10660(  1) - 04/05/05 12:23  - [  1]

    PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS   ST ScI Use Only
                                                       ID:      10660
                                                       Version: 1
                                                       Check-in Date: 05-Apr-2005
                                                                      16:23:14

1.Proposal Title:
The Spectral Energy Distributions of Low-luminosity AGNs
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2. Proposal For  3. Cycle  4. Parallel Pointing Tolerance
AR               14        <none>
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5. Investigators
                                                                                     Contact?
    PI: Dr. Luis C. Ho                    Carnegie Institution of Washington
   CoI: Mr. Hung-Yu Jian                  National Taiwan University, Dept. of          N
                                          Physics

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6. Abstract

The spectral energy distributions (SEDs) of AGNs encode valuable information on the
physics of accretion onto black holes. Until very recently, however, data on SEDs
for low-luminosity AGNs (LINERs and nearby Seyferts) have been sorely lacking.
Initial studies based on small samples indicate that the SEDs of low-luminosity AGNs
exhibit profound differences compared to those of their more luminous counterparts
such as classical Seyferts and quasars. The most noticeable trait is the weakness of
the "big blue bump, " a feature normally attributed to thermal emission from a thin
accretion disk. This unexpected but potentially very important result has led to
suggestions that low-luminosity AGNs accrete via a fundamentally different mode,
perhaps in a hot, radiatively inefficient flow. This proposition, if it can be
confirmed, has important implications for our understanding of black hole accretion
and for elucidating the physical properties of low-level nuclear activity, which is
extremely common in nearby galaxies. We propose to significantly enlarge the current
sample of SEDs for low-luminosity AGNs by combining existing high-resolution nuclear
fluxes measured in the radio (VLA) and X-rays (Chandra) with new optical and near-
infrared data points to be extracted from archival WFPC2, ACS, and NICMOS images.
This project will increase the current sample of SEDs by more than an order of
magnitude.
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                                                10660(  1) - 04/05/05 12:23  - [  2]

            Summary Form for Proposal  10660

  Item                         Used in this proposal
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  Proposal Category            AR
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