Transcript Spectroscopy in Cosmology and Galaxy Evolution 2005

Spectroscopy in
Cosmology and Galaxy
Evolution
2005-2015
Conference Summary
Michael Strauss
Princeton University
There are many imaging surveys
planned in the optical (e.g., PanSTARRS, VISTA, LSST), and
near-IR (UKIDSS, DUNE)
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People here don’t need convincing that real
spectroscopy is at least as valuable.
It is through spectra that we determine the astrophysics
of individual objects.
But photo-z’s remain powerful, as argued by Wolf,
Hildenbrandt, and Benítez.
The combination of imaging and spectroscopy is
particularly valuable (indeed, crucial, says Gunn). One
can use cross-correlation of the two to constrain redshift
distributions (Newman).
Spectra “good enough for a
redshift”?
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Focussed surveys to get redshifts only can go
much quicker than more comprehensive projects
(PRIMUS, ADEPT, HETDEX, FASTSOUND).
This is a fine approach to baryon oscillation
projects.
But high S/N spectra are tremendously valuable
for stellar populations, M/L, ages, star formation
rate, metallicities, velocity dispersions, emissionline diagnostics, AGN activity (Thomas, me),
serendipity…
Serendipity…
Gravitationally lensed galaxies
behind LRGs; Bolton
Ly emitters in
DEEP2; Davis
We’re never satisfied with the
quality of spectra we have…
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Excellent spectrophotometry was emphasized by Panter
and others.
Broad wavelength coverage, including NIR and into
Spitzer bands (Maraston, Gunn). The advent of FMOS
and SIDE are particularly exciting here.
High S/N, even for faint objects, as emphasized by
Smith, Chilingarian, and others.
High resolution (R=5000), to study dwarfs, and to
resolve the OH forest.
Studies of environment effects on galaxy properties,
especially clusters (Wolf, Maurogordato, Khochfar,
Tanaka, Kovac).
We also need spatially resolved
spectroscopy of galaxies!
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The aperture effects in SDSS are severe,
making it difficult to compare spectra at
low and high redshifts.
There is much to be learned from internal
kinematics of galaxies, as, e.g., the
SAURON survey has shown us for nearby
ellipticals. Multiple deployable IFU’s?
(KMOS, also SIDE with micro-IFU’s).
At what redshift do we want
to work?
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Shanks argues that the z<1 universe of galaxies
is “solved”. But we saw lots of reasons to study
it in more detail, including “archeology” via
detailed spectral modelling of z~0 galaxies
(Brinchmann, Maraston, Panter, Kauffmann,
Gonzàlez-Delgado and others).
We are still trying to understand observationally
the merger rate, and the drop in star formation
rate since z~1 (Tresse).
We shouldn’t forget the archeology of studying
our own Milky Way in detail, to learn about the
formation of the galaxy we know best (SEGUE,
RAVE, and other surveys).
The high redshift universe is
interesting too!
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Galaxy populations change dramatically at z>1.5. We
argue over the galaxy census at z=3 and its connection
to low redshift.
It is difficult work. Even getting redshifts at z>1.4
requires wide wavelength coverage, including NIR.
Physical studies are even more difficult, but are very
important. It will be a long time before we can hope for
SDSS-like spectra at high z.
VVDS (Le Fèvre) and DEEP2 (Davis) show we can do
large surveys at z~1, but we’re still very cosmic-variance
limited.
We heard almost nothing about surveys at z≥3.
There is much work to be
done on understanding UV
spectra of galaxies (and
stars!; Brinchmann, Heap),
needed for high-z surveys.
Emission-line ratios are interestingly
different at z=2-3 and z=0!
We also haven’t mentioned
other types of spectroscopy:
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SKA: A neutral hydrogen spectroscopic
census out to z~1: the cold gas
component of galaxies.
The IGM, as studied through the Ly
forest of quasars (or galaxies for the
ELTs), or via UV emission detected by
dedicated telescopes (Tresse, White).
BAO or galaxy studies?
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Why is there a choice? Surveys like SDSS have
shown that you can do cosmology and get
spectra to study galaxy properties at the same
time. This of course gets increasingly difficult as
you get fainter…
BAO is a growth industry (Nichol, Schlegel,
Totani, Shanks). We can argue about whether it
is “fundamental” and where we should put all our
energy, but the acceleration of the universe is an
astronomically observed fact, and we need to
probe it in as many ways as we can.
Making surveys work: it is not
just building an instrument!
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Line up funding in advance! (SDSS’ mistake…)
Get strong project management (another SDSS
mistake).
Build your system with specific surveys in mind!
Be patient.
Software is at least as important as the hardware. Don’t
cut corners. Automate redshift estimation!
Those that build the hardware and the survey will be too
tired/busy to do the science; make sure young people
have plenty of opportunity and freedom to lead the
science analyses. And make sure that the community
recognizes who did the work! (Nichol, White)
Outreach (Letterman, Google Earth…)
Wide-field spectroscopy in
the future
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We heard about many wonderful projects that
will soon get underway or are poposed: Wigglez,
FMOS ,
, zCOSMOS, WMOS, KMOS,
SIDE, BOSS, HETDEX (Sorry to Tom for the
acronyms!)
There are other related projects not discussed
here: LAMOST, ADEPT, SPM, RAVE, SKA,
SPACE. No doubt I’m missing some important
ones…
The field will remain vibrant with the advent of
the 20-40 meter telescopes (Colless).
Moreover, there will be plenty of survey work to
keep the 4- and 8-meters busy for at least
Let us close by thanking Paco, Antonio and
Christian for organizing such a scientifically
productive meeting in such a beautiful and
fascinating place!