Stellar and Gas Kinematics in the Core and Bar Regions of M100 Emma L. Allard, Johan H. Knapen, University of Hertfordsh

1. Stellar and Gas Kinematics in the Core and Bar Regionsof M100 Emma L. Allard, Johan H. Knapen, University of Hertfordshire, UK Reynier F. Peletier, University of Groningen, The Netherlands allard@star.herts.ac.uk 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 Results 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, ring-like structure. This work presents two-dimensional observations of the circumnuclear gas and star kinematics of M100. 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 Mean Gas Velocity Mean Stellar Velocity A B Observations and Data Reduction A’ 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 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). 2(a) arcsec 3(b) 3(a) 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 high-ionisation line this suggests there is some AGN activity in the nucleus. Hβ Flux 197 -208 208 -197 Stellar Velocity Dispersion Gas Velocity Dispersion 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 red-shifts, 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. E 2(b) D [OIII] Flux 3(c) C 3(d) 30 123 163 108 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. Conclusions 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. 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. 2(c) 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.