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Swaters R.A.,National Optical Astronomical Observatory | Bershady M.A.,University of Wisconsin - Madison | Martinsson T.P.K.,Leiden University | Westfall K.B.,University of Portsmouth | And 2 more authors.
Astrophysical Journal Letters | Year: 2014

We present the correlation between the extrapolated central disk surface brightness (μ) and extrapolated central surface mass density (Σ) for galaxies in the DiskMass sample. This μ-Σ relation has a small scatter of 30% at the high surface brightness (HSB) end. At the low surface brightness (LSB) end, galaxies fall above the μ-Σ relation, which we attribute to their higher dark matter content. After correcting for the dark matter as well as for the contribution of gas and the effects of radial gradients in the disk, the LSB end falls back on the linear μ-Σ relation. The resulting scatter around the corrected μ-Σ relation is 25% at the HSB end and about 50% at the LSB end. The intrinsic scatter in the μ-Σ relation is estimated to be 10%-20%. Thus, if μ K, 0 is known, the stellar surface mass density is known to within 10%-20% (random error). Assuming disks have an exponential vertical distribution of mass, the average is 0.24 M /L, with an intrinsic scatter around the mean of at most 0.05 M/L. This value for is 20% smaller than we found in Martinsson et al., mainly due to the correction for dark matter applied here. This small scatter means that among the galaxies in our sample, variations in scale height, vertical density profile shape, and/or the ratio of vertical over radial velocity dispersion must be small. © 2014. The American Astronomical Society. All rights reserved.

News Article | March 29, 2016
Site: phys.org

"We are privileged to have been selected to build this new instrument for the exoplanet community," Mahadevan said. "This is a testament to our multi-institutional and interdisciplinary team of talented graduate students, postdoctoral researchers, and senior scientists." The instrument is named NEID - derived from the word meaning "to discover/visualize" in the native language of the Tohono O'odham, on whose land Kitt Peak National Observatory is located. NEID also is short for "NN-EXPLORE Exoplanet Investigations with Doppler Spectroscopy." NEID will detect planets by the tiny gravitational tug they exert on their stars. "NEID will be more stable than any existing spectrograph, allowing astronomers around the world to make the precise measurements of the motions of nearby, Sun-like stars," said Jason Wright, associate professor of astronomy and astrophysics at Penn State and a member of the science advisory team. "Our team will use NEID to discover and measure the orbits of rocky planets at the right distances from their stars to host liquid water on their surfaces." "Winning this competition is a tremendous honor and a mark of recognition for our Center for Exoplanets and Habitable Worlds," said Donald Schneider, Distinguished Professor and Head of the Department of Astronomy and Astrophysics. Many NEID team members are graduate students and postdoctoral researchers. Schneider added, "We are proud that our junior scientists are a significant part of this ground-breaking project." NEID Project Manager and Senior Scientist Fred Hearty said, "Building this instrument is a wonderful opportunity for Penn State and our partners. R&D here at Penn State established a foundation to advance the state-of-the-art in planet finding almost thirty years ago. Today's Habitable-zone Planet Finder project is proving the entire system works as planned." NEID will be built over the next three years in laboratories at Innovation Park on the Penn State University Park Campus and at partnering institutions. It will be installed on the 3.5-meter WIYN telescope at Kitt Peak National Observatory (KPNO) in Arizona. NEID will provide new capabilities for the National Optical Astronomical Observatory (NOAO), which operates the Kitt Peak telescopes. When NEID is completed, astronomers worldwide will have access to this state-of-the-art planet finder. Astronomer and Penn State Research Associate Chad Bender, who will help to oversee the construction of the instrument, noted that "NEID's capabilities are critical to the success of NASA's upcoming exoplanet missions. NEID will follow-up on planets discovered by the Transiting Exoplanet Survey Satellite and also will identify exciting targets to be observed by the James Webb Space Telescope and the Wide-Field Infrared Survey Telescope." The NEID team is a multi-institutional collaboration, consisting of exoplanet scientists and engineers from Penn State, University of Pennsylvania, NASA Goddard Space Flight Center, University of Colorado, National Institute of Standards and Technology, Macquarie University in Australia, Australian Astronomical Observatory, and Physical Research Laboratory in India. "NEID is a transformative capability in the search for worlds like our own, Mahadevan said." NASA and NSF established the NN-EXPLORE partnership in February 2015 to take advantage of the full NOAO share of the 3.5-meter WIYN telescope at KPNO, to provide the science community with the tools and access to conduct ground-based observations that advance exoplanet science, and to support the observations of NASA space astrophysics missions. KPNO is operated on behalf of NSF by NOAO. The NEID project will be managed on behalf of NASA's Astrophysics Division by the Exoplanet Exploration Program Office at the Jet Propulsion Laboratory. Explore further: Hobby-Eberly Telescope measures two stars with one orbiting planet

Megeath S.T.,University of Toledo | Gutermuth R.,University of Massachusetts Amherst | Muzerolle J.,US Space Telescope Science Institute | Kryukova E.,University of Toledo | And 9 more authors.
Astronomical Journal | Year: 2012

We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments on board Spitzer. In total, five distinct fields were mapped, covering 9 deg 2 in five mid-IR bands spanning 3-24 μm. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630, and 1622 dark clouds, and the NGC 2023, 2024, 2068, and 2071 nebulae. These data are merged with the Two Micron All Sky Survey point source catalog to generate a catalog of eight-band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main-sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in two to three epochs over six months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5 μm bands. We find that 50% of the dusty YSOs show variability. The variations are typically small (∼0.2 mag) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8, and 8 μm variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots. © 2012. The American Astronomical Society. All rights reserved.

Chavarria L.,University of Chile | Chavarria L.,Harvard - Smithsonian Center for Astrophysics | Chavarria L.,Laboratoire Dastrophysique Of Bordeaux | Chavarria L.,CSIC - National Institute of Aerospace Technology | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538. Spitzer data is combined with NIR observations to identify and classify the young population while 12CO and 13CO observations are used to examine the parental molecular cloud.We detect in total 3021 young stellar objects (YSOs). Of those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material. We identify in total 41 embedded clusters containing between 52 and 73 per cent of the YSOs. Clusters are in general non-virialized, turbulent and have star formation efficiencies between 5 and 50 per cent.We compare the physical properties of embedded clusters harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc. © 2014 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Klebe D.,Denver Museum of Nature and Science | Sebag J.,National Optical Astronomical Observatory | Blatherwick R.D.,University of Denver | Zimmer P.C.,University of New Mexico
Publications of the Astronomical Society of the Pacific | Year: 2012

This article describes a novel calibration method developed for the All Sky Infrared Visible Analyzer (ASIVA). This instrument is principally designed to characterize sky conditions for purposes of improving ground-based astronomical observational performance. Calibration and detection performance of the ASIVA's midinfrared camera subsystem with particular emphasis on data products that are being developed to quantify photometric quality are described in detail. This analysis allows for the determination of a sky quality metric that can serve as a consistent and reliable metric for telescope scheduling purposes. © 2012. The Astronomical Society of the Pacific.

Lotz J.M.,National Optical Astronomical Observatory | Jonsson P.,Harvard - Smithsonian Center for Astrophysics | Cox T.J.,Carnegie Observatories | Primack J.R.,University of California at Santa Cruz
Monthly Notices of the Royal Astronomical Society | Year: 2010

The majority of galaxy mergers are expected to be minor mergers. The observational signatures of minor mergers are not well understood; thus, there exist few constraints on the minor merger rate. This paper seeks to address this gap in our understanding by determining if and when minor mergers exhibit disturbed morphologies and how they differ from the morphology of major mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying galaxy mergers via projected separation and quantitative morphology (the Gini coefficient G, asymmetry A and the second-order moment of the brightest 20 per cent of the light M20) depends on the merger mass ratio, relative orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1 baryonic mass ratio mergers as 1:1 mergers, with observability time-scales of ∼0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios between 4:1 and 1:1 (assuming local disc galaxy gas fractions). Asymmetry time-scales for moderate gas-fraction major disc mergers are ∼0.2-0.4 Gyr and less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative orientations and orbits have little effect on the time-scales for morphological disturbances. Observational studies of close pairs often select major mergers by choosing paired galaxies with similar luminosities and/or stellar masses. Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs) are sensitive to galaxy mergers of different mass ratios. By comparing the frequency of mergers selected by different techniques, one may place empirical constraints on the major and minor galaxy merger rates. © 2010 The Authors. Journal compilation © 2010 RAS.

Lotz J.M.,National Optical Astronomical Observatory | Jonsson P.,Harvard - Smithsonian Center for Astrophysics | Cox T.J.,Carnegie Observatories | Primack J.R.,University of California at Santa Cruz
Monthly Notices of the Royal Astronomical Society | Year: 2010

Gas-rich galaxy mergers are more easily identified by their disturbed morphologies than mergers with less gas. Because the typical gas fraction of galaxy mergers is expected to increase with redshift, the under-counting of low gas-fraction mergers may bias morphological estimates of the evolution of galaxy merger rate. To understand the magnitude of this bias, we explore the effect of gas fraction on the morphologies of a series of simulated disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying major and minor galaxy mergers via close projected pairs and quantitative morphology (the Gini coefficient G, the second-order moment of the brightest 20 per cent of the light M20 and asymmetry A) depends on baryonic gas fraction fgas. Strong asymmetries last significantly longer in high gas-fraction mergers of all mass ratios, with time-scales ranging from ≤300 Myr for fgas∼ 20 per cent to ≥1 Gyr for fgas∼ 50 per cent. Therefore, the strong evolution with redshift observed in the fraction of asymmetric galaxies may reflect evolution in the gas properties of galaxies rather than the global galaxy merger rate. On the other hand, the time-scale for identifying a galaxy merger via G-M20 is weakly dependent on gas fraction (∼200-400 Myr), consistent with the weak evolution observed for G-M20 mergers. © 2010 The Authors. Journal compilation © 2010 RAS.

Mendez A.J.,University of California at San Diego | Coil A.L.,University of California at San Diego | Lotz J.,National Optical Astronomical Observatory | Salim S.,National Optical Astronomical Observatory | And 2 more authors.
Astrophysical Journal | Year: 2011

We present quantitative morphologies of 300 galaxies in the optically defined green valley at 0.4 < z < 1.2, in order to constrain the mechanism(s) responsible for quenching star formation in the bulk of this population. The sample is selected from galaxies in the All-Wavelength Extended Groth Strip International Survey (AEGIS). While the green valley is defined using optical U - B colors, we find that using a green valley sample defined using NUV - R colors does not change the results. Using Hubble Space Telescope/Advanced Camera for Surveys imaging, we study several quantitative morphological parameters including CAS, B/T from GIM2D, and Gini/M20. We find that the green galaxy population is intermediate between the red and blue galaxy populations in terms of concentration, asymmetry, and morphological type and merger fraction estimated using Gini/M20. We find that most green galaxies are not classified as mergers; in fact, the merger fraction in the green valley is lower than in the blue cloud. We show that at a given stellar mass, green galaxies have higher concentration values than blue galaxies and lower concentration values than red galaxies. Additionally, we find that 12% of green galaxies have B/T = 0 and 21% have B/T ≤ 0.05. Our results show that green galaxies are generally massive (M* ∼ 10 10.5 M⊙) disk galaxies with high concentrations. We conclude that major mergers are likely not the sole mechanism responsible for quenching star formation in this population and that either other external processes or internal secular processes play an important role both in driving gas toward the center of these galaxies and in quenching star formation. © 2011. The American Astronomical Society. All rights reserved.

Maraston C.,University of Portsmouth | Pforr J.,University of Portsmouth | Renzini A.,National institute for astrophysics | Daddi E.,SAP | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

Fitting synthetic spectral energy distributions (SEDs) to the multiband photometry of galaxies to derive their star formation rates (SFRs), stellar masses, ages, etc. requires making a priori assumptions about their star formation histories (SFHs). A widely adopted parametrization of the SFH, the so-called τ models where SFR ∝ e-t/τ is shown to lead to unrealistically low ages when applied to a sample of actively star-forming galaxies at z ∼ 2, a problem shared by other SFHs when the age is left as a free parameter in the fitting procedure. This happens because the SED of such galaxies, at all wavelengths, is dominated by their youngest stellar populations, which outshine the older ones. Thus, the SED of such galaxies conveys little information on the beginning of star formation (SF), i.e. on the age of their oldest stellar populations. To cope with this problem, besides τ models (hereafter called direct-τ models), we explore a variety of SFHs, such as constant SFR and inverted-τ models (with SFR ∝ e+t/τ), along with various priors on age, including assuming that SF started at high redshift in all the galaxies in the test sample. We find that inverted-τ models with such latter assumption give SFRs and extinctions in excellent agreement with the values derived using only the UV part of the SED, which is the one most sensitive to ongoing SF and reddening. These models are also shown to accurately recover the SFRs and masses of mock galaxies at z ∼ 2 constructed from semi-analytic models, which we use as a further test. All other explored SFH templates do not fulfil these two tests as well as inverted-τ models do. In particular, direct-τ models with unconstrained age in the fitting procedure overestimate SFRs and underestimate stellar mass, and would exacerbate an apparent mismatch between the cosmic evolution of the volume densities of SFR and stellar mass. We conclude that for high-redshift star-forming galaxies an exponentially increasing SFR with a high formation redshift is preferable to other forms of the SFH so far adopted in the literature. © 2010 The Authors. Journal compilation © 2010 RAS.

Adamkovics M.,University of California at Berkeley | Najita J.R.,National Optical Astronomical Observatory | Glassgold A.E.,University of California at Berkeley
Astrophysical Journal | Year: 2016

Protoplanetary disks are strongly irradiated by a stellar FUV spectrum that is dominated by Lya photons. We investigate the impact of stellar Lya irradiation on the terrestrial planet region of disks (≲1 AU) using an updated thermal-chemical model of a disk atmosphere irradiated by stellar FUV and X-rays. The radiative transfer of Lya is implemented in a simple approach that includes scattering by H I and absorption by molecules and dust. Because of their non-radial propagation path, scattered Lya photons deposit their energy deeper in the disk atmosphere than the radially propagating FUV continuum photons. We find that Lya has a significant impact on the thermal structure of the atmosphere. Photochemical heating produced by scattered Lya photons interacting with water vapor and OH leads to a layer of hot (1500-2500 K) molecular gas. The temperature in the layer is high enough to thermally excite the H2 to vibrational levels from which they can be fluoresced by Lya to produce UV fluorescent H2 emission. The resulting atmospheric structure may help explain the origin of UV fluorescent H2 that is commonly observed from classical T Tauri stars. © 2016. The American Astronomical Society. All rights reserved.

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