Periodic Reporting for period 4 - ConTExt (Connecting the Extreme)
Reporting period: 2020-03-01 to 2021-02-28
Galaxies are the basic building blocks of the Universe, so understanding how they form and evolve is of crucial importance to understanding the Universe and everything we see around us.
Studies of galaxies in general, and the Universe in particular is one of the main areas that are driving physics forward, as this is the only way we can test physics unders extreme conditions.
This project investigates a proposed model for cosmic evolution of the most massive galaxies in the Universe.
The CONTEXT model (connecting the extremes) hypothesises that some of the most extreme observed galactic phenomena are different evolutionary phases of the same massive galaxies undergoing cosmic evolution.
In the early Universe, intense nuclear starbursts are ignited as galaxies merge. In this phase the starbursts are detectable as sub-mm galaxies. Shortly thereafter the galaxies are quenched, either due to gas depletion or feedback from the starburst or a supermassive central black hole (in which case they may be detectable as quasars). Shortly thereafter the galaxies appears as compact quiescent galaxies, which evolve into local elliptical galaxies primarily through merging with minor companions.
The project performs detailed investigations of all of these extreme different galaxy types through out cosmic history, to test if this CONTEXT model is a good description of the evolution of massive galaxies.
This is done through a range of studies at different wavelengths ranging from radio, sub millimeter, infrared, optical, and using both imaging and spectroscopy, and using both statistical studies of millions of galaxies and in depth studies of individual galaxies.
The conclusion is that the context model is an excellent overall description of the evolution of massive galaxies, with some refinements. E.g. starbursts are the origin of most high z quenched galaxies, but they are not triggered by major mergers, like is observed in the local Universe. Instead they often have undergoing minor merging and have regular gas disks. On the other had we also found examples of quiescent galaxies at z=2 with fast spinning disks, so this is consistent. When pushed to the highest redshift, z=4 QG have progenitors which in some cases are consistent with being on the main sequence, rather than being starbursts. However, in some sense the line between starbursts and main sequence starformation is blurred out at high z, as everything is forming stars and merging at high rates.
Studies of galaxies in general, and the Universe in particular is one of the main areas that are driving physics forward, as this is the only way we can test physics unders extreme conditions.
This project investigates a proposed model for cosmic evolution of the most massive galaxies in the Universe.
The CONTEXT model (connecting the extremes) hypothesises that some of the most extreme observed galactic phenomena are different evolutionary phases of the same massive galaxies undergoing cosmic evolution.
In the early Universe, intense nuclear starbursts are ignited as galaxies merge. In this phase the starbursts are detectable as sub-mm galaxies. Shortly thereafter the galaxies are quenched, either due to gas depletion or feedback from the starburst or a supermassive central black hole (in which case they may be detectable as quasars). Shortly thereafter the galaxies appears as compact quiescent galaxies, which evolve into local elliptical galaxies primarily through merging with minor companions.
The project performs detailed investigations of all of these extreme different galaxy types through out cosmic history, to test if this CONTEXT model is a good description of the evolution of massive galaxies.
This is done through a range of studies at different wavelengths ranging from radio, sub millimeter, infrared, optical, and using both imaging and spectroscopy, and using both statistical studies of millions of galaxies and in depth studies of individual galaxies.
The conclusion is that the context model is an excellent overall description of the evolution of massive galaxies, with some refinements. E.g. starbursts are the origin of most high z quenched galaxies, but they are not triggered by major mergers, like is observed in the local Universe. Instead they often have undergoing minor merging and have regular gas disks. On the other had we also found examples of quiescent galaxies at z=2 with fast spinning disks, so this is consistent. When pushed to the highest redshift, z=4 QG have progenitors which in some cases are consistent with being on the main sequence, rather than being starbursts. However, in some sense the line between starbursts and main sequence starformation is blurred out at high z, as everything is forming stars and merging at high rates.
1: Through stacking of far infrared and radio data of a large number of quiescent galaxy candidates as a function of both their mass and redshift, we have shown that genuinely quiescent galaxies exist all the way back to z=3, when the Universe was just 2 Gyr old. We also showed that quiescent galaxies have higher radio emission than expected from their low star formation rates, suggesting that they harbour radio loud active galactic nuclei that may be involved in quenching them.
This is an important result because it is inherently difficult to confirm the quiescent nature of galaxies from their UV-NIR emission alone, due to the dust/age degeneracy.
In a second study, published in Nature Astronomy, we show that the average dust mass and gas mass in high redshift quiescent galaxies is surprisingly high, given that they are not forming stars.
2: We have played in a key role in a large ALMA study of galaxies from z=0-3, probing their dust and gas. This study for the first time derived the accretion rates of gas onto galaxies from observations, and showed that these are very large. This further strengthens the mystery of early quenched galaxies. Not only is it strange that they finish their starformation so early in the history of the universe, but also that they remained quenched, despite the large amount of gas (fuel of star formation) that is pouring onto them from the cosmic filaments.
3. We have performed a high resolution study of the stellar populations and dusty starformation regions in a sample of the highest redshift starburst galaxies known. We find that the properties of these starburst galaxies are consistent with being progenitors of the highest redshift quiescent galaxies, once they have completed their nuclear starbursts and merged with minor companions.
4: A major result was derived from a detailed study of a gravitationally lensed quiescent galaxy at z=2. The lensing makes it possible for the first time to resolve its inner structure and stellar populations, both photometrically and spectroscopically. The galaxy turns out to be a rotationally supported disk galaxy, rather than a the dispersion dominated proto-bulge that was expected from theory. This has major consequences for how it formed. A major merger would not lead to a compact disk. We were able to measure gradients in its stellar populations, showing for the first time that the galaxy quenched inside out over a timescale of 300 Myr. We also found evidence for outflows from a central AGN which could explain the quenching.
This study is published in Nature.
5. We have studied a complete sample of spectroscopically confirmed ultra massive quiescent galaxies at z=2. This allowed us to link to their direct dependents in the local Universe, and show for the first time directly that the grow by by a factor of two in mass and four in size through minor mergong.
6. We spectroscopically confirmed a sample of the most distant known quiescent galaxies at z=4 and in some cases even constrained their kinematics, showing that already 1.5 Gyr after the big bang, fully evolved quiescent galaxies exist. We also showed that quiescent galaxies at z=4 are even more compact than similar mass galaxies at z=2. Compared to z=0, they are up to 10 times smaller. We showed that their progenitors are dusty starforming galaxies at z>5, and that state of the art cosmological simulations are currently not able to account for massive quiescent galaxies this early.
7. We have lead the creation of the new COSMOS2020 photometric catalog, which is currently under review.
This is an important result because it is inherently difficult to confirm the quiescent nature of galaxies from their UV-NIR emission alone, due to the dust/age degeneracy.
In a second study, published in Nature Astronomy, we show that the average dust mass and gas mass in high redshift quiescent galaxies is surprisingly high, given that they are not forming stars.
2: We have played in a key role in a large ALMA study of galaxies from z=0-3, probing their dust and gas. This study for the first time derived the accretion rates of gas onto galaxies from observations, and showed that these are very large. This further strengthens the mystery of early quenched galaxies. Not only is it strange that they finish their starformation so early in the history of the universe, but also that they remained quenched, despite the large amount of gas (fuel of star formation) that is pouring onto them from the cosmic filaments.
3. We have performed a high resolution study of the stellar populations and dusty starformation regions in a sample of the highest redshift starburst galaxies known. We find that the properties of these starburst galaxies are consistent with being progenitors of the highest redshift quiescent galaxies, once they have completed their nuclear starbursts and merged with minor companions.
4: A major result was derived from a detailed study of a gravitationally lensed quiescent galaxy at z=2. The lensing makes it possible for the first time to resolve its inner structure and stellar populations, both photometrically and spectroscopically. The galaxy turns out to be a rotationally supported disk galaxy, rather than a the dispersion dominated proto-bulge that was expected from theory. This has major consequences for how it formed. A major merger would not lead to a compact disk. We were able to measure gradients in its stellar populations, showing for the first time that the galaxy quenched inside out over a timescale of 300 Myr. We also found evidence for outflows from a central AGN which could explain the quenching.
This study is published in Nature.
5. We have studied a complete sample of spectroscopically confirmed ultra massive quiescent galaxies at z=2. This allowed us to link to their direct dependents in the local Universe, and show for the first time directly that the grow by by a factor of two in mass and four in size through minor mergong.
6. We spectroscopically confirmed a sample of the most distant known quiescent galaxies at z=4 and in some cases even constrained their kinematics, showing that already 1.5 Gyr after the big bang, fully evolved quiescent galaxies exist. We also showed that quiescent galaxies at z=4 are even more compact than similar mass galaxies at z=2. Compared to z=0, they are up to 10 times smaller. We showed that their progenitors are dusty starforming galaxies at z>5, and that state of the art cosmological simulations are currently not able to account for massive quiescent galaxies this early.
7. We have lead the creation of the new COSMOS2020 photometric catalog, which is currently under review.
Our stacking of FIR data for quiescent galaxies is beyond the state of the art, as it clearly demonstrates that dead galaxies truly exists in the early universe.
While the FIR emission is weak, we do detect it. This has paved the way to get approved observations with e.g. ALMA to directly detect gas in early quenched galaxies, which will provide strong constraints for the first time on what quenched them.
We have pioneered observations of gravitationally lensed quiecent galaxies, and for the first time studied their inner structure, both spectroscopically and photometrically.
This has led to a highly surprising result, which is acknowledged by publication in Nature, one of the highest impact journals, and the massive interrest from peers at presentation of the result at conferences.
In the new photometric catalog COSMOS2020 we use a novel, model profile fitting code to derive deblended photometry consistently across 32 different waveband images. The COSMOS2020 catalog is several magnitudes deeper than any previous wide area catalog and is likely to be a benchmark for galaxy evolution studies for the next decade. Several JWST proposals based on the catalog were approved, including the largest in Cycle 1: COSMOS-Webb.
While the FIR emission is weak, we do detect it. This has paved the way to get approved observations with e.g. ALMA to directly detect gas in early quenched galaxies, which will provide strong constraints for the first time on what quenched them.
We have pioneered observations of gravitationally lensed quiecent galaxies, and for the first time studied their inner structure, both spectroscopically and photometrically.
This has led to a highly surprising result, which is acknowledged by publication in Nature, one of the highest impact journals, and the massive interrest from peers at presentation of the result at conferences.
In the new photometric catalog COSMOS2020 we use a novel, model profile fitting code to derive deblended photometry consistently across 32 different waveband images. The COSMOS2020 catalog is several magnitudes deeper than any previous wide area catalog and is likely to be a benchmark for galaxy evolution studies for the next decade. Several JWST proposals based on the catalog were approved, including the largest in Cycle 1: COSMOS-Webb.