Topic group at UKATC workshop on Science with ELTs 25-26 September 2000
Chaired by Bruno Leibundgut, notes taken by Bob Mann
These notes are extremely wideranging and are presented with a view to acting as an aide-memoir and guide to relevant sub-topics which need to be included in the discussions at Leiden. (Chairpeople and sub-chairs please note.)
Present were : R. Abraham, E. Barton, A. Blain, R. Carlberg, C. Cesarsky, M. Franx, R. Gilmozzi, I. Hook, O. Le Fevre, B. Leibundgut, R. Mann, J. Miller, G. Monnet, S. Morris, B. Peterson, M.Postman, R. Rebolo, A. Renzini, J. Rodriguez-Espinosa, R. Sancisi, D. Schade, W. Sutherland, A. Taylor, E. van Kampen, S. White.
Day 1. 25 September 2000
Bruno Leibundgut set out some initial issues:
Sancisi: To what z can we reach with Cepheids for each diameter ELT?
Renzini: Thats a suggestion for science goal determine H(z)!
Carlberg: We want to know about evolution of cosmological properties with z.
Sancisi: Where is the Dark Matter at z=5?...
White: ...do we know there is DM at z=5?
Miller: What size of telescope do you need to do it?..and how do you do it?
White : Let's start by identifying main problems
Sancisi: How much DM at each redshift (1-5) and how is it distributed?
White : Deceleration over 1z5? * assembly paths for galaxies
Franx: History of Milky Way-type galaxies
Carlberg: Enrichement history of Universe.
White: - Where different elements come from
- Reionisation history of the Universe
- Structure of the IGM
Hudson: Connection bewteen black holes and AGN
Leibungut: Gamma ray bursters (GRBs)?
Blain: High-z supernovae?... (Monnet:... - address both their properties and their use as a tool)
Carlberg: Globular cluster formation at z=3-5... (Renzini:...- NGST sees them to z=6-7)
White: Star formation modes as a function of z - variation in IMF, etc
Le Fevre : The growth of Large-Scale Structure
Postman: There are two types of problems: - those issues we don't know the answer to and
- those where a bigger telescope makes things practical by reducing time needed
Hudson: Maybe only brightest objects will have been seen to high-z by 10m class
Renzini: - Which of these will not be solved in the next ten years?
(e.g., FLAMES will give 10^5 stellar spectra with resolution needed to reveal MW history).
Morris: These are qualitative questions...error bars will shrink - we need to quantify what level of solution we'll get Renzini: Cepheids to z=1 would give evolution of cosmological parameters with z...so want primary distance
indicators to z=1 - that would be really new!
Postman: Can get 200 km/s proper motions at 1 Mpc distance in 3 years with 10 microarcsec positions...
(many): ...- but Gaia will do that?
Sancisi: Go through list and see what will be answered within ten years
Le Fevre: Also want to look at first stars... (Monnet: ...that's reionisation history..)
Sancisi: How do we know where DM is at low z?....dynamics, lensing, X-rays
Renzini: Inefficient to use lensing at high z, due to lack of very high-z background galaxies to be lensed
Sancisi: - Disk dynamics impossible, as no disks(?) at high z
- X-rays fail, as no clusters
- So have to use velocity dispersions of ellipticals to show presence of DM
Renzini: Steidel spectra can't give vel dispersion of structure at z=3, but will soon be feasible
Franx: Many emission lines are from winds, so maybe don't trace stellar mass well
Carlberg: Emission, not absorption, lines only measured with Keck for high z cluster gakaxies so far
Renzini: Rare species missed at high z so far
White: Don't have good IR spectra for any - too hard
Renzini: Sample size is the problem - bigger sample, get brighter objects, and can take spectra
Barton: Can get Fundamental Plane to z=2.5 for bright gals, 10 hr exposure on 20m (overheads):
- assume de Vauc profiles and 5100A rest-frame festures to get FP...
(Franx : ...gals at z=2.5 may not have elliptical galaxy spectra.. and Balmer lines are rotationally broadened
and they may be all we can get at 2.5)
- Observed-I TF to z=1.5 or so for typical galaxy (L*)...
(Monnet: use IFU, rather than slit to get further gain...Barton agrees)
- Halpha S/N as func of z - for use in kinematic studies....for unresolved galaxies -
results depend on how clumpy SF is in galaxies.. use OII until it leaves optical, and then
switch to Halpha. At z>5, can only see extremely strong clumpy SF regions
Sancisi: This probes TF, not DM directly * what about elliptical galaxy kinematics?
White: - We want line profiles of z=3 galaxies in a number of IR lines at R=10000 - that's an ELT problem!
- Have to be able to separate populations in galaxies, so need to have S/N to distinguish lines from
different stellar populations, and measure their kinematics.
Carlberg: So we need to be able to resolve 10pc regions at z=3 and get spectra for these resolution elements... White/Franx: We need more photons to do that, so want larger regions
Monnet: Trade-off between spatial resolution and photon numbers
Sancisi: Only need 1kpc - not 10pc
Carlberg: r_e=0.5 kpc for LBGs, so need smaller scales for disks
Sancisi: DLAs - need lots of photons for kinematics...
Renzini: ...but they only absorb, so don't make many photons - VLT is trying to image absorbers in emission
White: We haven't seen the emission from all the absorbers in the HDF, in front of QSOs
Leibundgut: Need to know how to connect DLAs to galaxies....this is structure of the IGM in the list above
Morris: Can't lens at z=5, but can it be done at z=2?
Taylor: Depends on morphology - if fragments, not relaxed galaxies, then problems with intrinsic ellipticity...
(many): ...always problems with intrinsic ellipticity
Monnet: We want to study lensing near the diffraction limit
Postman: In a 2-3 arcmin field, can get background to K=28 or so
Monnet: 2010 - should be 10^9 pixels in WF detectors
Carlberg: By then also, there will be SZ detections, so can look for dark clusters - there will be some
genuine ones in due course...aren't yet.
Renzini: Hypothetical objects - how do you assemble so much mass without triggering SF?
Carlberg: We want to measure masses for z=5 clusters detected in SZ
Franx : We want to get spectra of EROs... (many) *...is this sufficiently different from what can be done with a 10m? Renzini: What are the limits within the next 10 years of what can be done, in the way of detecting cB58-type
(lensed) objects? - cluster lenses will find many of these.
- Lensing has different effects on point sources, e.g. Type Ia SNe at high z....
- We want to compare Cepheids and Type Ia SNe at z=1. This is more new than internal dynamics
of galaxies - this is a better application for an ELT.
Carlberg: Track time with redshift using cosmochronology
Renzini: Would be very model dependent - Thorium lines are tiny features in the spectrum of a red giant,
so can be swamped by internal motions
Carlberg: So use globular clusters
White: First objects issue....try to find objects at z=10 by high-res spec of blank fields to look for Lyman
alpha emission between OH lines. NGST won't have high resolution, so better to do this from the ground.
Carlberg: This is HDF in spectral space, but problem is that fields are small, so might not get anything
White: IFU gives wide field, so should get something. * maybe line widths smaller at very high z, which helps
Le Fevre: Use narrow line filter, not IFU - more efficient... (White:... OH line too close, so can't fit in filter...)
Le Fevre: Can get filters to fit.
Leibundgut: Maybe we need to know more about what you can do with a 10m before we can assess how
feasible this is.
Carlberg: We want a spectrum for every pixel in HDF...Keck doesn't get anything in most pixels - so there
is missing light there.
White: We have examples of objects to z=4, so can predict what we should see at z=10 * there are fossils of
reionisation history in absorption spectra of QSOs, due to ISM of absorbers.
Miller: Are quasars important? - in gal formation, and as tracers of interesting locations....10^4 will be found
in surveys, so follow up with ELT to see SF properties of their envrionments.
Leibundgut: z limit for Sloan is about 6.
Sutherland: VISTA will push to z=7-8, by going into IR and having bigger aperture
Monnet: This is tough - needs high spatial resolution and depth...so it is a good ELT project
White: May have seen most of the baryons at z=2-3... (Renzini:... may have seen only 10%...)
..to get all the baryons seen in the Lyman alpha clouds we must have seen all the nucleosynthesis baryons
Renzini: But metal abundance there is too low, so the metals must be in a different phase - 20-30% of stars
were made before z=3, so expect metallicity to be ~1/3 z=0 value...so where are the metals? - not in
Lyman alpha forest or DLAs, so must be yet another phase, presumably hotter....and that's never been
seen at low z....so where is it?
White: Depends on low-z Lyman forest, for which the there's only sparse data...but take general point.
Renzini: X-ray telescopes (e.g. Xeus) are designed to find Gunn-Peterson throat in metals....maybe not best
done in the optical
Leibundgut: Deceleration to z=5...need IR to do Type Ia supernovae - good case for NGST.
White: Does it have right spectral resolution?....
Leibundgut: ...do photometry from space and low-res spectroscopy
Postman: Why is this an interesting problem, given the CMB?
White: CMB gives geometry, not equation of state, which is what deceleration parameter can give you.
Leibundgut: Papers suggest degeneracies prevent extraction of deceleration parameter
Postman: Suggest we may want to split into smaller groups
for second day, to assess needs for
observations in each heading.
Day 2. 26 September 2000
Leibundgut: Summary of Day One.
.. Now occurred a shift of format, with different people leading discussion of main topics.
Peterson: Want J and H survey to find them, then point
ELT at them to study them.
White: - Need to get quantitative feel for just how faint these objects will be, and how large a telescope we need.
- If lines are narrow, then ELT beats NGST, which has max resolution of about 3000.
- Evaluate two cases: (i) line emission from these objects; (ii) continuum step
Renzini: GRB hypernovae as sites for early star formation?
- maybe next generation of gamma ray telescopes will do that science... (White: ...needs good
follow-up coverage - wide area, then deep spectroscopy)
- SWIFT - immediate release of alerts once bursts seen
White: Use absorption spectrum of material in front of burst
Peterson: Also want to know about host galaxies - but no idea yet what they are
Renzini: Before ELT, should be hundreds of z>6 GRB IDs - do we need ELT to see the host object.
Postman: Hosts have been studied with HST
Renzini: Hypernovae (50-60 M_solar), will be seen in IR and are good tracers of early star formation.
White: From known objects, can guess what magnitudes will be
Renzini: Several satellites and ground-based follow-up programes will work in next decade, yielding many
high-z (z=6-10) IDs...and ELT will be required to image the host galaxies.....GR satellite should
give positions to a few arcsec Leibundgut * can the time dilation in the decay be used to estimate z?... (many): .....isn't dispersion in intrinsic time delay too great?
White: - Absorption line spectroscopy can be done with a 10m, provided that you catch the burst quickly
enough - but host galaxy imaging needs ELT
- What is special about environments of GRBs, as compared to other SF regions?....and we should
answer that at lower redshift in next 10 years.
- Other method is high resolution absorption spectra along QSO LOS
Postman: Sloan should get about 100 z>6 QSOs at mags of z'=20
White: Need ELT to get high resolution spectra to detect fossils of processes out to z=20
Hudson: Want multiple skewers through structures to get spatial structure
White: ..... and that requires lower S/N spectra - so does that need an ELT??
Peterson: But lines will blend if resolution low
White: - Statistical measures only - don't need to identify all clouds
- Very high resolution needed for metal lines in walls of bubbles blown out by forming galaxies.
Morris: Arjun Dey has some of the required numbers already - for case of 30m.
Peterson: If z=10 objects have Lyman alpha lines, then profiles should show asymmetry due to absorption
in HII regions surrounding emission regions
Franx: Assembly of galaxies and evolution of MW-like objects
- What happens to LBGs? - may be a question for a lot of 10m tine....these
end up in clusters,
they're not normal spirals - are they related to them?
- Want to measure LSS of LBGs - be done in the next 10 years
- Progenitors of normal galaxies have R=27-28 at z=3 (Steinmetz prediction): so would then want
to study their clustering.
Hudson: Would also want pairwise velocities from spectra
to get some mass info.
Franx: Need simulations of surface brightness of these objects to assess requirements
White: Want LBG spectra in IR, to get rest frame optical, as well as UV, as now
Le Fevre: Also want to look in near/mid-IR to get census of galaxies including the dusty ones
Franx: Maybe submm-selection with ALMA would be best
Blain: ALMA gets CO lines (and redshifts) for most galaxies, but not all
Cesarsky: FIR-selection would be best, but no instrument expected
Renzini: - Want to know what LBGs look like, at level of 10^4 pixels per galaxy
- Latest "Madau plot" claims to have seen whole SF history, so no great hidden population
of Star-forming galaxies at high-z
White: Also want spatially-resolved spectrum to get kinematics
Postman: Not easy for even 100m telescope, based on HDF population
Sancisi: What is known of spectra of LBGs now?
Franx: Major question is whether there can be a good mass estimator
Monnet: Difficult if mergers go on....need bound systems
Franx: ALMA may be major competition - get kinematics (and masses) from CO lines
Renzini: - Really want stellar absorption lines, not gas absorption, which could be from gas flows...can also
get rotation curves
- Don't know how ALMA can get 5 mas - should be 50mas?
Le Fevre: Also want census of sources, to get LF, etc
Renzini: Need to prioritise what is the most important thing - look at LBGs in detail, or extend their LF
by a couple of magnitudes?
Carlberg: ALMA gives SF-selection, so need to complement with selection by old stellar pops, and probe
mass and Fundamental Plane, etc....and that will need an ELT, rather than a 10m.
Franx: Neglected physics of LBGs - know this for local galaxies, but have little idea at high-z.
Peterson: Want to follow stellar abundances and populations as a function of z - e.g. tracking possible
variation of the IMF.
White: Keck does better on cB58 than ELT will do on unlensed LBGs, which must make us cautious
about what can be done.
Franx: Missed properties of halos in which galaxies sit - but that's DM, as discussed yesterday
Sancisi: Out to ow far can 10m telescopes get Fundamental Plane? (Franx: ...to z=1 or so ..)..
Renzini: No Fundamental Plane for star-forming gals, so when most galaxies are making stars
the FP will vanish
White: Presumably the older population is lurking underneath, just hidden by younger stars
Renzini: Could be 1-1.5 GYr worth of older stars - and SIRTF will be very important in looking
for these stars, by rest frame NIR
Franx: Few non-SF galaxies found at z=3 (White: some radio galaxies only), which must limit the star
formation happening at z=10, suggesting there's not one burst at z=10, followed by passive evolution
Leibundgut: Our basic task is to see how popn we know at z=3 ties in to z=0 popn.
White: .... that will need stellar masses.
Le Fevre: Growth of Structure
- How do we form the clusters we see today? - e.g. Coma - we have
above z=1...some info at z=3, but little more.
- Problem is we see only brightest galaxies
- Need significant volumes to be probed to get real census of galaxy population and structure
White: What is the scientific goal here? - what have we learnt
in the 20 years since Peebles started
measuring clustering in Zwicky catalogue?
Postman: Learning about bias, and nature of DM from evolution of redshift
Carlberg: Small separation correlation function gives merging - that's physics, not just statistics
Sancisi: - What is the prediction at high-z?
- are there telling obsevations to be made?
- what if clustering is seen at level not expected?
Le Fevre: First step is to measure clustering, then interpret
Hudson: Want to study morphology-density relation, as probe of galaxy evolution
Carlberg: Not clear that we have a good theory yet - semi-analytical models will be ruled out by current data
White: Relationship between galaxy and mass distributions will be more complicated at z=3 than now,
so comparing clustering of different classes of galaxy at z=3 will yield info about galaxy
formation and evolution
Renzini: But this can be done with 10m? - large numbers of galaxies, if tip of iceberg, as far as LF
White: Need census of different types of galaxy
Postman: We got it wrong at low-z, when used only bright galaxies in the 80s - needed to go deeper
to see full richness of structure
Le Fevre: Weak lensing is only way to link galaxy and mass distribution fully
White: Cross-correlation of gals and absorption line spectra - assuming abs line popn is closer to
mass than galaxies
Le Fevre: Evolution of bias?
Postman: Higher order clustering possible with enough galaxies, and predictions strong at high z,
so gives powerful handle on bias
Renzini: What will be done by 2010?
Postman: Will be done out to z=1 or so
White: Better statistics on populations we know now, but little on other types of galaxy that we
can't get spectra for now
Renzini: - 99% of mass locally is in 1% of galaxies, so massive galaxies must be the
most interesting to study
- By z=1, we can assess whether the same holds, using 10m telescopes
- But at what point do we move to a regime where mass is dominated by the dwarfs
Schade: If we know the age distribution of stars in galaxies,
then we can assess where these stars are
(when they are formed?: Ed) as a function of redshift
Morris: Renzini's argument would lead one to study only cDs locally
White: No, space density of LBGs nearer to that of L* galaxies than Abell clusters
White: Only way to test theories is to look at predicted properties of different classes of galaxies
Le Fevre: Assembly of clusters
White: Want to find clusters out to z=2 - seeing ROSAT-like clusters there would rule out Gaussian picture
Hudson: Also want to look at groups, if there aren't clusters at z>2
White: Start with X-rays, then SZ and NIR follow-up
Renzini: Wide NIR surveys should find clusters to z=1.5 or so
Le Fevre: Work looking around radio galaxies - suggestion to date is that we're nearly finding z=2-3 clusters
Renzini: Want internal velocity dispersions of z=3 structures, to see if these are bound structures
White: LBG distribution doesn't really show clusters, as such, just clustering
Le Fevre: - Rich protoclusters will be rare - 1/ sq deg - so needs a lot of work
- Also get pointers from weak lensing maps
Franx: Weak lensing needs understanding of population between observer and lens
Leibundgut: Is it interesting to look at merger rates?
Carlberg: It's the link between LSS and galaxy evolution
White: That needs good imaging for all redshift range of interest
Postman: Galaxies and black holes:
- BH mass correlates
with central velocity dispersion of bulge, and size of bulge (with slightly
scatter)...so galaxy and BH know about each other.
- This is on the basis of about 30 galaxies
- Does BH have some role in formation of galaxy?....does gal/BH relation hold to high redshift?
- 10mas=70pc at z=1 or greater - need the best resolution, to get as close to the blackhole as possible.
White: Really needed HST - ground-based mass estimates
weren't accurate enough, as resolution
not good enough.
Postman: Limit is 10^8 M_solar at Virgo....so, an ELT can go to lower masses or get
10^8 M_solar BH at z=0.1.
Renzini: Goal is to determine m_BH-sigma relation out to z=1?... (Postman: yes)
- but we suppose that little BH evolution occurred at at z<1, as AGN activity is low
White: - But not clear that all ways of accreting mass will give light in the similar way.
- Want to test model predictions of build-up of bulge mass since z=1.
Renzini: Of all known AGN, only one has a bona fide binary BH...wouldn't you expect more with
lots of merging?
Franx: Presence of gas helps merging of black holes..
Renzini: ... not clear by how much
Postman: Should be able to go out to z=2 relatively easily...
Monnet: ... but would have to go to the NIR, which would make things harder
Franx : Could use emission lines, which would push to higher redshifts.
White: This is concentrating on hard aspects of AGN to observe - isn't there an easier
property of AGN we can use? Sancisi: Is this a case for 100m, versus 30m?
Leibundgut: What's the catch-phrase? - growth of BH?
Postman: More than that - could be key to important phase of galaxy evolution
Sancisi: 10m telescopes haven't addressed this yet - will they cover it once they have adaptive optics?...so hard to make case for 100m here...
Monnet: AO on 8-10m work will only start in earnest in 2-3 years
White: Could well be AO+10m project initially?
Leibundgut: How do BH form in the first place? - in detail....when should this happen?
Renzini: We see quasars out to z=6...
White: - Bulge-BH relation suggests bulge and BH formation are linked intimately.
- Need to do calculation to assess quantitative feasibility for extending relation to z=1-2.
Blain: Would an extra factor of ten in resolution help with general picture of AGN?...
Schade: ...maybe interferometry, since the nucleus is bright
White/Carlberg: Probe unified models, by resolving broad-line region, etc
White: - Can use narrow filter on bright lines
- But maybe VLTI will get there before an ELT.....but an easy case to make for a science driver
Summarising and preparation for afternoon presentation.
Leibundgut: Need list of high-priority things to do (as
at start of day)...and need to cut list down
to highest priorities...
Sancisi: ...and start to address what diameter is needed for each question
Renzini: Good to measure masses of globular cluster populations of galaxies as a function of
redshift - to be used as a tracer of the build-up of the mass in galaxies....the fact they
are pointlike maximises the advantage from a large telescope
Carlberg: Two broad categories: evolution of smooth component
(e.g. evolution of cosmological parameters), and evolution of structure
Renzini: Cepheids to z=0.8 can calibrate Type Ia SNe, which can be used to higher redshift
Leibundgut: Is this a science driver for a billion euro project?
Carlberg: Suggest cosmological parameter evolution may be better probed by geometry of 2D redshift-space correlation function
White: But isn't this a 10m project? - extending Steidel et al programme
Leibundgut: ... and from Planck, SNAP, etc
- Connect growth of structure, assembly of galaxies, and structure of IGM....
- But aren't all the questions identified connected to each other, at some level?
Postman: NGST will say when galaxies form, ELT will say how - that's the soundbite
- need to give detailed picture of how galaxies formed
Leibundgut: What observations contribute to answering that
White: Other top-level things, before breaking down that one (many)
- First objects/light
White: First light - the beginnings of galaxies
Morris: Evolution of cosmological parameters
Renzini: What does it add knowing parameters at z=1, etc, above and beyond knowing what it is now?
Carlberg/White: Quintessence - probing equation of state of Universe....constraining fundamental physics
Detailed picture of how galaxies form