GN-Z11 Oesch+16 4 R.A
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! Spectroscopic Exploration at the Cosmic Dawn Pascal Oesch Geneva Observatory Exploring the Universe with JWST II P. Oesch, Observatoire UniGE October 2016 The history of astronomy is a history of receding horizons. E. P. Hubble Epoch of Reionization Montreal, Oct 2016 P. Oesch, Observatoire UniGE 2 Unprecedented Galaxy Samples at z>=4 (from HST’s blank fields only) 3.5 10500 z~4-10 galaxies 3 (Bouwens, Illingworth, Oesch+15) 2.5 2 1.5 log Numbers 1 6 (z~10) 0.5 6000 (z~4) 3000 (z~5) 900 (z~6) 480 (z~7) 220 (z~8) 0 3 4 5 6 7 8 9 10 11 Redshift Almost 1000 galaxies in the epoch of reionization at z>6 Current frontier: z~9-10 Montreal, Oct 2016 P. Oesch, Observatoire UniGE 3 Mass and SFR Build-up Time [Gyr] 10 5 2 1 0.7 0.5 9 Oesch+14 8 50% ] 3 10% − 7 Mpc 1% ⊙ 6 + [M * ρ 0.1% log 5 z<4: logM > 8 z>4: MUV < -18 stellar mass density of galaxies 4 from Marchesini+09 from Stark+12 0 2 4 6 8 10 Redshift Are witnessing the assembly of the first 0.1% of local stellar mass density at z>8. The first two Gyr are a very active epoch of galaxy assembly. Montreal, Oct 2016 P. Oesch, Observatoire UniGE 4 8Our Oesch Current et al. Spectroscopic Census Age of the Universe [Gyr] 0.9 0.8 0.7 0.6 0.5 0.4 TABLE 2 −23 Summary of Measurements for GN-z11 Oesch+16 4 R.A. 12 : 36 : 25.46 GN-z11 Dec. +62 : 14 : 31.4 UV −22 +0.08 a (z=7)] 2 * Redshift zgrism 11.09 0.12 − UV Luminosity MUV 22.1 0.2 Half Light Radiusb 0−.6 0±.3kpc − c ± −21 1 log Mgal/M 9.0 0.4 log age/yr c 7.6 ± 0.4 ± 1 SFR 24 10 M yr− 0.5 ± AUV < 0.2mag −20 Absolute Magnitude M β d zspec UV Luminosity [L/L UV slope β (fλ λ ) 2.5 0.2 / − ± zphot 0.25 a Age of the Universe at z =11.09 using our cosmol- ogy: 402 Myr −19 b From Holwerda et al. (2015) 6 7 8 9 10 11 c Uncertainties are likely underestimated, since our Redshift photometry only partially covers the rest-frame opti- Fig. 7.— The redshift and UV luminosities of known high- cal for GN-z11 Spectroscopic samples are severaly lagging behind! d See also Wilkins et al. (2016) redshift galaxies from blank field surveys. Dark filled squares corre- spondOnly to a spectroscopicallydozen spectroscopic confirmed confirmations sources, while at smallz>7 to gray date. dots are photometric redshifts (Bouwens et al. 2015b). GN-z11 clearly to estimate how many such galaxies we could have ex- stands out as one of the most luminous currently known galaxies at Montreal, Oct 2016 all redshifts z>6andisbyfarthemostdistantmeasuredgalaxyP. Oesch, Observatoire UniGE 5 pected based on (1) the currently best estimates of the with spectroscopy (black squares; see Oesch et al. 2015b,forafull UV LF at z>8 and (2) based on theoretical models and list of references). Wider area surveys with future near-infrared simulations. telescopes (such as WFIRST) will be required to determine how Our target was found in a search of the GOODS fields, common such luminous sources really are at z>10. which amount to 160 arcmin2. However, in a sub- sequent search of the⇠ three remaining CANDELS fields no similar sources were found with likely redshifts at TABLE 3 Assumed LFs for z 10 11 Number Density Estimates z & 10 (Bouwens et al. 2015a). We therefore use the ⇠ − 2 full 750 arcmin of the CANDELS fields with match- 5 Reference φ /10− M ↵ Nexp ing WFC3/IR and ACS imaging for a volume estimate, ⇤ 3 ⇤ [Mpc− ][mag] (< 22.1) which amounts to 1.2 106 Mpc3 (assuming ∆z = 1). − ⇥ Bouwens et al. (2015b)1.65-20.97-2.380.06 Using the simple trends in the Schechter parameters of Finkelstein et al. (2015)0.96-20.55-2.900.002 the UV LFs measured UV at lower redshift (z 4 8) Mashian et al. (2016)0.25-21.20-2.200.03 and extrapolating these to z = 11, we can get an⇠ empir-− Mason et al. (2015)0.30-21.05-2.610.01 ical estimate of the number density of very bright galax- Trac et al. (2015)5.00-20.18-2.220.002 ies at z 11. This amounts to 0.06 (Bouwens et al. Note.—Theparametersφ , M ,and↵ represent the three 2015b) or⇠ 0.002 (Finkelstein et al. 2015) expected galax- parameters of the Schechter UV⇤ LF taken⇤ from the di↵erent papers. ies brighter than MUV = 22.1 in our survey correspond- ing to less than 0.3 per− surveyed square degree. Simi- larly, recent empirical models (Mashian et al. 2016; Ma- z11. Our 2D data show clear flux longward of 1.47 µm son et al. 2015; Trac et al. 2015) predict only 0.002 0.03 exactly along the trace of the target galaxy⇠ and zero galaxies as bright as GN-z11 in our survey or 0.01− 0.2 flux at shorter wavelengths, thanks to our comprehensive per deg2. All the assumed LF parameters together− with and accurate treatment of contamination by neighboring the resulting estimates of the number of expected bright galaxies. The interpretation that we indeed detect the galaxies Nexp are listed in Table 3. continuum flux from GN-z11 is supported by the mor- The above estimates illustrate that our discovery of phology of the spectrum, the fact that the counts fall o↵ the unexpectedly luminous galaxy GN-z11 may challenge exactly where the sensitivity of the G141 grism drops, as our current understanding of galaxy build-up at z>8. well as the consistency of the observed counts with the A possible solution is that the UV LF does not follow H-band magnitude of GN-z11 (see e.g. Fig 3). a Schechter function form at the very bright end as has The grism spectrum, combined with the photometric been suggested by some authors at z 7(Bowler et al. constraints, allows us to exclude plausible low-redshift 2014), motivated by inefficient feedback⇠ in the very early SEDs for GN-z11 at high confidence. In particular, we universe. However, current evidence for this is still weak can invalidate a low redshift SED of an extreme line emit- (see discussion in Bouwens et al. 2015b). Larger area ter galaxy at z 2 (see section 3 and Fig 4). Instead, studies will be required in the future (such as the planned the grism spectrum⇠ is completely consistent with a very +0.08 WFIRST High Latitude Survey; Spergel et al. 2015)sur- high-redshift solution at zgrism = 11.09 0.12 (see Figures veying several square degrees to determine the bright end 3 and 5). This indicates that this galaxy− lies at only of the UV LF to resolve this puzzle. 400 Myr after the Big Bang, extending the previous redshift⇠ record by 150 Myr. 5. SUMMARY GN-z11 is not only⇠ the most distant spectroscopically In this paper we present HST slitless grism spectra measured source, but is likely even more distant than for a uniquely bright z>10 galaxy candidate, which all other high-redshift candidates with photometric red- +0.6 we previously identified in the GOODS-North field, GN- shifts, including MACS0647-JD at zphot = 10.7 0.4 (Coe − Spectroscopic Features of High-z Galaxies 68 SHAPLEY ET AL. Vol. 588 to estimate stellar systemic redshifts for individual galaxies, we applied the formulae presented in Adelberger et al. Shapley+03 Lyα is the most promising feature of (2003), which predict a value of the systemic redshift for Lya high-redshift spectra three separate cases: when there is only a Ly emission red- Other emission lines very weak, but shift, when there is only an interstellar absorption redshift, possible to detect (e.g. Stark+15) and when there are both Ly emission and interstellar 10 Steven L. Finkelstein absorption redshifts. While no reference was made to stellar photospheric fea- spectroscopically confirm the redshifts of galaxies se- tures in the estimate of the systemic redshifts of individual lected to be at z>6. Figure 3 highlights the redshift of 8 Lyα galaxies, the rest-frame composite spectrum presented in the most distant spectroscopically-confirmed galaxy as non−Lyα a function of the year of discovery. the next section indicates a mean systemic velocity of The most widely used tool for the measurement of 1 Finkelstein 16 Dv 10 35 km s for the three strongest stellar fea- HeII 6 ¼À Æ À spectroscopic redshifts for distant star-forming galax- tures, which we have identified as C iii 1176, O iv 1343, CIII] ies is the Lyα emission line, with a rest-frame vacuum and S v 1501.4 It is worth noting possible contributions to wavelength of 1215.67 A.˚ While at z< 4, confirma- the O iv 1343 absorption from Si iii 1341 and to the S v 4 tion via interstellar medium absorption lines is possible 1501 absorption from Si iii 1501 if there is a significant B- (e.g., Steidel et al. 1999; Vanzella et al. 2009), the faint star component in the composite spectrum. However, at nature of more distant galaxies renders it nearly im- possible to obtain the signal-to-noise necessary on the Spectroscopic Redshift least the Si iii 1501 contribution will not change the 2 continuum emission to detect such features.