Neon Emission in HST Emission- Line Galaxies at z 2. Greg Zeimann

Transcription

1 Neon Emission in HST Emission- Line Galaxies at z 2 Greg Zeimann grzeimann@psu.edu

2 Using transfer modeling to infer the physical of the warm ionized gas and the ionizing source Modeling Inputs 1) Ionizing Spectrum 2) Nebular Density/Pressure 3) Parameter 4) 12 + Log (O/H) Informa@on 1) Hydrogen (Hα, Hβ) 2) Oxygen ([OII], [OIII]) 3) Nitrogen ([NII]) 4) Sulfur ([SII])

3 However, [Ne III] is rarely exploited, yet it a useful diagnos@c as the iso- electric equivalent of [O III] [O III] Emission" Ionization Energy: 35.1 kev! 1 S 0 [Ne III] Emission" Ionization Energy: 41.0 kev! 1 S 0 λ 4363 λ 2321 λ 3343 λ D 2 1 D 2 λ 5007 λ 4959 λ 3869 λ P 3 P

4 Because O++ and Ne++ are so similar, the ratio of [Ne III] λ3869 to [O III] λ5007 is roughly the ratio of their abundances. We see this constancy in PN, H II regions, and galaxies. PN H II Regions Henry (1989) Garnett (2002) [Ne III] / [O III] 1 / 12 Galaxies Izotov et al. (2011)

5 Visually inspected >50,000 spectra from HST C O S M O S" GOODS-S" GOODS-N" CANDELS 3DHST F140w 3DHST G141 7 Fλ (10 18 ergs s 1 cm 2 Å 1 ) λ (µm)

6 For 1.9 < z < 2.35, 3D- HST/AGHAST provides four key rest- frame op@cal emission lines Fλ (10 18 erg s 1 cm 2 Å 1 ) [OII] [NeIII] Hδ Hγ Hβ [OIII] 1) [OIII] ) Hβ 3) [NeIII] ) [OII] Rest-Frame Wavelength (Å) Gebhardt, Zeimann, et al. (2015)

7 For 1.9 < z < 2.35, 3D- HST/AGHAST provides four key rest- frame op@cal emission lines [OII] [Ne III] Hβ [OIII] Example 1-D and 2-D Spectrum [OIII] [OII] [Ne III] Hβ F λ -Continuum 1) R ~ 130 2) Spa@al Conv 3) ~1.5 kpc scale 4) FWHM ~ 90 Å F140W Wavelength Spatial

8 Different sample methods probe different parts of the M- SFR diagram Figure 1. Sample of our 2star-forminggalaxiesinthecontextoftheepoch s Zeimann et al. (2015)

9 For 1.9 < z < 2.35, 3D- HST/AGHAST provides four key rest- frame op@cal emission lines but at low S/N DHST 40 3DHST Number of galaxies Number of galaxies S/N of [OII]λ S/N of [NeIII]λ DHST 80 3DHST Number of galaxies Number of galaxies Gebhardt, Zeimann, et al. (2015) S/N of Hβ S/N of [OIII]λ5007

10 To increase our signal to noise, we stacked our spectra. Normalized Flux Density (Fλ) N=236 1-D Stack 2-D Stack [Ne III] [OII][NeIII] Hɛ Hδ Hγ [OIII] Hβ Rest-Frame Wavelength (Å) Zeimann et al. (2015) [O III]

11 a reference sample at z 0 through luminosity and EW cuts (M- ssfr matched) 7 This Work SDSS (L Hβ > ) SDSS (EW Hβ > 100 Å) Log ssfr (yr 1 ) Log M (M ) Zeimann et al. (2015)

12 a reference sample at z 0 through luminosity and EW cuts (M- ssfr matched) log(o/h) = 7.0 Log [OIII]/[OII] DHST: z 2.1 SDSS: z 0.1 SDSS Matched 12 + log(o/h) = Gebhardt, GRZ, et al. (2015) Log R 23

13 Since the HST grism data do not extend to Hα, we cannot measure the Balmer decrement. We can however, observe the slope of the rest-frame UV continuum. In the rest-frame UV, the SED of a vigorously starforming galaxy is power law, F λ λ β with β= 2.25.

14 Since the HST grism data do not extend to Hα, we cannot measure the Balmer decrement. We can however, observe the slope of the rest-frame UV continuum. In the rest-frame UV, the SED of a vigorously starforming galaxy is power law, F λ λ β with β= Any observed SED flatter than this is caused by reddening. For a Calzetti (2001) law, A Hβ = 1.91 Δβ

15 [Ne III] / [O III] is 1.5 ± higher at z = 2 Log [O III] λ4363 / (λ λ5007) T e /1000K Log [NeIII]/[OIII] Theore@cal Expecta@on for H II regions ssfr- matched SDSS sample (binned by stellar mass) 3D- HST sample (uncorrected for dust) 3D- HST sample (corrected for dust) Log M (M ) Zeimann et al. (2015)

16 What is different about Neon and Oxygen? Neon has a higher critical density N crit (Ne ++ ) ~ 10 7 cm -3, while N crit (O ++ ) ~ 10 6 cm -3, so [O III] will be suppressed in dense nebulae. But this will also lowers [O II] dramatically Neon has a higher ionization potential (41 vs. 35 ev) Requires harder ionizing spectrum Oxygen can be depleted on to dust grains Effects the ratio of [O III]/Hβ and [Ne III]/[O II]

17 As Neon is an inert gas, oxygen from z = 2 to z = 0 could explain high [NeIII]/[OIII] Log [O III] λ4363 / (λ λ5007) Log [O III] λ4363 / (λ λ5007) T e /1000K T e /1000K Log [NeIII]/[OII] SDSS 3D- HST Log [OIII]/H Log M (M ) Log M (M ) Zeimann et al. (2015)

18 Possible Explanation 1) Lots of Hidden AGN Non-thermal SEDs boost [Ne III] relative to [O III]. But the CDFS sources are not even visible in x-ray stacks. Are they all Compton-thick? 0.6 Log [NeIII]/[OIII] AGN-Dominated SF-Dominated Log M (M ) To explain [Ne III], ~ 40% of the [O III] luminosity must originate with the AGN.

19 Possible Explanation 1) Lots of Hidden AGN Non-thermal SEDs boost [Ne III] relative to [O III]. But the CDFS sources are not even visible in x-ray stacks. Are they all Compton-thick? Log [NeIII]/[OIII] AGN-Dominated SF-Dominated Log M (M ) LX [ kev] (erg s 1 ) % Upper Limit N H (cm 2 ) Xue et al. (2012) To explain [Ne III], ~ 40% of the [O III] luminosity must originate with the AGN.

20 2) Enhanced Neon Exotic Explanation 20 Ne is an α process element, created by supernovae and strongly tied to oxygen 22 Ne is produced in moderateand high-mass stars by mixing N-rich material from CNO burning into helium-burning shells Measurement 22 Ne/ 20 Ne Solar Wind 0.07 Cosmic Rays 0.4 Required O + 4 He 20 Ne 14 N + 4 He 18 F 18 O + e + 18 O + 4 He 22 Ne (also 22 Ne + 4 He 25 Mg + n for s-process elements) ç Enhanced ratio likely from Wolf-Rayet stars winds

21 Low of the HST grism and He I 3889 emission is the cause? ophysical Journal, 732:59 (12pp), 2011 May 1 Rigby et al. Hd H7 H8 O[II] O[II] Ne[III] Flux Rigby et al. (2011) 1 galaxy at z = Wavelength Masters et al. O[III] O[III] Ar[IV] The Astrophysical Journal, 785:153 (20pp), 2014 April 20 Hb Hgamma O[III] [OII] λ3726, Masters et al. (2014) 23 galaxies at z= [NeIII] λ3869 Flux Hβ [OIII] Wavelength [OIII] 4

22 Low of the HST grism and He I 3889 emission is the cause? 2.5 H9 [NeIII] H8+HeI H9 [NeIII] H8+HeI Normalized Fλ Normal [Ne III] High He I High [Ne III] No He I Wavelength (Å) Wavelength (Å)

23 [NeIII]/[OIII] at z = 2 are 50% ± 13% higher than at z = 0. But why? EXPLANATION 1) X- ray obscured AGN 2) Higher 22 Ne / 20 Ne at z = 2 3) Low Resolu@on Blending of other lines (residual H8 emission or HeI at ~3890) and/or dust correc@on conspiring to look like an enhancement Using new HST data at bluer wavelengths to measure the ra@o of [Ne V]/[Ne III] and test the AGN hypothesis Higher resolu@on spectroscopy can resolve this issue.

24 Spatial Wavelength (Å) <M> = 8.4 <M> = 9.3