Team and collaborations
Observations and theoretical simulations have now established a
framework for galaxy formation and evolution in the young Universe.
Galaxies formed as baryonic gas cooled at the center of collapsing
dark matter halos, and subsequently grew through mergers and
collisions leading to the hierarchical build-up of galaxy mass.
It remains unclear, however, when and how disks and spheroids
— the primary components of today's galaxies —
were formed, over what timescales, and which processes (internal
or external) were driving the early evolution of galaxies.
Moreover, as a result of new empirical evidence
— notably from our "SINS survey" —
and recent theoretical developments, the emphasis is shifting
from a merger-driven picture towards one in which smoother yet
efficient modes of gas accretion and internal dynamical processes
also played an important role in the formation and evolution of
distant massive galaxies.
To help make progress, it is crucial to gain further knowledge of
the relevant mechanisms that control the phase, angular momentum,
cooling, and dynamics of the baryonic matter.
The SINS survey
The SINS survey now sheds new light on these issues, from detailed
information on the dynamics, morphologies, and physical properties
of distant massive star-forming galaxies at early stages of evolution.
The survey focusses on the crucial epochs at lookback times of
8–12 billion years ago (cosmological redshifts z ~ 1–4),
when a major fraction of the mass in stars seen in present-day
galaxies is believed to have been put in place.
Observations at near-infrared (1–2.5 μm) wavelengths are
well-suited to study galaxies at z ~ 1–4 because many
key diagnostic spectral features that are present in the rest-frame
optical spectrum of galaxies are redshifted in the near-infrared bands.
This includes important emission lines from ionized gas tracing
the sites of intense star-formation activity or shock-excited
material (such as the hydrogen Balmer recombination lines of
Hα and Hβ, and the forbidden lines from atomic
fine-structure transitions of [NII],
Until only a few years ago, spatially-resolved information of such key
spectral diagnostics were virtually non-existent. This has now
changed with the advent of sensitive near-IR integral field
spectrographs mounted on 8–10 m ground-based telescopes,
Very Large Telescope on Cerro Paranal, Chile.
SINFONI consists of
(built by the IR/submm group at MPE),
a cryogenic near-infrared integral field spectrometer that provides
the spectrum of a full atmospheric band simultaneously at all positions
over the entire square field of view.
SPIFFI is coupled to a curvature-sensing adaptive optics (AO) module,
(built by ESO),
which can be used with a natural or laser guide star and enable
diffraction-limited observations at the Very Large Telescope (VLT)
The unique capabilities afforded by SINFONI make it possible to fully map
the relative motions and spatial distribution of the gas and stars within
distant galaxies and to relate directly spatial variations of the kinematics
and physical properties with morphological features.
To obtain a panoramic view of the properties of high redshift galaxies,
we drew our SINS targets from samples selected by a variety of methods
based on integrated colours and luminosities
(for instance, "BM/BX" and "BzK" objects at z ~ 2,
Lyman-break galaxies at z ~ 3, and K- and submillimeter-bright
galaxies at z ~ 1.5–3.5).
More specifically, we used SINFONI to:
The results from the SINS survey are providing unprecedented insights into the nature
of distant massive star-forming galaxies and the processes involved in their mass
assembly and early evolution;
a selection is summarized in these
and all published results can be found in these
- measure source sizes and morphologies in line and continuum emission,
- characterize the velocity fields as ordered rotational/orbital motions
such as for disk galaxies, or irregular/perturbed motions as expected
for interacting/merging systems,
- measure the dynamical mass and mass-to-light ratios,
- constrain the angular momenta,
- investigate the dynamical state and stability,
- relate the star formation properties to the structure, dynamics, and
gas content on kpc scales,
- map out spatial variations in the gas-phase chemical abundances and in
the age of the stellar population from maps of line ratios and line-to-continuum ratios,
- explore the presence of outflows from gradients in line ratios and spectral line profiles,
- determine line and continuum luminosities, classify the dominant activity type (starburst
versus AGN), velocity dispersions, and interstellar dust extinction, from both the integrated
spectrum and the various maps.
- constrain the relative role of major mergers, smooth gas accretion, and feedback from
star formation and AGN in the early phases of massive galaxy evolution.
The survey status
The observations carried out as part of the MPE SINFONI GTO observing
time are now completed. SINS represents the largest survey of fully
mapped emission line kinematics and morphologies of galaxies at
z ~ 1.5 – 3, with 80 galaxies observed and over 63 detected
in at least one rest-frame optical emission line.
The histogram below shows the distribution of SINS galaxies according
to their class, i.e. the primary selection criteria applied for the
photometric surveys from which we drew our targets. The majority of
the galaxies were observed in seeing-limited mode with typically
excellent seeing conditions resulting in a spatial resolution of
≈ 4–5 kpc. In addition, 12 of the galaxies were also
observed with the help of AO (using either a natural guide star or the
LGSF), resolving structures on scales as small as ≈ 1–2 kpc,
and AO-assisted observations of several more sources are pending.
Overview of the distribution of the 80 galaxies observed as part
of SINS with SINFONI among different classes of galaxy populations
at z ~ 1 – 4 (hatched histograms).
Of the total, 63 galaxies were detected in rest-frame optical line
emission (solid-filled histograms) for a success rate of 80%.
Building on the success of our SINS survey, our focus is now shifting
towards addressing very specific scientific questions with the highest
quality data from SINFONI as well as from other instruments providing
key complementary information.
On the observational front, we are:
- expanding our current SINFONI data sets, with particular emphasis
on AO-assisted observations in order to resolve a majority of our
targets on scales of ~ 1 kpc,
- complementing the main data on Hα and [NII]
emission with data in other bands targeting further key diagnostic emission
lines to constrain the physical conditions of the ISM,
- planning ultra-deep SINFONI integrations on selected representative
targets in order to study individual regions with the best S/N ratio
- combining the SINFONI data on line emission with very high angular
resolution broad-band imaging tracing the distribution of stellar mass,
using both the NICMOS/NIC2 camera on board the Hubble Space Telescope
and the NACO instrument
in combination with the LGSF
at ESO's VLT,
- exploiting the strong synergies between the SINS survey and a long-term program
involving several members of our team of spatially-resolved distribution and
dynamics of the molecular gas in distant galaxies using the IRAM/Plateau de Bure
To analyze the data and interpret the results, large efforts are dedicated
into the application and development of sophisticated analysis tools, theoretical
modeling, and comparisons to simulations of the formation and evolution of galaxies.
- extraction of robust kinematic parameters through the application of kinemetry
(originally developed by the SAURON team for local galaxies but now adapting
it to high-redshift studies) and adaptive binning based on Voronoi tesselations,
and on genetic algorithms for fitting the full 2D kinematic maps,
- quantitative characterization of the dynamics and of the stellar and gaseous
components using dynamical and evolutionary synthesis modeling codes,
- detailed comparisons to predictions from numerical N-body/hydrodynamical
and semi-analytical cosmological simulations, and to chemodynamical
simulations of the evolution of galaxies.
With this broad observational program and these unique data,
we aim at gaining new insights into some of the key issues
of modern cosmology:
- the importance of violent major mergers versus smoother
infall or minor mergers in the mass accretion process,
- the timescale for mass accretion and conversion of gas into stars,
- the dynamical evolution and stability of young galaxies,
- the relationship between bulge and disk formation,
- the efficiency of star formation at early stages of evolution,
- the role of angular momentum exchange and loss,
- the role of feedback processes from star formation and AGN powered
by massive accreting black holes,
- the chemical abundances and enrichment of galaxies
from stellar nucleosynthesis,
- the relationship between the young galaxies and their parent
dark matter halos.
© Infrared and Submillimeter Astronomy Group at MPE
03/06/2010, editor of this page: Natascha M. Förster Schreiber