astrobites 2017

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Galaxy Clusters across Cosmic Time

Postby bystander » Fri Mar 10, 2017 5:22 pm

Same ol’ same ol’? Galaxy Clusters across Cosmic Time
astrobites | 2017 Mar 09
Gourav Khullar wrote:
We have come a long way since the 1930s, when the words ‘galaxy cluster‘ were posited for the first time by Fritz Zwicky, in relation with the presence of dark matter in the Coma cluster. Developments in multi-wavelength astrophysics have allowed us to probe different components of a cluster with different telescopes. For example, star-forming galaxies of galaxy clusters are observed using optical telescopes because starlight in these galaxies loves emitting photons with the roughly the same energy that we see from the sun. Some of these galaxies are super-red, have no star-formation and a ton of dust, that is best seen from infra-red and radio telescopes. Today’s story takes us to the intermittent space between different galaxies inside a cluster, called the intra-cluster medium (ICM) and its emissions. ...

The Remarkable Similarity of Massive Galaxy Clusters from z~0 to z~1.9 - Michael McDonald et al
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How long do quasars shine?

Postby bystander » Fri Mar 10, 2017 5:30 pm

How long do quasars shine?
astrobites | 2017 Mar 10
Suk Sien Tie wrote:
In the deep center of every massive galaxy, extremely massive but invisible black holes reign supreme. How these supermassive black holes (SMBHs) grew to boast of their 107-109 Msun masses still eludes us today. These massive beasts are awakened when surrounding matter spirals in and falls into them, creating active galactic nuclei (AGN) as luminous as our Milky Way. In this state, they spew out radiation from the radio to the X-rays. When the accretion of matter is particularly high, the AGN becomes very luminous and is called a quasar. (Here is a handy guide on AGN taxonomy.) ...

This paper examines the episodic lifetime of quasars using singly-ionized helium (He II) as the probe. At redshift z~3, most of the Helium in the Universe is singly-ionized. The last electron in He II can be knocked free by the powerful radiation from quasars. As a quasar ionizes its surrounding He II, one can imagine a sphere of ionized He II around the quasar that expands outward with the ionizing radiation. The longer the quasar shines, the larger this sphere becomes. ...

Statistical Detection of the HeII Transverse Proximity Effect:
Evidence for Sustained Quasar Activity for >25 Million Years
- Tobias M. Schmidt et al
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Honey, it’s an Intermediate Mass Black Hole this time!

Postby bystander » Tue Mar 14, 2017 3:59 pm

Honey, it’s an Intermediate Mass Black Hole this time!
astrobites | 2017 Mar 13
Bhawna Motwani wrote:
Our universe is speculated to host a plethora of black holes, and they come in varied sizes: stellar mass (SBH), intermediate-mass (IMBH), and super-massive (SMBH). Of this assortment, SBHs, that have masses of a few to tens of times the mass of our Sun, as well as the SMBH variety that can be a million- to billion-fold heavier and found in the central engines of active galactic nuclei at large redshifts, have been studied and characterized for a long time. On the other hand, what remained elusive to this point, has been the existence and properties of a novel class of long-lived black holes (IMBHs), thought to represent the evolutionary bridge between SBHs and SMBHs. ...

Very recently, Kızıltan et al. published the evidence of an IMBH residing – in line with previous theoretical predictions – at the centre of 47 Tucanae (or NGC 104), one of the most massive globular clusters known. ...

An intermediate-mass black hole in the centre of the globular cluster 47 Tucanae - Bülent Kızıltan, Holger Baumgardt, Abraham Loeb

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Gemstones Askew in the Heavens

Postby bystander » Fri Mar 17, 2017 7:37 pm

Gemstones Askew in the Heavens
astrobites | 2017 Mar 14
Paddy Alton wrote:
In today’s article I want to take a closer look at gravitational lenses and open a window on some of the interesting science astronomers are using these objects for.

A gravitational lens results from a chance alignment of two galaxies, one near and one far. To understand how it works, we need to take a brief tour through Einstein’s General Theory of Relativity – but don’t panic! I’ll keep it light. In his landmark theory, now over a century old, Einstein outlined the mechanism by which gravity acts. Rather than being a fixed background against which events happen – a sort of cosmic stage – space itself can be warped and stretched by the presence of mass. The more massive the object, the stronger the distortion. The upshot is that anything following a straight path through space, such as a light ray, finds itself travelling a curved path instead when it passes near a mass – as if a force was acting directly upon it. It’s this apparent force that we call gravity. This effect was used in 1919 by Sir Arthur Eddington to confirm the predictions of General Relativity, to much excitement and confusion; during an eclipse, Eddington measured the angle through which the Sun’s gravity deflected the light of distant stars, showing that this matched the theory. In special circumstances, the same effect can focus the deflected light rays, just like a traditional lens ...

Planck's Dusty GEMS. III. A massive lensing galaxy with a
bottom-heavy stellar initial mass function at z=1.5
- R. Canameras et al
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Super Star Clusters Far Far Away

Postby bystander » Fri Mar 17, 2017 7:56 pm

Super Star Clusters Far Far Away
astrobites | 2017 Mar 15
Benny Tsang wrote:...
It always amazes me to see the manifestation of gravitational lensing in deep Hubble images – light from very-far-away galaxies being magnified and stretched into arcs by the strong gravity of the quite-far-away galaxy clusters. The gravity of the galaxy clusters acts as a “natural telescope” that focuses light to reveal background galaxies, which otherwise are too faint to be seen.

Astrophysicists have been puzzling over the mystery of reionization. How did reionization occur and what sources caused it? To try to answer these questions we need to know the origins and the properties of the early, far-away galaxies that were responsible. Recently, it was found that the huge number of faint galaxies may provide enough photons to reionize the Universe. The technique of gravitational lensing comes in very handy because it allows far-away and faint objects to be observed! ...

Magnifying the early episodes of star formation:
Super-star clusters at cosmological distances
- E. Vanzella et al
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When the Neighborhood Dwarf Galaxies were Kids

Postby bystander » Fri Mar 17, 2017 8:10 pm

When the Neighborhood Dwarf Galaxies were Kids
astrobites | 2017 Mar 16
Stacy Kim wrote:
The heavens bespeak a dark and quiet night, glinting here and there with distant stars and yet more distant galaxies. But in ages past, long before the birth of our stalwart Sun, before even the supernovae that spewed the calcium in our bones and the iron in our blood into the gas that formed the Sun and the Solar System, there was darkness. The cosmic dark ages reigned for nearly a million years before the first stars blinked blearily on.

Then suddenly there came an age of light. We’re not entirely sure what exactly lit up the universe, but among the suspects are the first galaxies. Once practically invisible, they were lit aflame as the first stars began to burn hot and bright within them. They generated copious amounts of ultra-violet (UV) light, energetic enough to ionize the hydrogen in the universe. So much UV flux was generated that nearly all the hydrogen in the universe was ionized, leaving the universe clear and transparent and allowing us the majestic views of faraway galaxies that we take for granted today. ...

Local Group Ultra-Faint Dwarf Galaxies in the Reionization Era - Daniel R. Weisz, Michael Boylan-Kolchin
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Re: Gemstones Askew in the Heavens

Postby Ann » Tue Mar 21, 2017 1:12 am

bystander wrote:Gemstones Askew in the Heavens
astrobites | 2017 Mar 14
Paddy Alton wrote:
In today’s article I want to take a closer look at gravitational lenses and open a window on some of the interesting science astronomers are using these objects for.

A gravitational lens results from a chance alignment of two galaxies, one near and one far. To understand how it works, we need to take a brief tour through Einstein’s General Theory of Relativity – but don’t panic! I’ll keep it light. In his landmark theory, now over a century old, Einstein outlined the mechanism by which gravity acts. Rather than being a fixed background against which events happen – a sort of cosmic stage – space itself can be warped and stretched by the presence of mass. The more massive the object, the stronger the distortion. The upshot is that anything following a straight path through space, such as a light ray, finds itself travelling a curved path instead when it passes near a mass – as if a force was acting directly upon it. It’s this apparent force that we call gravity. This effect was used in 1919 by Sir Arthur Eddington to confirm the predictions of General Relativity, to much excitement and confusion; during an eclipse, Eddington measured the angle through which the Sun’s gravity deflected the light of distant stars, showing that this matched the theory. In special circumstances, the same effect can focus the deflected light rays, just like a traditional lens ...

Planck's Dusty GEMS. III. A massive lensing galaxy with a
bottom-heavy stellar initial mass function at z=1.5
- R. Canameras et al


Paddy Alton wrote:
Following this method, the authors infer that the foreground galaxy is indeed more massive than might be expected from its brightness alone, indicative of an excess of dim dwarf stars. This is consistent with results from galaxies in the nearby universe, which have undergone billions of years of additional evolution, forging a crucial link between local galaxies and their antecedents.


Indeed, we may see an excess of dim dwarf stars in the local universe, too.

Deborah Byrd of EarthSky wrote:
Astronomers have peered into eight relatively nearby elliptical galaxies and made a discovery suggesting that small, dim red dwarf stars in these sorts of galaxies might be 20 times more plentiful than in our spiral-shaped Milky Way galaxy.


It may indeed be true that elliptical galaxies contain huge numbers of dim red dwarf stars, boosting the mass of the galaxies considerably but having little impact on the galaxies' light output.

Ann
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