- ID:
- ivo://CDS.VizieR/J/ApJ/766/60
- Title:
- GALEX Time Domain Survey I. UV variable sources
- Short Name:
- J/ApJ/766/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ~40deg^2^ of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of ~3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5{sigma} level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). We detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |{Delta}m|=4.6mag and 2.9mag, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with NUV<23mag and |{Delta}m|>0.2mag of ~8.0, 7.7, and 1.8deg^-2^ for quasars, active galactic nuclei, and RR Lyrae stars, respectively. We also calculate a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of ~15 and 52deg^-2^/yr for M dwarfs and extragalactic transients, respectively.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/728/23
- Title:
- GALEX UV-bright high-redshift quasars
- Short Name:
- J/ApJ/728/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the small population of high-redshift (z_em_>2.7) quasars detected by the Galaxy Evolution Explorer(GALEX), whose far-UV emission is not extinguished by intervening HI Lyman limit systems. We correlate almost all verified z_em_>2.7 quasars to the GALEX GR4 source catalog covering ~25000deg^2^, yielding 304 sources detected at signal-to-noise ratio (S/N)>3. However, ~50% of these are only detected in the GALEX NUV band, signaling the truncation of the FUV flux by low-redshift optically thick Lyman limit systems. We regard 52 quasars detected at S/N>3 to be most promising for Hubble Space Telescope follow-up, with an additional 114 quasars if we consider S/N>2 detections in the FUV. Combining the statistical properties of HI absorbers with the Sloan Digital Sky Survey (SDSS) quasar luminosity function, we predict a large all-sky population of ~200 quasars with z_em_>2.7 and i<~19 that should be detectable at the HeII edge at m_304_<21. However, SDSS provides just half of the NUV-bright quasars that should have been detected by SDSS and GALEX. With mock quasar photometry we revise the SDSS quasar selection function, finding that SDSS systematically misses quasars with blue u-g<~2 colors at 3<~z_em_<~3.5 due to overlap with the stellar locus in color space.
- ID:
- ivo://CDS.VizieR/J/ApJ/879/22
- Title:
- GALFA-HI search for local dwarf galaxies
- Short Name:
- J/ApJ/879/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In recent years, ultrafaint dwarf (UFD) galaxies have been found through systematic searches of large optical surveys. However, the existence of Leo T, a nearby gas-rich dwarf, suggests that there could be other nearby UFDs that are optically obscured but have gas detectable at nonoptical wavelengths. With this in mind, we perform a search of the full Galactic Arecibo L-band Feed Array HI (GALFA-HI) survey, a radio survey that covers one-third of the sky at velocities -650<V_LSR_<+650km/s, for neutral hydrogen sources. We are able to probe regions of the sky at lower Galactic latitudes and smaller |V_LSR_| compared to previous explorations. We use the Source Finding Application on GALFA-HI and select all sources with similar properties to Leo T and other local dwarf galaxies. We find 690 dwarf galaxy candidates, one of which is particularly promising and likely a new galaxy near the Galactic plane (b=-8{deg}) that is comparable in velocity width and HI-flux to other recently discovered local volume galaxies. We find we are sensitive to Leo T-like objects out to 1Mpc at velocities clear from background HI emission. We check each candidate's corresponding optical fields from Pan-STARRS and fit stars drawn from isochrones, but find no evidence of stellar populations. We thus find no other Leo T-like dwarfs within 500 kpc of the Milky Way in the one-third of the sky covered by the GALFA-HI footprint, and discuss our nondetection in a cosmological context.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/33
- Title:
- Gal. midplane Spitzer/IRAC candidate YSOs (SPICY)
- Short Name:
- J/ApJS/254/33
- Date:
- 19 Jan 2022 09:09:49
- Publisher:
- CDS
- Description:
- We present ~120000 Spitzer/IRAC candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between l~255{deg} and 110{deg}, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO data sets to take full advantage of Spitzer's spatial resolution and sensitivity in the mid-infrared ~3-9{mu}m range. Multiwavelength color/magnitude distributions provide intuition about how the classifier separates YSOs from other red IRAC sources and validate that the sample is consistent with expectations for disk/envelope-bearing pre-main-sequence stars. We also identify areas of IRAC color space associated with objects with strong silicate absorption or polycyclic aromatic hydrocarbon emission. Spatial distributions and variability properties help corroborate the youthful nature of our sample. Most of the candidates are in regions with mid-IR nebulosity, associated with star-forming clouds, but others appear distributed in the field. Using Gaia DR2 distance estimates, we find groups of YSO candidates associated with the Local Arm, the Sagittarius-Carina Arm, and the Scutum-Centaurus Arm. Candidate YSOs visible to the Zwicky Transient Facility tend to exhibit higher variability amplitudes than randomly selected field stars of the same magnitude, with many high-amplitude variables having light-curve morphologies characteristic of YSOs. Given that no current or planned instruments will significantly exceed IRAC's spatial resolution while possessing its wide-area mapping capabilities, Spitzer-based catalogs such as ours will remain the main resources for mid-infrared YSOs in the Galactic midplane for the near future.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/4116
- Title:
- GAMA. galaxy structure across green valley
- Short Name:
- J/MNRAS/477/4116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a sample of 472 local Universe (z<0.06) galaxies in the stellar mass range 10.25<logM*/M_{sun}_<10.75, we explore the variation in galaxy structure as a function of morphology and galaxy colour. Our sample of galaxies is sub-divided into red, green and blue colour groups and into elliptical and non-elliptical (disk-type) morphologies. Using KiDS and VIKING derived postage stamp images, a group of eight volunteers visually classified bars, rings, morphological lenses, tidal streams, shells and signs of merger activity for all systems. We find a significant surplus of rings (2.3{sigma}) and lenses (2.9{sigma}) in disk-type galaxies as they transition across the green valley. Combined, this implies a joint ring/lens green valley surplus significance of 3.3{sigma} relative to equivalent disk-types within either the blue cloud or the red sequence. We recover a bar fraction of ~44% which remains flat with colour, however, we find that the presence of a bar acts to modulate the incidence of rings and (to a lesser extent) lenses, with rings in barred disk-type galaxies more common by ~20-30 percentage points relative to their unbarred counterparts, regardless of colour. Additionally, green valley disk-type galaxies with a bar exhibit a significant 3.0{sigma} surplus of lenses relative to their blue/red analogues. The existence of such structures rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.
- ID:
- ivo://CDS.VizieR/J/ApJ/590/109
- Title:
- Gamma-ray blazar in northern sky
- Short Name:
- J/ApJ/590/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using survey data, we have re-evaluated the correlation of flat-spectrum radio sources with EGRET sources in the northern sky. An analysis incorporating the radio and X-ray properties and the gamma-ray source localization is used to gauge the reliability of associations and to search for counterparts of previously unidentified EGRET sources. Above |b|=10{deg}, where the classification is complete, we find that 70% of the northern EGRET sources have counterparts similar to the bright EGRET blazars. For several of these we identify known blazar counterparts more likely than the earlier proposed 3EG association; for ~20 we have new identifications. Spectroscopic confirmation of these candidates is in progress, and we have found flat-spectrum radio quasars and BL Lacertae counterparts with redshifts as high as 4. We also find strong evidence for a set of 28 objects with no plausible counterpart like the known EGRET blazars. These thus represent either a new extragalactic population or a population of Galactic objects with a large scale height. The survey has been extended into the plane, where we find several new blazar candidates; the bulk of the sources are, however, Galactic. Looking ahead to the GLAST era, we predict that several of the present 3EG sources are composite and that higher resolution data will break these into multiple blazar identifications.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A59
- Title:
- Gas kinematics in CALIFA survey
- Short Name:
- J/A+A/573/A59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ionized gas kinematics provide important clues to the dynamical structure of galaxies and hold constraints to the processes driving their evolution. The motivation of this work is to provide an overall characterization of the kinematic behavior of the ionized gas of the galaxies included in the Calar Alto Legacy Integral field Area (CALIFA), offering kinematic clues to potential users of the CALIFA survey for including kinematical criteria in their selection of targets for specific studies. From the first 200 galaxies observed by CALIFA survey in its two configurations, we present the two-dimensional kinematic view of the 177 galaxies satisfaying a gas content/detection threshold. After removing the stellar contribution, we used the cross-correlation technique to obtain the radial velocity of the dominant gaseous component for each spectrum in the CALIFA data cubes for different emission lines (namely, [OII] {lambda}{lambda}3726,3729, [OIII] {lambda}{lambda}4959,5007, H{alpha}+[NII] {lambda}{lambda}6548,6584, and [SII]{lambda}{lambda}6716,6730). The main kinematic parameters measured on the plane of the sky were directly derived from the radial velocities with no assumptions on the internal prevailing motions. Evidence of the presence of several gaseous components with different kinematics were detected by using [OIII] {lambda}{lambda}4959,5007 emission line profiles.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/290
- Title:
- GASS HI survey of the lower halo
- Short Name:
- J/ApJ/688/290
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected over 400 HI clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans 18{deg} in longitude, 40{deg} in latitude, and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6K, a median velocity width of 12.8km/s, and angular sizes <~1{deg}. The motion of these clouds is dominated by Galactic rotation with a random cloud-to-cloud velocity dispersion of 18km/s. A sample of clouds likely to be near tangent points was analyzed in detail. These clouds have radii on the order of 30pc and a median HI mass of 630M_{sun}_. The population has a vertical scale height of 400pc and is concentrated in Galactocentric radius, peaking at R=3.8kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/74
- Title:
- GASS HVCs in the Magellanic Leading Arm region
- Short Name:
- J/ApJ/764/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of high-velocity clouds in the region of the Magellanic Leading Arm. The catalog is based on neutral hydrogen (H I) observations from the Parkes Galactic All-Sky Survey. Excellent spectral resolution allows clouds with narrow-line components to be resolved. The total number of detected clouds is 419. We describe the method of cataloging and present the basic parameters of the clouds. We discuss the general distribution of the high-velocity clouds and classify the clouds based on their morphological type. The presence of a significant number of head-tail clouds and their distribution in the region is discussed in the context of Magellanic System simulations. We suggest that ram-pressure stripping is a more important factor than tidal forces for the morphology and formation of the Magellanic Leading Arm and that different environmental conditions might explain the morphological difference between the Magellanic Leading Arm and Magellanic Stream. We also discuss a newly identified population of clouds that forms the LA IV and a new diffuse bridge-like feature connecting the LA II and III complexes.
- ID:
- ivo://CDS.VizieR/J/PASP/125/477
- Title:
- Gas Survey of Protoplanetary Systems. I.
- Short Name:
- J/PASP/125/477
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the ACS instrument on the Herschel Space Observatory. This Open Time Key program, known as GASPS (Gas Survey of Protoplanetary Systems), targeted ~250 young stars in narrow wavelength regions covering the [OI] fine structure line at 63um the brightest far-infrared line in such objects. A subset of the brightest targets were also surveyed in [OI]145um, [CII] at 157um, as well as several transitions of HO and high-excitation CO lines at selected wavelengths between 78 and 180um. Additionally, GASPS included continuum photometry at 70, 100 and 160um, around the peak of the dust emission.
