Poster Abstract
The formation and evolution of galaxies is intrinsically linked to the cosmic web from which they are formed. Gas is accreted from the intergalactic medium, forming dusty gas clouds, stars and blackholes which in turn feed energy back into the galaxy’s interstellar medium, sweeping up matter and driving it out of the galaxy in the form of an outflow. Outflows are crucially important for the gas budget (the fuel for star formation), structural and chemical evolution of of their host galaxies by redistributing mass, angular momentum and metals. At the peak of star formation and black hole activity in the universe (1.5-3.5 Gyr after the big bang) such outflows must play a major role, but become extremely difficult to observe with spectral lines commonly used in the local universe. In this work we present our successful pilot project to test OH+ as an early universe outflow tracer, a line previously proven to be a sensitive outflow tracer in local Infra-red luminous galaxies. Additionally, OH+ has a line lying close to the CO(9-8) line such that both can be observed in one tuning with the state of the art ALMA interferometric telescope. We spatially resolve the galaxy, detecting the OH+ line in absorption, blueshifted with respect to the CO(9-8) which measures the bulk of the star forming gas within the galaxy. The outflow velocity and mass can be measured pixel-by-pixel across the 2D map of the outflow. In this poster I present our analysis of the neutral outflow associated with the gravitationally lensed dusty star forming galaxy G09v1.4, exploiting not only the OH+ line kinematics but also the sensitive molecular chemistry involved. We report a mass outflow rate between 250-3500 solar masses per year suggesting an extremely vigorous period of galaxy evolution.
Plain text summary
Galaxies form from within dark matter halos by accreting gas from the intergalactic medium into their potentials. A this gas cools and collapses to form stars and blackholes energy is injected back into interstellar medium, pushing gas out of the galaxy in the form of outflows. Galaxy outflows are ubiquitously observed in the local universe and can have mass out outflow rates equivalent or greater than the star formation rate of their galaxies. Galaxy theory requires outflows to form disky morphologies, regulate star formation and to shape fundamental galaxy relations such as the stellar mass and mass-metallicity relations (by transporting low angular momentum and metal enriched gas out of the disk).
We present observations of a massive neutral gas outflow in a gravitationally lensed dusty galaxy at the peak of the universe’s star formation rate density, 1.5-2 Gyr after the big bang, where the most impactful outflows must exist. We use the ALMA telescope array to observe the outflowing gas in OH+ and the host galaxy in dust continuum and CO(9-8) (warm dense gas). For each pixel in our spatially resolved maps, we have obtain spectra, providing a line of sight velocity of the galaxy disk and blue shifted outflow simultaneously.
We target a gravitational lens to exploit the magnification of both the flux and image, providing improved signal to noise and spatial resolution. To measure the intrinsic properties of the galaxy however, we must trace its image that has been distorted around the foreground galaxy back into the source plane. In slide 2 I show the image plane (observed) and source plane (reconstructed) morphologies of the dust, warm dense gas and stars of the galaxy and its outflowing gas, and respective velocity fields. The lens is modelled using the lens fitting code visilens (Hezaveh et al. 2013, Spilker et al. 2016a). The reconstructed maps reveal a conical outflow geometry with gas being driven out from the central dusty star forming region.
In slide 3 we investigate the impact of the outflowing gas on the galaxy. Firstly, we convert the observed OH+ mass into a total neutral gas mass using an abundance from Bialy et al. 2019. This results in a total outflow mass of 6.7 billion solar masses per year: more than a quarter of the mass in molecular gas in the host galaxy. To measure how rate at which gas is leaving the galaxy we derive a mass outflow rate, requiring values of the outflow’s velocity and radius. Since we observe a 2D projection of the outflow, measurements of the radius and velocity must be corrected for the effects of inclination along our line of sight. We can not directly observe inclination so we derive values of radius, velocity and mass outflow rate over a range of possible inclinations finding mass outflow rates between 230-3500 solar masses per year, far exceeding the star formation rate (Solar system science solar masses per year) over most of the inclination range.
In slide 4 we compare our outflow with other cool gas outflows in the local and early universe, on the mass outflow rate versus star formation rate plane. Our outflow lies at the most extreme end of the positive relation found across galaxies, suggesting a very rapid phase in galaxy evolution. Lastly we derive the momentum flux of our outflow and compare this to the available momentum flux injected by super novae explosions. With a star formation rate of Solar system science solar masses per year we expect approximately 15 super novae, which indeed provides enough momentum flux to drive the outflow over the majority of the inclination range.
Poster Title
Neutral Outflows in Dusty High Redshift Galaxies
