F I R S T S C I E N C E W I T H Seen through the lens of: why you should care about Lyman-alpha equivalent width distributions Steven Finkelstein - The University of Texas at Austin for the HETDEX team PI: Gary Hill (UT Austin) Project Scientist: Karl Gebhardt (UT Austin)
T H E R E I S A M Y S T E RY AT T H E E N D O F r r R E I O N I Z AT I O N ! LY M A N - A L P H A C A N H E L P ! < � r ~ t � r � � • Many models can successfully complete reionization by z~6 and t t ~ r µ + - ~ still match constraints of a significant neutral fraction at z >7. r = � > r r > ROBERTSON+15 � Galaxies are - the source f esc =10-20%, t = � 2 M lim =-13, ~ r t SF+15 ) r � � > log ξ ion ~ 25.2 ~ Most galaxies have very low escape fractions (<2%), with a small fraction with higher (>10%) escape fractions, and/or that f esc varies with mass/luminosity. r < - r » r = = = = - = < » + - t � t ~ r = - ~ � � = = - < = � ~ ~ > ~ > r < = < = < <
T H I S L E A D S T O A D I S C R E PA N C Y W I T H T H E M E A S U R E D I O N I Z I N G E M I S S I V I T I E S This doesn’t even consider AGNs, which we know are there at z < 4! Direct measurements of the total ionizing emissivity 52.0 52.0 Total HI Ionizing Emissivity (N HI ) Galaxy HI Ionizing Emissivity 51.5 51.5 AGN HI Ionizing Emissivity Galaxy N HI (f esc =13%, M lim =-13) Ionizing Emissivity 51.0 51.0 AGN HeII Ionizing Emissivity 50.5 50.5 50.0 50.0 49.5 49.5 49.0 49.0 SF+18, in prep Becker & Bolton 2013 48.5 48.5 2 4 4 6 6 8 8 10 10 12 12 14 14 Redshift
K I L L T W O B I R D S W I T H O N E M O D E L : C O M P L E T I N G T H E I G M W I T H L O W E R G A L A X Y E S C A P E F R A C T I O N S 1.0 Robertson+15 1.0 Cumulative Ionizing Emissivity This Work z=4 z=8 log M h =7.0 0.8 z=6 z=10 log M h =7.5 0.8 log M h =8.0 z=8 z=8 log M h =8.5 0.6 0.01L * 0.1L * z=8 log M h =9.0/9.5 L * 0.6 P(f esc ) log M h =10.0 0.4 0.4 0.2 SF+18, in prep 0.2 0.0 -22 -20 -18 -16 -14 -12 -10 0.0 Absolute UV Magnitude -5 -4 -3 -2 -1 0 Paardekooper+15 log f esc This leads to *very* faint galaxies being the dominant contributor Ionized Volume Filling Fraction 1.0 Q HII Q HeIII 0.8 It does successfully Robertson+15 McGreer+15 complete reionization 0.6 with <f esc > < 5%, and 0.4 matches emissivity 0.2 constraints 0.0 2 4 6 8 10 12 14 Redshift
First Ly α slide A L L I S W E L L ? • The constraints used in this analysis (dark pixels from McGreer+15, emissivities from Becker+13, and Planck 2015 optical depth) do not prohibit this reionization history. 1.0 Dark Pixel Fraction Ly � Clustering Ionized Volume Filling Fraction 0.8 Ly � LF Ly � EW Evolution QSO Damping Wing 0.6 Existing Ly α measurements at z ~ 7 prefer a lower ionized fraction (~50%) 0.4 This Work 0.2 Greig+15 Robertson+15 Rosdahl+18 0.0 6 7 8 9 10 SF+18, in prep Redshift
LY M A N - A L P H A A S A P R O B E O F R E I O N I Z AT I O N • Ly α photons are resonantly scattered by neutral HI gas, and so should be a unique tracer of the evolution of the IGM neutral fraction during reionization (e.g., Miralda-Escude+98, Malhotra & Rhoads 04, 06; Dijkstra+07). • This has often been traced by exploring the “Lyman-alpha” fraction. • This measure doesn’t include the continuum brightness of the galaxy, so analyses often split into multiple bins. • The EW distribution (P[W]) is a more straightforward way to trace this evolution. Mason+2018 • Now being used, see Pentericci+2018, Mason+2018, Jung+2018
� � � � � � � � � � � � � � � � For each mock emission line, i) We assign a wavelength for the Ly α line by drawing randomly from P(z) Baseline measurements at lower redshift are critical to interpret λ Ly α = (1+z phot ) × 1215.67Å these epoch of reionization Ly α results P(z) N detection (S/N > S - # � 5.0 6.0 7.0 8.0 z ii) We assign the simulated Ly α line strength from the assumed EW distribution � P (EW) � exp (-EW/W 0 ), W 0 =100Å where W 0 is an exponential scale length. P(EW) S (Signal-to-Noise) We perform this emission line simulation (described in the left) 0 200 400 600 800 1000 for our observations, measuring the posterior distribution of the EW [Å] expected number of detections as a function of S/N for e -folding iii) determine the S/N level of the simulated Ly α line at that wavelength. scales of W 0 =5-200Å. For each choice of W 0 , we carry out 1000 GOODS-S GOODS-N Monte Carlo simulations. The figure above shows the mean 5 σ detection limit expected number of detections, averaged over each set of 1000 simulations, as a function of S/N for a range of EW distributions Emission line detections at z ~ 5.5 - 6.7 from for z � 6.5. A larger choice of W 0 predicts a larger number of Ly ! detections. S E E P O S T E R B Y I N TA E � Ly ! Equivalent Width Distribution at z ~ 6.5 from MCMC sampling � � �
T H E H O B B Y E B E R LY T E L E S C O P E D A R K E N E R G Y E X P E R I M E N T • We’re creating the largest spectroscopic map of the distant universe through a blind spectroscopic survey on the 10m Hobby Eberly Telescope (HET), tracing structure via Ly α emission at 1.9 < z < 3.5. • Our instrument VIRUS is 78 spectrograph pairs (R=750 from 350nm – 550nm), covering 1/5 th of the focal plane with 35,000 fibers, which is currently being assembled on the upgraded HET (new top-end, upgrading FOV from 4’ to 22’). • Our fiducial survey is 450 square degrees over 3 years (taken in ~6000 pointings of 20 minutes each) at 1/5 fill, for nearly 100 deg 2 with spectra. • Expect ~1 million redshifts from 1.9<z<3.5 via Ly α • >1 million redshifts from 0<z<0.5 via [OII] • HETDEX will enable the creation of a baseline dataset for comparison with high redshift! S E E P O S T E R B Y G A RY H I L L
THE SURVEY FIELDS Spring field: 300 deg 2 in the North (in Ursa Major) Current status: 32 working spectrographs on the telescope. Four new arriving every month, VIRUS should be complete by the end of the year. Fall field: 150 deg 2 in Stripe 82 NB: At least single-band imaging data needed to constrain EWs to distinguish between LAEs at [OII] emitters (line will not be resolved).
W H E R E W E W E R E AT A Y E A R A G O : Talk at SnowCLAW
W H E R E W E A R E AT T O D AY: • We have been performing science verification observations in well-known deep fields: GOODS-N, EGS and COSMOS. • We are using the deep-field observations to help optimize our emission-line selection algorithms, characterize detection limits. • This is not trivial with these data! • Currently working on optimal combination of fibers to centroid object, matching with imaging counterpart, and optimal removal of sky emission. • We have also started general survey observations in both spring and fall fields.
W H E R E I S T H E C O N T I N U U M C O U N T E R PA R T ? • In fields with deep HST imaging (m limit ~28), assuming an EW scale length of 70 A, we should see counterparts to ~99% of our sources. • This can be very useful for understanding the positional accuracy of our emission line centroiding! • Current UT undergrad Yaswant Devarakonda has been exploring this in the CANDELS EGS field. Conclusion: Matches at < 1” are likely correct, but not always…
T H E P O W E R O F V I R U S • These green squares show the layout of a deep observation (4X HETDEX depth) we performed in GOODS-N, which obtained data in 20 IFUs. • We cover a similar volume as the MUSYC CDFS pointing to a similar depth (<~L Lya *), in 20X less integration time!! • Full VIRUS will cover 4X the volume in the same amount of time.
Some emission lines in GOODS-N
E A R LY L O O K I N T O T H E E W D I S T R I B U T I O N Are these Due to current real?!? high SNR • Using the observations taken requirements in GOODS-N and EGS, we can take a sneak peak into 14 HETDEX MUSYC the EW distribution. 12 10 Number • This is for the ~70 sources 8 Malhotra & 6 Rhoads 2002 with a continuum match 4 within 1” with W 0 > 20 A. 2 0 • There are ~20 others in 1.0 1.5 2.0 2.5 3.0 3.5 4.0 log Rest-Frame EW this sample, but need further reliability checks.
Here are some sources with W > 300 A, and a counterpart with a matching photo-z What does this mean? More work needs to be done to verify , but it could indicate that the EW distribution extends out to higher values than previously thought. *If* this is true, we will characterize this extremely well with HETDEX. Physical explanations? Extreme starbursts, AGN, low metallicities, other causes of increased ionization (top-heavy IMF, binary stars, etc), more inclusive of lower-SB emission?
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