10�1 100 101 102 103

Observation Angle [arcsec]10�11

10�10

10�9

10�8

10�7

10�6

10�5

10�4

10�3

Surf

ace

Bri

ghtn

ess

[cts

�1

arcs

ec�

2]

0.5-2 keV background

Grey foreground dust

Grey IGM1 um IGM

10�1 100 101 102 103

Observation angle [arcsec]100

101

102

103

104

105

�t[y

ears

] 0.1 um grains1.0 um grains

10�1 100 101 102 103

Observation Angle [arcsec]10�11

10�10

10�9

10�8

10�7

10�6

10�5

10�4

10�3

Surf

ace

Bri

ghtn

ess

[cts

�1

arcs

ec�

2]

0.5-2 keV background

Grey foreground dust

Grey IGM1 um IGM

�

– 8 –

show the individual halo profiles for several energies between 0.5 and 2.0 KeV for a

distribution of dust grains with 0.1 < a < 1.0 µm and p = 1.8. The black curve

shows the result of integrating the color curves using � = 2. The dashed line shows

the background count rates (counts per pixel) reported by the Chandra Source Catalog

(CSC).1

Fig. 4.— Caption for fig:qso1508

x =

� zsz

cdzH(z)� zs

0cdzH(z)

�scat

zs

z

1http://cxc.harvard.edu/csc/

– 8 –

show the individual halo profiles for several energies between 0.5 and 2.0 KeV for a

distribution of dust grains with 0.1 < a < 1.0 µm and p = 1.8. The black curve

shows the result of integrating the color curves using � = 2. The dashed line shows

the background count rates (counts per pixel) reported by the Chandra Source Catalog

(CSC).1

Fig. 4.— Caption for fig:qso1508

x =

� zsz

cdzH(z)� zs

0cdzH(z)

�scat

zs

z

1http://cxc.harvard.edu/csc/

– 9 –

0

3. Future Implications

REFERENCES

Aguirre, A. 1999, ApJ, 525, 583

Comastri, A., Setti, G., Zamorani, G., Elvis, M., Wilkes, B. J., McDowell, J. C., &

Giommi, P. 1992, ApJ, 384, 62

Inoue, A. K., & Kamaya, H. 2003, MNRAS, 341, L7

Mathis, J. S., Rumpl, W., & Nordsieck, K. H. 1977, ApJ, 217, 425

Mauche, C. W., & Gorenstein, P. 1986, ApJ, 302, 371

Menard, B., Scranton, R., Fukugita, M., & Richards, G. 2010, MNRAS, 405, 1025

Smith, R. K., & Dwek, E. 1998, ApJ, 503, 831

Weingartner, J. C., & Draine, B. T. 2001, ApJ, 548, 296

Wilkes, B. J., & Elvis, M. 1987, ApJ, 323, 243

Williams, O. R., et al. 1992, ApJ, 389, 157

This preprint was prepared with the AAS LATEX macros v5.2.

DR

Dust in the wind 1067

Figure 7. Comparison of reddening maps in the three dust models, eachnormalized to the MSFR result at 1 h!1 Mpc. The regions shown are aquadrant of the simulation cube, 25 " 25 " 50 (h!1 Mpc)3. Red/blue regionsindicate heavily/lightly reddened fields through the simulation, with thecolour scale running from E(g ! i) = 10!5 up to 0.1, logarithmically.

MSFR argue that the dust in Large Magellanic Cloud (LMC)-likedwarfs is insufficient to explain the magnitude of their reddeningsignal. We concur with this conclusion. Reproducing the MSFRdata in the hybrid model with a physical dust-to-metal mass ratiorequires including galaxies up to several times 1010 M#, far largerthan the $3 " 109 M# baryonic mass of the LMC (van der Marelet al. 2002). Furthermore, the No-Wind simulation predicts a galaxybaryonic mass function that is inconsistent with observations, withan excessive global fraction of baryons converted to stars (Oppen-heimer et al. 2010).6 We do not consider the hybrid dust model to benearly as plausible an explanation of the MSFR results as the Windmodel; we present it as a foil to illustrate what would be requiredto explain MSFR’s findings with dust in low-mass galaxies. For theWind model, the metals in low-mass galaxies contribute much lessreddening than the intergalactic metals (Fig. 5).

4 D ISCUSSION

For the Wind model to succeed, we require that the dust-to-metalmass ratio in the IGM be comparable to that in the ISM, allow-ing only $50 per cent of the ISM dust to be destroyed duringits expulsion from galaxies and subsequent residence in the IGM.The validity of this assumption is by no means obvious, as the de-struction time-scales for 0.01 µm dust grains by thermal sputteringare $107.5(nH/10!3 cm!3)!1 yr at T = 106 K (Draine & Salpeter1979, fig. 7), while wind particles in the simulation typically re-main in the IGM for $109 yr before re-accreting on to galaxies(Oppenheimer et al. 2010, fig. 2). However, the sputtering rates de-cline rapidly towards lower temperatures (e.g. a factor of 300 lowerat T = 105 K), and with the wind implementation used in this simu-lation most ejected gas never rises above a few "104 K. Ultraviolet(UV) or X-ray background photons are another possible destruc-tion mechanism for IGM dust, but the intergalactic radiation fieldis much lower intensity than the radiation field dust grains alreadyencounter in galactic star-forming regions.

A detailed consideration of dust survival in the IGM is beyondthe scope of this initial investigation, but the MSFR results clearlyraise it as an important subject for further study. The combinationof their measurements with our models gives a fairly clear idea ofwhat is required: survival of a substantial fraction of ejected dust,and an extinction curve that has roughly the colour dependence ofISM dust. The temperature sensitivity of thermal sputtering couldlead to preferential destruction of ejected dust in the higher masshaloes that host a shock heated gas halo (see Birnboim & Dekel2003; Keres et al. 2005, 2009a; Dekel & Birnboim 2006). In theWind model, most wind particles in haloes with M < 1013 M#have T < 105 K, but about 2/3 of the wind particles in haloes withM > 1013 M# have T > 3 " 106 K. If sputtering does destroyintergalactic dust at these temperatures, it could produce distinctivedrops in the galaxy–reddening correlation when it is evaluated formassive galaxies or for galaxies in dense environments. The recentstudy of McGee & Balogh (2010), which examines the correlationof background quasar colours with projected separation from galaxygroups of varying richness, provides some hint of such an effect,but their innermost point is at r = 1 h!1 Mpc, close to the virialradius of typical group mass haloes. Moreover, the Chelouche et al.(2007) measurements provide direct evidence for dust survival in

6 The Wind simulation predictions are reasonably consistent with the ob-served mass function for galaxies with L < L% , though it still predictsexcessive galaxy masses above L% .

C& 2010 The Authors, MNRAS 412, 1059–1069Monthly Notices of the Royal Astronomical Society C& 2010 RAS

Dust in the wind 1067

Figure 7. Comparison of reddening maps in the three dust models, eachnormalized to the MSFR result at 1 h!1 Mpc. The regions shown are aquadrant of the simulation cube, 25 " 25 " 50 (h!1 Mpc)3. Red/blue regionsindicate heavily/lightly reddened fields through the simulation, with thecolour scale running from E(g ! i) = 10!5 up to 0.1, logarithmically.

MSFR argue that the dust in Large Magellanic Cloud (LMC)-likedwarfs is insufficient to explain the magnitude of their reddeningsignal. We concur with this conclusion. Reproducing the MSFRdata in the hybrid model with a physical dust-to-metal mass ratiorequires including galaxies up to several times 1010 M#, far largerthan the $3 " 109 M# baryonic mass of the LMC (van der Marelet al. 2002). Furthermore, the No-Wind simulation predicts a galaxybaryonic mass function that is inconsistent with observations, withan excessive global fraction of baryons converted to stars (Oppen-heimer et al. 2010).6 We do not consider the hybrid dust model to benearly as plausible an explanation of the MSFR results as the Windmodel; we present it as a foil to illustrate what would be requiredto explain MSFR’s findings with dust in low-mass galaxies. For theWind model, the metals in low-mass galaxies contribute much lessreddening than the intergalactic metals (Fig. 5).

4 D ISCUSSION

For the Wind model to succeed, we require that the dust-to-metalmass ratio in the IGM be comparable to that in the ISM, allow-ing only $50 per cent of the ISM dust to be destroyed duringits expulsion from galaxies and subsequent residence in the IGM.The validity of this assumption is by no means obvious, as the de-struction time-scales for 0.01 µm dust grains by thermal sputteringare $107.5(nH/10!3 cm!3)!1 yr at T = 106 K (Draine & Salpeter1979, fig. 7), while wind particles in the simulation typically re-main in the IGM for $109 yr before re-accreting on to galaxies(Oppenheimer et al. 2010, fig. 2). However, the sputtering rates de-cline rapidly towards lower temperatures (e.g. a factor of 300 lowerat T = 105 K), and with the wind implementation used in this simu-lation most ejected gas never rises above a few "104 K. Ultraviolet(UV) or X-ray background photons are another possible destruc-tion mechanism for IGM dust, but the intergalactic radiation fieldis much lower intensity than the radiation field dust grains alreadyencounter in galactic star-forming regions.

A detailed consideration of dust survival in the IGM is beyondthe scope of this initial investigation, but the MSFR results clearlyraise it as an important subject for further study. The combinationof their measurements with our models gives a fairly clear idea ofwhat is required: survival of a substantial fraction of ejected dust,and an extinction curve that has roughly the colour dependence ofISM dust. The temperature sensitivity of thermal sputtering couldlead to preferential destruction of ejected dust in the higher masshaloes that host a shock heated gas halo (see Birnboim & Dekel2003; Keres et al. 2005, 2009a; Dekel & Birnboim 2006). In theWind model, most wind particles in haloes with M < 1013 M#have T < 105 K, but about 2/3 of the wind particles in haloes withM > 1013 M# have T > 3 " 106 K. If sputtering does destroyintergalactic dust at these temperatures, it could produce distinctivedrops in the galaxy–reddening correlation when it is evaluated formassive galaxies or for galaxies in dense environments. The recentstudy of McGee & Balogh (2010), which examines the correlationof background quasar colours with projected separation from galaxygroups of varying richness, provides some hint of such an effect,but their innermost point is at r = 1 h!1 Mpc, close to the virialradius of typical group mass haloes. Moreover, the Chelouche et al.(2007) measurements provide direct evidence for dust survival in

6 The Wind simulation predictions are reasonably consistent with the ob-served mass function for galaxies with L < L% , though it still predictsexcessive galaxy masses above L% .

C& 2010 The Authors, MNRAS 412, 1059–1069Monthly Notices of the Royal Astronomical Society C& 2010 RAS

X-ray Scattering through the Intergalactic Medium: Time Variability and Ghost Halos

Dust grains polluting the intergalactic medium (IGM) have a chance of being detected through the phenomenon of X-ray scattering, which produces a diffuse arcminute-scale halo around bright X-ray point sources. I present follow up work to Corrales & Paerels (2012) by calculating the expected intensity of intergalactic dust scattering halos using the more exact Mie scattering treatment. This adjustment is necessary to check for large 0.1-1 micron sized dust grains that would interfere with the photometry needed for high precision measurements of cosmological constants. Even with the supreme focusing power of Chandra, I find that the dust scattering halo intensity is much dimmer than the Chandra PSF wings. However, scattered light takes a longer path to reach the observer, causing intergalactic scattering halos to be delayed ~10,000 years. I investigate the possibility of detecting a scattering halo around a quasar that has recently become dim, or ghost halos from a past quasar that is no longer visible.

Motivation

Scattering Halo Intensity

Lia Corrales (1) Columbia University, NASA Earth and Space Science Fellow

(2) MIT Kavli Institute for Astrophysics and Space Research lia@space.mit.edu

1,2

SGR J1550-5418: Imaged by Swift, the X-ray outburst from this soft gamma-ray repeater passed through Galactic clouds, producing expanding rings of dust-scattered light (NASA/Swift/Halpern)

M82: Imaged by Hubble, the dusty outflows of this starburst

galaxy glow in the infrared, extending several kpc

beyond the stellar disk.(NASA/ESA/Hubble Heritage)

Zu+ 2011 [6]: These simulations of large scale structure predict the magnitude of dust extinction from enriched galaxy halos, attempting to reproduce the results of Ménard+ 2010 [3], who measured quasar color as a function of distance from foreground galaxies. Their results indicate that the mass of circumgalactic dust is comparable to that within the galaxy disks. The simulations shown here find that a model including momentum-driven winds [4] can easily reproduce the observed quasar colors (top), while simulations that only implement thermal feedback do not (bottom). The filling factor of dusty IGM is one crucial parameter for determining the expected number density of scattering halos.

The Astrophysical Journal, 737:26 (14pp), 2011 August 10 Novak, Ostriker, & Ciotti

Figure 6. Eddington ratio as a function of time, for three different time intervals in the A2 simulation.(A color version of this figure is available in the online journal.)

Figure 7. Power spectrum of the dimensionless mass accretion rate MBH/MEdd for A2. The units of the y-axis are arbitrary. For frequencies higher than the inverseof several times the central accretion disk timescale, the power spectrum is proportional to 1/f, the frequency response of the low-pass filter applied by our centralaccretion disk. For lower frequencies, the power spectra are determined by the physics of gas input, cooling, and feedback. At these low frequencies, the powerspectrum is nearly flat: ! f "1/4. That is, the accretion onto the SMBH has a power spectrum nearly the same as white noise.(A color version of this figure is available in the online journal.)

gas surrounding the SMBH. This would imply that isotropicfeedback would result in the least SMBH growth.

Figure 9 shows final SMBH masses versus wind openingangle. The largest SMBH growth occurs when the wind is

10

Novak+ 2011 [5]: These 2D simulations show that the accretion rate of AGN can vary by many orders of magnitude due to feedback events.

The accretion prescription used in this work has a characteristic smoothing time of 0.1 Myr.

The predicted 1 keV scattering halo surface brightness profile from grey (0.1-1 um) IGM dust illuminated by a very bright z=2 quasar is shown in comparison to the typical 0.5-2 keV Chandra background. The upper limit to foreground scattering from Galactic CGM is also calculated using the grey dust model. If the quasar luminosity never changes, the Chandra PSF would outshine the scattering halo, which is ~1% as bright as the point source (inset). However, accretion rates can be highly variable due to AGN feedback. A quasar that has recently dimmed or turned “off” may leave behind a scattering echo or “ghost halo.”

�t ⇡ ↵2DR

c

✓1� ↵

2⇠�

◆

Dust scattered light takes a longer path, leading to a characteristic time delay (100 to 100,000 years),

depending on the observation angle.

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Redshift (z)10�2

10�1

100

101

RO

SAT

coun

trat

e

RASS BSC

rassdssagn

ROSAT count rate for over 250 quasars capable of illuminating IGM dust to a level above the typical Chandra background: all of the quasars in the ROSAT bright sources catalog (blue) and a subset of SDSS quasars (red). Approximately 150 (15%) of the z>1 quasars are above the brightness threshold to produce 3-10’’ echoes.

FBSC � 5⇥ 10�13 cgs

10�1 100 101 102 103

Observation Angle [arcsec]10�12

10�11

10�10

10�9

10�8

10�7

10�6

10�5

10�4

10�3

10�2

10�1

100

Nor

mal

ized

inte

nsit

y[a

rcse

c�2]

PSFtemplate

10�1 100 101 102 103

Observation Angle [arcsec]10�11

10�10

10�9

10�8

10�7

10�6

10�5

10�4

10�3

Surf

ace

Bri

ghtn

ess

[cts

�1

arcs

ec�

2]

0.5-2 keV background

Grey foreground dust

Grey IGM1 um IGM

halo time delay

IGM filling factor

characteristic frequency of major

feedback event

quasar number density

minimum apparent flux⇠ 3⇥ 10�13 cgs

N ⇠ fIGM �t ⌫fb NQSO(F > Fa)

⌦IGMd = 3⇥ 10�6 [2]

Fps ⇠ 5⇥ 10�12 cgs

The very brightest quasars would leave

a 20 arcsec ghost halo a few hundred years

after fading.

⇠� =

1.040

aµm EkeV

characteristic scattering angle

Unfortunately, these events are likely to be

NQSO ⇠ 103

[5]⌫fb ⇠ 10�7 yr�1

(entire sky)

implying that one event

every 10,000 years is observable

by Chandra, and

N << 1

This work was supported in part by NASA Headquarters under the NASA Earth and Space Science Fellowship Program - Grant NNX11AO09H

References

High Energy Studies of Interstellar Dust Grains

Lia Corrales

Columbia University

lia@astro.columbia.edu

1. Abstract (submitted)

Dust grains polluting the intergalactic medium (IGM) have a chance of being detected through

the phenomenon of X-ray scattering, which produces a di↵use arcminute-scale halo around bright X-

ray point sources. I present follow up work to Corrales & Paerels (2012) by calculating the expected

intensity of intergalactic dust scattering halos using the more exact Mie scattering treatment. This

adjustment is necessary to check for large 0.1-1 micron sized dust grains that would interfere with

the photometry needed for high precision measurements of cosmological constants. Even with the

supreme focusing power of Chandra, I find that the dust scattering halo intensity is much dimmer

than the Chandra PSF wings. However, scattered light takes a longer path to reach the observer,

causing intergalactic scattering halos to be delayed 10,000 years. I investigate the possibility of

detecting a scattering halo around a quasar that has recently become dim, or ghost halos from a

past quasar that is no longer visible.

REFERENCES

[1] Corrales, L., & Paerels, F. 2012, ApJ, 751, 93

[2] Menard, B., & Fukugita, M. 2012, ApJ, 754, 116

[3] Menard, B., Scranton, R., Fukugita, M., & Richards, G. 2010, MNRAS, 405, 1025

[4] Murray, N., Quataert, E., & Thompson, T. A. 2005, ApJ, 618, 569

[5] Novak, G. S., Ostriker, J. P., & Ciotti, L. 2011, ApJ, 737, 26

[6] Zu, Y., Weinberg, D. H., Dave, R., et al. 2011, MNRAS, 412, 1059

This work was supported in part by NASA Headquarters under the NASA Earth and Space

Science Fellowship Program - Grant NNX11AO09H

This preprint was prepared with the AAS L

AT

E

X macros v5.2.

High Energy Studies of Interstellar Dust Grains

Lia Corrales

Columbia University

lia@astro.columbia.edu

1. Abstract (submitted)

Dust grains polluting the intergalactic medium (IGM) have a chance of being detected through

the phenomenon of X-ray scattering, which produces a di↵use arcminute-scale halo around bright X-

ray point sources. I present follow up work to Corrales & Paerels (2012) by calculating the expected

intensity of intergalactic dust scattering halos using the more exact Mie scattering treatment. This

adjustment is necessary to check for large 0.1-1 micron sized dust grains that would interfere with

the photometry needed for high precision measurements of cosmological constants. Even with the

supreme focusing power of Chandra, I find that the dust scattering halo intensity is much dimmer

than the Chandra PSF wings. However, scattered light takes a longer path to reach the observer,

causing intergalactic scattering halos to be delayed 10,000 years. I investigate the possibility of

detecting a scattering halo around a quasar that has recently become dim, or ghost halos from a

past quasar that is no longer visible.

REFERENCES

[1] Corrales, L., & Paerels, F. 2012, ApJ, 751, 93

[2] Menard, B., & Fukugita, M. 2012, ApJ, 754, 116

[3] Menard, B., Scranton, R., Fukugita, M., & Richards, G. 2010, MNRAS, 405, 1025

[4] Murray, N., Quataert, E., & Thompson, T. A. 2005, ApJ, 618, 569

[5] Novak, G. S., Ostriker, J. P., & Ciotti, L. 2011, ApJ, 737, 26

[6] Zu, Y., Weinberg, D. H., Dave, R., et al. 2011, MNRAS, 412, 1059

This work was supported in part by NASA Headquarters under the NASA Earth and Space

Science Fellowship Program - Grant NNX11AO09H

This preprint was prepared with the AAS L

AT

E

X macros v5.2.