Luminosity Functions beyond the spectroscopic limit. I. Method and near-infrared LFs in the HDF-N and HDF-S

We have developed a Monte Carlo method to compute the luminosity function of galaxies, based on photometric redshifts, which takes into account the non-gaussianity of the probability functions, and the presence of degenerate solutions in redshift. In this paper we describe the method and the mock tests performed to check its reliability. The NIR luminosity functions and the redshift distributions are determined for near infrared subsamples on the HDF-N and HDF-S. The results on the evolution of the NIR LF, the stellar mass function, and the luminosity density, are presented and discussed in view of the implications for the galaxy formation models. The main results are the lack of substantial evolution of the bright end of the NIR LF and the absence of decline of the luminosity density up to a redshift z ~ 2, implying that most of the stellar population in massive galaxies was already in place at such redshift.Comment: 23 pages, 19 figures. Accepted for publication in A&A. No change

Stellar populations and Lyman-alpha emission from lensed z > 6 galaxies

We present results from an SED analysis of two lensed high-z objects, the z=6.56 galaxy HCM6A behind the cluster Abell 370 discovered by Hu et al. (2002) and the triple arc at z~7 behind Abell 2218 found by Kneib et al. (2004). For HCM 6A we find indications for the presence of dust in this galaxy, and we estimate the properties of its stellar populations (SFR, age, etc.), and the intrinsic Lyman-alpha emission. From the "best fit" reddening (E(B-V)~0.25) its estimated luminosity is L~(1-4)e.+11 Lsun, in the range of luminous infrared galaxies. For the arc behind Abell 2218 we find a most likely redshift of z~6.0-7.2 taking into account both our photometric determination and lensing considerations. SED fits indicate generally a low extinction but do not strongly constrain the SF history. Best fits have typical ages of ~3 to 400 Myr. The apparent 4000 Ang break observed recently by Egami et al. (2004) from combination of IRAC/Spitzer and HST observations can also well be reproduced with templates of young populations (~15 Myr or even younger) and does not necessarily imply old ages. Finally, we briefly examine the detectability of dusty lensed high-z galaxies with Herschel and ALMA.Comment: To appear in "Impact Of Gravitational Lensing On Cosmology", IAU Symposium 225, Eds. Y. Mellier and G. Meyla

Stellar populations and Lya emission in two lensed z>~6 galaxies

We present an analysis of two strongly lensed galaxies at z=6.56 and z ~ 7 for which multi-band photometric and spectroscopic observations are available. For one source the data include recent HST and Spitzer observations. Using an SED fitting technique considering a number of parameters we attempt to constrain the properties of their stellar populations and their intrinsic Lya emission. The following main results are obtained for the individual galaxies: * Triple arc in Abell 2218: The most likely redshift of this source is z ~ 6.0-7.2. SED fits indicate generally a low extinction but do not strongly constrain the star formation (SF) history. Best fits have typical ages of ~3 to 400 Myr. The apparent 4000Ang break observed recently from combination of IRAC/Spitzer and HST observations, can also equally well be reproduced with the template of a young (~3-5 Myr). The estimated SFR is typically ~1 Msun/yr, in agreement with previous estimates. The unknowns on the age and star formation history could easily explain the apparent absence of Lya in this galaxy. * Abell 370 HCM 6A: The available Lya and continuum observations indicate two possible solutions: 1) a young burst or ongoing constant SF with non-negligible extinction or 2) a composite young+"old" stellar population. In the first case one obtains a best fit A_V ~ 0.5-1.8 at a 1 sigma level. In consequence we obtain SFR ~ 11-41 Msun/yr, higher than earlier estimates, and we estimate a fairly high total luminosity (L ~ (1-4)*10^{11} Lsun) for this galaxy, in the range LIRG. A Lya transmission of ~23-90% is estimated from our best fit models. Other properties remain largely unconstrained. In case of composite stellar populations the SFR, mass, and luminosity estimate is lower. The two scenarios may be distinguishable with IRAC/Spitzer observations at 3.6 and 4.5 micron.Comment: 12 pages, 9 figures, MNRAS, in pres

Observing the first galaxies - a case for an intermediate resolution multi-object IR spectrograph

We present a special science case for an intermediate resolution multi-object IR spectrograph for the VLT. We have constructed new models for massive Population III stars and metal-free stellar populations (see Schaerer 2001). The properties of individual stars and integrated populations, including their ionising fluxes and SEDs are discussed. We also study their dependence on the poorly known IMF and the star formation history. The synthetic spectra are used to simulate spectroscopic observations of the expected emission lines of Pop III galaxies. We show that such an instrument should allow the detection and efficient observations of the first galaxies with the VLT.Comment: To appear in "Scientific Drivers for ESO Future VLT/VLTI Instrumentation", J. Bergeron and G. Monnet, Eds., Springer Verlag. Related preprints and models also available at http://webast.ast.obs-mip.fr/people/schaerer