Star formation and molecular gas in (U)LIRGs

Paul van der Werf

Leiden Observatory

Star formation and molecular gas in (U)LIRGs

Sant CugatApril 17, 2012

CreditsKate Isaak (ESTEC)Padelis Papadopoulos (MPI für Radioastronomie)Marco Spaans (Kapteyn Astronomical Institute)Eduardo González-Alfonso (Henares)Rowin Meijerink (Leiden Observatory)Edo Loenen (Leiden Observatory)Alicia Berciano Alba (Leiden Observatory/ASTRON)Axel Weiß (MPI für Radioastronomie)+ the HerCULES team

2Molecular gas in (U)LIRGs

Conditions in ULIRGs Starbursts cannot be simply scaled up. More intense starbursts are also more efficient with their fuel. (Gao & Solomon 2001)

LIR SFR

LIR/LCO

SFR/MH2

SFE

1

1

1

1

1

H

400 :KL- BNOrion

54 :1-OMC

8.1 :GMCs Galactic

5.1 :WayMilky

100 :ULIRGs2

FIR

ML

ML

ML

ML

MLML


(U)LIRGs from low to high z

LIRGs dominate cosmic star formation at high redshift


(Magnelli et al. 2011)

ISM in luminous high-z galaxies

5

Even in ALMA era, limited spatial resolution on high-z galaxies.

For unresolved galaxies, multi-line spectroscopy will be a key diagnostic

(Weiß et al. 2007)

Molecular gas in (U)LIRGs

(Danielson et al. 2010)

Outline

CO as a probe of the energy source un (U)LIRGs

H2O emission in (U)LIRGs

The X-factor in (U)LIRGs


HerCULES

7

Herschel Comprehensive (U)LIRGEmissionSurvey

Open Time Key Program on the Herschel satellite


Who is HerCULES?Paul van der Werf (Leiden; PI)Susanne Aalto (Onsala)Lee Armus (Spitzer SC)Vassilis Charmandaris (Crete)Kalliopi Dasyra (CEA)Aaron Evans (Charlottesville)Jackie Fischer (NRL)Yu Gao (Purple Mountain)Eduardo González-Alfonso (Henares)Thomas Greve (Copenhagen)Rolf Güsten (MPIfR)Andy Harris (U Maryland)Chris Henkel (MPIfR)Kate Isaak (ESA)Frank Israel (Leiden)Carsten Kramer (IRAM)Edo Loenen (Leiden)Steve Lord (NASA Herschel SC)

Jesus Martín-Pintado (Madrid)Joe Mazzarella (IPAC)Rowin Meijerink (Leiden)David Naylor (Lethbridge)Padelis Papadopoulos (Bonn)Dave Sanders (U Hawaii)Giorgio Savini (Cardiff/UCL)Howard Smith (CfA)Marco Spaans (Groningen)Luigi Spinoglio (Rome)Gordon Stacey (Cornell)Sylvain Veilleux (U Maryland)Cat Vlahakis (Leiden/Santiago)Fabian Walter (MPIA)Axel Weiß (MPIfR)Martina Wiedner (Paris)Manolis Xilouris (Athens)


HerCULES in a nutshell HerCULES has uniformly and statistically

measured the neutral gas cooling lines in a flux-limited sample of 29 (U)LIRGs.

Sample: all IRAS RBGS ULIRGs with S60 > 12.19 Jy (6 sources) all IRAS RBGS LIRGs with S60 > 16.8 Jy (23 sources)

Observations: SPIRE/FTS full high-resolution scans: 200 to 670 m at R ≈ 600,

covering CO 4—3 to 13—12 and [CI] + any other bright lines PACS line scans of [CII] and both [OI] lines All targets observed to same (expected) S/N Extended sources observed at several positions


HerCULES sampleTarget log(LIR/L)Mrk 231 12.51IRAS F17207—0014

12.39

IRAS 13120—5453

12.26

Arp 220 12.21Mrk 273 12.14IRAS F05189—2524

12.11

Arp 299 11.88NGC 6240 11.85IRAS F18293—3413

11.81

Arp 193 11.67IC 1623 11.65NGC 1614 11.60NGC 7469 11.59NGC 3256 11.56

Target log(LIR/L)IC 4687/4686 11.55NGC 2623 11.54NGC 34 11.44MCG+12—02—001

11.44

Mrk 331 11.41IRAS 13242—5713

11.34

NGC 7771 11.34Zw 049.057 11.27NGC 1068 11.27NGC 5135 11.17IRAS F11506—3851

11.10

NGC 4418 11.08NGC 2146 11.07NGC 7552 11.03NGC 1365 11.00


Warning: may contain...

11

quiescent molecular (and atomic) gas star-forming molecular gas (PDRs) AGN (X-ray) excited gas (XDRs) cosmic ray heated gas shocks mechanically (dissipation of turbulence) heated gas warm very obcured gas (hot cores)


PDRs vs. XDRs

Four differences:

X-rays penetrate much larger column densities than UV photons

Gas heating efficiency in XDRs is ≈10—50%, compared to <3% in PDRs

Dust heating much more efficient in PDRs than in XDRs

High ionization levels in XDRs drive ion-molecule chemistry over large column density


PDRs vs. XDRs: CO lines

XDRs produce larger column densities of warmer gas

Identical incident energy densities give very different CO spectra

Very high J CO lines are excellent XDR tracers

Need good coverage of CO ladder

(Spaans & Meijerink 2008)


14

Mrk231

HST/ACS(Evans et al., 2008)

At z=0.042, one of the closest QSOs (DL=192 Mpc)

With LIR = 41012 L , the most luminous ULIRG in the IRAS Revised bright Galaxy Sample

“Warm” infrared colours Star-forming disk (~500

pc radius) + absorbed X-ray nucleus

Face-on molecular disk, MH2 ~ 5109 M


Mrk231

SPIREFTS

15

(Van der Werf et al., 2010)


CO excitation

2 PDRs + XDR 6.4:1:4.0

n=104.2, FX=28*

n=103.5, G0=102.0

n=105.0, G0=103.5

* 28 erg cm-2 s-1 G0=104.2


CO excitation

3 PDRs 6.4:1:0.03

n=106.5, G0=105.0

n=103.5, G0=102.0

n=105.0, G0=103.5


High-J lines: PDR or XDR? High-J CO lines can also be produced by PDR with n=106.5 cm—3 and G0=105, containing half the molecular

gas mass. Does this work?

G0=105 only out to 0.3 pc from O5 star; then we must have half of the molecular gas and dust in 0.7% of volume.

With G0=105, 50% of the dust mass would be at 170K, which is ruled out by the Spectral Energy Distribution

[OH+] and [H2O+] > 10—9 in dense gas requires efficient and penetrative source of ionization; PDR abundances factor 100—1000 lower


Only XDR model works!

High-J CO lines and AGNs

Highly excited CO ladders are found in all high luminosity/compact sources with an energetically dominant AGN (and only in those sources).


Outline

CO as a probe of the energy source in (U)LIRGs




Water in molecular clouds

H2O ice abundant in molecular clouds

Can be released into the gas phase by UV photons, X-rays, cosmic rays, shocks,...

Can be formed directly in the gas phase in warm molecular gas

Abundant, many strong transitions expected to be major coolant of warm, dense molecular gas

21Molecular gas in (U)LIRGsHerschel image of (part of) the Rosetta Molecular Cloud

Molecular gas in (U)LIRGs 22

Low-z H2O: M82 vs. Mrk231

At D = 3.9 Mpc, one of the closest starburst galaxies

With LIR = 31010 L , a very moderate starburst

At z=0.042, one of the closest QSOs (DL=192 Mpc)

With LIR = 41012 L , the most luminous ULIRG in the IRAS Revised bright Galaxy Sample

M82 Mrk231

H2O lines in M82

Faint lines, complex profiles

Only lines of low excitation 23Molecular gas in (U)LIRGs

(Weiß et al., 2010)

(Panuzzo et al., 2010)

Mrk231:strong H2O lines, high excitation


(Van der Werf et al., González-Alfonso et

al., 2010)

H2O lines in Mrk231 Low lines: pumping

by cool component + some collisional excitation

High lines: pumping by warm component

Radiative pumping dominates and reveals an infrared-opaque (100m ~ 1) disk.

(González-Alfonso et al., 2010) 25Molecular gas in (U)LIRGs

High-z connection: H2O at z=3.9


Line ratios similar to Mrk231 FIR pumping dominates, implies 100 m-opaque disk Radiation pressure dominates, Eddington-limited

Van der Werf et al., 2011

H2O in HerCULESTarget log(LIR/L)Mrk 231 12.51IRAS F17207—0014

12.39

IRAS 13120—5453

12.26

Arp 220 12.21Mrk 273 12.14IRAS F05189—2524

12.11

Arp 299 11.88NGC 6240 11.85IRAS F18293—3413

11.81

Arp 193 11.67IC 1623 11.65NGC 1614 11.60NGC 7469 11.59NGC 3256 11.56

Target log(LIR/L)IC 4687/4686 11.55NGC 2623 11.54NGC 34 11.44MCG+12—02—001

11.44

Mrk 331 11.41IRAS 13242—5713

11.34

NGC 7771 11.34Zw 049.057 11.27NGC 5135 11.17IRAS F11506—3851

11.10

NGC 4418 11.08NGC 2146 11.07NGC 7552 11.03NGC 1365 11.00 27Molecular gas in (U)LIRGs red = wet

Lessons from H2O (1 + 2 + 3 + 4)


1) In spite of high luminosities, H2O lines are unimportant

for cooling the warm molecular gas. 2) Radiatively H2O lines reveal extended infrared-

opaque circumnuclear gas disks.

3) Extinction and radiative pumping of highest CO lines.

4) Detection of H2O lines implies high FIR radiation field, but not the presence of an AGN.

Lessons from H2O (5)

Radiation pressure from the strong IR radiation field:


cTP /4d100rad

Since both 100 and Td are high, radiation pressure dominates the gasdynamics in the circumnuclear disk.

5) Conditions in the circumnuclear molecular disk are Eddington-limited.

Mechanical feedback Radiation pressure can drive

the observed molecular outflows (e.g., Murray et al., 2005)

Aalto et al., 2012: flow prominent in HCN dense gas

Key process in linking ULIRGs and QSOs?

Shocks probably of minor importance in Mrk231

30Molecular gas in (U)LIRGs (Feruglio et al., 2010)

(Fischer et al., 2010)

Possible consequences

Eddington-limited conditions account for LFIR-LHCN relation within factor 2 for standard dust/gas ratio (Andrews & Thompson 2011)

If accreting towards nuclear SMBH, can account for M*/M relation (Thompson et al., 2005)

Radiation pressure can expel nuclear fuel and produce Faber-Jackson relation (Murray et al., 2005)


(Andrews & Thompson, 2011)

Outline

CO as a probe of the energy source in (U)LIRGs




The X-factor Converting CO flux

(luminosity) into H2 column density (mass):

(MW: =4; ULIRGs: =0.8)Warning: discussions of the X-

factor have been the death-blow for many conferences.


(Papadopoulos, Van der Werf, Isaak & Xilouris,

astro-ph/1202.1803)

(U)LIRG sample

1line

2/1

32

12

6cm 200)H(

)CO()H(

KTnc

INX

1line

2/1

32

22

6cm 200)H(

)CO()H(

KTnc

LM

The X-factor and optical depth

Highly turbulent motions

low optical depths( high 12CO/13CO line ratios)

low X-factor

(e.g., ULIRGs: X=0.8,Downes & Solomon 1997)


drdvT

nX

line

H2 and Both

NB: Tline is Tb of the line, not kinetic temperature

Calculating X-factors Sample of 70 (U)LIRGs, 12CO

10, 21, 32, (43, 65) and 13CO 10, (21) lines

2 component model: high excitation and low excitation component

X-factor explicitly calculated using non-LTE excitation model and finite optical depths


X-factors based on low CO lines onlyAssumptions: One gas component Based on low-J CO lines only

Results: X-factors cluster between 0.5 and

1 (cf., Downes/Solomon value of 0.8 for ULIRGs) with tail up to and exceeding Milky Way values

Subthermal excitation

But: Higher CO lines and density

tracing lines reveal a substantial dense gas component


(Papadopoulos, Van der Werf, Isaak & Xilouris,

astro-ph/1202.1803)

(U)LIRG sample

X-factors in a 2-component model

Assumptions: Orion-like high excitation component (probably not needed with

denser coverage of CO ladder Herschel) Radiation pressure supported disk LFIR/M(star forming gas) =

constant (observed: LFIR/LHCN = constant; e.g., Gao & Solomon, Wu et al.)

Results: X-factors in (U)LIRGs dominated by dense, star-forming gas X-factors have values of the order 24 (i.e., significantly higher than

the Downes/Solomon value of 0.8)


Summary: getting at X Derive X from 12CO 10 65 + 13CO 10 (or 21); ideally,

use HCN (or HCO+ or CS) lines as well

Can be used at high z too, but 13CO is challenging

Aside: why did Downes & Solomon get it right (for the low-J lines) without 13CO? High quality data showing turbulent velocity field Correctly produced low optical depth Getting the optical depth right is key


Summary


CO-H2 conversion factor can be derived from multi-line CO data (up to J=6) – see Papadopoulos et al., 2012ab (astro-ph/1109.4176 and 1202.1803)

Multi-line CO data (up to at least J=11) can separate star formation and AGN accretion as power sources of unresolved galaxies (vdW et al., 2010)

Luminous H2O lines trace infrared-opaque nuclear disks and reveal Eddington-limited circumnuclear conditions (vdW et al., 2011)

Strong shocks are only a minor contributor to CO excitation, barring exceptional cases (in preparation).

OH+ emission requires a high electron abundance and forms another way to reveal XDRs (in preparation).

Documents

Star formation and molecular gas in (U)LIRGs