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Does Gas Cool From the Hot Phase? (onto galaxies). Hot Gas in/around Ellipticals: Lessons Learned Hot Gas Environment of the Milky Way and Local Group: Limits on Accretion Missing Baryons in Galaxies and Galaxy Groups. The MPA/ESO/MPE/USM 2007 Joint Astronomy Conference

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does gas cool from the hot phase onto galaxies
Does Gas Cool From the Hot Phase?(onto galaxies)

Hot Gas in/around Ellipticals: Lessons Learned

Hot Gas Environment of the Milky Way and Local Group: Limits on Accretion

Missing Baryons in Galaxies and Galaxy Groups

The MPA/ESO/MPE/USM 2007 Joint Astronomy Conference

Gas Accretion and Star Formation in Galaxies

Joel Bregman (Univ. of Michigan)

let s look at galaxies with a lot of hot gas that is cooling
Let’s Look at Galaxies with a lot of Hot Gas that is Cooling

This is known as

Cooling Flows

X-ray contours

  • Gas masses of 1E8-1E10 Msun
  • T = 3-8 E6 K; Lx ~ 1E41 erg/s
  • Cooling rate of 0.1-1 Msun/yr
how to speak cooling flow
How to Speak “Cooling Flow”

The last Cooling Flow Meeting

  • Two types of hot gas situations
    • Hot gas in clusters of galaxies
    • Hot gas in early-type galaxies
  • Clusters of Galaxies
    • Most of the baryons are gaseous (not galaxies)
    • 2-10x107 K
    • Cooling: Free-Free (X-Rays)
    • Last Millennia: cooling rates 100-1000 Msun/yr
    • This Millennia: cooling rates of 1-30 Msun/yr
cooling flow ellipticals
Cooling Flow Ellipticals
  • Most Ellipticals are not X-ray bright
    • Bright ones in groups/clusters (1041 erg/s)
      • “Lots” of hot gas (~109.5 Msun)
      • Gas is bound
      • X-rays mainly due to line emission
    • X-ray faint galaxies (1040 erg/s)
      • LMXBs + a little hot gas (~108 Msun)
      • Galactic Winds
  • Bright Ellipticals are well-studied
metallicity of the hot gas
Metallicity of the Hot Gas

X-Ray Observations (XMM-Newton)

Fe is about Solar ([Fe] = 0)

[O/Fe] = -0.3

Metallicity like stars

Not like Cluster/group [Fe] = -0.5

Gas from Stellar Mass Loss

Not dominated by accretion from cluster/group

XMM RGS spectrum of NGC 4636 (Xu et al. 2003)

does this gas cool
Does this Gas Cool?
  • Observe OVIII (hot, ambient; 5E6 K)
  • OVI often detected in X-ray bright galaxies
    • 3E5 K gas; evidence for cooling from hotter gas

Far Ultraviolet Spectroscopic Explorer (RIP)

OVI is detected in about 40% of galaxies

Some cooling gas at 3x105 K

Cooling rates of 0.1-0.5 Msun/yr

In central region; not distributed.

Bregman et al. (2005)

where does the cooled gas go
Where Does The Cooled Gas Go?
  • Es in the RSA Catalog (Hogg et al. 1990; Bregman et al. 1992)
  • 104 K gas detected
    • Same metallicity as stars and hot gas
    • Not much mass (< 1E5 Msun)
  • HI and H2 rarely detected
    • M(HI) < 3E7 Msun for many ellipticals; 5% detection rate
    • M(H2 ) < 2E8 Msun; 0% detected
    • Limits the mass of HI HVC
  • Low levels of star formation, if present
    • Probably less than 0.1 Msun/yr
lessons learned from ellipticals
Lessons Learned From Ellipticals
  • Ellipticals appear to have much more hot gas than Spirals (total ISM mass similar)
  • Cooling flows in Es don’t lead to detectable masses of cooled HI (< 3E7 Msun)
  • Not much evidence for accretion from surrounding group/cluster medium
  • Radially distributed cooling should not occur
    • Local Thermal Instabilities suppressed in near-hydrostatic situations (Balbus 1995)
    • Even most non-linear disturbances are suppressed (Reale et al. 1991)
hot gas around spirals and in galaxy groups
Hot Gas Around Spirals and in Galaxy Groups
  • Stellar evolution models for the Galaxy
    • Need to resolve the G-dwarf problem (Z > 0.2)
    • Accrete 1-2 Msun/yr of gas with [Fe/H] < -3
  • Lx = 4E40 (Mdot/1Msun/yr) (T/3E6 K) erg/s
  • Milky Way has Lx ~ 1039.3 erg/sec
  • Other similar spirals have Lx ~ 1039.5 erg/s
  • No obvious support for accretion with rates exceeding 0.1 Msun/yr
ngc 891 in x rays
NGC 891 in X-rays

Chandra ACIS-S; 108 ksec of cleaned data

Point sources removed; smoothed

Hot gas easily seen to a height of 4.5 kpc from disk (1.6’) Fainter emission goes to a height of 9 kpc (3’)

Extent along disk similar to Halpha, FIR


Chandra 0.3 keV gas; 8’ box

Thermal emission; 4E39 erg/s

Mdot = 0.1 Msun/yr

Oosterloo et al. 2007; NGC 891 HI

give up the idea of accreting pristine gas onto mw
Give Up The Idea Of Accreting Pristine Gas Onto MW
  • Every Galaxy Group with good X-ray data
    • 0.0 > [Fe/H] > -0.7
  • Sightlines out of the MW show OVII and OVIII in absorption (metals are present)
  • Need to adopt a different approach to solving the G-dwarf problem
    • pollute the gas with metals before accretion (Binney and Merrifield; Galactic Astronomy)
a census of 10 6 10 7 k gas in the milky way and local group
A Census of 106 -107 K Gas in the Milky Way and Local Group

Z = 0.1 Solar

N = 1019 cm-2

OVII, OVIII have X-ray resonance lines; best sensitivity

Detect Hot Gas by X-ray Absorption Lines

discriminating between a galactic halo and local group model
Discriminating Between a Galactic Halo and Local Group Model
  • Galactic Halo Model:
  • distribution largely spherical around the MW
  • column densities similar in all directions
  • might see evidence for the shape of the Galaxy
  • Local Group Model
  • Local Group is elongated along the MW-M31 axis
    • columns greater along this axis and especially toward M31
    • (the long way through the LG)
  • Concern: M31 may have its own extended halo

Group simulation like the Local Group (Moore) shows elongation of matter .

Column enhancement along major axis ~2-3x perpendicular to axis


Toward Bulge

26 Target AGNs; mean EW = 22 mÅ; 17 with rms < 10 mÅ

These are the 4 best.

Bregman and Lloyd-Davies (2007; arXiv:0707.1699)


Local Group Model Prediction

An AGN toward M31 (long axis of Local Group)

One of the smallest columns, not one of the largest


Prediction of Local Group Model

The OVII data don’t fit a Local Group Model


A Galactic (Halo) Model Works Better

Central Line Velocities close to MW


Correlation with Galactic ¾ keV X-Ray Background

Supports a Galatic Halo Origin (10-100 kpc)

Gas Mass of 108 – 1010 Msun

Compare to NGC 5746 (Rasmussen & Ponman 2004): 109 Msun for similar metallicity

other evidence for hot gas in local group
Other Evidence for Hot Gas In Local Group
  • Nearby LG dwarfs have no gas but distant ones have gas (Blitz & Robishaw 2000; Grcevich et al. 2007)
    • Ram pressure stripping
    • n = 2.5E-5 cm-3 at d = 200 kpc (less than column inferred from OVII line by 4x)
    • 1E10 Msun of gas
    • Cooling time longer than Hubble time

X-Ray Shadowing: CHVC and a Magellanic Stream Cloud

This would reveal the fraction of X-ray emission beyond these clouds

Help determine the hot gas component of the Local Group

JNB, Birgit Otte, J. Irwin, M. Putman, E. Lloyd-Davies, C. Breuns (2007)

We see a brightening, not a shadow toward both clouds.

Clouds are interacting with a hot medium within 100 kpc of the MW.

Density/Temp of the hot medium is model-dependent.

mini summary
  • There is hot gas around the Milky Way and in the Local Group
    • Masses are not large (0.1-10E9 Msun)
    • Cooling times are long (3E8-1E10 yr)
  • Observed Lx is consistent with only 0.05 Msun/yr of accretion onto MW (and other spirals)
  • HVC probably not dominated by condensations from the dilute hot gas
when the demons visit at night
When the Demons Visit at Night
  • Where did the Baryons go?
    • Cosmological value is 17%
    • Rich Clusters have not lost their baryons
    • Spirals (like MW) are missing 2/3 of baryons
    • Galaxy groups (T < 1 keV) also missing most of their baryons within r1000
  • Good News – Bad News
    • Lots of gas available for accretion
    • … but it’s nowhere in sight (unbound)
Make the galaxy, then blow out the baryons in a “superwind” (this must occur, but when?)
    • Pollutes the surroundings
    • Need to drive the gas way away from galaxy (to the outer parts of the groups)
  • Other Possibility: The Gas Never Fell In
    • Entropy floor (preheating is 0.4 keV; 5E6K)
      • Need about 1 SNe per 500 Msun of gas
    • Enrich the metals by distributed SNe (Pop III)
      • 0.2 Solar metals is also 1 SNe per 500 Msun of gas
    • Naturally solves the G-dwarf problem (accrete enriched gas to make the disk)
    • Need to form some parts of galaxy before preheating (halo stars; dwarf galaxies)
    • Predict that this SNe heating occurs at z > 2 (Pop III ?)
      • Disk is 10 Gyr old
    • Has a significant effect on modeling (e.g., Davé): gas supply is hot
How are galaxies so smart?
    • Tight relationship as more baryons are lost
    • Clever feedback/formation scheme?

5E6 K

Poor Groups