed to a stacked average) and, using these data, we will (1) determine whether stellar mass anti-correlates with Lyman-alpha emission, suggesting that Ly-alpha may be a signpost of young galaxies; (2) combine clustering and stellar mass measurements to infer duty cycles of LAEs and if they are triggered in the presence of larger scale structures; (3) combine number density and stellar masses to infer a stellar mass function of LAEs, which when compared with the mass function of all galaxies will shed new light on the importance of the LAE phase at different galaxy mass scales; and (4) quantify the ages of LAEs as inferred from the stellar mass and star formation rate measurements to ascertain the age distribution of low-z LAEs and compare with their higher redshift (z>3) counterparts, and compare the ages to the duty cycles of LAEs. IRAC imaging is a unique tool to pursue these investigations since 3.6 micron samples the peak of the stellar continuum and is less contaminated by current star formation at z~1.9 than at z>3 (where almost all studies have been focused). Thus, a first step to understanding the physical properties of LAEs as function of cosmic time hinges on our ability to rigorously investigate their nature at lower redshifts where the observations are more amenable.
    Spitzer Proposal. 04/2009;
  • Arjun Dey, Moire Prescott, Buell Jannuzi
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    ABSTRACT: Strong Lyα and He II emission in the absence of strong metal lines has been proposed in the theoretical literature as a potentially unique observational signature of primordial HII regions, powered by PopIII stars. Thus far, no convincing cases of Lyα+He II emitters have been found either in Lyα-emitting galaxy searches at high redshift (z>4) or in Lyα emitter surveys at lower redshifts. We have discovered a large ( 45 kpc) Lyα nebula (a `blob') at z 1.67 which exhibits strong, spatially-extended He II emission and very weak or absent C III and C IV emission. The current constraints from the detected emission lines suggests that the nebula contains very low metallicity gas (log(Z/Z_sun)<-2 to -3) and is powered by a hard ionizing continuum. Although no obvious AGN is observed in the vicinity, the discovery spectra are insufficient to determine whether the nebula is powered by an obscured AGN, very low metallicity (PopIII?) stars, or gravitational cooling radiation. We propose to map this Lyα+He II `blob' with deep optical and near-IR long-slit spectroscopy (using LRIS and NIRSPEC) in order to measure a host of diagnostic emission lines in the restframe UV and optical and put strong constraints on the temperature, ionization parameter, extinction, and metallicity of the gas. As the first known example of a Lyα+He II emitter, this source provides a completely unique opportunity to study low metallicity gas and search for evidence of very low metallicity star formation in what may be a site of ongoing galaxy formation.
    NOAO Proposal. 02/2009;
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    ABSTRACT: Large (>100 kpc) Lya nebulae or 'Lya blobs' are likely sites of ongoing massive galaxy formation. They have been found in small numbers around z 2-3, a key epoch of galaxy and black hole growth, but many fundamental questions remain about their environments, space density, and excitation mechanisms. While many Lya nebulae have been discovered via narrowband imaging of known overdensities, one of the largest Lya nebulae was discovered in the NOAO Deep Wide-Field Survey (NDWFS) without any a priori knowledge of its environment, offering an unbiased test of the association between Lya nebulae and overdensities. Using deep intermediate-band imaging we find that this Lya nebula is sitting within a factor of 3 overdensity of Lya-emitting galaxies and rule out a chance coincidence at the
    01/2009;
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    ABSTRACT: We have studied the relationship between the star formation rate (SFR), surface density, and gas surface density in the spiral galaxy M51a (NGC 5194), using multiwavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of Hα emission-line and 24 μm continuum luminosities, which provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis H I and CO maps has allowed us to probe the form of the spatially resolved star formation law on scales of 0.5-2 kpc. We find that the resolved SFR versus gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zero point and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of areal sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parameterization of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.
    The Astrophysical Journal 12/2008; 671(1):333. · 6.73 Impact Factor
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    ABSTRACT: Large nebulae ( 50 kpc) emitting strongly in Lyα (also known as Lyα "blobs") are likely signposts of ongoing massive galaxy formation. The relative rarity of these sources and their discovery in well-studied galaxy overdensities suggest that they may be associated with regions of high galaxy density. One of the largest Lyα nebulae, discovered at a redshift of z ≈ 2.7 via its strong mid-infrared emission, provides an unbiased test of this association. We have carried out a deep intermediate-band imaging survey for Lyα-emitting galaxies (LAEs) within a 30' × 26' field of view around this Lyα nebula. This is the first study of the environment of a Lyα nebula found without a priori knowledge of its surroundings. We find that the nebula is located in an overdense region, at least 20 × 50 h70−1 comoving Mpc in size, showing a factor of ~3 LAE number density enhancement relative to the edge of the field. Given the predicted number of such overdensities, we rule out the possibility of a chance coincidence at the 1% level. This study, in conjunction with previous work, provides strong confirmation of the association between the largest Lyα nebulae and overdense regions of the universe.
    The Astrophysical Journal 12/2008; 678(2):L77. · 6.73 Impact Factor
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    ABSTRACT: With the goal of investigating the degree to which the MIR emission traces the SFR, we analyze Spitzer 8 and 24 μm data of star-forming regions in a sample of 33 nearby galaxies with available HST NICMOS images in the Paα (1.8756 μm) emission line. The galaxies are drawn from the SINGS sample and cover a range of morphologies and a factor ~10 in oxygen abundance. Published data on local low-metallicity starburst galaxies and LIRGs are also included in the analysis. Both the stellar continuum-subtracted 8 μm emission and the 24 μm emission correlate with the extinction-corrected Paα line emission, although neither relationship is linear. Simple models of stellar populations and dust extinction and emission are able to reproduce the observed nonlinear trend of the 24 μm emission versus number of ionizing photons, including the modest deficiency of 24 μm emission in the low-metallicity regions, which results from a combination of decreasing dust opacity and dust temperature at low luminosities. Conversely, the trend of the 8 μm emission as a function of the number of ionizing photons is not well reproduced by the same models. The 8 μm emission is contributed, in larger measure than the 24 μm emission, by dust heated by nonionizing stellar populations, in addition to the ionizing ones, in agreement with previous findings. Two SFR calibrations, one using the 24 μm emission and the other using a combination of the 24 μm and Hα luminosities (Kennicutt and coworkers), are presented. No calibration is presented for the 8 μm emission because of its significant dependence on both metallicity and environment. The calibrations presented here should be directly applicable to systems dominated by ongoing star formation.
    The Astrophysical Journal 12/2008; 666(2):870. · 6.73 Impact Factor

Publication Stats

460 Citations
80.41 Total Impact Points

Institutions

  • 2014
    • National Optical Astronomy Observatory
      Tucson, Arizona, United States
  • 2011–2012
    • University of California, Santa Barbara
      • Department of Physics
      Santa Barbara, California, United States
    • CSU Mentor
      Long Beach, California, United States
  • 2008–2009
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States