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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. Source

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. Source

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. Source

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. Source

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. Source

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