# Presentation: 448769

## The ISM

- KU-4/2007

- K.D.Kuntz
- The Henry A. Rowland Department of Physics and Astronomy
- The Johns Hopkins University

- (Diffuse Emission in Galaxies)

## Xray Emission from Galaxies

- Point Sources

- Introduction

- XAS-7/2007

- LMXB

- HMXB

- Diffuse Emission

- SNR

- SFR

- Bubbles

- Super-Bubbles

- Un ID’d

- Multiple SW
- & SNE

## Outline

- Diffuse Emission in the Milky Way
- Large Scale Emission (LHB, Galactic Halo, Etc.)
- Super Bubbles
- Star-Forming Regions
- Diffuse Emission in Other Galaxies
- Global Correlations

- Introduction

- XAS-7/2007

## Fundamentals of X-ray Astronomy

- X-ray Absorption Cross-Section is E-2/3
- Lower energy photons more readily absorbed
- One can see further at higher energies

- Introduction

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## Fundamentals of X-ray Astronomy

- Typical hot ISM T~106K →emission below 0.7 keV
- Most parts of the hot ISM hidden from us
- Most of what we see at low E is local!

- Introduction

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## Diversion I

- A high Galactic latitude, bulk of sources are AGN
- Deep exposures reveal more & fainter sources

- LHB

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## Diversion I

- Does ΣAGN=total X-ray surface brightness?
- Yes, but...answer depends upon the energy.

- LHB

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## A Model of the Sky

- Consider a map of the absorbing column due to neutral and molecular gas in the Milky Way.
- If all of the emission is due to AGN, what does the sky look like?

- LHB

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## A Model of the Sky

- LHB

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- Absorption

- 1⁄4 keV em.

## A Model of the Sky

- LHB

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- R12= 1⁄4 keV

- Observed

- Model

## The Observed Sky

- LHB

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- 3⁄4 keV

-  1⁄4 keV

## The Observed Sky

- LHB

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- 1/4 keV

- 100μm

## The Observed Sky

- At 1⁄4 keV and 3⁄4 keV there is diffuse local emission
- Not identifiable with any single SN, SNR, or SFR
- Distribution in 1⁄4 keV and 3⁄4 keV bands is different
- (not just an effect of absorption)
- Distance to emission (and thus its mass) is unknown.

- LHB

- XAS-7/2007

## Diversion II

- Assume:
- Uniform local emission
- A screen of absorption
- Uniform distant emission

- LHB

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## Diversion II

- If τ=σNH varies with position
- Anticorrelation of τ and surface brightness
- By fitting anticorrelation
- Can determine
- IL and ID

- LHB

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## LHB

- From shadows, determine ID&IL in many directions
- Given distances to clouds
- → upper limit on size of local emitting region
- → lower limit on distance to distant emission

- XAS-7/2007

## LHB

- Assuming thermal emission
- ROSAT band values → local emission has T~106K
- Upper limit on size of region → crossing time~106 years
- 		→ n, T, L are relatively uniform
- Therefore IL proportional to R

- XAS-7/2007

## LHB

- The Local Hot Bubble:
- Irregular region filled with T=106K emission
- Inside a larger(?) region (Local Cavity)
- With below average density of neutral material
- Controversy: contamination by very local emission
- The heliosphere is X-ray bright
- Accounts for some unknown fraction of “LHB” emission
- Some truly LHB emission does exist

- XAS-7/2007

## LHB

- The Local Hot Bubble:
- At T~106K, emission is so low-energy that we can’t see similar bubbles further away than a few 100 pc.
- Could be a major component of galactic X-ray emission
- Bulk of emission below Chandra/XMM bandpass

- XAS-7/2007

## Galactic Halo

- At high Galactic latitude the ID component is the halo.
- In some directions the halo emission is substantial

- Halo

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-  1⁄4 keV

## Galactic Halo

- At high Galactic latitude the ID component is the halo.
- In some directions the halo emission is substantial

- Halo

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## Galactic Halo

- At high Galactic latitude the ID component is the halo.
- Distant emission at 1⁄4 keV is mottled

- Halo

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- Loop I Superbubble

- NGP

- SGP

## Galactic Halo

- At high Galactic latitude the ID component is the halo.
- Emission at 3⁄4 keV is smoother than at 1⁄4 keV

- Halo

- XAS-7/2007

- 3⁄4 keV

- 1⁄4 keV

## Galactic Halo

- Distance to emission is unknown
- 1⁄4 keV emission at z>300pc
- 3⁄4 keV emission beyond Magellanic Clouds?
- ROSAT: Two thermal components:
- Soft ( 1⁄4 keV component) kT~0.09, T~106K
- Since patchy possibly due to Galactic chimneys
- Hard ( 3⁄4 keV component) kT~0.25, T~3×106K
- Could be Galactic halo or Local Group or Extragalactic (low z)
- XMM: Temperature of hard component spatially variable.

- Halo

- XAS-7/2007

## Galactic Disk Emission

- In this image of the Galactic anticenter at 3⁄4 keV,
- The disk absorption is less than expected if all emission were extragalactic
- There must by X-ray emission due to the Galactic disk
- Must “exactly” balance the absorption
- Stars can provide some fraction
- Source population unclear
- Spatial distribution is unclear
- 	(due to emission and abs.
- 	being intermixed along LOS.)
- kT~0.6 keV

- Disk

- XAS-7/2007

- 3⁄4 keV

## Galactic Ridge Emission

- Hard (kT~7.0 keV) Emission along the Galactic plane:
- Truly diffuse emission or unresolved point sources?
- Seemingly diffuse component has same distribution as the near IR → distribution is stellar → due to point sources
- Identification of point source population problematic(?)
- Spectrum of emission is problematic(?)

- Ridge

- XAS-7/2007

## Star-Forming Regions

- From pop. synthesis models, expected source of X-rays:
- O star winds >>> B star winds
- O star SNe ~ B star SNe
- 		(depends on age)

- SFR

- XAS-7/2007

- From R.Chen

## Star-Forming Regions

- Observed SFRs (without SNe):

- SFR

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- M17 Shows plenty
- of diffuse emission

- While Orion does not.

## Star-Forming Regions

- Somewhat older SFR: What a mess!

- SFR

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- 30 Doradus

- SNR

- HII

## Miscellaneous

- Ridge

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- Loop I SuperBubble

- Galactic Bulge

## Milky Way Summary

- Summary

- XAS-7/2007

- Soft Halo kT~0.09 keV

- Hard Halo kT~0.2 keV

- Disk
- kT~0.6 keV

- Gal. Ridge
- kT~7.0 keV

- SuperBubble kT~0.25 keV

- Gal. Bulge kT~0.35 keV

- LHB
- kT~0.09

- SNR

- SFR kT~0.2,0.6

## Milky Way Summary

- What is the filling factor?
- Is it a pervasive hot medium with embedded cool clouds?
- Is it restricted to hot bubbles in a pervasive cool medium?

- Summary

- XAS-7/2007

## Other Galaxies

- Two Opposed Views

- Summary

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- Star Formation

- Galactic Potential

- Dominates is Late-Type Spirals

- Only the most massive galaxies

## Other Galaxies

- Global Correlations among X, B, H, 12μm, FIR, 6cm:
- Many correlations depend on morphology
- Reflecting differences in SFR, bulge vs. disk, AGN prob.
- 12μm, FIR, 6cm correlated (star formation)
- Small dust grains, Large dust grains, thermal free-free
- Linear correlations
- B, H correlated (stellar populations, IMF)
- Young massive stars, All ages of low mass stars
- Non-linear correlations
- But B,H not correlated well with 12μm,FIR,6cm

- Correlation

- XAS-7/2007

## Other Galaxies

- How is X correlated?
- Early-type galaxies – X and B weakly correlated
- Non-linear correlation
- Late-type galaxies – X and FIR strongly correlated
- LX/LB correlated w/ L60/L100 correlated with SFR
- X, FIR, 6cm all have linear correlations

- Correlation

- XAS-7/2007

## Other Galaxies

- Why?
- Point sources:
- HMXB: end products of massive star formation
- Short-lived, appear shortly after star formation
- LMXB: end products of low mass star formation
- Long lived, appear long after star formation
- Diffuse emission:
- Halo: determined by mass of the system
- Star formation: stellar winds & SNR
- Other components
- AGN:

- Correlation

- XAS-7/2007

- }B

- }B/H

- }H

- }FIR

- }?

## Other Galaxies

- What about the individual components X?
- Point source emission correlated non-linearly with B
- Roughly consistent with expectations
- Diffuse emission only weakly correlated with B
- Complicated since X-ray/FIR emission is immediate while the B-band emission lasts for as long as B stars.

- Correlation

- XAS-7/2007

## Other Galaxies

- Bottom line:
- X-ray emission from early-type galaxies dominated(?) by point source populations with possible contribution from hydrostatic halo and other, minor diffuse sources.
- X-ray emission from late-type galaxies dominated by star formation/hot ISM
- Concentrating on ISM → concentrating on late-type disks

- Correlation

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## Diffuse Emission in Sc-Sd

- Spatial distribution of the X-ray follows that of UV

- Correlation

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## Diffuse Emission in Sc-Sd

- X-ray surface brightness correlated with UV
- Trend may not be universal

- Correlation

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## Diffuse Emission in Sc-Sd

- Spectrum fit by two thermal components:
- kT~0.2 keV and kT~0.6 keV

- Correlation

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## Diffuse Emission in Sc-Sd

- Correlation

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| Galaxy | TS | TH | NH/NS | Hubble |
| --- | --- | --- | --- | --- |
| M61 | 0.25 | 0.79 | 3.33 | Sbc |
| M83 | 0.25 | 0.61 | 0.63 | Sc |
| N1637 | 0.3 | 0.7 | 1.43 | Sc |
| M101 | 0.20 | 0.75 | 0.35 | Scd |
| N2403 | 0.18 | 0.73 |  | Scd |
| N6946 | 0.25 | 0.70 | 0.14 | Scd |
| N3184 | 0.13 | 0.43 |  | Scd |

- Most late type galaxies have similar 2 temperature structure
- Ratio of emission strengths may vary with Hubble type.

## Diffuse Emission in Sc-Sd

- Why?
- Inflection points of the cooling curve?
- Similar to temperatures measured in Star-forming regions
- Characteristic temperatures of two different emission processes?
- Lack of spectral resolution
- Continuous E.M. distributions always produce kT=(0.2,0.6) at Chandra/XMM resolution

- Correlation

- XAS-7/2007

- Just delays the question

- Stars (kT~.6)?