Abstract-The Herschel-ATLAS: magnifications and physical sizes of 500μm-selected strongly lensed galaxies

A. Enia, M. Negrello, M. Gurwell, S. Dye, G. Rodighiero, M. Massardi, G. De Zotti, A. Franceschini, A. Cooray, P. van der Werf, M. Birkinshaw, M. J. Michałowski, I. Oteo

https://arxiv.org/abs/1801.01831

We perform lens modelling and source reconstruction of Submillimeter Array (SMA) data for a sample of 12 strongly lensed galaxies selected at 500μm in the Herschel Astrophysical Terahertz Large Area Survey H-ATLAS. A previous analysis of the same dataset used a single S\`ersic profile to model the light distribution of each background galaxy. Here we model the source brightness distribution with an adaptive pixel scale scheme, extended to work in the Fourier visibility space of interferometry. We also present new SMA observations for seven other candidate lensed galaxies from the H-ATLAS sample. Our derived lens model parameters are in general consistent with previous findings. However, our estimated magnification factors, ranging from 3 to 10, are lower. The discrepancies are observed in particular where the reconstructed source hints at the presence of multiple knots of emission. We define an effective radius of the reconstructed sources based on the area in the source plane where emission is detected above 5σ. We also fit the reconstructed source surface brightness with an elliptical Gaussian model. We derive a median value reff∼1.77kpc and a median Gaussian full width at half maximum ∼1.47kpc. After correction for magnification, our sources have intrinsic star formation rates SFR∼900−3500M⊙yr−1, resulting in a median star formation rate surface density ΣSFR∼132M⊙ yr−1 kpc−2 (or ∼218M⊙ yr−1 kpc−2 for the Gaussian fit). This is consistent with what observed for other star forming galaxies at similar redshifts, and is significantly below the Eddington limit for a radiation pressure regulated starburst.

STARS ARE THE UNIVERSE’S NEAT FREAKS

by Matt Williams

http://www.universetoday.com/129667/stars-universes-neat-freaks/#

Imagine, if you will, that the Universe was once a much dirtier place than it is today. Imagine also that what we see around us, a relatively clean and unobscured Universe, is the result of billions of years of stars behaving like giant celestial Roombas, cleaning up the space around them in preparation for our arrival. According to a set of recently published catalogues, which detail the latest findings from the ESA’s Herschel Space Observatory, this description is actually quite fitting.

These catalogues represents the work of an international team of over 100 astronomers who have spent the past seven years analyzing the infrared images taken by the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS). Presented earlier this week at theNational Astronomy Meeting in Nottingham, this catalogue revealed that as early as 1 billion years ago, the Universe looked much different than it does today.

In order to put this research into context, it is important to understand the important of infrared astronomy. Prior to the deployment of missions like Herschel (which was launched in 2009), astronomers were unable to see a good portion of the light emitted by stars and galaxies. With roughly half of this light being absorbed by interstellar dust grains, research into the birth and lives of galaxies was difficult.

Artist’s impression of the Herschel Space Telescope. Credit: ESA/AOES Medialab/NASA/ESA/STScI

But thanks to surveys like Herschel ATLAS – as well NASA’s Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE) – astronomers have been able to account for this missing energy. And what they have seen (especially from this latest survey) has been quite remarkable, presenting a Universe that is far denser than previously expected.

Last week (Friday, June 29th), during the final day of the National Astronomy Meeting, the first of the catalogues was presented. The images they showed gave all those present a glimpse of the unseen stars and galaxies that have existed over the last 12 billion years of cosmic history. In sum,  over half-a-million far-infrared sources have been spotted by the Herschel-ATLAS survey, and what they revealed was fascinating.

Many of these sources were galaxies that are nearby and similar to our own, and which are detectable using using conventional telescopes. The others were much more distant, their light taking billions of years to reach us, and were obscured by concentrations of cosmic dust. The most distant of these galaxies were roughly 12 billion light-years away, which means that they appeared as they would have 12 billion years ago.

Ergo, astronomers now know that 12 billion years ago (i.e. shortly after the Big Bang)., stars and galaxies were much dustier than they are now. They further concluded that the evolution of our galaxies since shortly after the Big Bang has essentially been a major clean-up effort, as stars gradually absorbed the dust that obscured their light, thus making it the more “visible” place it is today.

Herschel fig2smallAn illustration of the time reach of the Herschel ATLAS and the kinds of objects it has discovered. Credit: Herschel-ATLAS/ESA/ALMA/ NRAO

The data released by the survey includes several maps and additional files which were described in an article produced by Dr. Elisabetta Valiante and a research team from Cardiff University – titled “The Herschel-ATLAS Data Release 1 Paper I: Maps, Catalogues and Number Counts“. As Dr. Valiante told Universe Today via email:

“Gas and dust are the main components of stars: they collapse to form stars and they are ejected at the end of stars’ life. The interesting thing that has been discovered thanks to the Herschel data is that the two phenomena are not in equilibrium. We knew this was true 10 billion years ago, but we expected, according to the current models, that some equilibrium was reached at more recent times. Instead, the amount of dust in galaxies 5 billion years ago was much larger than the amount we see in galaxies today: this was unexpected.”

Until recently, such a survey would have been impossible due to the fact that many of these infrared sources would have  been invisible to astronomers. The reason for this, which was revealed by the survey, was that these galaxies were so dusty that they would have been virtually impossible to detect with conventional optics. What’s more, their light would have been gravitationally magnified by intervening galaxies.

The huge size of the survey has also meant that changes that have occurred in galaxies – relatively recent in cosmic history – can be studied for the first time. For instance, the survey showed that even only one billion years in the past, a small fraction of the age of the universe, galaxies were forming stars at a faster rate and contained more dust than they do today.

Infrared images (like the one captured by NASA’s Spitzer Space Telescope here) show countless stars and galaxies that are obscured in visible-light by cosmic dust. Credit: NASA/JPL-Caltech

Dr. Nathan Bourne – from the University of Edinburgh – is the lead author of another other paper describing the catalogues. As he told Universe Today via email:

“We can think of galaxies as big recycling machines. When they form, they accrete gas (mostly hydrogen and helium, with traces of lithium and a couple of other elements) from the universe around them, and they turn it into stars. As time goes on, the stars pump this gas back out into the galaxy, into the interstellar medium. Due to the nuclear processes within the stars, the gas is now enriched by heavy elements (what we call metals, though they include both metals and non-metals), and some of these form microscopic solid particles of dust, as a sort of by-product.

“But there are still stars forming, and the next generations of stars recycle this interstellar material, and now that it contains heavy elements and dust, things are a bit different, and planets can also form around the new stars, from accumulations of this heavy material. So, if you look at the big picture, when the first galaxies started forming within the first billion years after the Big Bang, they began using up the gas around them, and then while they are active they fill their interstellar medium up with gas and dust, but by the end of a galaxy’s lifecycle, it has used up all this gas and dust, and you could say that it has cleaned itself.”

The catalogues and maps of the hidden universe are a triumph for the Herschel team. Despite the fact that the last information obtained by the Herschel observatory was back in 2013, the maps and catalogues produced from its years of service have become vital to astronomers. In addition to showing the Universe’s hidden energy, they are also laying the groundwork for future research.

IR images of the entire sky take by the WISE All-Sky Data Release (top), and a projection of the IR sky created by images taken by the COBE spacecraft (bottom). Credit: NASA/JPL-Caltech/UCLA (top), NASA/DIRBE Team/COBE/ (bottom)

“Now we need to explain why there is dust where we did not expect to find it.” said Valiante. “And to explain this, we need to change our theories about how the Universe evolves. Our data poses a challenge we have accepted, but we haven’t overcome it yet!”

“[W]e understand a lot more about how galaxies evolve,” added Bourne, “about when most of the stars formed, what happens to the gas and dust as galaxies evolve, and how rapidly the star-forming activity in the Universe as a whole has faded in the latter half of the Universe’s history. It’s fair to say that this understanding comes from having a whole suite of different types of instruments studying different aspects of galaxies in complementary ways, but Herschel has certainly contributed a major part of that effort and will have a lasting legacy.”

The implications of these findings are also likely to have a far-reaching effect, ranging from cosmology and astronomy, to perhaps shedding some light on that tricky Fermi paradox. Could it be intelligent life that emerged billions of years ago didn’t venture to other star systems because they couldn’t see them? Just a thought…

This data release from the H-ATLAS team was coordinated with releases made in late June from the Herschel Extragalactic Project (HELP) team and the Herschel Multi-tiered Extragalactic Survey (HerMES). H-ATLAS and HerMES are parts of the EU Research Executive Agency’s HELP program, which brings together various extragalactic surveys carried out by Herschel and combines them with major surveys conducted by other observatories to give the Herschel mission a lasting legacy.

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Herschel Space Observatory opens a new terahertz window on the cold and dusty Universe

http://physicsinventions.com/index.php/herschel-space-observatory-discovers-the-clearing-out-of-star-forming-gas/
The European Space Agency (ESA) Herschel Space Observatory, home to the largest single mirror telescope in space, has detected massive amounts of molecular gas gusting at high velocities — in some cases in excess of 1000 kilometers per second — from the centers of a sample of merging galaxies. Herschel was built by a European-led, multi-national team, including U.S. contributions from researchers at NASA’s JPL, Caltech, and the Naval Research Laboratory (NRL). It opens a new terahertz window on the cold and dusty Universe, enabling its scientific objective: to investigate how planets, stars, and galaxies formed and continue to evolve. Driven by star formation and central black holes, these powerful storms are strong enough to sweep away billions of solar masses of molecular gas and to interfere with global galactic processes. The Herschel observations indicate that, in the galaxies hosting the brightest Active Galactic Nuclei, outflows can clear the entire supply for creating stars and feeding the black hole. This finding provides long-sought-after evidence of highly energetic feedback processes taking place in galaxies as they evolve. The discoveries are reported in papers in the journals Astronomy Astrophysics (volume 518, L41, 2010) and Astrophysical Journal Letters (volume 773, L16, 2011).
Together with an international team of investigators, Drs. Eckhard Sturm of the Max-Planck-Institut für extraterrestrische Physik (MPE) in Germany and Jacqueline Fischer of the NRL Remote Sensing Division, the Herschel Optical System Scientist, obtained terahertz spectroscopic observations in order to trace the evolution of merging gas-rich galaxies. The team observed a number of these mergers, which, because they are enshrouded in gas and dust therefore are very luminous in the infrared, are also known as Ultra-Luminous InfraRed Galaxies (ULIRGs). The mergers were observed with the spectrometer of Herschel’s PACS instrument, built by a team led by Dr. Albrecht Poglitsch (MPE), as part of the Survey with Herschel of the ISM in Nearby INfrared Galaxies (SHINING), headed by Dr. Sturm.
Massive outflows of gas from galactic centers are tell-tale signs that powerful, storm-like processes affecting the global galactic balance of mass and energy are underway. Within a galaxy, these storms can be generated in the regions of active star formation, stirred by stellar winds and shock waves from supernova explosions. They can also be triggered close to the central black hole, where radiation pressure from the accretion disc drives the surrounding gas away. When powerful enough, outflows can sweep away the galaxy’s entire reservoir of gas, depleting it of the raw material that creates stars and feeds the central black hole. This inhibits further star formation episodes and additional black hole growth. Thus, galactic outflows cause negative feedback, halting the same mechanisms that produced them in the first place.
Powerful outflows are key features in models of galactic formation and evolution, but while there have been other detections of galactic outflows, almost all previous observations dealt only with neutral and ionized gas. The Herschel discovery is unique in that, for the first time, the outflows were detected in the cool molecular gas from which stars are born, allowing their direct impact on star formation to be studied.
Elliptical galaxies are thought to arise from the merger of gas-rich spiral galaxies, a process in which ULIRGs represent an intermediate stage. Gas outflows develop naturally within this scenario, and they are crucial to explaining some observed characteristics of elliptical galaxies. Elliptical galaxies contain old stellar populations, relatively small amounts of gas and almost no sign of ongoing star formation. This is in contrast with spiral galaxies, which are dominated by young stars and are rich in gas necessary for intense star formation. For elliptical galaxies to derive from spiral galaxies, something must drain the cold gas and halt the production of stars, and outflows such as those observed by Herschel appear as ideal candidates for the job.
Another property that finds a natural explanation in galactic outflows is the strong correlation observed between the mass of black holes and the stellar mass of the spheroidal component of the galaxies hosting them: black holes that are relatively more massive appear to reside in galaxies with spheroids that contain more stars. This empirical relation suggests that black hole growth and star formation are intertwined, both initially drawing from the gas reservoir, and creating feedback mechanisms such as outflows that eventually suppress them.
Herschel’s sensitivity and spectral resolution enabled detection of the Doppler shifted signatures of these gigantic galactic storms, and demonstration for the first time, that they may be strong enough to shut down stellar production entirely. The outflows were traced via spectral lines of the hydroxyl molecule (OH). The excellent spectral resolution of PACS allowed astronomers to clearly identify the characteristic blue- and red-shifted profile caused by the system geometry. With velocities of 1000 kilometers per second and higher, the outflows are able to strip galaxies of gas amounting to several hundred solar masses every year.
The data set suggests that slower outflows may be initiated by star formation regions, whereas those with higher velocity appear to be related to the activity of Active Galactic Nuclei (AGN) powered by central black holes: brighter AGN seem to sweep gas away faster than their less luminous counterparts. However, it will be necessary to analyse a larger sample of galaxies in order to verify this claim that the measured velocity can be used as an indicator of the main mechanism driving the outflow.
Although observations of a larger sample is being collected, the early Herschel observations indicate that the galaxies hosting the strongest signatures of AGN are releasing gas at a much higher pace than their star formation rates, and thus they appear able to provide the mechanism needed exhaust their reservoirs of star-forming gas, as is necessary if they are to evolve into gas-poor elliptical galaxies. In the mergers observed to be undergoing strong feedback, star formation is estimated to cease on timescales shorter than 10 million years. This will produce galaxies with characteristics that match those observed in ellipticals: poor in cold gas and populated by old stars.
By catching molecular outflows ‘in the act,’ Herschel has yielded long-sought-after evidence that powerful processes with negative feedback do take place in galaxies and dramatically affect their evolution

Herschel Astrophysical Terahertz large Area Survey looks at evolution of dust in galaxies

The Herschel Space Observatory has been used to help astronomers at Cardiff, Nottingham University and Max-Planck Institute for Astrophysics to understand the amount of dust in galaxies at varying distances, it was heard at the National Astronomy Meeting held in Llandudno, North Wales, last week.
Dr Haley Gomez of Cardiff University, who presented the results at the conference, along with her colleagues, used data taken from the Herschel Astrophysical Terahertz large Area Survey, H-ATLAS, to take a look at the evolution of dust in galaxies over the past five billion years of cosmic history. H-ATLAS is the largest key astronomical project on ESA’s Herschel Space Observatory and surveys an amazing 550 square degrees of sky. With both its PACS and SPIRE cameras which snap pictures in the infrared and submillimetre wavebands, astronomers are able to unveil the cold Universe, studying the dusty cosmos in high detail. To tell us more about dust and Herschel, Astronomy Now reporter Gemma Lavender interviews Cardiff University’s Dr Haley Gomez in the video report below.
Now, the survey has provided Gomez and her team with an insight into the Universe, where they found that the galaxies they studied were dominated by cold dust with temperatures between 15 to 25 kelvin (–258 to –248 degrees Celsius). Their observations also revealed that the dust masses for large galaxies were about five times larger at redshifts of around 0.5 compared to galaxies which can be found in the local universe. The collaboration between the three institutions has also revealed that the mass of dust to stellar mass was three to four times larger in the past. The source of this interstellar dust is still uncertain and difficult to explain with standard models.
But why is this cold dust relevant? Dust contributes one percent of the mass of a galaxy but despite this small amount, it allows stars to form more efficiently. Without these cosmic particles, we would not have molecular hydrogen, which means no water traces in galaxies. “We’re talking about the building blocks of asteroids, the cores of comets and rocky planets,” says Gomez. “But we’re also talking about the building blocks of us – life is lumps of dust, of iron and carbon and so on, inside ourselves. So when you ask where dust comes from you’re asking where planets come from and where life comes from.”