Color Cut Research Articles

THE EFFECTS OF CLOSE COMPANIONS (AND ROTATION) ON THE MAGNETIC ACTIVITY OF M DWARFS

We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf -- main sequence binaries from Rebassa et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space to construct a sample of 1756 WD+dM high-quality pairs from the SDSS DR8 spectroscopic database. We separate the individual WD and dM from each spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the H{\alpha} emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types \leqM7. Our results show that early-type M dwarfs (\leqM4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems becomes more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk-disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully-convective stars. (Abridged)

ASSEMBLY OF MASSIVE GALAXIES IN A HIGH-zPROTOCLUSTER

We present the results of wide-field deep JHK imaging of the SSA22 field using the MOIRCS instrument equipped with the Subaru telescope. The observed field is 112 arcmin2 in area, which covers the z = 3.1 protocluster characterized by the overdensities of Lyα emitters (LAEs) and Lyα blobs (LABs). The 5σ limiting magnitude is KAB = 24.3. We extract the potential protocluster members from the K-selected sample by using the multi-band photometric-redshift selection as well as the simple color cut for distant red galaxies (DRGs; J − KAB > 1.4). The surface number density of DRGs in our observed fields shows clear excess compared with those in the blank fields, and the location of the densest area whose projected overdensity is twice the average coincides with the large-scale density peak of LAEs. We also found that K-band counterparts with zphot ≃ 3.1 are detected for 75% (15/20) of the LABs within their Lyα halo, and the 40% (8/20) of LABs have multiple components, which gives a direct evidence of the hierarchical multiple merging in galaxy formation. The stellar mass of LABs correlates with their luminosity, isophotal area, and the Lyα velocity widths, implying that the physical scale and the dynamical motion of Lyα emission are closely related to their previous star formation activities. Highly dust-obscured galaxies such as hyper extremely red objects (J − KAB > 2.1) and plausible K-band counterparts of submillimeter sources are also populated in the high-density region.

A MULTI-SURVEY APPROACH TO WHITE DWARF DISCOVERY

By selecting astrometric and photometric data from the Sloan Digital Sky Survey (SDSS), the L{\'e}pine & Shara Proper Motion North Catalog (LSPM-North), the Two Micron All Sky Survey (2MASS), and the USNO-B1.0 catalog, we use a succession of methods to isolate white dwarf candidates for follow-up spectroscopy. Our methods include: reduced proper motion diagram cuts, color cuts, and atmospheric model adherence. We present spectroscopy of 26 white dwarfs obtained from the CTIO 4m and APO 3.5m telescopes. Additionally, we confirm 28 white dwarfs with spectra available in the SDSS DR7 database but unpublished elsewhere, presenting a total of 54 WDs. We label one of these as a recovered WD while the remaining 53 are new discoveries. We determine physical parameters and estimate distances based on atmospheric model analyses. Three new white dwarfs are modeled to lie within 25 pc. Two additional white dwarfs are confirmed to be metal-polluted (DAZ). Follow-up time series photometry confirms another object to be a pulsating ZZ Ceti white dwarf.

Galaxy and Mass Assembly (GAMA): ugriz galaxy luminosity functions

Galaxy and Mass Assembly (GAMA) is a project to study galaxy formation and evolution, combining imaging data from ultraviolet to radio with spectroscopic data from the AAOmega spectrograph on the Anglo-Australian Telescope. Using data from phase 1 of GAMA, taken over three observing seasons, and correcting for various minor sources of incompleteness, we calculate galaxy luminosity functions (LFs) and their evolution in the ugriz passbands. At low redshift, z < 0.1, we find that blue galaxies, defined according to a magnitude-dependent but non-evolving colour cut, are reasonably well fit over a range of more than ten magnitudes by simple Schechter functions in all bands. Red galaxies, and the combined blue-plus-red sample, require double power-law Schechter functions to fit a dip in their LF faintward of the characteristic magnitude M* before a steepening faint end. This upturn is at least partly due to dust-reddened disk galaxies. We measure evolution of the galaxy LF over the redshift range 0.002 < z < 0.5 using both a parametric fit and by measuring binned LFs in redshift slices. The characteristic luminosity L* is found to increase with redshift in all bands, with red galaxies showing stronger luminosity evolution than blue galaxies. The comoving number density of blue galaxies increases with redshift, while that of red galaxies decreases, consistent with prevailing movement from blue cloud to red sequence. As well as being more numerous at higher redshift, blue galaxies also dominate the overall luminosity density beyond redshifts z = 0.2. At lower redshifts, the luminosity density is dominated by red galaxies in the riz bands, by blue galaxies in u and g.

HUBBLE SPACE TELESCOPEPIXEL ANALYSIS OF THE INTERACTING FACE-ON SPIRAL GALAXY NGC 5194 (M51A)

A pixel analysis is carried out on the interacting face-on spiral galaxy NGC 5194 (M51A), using the HST/ACS images in the F435W, F555W and F814W (BVI) bands. After 4x4 binning of the HST/ACS images to secure a sufficient signal-to-noise ratio for each pixel, we derive several quantities describing the pixel color-magnitude diagram (pCMD) of NGC 5194: blue/red color cut, red pixel sequence parameters, blue pixel sequence parameters and blue-to-red pixel ratio. The red sequence pixels are mostly older than 1 Gyr, while the blue sequence pixels are mostly younger than 1 Gyr, in their luminosity-weighted mean stellar ages. The color variation in the red pixel sequence from V = 20 mag arcsec^(-2) to V = 17 mag arcsec^(-2) corresponds to a metallicity variation of \Delta[Fe/H] ~ 2 or an optical depth variation of \Delta\tau_V ~ 4 by dust, but the actual sequence is thought to originate from the combination of those two effects. At V < 20 mag arcsec^(-2), the color variation in the blue pixel sequence corresponds to an age variation from 5 Myr to 300 Myr under the assumption of solar metallicity and \tau_V = 1. To investigate the spatial distributions of stellar populations, we divide pixel stellar populations using the pixel color-color diagram and population synthesis models. As a result, we find that the pixel population distributions across the spiral arms agree with a compressing process by spiral density waves: dense dust \rightarrow newly-formed stars. The tidal interaction between NGC 5194 and NGC 5195 appears to enhance the star formation at the tidal bridge connecting the two galaxies. We find that the pixels corresponding to the central active galactic nucleus (AGN) area of NGC 5194 show a tight sequence at the bright-end of the pCMD, which are in the region of R ~ 100 pc and may be a photometric indicator of AGN properties.

GOODS-Herschel: a population of 24 μm dropout sources atz &lt; 2

Using extremely deep PACS 100- and 160um Herschel data from the GOODS-Herschel program, we identify 21 infrared bright galaxies previously missed in the deepest 24um surveys performed by MIPS. These MIPS dropouts are predominantly found in two redshift bins, centred at z ~0.4 and ~1.3. Their S_100/S_24 flux density ratios are similar to those of local LIRGs and ULIRGs, whose silicate absorption features at 18um (at z ~ 0.4) and 9.7um (at z ~ 1.3) are shifted into the 24um MIPS band at these redshifts. The high-z sub-sample consists of 11 infrared luminous sources, accounting for ~2% of the whole GOODS-Herschel sample and putting strong upper limits on the fraction of LIRGs/ULIRGs at 1.0<z<1.7 that are missed by the 24um surveys. We find that a S_100/S_24 > 43 colour cut selects galaxies with a redshift distribution similar to that of the MIPS dropouts and when combined with a second colour cut, S_16/S_8 > 4, isolates sources at 1.0 < z < 1.7. We show that these sources have elevated specific star formation rates (sSFR) compared to main sequence galaxies at these redshifts and are likely to be compact starbursts with moderate/strong 9.7um silicate absorption features in their mid-IR spectra. Herschel data reveal that their infrared luminosities extrapolated from the 24um flux density are underestimated, on average, by a factor of ~3. These silicate break galaxies account for 16% (8%) of the ULIRG (LIRG) population in the GOODS fields, indicating a lower limit in their space density of 2.0 \times 10^(-5) Mpc^(-3). Finally, we provide estimates of the fraction of z < 2 MIPS dropout sources as a function of the 24-, 100-, 160-, 250- and 350um sensitivity limits, and conclude that previous predictions of a population of silicate break galaxies missed by the major 24um extragalactic surveys have been overestimated.

AN ALL-SKY CATALOG OF BRIGHT M DWARFS

We present an all-sky catalog of M dwarf stars with apparent infrared magnitude J<10. The 8,889 stars are selected from the ongoing SUPERBLINK survey of stars with proper motion >40 mas/yr, supplemented on the bright end with the TYCHO-2 catalog. Completeness tests which account for kinematic (proper motion) bias suggest that our catalog represents ~75% of the estimated ~11,900 M dwarfs with J<10 expected to populate the entire sky. Our catalog is, however, significantly more complete for the Northern sky (~90%) than it is for the South (~60%). Stars are identified as cool, red M dwarfs from a combination of optical and infrared color cuts, and are distinguished from background M giants and highly-reddened stars using either existing parallax measurements or, if such measurements are lacking, on their location in an optical-to-infrared reduced proper motion diagram. These bright M dwarfs are all prime targets for exoplanet surveys using the Doppler radial velocity or transit methods; the combination of low-mass and bright apparent magnitude should make possible the detection of Earth-size planets on short-period orbits using currently available techniques. Parallax measurements, when available, and photometric distance estimates are provided for all stars, and these place most systems within 60 parsecs of the Sun. Spectral type estimated from V-J color shows that most of the stars range from K7 to M4, with only a few late M dwarfs, all within 20 pc. Proximity to the Sun also makes these stars good targets for high-resolution exoplanet imaging searches, especially if younger objects can be identified on the basis of X-ray or UV excess. For that purpose, we include X-ray flux from ROSAT and FUV/NUV ultraviolet magnitudes from GALEX for all stars for which a counterpart can be identified in those catalogs.

The morphology of galaxies in the Baryon Oscillation Spectroscopic Survey

We study the morphology of luminous and massive galaxies at 0.3<z<0.7 targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly available Hubble Space Telescope imaging from COSMOS. Our sample (240 objects) provides a unique opportunity to check the visual morphology of these galaxies which were targeted based solely on stellar population modelling. We find that the majority (74+/-6%) possess an early-type morphology (elliptical or S0), while the remainder have a late-type morphology. This is as expected from the goals of the BOSS target selection which aimed to predominantly select slowly evolving galaxies, for use as cosmological probes, while still obtaining a fair fraction of actively star forming galaxies for galaxy evolution studies. We show that a colour cut of (g-i)>2.35 selects a sub-sample of BOSS galaxies with 90% early-type morphology - more comparable to the earlier Luminous Red Galaxy (LRG) samples of SDSS-I/II. The remaining 10% of galaxies above this cut have a late-type morphology and may be analogous to the "passive spirals" found at lower redshift. We find that 23+/-4% of the early-type galaxies are unresolved multiple systems in the SDSS imaging. We estimate that at least 50% of these are real associations (not projection effects) and may represent a significant "dry merger" fraction. We study the SDSS pipeline sizes of BOSS galaxies which we find to be systematically larger (by 40%) than those measured from HST images, and provide a statistical correction for the difference. These details of the BOSS galaxies will help users of the data fine-tune their selection criteria, dependent on their science applications. For example, the main goal of BOSS is to measure the cosmic distance scale and expansion rate of the Universe to percent-level precision - a point where systematic effects due to the details of target selection may become important.

Massive, red galaxies in a hierarchical universe - II. Clustering of Extremely Red Objects

We present predictions for the clustering of Extremely Red Objects (EROs) in a \Lambda cold dark matter Universe, using a semi-analytical galaxy formation model in combination with a cosmological N-body simulation. EROs are red, massive galaxies observed at 0.7< z < 3, and their numbers and properties have posed a challenge to hierarchical galaxy formation models. We analyse the halo occupation distribution and two-point correlation function of EROs, exploring how these quantities change with apparent magnitude, colour cut and redshift. Our model predicts a halo occupation distribution that is significantly different from that typically assumed. This is due to the inclusion of AGN feedback, which changes the slope and scatter of the luminosity-host halo mass relation above the mass where AGN feedback first becomes important. We predict that, on average, dark matter haloes with masses above 10^{13}h^{-1}Msun host at least one ERO at 1.5 < z < 2.5. Taking into account sample variance in observational estimates, the predicted angular clustering for EROs with either (R-K)>5 or (i-K)>4.5 is in reasonable agreement with current observations.

PROPERTIES OF SATELLITE GALAXIES IN THE SDSS PHOTOMETRIC SURVEY: LUMINOSITIES, COLORS, AND PROJECTED NUMBER DENSITY PROFILES

We analyze photometric data in SDSS-DR7 to infer statistical properties of faint satellites associated to isolated bright galaxies (M_r<-20.5) in the redshift range 0.03<z<0.1. The mean projected radial profile shows an excess of companions in the photometric sample around the primaries, with approximately a power law shape that extends up to ~700kpc. Given this overdensity signal, a suitable background subtraction method is used to study the statistical properties of the population of bound satellites, down to magnitude M_r=-14.5, in the projected radial distance range 100 < r_p/kpc < 3 R_{vir}. We have also considered a color cut consistent with the observed colors of spectroscopic satellites in nearby galaxies so that distant redshifted galaxies do not dominate the statistics. We have tested the implementation of this procedure using a mock catalog. We find that the method is effective in reproducing the true projected radial satellite number density profile and luminosity distributions, providing confidence in the results derived from SDSS data. The spatial extent of satellites is larger for bright, red primaries. Also, we find a larger spatial distribution of blue satellites. For the different samples analyzed, we derive the average number of satellites and their luminosity distributions down to M_r=-14.5. The mean number of satellites depends very strongly on host luminosity. Bright primaries (M_r<-21.5) host on average ~6 satellites with M_r<-14.5, while primaries with -21.5<M_r<-20.5 have less than 1 satellite per host. We provide Schechter function fits to the luminosity distributions of satellite galaxies with faint-end slopes -1.3+/-0.2. This shows that satellites of bright primaries lack an excess population of faint objects, in agreement with the results in the Milky Way and nearby galaxies.

THE SEARCH FOR LOW-MASS COMPANIONS OF B STARS IN THE CARINA NEBULA CLUSTER TRUMPLER 16

We have developed lists of likely B3--A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of Eta Car, an appropriate V and B-V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B-V) =0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project (CCCP). Previous studies have shown that only very rarely (if at all) do late main sequence B stars produce X-rays. We present evidence that the X-ray detected sources are binaries with low-mass companions, since stars less massive than 1.4 Msun are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate mass stars are complementary to spectroscopic and interferometric results, and probe new parameter space of low mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 Msun) primaries, such as would be found by random pairing from the Initial Mass Function.

Catalogues of hot white dwarfs in the Milky Way from GALEX’s ultraviolet sky surveys: constraining stellar evolution

We present comprehensive catalogs of hot star candidates in the Milky Way, selected from GALEX far-UV (FUV, 1344-1786 AA) and near-UV (NUV, 1771-2831 AA) imaging. The FUV and NUV photometry allows us to extract the hottest stellar objects, in particular hot white dwarfs (WD), which are elusive at other wavelengths because of their high temperatures and faint optical luminosities. We generated catalogs of UV sources from two GALEX's surveys: AIS (All-Sky Imaging Survey, depth ABmag~19.9/20.8 in FUV/NUV) and MIS (Medium-depth Imaging Survey, depth ~22.6/22.7mag). The two catalogs (from GALEX fifth data release) contain 65.3/12.6 million (AIS/MIS) unique UV sources with error(NUV)<0.5mag, over 21,435/1,579 square degrees. We also constructed subcatalogs of the UV sources with matched optical photometry from SDSS (7th data release): these contain 0.6/0.9million (AIS/MIS) sources with errors <0.3mag in both FUV and NUV, excluding sources with multiple optical counterparts, over an area of 7,325/1,103 square degrees. All catalogs are available online. We then selected 28,319(AIS)/9,028(MIS) matched sources with FUV-NUV<-0.13; this color cut corresponds to stellar Teff hotter than ~18,000 K. An additional color cut of NUV-r>0.1 isolates binaries with largely differing Teff's, and some intruding QSOs. Available spectroscopy for a subsample indicates that hot-star candidates with NUV-r<0.1 have negligible contamination by non-stellar objects. We discuss the distribution of sources in the catalogs, and the effects of error and color cuts on the samples. The density of hot-star candidates increases from high to low Galactic latitudes, but drops on the MW plane due to dust extinction. Our hot-star counts at all latitudes are better matched by Milky Way models computed with an initial-final mass relation that favours lower final masses. (ABRIDGED)

SPITZERINFRARED SPECTROMETER 16 μm OBSERVATIONS OF THE GOODS FIELDS

We present Spitzer 16 micron imaging of the Great Observatories Origins Deep Survey (GOODS) fields. We survey 150 square arcminutes in each of the two GOODS fields (North and South), to an average 3 sigma depth of 40 and 65 micro-Jy respectively. We detect about 1300 sources in both fields combined. We validate the photometry using the 3-24 micron spectral energy distribution of stars in the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM and AKARI observations in the same fields show reasonable agreement, though the uncertainties are large. We provide a catalog of photometry, with sources cross correlated with available Spitzer, Chandra, and HST data. Galaxy number counts show good agreement with previous results from ISOCAM and AKARI, with improved uncertainties. We examine the 16 to 24 micron flux ratio and find that for most sources it lies within the expected locus for starbursts and infrared luminous galaxies. A color cut of S_{16}/S_{24}>1.4 selects mostly sources which lie at 1.1<z<1.6, where the 24 micron passband contains both the redshifted 9.7 micron silicate absorption and the minimum between PAH emission peaks. We measure the integrated galaxy light of 16 micron sources, and find a lower limit on the galaxy contribution to the extragalactic background light at this wavelength to be 2.2\pm 0.2$ nW m^{-2} sr^{-1}.

BINARY CONTAMINATION IN THE SEGUE SAMPLE: EFFECTS ON SSPP DETERMINATIONS OF STELLAR ATMOSPHERIC PARAMETERS

Using numerical modeling and a grid of synthetic spectra, we examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for SEGUE targets measured using the SEGUE Stellar Parameter Pipeline (SSPP). To model undetected binaries that may be in the SEGUE sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G-K dwarf stars, as defined by SDSS color cuts, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, we synthesize a grid of model spectra from 3275 to 7850 K (~0.1 to 1.0 \msun) and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. We analyze both "infinite" signal-to-noise ratio (S/N) models and degraded versions, at median S/N of 50, 25 and 10. By running individual and combined spectra (representing the binaries) through the SSPP, we determine that ~10% of the blended G-K dwarf pairs with S/N>=25 will have their atmospheric parameter determinations, in particular temperature and metallicity, noticeably affected by the presence of an undetected secondary. To account for the additional uncertainty from binary contamination at a S/N~10, uncertainties of ~140 K and ~0.17 dex in [Fe/H] must be added in quadrature to the published uncertainties of the SSPP. (Abridged)

The active and passive populations of extremely red objects

[abridged] The properties of galaxies with the reddest observed R-K colors (Extremely Red Objects, EROs), including their apparent division into passive and obscured active objects with roughly similar number densities, are a known challenge for models of galaxy formation. We produce mock catalogues generated by interfacing the predictions of the semi-analytical MORGANA model for the evolution of galaxies in a Lambda-CDM cosmology with the spectro-photometric + radiative transfer code GRASIL and Infrared (IR) template library to show that the model correctly reproduces number counts, redshift distributions and active fractions of R-K>5 sources. We test the robustness of our results against different dust attenuations and, most importantly, against the inclusion of TP-AGB stars in Simple Stellar Populations used to generate galaxy spectra, and find that the inclusion of TP-AGBs has a relevant effect, in that it allows to increase by a large factor the number of very red active objects at all color cuts. We find that though the most passive and the most obscured active galaxies have a higher probability of being selected as EROs, many EROs have intermediate properties and the population does not show bimodality in specific star formation rate (SSFR). We predict that deep observations in the Far-IR, from 100 to 500 micron, are the most efficient way to constrain the SSFR of these objects; we give predictions for future Herschel observations. Finally, we test whether a simple evolutionary sequence for the formation of z=0 massive galaxies, going through a sub-mm-bright phase and then a ERO phase, are typical in this galaxy formation model. We find that this sequence holds for ~25 per cent of z=0 massive galaxies, while the model typically shows a more complex connection between sub-mm, ERO and massive galaxies. [abridged]

Constraints on star-forming galaxies atz≥ 6.5 from HAWK-IY-band imaging of GOODS-South

We present the results of our search for high-redshift Lyman-break galaxies over the GOODS-South field. We use Hubble Space Telescope (HST)-ACS data in B, V, i′ & z′, Very Large Telescope (VLT)-ISAAC J and Ks, Spitzer–Infrared Array Camera (IRAC) 3.6, 4.5, 5.8 and 8.0 μm data in conjunction with the new HAWK-I Y-band science verification data to search for dropout galaxies in the redshift range 6 < z < 9. We survey ≈119 arcmin2 to YAB= 25.7 (5σ), of which 37.5 arcmin2 reaches YAB= 25.9. Candidate z′ and Y dropouts were selected on the basis of a colour cut of (Y−J)AB > 0.75 mag and (z′−Y)AB > 1.0 mag, respectively. We find no robust Y-drops (z≈ 9) brighter than JAB < 25.4. In our search for z′-band dropouts (z≈ 6.5– 7.5), we identify four possible candidates, two with z′-drop colours and clear Spitzer–IRAC detections and two less likely candidates. We also identify two previously known Galactic T-dwarf stellar contaminants with these colours, and two likely transient objects seen in the Y-band data. The implications if all or none of our candidates is real on the ultraviolet galaxy luminosity functions at z > 6.5 are explored. We find our number of z′-drop candidates to be insufficient based on the expected number of z′ drops in a simple no-evolution scenario from the z= 3 Lyman-break galaxy luminosity function but we are consistent with the observed luminosity function at z≈ 6 (if all our candidates are real). However, if one or both of our best z′-drop candidates are not z > 6.5 galaxies, this would demand evolution of the luminosity function at early epochs, in the sense that the number density of ultraviolet luminous star-forming galaxies at z > 7 is less than at z∼ 6. We show that the future surveys to be conducted with the European Southern Observatory VISTA telescope over the next 5 yr will be able to measure the bulk of the luminosity function for both z′ and Y dropouts and thus provide the strongest constraints on the level of star-formation within the epoch of reionization.

Galaxies at z= 6-9 from the WFC3/IR imaging of the Hubble Ultra Deep Field

We present the results of a systematic search for galaxies in the redshift range z = 6 - 9, within the new, deep, near-infrared imaging of the Hubble Ultra Deep Field provided by the Wide Field Camera 3 (WFC3) on HST. We have performed full SED fitting to the optical+infrared photometry of all high-redshift galaxy candidates detected at greater than 5-sigma in at least one of the WFC3/IR broad-band filters. After rejection of contaminants, the result is a sample of 49 galaxies with primary redshift solutions z > 5.9. Our sample, selected without recourse to specific colour cuts, re-selects all but the faintest one of the 16 z-drops selected by Oesch et al. (2009), recovers all 5 of the Y-drops reported by Bouwens et al. (2009), and adds a further 29 galaxy candidates, of which 12 lie beyond z = 6.3, and 4 lie beyond z = 7. We also present confidence intervals on our photometric redshift estimates, and caution that acceptable low-redshift (z < 2) solutions exist for 28 out of the 37 galaxies at z > 6.3, and for all 8 galaxy candidates at z > 7.5. Nevertheless, the very highest redshift candidates appear to be strongly clustered in the field. We derive new estimates of the ultraviolet galaxy luminosity function at z = 7 and z = 8. Where our results are most robust, at a characteristic luminosity M(1500) ~ -19.5 (AB), we find that the comoving number density of galaxies declines by a factor of ~ 2.5 between z = 6 and z = 7, and by a further factor of ~ 2 by z = 8. These results suggest that it is difficult for the observed population of high-redshift star-forming galaxies to achieve reionisation by z ~ 6 without a significant contribution from galaxies well below the detection limits, plus alterations in the escape fraction of ionising photons and/or continued vigorous star formation at z > 15.

The Southern 2MASS Active Galactic Nuclei Survey: Spectroscopic Follow-up with Six Degree Field

AbstractThe Two Micron All-Sky Survey (2MASS) has provided a uniform photometric catalog to search for previously unknown red active galactic nuclei (AGN) and Quasi-Stellar Objects (QSOs).We have extended the search to the southern equatorial sky by obtaining spectra for 1182 AGN candidates using the six degree field (6dF) multifibre spectrograph on the UK Schmidt Telescope. These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey. The candidates were selected using a single color cut of J – Ks &gt; 2 to Ks ≲ 15.5 and a galactic latitude of lbl &gt; 30°. 432 spectra were of sufficient quality to enable a reliable classification. 116 sources (∼27%) were securely classified as type I AGN, 20 as probable type I AGN, and 57 as probable type II AGN. Most of them span the redshift range 0.05 &lt; z &lt; 0.5 and only 8 (∼6%) were previously identified as AGN or QSOs. Our selection leads to a significantly higher AGN identification rate amongst local galaxies (&gt;20%) than in any previous (mostly blue-selected) galaxy survey. A small fraction of the type I AGN could have their optical colors reddened by optically thin dust with AV &lt; 2 mag relative to optically selected QSOs. A handful show evidence of excess far-infrared (IR) emission. The equivalent width (EW) and color distributions of the type I and II AGN are consistent with AGN unified models. In particular, the EW of the [Oiii] emission line weakly correlates with optical–near-IR color in each class of AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the optical properties of the 2MASS red AGN are not dramatically different from those of optically-selected QSOs. Our near-IR selection appears to detect the most near-IR luminous QSOs in the local universe to z≃0.6 and provides incentive to extend the search to deeper near-IR surveys.

Luminosity functions of XMM–LSS C1 galaxy clusters

Canada–France–Hawaii Telescope Legacy Survey optical photometry has been used to study the galaxy luminosity functions (LFs) of 14 X-ray selected clusters from the XMM Large Scale Survey (XMM–LSS) survey. These are mostly groups and poor clusters, with masses (M500) in the range 0.6 to 19 × 1013 M⊙ and redshifts 0.05 ≤z≤ 0.61. Hence, these are some of the highest redshift X-ray selected groups to have been studied. Lower and upper colour cuts were used to determine cluster members. We derive individual LFs for all clusters as well as redshift-stacked and temperature-stacked LFs in three filters, g′, r′ and z′, down to M=−14.5. All LFs were fitted by Schechter functions which constrained the faint-end slope, α, but did not always fit well to the bright end. Derived values of α ranged from −1.03 to as steep as −2.1. We find no evidence for upturns at faint magnitudes. Evolution in α was apparent in all bands: it becomes shallower with increasing redshift; for example, in the z′ band it flattened from −1.75 at low redshift to −1.22 in the redshift range z= 0.43–0.61. Eight of our systems lie at z∼ 0.3, and we combine these to generate a galaxy LF in three colours for X-ray selected groups and poor clusters at redshift 0.3. We find that at z∼ 0.3 α is steeper (−1.67) in the green (g′) band than it is (−1.30) in the red (z′) band. This colour trend disappears at low redshift, which we attribute to reddening of faint blue galaxies from z∼ 0.3 to 0. We also calculated the total optical luminosity and found it to correlate strongly with X-ray luminosity (LX∝L2.1OPT), and also with ICM temperature (LOPT∝T1.62), consistent with expectations for self-similar clusters with constant mass-to-light ratio. We did not find any convincing correlation of Schechter parameters with mean cluster temperature.

Recent developments in Fourier Domain Mode Locked lasers for optical coherence tomography: Imaging at 1310 nm vs. 1550 nm wavelength

We report on recent progress in Fourier domain mode-locking (FDML) technology. The paper focuses on developments beyond pushing the speed of these laser sources. After an overview of improvements to FDML over the last three years, a brief analysis of OCT imaging using FDML lasers with different wavelengths is presented. For the first time, high speed, high quality FDML imaging at 1550 nm is presented and compared to a system at 1310 nm. The imaging results of human skin for both wavelengths are compared and analyzed. Sample arm optics, power on the sample, heterodyne gain, detection bandwidth, colour cut levels and sample location have been identical to identify the influence of difference in scattering and water absorption. The imaging performance at 1310 nm in human skin is only slightly better and the results suggest that water absorption only marginally affects the penetration depth in human skin at 1550 nm. For several applications this wavelength may be preferred.