MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)1 The Nature of High Equivalent- Width Lyman-α Galaxies Steven Finkelstein, James Rhoads, Sangeeta Malhotra (ASU), Norbert Pirzkal (STScI) & Junxian Wang (USTC)

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)2 Outline Why do we study Lyman Alpha Emitters (LAEs) ? Why do we study Lyman Alpha Emitters (LAEs) ? Intro to LALA survey Intro to LALA survey MMT/Megacam data acquisition/reduction MMT/Megacam data acquisition/reduction Results Results Discussion Discussion Future Work Future Work

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)3 Lyman Alpha Emitters - Background Lyα gives an easy way to spot high-z galaxies Lyα gives an easy way to spot high-z galaxies Lyα emission was proposed as a signpost of primitive galaxies in formation (Partridge & Peebles 1967) Lyα emission was proposed as a signpost of primitive galaxies in formation (Partridge & Peebles 1967) Past optical and X-ray work show the Lyα emission is not powered by AGN (Malhotra et al. 2003; Dawson et al. 2004). Past optical and X-ray work show the Lyα emission is not powered by AGN (Malhotra et al. 2003; Dawson et al. 2004). Lyα too narrow to be Type I (broad-lined) AGN Lyα too narrow to be Type I (broad-lined) AGN Chandra data show no X-ray detections of 49 LAEs, so Type II AGN ruled out Chandra data show no X-ray detections of 49 LAEs, so Type II AGN ruled out

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)4 Large Area Lyman Alpha (LALA) Survey LALA began in 1998 at KPNO (Rhoads et al. 2000) LALA began in 1998 at KPNO (Rhoads et al. 2000) Final area of 0.72 deg 2 in two fields, Boötes (14:25:57 +35:32) and Cetus (02:05:20 -04:55). Final area of 0.72 deg 2 in two fields, Boötes (14:25:57 +35:32) and Cetus (02:05:20 -04:55). This survey includes broad and narrow band imaging, as well as spectroscopic data on LAEs. This survey includes broad and narrow band imaging, as well as spectroscopic data on LAEs. Spectroscopic success rate of up to 70% Spectroscopic success rate of up to 70% This survey represents ~ 40 nights on the Kitt Peak 4m, 8 nights on Keck, 7 nights (so far) on the MMT, and ongoing programs at the Magellan Observatory. This survey represents ~ 40 nights on the Kitt Peak 4m, 8 nights on Keck, 7 nights (so far) on the MMT, and ongoing programs at the Magellan Observatory. 12+ published papers 12+ published papers

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)5 What is causing the emission? EW ~ 80 Å for a normal stellar population EW ~ 80 Å for a normal stellar population Malhotra and Rhoads (2002) found numerous LAEs with EWs > 200 Å Malhotra and Rhoads (2002) found numerous LAEs with EWs > 200 Å Large EW could be produced via star formation if the stellar photospheres were hotter than normal Large EW could be produced via star formation if the stellar photospheres were hotter than normal – Could be true in: Low metallicity galaxies Low metallicity galaxies Galaxies with an extreme IMF Galaxies with an extreme IMF Both scenarios possible in primitive galaxies, which contain young stars and little dust Both scenarios possible in primitive galaxies, which contain young stars and little dust EW could be enhanced from the geometry of the ISM EW could be enhanced from the geometry of the ISM – Dusty clouds embedded in a tenuous inter-cloud medium

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)6 Dusty Scenario If the dust is primarily in cold neutral clouds: If the dust is primarily in cold neutral clouds: Lyα photons scatter of the clouds and spent most of their time in the inter-cloud medium Lyα photons scatter of the clouds and spent most of their time in the inter-cloud medium  ICM hot, mainly ionized Continuum photons penetrate deep into the clouds and suffer greater extinction (Neufeld 1991; Hansen & Oh 2006) Continuum photons penetrate deep into the clouds and suffer greater extinction (Neufeld 1991; Hansen & Oh 2006) ISM of our Galaxy is known to be clumpy down to small scales ISM of our Galaxy is known to be clumpy down to small scales If the continuum is more absorbed than the Lyα photons, than the transmitted EW is larger than the source EW If the continuum is more absorbed than the Lyα photons, than the transmitted EW is larger than the source EW

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)7 Dusty Scenario Continuum Photons To Observer (Neufeld 1991)

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)8 Dusty Scenario Lyman α Photons To Observer (Neufeld 1991)

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)9 MMT Goals The colors of these galaxies might distinguish the cause of the large EW The colors of these galaxies might distinguish the cause of the large EW Blue colors would indicate young stars with hot photospheres Blue colors would indicate young stars with hot photospheres Red colors would indicate dust quenching of the continuum, enhancing the Lyα EW Red colors would indicate dust quenching of the continuum, enhancing the Lyα EW Our goal was to obtain deep broadband imaging in the g’, r’, i’ and z’ bands in order to distinguish between the two scenarios for the cause of the large EW. Our goal was to obtain deep broadband imaging in the g’, r’, i’ and z’ bands in order to distinguish between the two scenarios for the cause of the large EW. Observations were of the LALA Cetus Field Observations were of the LALA Cetus Field z = 4.5 z = 4.5 We used this data to study the continuum properties of individual LAEs at this redshift for the first time. We used this data to study the continuum properties of individual LAEs at this redshift for the first time.

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)10 Observations We observed with Megacam at the MMT on three whole nights from 11/3/05 – 11/5/05, and on four 1 / 4 nights from 1/1/06 – 1/4/06. We observed with Megacam at the MMT on three whole nights from 11/3/05 – 11/5/05, and on four 1 / 4 nights from 1/1/06 – 1/4/06. Total exposure times were: Total exposure times were: g’: 4.33 hours 3σ detection = g’: 4.33 hours 3σ detection = r’: 3.50 hours 3σ detection = r’: 3.50 hours 3σ detection = i’: 4.78 hours 3σ detection = i’: 4.78 hours 3σ detection = z’: 5.33 hours 3σ detection = z’: 5.33 hours 3σ detection = 24.78

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)11 Data Reduction We developed a pipeline using the MSCRED (Valdes & Tody 1998; Valdes 1998) and MEGARED (McLeod) packages in IRAF (Tody 1986, 1993), along with the image combining software SWarp (Bertin). We developed a pipeline using the MSCRED (Valdes & Tody 1998; Valdes 1998) and MEGARED (McLeod) packages in IRAF (Tody 1986, 1993), along with the image combining software SWarp (Bertin). We gave SWarp an input weight map which flagged the MEGARED bad pixels and cosmic rays We gave SWarp an input weight map which flagged the MEGARED bad pixels and cosmic rays Photometric zeropoints calculated in each band using standard stars from Landolt (1992). Photometric zeropoints calculated in each band using standard stars from Landolt (1992). – Used transforms to SDSS bands from Fukugita et al. (1996).

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)12 Lyα Galaxy Selection We used narrow band images from LALA to find LAEs at z ~ 4.5 We used narrow band images from LALA to find LAEs at z ~ 4.5 – 5 filters: λλ6559,6611,6650,6695,6730 – FWHM = 80Å – Redshift coverage 4.37 < z < 4.57 Also used broadband data from the NOAO Deep Wide- Field Survey (Jannuzi & Dey 1999). Also used broadband data from the NOAO Deep Wide- Field Survey (Jannuzi & Dey 1999). – Bw, R & I Used SExtractor (Bertin & Arnouts 1996) to identify the objects and perform photometry Used SExtractor (Bertin & Arnouts 1996) to identify the objects and perform photometry The Megacam data was registered and remapped onto the same grid as the narrow band data (0.26 “/pixel). The Megacam data was registered and remapped onto the same grid as the narrow band data (0.26 “/pixel). SExtractor used a nine pixel (2.32”) aperture SExtractor used a nine pixel (2.32”) aperture

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)13 Lyα Galaxy Selection Lyα galaxy detection criteria: Lyα galaxy detection criteria: – 5σ significance detection in the narrowband Calculated using a SExtractor aperture flux with the associated flux error: flux/error ≤ 5. Calculated using a SExtractor aperture flux with the associated flux error: flux/error ≤ 5. – 4σ significant excess of narrowband flux Calculated via (narrow flux – broad flux)/sqrt(error n 2 + error b 2 ) ≥ 4. Calculated via (narrow flux – broad flux)/sqrt(error n 2 + error b 2 ) ≥ 4. – Factor of ≥ 2 ratio between narrow and broad band flux densities. – No more than 2σ significant flux in the B w filter.

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)14 Results 98 galaxies met our detection criteria within the 24’ x 24’ Megacam field of view 98 galaxies met our detection criteria within the 24’ x 24’ Megacam field of view 22 of those had ≥ 2σ detections in two of the r’, i’ or z’ bands. 22 of those had ≥ 2σ detections in two of the r’, i’ or z’ bands. – 14 of the 22 galaxies have Magellan – IMACS spectra 7 of these have confirmed Lyα lines putting the galaxies at z ~ of these have confirmed Lyα lines putting the galaxies at z ~ 4.5 – Other 7 do not show a strong Lyα line, but 3-4 of these may with deeper spectra – 12 of the 22 galaxies detected in the H0 (6559 Å) filter, 6 in H8 (6650 Å) and 4 in H16 (6730 Å)

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)15 i’ Band Examples Cetus 86 z = Cetus 23 z = 4.392

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)16 Cetus Field i’ band

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)17 EW Distribution All EW reported are rest- frame These are photometric EW using the narrowband from KPNO and the broad band from the MMT These are photometric EW using the narrowband from KPNO and the broad band from the MMT EW calculated as the ratio of the line flux to the continuum flux density EW calculated as the ratio of the line flux to the continuum flux density Normal stellar population: EW ~ 80 Å Data range 106 < EW < 202 Å Object with EW = 23 Å is likely interloper Data shown is only the 22 high- quality galaxies, the other 76 we detected will tend to lie at higher EWs Implies something is causing EW to be higher than “normal” Massive stars or dust enhancement?

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)18 Stellar Population Models Bruzual and Charlot (2003) (BC03) Bruzual and Charlot (2003) (BC03) Model Parameters: Model Parameters: Age: 10 6 – 10 9 years Age: 10 6 – 10 9 years Metallicity:.02*Solar – Solar Metallicity:.02*Solar – Solar Lyα emission: Calculated from the number of ionizing photons produced from a given stellar population Lyα emission: Calculated from the number of ionizing photons produced from a given stellar population SFR: Exponential Decay SFR: Exponential Decay  Tau = 10 3 years (Instantaneous burst)  Tau = 10 7 years  Tau = 10 8 years  Tau = 2*10 9 years (Continuous SF) Calzetti Law (1994) dust extinction (0-2 mags at 1200 Å) Calzetti Law (1994) dust extinction (0-2 mags at 1200 Å)  Applied only to the continuum light (i.e. not the Lyα emission) in order to model the clumpy dust scenario. IGM Absorption via Madau (1995) IGM Absorption via Madau (1995)

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)19 r’-i’ Color Distribution

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)20 Color-Color Plot Model tracks run from A dust = 0-2 Model tracks run from A dust = 0-2 Dotted line connects zero dust end of models Dotted line connects zero dust end of models All models are.02*solar metallicity All models are.02*solar metallicity

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)21 Color – Color Plot Three groups identified: Three groups identified: – Group of intrinsically blue objects Located below dotted line Located below dotted line Young hot stars, homogeneous dust suppresses both line and continuum Young hot stars, homogeneous dust suppresses both line and continuum – Group of objects with EW enhanced via dust Upper-right 4-6 objects Upper-right 4-6 objects High EW + red colors High EW + red colors – A few objects which are older with lower EW Objects at r’-i’~1, with r’-nb~ Objects at r’-i’~1, with r’-nb~ Conclusion: We see both scenarios, future work will determine the likelihood of each scenario in a given galaxy. Conclusion: We see both scenarios, future work will determine the likelihood of each scenario in a given galaxy.

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)22 Work In Progress We plan to fit the 22 individual LAEs to BC03 models to determine: We plan to fit the 22 individual LAEs to BC03 models to determine: Age Age Mass Mass Metallicity Metallicity Star formation history Star formation history Dust content Dust content Stacking analysis of 76 other galaxies Stacking analysis of 76 other galaxies

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)23 SWIRC Three full nights, May 15-17, 2006 Three full nights, May 15-17, 2006 Goal: Obtain NIR broadband photometry of LAEs in the LALA Boötes Field. Goal: Obtain NIR broadband photometry of LAEs in the LALA Boötes Field. So far: 3 objects detected in J band, 1 in H band So far: 3 objects detected in J band, 1 in H band

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)24 Future Work We plan to do a similar analysis with broadband data for the Boötes Field We plan to do a similar analysis with broadband data for the Boötes Field Using broadband photometry from the KPNO 4m and the NIR data from SWIRC Using broadband photometry from the KPNO 4m and the NIR data from SWIRC Larger wavelength baseline, more accurately determine existence of dusty scenario Larger wavelength baseline, more accurately determine existence of dusty scenario Continue work out to higher redshifts Continue work out to higher redshifts z = 5.7 z = 5.7 z = 6.5 z = 6.5

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)25 The End This work was supported by the ASU/NASA Space Grant and the ASU Dept. of Physics and Astronomy. This work was supported by the ASU/NASA Space Grant and the ASU Dept. of Physics and Astronomy. Abbreviated References Abbreviated References – Bruzual, G. & Charlot, S. 2003, MNRAS, 344, 1000 – Dawson, S. et al. 2004, ApJ, 617, 707 – Hansen, M., & Oh, S. P. 2006, MNRAS, 367, 979 – Malhotra, S. et al. 2003, ApJ, 585, L25 – Malhotra, S. & Rhoads, J.E. 2002, ApJ, 565, L71 – Neufeld, D.A. 1991, ApJ, 370, L85 – Papovich, C., Dickinson, M. & Ferguson, H. C. 2001, ApJ, 559, 620 – Partridge, R.B. & Peebles, P.J.E. 1967, ApJ, 147, 868 – Rhoads, J.E. et al. 2000, ApJ, 545, L85

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)26 Abstract Lyman alpha emission lines from high redshift galaxies often show equivalent widths beyond those expected for normal stellar populations. Spectroscopy and x-ray photometry of these galaxies demonstrates that the Lyman alpha emission is predominantly powered by star formation rather than by accretion power. To explain the largest equivalent widths then requires either (a) unusually hot stellar populations, as might be expected from a top heavy initial mass function or from low stellar metallicity; or (b) differences in the radiative transfer of Lyman alpha and continuum photons, which could allow Lyman alpha photons to escape even while continuum light is suppressed by dust. Lyman alpha emission lines from high redshift galaxies often show equivalent widths beyond those expected for normal stellar populations. Spectroscopy and x-ray photometry of these galaxies demonstrates that the Lyman alpha emission is predominantly powered by star formation rather than by accretion power. To explain the largest equivalent widths then requires either (a) unusually hot stellar populations, as might be expected from a top heavy initial mass function or from low stellar metallicity; or (b) differences in the radiative transfer of Lyman alpha and continuum photons, which could allow Lyman alpha photons to escape even while continuum light is suppressed by dust. Broad band colors can be used to distinguish between these two scenarios, because hot photospheres will result in a blue continuum while dust absorption will redden the escaping continuum light. We have used Megacam on the MMT to obtain broad band colors of about 100 Lyman alpha galaxies. We will present our photometry and compare it with model colors expected under these two alternative scenarios. Broad band colors can be used to distinguish between these two scenarios, because hot photospheres will result in a blue continuum while dust absorption will redden the escaping continuum light. We have used Megacam on the MMT to obtain broad band colors of about 100 Lyman alpha galaxies. We will present our photometry and compare it with model colors expected under these two alternative scenarios.

MMT Symposium June 14th, 2006 Steven Finkelstein (ASU)27 LALA Publications First Results from the Large Area Lyman Alpha Survey; Rhoads, J. E. et al First Results from the Large Area Lyman Alpha Survey; Rhoads, J. E. et al Lyman Alpha Emitters at Redshift z=5.7; Rhoads, J. E. and Malhotra, S Lyman Alpha Emitters at Redshift z=5.7; Rhoads, J. E. and Malhotra, S Large Equivalent Width Lyman-alpha Line Emission at z=4.5: Young Galaxies in a Young Universe; Malhotra, S. & Rhoads, J. E Large Equivalent Width Lyman-alpha Line Emission at z=4.5: Young Galaxies in a Young Universe; Malhotra, S. & Rhoads, J. E Spectroscopic Confirmation of Three Redshift z~5.7 Lyman-Alpha Emitters from the Large-Area Lyman Alpha Survey; Rhoads, J. E. et al Spectroscopic Confirmation of Three Redshift z~5.7 Lyman-Alpha Emitters from the Large-Area Lyman Alpha Survey; Rhoads, J. E. et al No X-Ray-bright Type II Quasars among the Lyman-Alpha Emitters; Malhotra, S. et al No X-Ray-bright Type II Quasars among the Lyman-Alpha Emitters; Malhotra, S. et al A Luminous Lyman-alpha Emitting Galaxy at Redshift z=6.535: Discovery and Spectroscopic Confirmation; Rhoads, J. E. et al A Luminous Lyman-alpha Emitting Galaxy at Redshift z=6.535: Discovery and Spectroscopic Confirmation; Rhoads, J. E. et al X-ray Nondetection of the Lyman alpha Emitters at z~4.5; Wang, J. et al X-ray Nondetection of the Lyman alpha Emitters at z~4.5; Wang, J. et al Spectroscopic Properties of the z=4.5 Lyman Alpha Emitters; Dawson, S. et al Spectroscopic Properties of the z=4.5 Lyman Alpha Emitters; Dawson, S. et al ks Chandra Exposure of the LALA Boötes Field: X-ray Source Catalog; Wang, J. et al ks Chandra Exposure of the LALA Boötes Field: X-ray Source Catalog; Wang, J. et al 2004 Luminosity Functions of Lyman alpha Emitters at Redshift z=6.5 and z=5.7: Evidence Against Reionization at z=6; Malhotra, S. & Rhoads, J. E Luminosity Functions of Lyman alpha Emitters at Redshift z=6.5 and z=5.7: Evidence Against Reionization at z=6; Malhotra, S. & Rhoads, J. E A Luminous Lyman alpha Emitting Galaxy at Redshift z = 6.535: Discovery and Spectroscopic Confirmation; Rhoads, J. E. et al A Luminous Lyman alpha Emitting Galaxy at Redshift z = 6.535: Discovery and Spectroscopic Confirmation; Rhoads, J. E. et al The Volume Fraction of Ionized Intergalactic Gas at Redshift z = 6.5; Malhotra, S. & Rhoads, J. E The Volume Fraction of Ionized Intergalactic Gas at Redshift z = 6.5; Malhotra, S. & Rhoads, J. E Physical Properties of Lyman Alpha Emitting Galaxies at z ~ 4.5; Finkelstein, S. L. et al. in preparation Physical Properties of Lyman Alpha Emitting Galaxies at z ~ 4.5; Finkelstein, S. L. et al. in preparation