Re: acs04-076 host colors (fwd)

From: Ariel Goobar (ariel@physto.se)
Date: Tue Dec 14 2004 - 06:09:18 PST

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    Message from Tomas on photo-z below. As he is not on hstsearch@lbl.gov
    he cannot himself post this message.
    --------------------------------------------------------------------------
    Hi Rachel et al.

    Based on the latest photometry, I get the following phot-zs for the host:
    SE knot, 0.18 arcsec aperture: z=1.47
    NW knot, 0.18 arcsec aperture: z=1.58
    SW knot, 0.18 arcsec aperture: z=1.65
    all, 0.75 arcsec aperture: z=1.59
    all, 1.05 arcsec aperture: z=1.62.

    I wouldn't trust the 'knot' measurements too much since these are
    measured in small
    apertures where color dependent aperture corrections should be applied
    (and where
    alignment/registration between filters/instruments is crucial).
    The 'large aperture' measurements should be more correct. This, of course,
    assumes that the knots really are at the same redshift. Considering the
    close phot-zs for the knots, I think we can assume that they are. My
    choice between the two large aperture would be the 1 arcsec, i.e.,
    the phot-z is z ~1.62. From the plotted probability distributions, I would
    assume a 1sigma error of about ±0.08. I more conservative estimate
    would be z=1.6 ±0.1
    The spectral type of the host is approximately consistent an Sab spiral

    In the attached plot, IDs=6, 7, 8, 9 and 10, corresponds to SE, NW, SW
    knots and 0.75+1.05 apertures, respectively.

    Tomas





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