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26 April 2024 |
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Article overview
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Continuum subtracting Lyman-alpha images: Low redshift studies using the Solar Blind Channel of HST/ACS | | Matthew Hayes
; Goran Ostlin
; J. Miguel Mas-Hesse
; Daniel Kunth
; | | Date: |
7 Mar 2008 | | Abstract: | (Abridged) We are undertaking an imaging study of local star-forming galaxies
in the Lyman-alpha (Lya) emission line using the Solar Blind Channel (SBC) of
the ACS onboard HST. Observations have been obtained in Lya and H-alpha and six
line-free continuum filters between ~1500 AA and the I-band. In a previous
article Hayes et al. (2005) we demonstrated that the production of Lya
line-only images (i.e. continuum subtraction) in the SBC-only data-set is
non-trivial and that supporting data is a requirement. We here develop various
methods of continuum subtraction and assess their relative performance for
given input spectral energy distributions (SED). We show that simple
assumptions about the behavior of the UV continuum consistently lead to results
that are significantly in error, and determine that a spectral fitting approach
is essential. Furthermore, fitting of a single component stellar or
stellar+nebular spectrum is not always sufficient for realistic template SEDs
and, in order to successfully recover the input observables, care must be taken
to control the contribution of nebular gas and any underlying stellar
population. Independent measurements of the metallicity must first be obtained,
while details of the initial mass function play only a small role. We identify
the need to bin together pixels to obtain signal--to--noise (S/N) ratios of
around 10 in each band before processing. At S/N=10 we are able to recover Lya
fluxes accurate to within ~30% for Lya lines with intrinsic equivalent width
W(Lya) of 10AA. This accuracy improves to <~10% for W(Lya)=100 AA. We describe
the image processing applied to the observations presented in "Ostlin et al.
(2008) and the associated data-release. We also present simulations for an
observing strategy for a future low-z Lya imaging campaign using ACS/SBC. | | Source: | arXiv, 0803.1176 | | Services: | Forum | Review | PDF | Favorites | |
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