J/other/Sci/345.791 Pseudo-3D maps of DIB at 862nm (Kos+ 2014)
Pseudo-three-dimensional maps of the diffuse interstellar band at 862 nm.
Kos J., Zwitter T., Wyse R., Bienayme O., Binney J., Bland-Hawthorn J.,
Freeman K., Gibson B. K., Gilmore G., Grebel E. K., Helmi A.,
Kordopatis G., Munari U., Navarro J., Parker Q., Reid W.A., Seabroke G.,
Sharma S., Siebert A., Siviero A., Steinmetz M., Watson F.G.,
Williams M.E.K.
<Science, 345, 791-795 (2014)>
=2014Sci...345..791K 2014Sci...345..791K
ADC_Keywords: Interstellar medium ; Equivalent widths ; Extinction
Keywords: Galaxy - spectroscopy - interstellar medium -
diffuse interstellar bands - dust - extinction - optical - infrared -
maps
Abstract:
The diffuse interstellar bands (DIBs) are absorption lines observed in
visual and near-infrared spectra of stars. Understanding their origin
in the interstellar medium is one of the oldest problems in
astronomical spectroscopy, as DIBs have been known since 1922. In a
completely new approach to understanding DIBs, we combined information
from nearly 500,000 stellar spectra obtained by the massive
spectroscopic survey RAVE (Radial Velocity Experiment) to produce the
first pseudo-three-dimensional map of the strength of the DIB at 8620
angstroms covering the nearest 3 kiloparsecs from the Sun, and show
that it follows our independently constructed spatial distribution of
extinction by interstellar dust along the Galactic plane. Despite
having a similar distribution in the Galactic plane, the DIB 8620
carrier has a significantly larger vertical scale height than the
dust. Even if one DIB may not represent the general DIB population,
our observations outline the future direction of DIB research.
Description:
Equivalent widths of DIB 8620 and reddening is presented as calculated
from the RAVE survey. Data represent pseudo-3-dimensional map given as
values in 1292 bins for the northern and 2212 bins for the southern
galactic hemisphere, covering a wide range of galactic longitudes and
distances up to 3kpc. Only two layers represent the dimension along
the galactic latitude, thus the name pseudo. Perpendicular to the
galactic plane a scale height is calculated. The value is
117.7±4.7pc for the dust absorption and 209.0±11.9pc for the DIB's
equivalent width. The values of the equivalent width and reddening are
not direct measurements, but are projected values into the galactic
plane according to the exponential law with the mentioned scale
height. The maps represent measurements made in spectra of stars at
different galactic latitudes, so for the measurements to be comparable,
the values must be rescaled. The mapped values are therefore the
values one would measure if the observer and the source both lied in
the galactic plane. Note that the observations do not cover the
galactic plane and the measured values might not reflect the state of
the ISM in the plane. Each bin represents a column stretching from the
galactic plane, symetricaly to the south and to the north. The cross
section of the bin has a shape of a slice of an annulus. The nearest
annulus has 3 slices and the following ones so many that they have as
equal area as possible. See paper for easier visualization.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
north.dat 79 1292 Values in bins of the northern galactic hemisphere
south.dat 79 2212 Values in bins of the southern galactic hemisphere
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See also:
III/272 : RAVE 4th data release (Kordopatis+, 2013)
Byte-by-byte Description of file: north.dat south.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 kpc b_d [0/3] Lower distance edge of a bin
7- 11 F5.3 kpc B_d [0/3] Upper distance edge of a bin
13- 17 F5.3 rad b_l [0/6.29] Lower Galactic longitude edge of a bin
19- 23 F5.3 rad B_l [0/6.29] Upper Galactic longitude edge of a bin
25- 29 F5.3 kpc d [0/3] Distance midpoint of a bin (1)
31- 35 F5.3 rad l [0/6.29] Galactic longitude midpoint of a bin (2)
37- 43 F7.5 0.1nm EW [0/2] Equivalent width of the DIB (diffuse
interstellar interstellar band) at 862nm
45- 51 F7.5 0.1nm e_EW [0.002/0.3] rms uncertainty on EW
53- 59 F7.4 mag AV [0.007/89] Extinction in V magnitude
61- 67 F7.4 mag e_AV [0.0002/1.5] rms uncertainty on AV
69- 73 F5.1 --- Nsp [20/100] Number of spectra used to calculate
values in this bin (3)
75- 79 F5.3 kpc Res [0.075/0.5] Resolution of the map in this bin
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Note (1): d is calculated as d=(bd+Bd)/2
Note (2): l is calculated as l=(bl+Bl)/2
Note (3): Does not have to be an integer, because values in one bin are composed
from a range of initial maps that have a constant resolution and a whole
number of used spectra.
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Acknowledgements:
Janez Kos, janez.kos(at)fmf.uni-lj.si
(End) Janez Kos [Univ. of Ljubljana], Patricia Vannier [CDS] 12-May-2015