Fast and Furious: The Earliest Galactic Fart Blasts Through Space

Paper title: Fast Outflow in the Host Galaxy of the Luminous z = 7.5 Quasar J1007+2115

Authors: Weizhe Liu, Xiaohui Fan, Jinyi Yang, Eduardo Bañados, Feige Wang et al.

First Author’s Institution: Steward Observatory, University of Arizona, USA

Status: Uploaded to ArXiV

As we observe more distant (and therefore older) regions of the Universe, the new observations leave us scratching our heads with even more questions. For example, astronomers have spotted super-bright quasars just a billion years after the Big Bang. Our current understanding of the universe can’t quite explain how such massive galaxies appeared this early in the Universe  (check out this Astrobite).

Looking at galaxies closer to us, we see a connection between supermassive black holes (SMBHs) and the galaxies they live in. We see that more massive black holes tend to live in galaxies with specific properties, including more stars moving at faster speeds or a heavier galactic bulge (read more here).  But are these factors connected, and do they contribute to each other’s growth? We’re able to relate these factors together for nearby galaxies, but for galaxies far from home we’re not sure.

One idea is that active galactic nuclei, or AGN, might have played a significant role. These systems of a black hole and accretion disk blast out powerful winds known as AGN outflows. These outflows have a huge impact on the galaxy and may either slow down or boost star formation. On one hand, they can push gas out of the galaxy, shutting down the birth of new stars. But on the other hand, they might kickstart star formation by squeezing gas together and creating the perfect conditions for new stars to form.

The authors picked one of the most distant quasars, named J1007+2115, sitting at a redshift of 7.5, to see if they could spot any signs of outflows in the quasar’s spectrum and its host galaxy using JWST.

Outflow in the Quasar

The light from the quasar shows a smooth continuum, along with iron emission lines, H-beta, H-gamma, and the [OIII] doublet.

The broad line region (BLR) of the quasar contributes to the Balmer lines: H-beta and H-gamma (learn more here). As the BLR is close to the black hole, the gas revolves fast around it at speeds of ≳1000km/s  (just like how mercury revolves faster than Earth because it is closer to the sun). The heavier the black hole, the faster it revolves. Hence, by measuring how broad the H-beta line is, they estimated the black hole’s mass, which is a whopping 1.4 billion times the mass of the Sun. That’s 300 times more massive than SgrA*, the black hole at the center of our Milky Way.

This black hole has a high Eddington ratio, which defines how fast the black hole is accreting matter. The authors estimated this by measuring strong iron lines and weaker oxygen lines. A high Eddington ratio means the black hole is devouring material at a super-fast rate.

The [OIII] line, broad and blueshifted, moving at speed ~1400km/s towards us. Emission from [OIII] can’t come from the broad line region since it’s a forbidden transition. That means it’s most likely coming from quasar-driven outflows. These outflows remove as much as 250 times the Sun’s mass in gas from their galaxies every year.

Figure 1: The spectrum of the quasar. The spectrum shows a smooth continuum, along with iron emission lines, H-beta, H-gamma, and the [OIII] doublet in the top panel. The bottom panel is the same spectrum minus the continuum and the iron lines to give us a better visualization of the emission lines. (Figure 1 from the paper)

Separating the light from the quasar and the host galaxy

The authors also wanted to study the light from the galaxy hosting it. To do that, they have a problem: the quasar is way too bright! When an object is too bright and too far away, the light leaks into the adjacent pixels due to diffraction in the telescope. The shape the point smudges into is a point spread function (PSF). Each telescope has its own PSF, and the authors modeled the JWST’s PSF, subtracted it from the image, and—voilà!—they were left with the light from the host galaxy.

Figure 2: The “flower” of the JWST modeled to be subtracted from the image. Ideally, the light from the quasar should take up one pixel as it is considered a point source. But because of this leak, the bright light from the quasar can overwhelm the faint light from the host galaxy in adjacent pixels.(Figure 2 from the paper)

When they looked at the quasar-subtracted galaxy spectrum, they spotted two key emission lines: H-beta and [OIII]. The [OIII] line here is also highly blueshifted and broad. They found that the nebula producing the [OIII] line was southwest of the quasar and this line is too broad to be caused by rotating gas or a nearby companion galaxy. The authors concluded it’s likely driven by outflows from the quasar itself. These outflows remove around 47 times the sun’s mass in gas every year. This is the earliest known galactic-scale outflow we’ve ever observed!

Figure 3: The left-hand image is the spectrum from the extended emission, and the image on the right-hand side is made with the [OIII] flux from the spectrum on the left-hand side (Figures 3 and 4 from the paper)

Outflows properties

The outflows are super powerful, which makes us think it is largely the energy of the quasar that is transferred to them. But the host galaxy of the quasar is also cranking out a ton of new stars (anywhere between 60 to 300 sun-like stars every year), so stellar processes like supernovas may also play a part in driving these outflows. And since these outflows move fast—around the escape velocity of the system—they can push gas out of the galaxy. This cuts down on star formation, creating a kind of negative feedback.

At the end of the day, what we’re seeing here is just the ionized outflow. But outflows come in different phases—they can also be neutral and molecular. And these other phases usually carry way more mass and energy. So, if we want to understand how outflows affect galaxy evolution, we need to study all of these outflow phases together.

Astrobite edited by Roel Lefever and Lindsey Gordon

Featured image: Artist’s impression of an outflow of molecular gas from the quasar J2054-0005. Credit: ALMA (ESO/NAOJ/NRAO)

Author

  • Sowkhya Shanbhog

    I am currently a first-year PhD student at Scuola Normale Superiore in Pisa, Italy, where I am focusing on studying high redshift quasars. Prior to this, I completed a dual BS-MS degree at the Indian Institute of Science Education and Research in Pune, India. Now, I am eager to expand my involvement in science communication and outreach initiatives. I have recently developed an interest in cooking, particularly since moving to a new city. I find solace in listening to music during my leisure time.

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