We have developed an automatic technique to search for low-surface-brightness (LSB) galaxies in the local Universe (v<=5000km/s) using the automated plate measuring (APM) scan data of UK Schmidt photographic plates. We optimized our technique and selection criteria by surveying the known LSB galaxies in the Fornax cluster. Plate-to-plate magnitude calibrations were carried out using independent CCD sequences. The galaxies we detected are brighter than 20Bmag, have scalesizes greater than 3arcsec and a central surface brightness fainter than 22.5mag/arcsec^2^. In total 2435 LSB galaxies were detected over a total area of 2187deg^2^. The survey covers the Fornax cluster, NGC 1400, Sculptor and Dorado groups and the field between. We detect on average 32 LSB galaxies per 5.8{deg}x5.8{deg} field. We have estimated the background (v>5000km/s) contamination in three ways: by numerical modelling, using a limited redshift sample and comparing our Fornax data with those of Ferguson. The results indicate a contamination of about 19 galaxies per field.
The LSPM catalog is a comprehensive list of 61,977 stars north of the J2000 celestial equator that have proper motions larger than 0.15"/yr (local-background-stars frame). The catalog has been generated primarily as a result of our systematic search for high proper motion stars in the Digitized Sky Surveys using our SUPERBLINK software. At brighter magnitudes, the catalog incorporates stars and data from the Tycho-2 Catalogue (I/259) and also, to a lesser extent, from the All-Sky Compiled Catalogue of 2.5million stars (ASCC-2.5, Cat. I/280). The LSPM catalog considerably expands over the old Luyten (Luyten Half-Second [LHS, Cat. I/87] and New Luyten Two-Tenths [NLTT, Cat. I/98]) catalogs, superseding them for northern declinations. Positions are given with an accuracy of <~100 mas at the 2000.0 epoch, and absolute proper motions are given with an accuracy of ~8 mas/yr. Corrections to the local-background-stars proper motions have been calculated, and absolute proper motions in the extragalactic frame are given. Whenever available, we also give optical BT and VT magnitudes (from Tycho-2, ASCC-2.5), photographic BJ, RF, and IN magnitudes (from USNO-B1 catalog, I/284), and infrared J, H, and Ks magnitudes (from 2MASS, Cat. II/246). We also provide an estimated V magnitude and V-J color for nearly all catalog entries, useful for initial classification of the stars. The catalog is estimated to be over 99% complete at high Galactic latitudes (|b|>15{deg}) and over 90% complete at low Galactic latitudes (|b|>15{deg}), down to a magnitude V=19.0, and has a limiting magnitude V=21.0. All the northern stars listed in the LHS and NLTT catalogs have been reidentified, and their positions, proper motions, and magnitudes reevaluated. The catalog also lists a large number of completely new objects, which promise to expand very significantly the census of red dwarfs, subdwarfs, and white dwarfs in the vicinity of the Sun. All Luyten's NLTT stars north of the J2000 celestial equator that do not appear in the LSPM catalog are given in table3, with an explanation as to why they were not included in the LSPM catalog.
A list of 4131 dwarfs, subgiants, and giants located or suspected to be located within 33pc of the Sun is presented. All the stars are drawn from the new Lepine Shara Proper Motion (LSPM)-North catalog (Cat. <I/298>) of 61,976 stars with annual proper motions larger than 0.15"/yr. Trigonometric parallax measurements are found in the literature for 1676 of the stars in the sample; photometric and spectroscopic distance moduli are found for another 783 objects. The remaining 1672 objects are reported here as nearby star candidates for the first time. Photometric distance moduli are calculated for the new stars based on the (M_V_, V-J) relationship, calibrated with the subsample of stars that have trigonometric parallaxes. The list of new candidates includes 539 stars that are suspected to be within 25pc of the Sun, including 63 stars estimated to be within only 15pc.
The evolution of brown dwarfs from L to T spectral types is one of the least understood aspects of the ultracool population, partly for lack of a large, well-defined, and well-characterized sample in the L/T transition. To improve the existing census, we have searched ~28000deg^2^ using the Pan-STARRS1 and Wide-field Infrared Survey Explorer surveys for L/T transition dwarfs within 25pc. We present 130 ultracool dwarf discoveries with estimated distances ~9-130pc, including 21 that were independently discovered by other authors and 3 that were previously identified as photometric candidates. Seventy-nine of our objects have near-IR spectral types of L6-T4.5, the most L/T transition dwarfs from any search to date, and we have increased the census of L9-T1.5 objects within 25pc by over 50%. The color distribution of our discoveries provides further evidence for the "L/T gap", a deficit of objects with (J-K)_MKO_~0.0-0.5mag in the L/T transition, and thus reinforces the idea that the transition from cloudy to clear photospheres occurs rapidly. Among our discoveries are 31 candidate binaries based on their low-resolution spectral features. Two of these candidates are common proper motion companions to nearby main sequence stars; if confirmed as binaries, these would be rare benchmark systems with the potential to stringently test ultracool evolutionary models. Our search also serendipitously identified 23 late-M and L dwarfs with spectroscopic signs of low gravity implying youth, including 10 with vl-g or int-g gravity classifications and another 13 with indications of low gravity whose spectral types or modest spectral signal-to-noise ratio do not allow us to assign formal classifications. Finally, we identify 10 candidate members of nearby young moving groups (YMG) with spectral types L7-T4.5, including three showing spectroscopic signs of low gravity. If confirmed, any of these would be among the coolest known YMG members and would help to determine the effective temperature at which young brown dwarfs cross the L/T transition.
We aim to constrain the evolution of active galactic nuclei (AGNs) as a function of obscuration using an X-ray-selected sample of ~2000 AGNs from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS, and XMM-XXL fields. The spectra of individual X-ray sources are analyzed using a Bayesian methodology with a physically realistic model to infer the posterior distribution of the hydrogen column density and intrinsic X-ray luminosity. We develop a novel non-parametric method that allows us to robustly infer the distribution of the AGN population in X-ray luminosity, redshift, and obscuring column density, relying only on minimal smoothness assumptions. Our analysis properly incorporates uncertainties from low count spectra, photometric redshift measurements, association incompleteness, and the limited sample size. We find that obscured AGNs with N_H_>10^22^/cm2 account for 77_-5_^+4^% of the number density and luminosity density of the accretion supermassive black hole population with L_X_>10^43^erg/s, averaged over cosmic time. Compton-thick AGNs account for approximately half the number and luminosity density of the obscured population, and 38_-7_^+8^% of the total. We also find evidence that the evolution is obscuration dependent, with the strongest evolution around N_H_{approx}10^23^/cm2. We highlight this by measuring the obscured fraction in Compton-thin AGNs, which increases toward z~3, where it is 25% higher than the local value. In contrast, the fraction of Compton-thick AGNs is consistent with being constant at {approx}35%, independent of redshift and accretion luminosity. We discuss our findings in the context of existing models and conclude that the observed evolution is, to first order, a side effect of anti-hierarchical growth.
We identify and characterize a population of luminous, dust-poor quasars at 0<z<5 that is photometrically similar to objects previously found at z>6. This class of active galactic nuclei is known to show little IR emission from dusty structure, but it is poorly understood in terms of number evolution and dependence on physical quantities. To better understand the properties of these quasars, we compile a rest-frame UV to IR library of 41000 optically selected type 1 quasars with L_bol_>10^45.7^erg/s. After fitting the broadband spectral energy distributions (SEDs) with accretion disk and dust components, we find 0.6% of our sample to be hot dust-poor, with rest-frame 2.3{mu}m to 0.51{mu}m flux density ratios of -0.5dex or less. The dust-poor SEDs are blue in the UV-optical and weak in the mid-IR, such that their accretion disks are less obscured and the hot dust emission traces that of warm dust down to the dust-poor regime. At a given bolometric luminosity, dust-poor quasars are lower in black hole mass and higher in Eddington ratio than general luminous quasars, suggesting that they are in a rapidly growing evolutionary state in which the dust-poor phase appears as a short or rare phenomenon. The dust-poor fraction increases with redshift, and possible implications for their evolution are discussed.
The largest K-band flux-limited sample of luminous quasars to date has been constructed from the UKIRT (UK Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release, covering an effective area of 12.8deg^2^. Exploiting the K-band excess (KX) of all quasars with respect to foreground stars, including quasars experiencing dust reddening and objects with non-standard spectral energy distributions (SEDs), a list of targets suitable for spectroscopic follow-up observations with the AAOmega multi-object spectrograph is constructed, resulting in more than 200 confirmed active galactic nuclei (AGN). KX selection successfully identifies as quasar candidates objects that are excluded from the Sloan Digital Sky Survey (SDSS) quasar selection algorithm due to their colours being consistent with the stellar locus in optical colour space (with the space density of the excluded objects agreeing well with results from existing completeness analyses). Nearly half of the KX-selected quasars with K<=17.0 at z<3 are too faint in the i band to have been targeted by the SDSS quasar selection algorithm, revealing a large population of quasars with red i-K colours.
Using Chandra archive data we conduct a thorough survey of luminous X-ray sources. We directly analyze about 9400 ACIS Observations and cross-correlate the X-ray sources with 77000 galaxies within 250Mpc. The final catalog includes 119 unique luminous X-ray source candidates with L_X_>3x10^40^erg/s from 93 galaxies or 41 HLX candidates with L_X_>1x10^41^erg/s from 35 galaxies. We derive a moderate contamination rate due to foreground or background sources. We also cross-correlate the catalog with FIRST, perform variability and periodicity tests, and analyze one HLX candidate in particular. Our catalog could be a starting point to perform follow-up observations.
We present an near-ultraviolet star catalogue extracted from the Lunar-based Ultraviolet Telescope (LUT) survey program. LUT's observable sky area is a circular belt around the Moon's north pole, and the survey program covers a preferred area for about 2400 square degrees which includes a region of the Galactic plane. All the sources have signal-to-noise ratio larger than 5, and the corresponding magnitude limit is typically 14.4mag, which can be deeper as ~16 mag if the stray light contamination is in the lowest level. A total number of 86,467 stars are recorded in the catalogue.
In this paper we measure the far-infrared (FIR) and radio flux densities of a sample of 82 local gas-rich galaxies, including 70 "dwarf" galaxies (M_*_<10^9^M_{sun}_), from the Local Volume HI Survey (LVHIS), which is close to volume limited. It is found that LVHIS galaxies hold a tight linear FIR-radio correlation (FRC) over four orders of magnitude. However, for detected galaxies only, a trend of larger FIR-to-radio ratio with decreasing flux density is observed. We estimate the star formation rate by combining UV and mid-IR data using empirical calibration. It is confirmed that both FIR and radio emission are strongly connected with star formation but with significant non-linearity. Dwarf galaxies are found radiation deficient in both bands, when normalized by star formation rate. It urges a "conspiracy" to keep the FIR-to-radio ratio generally constant. By using partial correlation coefficient in Pearson definition, we identify the key galaxy properties associated with the FIR and radio deficiency. Some major factors, such as stellar mass surface density, will cancel out when taking the ratio between FIR and radio fluxes. The remaining factors, such as HI-to-stellar mass ratio and galaxy size, are expected to cancel each other due to the distribution of galaxies in the parameter space. Such cancellation is probably responsible for the "conspiracy" to keep the FRC alive.
