SINS

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Hydrogen recombination line emission of Hα of the massive star-forming galaxy BzK-15504 eleven billion light-years away (redshift z = 2.38). The observations were carried out with SINFONI in adaptive-optics mode, resulting in an angular resolution of ≈ 0.15 arcsec, or a mere 1.2 kpc (4000 light-years; indicated by the grey filled circle) at the redshift of BzK-15504. The top left panel is a color-composite map of the integrated Hα line emission, showing from blue to red the ionized gas that is blueshifted to redshifted relative to the systemic velocity of the galaxy. The other panels are channel maps showing the spatial distribution of the Hα emitting gas moving at different velocities (given in km/s) relative to the systemic velocity.

Our finely resolved SINFONI data of BzK-15504 reveal a large galaxy about 16 kpc (53,000 light-years) across, with several prominent bright knots corresponding to luminous sites of active star formation. The galaxy appears to be a disk rotating with a maximum speed of 230 km/s, implying a large dynamical mass of   ≈ 10¹¹ M_sun. The details of the kinematics further suggest that gas is being channeled via radial flows (outlined by the dotted line) towards a growing central bulge, and indicate the presence of a broad and high velocity component (bottom right panel) likely due to an outflow from the active galactic nucleus (AGN) powered by a massive accreting black hole. The high surface density of gas (~ 350 M_sun/pc²), the high rate of star formation (~ 150 M_sun/yr), and the moderately young stellar ages (~ 500 million years) suggest rapid assembly, fragmentation, and conversion to stars of an initially gas-rich protodisk. Surprisingly, there are no obvious signs for a recent major merger event, which would have led to the rapid mass assembly and triggerred the intense star formation activity. This may suggest that BzK-15504 assembled its mass via smoother infall such as in the "cold flow" accretion mechanism, or through a series of minor mergers. BzK-15504 could later evolve into a massive elliptical galaxy.

These results appeared in Genzel et al. 2006, Nature, 442, 786

Spatial distribution (top row) and motions (bottom row) of the Hα line emission in six large star-forming galaxies at cosmological redshifts z ~ 2. The observations were carried out with SINFONI in seeing-limited mode, under typical seeing conditions of ≈ 0.5–0.6 arcsec, corresponding to a spatial resolution of 4–5 kpc at the redshift of the sources. The maximum velocities, relative to the systemic velocity, are given in km/s for each source.

During the first year of the SINS survey, our SINFONI observations revealed many large star-forming galaxies with irregular and clumpy morphologies in Hα line emission but smooth and regular velocity fields. For the majority of the larger systems, the ionized gas kinematics exhibit monotonic variations across the galaxy with steepest gradient along the geometric/kinematic major axis (e.g., the four leftmost galaxies in the figure above) and in three of them the velocity profile flattens at large radii. These features are expected signatures of ordered rotation in a disk-like structure, and provided the first convincing evidence for the existence of large massive rotating disks at z ~ 2. The case of BzK-15504, observed with adaptive optics but otherwise similar in its overall properties, offers an unparalleled view into one such system, with 3–4 times finer detail. Interestingly, Q1623-BX663 is probably more consistent with an advanced merger or disturbed spiral hosting an AGN responsible for the high velocity dispersion measured at the location of the dominant Hα peak off the center. For Q1623-BX528, the reversal in velocities along the major axis could be indicative of a counter-rotating merger.
The discovery of so many massive rotating disks among our SINS sample was surprising. In view of the higher rate of major mergers at high redshift, we had expected that most of the larger systems would exhibit more complex gas motions. From a more detailed analysis of the best resolved cases, it appears that their disks are quite turbulent, probably fairly gas-rich, and likely unstable to global star formation and fragmentation. As some simulations of the evolution of gas-rich galactic disks suggest, the star-forming clumps could later sink towards the gravitational center by dynamical friction to form a central bulge on a timescale of order of 1 billion years. This could provide a mechanism whereby some of the young disks uncovered in the SINS survey evolve into elliptical galaxies or disk galaxies with a dominant massive bulge, as those observed in the present-day Universe.

These results appeared in Förster Schreiber et al. 2006, ApJ, 645, 1062

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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, over what timescales galaxies were assembled, and when and how disks and bulges — the primary components of today's galaxies — were formed. The major limitation is our incomplete knowledge of the relevant mechanisms that control the phase, angular momentum, cooling, and dynamics of the baryonic matter.

The SINS survey now sheds new light on these issues, from detailed information on the dynamics and physical properties of distant luminous galaxies at early stages of evolution. The study 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) 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], [OIII], [OII], [SII]).
Until only recently, spatially-resolved information of such key spectral diagnostics were virtually non-existent. This has now changed with the SINFONI instrument mounted at the ESO Very Large Telescope. SINFONI consists of SPIFFI (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, MACAO (built by ESO), which can be used with a natural or laser guide star and enable diffraction-limited observations at the VLT 8-m telescope.

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 in the kinematics and physical properties with morphological features. To obtain a panoramic view of the properties of high redshift galaxies, we draw 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 use SINFONI to:

• measure source sizes and morphologies in line and continuum emission,
• characterize the velocity fields as ordered orbital motions or irregular motions,
• measure the dynamical mass and mass-to-light ratios,
• constrain the angular momenta,
• investigate 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.

The SINS survey is an on-going effort as further SINFONI data are collected to expand the current samples. To analyze the data and interpret the results, large efforts are now dedicated into the development and application of sophisticated analysis tools, theoretical modeling, and comparisons to simulations of the formation and evolution of galaxies. These include:

• 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 fitting algorithms,
• 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.

• 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.

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Far away galaxy under the microscope

ESO Press Release

MPG Press Release (German)

	SINFONI integral field spectroscopy of z~2 UV-selected galaxies: rotation curves and dynamical evolution       Förster Schreiber, N. M., et al. 2006, ApJ, 645, 1062
	The rapid formation of a large rotating disk galaxy three billion years after the Big Bang       Genzel, R., et al. 2006, Nature, 442, 786
	Intense star-formation and feedback at high redshift: spatially-resolved properties of the z = 2.6 submillimeter galaxy SMMJ14011+0252       Nesvadba, N., et al. 2006, ApJ, in press (astro-ph/0611769)
	Extreme gas kinematics in the z=2.2 powerful radio galaxy MRC 1138-262: evidence for efficient AGN feedback in the early Universe?       Nesvadba, N., et al. 2006, ApJ, 650, 693
	Lyman-break galaxies under a microscope: the small-scale dynamics and mass of an arc in the cluster 1E0657-56       Nesvadba, N., et al. 2006, ApJ, 650, 661
	SPIFFI observations of the starburst SMM J14011+0252: already old, fat, and rich by z = 2.565       Tecza, M., et al. 2004, ApJ, 605, L109

	The SINS survey: rotation curves and dynamical evolution of distant galaxies with SINFONI       Förster Schreiber, N.M., et al. 2006, The Messenger, 125, 11
	The universe in 3D — First observations with SPIFFI, the infrared integral field spectrometer for the VLT       Eisenhauer, F., et al. 2003, The Messenger, 113, 17
	First light of SINFONI at the VLT       Bonnet, H., et al. 2004, The Messenger, 117, 17

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N.M. Förster Schreiber, R. Genzel, N. Bouché, F. Eisenhauer, L. J. Tacconi, R. Davies, G. Cresci, S. Genel, D. Lutz, P. Buschkamp, S. Gillessen, E. K. Strobel Hicks (all at MPE),
M. D. Lehnert (Meudon), N.P.H. Nesvadba (Meudon), K. Shapiro (Berkeley), A. Sternberg (Tel Aviv), A. Verma (Oxford), R. Abuter (ESO).

A. Cimatti (Bologna), E. Daddi (Saclay), A. Renzini (Padova), X. Kong (Heifei), N. Arimoto (Tokyo), M. Mignoli (Bologna),
D. Erb (Harvard), A. E. Shapley (Princeton), C. C. Steidel (Caltech),
T. Naab and A. Burkert (USM München).

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