Search

We present a search for extreme emission line galaxies (EELGs) at z, Accepted for publication in ApJ. 18 pages, 10 Figures, 2 Tables

We report on a search for ultraluminous Lyman alpha emitting galaxies (LAEs) at z=6.6 using the NB921 filter on Hyper Suprime-Cam on the Subaru telescope. We searched a 30 degree squared area around the North Ecliptic Pole, which we observed in broadband g', r', i', z', and y' and narrowband NB816 and NB921, for sources with NB921 < 23.5 and z' - NB921 > 1.3. This corresponds to a selection of log L(Ly-alpha) > 43.5 erg/s. We followed up seven candidate LAEs (out of thirteen) with the Keck DEIMOS spectrograph and confirmed five z=6.6 LAEs, one z=6.6 AGN with a broad Ly-alpha line and a strong red continuum, and one low-redshift ([OIII]5007) galaxy. The five ultraluminous LAEs have wider line profiles than lower luminosity LAEs, and one source, NEPLA4, has a complex line profile similar to that of COLA1. In combination with previous results, we show that the line profiles of the z=6.6 ultraluminous LAEs are systematically different than those of lower luminosity LAEs at this redshift. This result suggests that ultraluminous LAEs generate highly ionized regions of the intergalactic medium in their vicinity that allow the full Lyman alpha profile of the galaxy---including any blue wings---to be visible. If this interpretation is correct, then ultraluminous LAEs offer a unique opportunity to determine the properties of the ionized zones around them, which will help in understanding the ionization of the z ~ 7 intergalactic medium. A simple calculation gives a very rough estimate of 0.015 for the escape fraction of ionizing photons, but more sophisticated calculations are needed to fully characterize the uncertainties., Accepted for publication in ApJ. 13 pages, 13 figures

We use ultradeep 20 cm data from the Karl G. Jansky Very Large Array and 850 micron data from SCUBA-2 and the Submillimeter Array of an 124 arcmin^2 region of the Chandra Deep Field-north to analyze the high radio power (P_20cm>10^31 erg s^-1 Hz^-1) population. We find that 20 (42+/-9%) of the spectroscopically identified z>0.8 sources have consistent star formation rates (SFRs) inferred from both submillimeter and radio observations, while the remaining sources have lower (mostly undetected) submillimeter fluxes, suggesting that active galactic nucleus (AGN) activity dominates the radio power in these sources. We develop a classification scheme based on the ratio of submillimeter flux to radio power versus radio power and find that it agrees with AGN and star-forming galaxy classifications from Very Long Baseline Interferometry. Our results provide support for an extremely rapid drop in the number of high SFR galaxies above about a thousand solar masses per year (Kroupa initial mass function) and for the locally determined relation between X-ray luminosity and radio power for star-forming galaxies applying at high redshifts and high radio powers. We measure far-infrared (FIR) luminosities and find that some AGNs lie on the FIR-radio correlation, while others scatter below. The AGNs that lie on the correlation appear to do so based on their emission from the AGN torus. We measure a median radio size of 1.0+/-0.3 arcsecond for the star-forming galaxies. The radio sizes of the star-forming galaxies are generally larger than those of the AGNs., Published in ApJ. 10 pages, 8 figures

We present a flux-limited sample of $z\sim0.3$ Ly$\alpha$ emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism spectroscopic data. The published GALEX $z\sim0.3$ LAE sample is pre-selected from continuum-bright objects and thus is biased against high equivalent width (EW) LAEs. We remove this continuum pre-selection and compute the EW distribution and the luminosity function of the Ly$\alpha$ emission line directly from our sample. We examine the evolution of these quantities from $z\sim0.3$ to $2.2$ and find that the EW distribution shows little evidence for evolution over this redshift range. As shown by previous studies, the Ly$\alpha$ luminosity density from star-forming galaxies declines rapidly with declining redshift. However, we find that the decline in Ly$\alpha$ luminosity density from $z=2.2$ to $z=0.3$ may simply mirror the decline seen in the H$\alpha$ luminosity density from $z=2.2$ to $z=0.4$, implying little change in the volumetric Ly$\alpha$ escape fraction. Finally, we show that the observed Ly$\alpha$ luminosity density from AGNs is comparable to the observed Ly$\alpha$ luminosity density from star-forming galaxies at $z=0.3$. We suggest that this significant contribution from AGNs to the total observed Ly$\alpha$ luminosity density persists out to $z\sim2.2$., Comment: 27 pages, 19 figures, accepted for publication in ApJ

We obtained SMA observations of eight faint (intrinsic 850 $��$m fluxes $, 12 pages, 11 figures, ApJ in press

We present the results of SCUBA2 observations at 450 micron and 850 micron of the field lensed by the massive cluster A370. With a total survey area > 100 arcmin2 and 1 sigma sensitivities of 3.92 and 0.82 mJy/beam at 450 and 850 micron respectively, we find a secure sample of 20 sources at 450 micron and 26 sources at 850 micron with a signal-to-noise ratio > 4. Using the latest lensing model of A370 and Monte Carlo simulations, we derive the number counts at both wavelengths. The 450 micron number counts probe a factor of four deeper than the counts recently obtained from the Herschel Space Telescope at similar wavelengths, and we estimate that ~47-61% of the 450 micron extragalactic background light (EBL) resolved into individual sources with 450 micron fluxes greater than 4.5 mJy. The faint 450 micron sources in the 4 sigma sample have positional accuracies of 3 arcseconds, while brighter sources (signal-to-noise > 6 sigma) are good to 1.4 arcseconds. Using the deep radio map (1 sigma ~ 6 uJy) we find that the percentage of submillimeter sources having secure radio counterparts is 85% for 450 micron sources with intrinsic fluxes > 6 mJy and 67% for 850 micron sources with intrinsic fluxes > 4 mJy. We also find that 67% of the > 4 sigma 450 micron sources are detected at 850 micron, while the recovery rate at 450 micron of > 4 sigma 850 micron sources is 54%. Combined with the source redshifts estimated using millimetric flux ratios, the recovered rate is consistent with the scenario where both 450 micron and 20 cm emission preferentially select lower redshift dusty sources, while 850 micron emission traces a higher fraction of dusty sources at higher redshifts. [Abridge], 22 pages, 14 figures, ApJ in press. Minor changes to the submitted version

Current studies on Submillimeter Galaxies (SMGs) mostly focus on bright sources with 850 micron flux greater than 2 mJy, and the results have shown that they are likely high redshift mergers with z > 2 and could be a dominant population on star formation in the early Universe. However, bright SMGs only contributes 20-30% of the 850 micron extragalactic background light (EBL), meaning the bulk of the cosmic star formation still hidden by dust and our current understanding is biased. We have started a program to study an unbiased sample of highly-amplified and intrinsically faint SCUBA detected SMGs in the field of massive lensing clusters. Here we report the newly obtained SMA observations at 850 micron on one of our sample source, A2390-5, behind the massive lensing cluster A2390. We successfully detect the source with a flux of 3.95 mJy. Surprisingly, it does not have any counterpart in any other wavelengths even though there are tentative candidates, which implies a very dusty and high-z nature. With less than 1" positional accuracy and the adoption of z = 5, we obtain the amplification factor of 12 using current lensing model, which makes A2390-5 a faint SMG with a de-lensed flux of 0.33 mJy. Together with our previous detection on another faint SMG, both of them have no counterpart in other wavelengths and their properties are very different than previously thought from the single-dish data. We emphasize the importance of direct submillimeter high-resolution studies on faint SMGs, which could be the dominant population of the high-z star formation., 4 pages, 2 figures, Conference Proceedings for Galaxy Mergers in an Evolving Universe (GMiEU) at Hualien, Taiwan, on 10/23-28, 2011; Website: http://events.asiaa.sinica.edu.tw/workshop/20111023/

We present a study of three Lyman-alpha emitting galaxies (LAEs), selected via a narrow-band survey in the GOODS northern field, and spectroscopically confirmed to have redshifts of z ~ 5.65. Using HST ACS and Spitzer IRAC data, we constrain the rest-frame UV-to-optical spectral energy distributions (SEDs) of the galaxies. Fitting stellar population synthesis models to the observed SEDs, we find best-fit stellar populations with masses between ~ 10^9 - 10^10 M_sun and ages between ~ 5 - 100 Myr, assuming a simple starburst star formation history. However, stellar populations as old as 700 Myr are admissible if a constant star formation rate model is considered. Very deep near-IR observations may help to narrow the range of allowed models by providing extra constraints on the rest-frame UV spectral slope. Our narrow-band selected objects and other IRAC-detected z ~ 6 i'-dropout galaxies have similar 3.6 um magnitudes and z' - [3.6] colors, suggesting that they posses stellar populations of similar masses and ages. This similarity may be the result of a selection bias, since the IRAC-detected LAEs and i'-dropouts probably only sample the bright end of the luminosity function. On the other hand, our LAEs have blue i' - z' colors compared to the i'-dropouts, and would have been missed by the i'-dropout selection criterion. A better understanding of the overlap between the LAE and the i'-dropout populations is necessary in order to constrain the properties of the overall high-redshift galaxy population, such as the total stellar mass density at z ~ 6., Comment: 10 pages, 8 figures. Accepted for publication in ApJ

We analyze the Ly alpha forest properties of a sample of 15 high redshift quasars lying between z = 4.42 and z = 5.75, using high signal-to-noise spectra obtained with ESI on the Keck II 10 m telescope. The distribution of transmissions in the Ly alpha region in this redshift range is shown to be consistent with that found in lambda cold dark matter simulations with a smoothly evolving ionization rate as a function of redshift. The extrapolation of the ionizing flux to z = 6.05 lies a factor of two higher than a 2 sigma upper limit placed by Cen & McDonald (2001) at this redshift, based on the Becker et al. (2001) spectra of the z = 6.28 quasar SDSS 1030+0524. However, the data are also consistent with models in which there is substantial variation of the ionization parameter about the mean value, and in this case, dark gaps such as those seen by Becker et al. become much more likely. We conclude that further data are needed before we can be sure that we have seen the epoch of reionization. We also summarize the damped Ly alpha systems seen in these quasar lines of sight and measure their metallicities and kinematic properties. We argue that the mean DLA metallicity has dropped substantially by z = 5 compared with its value at z < 4., 17 pages, including 13 figures. Accepted for publication in Astronomical Journal (May 2002)

We report the discovery of a redshift z=6.56 galaxy lying behind the cluster Abell 370. The object HCM 6A was found in a narrowband imaging survey using a 118 Angstrom bandpass filter centered at 9152 Ang in the LRIS camera on the 10 m Keck II Telescope. Candidate Lyman alpha emitters were identified by the equivalent width of the emission and the absence of lower wavelength flux in ultradeep broadband images. HCM6A is the first galaxy to be confirmed at redshift z>6, and has W_lambda(observed)=190 Angstroms, flux = 2.7 x 10^-17 erg cm^-2 s^-1. Spectra obtained with LRIS confirm the emission line and the continuum break across the line, and show an asymmetric line profile with steep fall-off on the blue side. Deep Subaru near-infrared CISCO images in J, H and K' which extend the sampled continuum to longer wavelengths give a consistent estimate of the continuum flux density in these line-free regions of 2.6+/-0.7 x 10^-30 erg cm^-2 s^-1 Hz^-1. The line width and strength, asymmetric profile, and very deep spectral break are only consistent with the interpretation of the line as a redshifted Lyman alpha feature. From the detailed lensing model of this cluster, we estimate a lensing amplification of 4.5 for this galaxy, which is located slightly over an arcminute from the center of the cluster, for an unlensed flux of 6.5 x 10^-18 erg cm^-2 s^-1. The presence of such a galaxy suggests that the reionizing epoch is beyond z=6.6., 5 pages, 4 PostScript figures, uses emulateapj5, to appear in the April 1, 2002 issue of the Astrophysical Journal Letters

The rate of mass accumulation due to galaxy merging depends on the mass, density, and velocity distribution of galaxies in the near neighborhood of a host galaxy. The fractional luminosity in kinematic pairs combines all of these effects in a single estimator which is relatively insensitive to population evolution. Here we use a k-corrected and evolution compensated volume-limited sample drawing about 300 redshifts from CFGRS and 3000 from CNOC2 to measure the rate and redshift evolution of merging. We identify kinematic pairs with projected separations less than either 50 or 100 \hkpc and rest-frame velocity differences of less than 1000\kms. The fractional luminosity in pairs is modeled as f_L(Delta v,r_p,M_r^{ke})(1+z)^{m_L} where [f_L,m_L] are [0.14+/-0.07,0+/-1.4] and [0.37+/-0.7,0.1+/-0.5] for r_p= 0.2 M*) is 0.02+/-0.01(1+z)^{0.1+/-0.5} M*~Gyr^{-1}. Present day high-luminosity galaxies therefore have accreted approximately 0.15M* of their mass over the approximately 7 Gyr to redshift one. (abridged), accepted for publication in ApJ Letters

We report the discovery of an extremely luminous galaxy lying at a redshift of z=5.74, SSA22-HCM1. The object was found in narrowband imaging of the SSA22 field using a 105 Angstrom bandpass filter centered at 8185 Angstroms during the course of the Hawaii narrowband survey using LRIS on the 10 m Keck II Telescope, and was identified by the equivalent width of the emission W_lambda(observed)=175 Angstroms, flux = 1.7 x 10^{-17} erg cm^{-2} s^{-1}). Comparison with broadband colors shows the presence of an extremely strong break (> 4.2 at the 2 sigma level) between the Z band above the line, where the AB magnitude is 25.5, and the R band below, where the object is no longer visible at a 2 sigma upper limit of 27.1 (AB mags). These properties are only consistent with this object's being a high-z Ly alpha emitter. A 10,800 s spectrum obtained with LRIS yields a redshift of 5.74. The object is similar in its continuum shape, line properties, and observed equivalent width to the z=5.60 galaxy, HDF 4-473.0, as recently described by Weymann et al. (1998), but is 2-3 times more luminous in the line and in the red continuum. For H_0 = 65 km s^{-1} Mpc^{-1} and q_0 = (0.02, 0.5) we would require star formation rates of around (40, 7) solar masses per year to produce the UV continuum in the absence of extinction., 5 pages, 4 figures, Latex with emulateapj style file; to appear in the Astrophysical Journal (Letters)

We review the properties of z>5 galaxies studied with HST and with the Keck telescopes, and discuss the detectability of Lyman alpha emission-line galaxies out to z~6.5 based on these data and ongoing narrowband imaging surveys. The brightest sources may show (R-Z) color breaks, although the high sky background at Z (lambda_{eff} ~ 9200 Ang), makes such observations challenging for typical faint sources. Keck LRIS observations of the z=5 SDSS quasar and z>5 galaxies observed with HST in the HDF show that the strength of the Lyman break is evolving more slowly than extrapolations from models at z~3 would predict., 12 pages, 7 encapsulated PostScript figures, paspconf.sty. Invited review, to appear in "The Hy-Redshift Universe: Galaxy Formation and Evolution at High Redshift" held in Berkeley, June 21-24, 1999, eds. A.J. Bunker and W.J.M. van Breugel, A.S.P. Conf.Ser. in press (1999)

We have utilized various magnitude-limited samples drawn from an extremely deep and highly complete spectroscopic redshift survey of galaxies observed in seven colors in the Hawaii Survey Fields and the Hubble Deep Field to investigate the evolution of the universal rest-frame ultraviolet luminosity density from z = 1 to the present. The multi-color data (U', B, V, R, I, J, HK') enable the sample selection to be made in the rest-frame ultraviolet for the entire redshift range. Due to the large sample size and depth (U_{AB} = 24.75, B_{AB} = 24.75, I_{AB} = 23.5), we are able to accurately determine the luminosity density to z = 1. We do not confirm the very steep evolution reported by Lilly et al. (1996) but instead find a shallower slope, approximately (1+z)^{1.5} for q0 = 0.5, which would imply that galaxy formation is continuing smoothly to the present time rather than peaking at z = 1. Much of the present formation is taking place in smaller galaxies. Detailed comparisons with other recent determinations of the evolution are presented., 37 pages including 18 figures. Also available at http://www.ifa.hawaii.edu/~acowie/uvlum.html To be published in the August, 1999 Astronomical Journal (accepted April 22, 1999)

We describe narrowband and spectroscopic searches for emission-line star forming galaxies in the redshift range 3 to 6 with the 10 m Keck II Telescope. These searches yield a substantial population of objects with only a single strong (equivalent width >> 100 Angstrom) emission line, lying in the 4000 - 10,000 Angstrom range. Spectra of the objects found in narrowband-selected samples at lambda ~5390 Angstroms and ~6741 Angstroms show that these very high equivalent width emission lines are generally redshifted Lyman alpha 1216 Angstrom at z~3.4 and 4.5. The density of these emitters above the 5 sigma detection limit of 1.5 e-17 ergs/cm^2/s is roughly 15,000 per square degree per unit redshift interval at both z~3.4 and 4.5. A complementary deeper (1 sigma \~1.0 e-18 ergs/cm^2/s) slit spectroscopic search covering a wide redshift range but a more limited spatial area (200 square arcminutes) shows such objects can be found over the redshift range 3 to 6, with the currently highest redshift detected being at z=5.64. The Lyman alpha flux distribution can be used to estimate a minimum star formation rate in the absence of reddening of roughly 0.01 solar masses/Mpc^3/year (H_0 = 65 km/s/Mpc and q_0 = 0.5). Corrections for reddening are likely to be no larger than a factor of two, since observed equivalent widths are close to the maximum values obtainable from ionization by a massive star population. Within the still significant uncertainties, the star formation rate from the Lyman alpha-selected sample is comparable to that of the color-break-selected samples at z~3, but may represent an increasing fraction of the total rates at higher redshifts. This higher-z population can be readily studied with large ground-based telescopes., 7 pages, 5 encapsulated figures; aastex, emulateapj, psfig and lscape style files. Separate gif files for 2 gray-scale images also available at http://www.ifa.hawaii.edu/faculty/hu/emitters.html . Added discussion of foreground contaminants. Updated discussion of comparison with external surveys (Sec. 5 and Fig. 5). Note: continuum break strength limits (Fig. 3 caption) are correct here -- published ApJL text has a sign error

The recent discovery of carbon in close to half of the low neutral hydrogen column density [$N({\rm H~I}) > 3\ten{14}\cm2$] Lyman forest clouds toward $z \sim 3$ quasars has challenged the widely held view of this forest as a chemically pristine population uniformly distributed in the intergalactic medium, but has not eliminated the possibility that a primordial population might be present as well. Using extremely high signal-to-noise observations of a sample of quasars we now show that \ion{C}{4} can be found in 75% of clouds with $N({\rm H~I}) > 3\ten{14}\cm2$ and more than 90% of those with $N({\rm H~I}) > 1.6\ten{15}\cm2$. Clouds with $N({\rm H~I}) > 10^{15}\cm2$ show a narrow range of ionization ratios, spanning less than an order of magnitude in \ion{C}{4}/\ion{H}{1}, \ion{C}{2}/\ion{C}{4}, \ion{Si}{4}/\ion{C}{4} and \ion{N}{5}/\ion{C}{4}, and their line widths require that they be photoionized rather than collisionally ionized. This in turn implies that the systems have a spread of less than an order of magnitude in both volume density and metallicity. Carbon is seen to have a typical abundance of very approximately $10^{-2}$ of solar and Si/C about three times solar, so that the chemical abundances of these clouds are very similar to those of Galactic halo stars. \ion{Si}{4}/\ion{C}{4} decreases rapidly with redshift from high values ($> 0.1$) at $z > 3.1$, a circumstance which we interpret as a change in the ionizing spectrum as the intergalactic medium becomes optically thin to He$^+$\ ionizing photons. Weak clustering is seen in the \ion{C}{4} systems for $��v < 250\kms$, which we argue provides an upper limit to the clustering of \ion{H}{1} clouds. If the clouds are associated with galaxies, this requires a rapid evolution in galaxy clustering between $z = 3$ and $z = 0$., 31 pages plus 5 tables, 21 Postscript figures, Figures 1 and 2 available at http://www.ifa.hawaii.edu/faculty/acowie/igm_aj.html . To be published in Astronomical Journal

The complex problem of when and how galaxies formed has not until recently been susceptible of direct attack. It has been known for some time that the excessive number of blue galaxies counted at faint magnitudes implies that a considerable fraction of the massive star formation in the universe occurred at z < 3, but, surprisingly, spectroscopic studies of galaxies down to a B magnitude of 24 found little sign of the expected high-z progenitors of current massive galaxies, but rather, in large part, small blue galaxies at modest redshifts z \sim 0.3. This unexpected population has diverted attention from the possibility that early massive star-forming galaxies might also be found in the faint blue excess. From KECK spectroscopic observations deep enough to encompass a large population of z > 1 field galaxies, we can now show directly that in fact these forming galaxies are present in substantial numbers at B \sim 24, and that the era from redshifts 1 to 2 was clearly a major period of galaxy formation. These z > 1 galaxies have very unusual morphologies as seen in deep HST WFPC2 images., 10 pages LaTeX + 5 PostScript figures in uuencoded gzipped tar file; aasms4.sty, flushrt.sty, overcite.sty (the two aastex4.0 and overcite.sty macros are available from xxx.lanl.gov) Also available (along with style files) via anonymous ftp to ftp://hubble.ifa.hawaii.edu/pub/preprints . E-print version of paper adds citation cross-references to other archived e-prints, where available. To appear in Nature October 19, 1995