Z-band Imaging Research Articles

Bar Presence in Local Galaxies: Dependence on Morphology in Field Galaxies

Abstract We analyzed the fractions of barred galaxies in the local universe using a volume-limited sample of galaxies from the Sloan Digital Sky Survey Data Release 3. We examined 116 field galaxies with redshifts between 0.0207 and 0.030, using r and z-band images. Overall, the bar fraction was 26% in the r-band and 19% in the z-band. For distinct morphological groups, barred spiral galaxies had fractions of 33% in the r-band and 22% in the z-band, while barred lenticular galaxies had 25% in the r-band and 12% in the z-band. We observed that the bar fraction in spiral galaxies increases for stellar masses log(M∗/M⊙) > 10.5 and for galaxies with red colors (u − r) > 2.0. Additionally, most barred galaxies have a bulge-to-total ratio B/T ≤ 0.2. Our results indicate that the bar fraction is more dependent on internal morphology than on the galaxy environment.

Major merger fraction along the massive galaxy-quenching channel at 0.2 < z < 0.7

Abstract We study the major merger fraction along the massive galaxy-quenching channel (traced with rest-frame $\mathrm{NUV}-r$ color) at z = 0.2–0.7, aiming to examine the cosmic web detachment (CWD) scenario of galaxy quenching. In this scenario, the major merger fraction is expected to be high in green-valley galaxies as compared with those in star-forming and quiescent galaxies of similar stellar mass. We used photometry in the E-COSMOS field to select 1491 (2334) massive ($M_\ast \\gt 10^{9.5}\, M_{\odot }$) galaxies with $m_i\\lt 22$ mag ($m_z\\lt 22$ mag) at z = 0.2–0.4 (z = 0.4–0.7) in the rest-frame color range of $0.8\\lt r-K_{\rm s}\\lt 1.3$. We define a major galaxy–galaxy merger as a galaxy pair of comparable angular size and luminosity with tidal tails or bridges, and we identified such major mergers through visual inspection of Subaru HSC-SSP PDR 2 i- and z-band images. We classify 92 (123) galaxies as major merger galaxies at z = 0.2–0.4 (z = 0.4–0.7). The resulting major merger fraction is 5%–6% and this fraction does not change with galaxy color along the massive galaxy-quenching channel. The result is not consistent with the expectation based of the CWD scenario as the dominant mechanism of massive galaxy quenching. However, there are some caveats such as (i) the mergers that cause quenching may lose their visible merger signatures rapidly before they enter the green valley, (ii) our method may not trace the cosmic web sufficiently well, and (iii) because of our mass limit, most of the galaxies in our sample may have already experienced CWD events at higher redshifts than those studied here. Further studies with deeper data are desirable in the future.

Optical properties of metal-poor T dwarf candidates

Context. Metal-poor brown dwarfs are poorly understood because they are extremely faint and rare. Only a few candidates have been identified as T-type subdwarfs in infrared surveys and their optical properties remain unconstrained. Aims. We aim to improve the knowledge of the optical properties of T subdwarf candidates to break the degeneracy between metallicity and temperature and to investigate their atmospheric properties. Methods. Deep z-band images of ten known T subdwarf candidates were collected with the 10.4-m Gran Telescopio Canarias. Low-resolution optical spectra for two of them were obtained with the same telescope. Photometric measurements of the z-band flux were performed for all the targets and they were combined with infrared photometry in J, H, K, W1, and W2 bands from the literature to obtain the colours. The spectra were compared with solar-metallicity T dwarf templates and with laboratory spectra. Results. We found that the targets segregate into three distinct groups in the W1 − W2 versus z − W1 colour-colour diagram. Group I objects are mixed with solar-metallicity T dwarfs. Group III objects have W1 − W2 colours similar to T dwarfs but very red z − W1 colours. Group II objects lie between Group I and III. The two targets for which we obtained spectra are located in Group I and their spectroscopic properties resemble normal T dwarfs but with water features that are deeper and have a shape akin to pure water. Conclusions. We conclude that the W1 − W2 versus z − W1 colour-colour diagram is excellent to break the metallicity-temperature degeneracy for objects cooler than L-type ones. A revision of the spectral classification of a T subdwarf might be needed in the future, according to the photometric and spectroscopic properties of WISE1810 and WISE0414 in Group III discussed in this work.

An overdensity of Lyman break galaxies around the hot dust-obscured galaxy WISE J224607.56−052634.9

We report the identification of Lyman break galaxy (LBG) candidates around the most luminous hot dust-Obscured galaxy (Hot DOG) known, WISE J224607.56−052634.9 (W2246−0526) at z = 4.601, using deep r-, i-, and z-band imaging from the Gemini Multi-Object Spectrograph South (GMOS-S). We used the surface density of LBGs to probe the megaparsec-scale environment of W2246−0526 to characterize its richness and evolutionary state. We identified LBG candidates in the vicinity of W2246−0526 using the selection criteria developed in the Subaru Deep Field and in the Subaru XMM-Newton Deep Field, slightly modified to account for the difference between the filters used, and we find 37 and 55 LBG candidates, respectively. Matching to the z-band depths of those studies, this corresponds to δ = 5.8−1.9+2.4 times the surface density of LBGs expected in the field. Interestingly, the Hot DOG itself, as well as a confirmed neighbor, do not satisfy either LBG selection criteria, suggesting we may be missing a large number of companion galaxies. Our analysis shows that we have mostly likely only found those with a higher than average intergalactic medium (IGM) optical depth or moderately high dust obscuration. The number density of LBG candidates is not concentrated around W2246−0526, suggesting an early evolutionary stage for the proto-cluster, that the Hot DOG may not be the most massive galaxy, or that the Hot DOG may be affecting the IGM transparency in its vicinity. The overdensity around W2246−0526 is comparable to overdensities found around other Hot DOGs and is somewhat higher than what is typically found for radio galaxies and luminous quasars at a similar redshift.

A Detailed Morphological and Spectroscopic Study of Merging Dwarf Galaxy PGC 030133

We present a detailed morphology and spectroscopic study of a merging dwarf galaxy PGC 030133. Using the publicly available fiber spectroscopic data from the Sloan Digital Sky Survey (SDSS), we analyzed nine-strong emission lines of wavelength range 4336 Å to 6739 Å. We find that the strongest emission line is OIII5007, with an intensity of 146.32 × 10-17 erg/s/cm2 /Å. The observed emission lines are well fitted with a Gaussian profile with a coefficient of regression greater than 96%, and the derived full-width half maximum (FWHM) is less than 4.2Å. The Balmer decrement, characterized by the line ratio between Hα and Hβ is 3.07, suggesting a presence of dust at the center of PGC 030133. We derived the star-formation rate and emission line metallicity of PGC 030133 using extinction corrected emission line fluxes. SFR derived from Hα emission line flux is 0.0033 Mʘyear-1 and emission line metallicity derived from flux ratio between NII and Hα is 8.13 dex. Using the SDSS, g, and z-band imaging data, we derived morphological parameters. PGC 030133 has a half-light radius of 3.38 arc second and 3.05 arc second in g-band and z-band respectively and observed one-dimensional light profile is well fitted with a Sersic function with near exponential Sersic index ~ 0.9.

Avoiding the Geometric Boundary Effect in Shear Measurement

Abstract In image processing, source detections are inevitably affected by the presence of the geometric boundaries in the images, including the physical boundaries of the CCD, and the boundaries of masked regions due to column defects, bright diffraction spikes, etc. These boundary conditions make the source detection process not statistically isotropic and can lead to additive shear bias near the boundaries. We build a phenomenological model to understand the bias, and propose a simple method to effectively eliminate the influence of geometric boundaries on shear measurement. We demonstrate the accuracy and efficiency of this method using both simulations and the z-band imaging data from the third data release of the DECam Legacy Survey.

Optical follow-up study of 32 high-redshift galaxy cluster candidates from Planck with the William Herschel Telescope

Abstract The Planck satellite has detected cluster candidates via the Sunyaev Zel’dovich (SZ) effect, but the optical follow-up required to confirm these candidates is still incomplete, especially at high redshifts and for SZ detections at low significance. In this work, we present our analysis of optical observations obtained for 32 Planck cluster candidates using ACAM on the 4.2-m William Herschel Telescope. These cluster candidates were pre-selected using SDSS, WISE, and Pan-STARRS images to likely represent distant clusters at redshifts z ≳ 0.7. We obtain photometric redshift and richness estimates for all of the cluster candidates from a red-sequence analysis of r-, i-, and z-band imaging data. In addition, long-slit observations allow us to measure the redshifts of a subset of the clusters spectroscopically. The optical richness is often lower than expected from the inferred SZ mass when compared to scaling relations previously calibrated at low redshifts. This likely indicates the impact of Eddington bias and projection effects or noise-induced detections, especially at low-SZ significance. Thus, optical follow-up not only provides redshift measurements, but also an important independent verification method. We find that 18 (7) of the candidates at redshifts z > 0.5 (z > 0.8) are at least half as rich as expected from scaling relations, thereby clearly confirming these candidates as massive clusters. While the complex selection function of our sample due to our pre-selection hampers its use for cosmological studies, we do provide a validation of massive high-redshift clusters particularly suitable for further astrophysical investigations.

A challenge to identify an optical counterpart of the gravitational wave event GW151226 with Hyper Suprime-Cam

Abstract We present the results of detailed analysis of an optical imaging survey conducted using the Subaru/Hyper Suprime-Cam (HSC) that aimed to identify an optical counterpart to the gravitational wave event GW151226. In half a night, the i- and z-band imaging survey by HSC covered 63.5 deg2 of the error region, which contains about 7% of the LIGO localization probability, and the same field was observed in three different epochs. The detectable magnitude of the candidates in a differenced image is evaluated as i ∼ 23.2 mag for the requirement of at least two 5 σ detections, and 1744 candidates are discovered. Assuming a kilonova as an optical counterpart, we compare the optical properties of the candidates with model predictions. A red and rapidly declining light curve condition enables the discrimination of a kilonova from other transients, and a small number of candidates satisfy this condition. The presence of stellar-like counterparts in the reference frame suggests that the surviving candidates are likely to be flare stars. The fact that most of those candidates are in the galactic plane, |b| < 5°, supports this interpretation. We also check whether the candidates are associated with the nearby GLADE galaxies, which reduces the number of contaminants even with a looser color cut. When a better probability map (with localization accuracy of ∼50 deg2) is available, kilonova searches of up to approximately 200 Mpc will become feasible by conducting immediate follow-up observations with an interval of 3–6 d.

A Candidate Wide Brown Dwarf Binary in the Argus Association: 2MASS J14504216–7841413 and 2MASS J14504113–7841383

Widely-separated (≳100 au) multiples are rare among the lowest mass stars and brown dwarfs (Caballero 2007; Kraus & Hillenbrand 2009), and often (but not exclusively) associated with young (≾100 Myr), nearby stellar associations (e.g., Close et al. 2007). We report the discovery of a wide, very low mass, and potentially young binary, 2MASS J14504216–7841413 and 2MASS J14504113–7841383 (hereafter 2MASS J1450–7841AB). The primary was initially identified in the DENIS (Epchtein et al. 1997) and 2MASS (Skrutskie et al. 2006) surveys as a candidate late-M dwarf based on its red optical/infrared colors (DENIS I = 18.03 ± 0.16, I − J = 3.32 ± 0.19, 2MASS J = 14.71 ± 0.06, J – K_s = 1.38 ± 0.08). A faint red companion, 2MASS J14504113–7841383, is present in the 2MASS Point Source Catalog (J = 15.64 ± 0.09, J – K_s = 1.28 ± 0.14) separated by 4.”23 ± 0.”11 at position angle 314°. We observed 2MASS J1450–7841AB with the Low Dispersion Survey Spectrograph 3 (LDSS-3; Allington-Smith et al. 1994) on the Magellan 6.5 m Clay Telescope on 2007 May 9 (UT). The system was resolved in i- and z-band imaging data at an identical separation (4.”28 ± 0.”14 at 314°; Figure 1) as 2MASS, with Δi = 1.03 ± 0.05 and Δz = 1.01 ± 0.05. Combining astrometry from 2MASS and LDSS-3, we measure identical proper motions of (μ_α cos δ, μδ) = (22 ± 32, −59 ± 34) mas/yr for 2MASS J1450–7841A and (−12 ± 23, −4 ± 23) mas/yr for 2MASS J1450–7841B.

Prospects for high-zcluster detections withPlanck, based on a follow-up of 28 candidates using MegaCam at CFHT

The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at redshift z>0.5, and in particular z>0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts $z\gtrsim0.5$. By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000A rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z~0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias.

The SAMI Galaxy Survey: gas streaming and dynamical M/L in rotationally supported systems

Line-of-sight velocities of gas and stars can constrain dark matter (DM) within rotationally supported galaxies if they trace circular orbits extensively. Photometric asymmetries may signify non-circular motions, requiring spectra with dense spatial coverage. Our integral-field spectroscopy of 178 galaxies spanned the mass range of the SAMI Galaxy Survey. We derived circular speed curves (CSCs) of gas and stars from non-parametric Diskfit fits out to $r\sim2r_e$. For 12/14 with measured H I profiles, ionized gas and H I maximum velocities agreed. We fitted mass-follows-light models to 163 galaxies by approximating the radial starlight profile as nested, very flattened mass homeoids viewed as a S\'ersic form. Fitting broad-band SEDs to SDSS images gave median stellar mass/light 1.7 assuming a Kroupa IMF vs. 2.6 dynamically. Two-thirds of the dynamical mass/light measures were consistent with star+remnant IMFs. One-fifth required upscaled starlight to fit, hence comparable mass of unobserved baryons and/or DM distributed similarly across the SAMI aperture that came to dominate motions as the starlight CSC declined rapidly. The rest had mass distributed differently from starlight. Subtracting fits of S\'ersic profiles to 13 VIKING Z-band images revealed residual weak bars. Near the bar PA, we assessed m = 2 streaming velocities, and found deviations usually <30 km/s from the CSC; three showed no deviation. Thus, asymmetries rarely influenced our CSCs despite co-located shock-indicating, emission-line flux ratios in more than 2/3.

Spectroscopic follow-up of L- and T-type proper-motion member candidates in the Pleiades

(Abridged) We report on the near-infrared low-resolution spectroscopy and red optical (Z-band) photometry of seven proper-motion, very low-mass substellar member candidates of the Pleiades cluster with magnitudes in the interval J=17.5-20.8 and K=16.1-18.5 mag. Spectra were acquired for six objects with the LIRIS and NIRSPEC instruments mounted on the 4.2-m WHT and the 10-m Keck II telescopes. Z-band images of two of the faintest candidates were collected with ACAM/WHT. The new data confirm the low temperatures of all seven Pleiades candidates. From the imaging observations, we find extremely red Z-J and Z-K colors that suggest that the faintest target, Calar Pleiades 25, has a Galactic rather than extragalactic nature. We tentatively classify the spectroscopic targets from early-L to ~T0 and suggest that the L/T transition, which accounts for the onset of methane absorption at 2.1 micron, may take place at J,K ~ 20.3, 17.8 mag in the Pleiades (absolute values of M_J ~ 14.7 and M_K ~ 12.2 mag). We find evidence of likely low-gravity atmospheres based on the presence of triangular-shape H-band fluxes and the high flux ratio K/H (compatible with red H-K colors) of Calar Pleiades 20, 21, and 22, which is a feature also seen in field low-gravity dwarfs. Weak KI absorption lines at around 1.25 micron are probably seen in two targets. These observations add support to the cluster membership of all seven objects in the Pleiades. The trend delineated by the spectroscopic sequence of Pleiades late-M and L dwarfs resembles that of the field. With masses estimated at 0.012-0.015 Msol (solar metallicity and 120 Myr), Calar Pleiades 20 (L6 +/- 1), 21 (L7 +/- 1), and 22 (L/T) may become the coolest and least massive Pleiades members that are corroborated with photometry, astrometry, and spectroscopy. Calar Pleiades 25 (<0.012 Msol) is a firm free-floating planetary-mass candidate in the Pleiades.

Probing the Upper Scorpius mass function in the planetary-mass regime★

We present the results of a deep ZYJ near-infrared survey of 13.5 square degrees in the Upper Scorpius (USco) OB association. We photometrically selected ~100 cluster member candidates with masses in the range 30-5 Jupiters, according to state-of-the-art evolutionary models. We identified 67 ZYJ candidates as bona-fide members, based on complementary photometry and astrometry. We also extracted five candidates detected with VISTA at YJ-only. One is excluded using deep optical z-band imaging, while two are likely non-members, and three remain as potential members. We conclude that the USco mass function is more likely decreasing in the planetary-mass regime (although a flat mass function cannot yet be discarded), consistent with surveys in other regions.

TRACKING DOWN THE SOURCE POPULATION RESPONSIBLE FOR THE UNRESOLVED COSMIC 6–8 keV BACKGROUND

Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray undetected galaxies that dominates the unresolved ~ 20-25% of the 6-8 keV cosmic X-ray background (XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South HST z-band imaging of the central 6'-radius area of the 4 Ms CDF-S. The stacked 6-8 keV detection is significant at the 3.9 sigma level, but the stacked emission was not detected in the 4-6 keV band which indicates the existence of an underlying population of highly obscured active galactic nuclei (AGNs). Further examinations of these 6845 galaxies indicate that the galaxies on the top of the blue cloud and with redshifts of 1 < z < 3, magnitudes of 25 < z_850 < 28, and stellar masses of 2E8 < M_star/M_sun < 2E9 make the majority contributions to the unresolved 6-8 keV XRB. Such a population is seemingly surprising given that the majority of the X-ray detected AGNs reside in massive (> ~1E10 M_sun) galaxies. We discuss constraints upon this underlying AGN population, supporting evidence for relatively low-mass galaxies hosting highly obscured AGNs, and prospects for further boosting the stacked signal.

THE SERENDIPITOUS OBSERVATION OF A GRAVITATIONALLY LENSED GALAXY ATz= 0.9057 FROM THE BLANCO COSMOLOGY SURVEY: THE ELLIOT ARC

We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z=0.3838. The lens (BCS J2352-5452) was discovered while examining i- and z-band images being acquired in October 2006 during a BCS observing run. Follow-up spectroscopic observations with the GMOS instrument on the Gemini South 8m telescope confirmed the lensing nature of this system. Using weak plus strong lensing, velocity dispersion, cluster richness N_200, and fitting to an NFW cluster mass density profile, we have made three independent estimates of the mass M_200 which are all very consistent with each other. The combination of the results from the three methods gives M_200 = (5.1 +- 1.3) x 10^14 M_Sun, which is fully consistent with the individual measurements. The final NFW concentration c_200 from the combined fit is c_200 = 5.4(+1.4 -1.1). We have compared our measurements of M_200 and c_200 with predictions for (a) clusters from Lambda_CDM simulations, (b) lensing selected clusters from simulations, and (c) a real sample of cluster lenses. We find that we are most compatible with the predictions for Lambda_CDM simulations for lensing clusters, and we see no evidence based on this one system for an increased concentration compared to Lambda_CDM. Finally, using the flux measured from the [OII]3727 line we have determined the star formation rate (SFR) of the source galaxy and find it to be rather modest given the assumed lens magnification.

Probing ∼L* Lyman-break galaxies at z≈ 7 in GOODS-South with WFC3 on Hubble Space Telescope

We analyse recently acquired near-infrared Hubble Space Telescope imaging of the GOODS-South field to search for star forming galaxies at z~7.0. By comparing WFC 3 0.98 micron Y-band images with ACS z-band (0.85 micron) images, we identify objects with colours consistent with Lyman break galaxies at z~6.4-7.4. This new data covers an area five times larger than that previously reported in the WFC3 imaging of the Hubble Ultra Deep Field, and affords a valuable constraint on the bright end of the luminosity function. Using additional imaging of the region in the ACS B, V and i-bands from GOODS v2.0 and the WFC3 J-band we attempt to remove any low-redshift interlopers. Our selection criteria yields 6 candidates brighter than Y_AB = 27.0, of which all except one are detected in the ACS z-band imaging and are thus unlikely to be transients. Assuming all 6 candidates are at z~7 this implies a surface density of objects brighter than Y_AB = 27.0 of 0.30\pm0.12 arcmin-2, a value significantly smaller than the prediction from the z ~ 6 luminosity function. This suggests continued evolution of the bright end of the luminosity function between z = 6 to 7, with number densities lower at higher redshift.

Morphological Classification of Galaxies by Shapelet Decomposition in the Sloan Digital Sky Survey. II. Multiwavelength Classification

We describe the application of the linear decomposition of galaxy images to multiwavelength morphological classification using the u-, g-, r-, i-, and z-band images of 1519 galaxies from the Sloan Digital Sky Survey. This combination of morphological information in a variety of bands is unique and allows automatic separation of different classes in ways that are impossible using single-band images or simple spectrophotometric measurements such as color. We use elliptical shapelets to remove to first order the effect of inclination on morphology. After decomposing the galaxies, we perform a principal component analysis on the shapelet coefficients to reduce the dimensionality of the spectral morphological parameter space. We give a description of each of the first 10 principal components' contributions to a galaxy's spectral morphology. We find that galaxies of different broad Hubble type separate cleanly in the principal component space. We apply a mixture-of-Gaussians model to the two-dimensional space spanned by the first two principal components and use the results as a basis for classification. Using the mixture model, we separate galaxies into three classes and give a description of each class's physical and morphological properties. Galaxies were typically robustly classified, with 80% of galaxies having a probability of ≥90% of occupying their respective class. We find that the two dominant mixture-model classes correspond to early- and late-type galaxies, respectively, both in their morphology and their physical parameters (e.g., color, velocity dispersions). The third class has, on average, a blue, extended core surrounded by a faint red halo and typically exhibits some asymmetry. The third class cannot be associated with any broad Hubble type; however, it is the most probable class for irregular galaxies. We compare our method to a simple cut on u - r color and find the shapelet method to be superior in separating galaxies. Furthermore, we find evidence that the u - r = 2.22 decision boundary may not be optimal for separation between early- and late-type galaxies and suggest that the optimal cut may be u - r ~ 2.4. We conclude with a discussion of the limitations of our method and ways in which it may be improved. Our framework provides an objective and quantitative alternative to traditional one-color visual classification, and the powerful use of both spectral and morphological information gives our method an advantage over separation techniques based on simpler calculations.

The Number and Observability of Population III Supernovae at High Redshifts

We consider the feasibility of detecting Population III pair-instability supernovae (PISN) at very high redshifts with the James Webb Space Telescope (JWST). Four published estimates for the PISNe rate show a rather wide dispersion, between 50-2200 deg-2 yr-1. Correcting problems with several of these, we conclude that even a fairly optimistic estimate is probably a further order of magnitude lower than this range, at a rate of order 4 deg-2 yr-1 at z \~ 15 and 0.2 deg-2 yr-1 at z ~ 25, both with substantial uncertainty. Although such supernovae would be bright enough to be readily detectable with the JWST at any relevant redshift, the lower number densities derived here will likely require either a dedicated wide-angle search strategy or a serendipitous search. We expect that typically about 1 deg2 (or 500 JWST NIRCam images) per detected supernova at 4.5 mm must be imaged to detect one PISN at z ~ 15 and about 35 deg2 to detect one at z ~ 25. If some Population III star-formation persists to lower redshifts z ~ 5, then PISNe may also be detectable in wide-angle ground-based Z-band imaging surveys at ZAB ~ 23, at a density of order 1 deg-2 of surveyed area. In an Appendix, we consider the possible effects of intergalactic dust in obscuring high redshift supernovae or other high redshift sources. We show that the obscuration at a given rest-wavelength will peak at some maximum redshift and thereafter decline. While it may be a significant effect in observations of the very high redshift Universe, it is unlikely, even under rather pessimistic assumptions, to completely obscure primordial objects.

The Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey of 104 deg2 in the North Galactic Cap, currently underway with the 2.5-m SDSS Telescope at the Apache Point Observatory in New Mexico. The data products will include u, g, r, i and z-band imaging of several 108 sources and R = 2000 spectra of 106 galaxies. The imaging will have 10-sigma limiting (AB) magnitudes of (u, g, r, i, z) = (21.4, 22.6, 22.3, 21.7, 20.1). The “Main” sample of 9 x 105 galaxies, selected to have r &lt; 17.7 mag, will have spectra with signal-to-noise ratio on the order of ~ 10 per resolution element, and median redshift z ~ 0.1. There will also be a sample of 105 luminous elliptical galaxies, selected on the basis of apparent color and magnitude, which will extend out to redshift z ~ 0.4. The data will be released steadily over the next five years.On the order of one percent of the eventual data volume has been assembled at the time of this meeting, with a few hundred square degrees of survey-quality 5-band imaging, and over 104 survey-quality spectra. In the refereed literature there are detailed descriptions of the survey design, goals and hardware (York et al 2000; Gunn et al. 1998) and first scientific results (e.g., Ivezic et al 2000; Fischer et al. 2000; Leggett et al. 2000; Yanny et al. 2000).Relevant to measures of the extragalactic background emission, the survey has found many z &gt; 4 quasars and has measured the evolution in their space density (e.g., Fan et al. 2000). Measures of bright galaxy counts, the local galaxy luminosity function, and the evolution of elliptical galaxies are in preparation.