From Isaac Newton Group of Telescopes: “Three Dynamically Distinct Stellar Populations in the Halo of M49” and “Quantum Entanglement Confirmed with Light from Distant Quasars”

Isaac Newton Group of Telescopes Logo
From Isaac Newton Group of Telescopes

Three Dynamically Distinct Stellar Populations in the Halo of M49

01 October, 2018
Javier Mendez

In the current hierarchical paradigm of galaxy formation, early-type galaxies assemble their masses with time. Their formation entails two phases: an initial one of strong star formation is followed by an extensive growth through accretion and mergers of smaller satellites, that causes a dramatic increase of their sizes towards low redshifts.

Numerical cosmological simulations predict that the mergers which build up the halos of massive galaxies at the centre of clusters and groups involve satellites with mass ratios 1:5. As massive galaxies typically have a larger metal-content, one would expect that the light in these halos comes mostly from stars at about half-solar metallicity and thus with redder optical colours.

It comes as a surprise that the outermost halos of the nearby massive galaxies are bluer instead, indicating that the satellite galaxy progenitors where these stars were born had to be either overall very young in age (hence star-forming) or very small in mass.

Using data obtained with the Planetary Nebula Spectrograph (PN.S) on the William Herschel Telescope (WHT), J. Hartke, M. Arnaboldi and collaborators pursued an original investigation to constrain the mass of the satellite progenitors of the stars in the halos and determine a proxy for their dynamical age by measuring the motions along the lines of sight of hundreds of stars that are in a particular stage of their evolution: the Planetary Nebulae (PNe).

ING 4 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

PNe are the late stages of Sun-like stars whose [OIII] 5007 Å emission is relatively strong. Such ‘green’ monochromatic light makes them similar to beacons whose motions are easy to measure. Previous studies have shown that the distribution of the PN velocities is a fair sampling of that of the parent stars. For this study, Harke et al. used the PN velocities in the halo of the brightest galaxy in the Virgo cluster, NGC 4472 or Messier 49.

By combining accurate velocities from the PN.S instrument with magnitudes measured during an imaging campaign at the Subaru telescope, Hartke et al. identified distinct components in the magnitude-velocity plane of the entire PN sample.

NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

Instead of a uniform stellar population floating in the gravitational potential of the galaxy, astronomers identified three populations, one associated with the smooth halo of M49, a sub-component of bright planetary nebulae associate with the recent accretion of a dwarf galaxy (VCC 1249), and a population of stars associated with the intra-group light.

As shown in the following figure, the distinct velocity-dispersion profiles are plotted from the whole, bright and faint subsamples. The combination of precise photometry from SuprimeCam on the Subaru telescope with the accurate velocities measured with the PN.S instrument on the WHT made it possible to identify these populations with confidence.

Line-of-sight velocity dispersion profile as a function of the major-axis radius of the total (open black circles), bright (open light blue diamonds) and faint (filled red squares) planetary nebulae in the halo of M49. The coloured bands indicate the 1-sigma errors. The stellar velocity-dispersion profile is indicated by the dashed black profile. The grey error bars connected with a dashed grey line shows the velocity dispersion of galaxies in the Virgo Subcluster B. The velocity dispersion of the faint-planetary nebulae sample reaches that of the galaxies in the Subcluster B at large radii, which indicates that these planetary nebulae are tracing the motions of the stars in the intra-group light. Credit: Magda Arnaboldi, Johanna Hartke.

The intra-group light is from stars that are not bound to individual galaxies, but instead are under the influence of the gravity of the group itself. Hence the measurements of the chaotic motions show an increase with distance from the center of M49, reaching as high velocity dispersion as that measured from the motions of galaxies in the subcluster. This is the first time that the transition from halo to intra-group light is based on velocities of individual stars and indicates that these stars are indeed orbiting in the potential of the group.

The result on the smoothness of the intra-group light and outer halo is also very relevant to constrain the feedback mechanism from star formation and SN explosions in low-mass satellites in cosmological simulations. The results from the study of M49 points towards a fine tuning of these mechanisms such that these low-mass satellites form enough blue stars to contribute a significant fraction (about 10% ) of the total light in the halo as measured in the very outskirts of M49.

Science paper:
J. Hartke, M. Arnaboldi, O. Gerhard, A. Agnello, A. Longobardi, L. Coccato, C. Pulsoni, K.C. Freeman, M. Merrifield, 2018 Three dynamically distinct stellar populations in the halo of M49 A&A

See the full article here .

Quantum Entanglement Confirmed with Light from Distant Quasars

01 October 2018
Javier Mendez

A team of scientists led by quantum physicist Anton Zeilinger from the Austrian Academy of Sciences and the University of Vienna has made a new test of quantum entanglement this time using photons from distant astronomical objects as collected by the William Herschel Telescope (WHT) and the Telescopio Nazionale Galileo (TNG).

ING 4 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

Telescopio Nazionale Galileo a 3.58-meter Italian telescope, located at the Roque de los Muchachos Observatory on the island of La Palma in the Canary Islands, Spain, Altitude 2,396 m (7,861 ft)

In the experiment, entangled pairs of photons were created and sent to receiving stations the researchers set up right next to the two telescopes. The telescopes looked at two different, almost opposite locations in the sky and observed quasars. Variations of the colour in the quasar light were then used to control which kind of measurement was performed on the two photons from an entangled pair created in a mobile laboratory located near the Nordic Optical Telescope (NOT).

Of these photons, one was sent to a receiving station near the WHT, the other one to another receiver next to the TNG. There, the individual polarisation of each entangled photon was measured as decided by the fluctuations of the light from its respective quasar.

A source of entangled photons sends light particles to receiver stations from a mobile quantum physical laboratory located near NOT telescope. The measurement of the entangled photons was controlled by the light of distant quasars which was captured by the WHT and the TNG. Credit: Massimo Cecconi.

The measurement of one photon of an entangled pair has an instant influence on the measurement result of the other one. This was called by Einstein “spooky action at a distance”, and he was hoping for a physics without entanglement. The question is: how is it decided which measurements are performed on the two photons?

It is evident that it would be desirable to have decisions made completely independently, such that they cannot be influenced by a common cause. In the new experiment, the fluctuations of the light from two quasars decided on each entangled photon separately which polarisation is measured.

In the 1960s, the physicist John Bell calculated a theoretical limit beyond which such correlations must have a quantum, rather than a classical, explanation.

The quasars used for this experiment are about 12 and 8 billion light-years away, on almost opposite directions in the sky. This is rather short after the Big Bang 13.8 billion years ago, and any possible influence on both quasars could have happened in only 4% of the known Universe.

The researchers ran their experiment twice, each for around 15 minutes and with two different pairs of quasars. For each run, they measured 17,663 and 12,420 pairs of entangled photons, respectively. Within hours of closing the telescope domes and looking through preliminary data, the team could tell there were strong correlations among the photon pairs, beyond the limit that Bell calculated, indicating that the photons were correlated in a quantum-mechanical manner.

“The crucial challenge in the experiment was to make sure that the choice of polarisation measurements on each of the entangled photons was done completely independently from us and from any environment, no matter how large”, says Dominik Rauch, from the Austrian Academy of Sciences and the University of Vienna. “This light, that is completely independent from us and almost our entire past, allowed us to use these distant quasars as cosmic random number generators.”

The cosmic light used was in that sense ideally suited for the experiment. It also provides a new way to obtain random numbers. That way, distant quasars where for the first time applied as random number generators.

Anton Zeilinger explains: “This is the first time that light travelling to us from nearly the edge of the known Universe has been used in a quantum experiment. The results on the entangled photons confirmed the predictions of quantum mechanics. This is also very important for quantum technologies, because uninfluenced measurements on entangled states are important for a definitive proof of the security of various quantum procedures.”

Science paper:
Cosmic Bell test using random measurement settings from high-redshift quasars Physical Review Letters

See the full article here .


Please help promote STEM in your local schools.

Stem Education Coalition

Isaac Newton Group telescopes
Isaac Newton Group telescopes

ING 4 meter William Herschel Telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, 2,396 m (7,861 ft)

ING Isaac Newton 2.5m telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, Spain, Altitude 2,344 m (7,690 ft)