Transcript 36x48 vertical poster template

Stellar and Gas Kinematics in the Core and Bar Regions of M100
Emma L. Allard, Johan H. Knapen, University of Hertfordshire, UK
Reynier F. Peletier, University of Groningen, The Netherlands
[email protected]
Abstract
The stellar and gas kinematics of the bar and starbursting circumnuclear region in the barred spiral galaxy M100 have been measured and are presented here as two-dimensional maps. The data have been obtained using the SAURON integral field spectrograph on the William Herschel
Telescope. In this progress report, we present maps of the total intensity, [OIII] and Hβ intensity, mean velocity, and velocity dispersion for the stars and the gas. The gas velocity field shows significant kinematic signatures of gas streaming along the inner part of the bar, and of density wave
streaming motions across the miniature spiral arms in the nuclear pseudo-ring. The stellar velocity field, presented here for the first time, shows similar non-circular motions. The gas velocity dispersion is notably smaller where the star formation occurs in the nuclear zone. We outline our
further plans with the data set.
Introduction
The circumnuclear regions of spiral galaxies are often sites of intense star
formation. Barred galaxies often experience starburst activity in their centers, and
the bar is thought to help drive gas into the central kiloparsec. Nuclear rings of
star formation are often observed, as a result of gas piling up near the location of
the inner Lindblad resonances. Kinematic observations are needed to constrain
the behaviour of the gas and stars, and to study how this inflow leads to star
formation.
M100 is a barred spiral galaxy which hosts a circumnuclear, star-forming, ringlike structure. This work presents two-dimensional observations of the
circumnuclear gas and star kinematics of M100.
Results
Figure 2.-(a) The reconstructed
total intensity map was produced
by collapsing our datacube along
the spectral dimension between
4800Å and 5380Å. In the center
we see the tightly wound armlets,
forming a ring-like feature. The
offset dustlanes can be seen
entering the field, and a number of
HII regions are visible in the outer
parts of the field.
Total Reconstructed
Intensity
Observations and Data Reduction
The SAURON integral-field spectrograph was used on the 4.2m William
Herschel Telescope. A field of view of 33x41 is achieved, fully sampled by 1431
-60 -50 -40 -30 -20 -10 0
square lenses 0.94x0.94 arcsec in size.
The wavelength range 4800-5380Å is covered at 4.2Å spectral resolution with a
sampling of 1.1 A per pixel. This range contains the stellar absorption lines Hβ,
Mgb and Fe, and emission lines Hβ, [OIII] and [NI].
Three adjacent fields were observed to cover the complete bar and circumnuclear
region of M100.
The resulting data was reduced with the XSauron software (Bacon et al. 2001).
Mean Gas Velocity
Mean Stellar
Velocity
A
B
A’
2(a)
10 20 30 40 50 60
arcsec
Figure 2.-(b) & (c) The Hβ and
[OIII] flux maps were produced by
collapsing the datacube between the
wavelength ranges containing the
emission lines.
The Hβ line clearly shows where the
star formation is occurring, and is
most
prominent
in
the
circumnuclear ring and the HII
regions.
The [OIII] line is brightest at the
center, and as this is a highionisation line this suggests there is
some AGN activity in the nucleus.
Hβ Flux
All maps were produced using the Penalized Pixel Fitting method of Cappellari
& Emsellem (2004). White isophotes indicate lines of constant flux, and are
plotted on each map at 1 magnitude intervals. Red indicates high values, or redshifts, blue indicates high values or blue-shifts. All velocities are in kilometers
per second, and are relative to the systemic velocity of the galaxy. North is up,
east is to the left.
197
-197
208
E
D
[OIII] Flux
C
108
Figure 1 (left). Real-colour picture of M100, showing the
nuclear region as well as the complete disk of the galaxy.
The area observed with SAURON is shown.
-208
3(b)
Stellar Velocity
Dispersion
Gas Velocity
Dispersion
2(b)
2(c)
3(a)
Figure 3.-(a) The mean gas velocity
has been determined using the [OIII]
line. Although circular motions
dominate the field, an S-shaped
deviation is clearly visible at the
center. Features A and A’ may be
signatures of a bar-induced spiral
density wave, and feature B may be
evidence of gas streaming along the
bar.
3.-(b) The stellar velocity was
determined by fitting the parts of the
spectrum which did not contain
emission lines to a stellar template
library (Vazdekis 1999). The stars
also follow predominantly circular
motions, although like the gas,
some distortions from this are
visible.
3.-(c) The gas dispersion map shows a
high value at the center (feature D), and
in a region some 20-30 arcsec from the
center, but there is a ring of low
dispersion material (feature C) coinciding
with the regions of high Hβ flux as seen
in figure 2b. We infer that there is a large
amount of cold gas present, that has been
slowed down and trapped at an ILR.
Massive stars form out of this cold gas.
3.-(d) The stellar dispersion map shows a
high value for example where the HII
regions are found (feature E) in contrast
to the gas dispersion, although areas of
large dispersion in the stellar map can be
correlated with areas in the gas map.
163
3(c)
30
3(d)
123
Conclusions
We have presented here our preliminary results of M100, taken with the
SAURON integral field spectrograph. We have confirmed there are
indications for non-circular motions due to spiral armlets and/or the bar.
The low dispersion material seen in the gas dispersion map lies where
the massive star-formation occurs.
The main purpose of the work done so far is to provide observational
constraints on dynamical models of the circumnuclear regions of M100.
Gas kinematics are alone not enough and through our new data we will
be able to obtain more accurate estimates for quantities such as the bar
pattern speed and the characteristic stellar bar orbits. In addition to the
kinematical information, the presence of stellar absorption and gas
emission lines in our data will allow the study of the stellar populations
in the star-forming regions, to learn about the detailed physical
processes which connect galaxy dynamics with massive star formation
under the influence of a bar.