<=== observer ===>
"PVDWERF",\
"van der Werf, P.P.",\
"",\
"European Southern Observatory",\
"Karl-Schwarzschild-Strasse 2",\
"",\
"85748",\
"Garching bei Muenchen",\
"Germany",\
"49 89 32006420",\
"49 89 32006480",\
"pvdwerf@eso.org"
<=== proposal ===>
"PPW_VDOS", 1, 4,\
{"active galactic nuclei",\
"galaxy formation",\
"quasars",\
"starburst galaxies"},\
{"G.K. Miley",\
"Th. de Graauw"}
<=== title ===>
Star formation and active nucleus in distant radio galaxies: a pilot study
<=== abstract ===>
SCIENTIFIC ABSTRACT
We propose to probe the interstellar medium in the z=1.1 radio
galaxy 3C368 (autumn launch) or 3C356 (spring launch) with SWS, PHOT
and LWS, in order to gain insight into the relative importance of star
formation and active nucleus in these distant objects. Strong
indications for active star formation have been found in photometry,
imaging and imaging spectroscopy in distant radio galaxies.
These include (1) the alignment effect between the radio axis and
optical/near-IR continuum light (2) extended emission line regions
(in e.g. Lyman alpha, [O II], [O III]) aligned with the optical/radio
continuum axis (3) spectral energy distributions (SEDs) which show a
strong blue component (4) mm-wave continuum detections far exceeding
the expected synchrotron flux and thus attributed to thermal dust
emission (5) the detection of large quantities of molecular gas in a
number of radio galaxies with z between 1 and 3 (including one of our
candidate sources). The properties (1)-(3) are interpreted in terms of
intense star formation induced by the radio jet, or scattering of the
nuclear light. Both interpretations have problems, and it is likely
that a combination of both is at work. The relative importance of star
formation and active nucleus for the observed properties is one of the most
outstanding question in the study of these objects. Properties (4)-(5)
above show that the raw material for forming stars is abundantly
present, and bring to mind the probable primeval galaxy IRAS F10214+4724.
They also directly show that these objects are very dusty and their
nuclear regions can therefore only be probed at mid-IR and longer
wavelengths. The brightest and most important lines fall in wavelength
regions that are inaccessible from the ground, and are too faint to be
observed from the KAO. They can thus ONLY be observed with ISO.
Therefore, in order to study the properties and excitation of the
interstellar medium (ISM) in these objects we will (1) use PHOT to measure
intensity and spectral index of the dust emission on the (rest frame)
Wien side of the dust emission spectrum, yielding dust temperature and
luminosity, (2) use SWS and LWS to measure 5 bright and diagnostic
fine-structure lines, covering a range of excitation potentials. Line
strengths (or useful limits) and ratios will allow us to determine
such parameters as slope and cutoff of the ionizing continuum, and
ionization parameter (unhindered by obscuring dust), with
straightforward implications for the relative importance of star
formation and active nucleus. Since high z radio galaxies are
currently our only way to probe galaxies at relatively early cosmological
epochs, the result will have direct implications for our understanding
of the early evolution of galaxies. The ISO observations will be
complemented with ground-based measurements, e.g., of the submm continuum.
OBSERVATION SUMMARY
Line measurements: selected lines are listed below under Scientific
Justification. With this choice we (1) cover a sufficient range of excitation
conditions (2) optimize for the brightest lines (3) avoid uncertain
abundance corrections by using ratios of lines from the same species,
and (4) probe various phases of the ISM including photodissociation
regions ([O I]), HII regions ([Ne II], [O III]), AGN narrow line
region ([O III], [Ne III]) and coronal line region ([O IV]).
As an illustration of the diagnostic power of this selection, we note
that for a starburst model [Ne II] / [Ne III] >> 1, whereas in an AGN
model [Ne II] / [Ne III] << 1. The detection of [O IV] directly
implies the hard UV continuum of an AGN, where a coronal line region
strongly radiates in this line.
Continuum measurements: PHOT-C will be used at 60, 100 and 200 micron,
corresponding to rest wavelengths of 30, 50 and 100 micron. This will
allow us to probe the Wien side (and for warm dust the peak) of the
SED and will allow a direct comparison of these sources to starburst
galaxies, AGNs and ultraluminous galaxies detected by IRAS in terms of
luminosity and temperature of the dust.
Line strength predictions are based on observations of M82 and NGC1068
for [Ne II], [O I] and [O III], scaled by CO luminosity and placed at
a redshift of 1.1. For [Ne III] and [O IV] model predictions are used,
scaled in a similar way. This yields e.g. an estimated 1e-17 W/m2 for
[Ne II] which is within easy reach with the SWS.
Our calculations indicate that the neon lines are expected to be
detected at high significance in about 15 minutes of integration time
(per line). For the [O I] line we expect a S/N of 4 after 30 minutes,
while (in case of an AGN) [O IV] will give S/N=3 in 30 minutes.
The same approach has been used to predict the continuum strengths.
During the SWS observations, simultaneous measurements will be carried
out of the H2 v=1-0 S(1) line (redshifted to 4.5 micron) and the [Si IX]
3.935 micron line (which is bright in Seyfert nuclei). These lines do
not form part of the main programme and are merely included in order
to use the freely available time in the other SWS band.
<=== scientific_justification ===>
Breakdown of observing time contributions:
==========================================
Time distribution for autumn launch targets:
Team top 40% second 30% last 30%
SWS : 3153 2380 4602
Time distribution for spring launch targets:
Team top 40% second 30% last 30%
SWS : 3153 2380 4602
Summary of proposed measurements:
=================================
Line/ Excitation Observed wavelength TDT AOT Priority
continuum potential 3C368 3C356
(autumn) (spring)
[eV] [micron] [micron] [sec]
[Ne II] 21.56 27.3095 26.6650 )_ 1760 SWS02 1
[Ne III] 40.96 33.1417 32.3596 )
[O I] 0 134.6634 131.4853 2560 LWS02 3
[O III] 35.12 110.4322 107.8260 2042 LWS02 3
[O IV] 54.93 55.2284 53.9250 2380 LWS02 2
60 micron 60 60 )
100 micron 100 100 )- 1393 PHT22 1
200 micron 200 200 )
-----
10135 seconds ~= 2.8 hours
<=== autumn_launch_targets ===>
1,"SWS02",1.,"N", "3C368 ",18.04600, +11.02083, 1950, 0., 0., 1760,0
2,"LWS02",2.,"N", "3C368 ",18.04600, +11.02083, 1950, 0., 0., 2380,0
3,"LWS02",3.,"N", "3C368 ",18.04600, +11.02083, 1950, 0., 0., 2560,0
4,"LWS02",3.,"N", "3C368 ",18.04600, +11.02083, 1950, 0., 0., 2042,0
5,"PHT22",1.,"N", "3C368 ",18.04600, +11.02083, 1950, 0., 0., 1393,0
<=== spring_launch_targets ===>
1,"SWS02",1.,"N", "3C356 ",17.38533, +51.00306, 1950, 0., 0., 1760,0
2,"LWS02",2.,"N", "3C356 ",17.38533, +51.00306, 1950, 0., 0., 2380,0
3,"LWS02",3.,"N", "3C356 ",17.38533, +51.00306, 1950, 0., 0., 2560,0
4,"LWS02",3.,"N", "3C356 ",17.38533, +51.00306, 1950, 0., 0., 2042,0
5,"PHT22",1.,"N", "3C356 ",17.38533, +51.00306, 1950, 0., 0., 1393,0