J/ApJ/737/73   Infrared extinction toward the Galactic Centre  (Fritz+, 2011)
Line derived infrared extinction toward the Galactic Center.
    Fritz T.K., Gillessen S., Dodds-Eden K., Lutz D., Genzel R., Raab W.,
    Ott T., Pfuhl O., Eisenhauer F., Yusef-Zadeh F.
   <Astrophys. J., 737, 73 (2011)>
   =2011ApJ...737...73F 2011ApJ...737...73F
ADC_Keywords: Extinction ; Milky Way ; Galaxies, spectra ; Galaxies, IR
Keywords: dust, extinction - Galaxy: center - Galaxy: fundamental parameters

Abstract:
    We derive the extinction curve toward the Galactic center (GC) from 1
    to 19um. We use hydrogen emission lines of the minispiral observed by
    ISO-SWS and SINFONI. The extinction-free flux reference is the 2cm
    continuum emission observed by the Very Large Array. Toward the inner
    14"x20", we find an extinction of A2.166um=2.62±0.11, with a
    power-law slope of α=-2.11±0.06 shortward of 2.8um, consistent
    with the average near-infrared slope from the recent literature. At
    longer wavelengths, however, we find that the extinction is grayer
    than shortward of 2.8um. We find that it is not possible to fit the
    observed extinction curve with a dust model consisting of pure
    carbonaceous and silicate grains only, and the addition of composite
    particles, including ices, is needed to explain the observations.
    Combining a distance-dependent extinction with our
    distance-independent extinction, we derive the distance to the GC to
    be R0=7.94±0.65kpc. Toward Sgr A* (r<0.5"), we obtain
    AH=4.21±0.10, AKs=2.42±0.10, and AL'=1.09±0.13.

Description:
    In this paper, we use the emission of the minispiral from 1.28 to 19um
    to derive relative extinction values from line emission, which are
    compared to 2cm radio continuum data to compute the absolute
    extinction. We used a Very Large Array (VLA) radio (2cm continuum)
    map, ISO-SWS spectra (2.4-45um) and SINFONI imaging spectroscopy
    (1.2-2.4um), of which the latter is used to construct line maps at
    Brackett-γ (2.166um), Brackett-ζ (1.736um), and
    Paschen-β (1.283um).

    Details of phase and amplitude calibration of each data set taken in
    different configurations of the VLA can be found in Yusef-Zadeh &
    Wardle (1993ApJ...405..584Y 1993ApJ...405..584Y) and Yusef-Zadeh et al. (1998ApJ...499L.159Y 1998ApJ...499L.159Y).
    We use the ISO-SWS data of Lutz (1999ESASP.427..623L 1999ESASP.427..623L).

    For shorter wavelengths (1.2-2.4um), we use spectra obtained with the
    integral field spectrometer SINFONI at UT4 of the Very Large
    Telescope. We use the following data: H+K band (spectral resolution
    1500) covering an area of about 37"x30" around Sgr A* from 2003 April
    9, and J band (spectral resolution 2000) of most areas of the
    minispiral obtained 2010 May 21 and July 6.

File Summary:
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 FileName   Lrecl  Records   Explanations
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ReadMe         80        .   This file
table8.dat     25    23893   Interpolated infrared extinction curve
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Byte-by-byte Description of file: table8.dat
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   Bytes Format Units   Label     Explanations
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   1-  8  F8.5  um      lambda    [1/27] Wavelength
  10- 17  F8.5  mag            Average extinction at lambda (1)
  19- 25  F7.5  mag   e_       Error in 
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Note (1): Towards the central 14"x20" of the Galactic Center. The errors
     includes all effects. Some effects matter only for comparison over big
     wavelength ranges. Locally the error is smaller for most of ISO-SWS
     range (2.6 to 27 microns). This curve can be used for A(λ) in
     Formula C1 for obtaining the extinction for other objects and filters.
     Scaled to other absolute extinctions it can be also useful outside the
     Galactic Center.
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History:
    From electronic version of the journal

(End)                 Greg Schwarz [AAS], Emmanuelle Perret [CDS]    08-Jan-2013