Extragalactic abstracts - IRSA - California Institute of Technology

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Spitzer_Approved_Extragalactic Mar 25, 10 16:24 Page 39/742 Spitzer Space Telescope − Guaranteed Time Observer Proposal #99 Giant Extragalactic H II Regions in M31 Principal Investigator: George Rieke Institution: The University of Arizona Technical Contact: Karl Gordon, The University of Arizona Science Category: local group galaxies Observing Modes: MipsScan Hours Approved: 17.1 Abstract: This program is aimed at investigating the H II regions in M31. These regions will be used as analoges of starbursts and to probe the evolution of dust grain properties as a function of star formation activity. This program will acquire 24, 70, & 160 micron photometric spectral energy distributions on a large number of H II regions in M31. When combined with existing ultraviolet, optical, and near−IR images of M31, the data will be used to the star formation process and the properties of dust associated with H II regions. Spitzer_Approved_Extragalactic Printed_by_SSC Mar 25, 10 16:24 Page 40/742 Spitzer Space Telescope − General Observer Proposal #20057 Galactic Chemical Evolution & the Hot Star−H II Region Connection in M33 Principal Investigator: Robert Rubin Institution: NASA Ames Research Center Technical Contact: Robert Rubin, NASA Ames Research Center Co−Investigators: Janet Simpson, NASA Ames Research Center Adi Pauldrach, University Munich Sean Colgan, NASA Ames Research Center Reginald Dufour, Rice University Edwin Erickson, NASA Ames Research Center Michael Haas, NASA Ames Research Center Science Category: local group galaxies Observing Modes: IrsMap Hours Approved: 23.9 Abstract: H II regions play a crucial role in the measurement of current interstellar abundances while also serving as laboratories for atomic physics. They provide fundamental data about heavy element abundances that serve to constrain models of galactic chemical evolution. We propose to use Spitzer/IRS to measure the Ne/H and S/H abundances in H II regions in the nearby spiral galaxy M33. By observing a substantially face−on galaxy with a significant abundance gradient, we will cover a full range of galactocentric radii (R_G) & abundances, and avoid the extinction problems that plague optical/near IR Milky Way studies, particularly in the inner Galaxy. An important advantage compared with prior optical studies is that the IR lines have a weak and similar electron temperature (Te) dependence while optical lines vary exponentially with Te. We plan to observe 5 emission lines: S IV 10.5, Ne II 12.8, Ne III 15.6, S III 18.7, & H7−6 12.4 micron cospatially with IRS/SH. By virtue of being able to measure lines from all the major ionic states of Ne and S in H II regions, together with an H line, in the SAME spectrum, there is a unique opportunity to obtain reliable Ne/H & S/H ratios and determine how they vary with R_G. Our prior measurements of the Galactic Ne/O ratio using far−IR lines, showed the observed Ne++/O++ ratio significantly exceeds model predictions. This has been referred to as the "Ne III problem". The nebular models rely on stellar atmosphere models to provide the ionizing spectral energy distribution (SED) for hot stars. The SED used is the largest source of uncertainty when comparing theory and observations to determine nebular abundances in general and galactochemical gradients. We will use novel diagnostic tools designed to investigate the Ne III problem via the proposed observations to validate the SED input to the nebular code. These observations will pave the way for similar Spitzer studies of other galaxies to yield the most detailed, reliable data by far of S/H and Ne/H abundance variations. Thursday March 25, 2010 xgal_covers.txt 20/371
Spitzer_Approved_Extragalactic Mar 25, 10 16:24 Page 41/742 Spitzer Space Telescope − General Observer Proposal #40910 Galactic Chemical Evolution & the Hot Star − H II Region Connection in NGC6822 Principal Investigator: Robert Rubin Institution: NASA Ames Research Center Technical Contact: Robert Rubin, NASA Ames Research Center Co−Investigators: Sean Colgan, NASA Ames Research Center Simpson Janet, NASA Ames Research Center Adalbert Pauldrach, University Munich Reginald Dufour, Rice University Edwin Erickson, NASA Ames Research Center Michael Haas, NASA Ames Research Center Brent Buckalew, Caltech/IPAC Science Category: local group galaxies Observing Modes: IrsMap Hours Approved: 27.5 Abstract: H II regions provide fundamental data about heavy element abundances that constrain galactic chemical evolution (GCE) models. We propose to use Spitzer/IRS to follow up on our Spitzer observations of M83 and M33 H II regions. We will measure S IV 10.5, Ne II 12.8, Ne III 15.6, S III 18.7, & H7−6 12.4 micron cospatially with IRS/SH. By measuring all the major ionic states of Ne and S in H II regions with an H line, there is a unique opportunity to estimate S3+/S++, Ne++/Ne+, Ne/H, S/H, & Ne/S ratios and test if they vary with galactocentric radius (R_G). The high Ne/S ratios we derived for M83 are likely upper limits due to our estimate of the S abundance not accounting for S+ or dust. The M33 H II regions have much lower metallicity and higher ionization, leading to a truer total S abundance & a Ne/S close to the Orion Nebula value 14. The H II regions in the nearby, dwarf irregular galaxy NGC6822 are both low metallicity (O/H ~3.5x lower than Solar) and high ionization, allowing a reliable derivation of gas−phase Ne/S. The solar Ne abundance is very controversial, with much evidence pointing to a higher Ne value than the current Ne/S~5. NGC6822 observations will test how robust and universal the ratio of ~14 is. Such a finding will place important constraints upon GCE models. Our derivation of ionic abundances from Spitzer data depends on nebular models, which rely on the spectral energy distribution (SED) which comes from stellar atmosphere models. From our M83 and M33 data, we derive / & / vs. / ratios for the various H II regions and compare with theoretical loci, which show a factor >10 spread in y at a given x. The data points best follow the trend of the loci using the supergiant SEDs of Pauldrach, who will compute a set of atmosphere models with metallicity similar to that of NGC6822. Data for a third galaxy with a very different history and gas content will further validate whether or not any SED set preferentially fits the nebular observations. Spitzer_Approved_Extragalactic Printed_by_SSC Mar 25, 10 16:24 Page 42/742 Spitzer Space Telescope − General Observer Proposal #50088 A Population of Dusty B Stars in the SMC: The First Extragalactic Debris Disks? Principal Investigator: Joshua Simon Institution: California Institute of Technology Technical Contact: Joshua Simon, California Institute of Technology Co−Investigators: Alberto Bolatto, University of Maryland Jacco van Loon, Keele University Joana Oliveira, Keele University Luke Keller, Ithaca College Greg Sloan, Cornell University Karin Sandstrom, UC Berkeley Science Category: local group galaxies Observing Modes: IrsStare IrsPeakupImage Hours Approved: 32.7 Abstract: Using data from the Spitzer Survey of the SMC, we have discovered a population of 120 B stars with large 24 micron excesses. Optical spectroscopy and the IRAC SEDs demonstrate that they are not ordinary YSOs or Be stars. We suggest instead that these objects may be debris disks around massive main sequence stars. Confirmation of this hypothesis would provide one of the only ways to study the process of planet formation in a low−metallicity external galaxy. We propose Spitzer IRS spectroscopy to measure the long−wavelength SED of the dust emission and blue peak−up imaging to better constrain the size of the emitting region around each star. From the mid−infrared SEDs, we will determine the dust temperature, thereby placing strong constraints on its location and relationship to the B stars. If the B stars do indeed host debris disks, they provide perhaps the only plausible method for constraining planet formation in an external galaxy for the foreseeable future. Thursday March 25, 2010 xgal_covers.txt 21/371
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