# Presentation: 116038

## Mass-to-light Ratio of Lyα Emitters: Implications of Lyα Surveys at Redshifts z=5.7, 6.5, 7, and 8.8

***Mass-to-light Ratio of Ly******α****** Emitters: Implications of Ly******α****** Surveys at Redshifts z=5.7, 6.5, 7, and 8.8***

***Elizabeth Fernandez and Eiichiro Komatsu***
***The University of Texas at Austin***
***beth@astro.as.utexas.edu***

**Introduction**
- There is now plentiful evidence for early star formation – from observations of a reionized universe at high redshifts to metals seen in the IGM to the Near Infrared Background.  Do these stars form galaxies that are bright enough to be seen today?  New powerful telescopes are now trying to locate galaxies at high redshifts (z=6-9) using Lyα surveys.  We present a simple and relatively model-independent way to calculate the luminosity function of high redshift galaxies and to interpret the results of these galaxy surveys.

**High Redshift Galaxy Surveys**
- We analyzed several high redshift, narrow-band Lyα surveys.  For the Subaru survey at z=5.7, 89 candidates were found, 63 were followed up with spectroscopy and 34 were confirmed as high redshift Lyα emitters.  The Subaru survey at z = 6.56 detected 58 candidates, 53 had follow up spectroscopy and 17 were confirmed.  LALA and the Subaru survey at z~7 each found one Lyα emitters, while ZEN and ISAAC ext found no galaxies.

**Formalism**
- The number of galaxies above the flux limitation of the survey (Flimit) is given by:

**The mass-to-”observed” light ratio**
- The mass to light ratio was varied and matched to the observed number of galaxies.  For the Subaru fields at z=5.7 and 6.56, enough galaxies were observed that the Schechter-fit for the luminosity function could be matched.  For the other fields, since only one (or no) galaxies were observed, we plot the number of galaxies expected for various values of Mh/Lband  to match observations.

- Subaru, z= 5.7    	Mh/Lband 95-120				LALA, z = 6.55	Mh/Lband ~160
- Subaru , z= 6.56    	Mh/Lband 85-100				Subaru, z = 7.025	Mh/Lband ~100
- Zen, z = 8.76		Mh/Lband > 7					ISAAC ext, z = 8.76	Mh/Lband > 3

**Abstract**
**We present a simple, relatively model-independent method to interpret the galaxy number count data at z>6.  The only free parameter is a mass-to-”observed light” ratio, M****h****/L****band****, where M****h**** refers to the total mass of the host halo, and L****band**** refers to the observed luminosity of the source.  For narrow-band surveys, L****band**** is simply related to the intrinsic Ly****α**** luminosity with a survival fraction of Ly****α** ** photons, ****α**e**sc****.  The  mass-to-”bolometric light”, M****h****/L****bol****, can also be found, once the metallicity and initial mass function of stellar populations are given.  We find constraints on the mass-to-light ratio of Ly****α** ** emitters from 5.7<z<8.8 of (M****h****/L****bol****) (****α****esc****ε****1/****γ****)=21-38, 14-26, and 9-17 for Z=0, 1/50, and 1 Z********, respectively, where ****ε**** is the duty cycle and ****γ**** is the local shape of the cumulative luminosity function, to which current data are sensitive. To interpret our results, we use ****ε****~1, which is allowed by the current data.  Therefore, Ly****α** **emitters are consistent with either starburst galaxies (M****h****/L****bol****~0.1-1) for reasonable values of the Ly****α**** survival fraction, ****α****esc****ε****1/****γ****~0.01-0.05, or normal populations (M****h****/L****bol****~10) if a good fraction of Ly****α**** photons survived.  We find no evidence for the end of reionization from current survey observations.  The data are consistent with no evolution of intrinsic properties of Ly****α**** emitters or neutral fraction in the intergalactic medium.  We also show that the lack of detections at z=8.8 does not rule out the high-z galaxies being the origin of the excess near infrared background.**

- The only unknown in this equation is Mh/Lband, which is the mass-to- “observed” light ratio.  All other quantities are known or depend on the survey properties.  Therefore, we treat Mh/Lband as a free parameter.

- Where dn/dMh is the Sheth and Tormen mass function and θ(Mh-Mmin) is zero if the halo mass is below a critical mass needed for star formation, Mmin, and 1 otherwise.  By relating the flux to the luminosity of the galaxy, we get:

- Luminosity of a sample cluster in erg s-1 Hz-1 M-1(see Fernandez & Komatsu, 2006).

**Results**
- By multiplying the fraction of light within the band by the Mh/Lband for each field, we obtain Mh/Lbol (αescε1/γ)-1 for each field.

**Conclusions**
- The inferred mass-to-light ratios are consistent with no evolution in the properties of Lyα emitters and the IGM over redshift, and do not provide evidence for the end of reionization. The galaxies found in these surveys can either be starburst galaxies (Mh/Lbol~1) in which only about 1-10% of Lyα photons have escaped, or a normal population (Mh/Lbol~10) in which all the Lyα photons have escaped.   For the Subaru fields at 5.7 and 6.56, we observe nearly a 40% decrease in Mh/Lbol (αescε1/γ)-1.  If this is indeed a real effect, this seems to imply either a larger αesc at high redshift, perhaps due to less dust content within the galaxies.  Alternatively, Lyα emitters could have been brighter in the past.

-  The mass spectra that were modeled were:

**The mass-to-bolometric light ratio**
- Mh/Lband is not a physical quantity, rather, the luminosity depends on the band of the survey.  To convert this to the bolometric mass to light ratio, we did two things
- 	- Model a stellar population (depending on mass spectrum and metallicity) to compare the bolometric luminosity with that in the band
- 	- Take into account the survival fraction of Lyα photons, αesc, which is the product of the fraction of photons that escape the halo, fesc, and the photons that are not destroyed in the IGM

- 1) Salpeter

- 2) Larson, with mc = 10 and 50 M

- 3) Top Heavy

- 4) Delta function at 300 M

-   The metallicities modeled were Z = 0, 1/50, and 1 Z

- Then the luminosity is integrated over the bandwidth and compared to the bolometric luminosity.  This allows us to convert from Lband to Lbol.

**References:**
- Cuby J.-G. et al. 2007, A&A, 461, 911
- Fernandez E., Komatsu E., 2006, ApJ, 646, 703
- Iye M. et al., 2006, Nat, 443,186
- Kashikawa N. et al. 2006, ApJ, 648, 7
- Rhoads J.E. et al. 2004, ApJ, 611, 59
- Shimasaku K. et al., 2006, PASJ, 58, 313
- Taniguchi Y. et al., 2005, PASJ, 57, 165
- Willis J.P., Courbin F., 2005, MNRAS 357,1348
- Willis J.P. et al., 2006, New Astronomy Reviews, 50, 70