Where are all the baryons? Baryon census (2013) of the local universe, contd. Now that we've introduced DM, chemistry and gas evolution, we'll put these all together in a story starting with the first stars, the first galaxies, moving towards modern day galaxies.
Baryon census (2013) of the local universe, contd.
Now that we've introduced DM, chemistry and gas evolution, we'll put these all together in a story starting with the first stars, the first galaxies, moving towards modern day galaxies.
Joss Bland-Hawthorn University of Sydney
Baryon census (z~0)
fixed cosmic abundances
This is a real problem since we don’t know how metals vary between ISM and IGM
Most recent summary
from Shull+ 2012
n★ is a normalization factor which defines the overall density of galaxies (number per cubic Mpc)
L★ is a characteristic galaxy luminosity. An L★ galaxy is a bright galaxy, roughly comparable in luminosity to the Milky Way. A galaxy with
L < 0.1 L★ is a dwarf.
α defines the `faint-end slope’ of the luminosity function. α is typically negative, implying large numbers of galaxies with low luminosities.
Large galaxy surveys of the local universe – 2dFGRS (Colless+ 2001), SDSS (Blanton+ 2001), GAMA (Driver+ 2012)
GF favours disks over spheroids
2:1 (Driver+07; cf. FHP96)
we see this function vary across galaxy types and in cosmic time
There is a good reason for why we only include cold gas in galaxies (and not in the IGM) in the inventory.
corrected for cold He I, H2 (FP04)
Confirmation: ALFALFA survey (Darling+11)
Sancisi dictat: All cold gas is associated with galaxies (i.e. dark matter)
Extragalactic HI always associated with galaxies, e.g. tidal tails like the Magellanic Stream.
If you can find a truly isolated cloud, you will be famous!
COLD GAS (2%)
blue = hot x-ray gas (107 K)
bremmstrahlung = emission ("braking rays" when e- decelerated by p)
The Galaxy – classic paper (followed by Kahn & Woltjer 1959 for the LG)
Pedersen+ 06; Rasmussen+ 06 1959 for the LG)
not confirmed: smoothed out nuclear source!
(2011) 1959 for the LG)
Vrot ~ 400 km/s
This appears to be first reliable detection in emission after the Galaxy
see also Dai+12 (UGC 12591; Vrot ~ 470 km/s)
INTRACLUSTER MEDIA (4%): can often dominate over stars 1959 for the LG)
Where does this hot gas come from?
Large-scale shocks associated with accretion onto A3376 1959 for the LG)
This provides us with a clue about why so much gas is rendered (almost) invisible to modern instruments.
Cooling times are longer than the age of the Universe (Hubble time) at low densities (n α r-2) beyond the virial radius...
Sutherland & Dopita (1993):
Solar, 0.3, 0.1, 0.01, 0.001 Solar
This is an important clue that lots of gas can escape detection by being hot and at low densities...
harder to detect
(hard UV photons)
easier to detect
(soft and hard x-rays)
2012 (Hubble time) at low densities (n
The first systematic survey has found warm gas at the outskirts of the Virgo cluster
(100%; NHI > 1013 cm-2) – circumcluster medium ? Not just as simple as hot halos.
Baryon fractions in groups & clusters (Hubble time) at low densities (n
Joss' rule of thumb:
below 0.1Z from outside, above 0.2Z
Way more scatter than implied by McGaugh+ 2010 figure.
Baryon fractions down to galaxy masses (Hubble time) at low densities (n
(note where the Milky Way is)
So even with corrections for missing hot gas (e.g. Anderson, NGC 1961), galaxies appear to fall below the cosmic baryon fraction. So maybe the gas never got in? or maybe the gas was once there but then removed?
− the new frontier −
gas distributed on the scale of the dark matter halo, i.e. out to the so-called virial radius
Circumgalactic media (Hubble time) at low densities (n (5%)
Lyα halos at z~3 – 92 LBGs stacked
So huge haloes of warm/cool gas do exist. We need to look to high z to see these because Lyα map only detectable when redshifted out of extreme UV. Where do these come from?
CGM − Why the new frontier? (Hubble time) at low densities (n
It may soon be possible
to resolve how gas gets
Keres+ 2005, 2009 (Hubble time) at low densities (n
Circumgalactic media (Hubble time) at low densities (n (5%)
See also OVI absorbers in the Galaxy (Richter+09)
OVI absorbers in
Important clue to
metals in the IGM?
How does gas move out of voids? (Hubble time) at low densities (n
Sheth & van de Weygaert 2004
Sheth & vdW 2004
Mo et al 2010: (Hubble time) at low densities (n
a lot of detail handled
in on-line codes that borrow from many sources, e.g. Fyris,
Gadget II, VH-1, etc.
First to simulate the IGM and noted relevance to missing baryons. Very simple shock physics was used.
WHIM: large-scale shocks baryons. Very simple shock physics was used.
You've been introduced to shocks in BMG's lectures.
Cen: you have a lump of dark matter of size L at some redshift z. Gas has been infalling for the age of the Universe, i.e. To = 1/Ho(z). The infall velocity VI ~ HoL.
The potential energy of the gas is converted into internal (heat) energy through the shock, which will heat the gas to the virial temperature TVIR of the halo. The sound speed Cs in the shocked gas (TSH~TVIR) is comparable to the infall speed ~ rotation speed Vc.
The post-shock conditions depend on geometry,
e.g. no = pre-shock, n1 = post-shock density
3D: n1/no = 64 (collapse onto DM sphere)
2D: n1/no = 16 (collapse onto DM filament)
1D: n1/no = 4 (collapse onto DM sheet)
(adiabatic case, i.e. no heat lost or gained from system)
δ > 10 baryons. Very simple shock physics was used.
δ > 100
δ > 1000 (galaxy halos)
T ~ 105-7 K
Formation of the WHIM near sheets and filaments (O'Shea) baryons. Very simple shock physics was used.
v baryons. Very simple shock physics was used.s < 150 km s-1
Ts < 105 K
vs > 700 km s-1
Ts > 107 K
Chandra/XMM spectroscopy baryons. Very simple shock physics was used.
HST COS UV spectroscopy baryons. Very simple shock physics was used.
It's not all hot in the IGM. The mysterious Lyman α forest (LyαF) appears to be huge diffuse clouds of photoionized, low density gas. Near to galaxies, groups and filaments?
We detect metals in the LyαF.
Evidence for shocks: baryons. Very simple shock physics was used.
much of this appears
Danforth & Shull 05,08
Thom & Chen 08
really need e.g. Ne VIII
missing phase e.g. hotter WHIM?
broad Lyα absorbers
integrated to log NH > 12.5
rises to 31% if down to 12.0
much of this is photoionized
85% baryons uncollapsed, half still missing.
We need to understand the physical state of each gas phase before talking about a complete inventory (e.g. CGM inflow? outflow?).
We know little about the dynamics of gas flows onto mass structures on any scale, although there may be some evidence that these processes are now being observed. Most of the action was at high redshift but the same processes are still ongoing.