Carbon in the ISM of z=4 dusty starburst galaxies

Transcription

1 ESO Band 5 Workshop Carbon in the ISM of z=4 dusty starburst galaxies Matt Bothwell (Cambridge) + the SPT SMG team

2 Observing gas at high redshift 1. Traditional approach use a visible tracer molecule ( 12 CO) 2. Alternative use dust mass and gas/dust ratio 3. Potential alternate tracer atomic carbon, [CI]

3 Problems with 12 CO, (I) H2

4 12 Problems with CO, (I) H2 CO

5 Problems with 12 CO, (I)

6 log αco 12 Problems with CO, (I) Metallicity

7 12 Problems with CO, (I) is a very inefficient tracer of molecular gas at low metallicity log αco 12CO Metallicity

8 Problems with 12 CO, (II) CO Even at fixed metallicity, can vary based on the structure of the ISM

9 Problems with 12 CO, (II) CO Even at fixed metallicity, can vary based on the structure of the ISM The classic Milky Way value ( CO = 4.6 M (K km s -1 pc 2 ) -1 ) is derived assuming molecular clouds are separate and virialised

10 Problems with 12 CO, (II) CO Even at fixed metallicity, can vary based on the structure of the ISM The classic Milky Way value ( CO = 4.6 M (K km s -1 pc 2 ) -1 ) is derived assuming molecular clouds are separate and virialised In the early 1990s, it was realised that using this value for ULIRGs produced M(gas) > M(dyn) (Scoville et al. 1991) Led to a new ULIRG value for α, of ~0.8 alongside the normal value of ~4.5

11 Problems with 12 CO, (III) 12 CO is also dissociated by cosmic rays. In high SFR environments, CO may be a poor gas tracer (Bisbas+15)

12 line ) between at redshift z and at z = 0. The ratios are obtained Figure 5. Predicted brightness ratios of line emission (RB line when using LVG modelling which assumes a molecular density of 103 cm 3 and virialised conditions. Left: RB z=0 = T z=0 = 20 K. Right: Rline when assuming T z=0 = T z=0 = 50 K. assuming Tkin B d kin d 12 Problems with CO, (IV) CO J=(1-0) Zhang+16 12CO also becomes difficult to see against the CMB at high redshifts TCMB goes like (1+z) at high-z, observations in Raleigh-Jeans domain lack contrast against CMB

13 Observing gas with dust emission Eales+12 Also possible to measure a total dust mass (via SED fitting), and combine with a gas-to-dust ratio, to measure Mgas Advantage: observations are cheap compared to mm lines. Disadvantage: no kinematic information, dust-to-gas ratio not well understood

14 Tracing gas with atomic carbon

15 Tracing gas with atomic carbon Atomic carbon, [CI], is closely associated with low-j CO emission across a wide range of environments (e.g., Papadopoulos+04; Walter+11; Israel+15)

16 Tracing gas with atomic carbon Atomic carbon, [CI], is closely associated with low-j CO emission across a wide range of environments (e.g., Papadopoulos+04; Walter+11; Israel+15) Carbon is simple compared to CO, so physical parameters (excitation temperature, carbon mass) can be easily calculated

17 Tracing gas with atomic carbon SPT z=5.698 SPT z=5.656 SPT z=4.856 SPT z=4.798 SPT z=4.567 SPT z=4.477 SPT z=4.435 SPT z=4.296 SPT z=4.232 SPT z=4.224 SPT z=3.955 SPT z=3.761 SPT z=3.615 SPT z=3.594 SPT z=3.399 SPT z=3.369 SPT z=3.090 SPT z=2.780 SPT z=2.515 SPT z=2.234 SPT z=2.123 SPT z=2.096 SPT z=2.010 SPT SPT SPT CO (3 2) 12 CO (3 2) 13 CO (4 3) 12 CO (4 3) [C I] 3 P 1 3 P Rest Frequency (GHz) 13 CO (5 4) o H 2 O CO (5 4) 13 CO (6 5) 12 CO (6 5) o H 2 O p H 2 O Vieira, MB+2013, Weiß

18 [CI](1-0) Tracing gas with atomic carbon Flux (mjy) Flux (mjy) Flux (mjy) Flux (mjy) Redshift [CI](1-0) [CI](1-0) SPT SPT CO(2-1) Velocity (km/s) Redshift [CI](1-0) [CI](1-0) CO(2-1) SPT SPT Velocity (km/s) Redshift [CI](1-0) [CI](1-0) [CI](1-0) CO(2-1) SPT CO(2-1) SPT Velocity (km/s) Redshift [CI](1-0) [CI](1-0) CO(2-1) SPT SPT Velocity (km/s) Redshift [CI](1-0) Flux (mjy) Flux (mjy) Flux (mjy) Flux (mjy) Velocity (km/s) Redshift [CI](1-0) [CI](1-0) [CI](1-0) CO(2-1) CO(2-1) SPT SPT Velocity (km/s) Redshift [CI](1-0) [CI](1-0) CO(2-1) SPT SPT Velocity (km/s) Redshift [CI](1-0) [CI](1-0) 6 SPT CO(2-1) SPT Redshift [CI](1-0) SPT Velocity (km/s) Redshift [CI](1-0) Some of our [CI] spectra; Grey = [CI] Blue = CO(2-1), normalised 13 sources in total (12 with good detections)

19 Deriving gas mass from [CI] M(H 2 ) = D 2 L (1 + z) 1 X[CI] A s 1 1 Q 1 10 S [CI] v, Papadopoulos & Greve 04

20 Deriving gas mass from [CI] [CI] abundance Einstein A coefficient M(H 2 ) = D 2 L (1 + z) 1 X[CI] A s 1 1 Q 1 10 S [CI] v, Excitation factor (=0.5) Papadopoulos & Greve 04

21 Deriving gas mass from [CI] Three approaches (I) M(H 2 )= CO L 0 CO

22 Deriving gas mass from [CI] Three approaches (I) (II) M(H 2 )= CO L 0 CO M(H 2 )=X [CI] I [CI] ( C)

23 Deriving gas mass from [CI] Three approaches (I) (II) M(H 2 )= CO L 0 CO M(H 2 )=X [CI] I [CI] ( C) (III) M(H 2 )= GDR M(dust)

24 Deriving gas mass from [CI] Three approaches (I) (II) M(H 2 )= CO L 0 CO M(H 2 )=X [CI] I [CI] ( C) (III) M(H 2 )= GDR M(dust) All methods use an observable, multiplied by an unknown `conversion factor So why the claim that CI is a superior diagnostic?

25 Deriving gas mass from [CI] CO and GDR are ~quadratically dependent on metallicity X [CI] is ~linearly dependent on metallicity So given an unknown metallicity, derived M(H2) via [CI] involves smaller uncertainty and [CI] isn t destroyed by cosmic rays; and [CI] can be seen against the CMB at high-z; and [CI](1-0) is easily accessible at high-z and [CI](1-0) provides kinematic information

26 Gas masses: [CI] vs CO MNRAS 457, (2016) Advance Access publication 2016 February 9 doi: /mnras/stw275 A survey of the cold molecular gas in gravitationally lensed star-forming galaxies at z > 2 M. Aravena, 1 J. S. Spilker, 2 M. Bethermin, 3 M. Bothwell, 4 S. C. Chapman, 5 C. de Breuck, 3 R. M. Furstenau, 6 J. Gónzalez-López, 7 T. R. Greve, 8 K. Litke, 2 J. Ma, 9 M. Malkan, 10 D. P. Marrone, 2 E. J. Murphy, 11 A. Stark, 12 M. Strandet, 13 J. D. Vieira, 6 A. Weiss, 13 N. Welikala, 14 G. F. Wong 15,16 and J. D. Collier 15,16 1 Aravena, MB et al. (2016) low-j CO survey of SPT DSFGs Allows CO-based gas masses to be calculated for same sample

27 Gas masses: [CI] vs CO Aravena, MB et al. (2016) low-j CO survey of SPT DSFGs Allows CO-based gas masses to be calculated for same sample

28 Gas masses: [CI] vs CO M(H2), CO ( CO = 0.8) SPT DSFGs, low-j CO SPT DSFGs, high-j CO Literature DSFGs, low-j CO Literature DSFGs, high-j CO Literature AGN M(H2), [CI]

29 Gas masses: [CI] vs CO H2 masses from [CI] are systematically larger than from CO Have high-z gas masses (derived using CO) been systematically underestimated? Culprit incorrect CO/H2 conversion factor M(H2), CO ( CO = 0.8) SPT DSFGs, low-j CO SPT DSFGs, high-j CO Literature DSFGs, low-j CO Literature DSFGs, high-j CO Literature AGN M(H2), [CI]

30 Gas masses: [CI] vs CO M(H 2) (CI) / L CO(1-0) [M O (K km s -1 pc 2 ) -1 ] SPT DSFGs, low J CO SPT DSFGs, high J CO Literature DSFGs, low J CO Literature DSFGs, high J CO Literature AGN MW Value ULIRG value Implied α CO L(FIR) [ L O ] 1

31 Gas masses: [CI] vs CO M(H 2) (CI) / L CO(1-0) [M O (K km s -1 pc 2 ) -1 ] SPT DSFGs, low J CO SPT DSFGs, high J CO Literature DSFGs, low J CO Literature DSFGs, high J CO Literature AGN MW Value 2Sample average α CO = ULIRG value L(FIR) [ L O ] Implied α CO

32 What about dust-based M(H 2 )? Aravena et al. (2016) also calculate dust masses for our sample of DSFGs Combined with a dust-to-gas ratio, this gives us another measure of M(H2). We can compare our three independently-derived gas masses

33 Three measures of gas mass CO (+ alpha_co, assume alpha_co ~ 1) Dust (+ GDR, assume GDR ~ 100) [CI] (+ [CI] abundance, assume X CI ~ 3e-5) These disagree!

34 Three measures of gas mass ~7e10 XCI ~ 3e-5 M(H2) [M_sun] ~3e10 GDR~100 alpha_co~1

35 Three measures of gas mass ~7e10 XCI ~ 3e-5 M(H2) [M_sun] ~3e10 GDR~100 alpha_co~1 Solution (a) GDR~240, alpha_co~2.5, X CI ~3e-5 Solution (b) GDR~100, alpha_co~1, X CI ~7e-5

36 Three measures of gas mass Solution (a) GDR~240, alpha_co~2.5, X CI ~3e-5 Solution (b) GDR~100, alpha_co~1, X CI ~7e-5 Either alpha_co and DGR are 2-3 higher than normal, or X CI is 2-3 higher than normal NB Strandet (in prep) modelling points towards solution (a), implying we have been underestimating high-z gas masses

37 Gas mass from [CI] Future need more [CI] observations!!

38 Gas mass from [CI] [CI] 610µm in Band 5 = 1.3 < z < 2.1 [CI] 371µm in Band 5 = 3.8 < z < 5.1

39 [CI] with SEPIA band 5 Range of ratios [CI] 371µm CO(7-6) Béthermin et al. in prep.