New Results From HVC Ppt

7/26/2019 New Results From HVC Ppt

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New Results fromHigh Velocity Clouds

Nicolas Lehner

University of Notre Dame

In collaboration with:

Chris Howk (ND)&

Tripp (UMass), Tumlinson, Thom, Fox (STScI)


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Outline

! What are high-velocity clouds (HVCs)?! Why do we care?! What are some of the key properties: distance,

metallicity, velocity, mass! New discoveries

! What are HVCs?! Some new problems! Future


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Wakker et al. (2003)

High-velocity clouds are clouds moving at fast speed

HVCs exhibit H I 21cm emission that covers ~18% HI covering factor at at NHI> 2 x 1018cm-2 (Wakker 1991).


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High velocity clouds observed in HI 21 cm emission


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High velocity clouds as evidence for a Galactic corona


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What are high velocity clouds?

M I L KY W A Y H A L O

RecycledGalactic gas

from supernovae


from supernovae

HVCs fromintergalactic space

SunMilky Way Disk

Recycled HVCs from dwarf galaxies

Lehner & Howk, 2011, illustration credit: Feild

Evidence for gas flows in Galactic halo or intergalactic clouds


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Key Parameter: Distances of HVCs

Illustration source: Wakker & Richter,SciAM, 2004


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High velocity clouds located in the Milky Ways halo

z

Wakker+ (1996)

d =!

d = 4 kpc d = 0.7 kpc

Complex A not seen towardstars at -160 km/s, placing itbeyond 4 kpc (z ~ 3 kpc).

More recent work with Keck/VLT:Thom+ (2008), Wakker+ (2008), Wakker+(2007)

H I HVCs within ~515 kpc.


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Key Parameter: Metallicity of HVCs

Complex C

Mrk290

1.0

0.5

0.0

1.0

0.5

0.030

0

30

60

90

3

2

1

0

3

2

1

0

3

2

1

0

12

9

6

3

0

4

3

2

1

0

300 200 100 0

300 200 100 0

SII1253 (GHRS)N(SII)=1.71014cm2

CaK (WHT)N(CaII)=2.41012cm2

HI (WSRT+Effelsberg;2'N(HI)=9.21019cm2

HI (Effelsberg;9')N(HI)=12.31019cm2

HI (LDS;1)N(HI)=7.11019cm2

H!(WHAM;1)I=0.187 R

[SII]6716 (WHAM;1)I


10/28

Milky Way HVCs: recycled fountain matter

Z

ech+

(2008)

Not all the gas is coming in...and not all of

it has low metallicities.

*Also observed in C II, C IV, Si II, Si III, Fe II, Al II, S III

Messier 5: (l,b)=(3, 48); d~7.5 kpc,z~5.3 kpc

x

Zech+ (2008) identified an HVC along a sight linetoward the inner Galaxy globular cluster Messier 5with super-solar metallicity:

[O/H] = +0.22 0.10

log N(H I) = 16.500.06

See Keeney+ (2006) for HVCs near Galactic bulge...


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HI emission observations: A bias view of the Galactic sky

Sembach+95,99 Lehner+01

H I emission observations have a sensitivity cut-off determined by the depth of theobservations and limitation of radio observations.


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UV observations of the Galactic sky

H I 21cm EmissionFUSE O VI Absorption

Sembach et al. 2003Fox et al. 2006

Covering fraction: 60% 85% of sky covered at N(H+) "1018 cm-2(for SMC metallicity)


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UV observations of the Galactic sky

STIS Si III AbsorptionShull et al. 2009, Collins et al. 2009(see also Richter et al. 2009 for CaII observations)


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Lehner+ (2012), Lehner & Howk (2011)

High velocity clouds: New COS results


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Examples of HVC absorption in stellar spectra

Lehner & Howk 10,11 - Zech, Lehner, Howk+08


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About 70% of the high latitude

sky is covered with highvelocity metal ion absorption.

Because the covering factor isso high, any random sight lineto objects more distant thanthe majority of the HVCs will

have a high chance of showingabsorption.

Comparing the covering factorof AGN sight lines with that forstellar sight lines can showwhat fraction of the low H I

column density HVCs arewithin ~5-15 kpc of the sun(z~10 kpc).

A statistical measure of HVC distances

ll

l

l

ll


Onlyposs

iblethank

stothehighCO

Ssensitivit

y:

1HSTorb

itperstar.


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A statistical measure of HVC distances

The detection rates toward AGNs (~infinite distance) and stars are indistinguishable.Thus, the absorbing HVCs are at d < 515 kpc andz< 6-10 kpc.

The mass of the population isMHVC~ (0.2 2.0)x108M!giving an infall rate of ~ 0.4

1.0 M!yr-1(see also Shull+ 2009).

90 < |vLSR| < 170 km/s |vLSR| > 170 km/s

Warning:This doesntreally constraintcompact HVCs.


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NEUTRAL AND IONIZED HVCs IN 3D SPACE

Figure from Putman+12

Several HVCs seen in UV absorption are the extended ionized halos of their neutralcounterparts.


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Very high-velocity Galactic sky

The VHVCs are notrandomly distributed onthe Galactic sky andappear mostly to beassociated to known large

structures.

**We might miss a population ofcompact HVCs with very smallangular scales at very largedistances (or that they may be

confused with the more nearbyVHVCs).

Lehner+12


20/28

New problem: Extended hot Galactic halo?

M I L K Y W A Y H A L O


from supernovae


from supernovae


SunMilky Way Disk


Most HVCs are within 5-15 kpc, including the OVI HVCs.


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New problem: Extended hot Galactic halo?

Putman+ (2003)

d ~ 50-70 kpc

Magellanic stream is probably the best evidence for an extended hot Galaxy halo.


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HVCs are found in other galaxies

Accretion onto Spiral Galaxies

M 31

Thilker et al. (2004)

Disk gas

HVCs

High velocity clouds are found several galaxies


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Sancisi+ (2008)

Table 2 Extra-planar gas in spiral galaxies

Galaxy Type incl vflat MHIhaloMHI

halo

MHItot

Ref.

(deg) (k ms1) (108M) (%)

Milky Way Sb - 220 > 0.2 > 1a [141]

M 31 Sb 77 226 > 0.3 > 1 [127]NGC 891 Sb 90 230 12 30 [85]NGC 6946 Scd 38 175 >2.9 >4 [15]NGC 4559 Scd 67 120 5.9 11 [4]NGC 2403 Scd 63 130 3 10 [37]UGC 7321 Sd 88 110 >

0.1 >

1 [77]

NGC 2613 Sb 80 300 4.4b 5 [27]NGC 253 Sc 75 185 0.8 3 [14]

a Only HVCs (IVCs not included); b from sum of the various extra-planar clouds.

. . , . . .

.

.

.,

.,

. ,,

.

, . .,

.

, .

,.

,,

.

,

.

.. .

. .

,.

,. . , ,

. . ,,

.,

.,

,

Miller+ (2009)

M 33M 83

.

. . .

.,

.,

M 83

Anomalous velocity gas is common around other galaxies


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HVCs toward LMC: Evidence for outflow in a dwarf galaxy

Large (> 106M!)

HVC complexthat is linked tostellar feedbackoccurring in adwarf spiral galaxy.

But all the HVCs in the Local group are within about 15-50 kpc (except possibly theMagellanic Stream, but that could a pretty unique feature, see Putman+12).

What are the higher redshift analogs?

Lehner & Howk 2007, Lehner+09


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Near future: Studying the fall of HVCs onto the Galactic disk

300 2400 60120180

30

60

-30

-60

Approved Cycle 20 program: COS/STIS observations of lower z-height stars.

Are the Milky Way's High Velocity Clouds Fuel for Star Formation or for the GalacticCorona?


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Near future: Metallicity map of the HI HVCs


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Future beyond HST (?)

HVC absorption study in other galaxies beyond the Milky Way and LMC/SMCNeed even more sensitive UV spectrograph

Tomography in the UV of the HVCs (CII, CIV, OI, OVI), their metallicity.


M 31


Disk gas

HVCs

High velocity clouds are found several galaxies Transforming mission/instrument: FUSEand COS

- hundreds of background targets, wavelength,resolution, S/N

Important instruments: STIS(GHRS) (metallicity,ionization structure).

HI H# Bagger+12

Complex A


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UV spectroscopy has transformed ourunderstanding of the large-scale flowsthrough the Galaxy halo.

Summary

In the near future, we should have abetter idea of the metallicitydistribution and if/how HVCs canreach the galactic disk.

In the future, we should aim to study theHVCs (gas flows) in the local group ofgalaxies of different masses or stellaractivities.

M I L KY W A Y H A L O


from supernovae


from supernovae


SunMilky Way Disk



M 31


Disk gas

HVCs

High velocity clouds are found several galaxies

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New Results From HVC Ppt