High Resolution Observations of CO(3-2) in Haro 2: Cool Molecular Outflows of a Ly$α$ Emitter

TL;DR

Haro 2 hosts multiphase gas outflows in a nearby Lyα emitter. Using SMA CO(3-2) at $\sim 1.1''$ resolution, the study resolves a far-side counterpart to the NE molecular outflow and discovers a new SE outflow cone, with velocities within $\lesssim \pm 50\,km\,s^{-1}$ of the systemic velocity. The CO(3-2) emission concentrates near the two giant starburst clusters, and the CO(3-2)/CO(2-1) ratio, $R_{32}$, is higher in star-forming clumps and lower in the bubble, indicating warmer gas near clusters and cooler gas in the hot outflow region. The total molecular outflow mass is $\sim 10^{8}\,M_\odot$, larger than the ionized component, consistent with multiphase winds driven by cluster winds via entrainment. The results highlight how a relatively modest dwarf starburst can drive substantial, observable feedback and provide a laboratory for studying Lyα-emitter environments and gas dynamics.

Abstract

Haro 2 is a blue compact dwarf galaxy and the closest (at 21Mpc) known $Lyα$ emitter. UV and optical observations have found Haro 2 to be immersed in shells of partly ionized gas expanding at $\sim200$km/s. Observations of CO(2-1) (Becket et al 2020; Paper 1) with moderate ($2^{\prime\prime}$) resolution discovered a large-scale one-sided outflow associated with a soft X-ray bubble and apparently driven by the young star clusters created in the recent starburst. We present here SMA observations of CO(3-2) with $1.1^{\prime\prime}$ resolution in Haro 2. The opposite-side component of the large molecular outflow is detected lying in the direction of the fast ionized outflow; it is very confined in area. An additional outflow is apparent in the CO(3-2); it is south-east of the galaxy in a region holding weak star formation and a moderate-luminosity hard X-ray source. All the molecular outflow and filament velocities are within $\lesssim\pm50$km/s of the systemic velocity of the galaxy.

Figures (5)

• Figure 1: Top: The integrated intensity (moment 0) of the CO(3-2) line on Haro 2. The color bar has units $(Jy/bm)(km/s)$. The beam is shown in the lower left. Bottom: The peak intensity (moment 8) of CO(3-2) on Haro 2. Color bar units are $(Jy/bm)$. The two great starburst clusters are marked with small white stars, the superbubble or outflow region of hot gas is indicated with a white oval and letter 'B' and the south-east extended star formation region with a white oval and 'SE+'
• Figure 2: Moment 0 of the CO(3-2) map in color, with color bar units $(Jy/bm)(km/s)$, and moment 0 of the CO(2-1) emission in contours at levels $4,6,8,10 (Jy/bm)(km/s)$
• Figure 3: First moment or weighted mean velocity of CO(3-2) in Haro 2. Units of the color bar are velocities in (Km/s). The data cube was clipped at $3.5\times10^{-2}Jy/bm$. The great star clusters are marked with black stars. The outer border of the mapped region corresponds roughly to the $0.8(Jy/bm)(Km/s)$ level of the zero moment map.
• Figure 4: Top Left: The first moment map of CO(3-2), as in the previous figure, marked with three dotted lines showing where Position-Velocity Diagrams were obtained. The positions are identified with numbers 1 for the NE 'superbubble', 2 for the SE region, and 3 for the SW structure that we believe to be the other side of the 'superbubble'. Clockwise from top left: the Position-Velocity Diagram on each marked line. Units of the color bar are $(Jy/bm)$ and units of Offset are distance in arcseconds from the center of the line. Dashed curves are sketched on each PVD to accentuate the velocity structure.
• Figure 5: Left: The moment 8 map with the positions of the spectral profiles marked with beam-sized circles. The colors of the circles correspond to the colors of the spectral profiles on the right. Right: The spectral profiles of the CO(3-2) line in the positions given on the right. The X axis is velocity in km s$^{-1}$ and the Y axis intensity in Jy/bm. The order is yellow-blue-green-red east to west.