FWD from Bahram: Re: Host galaxy for acs04-076 (aka Zamorano)

From: Tony Spadafora (ALSpadafora@lbl.gov)
Date: Mon Apr 05 2004 - 19:17:51 PDT

  • Next message: Saul Perlmutter: "Choice of which candidates to prioritize for careful "handwork" photo-z's from Mobasher."

    Begin forwarded message:
    > Date: Mon, 5 Apr 2004 22:11:28 -0400 (EDT)
    > From: Bahram Mobasher <mobasher@stsci.edu>
    > To: Greg Aldering <aldering@panisse.lbl.gov>
    > cc: hstsearch@lbl.gov
    > Subject: Re: Host galaxy for acs04-076 (aka Zamorano)
    > In-Reply-To: <Pine.GSO.4.20.0404051848220.21269-101000@europa.lbl.gov>
    > Message-ID: <Pine.GSO.4.44.0404052159500.9579-100000@ra.stsci.edu>
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    >
    >
    > Hi Greg
    >
    > At relatively high redshifts (z > 1), trying to match colors and
    > observed
    > morphologies is often mis-leading. Any interpretation of the type
    > of galaxy, based on its colors at these redshifts are not satisfactory.
    > What we do here is to say that a "local" elliptical SED, once shifted
    > to
    > the redshift of this object, gives the best fit to its observed SED.
    > This
    > will then be interpreted as the progenitor of local elliptical at
    > z=1.5.
    > Of course, if you include dust in your SED, you might get a similar
    > result
    > using a starburst SED. THis is the famous redshift-dust degeneracy
    > in estimating spectra type and redshift of objects. I guess you need
    > the
    > type
    > to identify if the host galaxy is an elliptical and hence, if the Sne
    > is
    > Type Ia. For this purpose, it may be better to use the Sne color as a
    > diagnostic.
    >
    > The photometry and redshift quoted is for both the objects, although it
    > looks as double nuclei. The point is that we are here looking at the
    > ACS
    > data where we see the two nuclei. However, on the ground-based
    > infrared
    > data, which is combined with the ACS, we only see one object due to its
    > lower resolution. We convolve the ACS with the ground-based psf when
    > doing
    > the photometry and hence, objects like this will be considered as a
    > single
    > galaxy. the alternative is to use the ACS data alone without the
    > supporting subaru and near-IR data. However, for objects at z > 1, the
    > absence of NIR data will cause problem.
    >
    > cheers
    >
    > Bahram
    >
    > ***********************************************************************
    > *****
    > * *
    > *
    > * Bahram Mobasher * Phone: (410) 338 4974
    > *
    > * Space Telescope Science Institute *
    > *
    > * 3700 San Martin Drive * fax: (410) 338 5090
    > *
    > * Baltimore MD 21218 *
    > *
    > * USA * email:
    > mobasher@stsci.edu *
    > * *
    > *
    > ***********************************************************************
    > *****
    >
    >
    > On Mon, 5 Apr 2004, Greg Aldering wrote:
    >
    >>
    >> Hi Bahram,
    >>
    >> We where just looking at the host galaxy for Zamorano, for which you
    >> quoted E-galaxy colors and z = 1.6. On the ACS 2003 coadditions there
    >> are
    >> clearly two nuclei and the hints of spiral arms. (See object in the
    >> center
    >> of the attached PS file.) Is this the same galaxy that you typed? In
    >> your
    >> experience, how often do you get an early spectrum for objects which
    >> are
    >> morphologically not early type galaxies (in the restframe UV)?
    >>
    >> Also, could you send the phot-z for Pine? We seem to be missing it
    >> according to Saul.
    >>
    >> Thanks!
    >>
    >> Greg
    >>
    >

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