Twenty-five Years of QSO Absorption Studies with HST: A Windfall of Missing Baryons, Gastrophysical Diagnostics, and Puzzles

Todd M. Tripp, University of Massachusetts

From Day 1, HST has produced spectacular and entirely unique results via point-source spectroscopy.

This talk: a highly biased and incomplete discussion of HST QSO absorber studies − historical results, puzzles, and potential .

HST does QSO Absorption Lines: A Windfall of Missing Baryons• Jan. 14-16, 1991, Feb. 23, 1991: UV spectroscopy of

3C273 with HST (Morris et al. 1991; Bahcall et al. 1991)

GHRS data (Morris et al. 1991)

• Extrapolation from high redshift predicted: 0.9 – 2.3 Lyα lines (EQW > 25 mÅ); Morris et al. detected 14!

The COS Absorption Survey of Baryon Harbors (CASBaH)

1. Probing warm-hot intergalactic gas at 0.5 < z < 1.3 with a blind Survey for O VI, NeVIII, Mg X, and Si XII Absorption Systems (and lots of other goodies)

2. CASBaH-x: Near-UV extension to completely cover Lyα (and other key species, e.g., O VI) from z = 0 to z(QSO)

COS vitals High spectral resolution: 15 km/s FWHM FUV+NUV coverage: observed λ = 1150 – 3000 Å Sensitivity: 20x previous HST spectrographs

An Untapped Discovery Space: The Extreme UV

The high density of lines in the EUV provides anextraordinary array of gas diagnostics.

See seminal papers of Verner, Tytler, & Barthel (1994a,b)

Fan et al.

Diagnostic Power of the Extreme UVThe high densityof lines in the FUVand EUV provides an extraordinaryarray of gasdiagnostics.

Data Quality (CASBaH Program)

Data Quality (CASBaH Program)

This sight line reveals:• COS FUV spectrum only: 803 absorption lines• FUV+NUV data: 1078 absorption lines, and we don’t have all of the NUV data yet!• Species detected in this single sight line:

– H I Lyα up to Lyτ (i.e., H19)– He I– C II, C III, C IV– N II, N III, N IV, N V– O II, O III, O IV, O V, O VI– Ne V, Ne VIII– Mg II– Al II, Al III– Si II, Si III, Si IV– Fe II, Fe III

Data Quality (CASBaH Program)

Publications so far:

• Our group: Ribaudo et al. 2011; Tripp et al. 2011; Lehner et al. 2012,2013; Meiring et al. 2013; Fox et al. 2013; Burchett et al. 2013; Johnson et al. 2014

• Archival researchers: Shull et al. 2012; Muzahid et al. 2013; Stevans et al. 2014; Hussain et al. 2015; Johnson et al. 2015

HST does QSO Absorption Lines: A Windfall of Missing Baryons

• Weymann et al. (1998): number of Lyα lines per unit redshift as a function of redshift

Log (1+z)

Log

(dN/dz)

(i.e.

, num

ber p

er u

nit r

edsh

ift)

987 Lyα lines from HST

HST does QSO Absorption Lines: A Windfall of Missing Baryons

• Weymann et al. (1998): number of Lyα lines per unit redshift as a function of redshift

Log (1+z)

Log

(dN/dz)

(i.e.

, num

ber p

er u

nit r

edsh

ift)

High redshiftdecline drivenby expansion ofthe universe

At low z, decline is mitigated by disappearance of QSOs and decline of UV bkg.

A Sea Change in Theoretical Astrophysics: The Rise of the Cosmological Simulations

Mpc

Mpc

BARYONS DARK MATTER GAS TEMP.

• At the present epoch, stars account for a tiny fraction of the baryons, ≤ 10% (Persic & Salucci 1992; Gnedin & Ostriker 1992, Fukugita et al. 1998, Bell et al. 2003)

Cosmological simulation(Oppenheimer et al.)

HST does QSO Absorption Lines: A Windfall of Missing Baryons

HST does QSO Absorption Lines: A Windfall of Missing Baryons

• Hydrodynamic cosmological simulations predict that 30 - 50% of the baryons are in low-density, shock-heated gas at 105 - 107 K at z = 0

• WHIM = robust prediction from many studies (e.g., Cen & Ostriker 1999; Davé et al. 2001; Cen & Ostriker 2006; Cen & Chisara et al. 2011; Smith et al. 2011)

Cen & Chisara (2011)

Lyα forest

STARS

“Warm-hot” intergalacticMedium (WHIM)

• OVI: a most excellent WHIM probe

HST does QSO Absorption Lines: A Windfall of Missing Baryons

Non-eq., cooling modelsCollisional eq.

• OVI: a most excellent WHIM probe

HST does QSO Absorption Lines: A Windfall of Missing Baryons

Non-eq., cooling modelsCollisional eq.

Tripp et al. (1998, 2000a, 2000b, 2001, 2003, 2008, 2012)

• OVI: a most excellent WHIM probe

HST does QSO Absorption Lines: A Windfall of Missing Baryons

Non-eq., cooling modelsCollisional eq.

Tripp et al. (1998, 2000a, 2000b, 2001, 2003, 2008, 2012)

HST does QSO Absorption Lines: A Windfall of Missing Baryons

Tripp et al. 2008

Danforth & Shull 2005,2008; Shull et al. 2006; Stocke et al. 2006; Wakker & Savage2009; Prochaska et al. 2004,2006,2011a,b; Thom & Chen 2008a,b; Howk etal. 2009; Lehner et al. 2009; Mulchaey & Chen 2009; Chen & Mulchaey 2009

HST does QSO Absorption Lines: Wait, wut?

Tripp et al. 2008

Aligned OVI absorbersare photoionized?

Ion Xi-1 (eV) Xi (eV)

C III 24.4 47.9

O III 35.1 54.9

O IV 54.9 77.4

S IV 34.9 47.2

S V 47.2 72.6

Ne VIII 207.3 239.1

Ionization Potentials

Tripp et al. (2011)

Cold gas:photoionized

When CLOUDY fits the observed S III/S IV, it slightly underpredictsthe S V and vastly underpredictsthe Ne VIII (off by many orders ofmagnitude). The Ne VIII arises in hot gas.

Hot gas: hot

HST does QSO Absorption Lines: Testing Cosmological Simulations

H I Column Density (cm-2)

b va

lue

(km

s-1

)

High resolution (7 km s-1)STIS observations

Simulation measurements(from mock STIS data)

HST does QSO Absorption Lines: Testing Cosmological Simulations

H I Column Density (cm-2)

b va

lue

(km

s-1

)

High resolution (7 km s-1)STIS observations

Simulation measurements(from mock STIS data)

HST does QSO Absorption Lines: Testing Cosmological Simulations

Colu

mn

Den

sity

D

istrib

ution

log [H I Column Density (cm-2)]

HST does QSO Absorption Lines: Testing Cosmological Simulations

Colu

mn

Den

sity

D

istrib

ution

log [H I Column Density (cm-2)]

Kollmeier et al. (2014)

HST does QSO Absorption Lines: Testing Cosmological Simulations

Colu

mn

Den

sity

D

istrib

ution

log [H I Column Density (cm-2)]

Kollmeier et al. (2014)

Many (most?) of these H I absorbers are NOT

intergalactic; this is gas in the gaseous halos

and circumgalatic media of galaxies.

Result 1: Star-Forming Galaxies Have Huge, Metal-Enriched, Highly Ionized Halos

Tumlinson et al. 2011

Red sequence

BlueCloud

Grayscale: galaxy color-stellar mass data from SDSS+GALEX(Schiminovich et al. 2007)

Result 1: Star-Forming Galaxies Have Huge, Metal-Enriched, Highly Ionized Halos• Are these huge halos substantial mass reservoirs?• A back-of-the envelope calculation:

• To estimate the total mass, we must account for the gas metallicity:

With fhit = 0.8, R = 150 kpc, and <NOVI> = 1014.5 cm-2,

MO ≈ 107 M

With fOVI = 0.2 and solarmetallicity,

Mgas ≈ 109 M

Result 1: However, there are some caveats• Some of the

absorbers show indications of very high metallicities

• OVI system, z=0.70152,

• log N(OVI)=14.42

Meiring, Tripp et al.(2013, in press,arXiv 1209.0939)

-200 +200Absorber Velocity (km/s)

• z=0.70152• Log N(HI) < 13.6

• Z > 1.6 Z

• log N(OVI)=14.42

• Z=0.72152• Log N(HI) < 13.7

• Z > 1.0 Z

• Log N(OVI) = 13.86

Result 1: However, there are some caveats

Meiring, Tripp et al.(2013, in press,arXiv 1209.0939) -200 +200Absorber Velocity (km/s)

• z=0.70152• Log N(HI) < 13.6

• Z > 1.6 Z

• log N(OVI)=14.42

• Z=0.72152• Log N(HI) < 13.7

• Z > 1.0 Z

• Log N(OVI) = 13.86

Result 1: However, there are some caveats

Meiring, Tripp et al.(2013, in press,arXiv 1209.0939) -200 +200Absorber Velocity (km/s)

• Impact parameter = 217 kpc• SFR = 6.4 M yr-1

• [O/H] = +0.22

QSO-Galaxy Connections:Large-Scale Environment is important!

• Survey of very low-z absorbers with 100% completeness for L > 0.01 L*

No. Galaxies within 1500 kpc

log

[C IV

col

umn

dens

ity (c

m-2

)]

C IV DETECTIONS

C IV NON-DETECTIONS

Some take-aways• High-resolution UV

spectroscopy can yield huge samples of absorbers rich in information; these data will remain uniquely valuable for years/decades

• OVI/NeVIII absorbers are not photoionized and arise in complex, multi-multi phase entities; physics here is poorly understood

• These absorbers sometimes exhibit extremely high metallicities; again, wut?

• Cosmological simulations have difficulty with even the most simple case of intergalactic (?) Lyα clouds