Re: acs04-076 host colors (fwd)

From: Rachel Gibbons (rachel.a.gibbons@vanderbilt.edu)
Date: Thu Dec 09 2004 - 06:30:38 PST

  • Next message: Ariel Goobar: "Re: acs04-076 host colors (fwd)"

    Hi Tomas,

        I've posted new measurements on the TWiki. As explained in the
    notes there, these colors should bring the redshift fit down from 1.8.
    I've also added fluxes for a 3rd knot not fitted previously, and for
    a larger 0''.75 aperture.

    Rachel

    On Tue, Dec 07, 2004 at 09:54:45AM +0100, Tomas Dahlen wrote:
    > Hi Rachel,
    >
    > that sounds fine. Let me have the new measurements when you have them
    > and I'll rerun the phot-zs. The best fit spectral type for the old
    > measurements
    > was ~1.4 (an interpolation between 1=E and 2=Sbc), that is
    > approximately a Sa-Sab galaxy -
    > a rather old/red spiral. This may, however, change with the new photometry.
    >
    > Tomas
    >
    > Rachel Gibbons wrote:
    >
    > >Tomas,
    > >
    > > I just realized I didn't match the ACS and NICMOS apertures,
    > >the ACS imaging is on a smaller scale than I thought. I'll update
    > >the numbers on the TWiki tomorrow and let you know when I do.
    > >
    > >Rachel
    > >
    > >On Mon, Dec 06, 2004 at 09:27:29AM +0100, Tomas Dahlen wrote:
    > >
    > >
    > >>Hi Ariel & Rachel,
    > >>
    > >>
    > >>Thanks for sending the errors estimates for the ACS. I'll recalculate
    > >>the phot-zs
    > >>using these.
    > >>Besides that test, we should probably do another test to check the
    > >>phot-zs.
    > >>
    > >>With the small apertures used to measure flux, we may loose relatively
    > >>more flux in NICMOS compared to
    > >>ACS due to the larger fwhm in NICMOS (generally, when doing phot-zs I
    > >>usually use an aperture with
    > >>diameter 2-3 times the fwhm). This could bias the determination of the
    > >>phot-zs.
    > >>
    > >>What I propose is to measure the flux in a large aperture that covers
    > >>both knots (since they obviously are at the same redshift).
    > >>Maybe ~1 arcsec would be fine. An alternative is to put as large
    > >>apertures as possible over each knot (without them overlapping)
    > >>if this aperture will be as large as ~0.5 arcsec (diameter).
    > >>
    > >>I hope this doesn?t mean too much extra work, but I think it is worth
    > >>checking.
    > >>
    > >>Cheers,
    > >>
    > >>Tomas
    > >>
    > >>
    > >>
    > >>
    > >
    > >
    > >
    >
    >

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