In this Paper we present the source catalog obtained from a 942 ks exposure of the Chandra Deep Field South (CDFS), using the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. Eleven individual pointings made between October 1999 and December 2000 were combined to generate the final image used for object detection. Catalog generation proceeded simultaneously using two different methods; a method of our own design using a modified version of the SExtractor algorithm, and a wavelet transform technique developed specifically for Chandra observations. The detection threshold has been set in order to have less than 10 spurious sources, as assessed by extensive simulations. We subdivided the catalog into four sections. The primary list consists of objects common to the two detection methods. Two secondary lists contain sources which were detected by: 1) the SExtractor algorithm alone and 2) the wavelet technique alone. The fourth list consists of possible diffuse or extended sources. The flux limits at the aimpoint for the soft (0.5-2 keV) and -2hard (2-10 keV) bands are 5.5×10 −17 erg s −1 cm −2 and 4.5×10 −16 erg s −1 cm −2 respectively. The total number of sources is 346; out of them, 307 were detected in the 0.5-2 keV band, and 251 in the 2-10 keV band.We also present optical identifications for the catalogued sources. Our primary optical data is R band imaging from VLT/FORS1 to a depth of R ∼ 26.5 (Vega). In regions of the field not covered by the VLT/FORS1 deep imaging, we use R-band data obtained with the Wide Field Imager (WFI) on the ESO-MPI 2.2m, as part of the ESO Imaging Survey (EIS), which covers the entire X-ray survey. We found that the FORS1/Chandra offsets are small, ∼ 1 ′′ . Coordinate cross-correlation finds 85% of the Chandra sources covered by FORS1 R to have counterparts within the 3σ error box ( 1.5 ′′ depending on off-axis angle and signal-to-noise). The unidentified fraction of sources, approximately ∼ 10-15%, is close to the limit expected from the observed X-ray flux to R-band ratio distribution for the identified sample.

We studied Lyman-α (Lyα) escape in a statistical sample of 43 Green Peas with HST/COS Lyα spectra. Green Peas are nearby star-forming galaxies with strong [OIII]λ5007 emission lines. Our sample is four times larger than the previous sample and covers a much more complete range of Green Pea properties. We found that about 2/3 of Green Peas are strong Lyα line emitters with rest-frame Lyα equivalent width > 20Å. The Lyα profiles of Green Peas are diverse. The Lyα escape fraction, defined as the ratio of observed Lyα flux to intrinsic Lyα flux, shows anti-correlations with a few Lyα kinematic features -both the blue peak and red peak velocities, the peak separations, and FWHM of the red portion of the Lyα profile. Using properties measured from SDSS optical spectra, we found many correlations -Lyα escape fraction generally increases at lower dust reddening, lower metallicity, lower stellar mass, and higher [OIII]/[OII] ratio. We fit their Lyα profiles with the HI shell radiative transfer model and found Lyα escape fraction anti-correlates with the best-fit N HI . Finally, we fit an empirical linear relation to predict f Lyα esc from the dust extinction and Lyα red peak velocity. The standard deviation of this relation is about 0.3 dex. This relation can be used to isolate the effect of IGM scatterings from Lyα escape and to probe the IGM optical depth along the line of sight of each z > 7 Lyα emission line galaxy in the JWST era.

We present Keck Low Resolution Imaging Spectrometer optical spectra of 17 Ly-emitting galaxies and one Lyman break galaxy at z % 4:5 discovered in the Large Area Lyman Alpha survey. The survey has identified a sample of $350 candidate Ly-emitting galaxies at z % 4:5 in a search volume of 1:5 ; 10 6 comoving Mpc 3 . We targeted 25 candidates for spectroscopy; hence, the 18 confirmations presented herein suggest a selection reliability of 72%. The large equivalent widths (median W rest k % 80 8) but narrow physical widths (Áv < 500 km s À1 ) of the Ly emission lines, along with the lack of accompanying high-ionization state emission lines, suggest that these galaxies are young systems powered by star formation rather than by active galactic nucleus activity. Theoretical models of galaxy formation in the primordial universe suggest that a small fraction of Ly-emitting galaxies at z % 4:5 may still be nascent, metal-free objects. Indeed, we find with 90% confidence that three to five of the confirmed sources show W rest k > 240 8, exceeding the maximum Ly equivalent width predicted for normal stellar populations. Nonetheless, we find no evidence for He ii k1640 emission in either individual or composite spectra, indicating that although these galaxies are young, they are not truly primitive, Population III objects.

We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for z ∼ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg 2 COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE) candidates at z = 6.9 in the central 2-deg 2 region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function can be described as a Schechter function modified by a significant excess at the bright end (4 galaxies with L Lyα ∼ 10 43.4±0.2 erg s −1 ). The number density at L Lyα ∼ 10 43.4±0.2 erg s −1 is little changed from z = 6.6, while at fainter L Lyα it is substantially reduced. Overall, we see a fourfold reduction in Lyα luminosity density from z = 5.7 to 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of ∼ 3 suppression of Lyα by radiative transfer through the z ∼ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction x HI ∼ 0.4-0.6 (assuming Lyα velocity offsets of 100-200 km s −1 ). The changing shape of the Lyα luminosity function between z 6.6 and z = 6.9 supports the hypothesis of ionized bubbles in a patchy reionization at z ∼ 7.

We present a catalog of 59 z % 4:5 Ly -emitting galaxies spectroscopically confirmed in a campaign of Keck DEIMOS follow-up observations to candidates selected in the Large Area Ly (LALA) narrowband imaging survey. We targeted 97 candidates for spectroscopic follow-up; by accounting for the variety of conditions under which we performed spectroscopy, we estimate a selection reliability of $76%. Together with our previous sample of Keck LRIS confirmations, the 59 sources confirmed herein bring the total catalog to 73 spectroscopically confirmed z % 4:5 Lyemitting galaxies in the %0.7 deg 2 covered by the LALA imaging. As with the Keck LRIS sample, we find that a nonnegligible fraction of the confirmed Ly lines have rest-frame equivalent widths (W rest k ) that exceed the maximum predicted for normal stellar populations: 17%Y31% (93% confidence) of the detected galaxies show W rest k > 190 8, and 12%Y27% (90% confidence) show W rest k > 240 8. We construct a luminosity function of z % 4:5 Ly emission lines for comparison to Ly luminosity functions spanning 3:1 < z < 6:6. We find no significant evidence for Ly luminosity function evolution from z % 3 to z % 6. This result supports the conclusion that the intergalactic medium remains largely reionized from the local universe out to z % 6:5. It is somewhat at odds with the pronounced drop in the cosmic star formation rate density recently measured between z $ 3 and z $ 6 in continuum-selected Lyman-break galaxies, and therefore potentially sheds light on the relationship between the two populations.

The cosmological star formation rate in the combined Chandra Deep Fields North and South is derived from our X-ray luminosity function for galaxies in these deep fields. Mild evolution is seen up to redshift order unity with star formation rate $ (1 þ z) 2:7 . This is the first directly observed normal star-forming galaxy X-ray luminosity function (XLF) at cosmologically interesting redshifts (z > 0). This provides the most direct measure yet of the X-ray-derived cosmic star formation history of the universe. We make use of Bayesian statistical methods to classify the galaxies and the two types of active galactic nuclei (AGNs), finding the most useful discriminators to be the X-ray luminosity, X-ray hardness ratio, and X-ray to optical flux ratio. There is some residual AGN contamination in the sample at the bright end of the luminosity function. Incompleteness slightly flattens the XLF at the faint end of the luminosity function. The XLF has a lognormal distribution and agrees well with the radio and infrared luminosity functions. However, the XLF does not agree with the Schechter luminosity function for the H LF, indicating that, as discussed in the text, additional and different physical processes may be involved in the establishment of the lognormal form of the XLF. The agreement of our star formation history points with the other star formation determinations in different wavebands (IR, radio, H ) gives an interesting constraint on the initial mass function (IMF). The X-ray emission in the Chandra band is most likely due to binary stars, although X-ray emission from nonstellar sources (e.g., intermediate-mass black holes and/or low-luminosity AGNs) remains a possibility. Under the assumption that it is due to binary stars, the overall consistency and correlations between single-star effects and binary-star effects indicate that not only is the one-parameter IMF (M ) constant but also the bivariate IMF(M 1 , M 2 ) must be constant, at least at the high-mass end. Another way to put this, quite simply, is that X-ray observations may be measuring directly the binary-star formation history of the universe. X-ray studies will continue to be useful for probing the star formation history of the universe by avoiding problems of obscuration. Star formation may therefore be measured in more detail by deep surveys with future X-ray missions.

We present a redshift z = 6.535 galaxy discovered by its Lyman-α emission in a 9180Å narrowband image from the Large Area Lyman Alpha (LALA) survey. The Lyman-α line luminosity (1.1×10 43 erg s −1 ) is among the largest known for star forming galaxies at z ≈ 6.5. The line shows the distinct asymmetry that is characteristic of high-redshift Lyman-α. The 2σ lower bound on the observer-frame equivalent width is > 530Å. This is hard to reconcile with a neutral intergalactic medium unless the Lyman-α line is intrinsically strong and is emitted from its host galaxy with an intrinsic Doppler shift of several hundred km s −1 . If the IGM is ionized, it corresponds to a rest frame equivalent width > 40Å after correcting for Lyman-α forest absorption. We also present complete spectroscopic followup of the remaining candidates with line flux > 2×10 −17 erg cm −2 s −1 in our 1200✷ ′ narrowband image. These include another galaxy with a strong emission line at 9136Å and no detected continuum flux, which however is most likely an [O III] λ5007 source at z = 0.824 based on a weak detection of the [O III] λ4959 line.

Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Lyα emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts (z 0.05) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at z 0.05 (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broad band colors, and studied their properties with MMT spectroscopy. From the whole SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. (An additional 7 candidates are contaminants, and 4 remain without spectra.) These blueberries are dwarf starburst galaxies with very small sizes (< 1kpc), and very high ionization ([OIII]/[OII]∼ 10−60). They also have some of the lowest stellar masses (log(M/M ) ∼ 6.5−7.5) and lowest metallicities (7.1 < 12 + log(O/H) < 7.8) starburst galaxies. Thus they are small counterparts to green peas and high redshift Lyα emitting galaxies.