GSMT Science Use Case
Title: 30m-class Follow-up Observations of JWST Imaged
Galaxies & AGN
Authors: Chris Packham (Florida), Almudena Alonso-Herrero (CSIC, Spain),
Nancy A. Levenson (Kentucky, USA), Rachel E. Mason (Gemini) & Pat Roche (Oxford,
UK)
Summary Table:
Summarize the observations in terms of telescope, instruments, number of nights,
observing mode and instrument and AO requirements.
Telescope Instrument # Nights
Mode
GMT
MISE
A few
tens of
nights
Imaging &
lo-res
spectroscopy
TMT
MIRES
A few
tens of
nights
Imaging &
lo-res
spectroscopy
 range(m)
FOV
/ AO
Mode
N (imaging & R~100 MIR 15”+
spec.) & Q
AO
Band
(imaging)
N (imaging & R~100 MIR 15”+
spec.) & Q
AO
Band
(imaging)
Scientific Motivation:
Why is this use case of scientific interest?
The fueling of black holes occurring in active galactic nuclei (AGN) is fundamental to
the evolution of galaxies. AGN themselves are largely explained in the context of a
unified theory, by which a geometrically and optically thick torus of gas and dust
obscures the AGN central engine. The exact properties of the torus remain uncertain, and
there are still several open questions: (a) What is the nature of the torus material and its
connection with the ISM of the host galaxy, (b) How do the properties, such as, geometry
and optical depth, of the torus depend on the AGN luminosity and/or activity class, (c)
Do the dust properties change with the AGN luminosity/type, and (d) What is the role of
nuclear (<100 pc) starbursts in feeding and/or obscuring AGNs? Observations at mid-IR
(MIR, 7-26µm) wavelengths are essential to these investigations as the torus intercepts
and re-radiates a substantial amount of flux from the central engine, peaking in the MIR.
We propose to obtain high spatial resolution images and low-spectral resolution
spectroscopy of AGN and luminous IR galaxies (LIRGs). These observations will be
made in synergy with the results that will be obtained from the JWST and hence are
analogous to the recent observations we have made using Gemini to help to fully interpret
the Spitzer observations. In both the Spitzer and JWST epochs, only the superior spatial
afforded by the largest ground based telescopes observing at the diffraction limit, allows
the AGN, star formation sites, and diffuse emission to be disentangled from each other.
Such observations are crucial to understand the local universe for application to more
distant objects. JWST observations will form the foundation stone of understanding
galaxy and AGN formation, where black hole and AGN evolution may become evident.
However, it is clear that even JWST observations will have contamination from emission
from diffuse HII regions, necessitating the use of 30m class telescopes. We note that a
z=0.5, the spatial resolution of JWST is 1.5kpc (including galactic star forming rings,
etc.), whereas for the GSMT the spatial resolution is 330 pc (nuclear dominated). JWST
will be an outstanding resource for taking integrated imaging and spectroscopic
observations of AGN and galaxies, but only the spatial resolution afforded by the GSMTs
will allow targeted and fine scale investigations of the JWST results.
As an illustration of the type of synergistic work one can perform from 30m ground
based telescopes and that of the JWST, we show a comparison of images and spectra
taken from the Spitzer and Gemini at similar wavelengths below (see for example
Alonso-Herrero et al. 2006, Diaz-Santos et al. 2008).
To illustrate the differences this can cause to the observed spectrum of galaxies, we show
below a comparison of Spitzer (~600 pc) and T-ReCS (~60 pc) spectra of NGC3256
(Diaz-Santos et al., in prep), showing significantly different results. In this case, silicate
absorption is essentially only from southern condensate whereas PAH dominates the
nucleus, as shown when comparing the T-ReCS spectra (dotted) to the Spitzer spectra
(solid). Note in the figure below the very substantial variation between the T-ReCS and
Spitzer spectra due to the different extraction aperture sizes, where surrounding diffuse
emission can easily confuse and contaminate the spectra, possibly misdiagnosing any
present nuclear activity, star forming regions, and the torus parameter.
Approach:
How can you use TMT and/or GMT and their candidate instruments to address this
problem? Describe the observing strategy, including target selection and the needed
measurements.
We plan imaging observations using MISE and MIRES through either broad band N or
through the 1µm wide filters with c~8.7m. We will use these observations to plot
color-color diagrams to investigate the star formation rate, with minimal contamination
from surrounding emission sites. We will obtain a Q band image, which when combined
with other data, helps to strongly constrains models of local dusty environments. We also
plan N band spectroscopic observations of the central regions, which will allow an
unprecedentedly precise view of the torus, allowing key predictions of the so-called
clumpy model of AGN to be probed (Nenkova et al. 2008a, b). Clumpy models suggest
that the torus is compact, necessitating the use of the highest available spatial resolution
MIR observations. If available, polarimetry of the nuclear regions will be used.
Targets will be selected to form a homogenous survey of AGN and LIRGs across a wide
range of luminosities. There are already observational and theoretical hints that the
AGN, torus, and host galaxy are affected by the level of accretion, and a high spatial
resolution MIR survey presents an ideal method to probe the activity and its effects on
the host galaxy. Where possible, targets will be selected to follow-up ongoing MIR
surveys from existing 8m class telescopes and observations from the JWST. The number
of sources to produce a sample could number in the 100-200 objects.
Limiting Factors and the Current State of the Art:
What are the limiting factors for this problem (e.g. sensitivity, spatial resolution, time
resolution)? Why hasn’t this problem been solved with current facilities?
Previous observations have been limited to by the sensitivity and spatial resolution of the
8m telescopes. We note that if the D4 gain in observational speed (and with all other
parameters remaining equal, such as thermal background) is realized on the GSMTs, this
would result in a speed increase of ~200 times that of the existing 8m telescopes. Despite
this, the JWST will maintain a 1-2 order of magnitude better point source sensitivity over
that of the GSMT’s, but with a factor of ~4 times worse spatial resolution. We therefore
encourage the development and optimization of high spatial resolution imaging and
spectroscopy on the MIR instrumentation of the GSMT’s. Further, we encourage the use
of novel observing modes, such as the already envisioned nulling mode of MISE, and the
adoption of polarimetry (as discussed below). It is our understanding that the brightness
limits of the JWST will preclude observations of objects brighter than 4mJy, leaving
many of the brightest and often ‘favorite’ objects for the GSMT in this epoch. Finally,
we note that maintaining high image quality or high Strehl ratios on the existing 8m class
telescopes in the MIR has been challenging. As the high spatial resolution domain is a
key area of MIR GSMT science, we encourage the careful consideration of this during
the design phases.
Comparison of point source sensitivity of contemporary IR and submillimeter instruments to
MIDIR on a 30/42/60 m ELT. Taken from the MIDIR E-ELT conceptual design study.
Technical Details:
How would you actually carry out this program? Justify the sensitivities, exposure times,
number of fields, total cost in terms of telescope hours or nights. Mode of observation,
queue, classical, TOO, synoptic etc.
The observations would ideally be made in queue mode. The number of objects, to make
a detailed survey, could number around 100-200. Whilst just a very approximate
estimate, each observation may take 2-5 hours.
Preparatory, Supporting, and Followup Observations:
What data are needed in advance of, or in support of these projects? If these require
observing time on 4-10m class telescopes estimate the amount of time needed. What
followup observations are needed?
These observations would in many senses be complimentary to JWST observations, and
existing programs of observations on the current 8m class telescopes will form essential
preparatory work.
Anticipated Results:
What would you expect to get from the observations? Describe simulated data and results
where appropriate.
Please see the above scientific motivation.
Requirements and Goals Beyond the GMT and TMT Baseline Instrument Designs:
Are there capabilities needed for this science that are not in the TMT and GMT telescope,
AO system and baseline instrument configurations? If so, what is the flow-down from the
high level goals to the instrument requirements?
High spatial resolution imaging and low-spectral resolution (R~100) spectroscopy is
needed for this program. We note that MISE have these capabilities, but that MIRES
does not, and we encourage the adoption of these modes in MIRES.
Polarimetry is highly desirable, and would help to clearly distinguish the GSMTs from
the JWST’s capabilities, as there is no polarimetry on the JWST, nor other upcoming
space-based missions at IR wavelengths (to our knowledge). We note in general that
polarimetry would be a highly desirable mode on the GSMTs. The polarimetric
community is small but significant, and we note that ~9% of time requests on instruments
that offer polarimetry (using the WHT’s ISIS as a guide) as a standard mode are for
imaging- and/or spectro-polarimetric observations. Polarimetry has proven fundamental
to addressing comets, debris discs, & AGN, but is a particularly ‘photon-hungry’ and
high spatial resolution application. As there is little or no deployment on space based
observatories it is a clear area of exploitation-space open for GSMT at all wavelengths.
Describe the need for specific observing conditions or operations mode(s) (needed image
quality; atmospheric transmission; need for ‘interrupt-driven’ observations)
Queue mode observations for MIR observations have proven crucial to matching the
often specific observing constraints optimal for observations of this type. Diffraction
limited observing will also be fundamental to realizing the potential of this science case.
Describe the potential of the resulting database for ‘mining’ in service of carrying out
complementary scientific programs; planning future programs
Describe the potential role of other ground- and space- based facilities in carrying out
the proposed investigation (e.g. JWST; ALMA; LST)
As noted above, these observations are complimentary and synergistic with JWST.
Summary: