Towards an informed quest for accretion disc winds in quasars:
the intriguing case of Ton 28
November 25, 2018
IMAGE member Elisabeta Lusso, in partnership with international collaborators, has recently reported on the detection of a blueshifted absorption feature from highly ionized iron in two consecutive XMM–Newton observations (red and blue data points in the figure, where green crosses represent the combined data) of the luminous blue quasar Ton 28. The rest energy in the X-ray (marked in the left panel at 9.2 keV) implies the presence of an accretion disc wind with a bulk outflow velocity of approximately 0.3 times the speed of light, and kinetic power of at least a few per cent of the quasar bolometric luminosity. In the figure, the blue area highlights the wind absorption feature. To understand whether ongoing powerful X-ray winds leave any distinctive signatures imprinted at other wavelengths on the intrinsic quasar spectrum, the authors developed a backwards selection method to single out a quasar in its so-called ``X-ray blow-out'' evolutionary phase, which is believed to represent the initial stage of quasar feedback. Provided that the effectiveness of this selection method is confirmed with sources similar to Ton 28, this result could represent the first step towards the characterization of the fastest black-hole winds through multiwavelength indicators in the absence of high-quality X-ray spectra.
Click here to read the paper.
IMAGE members to lead deepest spectroscopic survey to date in the infrared
November 18, 2018
Members of the IMAGE group have been awarded 90 orbits on the Hubble Space Telescope
to complete the deepest spectroscopic survey to date in the near infrared.
This programme, co-led by scientists at the Space Telescope Science Institute
in the US, will deliver very deep spectroscopy using the WFC3 grism
to survey low-mass galaxies within the MUSE Ultra Deep Field, a region of the sky
that contains two bright quasars and is targeted by ultra-deep MUSE spectroscopy.
By combining the information encoded in these galaxy spectra with the absorption signatures present
in the two quasar spectra, this programme will provide an unprecedented view of the distribution of
gas and metals around low-mass galaxies at the peak of the cosmic star formation history (see figure above).
Combined with MUSE observations, this programme will also provide novel insight into the physics of
high redshift galaxies and their evolution in different environments.
A measurement of the primordial helium abundance of the Intergalactic Medium
October 15, 2018
Members of the IMAGE group have recently reported the first determination of the
primordial helium abundance based on a near-pristine intergalactic gas cloud that
is seen in absorption against the light of a background quasar. The figure above
shows the absorption profiles from the hydrogen Lyman Limit (top panel) and a
selection of neutral helium absorption lines (remaining panels). The red curves
show a model fit to the data (black histogram), and the tick marks above each
spectrum indicates the locations of the absorbing gas clouds that comprise the
partial Lyman Limit System (pLLS).
This pLLS, at a redshift z=1.724 (i.e. when the Universe was just one-third
of its present age), has a metal content 100 times less than the Sun, and contains
30 per cent fewer metals than the most metal-poor H II region currently
known where a determination of the primordial helium abundance is afforded.
Since the primordial helium abundance offers a sensitive test of new physics
beyond the Standard Model just a few minutes after the Big Bang, its determination
is of acute interest in cosmology. This study reports a 10 per cent measure
that agrees with the Standard Model value.
Click here to read the paper.
Quasar pairs trace the structure of the cosmic web
May 10, 2018
Members of the IMAGE group have conducted a survey to observe 54 closely projected quasar pairs at similar cosmological distances with the Wide Field Camera 3 on-board the Hubble Space Telescope. These quasar pairs act as double flashlights, piercing the tenuous environment in two sightlines, thus providing a 2-D map of both the large and small-scale structure of the cosmic web. The first results of this campaign reveal that these closely-projected quasar pairs show moderate excess of gas absorbing Lyman continuum photons compared to single quasars. By measuring the path of ionising photons and constructing a composite ultraviolet spectrum of pairs -- shown in figure -- IMAGE members found that the shape of the composite spectrum of pairs differ from the one of single quasars in the extreme ultraviolet. This is indicative of an excess of gas absorbing Lyman continuum photons, as also seen when measuring the mean free path (i.e. how far photons travel in the Universe before being absorbed) of ionising photons as a function of redshift. This excess of gas is thought to arise within large-scale structures or partially neutral regions inside the dark matter halos where the close pairs reside.
Click here to read the paper.
IMAGE members to lead a new Large Programme on MUSE
December 21, 2017
Members of the IMAGE group have been awarded a new ESO Large Programme. In partnership with international collaborators, IMAGE members will use the MUSE instrument at the VLT to acquire the deepest spectroscopic observations (for up to 150 hours) ever collected in a field with multiple quasars. Building on a successful pilot programme that has revealed extended hydrogen Lyman-α emission near these quasars (red in the Figure showing an image reconstructed from our pilot MUSE data), the newly-awarded programme aims at acquiring a detailed view of the cosmic web that is expected to connect galaxy halos in the early universe. Thanks to the groundbreaking capabilities of MUSE, these data will also provide a wealth of information on the physics of gas near galaxies and in groups across 5 billion years of cosmic history, and will form one of the deepest spectroscopic surveys in blank fields.
A one per cent determination of the primordial deuterium abundance
November 1, 2017
IMAGE member Ryan Cooke has recently reported a one per cent determination of the
primordial deuterium abundance. Assuming the Standard Model of particle physics and
cosmology, this measurement corresponds to a Universal density of baryons in good
agreement with the recent measurement derived from the Cosmic Microwave Background
temperature fluctuations recorded by the Planck Satellite.
The figure above shows seven high precision measurements of the deuterium to hydrogen ratio
over a broad range of metallicity (blue symbols). The weighted mean of these seven
independent measurements is shown by the red horizontal lines. The grey horizontal
band shows the Planck measure of the baryon density, assuming the Standard Model.
Click here to read the paper.
IMAGE member awarded European Research Council Starting Grant
September 20, 2017
IMAGE member Michele Fumagalli has been awarded a prestigious Starting Grant, worth 1.5 million euros, from the European Research Council. The grant will fund several students and postdocs over the next 5 years to work within the IMAGE group on the project entitled "A new vantage point on how gas flows regulate the build-up of galaxies in the early universe". This project will focus on understanding the inflow and outflow of gas from galaxies and into the wider cosmic web — a process that regulates star-formation and the evolution of galaxies across cosmic time. The research will tackle the dual questions of how gas accretion regulates the build-up of galaxies and how efficiently outflows remove gas from star-forming regions within galaxies, using both state-of-the art simulations and new observational techniques.
IMAGE members get a taste of GALACSI at VLT
August 20, 2017
On the night of August 15, IMAGE members were the first visiting scientists to
turn on the four powerful lasers (shown here in a picture by IMAGE member Ruari Mackenzie)
of the recently-commissioned GALACSI system at VLT/UT4. With the aid of the
new adaptive-optics system, MUSE observations of a sky region known to host three physically-associated
quasars were collected with an exquisite image quality of less than 0.5 arcsec. These data will enable
a detailed study of the environment surrounding these bright quasars, as well as of the
intergalactic medium probed by multiple closely-spaced lines of sight.
Click here to watch a video by Ruari Mackenzie
of the UT4 lasers.
Large nebula uncovered next to a z~3 gas cloud
August 1, 2017
An extended nebula - one billion times larger than the distance between the Earth and the Sun - has been
uncovered by members of the IMAGE group next to a damped Lyman-α system (DLA), a dense gas cloud rich in
neutral hydrogen and heavy elements. Located at a large cosmological distance, DLAs are believed to trace the reservoir
of neutral hydrogen next to galaxies that are assembling a few billion years after the Big Bang.
This nebula (shown in the Figure above) is one of the largest known to date next to a DLA, and is believed to be
a signpost of an extended cosmic structure within which multiple galaxies are assembling. While commonly
predicted by cosmological simulations, these structures have been mostly elusive so far. However, equipped with the
MUSE instrument of the European Southern Observatory’s Very Large Telescope, IMAGE members are on the lookout
for even more examples of these nebulae near DLAs, which can provide new clues about how galaxies
form inside cosmic filaments by converting gas into stars.
Click here to read the discovery paper.
Most primitive galaxy known in our cosmic neighbourhood unveiled
July 4, 2017
A near-pristine galaxy (nicknamed the Little Cub, because it is
located in the Ursa Major, or Great Bear, constellation) has
recently been discovered by members of the IMAGE group at Durham
(Little Cub is located in the inner blue contour in the figure above).
Little Cub is among the most metal-poor star forming
galaxies currently known and is being cannibalised by a nearby
grand design spiral galaxy (NGC 3359 - the spiral galaxy
seen in the figure above). The discovery has enabled us to
learn about the processes that strip low mass galaxies of their gas and
stars. The discovery also allows us to study the genesis of the first
chemical elements (including hydrogen and helium), that were created
just minutes after the Big Bang.
Click here to find out more and
click here to read the discovery paper.
What Matter(s) Around Galaxies
June 30, 2017
Over 100 scientists from around the globe gathered at Durham University for the conference "What Matter(s) Around Galaxies: Resolving the physics of the circumgalactic medium", which took place between the 19th and 23rd of June 2017. Under the attentive supervision of IMAGE members involved in the local and scientific organisation, participants presented and discussed the latest developments in our understanding of the circumgalactic medium. Talks covered a wide range of topics, focusing on the use of different methodologies (analytic theory, numerical simulations, observations) and tracers (from radio to optical, to X-ray) to address key open questions on the nature of the circumgalactic medium.
Visit the conference website for more information and for the PDFs of the talks.
First detection of fluorescence induced by ultraviolet background
March 20, 2017
Fluorescent emission - a red glow that appears when ultraviolet (UV) light interacts with gas -
has been observed near the edge of the UGC 7321 galaxy at 30 million light years from Earth. Members of the IMAGE group
in collaboration with European and US scientists, pointed the MUSE instrument of the European Southern Observatory’s
Very Large Telescope to map the red light produced by the UV radiation illuminating the gas in UGC 7321.
By measuring the intensity of this very faint glow - shown in an artistic impression in the above Figure -
it has been possible to infer the presence of the elusive UV background. This study paves the ground for new ways to map the
temperature of the cosmos and to understand why there are so few small galaxies in the Universe.
Click here to find out more and
click here to read the paper.
IMAGE group meeting
First Friday of each month, 11 am. Room: OCW116
Group discussion of the latest science highlights from IMAGE. See calendar of events
for the schedule of the upcoming meetings.
IGM Journal Club
Fortnightly. Room: R5
In-depth discussion of recent papers on topics of interest to the
IMAGE group. All are welcome to join. See calendar of events for the times of the
upcoming meetings together with title of the papers for discussion.