Star Forming Galaxies at z > 5

We present recent progress in searching for galaxies at redshift from z = 5 to z = 10. Wide-field and senstive surveys with 8m class telescopes have been providing more than several hundreds of star forming galaxies at z =5 - 7 that are probed in the optical window. These galaxies are used to study the early cosmic star formation activity as well as the early structure formation in the universe. Moreover, near infrared deep imaging and spectropscopic surveys have found probable candidates of galaxies from z = 7 to z = 10. Although these candidates are too faint to be identified unambiguously, we human being are now going to the universe beyond 13 billion light years, close to the epoch of first-generations stars; i.e., Population III stars. We also mention about challanges to find Population III-dominated galaxies in the early universe.Comment: 8 pages, no figure, Proceeding of IAU Symposium 250, in pres

Optimal slit orientation for long multi-object spectroscopic exposures

Historically, long-slit spectroscopic observations were carried out using the parallactic angle for the slit orientation if slit loss was an important consideration (either to maximize the signal-to-noise or to do spectrophotometry). This requires periodic realignment of the slit position angle as the parallactic angle changes. This is not possible for multi-slit observations where one slit position angle must be chosen for the entire exposure. Common wisdom suggests using the parallactic angle at the meridian (HA=0). In this paper, I examine what the best strategy is for long, multi-slit exposures. I find that in extreme cases (very long exposure time) the best choice is to orient the slit \emph{perpendicular} to the parallactic angle at the meridian. There are two effects to consider: the increasing dispersion with increasing airmass and the changing angle between the parallactic angle and the slit. In the case of \emph{traditional} slit orientation, the two effects amplify each other, thus rendering a significant fraction of the observation useless. Using the perpendicular orientation, the two processes work against each other, thus most of the observation remains useful. I will use, as an example, our 8 hour Lockman Hole observations using the Keck telescope, but generic methods are given to evaluate a particular observation. I also make the tools available to the community.Comment: Accepted by A&A (20/06/2005

Empowering Instructional Practices of Technology Using Teachers of Low-Income African American Students

The purpose of this case study was to investigate the empowering instructional practices of three technology-using teachers in an elementary school populated by low-income African American students. The participants, from Ladson ES, had been teaching a variety of grade levels and had between six and ten years of experience. Over the course of six months the researcher collected data including field observations, interviews, and artifact reviews, such as lesson plans and student assignments. Portions of frameworks of multicultural education, empowering education, and culturally relevant pedagogy were linked to examine and document the teachers’ instructional strategies and technology use as it related to empowerment education. Analysis occurred through an iterative process where data was coded and recoded until saturation was reached and themes emerged. Findings from this study indicated that teachers used technology and empowerment as a way to provide exposure, increase self-esteem, and prepare students for their futures. Through a variety of software tools and instructional practices, including cooperative groups, classroom roles, and student discussions students engaged in the learning process and teachers created an environment that was pleasant for student learning and engagement. Students were empowered in a variety of ways: through the use of videos to expose them to different cultures, building of confidence, and use of cooperative groups to help them learn how to work together. The results of this study indicate that teachers would benefit from training on how to integrate technology with multicultural education and how to further instruct for empowerment especially in elementary school classrooms. Additionally, the results also point out the need for more empowerment in classrooms for both teachers and students

IR Colors and Sizes of Faint Galaxies

We present J and Ks band galaxy counts down to J=24 and Ks=22.5 obtained with the new infrared imager/spectrometer, SOFI, at the ESO New Technology Telescope. The co-addition of short, dithered, images led to a total exposure time of 256 and 624 minutes respectively, over an area of $\sim20$ arcmin$^2$ centered on the NTT Deep Field. The total number of sources with S/N$>5$ is 1569 in the J sample and 1025 in the Ks-selected sample. These are the largest samples currently available at these depths. A d$logN$/d$m$ relation with slope of $\sim0.36$ in J and $\sim0.38$ in Ks is found with no evident sign of a decline at the magnitude limit. The observed surface density of ``small'' sources is much lower than ``large'' ones at bright magnitudes and rises more steeply than the large sources to fainter magnitudes. Fainter than $J\sim22.5$ and Ks$\sim21.5$, small sources dominate the number counts. Galaxies get redder in J-K down to J$\sim20$ and Ks$\sim19$. At fainter magnitudes, the median color becomes bluer with an accompanying increase in the compactness of the galaxies. We show that the blue, small sources which dominate the faint IR counts are not compatible with a high redshift ($z>1$) population. On the contrary, the observed color and compactness trends, together with the absence of a turnover at faint magnitudes and the dominance of small sources, can be naturally explained by an increasing contribution of sub-$L^*$ galaxies when going to fainter apparent magnitudes. Such evidence strongly supports the existence of a steeply rising ($\alpha\ll-1$) faint end of the local infrared luminosity function of galaxies - at least for luminosities $L<0.01L^*$.Comment: Accepted for publication on A&A; 15 pages, 13 figure

Properties of galaxies at the faint end of the Hα\alpha luminosity function at z∼0.62z\sim0.62

Studies measuring the star formation rate density, luminosity function, and properties of star-forming galaxies are numerous. However, it exists a gap at $0.5<z<0.8$ in H$\alpha$-based studies. Our main goal is to study the properties of a sample of faint H$\alpha$ emitters at $z\sim0.62$. We focus on their contribution to the faint end of the luminosity function and derived star formation rate density, characterising their morphologies and basic photometric and spectroscopic properties. We use a narrow-band technique in the near-infrared, with a filter centred at 1.06 $\mu$m. The data come from ultra-deep VLT/HAWK-I observations in the GOODS-S field with a total of 31.9 h in the narrow-band filter. We perform a visual classification of the sample and study their morphologies from structural parameters available in CANDELS. Our 28 H$\alpha$-selected sample of faint star-forming galaxies reveals a robust faint-end slope of the luminosity function $\alpha=-1.46_{-0.08}^{+0.16}$. The derived star formation rate density at $z\sim0.62$ is $\rho_\mathrm{SFR} = 0.036_{-0.008}^{+0.012} M_{\odot}~\mathrm{yr^{-1}~Mpc^{-3}}$. The sample is mainly composed of disks, but an important contribution of compact galaxies with S\'ersic indexes $n\sim2$ display the highest specific star formation rates. The luminosity function at $z\sim0.62$ from our ultra-deep data points towards a steeper $\alpha$ when an individual extinction correction for each object is applied. Compact galaxies are low-mass, low-luminosity, and starburst-dominated objects with a light profile in an intermediate stage from early to late types.Comment: Published in Astronomy & Astrophysics. 19 pages, 14 figures. New version includes language edited by the journa

The circumstellar environment of the YSO TMR-1 and a revisit to the candidate very low-mass object TMR-1C

TMR-1 (IRAS~04361+2547) is a class~I proto-stellar source located in the nearby Taurus star-forming region. Its circumstellar environment is characterized by extended dust emission with complex structures and conspicuous filaments. A faint companion, called TMR-1C, located near the proto-star had been detected in previous studies, but its nature as a very young substellar object remained inconclusive. To improve the constraints on the nature of TMR-1C, and to investigate the process of very low-mass star formation in the TMR-1 system we use very sensitive infrared imaging observations as well as NIR spectroscopy. We construct the SED of TMR-1C over a much larger wavelength range as had been possible in previous work and compare it with models of extincted background stars, young sub-stellar objects, and very low-mass stars with circumstellar disk and envelope emission. We also search for additional low-luminosity objects in the immediate environment of the TMR-1, study the surrounding NIR dust morphology, and analyse the emission line spectrum of a filamentary structure in the physical context of a bow-shock model. We find that the observed SED of TMR-1C is inconsistent with an extincted background star, nor can be fitted with available models for a young extremely low-mass (<12M_Jup) object. Our near-IR spectrum indicates an effective temperature of at least ~3000K. Based on a good match of TMR-1C's SED with radiation transfer models of young stellar objects with circumstellar disks, we propose that TMR-1C is most likely a very low-mass star with M~0.1-0.2M_sun surrounded by a circumstellar disk with high inclination, i>80deg. Moreover, we detect an additional very faint source, which we call TMR-1D, and that shows a quite striking symmetry in position with TMR-1C. TMR-1C and TMR-1D may have been formed from a common triggered star-formation event, caused by... (abstract abridged)Comment: 15 pages, 11 figures, accepted for publication in A&

The Galactic disk mass-budget : II. Brown dwarf mass-function and density

In this paper, we extend the calculations conducted previously in the stellar regime to determine the brown dwarf IMF in the Galactic disk. We perform Monte Carlo calculations taking into account the brown dwarf formation rate, spatial distribution and binary fraction. Comparison with existing surveys seems to exclude a power-law MF as steep as the one determined in the stellar regime below 1 \msol and tends to favor a more flatish behaviour. Comparison with methane-dwarf detections tends to favor an eventually decreasing form like the lognormal or the more general exponential distributions determined in the previous paper. We calculate predicting brown dwarf counts in near-infrared color diagrams and brown dwarf discovery functions. These calculations yield the presently most accurate determination of the brown dwarf census in the Galactic disk. The brown dwarf number density is comparable to the stellar one, $n_{BD}\simeq n_\star\simeq 0.1$ pc$^{-3}$. The corresponding brown dwarf mass density, however, represents only about 10% of the stellar contribution, i.e. \rho_{BD}\simle 5.0\times 10^{-3} \mvol. Adding up the local stellar density determined previously yields the density of star-like objects, stars and brown dwarfs, in the solar neighborhood \rho_\odot \approx 5.0\times 10^{-2} \mvol.Comment: 39 pages, Latex file, uses aasms4.sty, to be published in ApJ, corrected version with correct figure

A narrow-band search for Ly alpha emitting galaxies at z = 8.8

Aims: The first star forming galaxies in the early universe should be copious Ly alpha emitters, and may play a significant role in ionizing the intergalactic medium (IGM). It has been proposed that the luminosity function of Lya emitting galaxies beyond z~6 may be used to constrain the neutral fraction of the IGM during this epoch. In this work we report on a search for Ly alpha emitters at redshift 8.8. Methods: We performed a narrow band imaging programme using ISAAC at the ESO VLT. Seven fields, covering a total area of 31sq. arcmin and for which optical and broad band infra-red images have been obtained in the GOODS survey, were imaged to a limiting flux (respectively luminosity) of ~ 1.3 x 10^{-17} ergs.s^{-1}.cm^{-2} (respectively ~ 1.3 x 10^{43} ergs.s^{-1} in a narrow band filter centered in a region of low OH sky emission at 1.19 micron. Candidate Lyman alpha emitters are objects that are detected in the ISAAC NB images and undetected in the visible broad band images. Results: No z=8.8 Ly alpha emitting galaxies were detected to a limit approaching recent estimates of the luminosity function at z ~ 6. Our results do suggest, however, that detections or substantial constraints could be achieved by this method in the near future with larger field instruments planned for various telescopes.Comment: 7 pages, accepted for publication in A&

An Improved Red Spectrum of the Methane or T-dwarf SDSS 1624+0029: Role of the Alkali Metals

A Keck~II low resolution spectrum shortward of ome-micron is presented for SDSS 1624+0029, the first field methane or T dwarf discovered in the Sloan Digital Sky Survey. Significant flux is detected down to the spectrum's short wavelength limit of 6200\AA. The spectrum exhibits a broad absorption feature centered at 7700\AA, which we interpret as the K~I 7665/7699 resonance doublet. The observed flux declines shortward of 7000\AA, due most likely to the red wing of the Na~I doublet. Both Cs~I doublet lines are detected more strongly than in an earlier red spectrum. Neither Li~I absorption nor H$\alpha$ emission are detected. An exploratory model fit to the spectrum suggests that the shape of the red spectrum can be primarily accounted for by the broad wings of the K~I and Na~I doublets. This behavior is consistent with the argument proffered by Burrows, Marley and Sharp that strong alkali absorption is principally responsible for depressing T dwarf spectra shortward of 1$\mu$m. In particular, there seems no compelling reason at this time to introduce dust or an additional opacity source in the atmosphere of the SDSS object. The width of the K~I and strengths of the Cs~I lines also indicate that the Sloan object is warmer than Gl~229B.Comment: accepted March 3, 2000 for Ap.J. Letters, LaTeX, 2 figure