Far-infrared Herschel SPIRE spectroscopy reveals physical conditions of ionised gas in high-redshift lensed starbursts

Transcription

1 Far-infrared Herschel SPIRE spectroscopy reveals physical conditions of ionised gas in high-redshift lensed starbursts Zhi-Yu (Z-Y) Zhang 张智昱 U. Edinburgh/ESO

2 Outline Background Sample description Herschel SPIRE/PACS Observations Stacking Physical properties of ionised gas Summary

3 Gas phase structure in ISM Hollenbach and Tielens (1997) Goicoechea et al. (2015) Ionised Atomic Molecular

4 Fine-structure lines at far-ir Most abundance elements: C, N, O. Species have ground state into simple energy levels. Excited by collision with (mostly) electrons. Mostly optically thin. Mostly not have strong dust extinction. Carry a lot of energy important for cooling. Not affected by the CMB effects for high-z systems. Draine (2011) Goldsmith (2015) Dinerstein et al. (1985)

5 Fine-structure lines at far-ir Diagnostics of physical conditions of neutral and ionised gas. PDR HII AGN Coronal Powerful diagnostic of warm+cold ISM. Various gas density and radiation conditions. Large span of ISM phases. Different origins of line excitation (e, HI, H2) Spingolio et al

6 Far-IR line diagnostics - [CII] Originates from PDR, atomic gas, and ionised gas Ionisation potential: 11.26eV (< 13.6 ev) Critical density: The Milky Way 3x10 3 cm -3 with H2 50 cm -3 with e The strongest cooling line in galaxies: ~ 0.1-1% LFIR. (Stacey et al. 2010) Pineda

7 Far-IR line diagnostics - [OI] Originates from PDR and shocked neutral gas Ionisation potential: ev ~ (13.6 ev) Critical densities: [OI] 63 um: 4x10 5 cm -3 with H2 [OI] 145 um:8x10 4 cm -3 with H2 Dominate line cooling in dense PDRs. Shocks may enhance [OI] emission. τo I 63 μm~ 1-3 (Liseau et al. 2006; Hughes et al. 2015) Sturm et al. (2010) For PDR, [CII]/[OI] ratio is density sensitive, and the sum is a better cooling estimate.

8 Far-IR line diagnostics - [NII] Originates from total ionised gas. Ionisation potential: ev > (13.6 ev) Critical densities: [NII] 122 um: 300 cm -3 with e [NII] 205 um: 50 cm -3 with e [NII] 205/122 traces electron density (ne). Herrera-Camus [NII]/[CII] probes [CII] from ionised gas highly dependent on C/N abundance ratio.

9 Far-IR line diagnostics - [OIII] Originates from dense and highly ionised gas. Ionisation potential: ev >> (13.6 ev) Critical densities: [OIII] 52 um: 300 cm -3 with e [OIII] 88 um: 500 cm -3 with e [OIII] 52/88 traces ne in dense HII regions. [OIII]/[NII] ratio is insensitive to ne, but sensitive to Teff. probe of radiation hardness. Effective temperature of stellar radiation field (K) Rubin 1985

10 Starbursts at z~2 H-ATLAS 550 deg2 HerMES 110deg2 LeLMS 270 deg2

11 Starbursts at z~2 Swinbank et al Simpson et al Extreme starburst: ~10% of the cosmic SFR SFR> 500 Msun/yr Lifetime ~ 100 Myr LIR> 3x10 12 Lsun Very dusty and metal enriched Toft et al. 2014

12 Strongly lensed systems S 350μm 200mJy Negrello et al SDP.81 S350μm>100 mjy, and ensure [CII] within the SPIRE band

13 Herschel Far-IR spectroscopy In total 38 galaxies ~3.7 hrs/target PACS parallel imaging Carilli & Walter 2013

14 Zhang et al. 2018, MNRAS. arxiv: The sample Green: our sample Black: Negrello lensed sample Dashed: Eyelash simulation 10 6 random modified black-body Td: K z : 1-6 beta: 1-2.5

15 Zhang et al. 2018, MNRAS. arxiv: PACS images and dust SED fitting ~ 1/3 targets are resolved by PACS 100/160 um. ~ 1/3 targets can not be well fitted with a single MBB We fit a power law Md with a Td distribution of: (Kovacs+201 γ=7.2

16 Zhang et al. 2018, MNRAS. arxiv: SPIRE line detections 28 Zhang et al. (b) Spectra obtained using Herschel SPIRE/FTS Rest frame wavelength [µm] Rest frame wavelength [µm] > 5 sigma: 15 [CII] 2 [OIII] 88 um 2 OH 119um > 3 sigma: 17 [CII] 5 [OIII] 88 um 3 [OI] 63 um 3 OH 119um Flux density / Jy [C I] [C I] SDP.9 z = S 350µm = 328mJy SDP.11 z = S 350µm = 371mJy SDP.17 z = S 350µm = 339mJy SDP.81 z = S 350µm = 186mJy SDP.130 z = S 350µm = 137mJy G09-v1.40 z = S 350µm = 368mJy G09-v1.97 z = S 350µm = 305mJy G09-v1.124 z = S 350µm = 249mJy G09-v1.326 z = S 350µm = 151mJy 0 [C I] [C I] [N II] 3 P 1 3 P0 [N II] H 2 O H 2 O [C II] 2 P 2 3/2 P1/2 [O I] 3 P 3 0 P1 [C II] [O I] [Si I] 3 [N II] 3 P 3 1 P0 P 3 2 P1 OH 3/2 3/2 [Si I] [N II] OH [O III] 3 P 1 3 P0 [O III] Rest frame frequency [GHz] [Si I] 3 P 2 3 P1 [Si I] [O I] 3 P 1 3 P2 [O I] [N III] 2 P 2 3/2 P1/2 [S I] 3 P 3 0 P1 [N III] [S I] [O III] 3 P 2 3 P1 [O III] Velocity [kms 1 ] Significant Significant Not detected Significant Not detected Low significant Not covered Low significance Not detected Velocity [kms 1 ] 2 2 Flux density / Jy [C I] [C I] G12-v2.30 z = S 350µm = 358mJy G12-v2.43 z = S 350µm = 284mJy G12-v2.257 z = S 350µm = 124mJy G15-v2.19 z = S 350µm = 438mJy G15-v2.235 z = S 350µm = 217mJy NA.v1.56 z = S 350µm = 466mJy NA.v1.144 z = S 350µm = 286mJy NA.v1.177 z = S 350µm = 296mJy NA.v1.186 z = S 350µm = 227mJy NB.v1.43 z = S 350µm = 371mJy 0 [C I] [C I] [N II] 3 P 1 3 P0 [N II] H 2 O H 2 O [C II] 2 P 2 3/2 P1/2 [O I] 3 P 3 0 P1 [C II] [O I] [Si I] 3 [N II] 3 P 3 1 P0 P 3 2 P1 OH 3/2 3/2 [Si I] [N II] OH [O III] 3 P 1 3 P0 [O III] Rest frame frequency [GHz] [Si I] 3 P 2 3 P1 [Si I] [O I] 3 P 1 3 P2 [O I] [N III] 2 P 2 3/2 P1/2 [S I] 3 P 3 0 P1 [N III] [S I] [O III] 3 P 2 3 P1 [O III] Velocity [kms 1 ] Not covered Not detected Low significance Significant Not detected Low significant Not detected Not detected Significant Significant Velocity [kms 1 ] 2 2 c 0000 RA

17 [CII] deficit High redshift starbursts extend the [CII] deficit trend. However they are more similar to local LIRGs, instead of the local ULIRGs. z~2 starbursts showing intermediate SFE and [CII] deficit. Lower ionisation parameter (U) than local ULIRGs? Optical depth? Zhang et al. 2018, MNRAS. arxiv:

18 Zhang et al. 2018, MNRAS. arxiv: Stacking To detect the weak lines, and derive the average conditions of the galaxy population. Three stacking methods: Intrinsic luminosity: 1) shift to rest frequencies. 2) correct lensing magnifications. 3) stack with 1/σ 2 weighting. Intrinsic properties. Scaling to a common z: 1) shift to a common redshift 2) scale fluxes using 500um 3) stack with 1/σ 2 weighting. Dust scaled properties. Needs lensing models. Median: To see if the other two stacked signal is highly biased by weighting.

19 Intrinsic Stacking Zhang et al. 2018, MNRAS. arxiv:

20 Scaled Stacking Zhang et al. 2018, MNRAS. arxiv:

21 Minimum Ionised gas mass traced by [NII] 122um The minimum ionised gas mass can be obtained from [NII] lines. MH+ min ~ 7-10 x 10 8 Msun Stacked SED gives MH2 ~10 11 Msun which is similar to the average MH2 obtained from. MH+/MH2 ~> 1% gas-to-dust =200 Td ~ 35 K Zhang et al. 2018, MNRAS. arxiv:

22 Zhang et al. 2018, MNRAS. arxiv: [NII] 122/205 um limits High electron density traced by [NII] lines. Diffuse HII regions

23 Zhang et al. 2018, MNRAS. arxiv: [OIII] 52/88 um ratio High electron density traced by [OIII] lines. Dense HII regions

24 Zhang et al. 2018, MNRAS. arxiv: Ionised gas contribution to [CII] Savage & Sembach 1996 Many past publications adopts C and N abundances measured in diffuse clouds. But we are accounting the [CII] from ionised gas For diffuse gas abundances, ionised gas contributes ~ 10-15% [CII] emission. For HII region abundances, ionised gas contributes 30-60% [CII] emission, depending on the ne adopted.

25 Zhang et al. 2018, MNRAS. arxiv: [NII] 88 /[OIII] 122 radiation field similar critical densities ~ cm -3 ionisation potentiel : 14.5 ev and 35 ev Optically thin Insensitive to Te Abundances in HII region. 3-5x10 7 O8 or O9 stars are needed ~1-2 x 10 9 Msun in H+, consistent of MH+ min ~ 2% gas mass is ionised, in contrast to 20% ( Ferkinhoff 2011)

26 Summary A systematic Herschel survey of [CII] in lensed starburst at z~2 [CII] deficit close to local LIRGs, lower than ULIRGs High electron density revealed by [NII] and [OIII] lines. Ionised gas contribution to [CII] is heavily affected by element abundance % for diffuse gas, and 30-50% for HII region. Ionised gas mass ~ 2% of H2 gas mass.

27 Thank you!

28 [OI] 63/145 um / [CII] 158 um Liseau Sturm et al [OI] 63/145 > 1.3 [CII]/[OI]63 ~ 3-4