Figure 1.
The Ha intensity,
velocity, and velocity
dispersion maps of two
of the SMGs observed
with NIFS. We show
HST imaging also.
All the SMG systems
observed show
disturbed dynamics
and multiple peaks
of star formation
intensity.
Triggering the Rapid Star
Formation
SMGs have large reservoirs of molecular gas
that provide the fuel for rapid star formation.
Indeed, SMGs can grow quickly, creating a
massive galaxy in only 100 million years. SMGs
therefore represent an immensely active
phase in galaxy evolution and are thought
to be the progenitors of the massive elliptical
galaxies observed in the local universe.
After 15 years of intense study, our detailed
understanding of SMGs is still limited to only
a handful of objects with spatially resolved
images and spectra. In particular, we still
don’t fully understand what triggers the extreme star formation in SMGs. Galaxy simulations predict that two galaxies merging could
cause an ultra-luminous burst, as observed in
SMGs. To test this hypothesis, we need to observe the dynamics and morphologies of the
gas within the SMGs, hunting for the signatures of multiple colliding components.
Tracing the gas dynamics within high-redshift
systems has only been made possible in recent years with the development of Integral
Field Units (IFUs), such as the Near-Infrared
Integral Field Spectrometer (NIFS) on Gemini
14
GeminiFocus
North and the Spectrograph for INtegral Field
Observations in the Near Infrared (SINFONI)
on the Very Large Telescope (VLT). These units
enable us to trace the emission lines across
the galaxies. The gas dynamics can then be
spatially resolved by tracing the shape and
position of emission lines detected.
Tracing the Star Forming Gas
The hydrogen-alpha (Hα) spectral line is emitted from regions where hydrogen is ionized
by hot young stars and therefore traces the
star-forming gas. We mapped this emission
line within five SMGs using NIFS and also
three SMGs using SINFON to gain spatially resolved information about the intensity of star
formation and the velocity and dispersion of
the gas. The intensities of the Hα line map the
star formation distribution across the galaxy;
the position of the line (in wavelength) gives
the velocity map of the gas, and the width of
the line gives the velocity dispersion map of
the gas.
We established that the gas within SMGs is
disturbed and turbulent, often tracing multiple interacting components (Figure 1). There
are no clear rotation curves in these systems,
December2012