- ID:
- ivo://CDS.VizieR/J/other/ApSS/365.89
- Title:
- Gaia Alerts with LAMOST and SDSS
- Short Name:
- J/other/ApSS/365
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ESA-Gaia satellite is regularly producing Alerts on objects where photometric variability has been detected after several passages over the same region of the sky. The physical nature of these objects has often to be determined with the help of complementary observations from ground-based facilities. We have compared the list of Gaia Alerts (from the beginning in 2014 to Nov. 1st, 2018) with archival LAMOST and SDSS spectroscopic data. A search radius of 3" has been adopted. In using survey data, the date of the ground-based observation rarely corresponds to the date of the Alert, but this allows at least the identification of the source if it is persistent, or the host galaxy if the object was only transient like a supernova (SN). Some of the objects have several LAMOST observations, and we complemented this search by adding also SDSS DR15 data in order to look for long-term variability. A list of Gaia Nuclear Transients (GNT) from Kostrzewa-Rutkowska et al. (2018. 2018MNRAS.481..307K, Cat. J/MNRAS/481/307), has been included in this search also. We found 26 Gaia Alerts with spectra in LAMOST+SDSS labelled as stars, among which 12 have multi-epoch spectra. A majority of them are Cataclysmic Variables (CVs). Similarly, 206 Gaia Alerts have associated spectra labelled as galaxies, among which 49 have multi-epoch spectra. Those spectra were generally obtained on a date widely different from the Alert date, and are mostly emission-line galaxies with no particularity (except a few Seyferts), leading to the suspicion that most of the Alerts were due to a SN. As for the GNT list, we found 55 associated spectra labelled as galaxies, among them 13 with multi-epoch spectra. In these two galaxy samples, in only two cases, Gaia17aal and GNTJ170213+2543, was the date of the spectroscopic observation close enough to the Alert date: we find a trace of the SN itself in their LAMOST spectrum, both being now classified here as a type Ia SN. Compared to the galaxy sample from the Gaia alerts, the GNT sample has a higher proportion of AGNs, suggesting that some of the detected variations are also due to the AGN itself. Similarly for Quasars, we found only 30 Gaia Alerts but 68 GNT cases associated with single epoch quasar spectra in the databases. In addition to those, 12 plus 23 are quasars where multi-epoch spectra are available. For ten out of these 35, their multi-epoch spectra show appearance or disappearance of the broad Balmer lines and also variations in the continuum, qualifying them as "Changing Look Quasars" and therefore significantly increasing the available sample of such objects.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/611/A52
- Title:
- Gaia DR1 QSO magnitude
- Short Name:
- J/A+A/611/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first release of the Gaia catalog is available since 14 September 2016. It is a first step in the realization of the future Gaia reference frame. This reference frame will be materialized by the optical positions of the sources and will be compared with and linked to the International Celestial Reference Frame, materialized by the radio position of extragalactic sources. As in the radio domain, it can be reasonably postulated that quasar optical flux variations can alert us to potential changes in the source structure. These changes could have important implications for the position of the target photocenters (together with the evolution in time of these centers) and in parallel have consequences for the link of the reference systems. A set of nine optical telescopes was used to monitor the magnitude variations, often at the same time as Gaia, thanks to the Gaia Observation Forecast Tool. The Allan variances, which are statistical tools widely used in the atomic time and frequency community, are introduced.
- ID:
- ivo://CDS.VizieR/VII/285
- Title:
- Gaia DR2 quasar and galaxy classification
- Short Name:
- VII/285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide probabilistic quasar and galaxy classifications for 2.7 million sources in Gaia Data Release 2. This has been achieved using a supervised classification method (Gaussian Mixture Models) based only on photometric and astrometric data (8 features) in Gaia-DR2. The model is trained empirically to classify objects into three classes - star, quasar, galaxy - for all objects with G>=14.5mag down to the Gaia magnitude limit of G=21.0mag. We provide the probabilities for being a quasar (pqso) and a galaxy (pgal); the probability of being a star is pstar = 1-(pqso+pgal), and all other Gaia data can be obtained by cross-matching Gaia-DR2 using the source identifier. As our main goal is to identify extragalactic objects, we only report objects with pqso+pgal>0.5. These probabilities incorporate a sensible class prior, namely that quasars are 500 times rarer than stars, and that galaxies 7500 times rarer than stars. See the paper for details of the purity and completeness of samples drawn from this catalogue, and for more details of its construction, contents, and validation.
- ID:
- ivo://CDS.VizieR/J/ApJS/105/369
- Title:
- Galactic H I column densities
- Short Name:
- J/ApJS/105/369
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined accurate values of the Galactic neutral hydrogen column density, N_H_, toward 220 quasars and active galactic nuclei from 21cm H I measurements made on the 130 Foot Telescope (42.7m). Accurate values of N_H_ have now been obtained for the whole PG bright quasar sample and most quasars that have been observed by ROSAT and the Hubble Space Telescope through mid-1993. The spectra were corrected for stray 21cm radiation yielding values of N_H_ with a typical uncertainty of 1x10^19cm^-2 for high Galactic latitude directions. The H I column densities will be useful for correcting for interstellar opacity at UV and soft X-ray wavelengths, and for estimating the reddening and extinction toward these objects.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A136
- Title:
- Galaxies and QSOs FIR size and surface brightness
- Short Name:
- J/A+A/591/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Herschel 70 to 160{mu}m images to study the size of the far-infrared emitting region in about 400 local galaxies and quasar (QSO) hosts. The sample includes normal "main-sequence" star-forming galaxies, as well as infrared luminous galaxies and Palomar-Green QSOs, with different levels and structures of star formation. Assuming Gaussian spatial distribution of the far-infrared (FIR) emission, the excellent stability of the Herschel point spread function (PSF) enables us to measure sizes well below the PSF width, by subtracting widths in quadrature. We derive scalings of FIR size and surface brightness of local galaxies with FIR luminosity, with distance from the star-forming main-sequence, and with FIR color. Luminosities L_FIR_~10^11^L_{sun}_ can be reached with a variety of structures spanning 2dex in size. Ultraluminous L_FIR_~10^12^L_{sun}_ galaxies far above the main-sequence inevitably have small R_e,70_~0.5kpc FIR emitting regions with large surface brightness, and can be close to optically thick in the FIR on average over these regions. Compared to these local relations, first ALMA sizes for the dust emission regions in high redshift galaxies, measured at somewhat longer rest wavelengths, suggest larger sizes at the same IR luminosity. We report a remarkably tight relation with 0.15dex scatter between FIR surface brightness and the ratio of [CII] 158{mu}m emission and FIR emission - the so-called [CII]-deficit is more tightly linked to surface brightness than to FIR luminosity or FIR color. Among 33 z<=0.1 PG QSOs with typical L_FIR_/L_Bol,AGN_~0.1, 19 have a measured 70{mu}m half light radius, with median R_e,70_=1.1kpc. This is consistent with the FIR size for galaxies with similar L_FIR_ but lacking a QSO, in accordance with a scenario where the rest FIR emission of these types of QSOs is, in most cases, due to host star formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/40
- Title:
- Galaxy clusters aligned with quasars. III.
- Short Name:
- J/ApJ/774/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Gemini/GMOS-S multi-object spectroscopy of 31 galaxy cluster candidates at redshifts between 0.2 and 1.0 and centered on QSO sight lines taken from Lopez et al. (Paper I, J/ApJ/679/1144). The targets were selected based on the presence of an intervening MgII absorption system at a similar redshift to that of a galaxy cluster candidate lying at a projected distance <2h_71_^-1^Mpc from the QSO sight line (a "photometric hit"). The absorption systems span rest-frame equivalent widths between 0.015 and 2.028{AA}. The general population of our confirmed absorbing galaxies have luminosities L_B_~L_B_^*^ and mean rest-frame colors (R_c_-z') typical of S_cd_ galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/679/1144
- Title:
- Galaxy clusters in LOS to background QSOs. I.
- Short Name:
- J/ApJ/679/1144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the first optical survey of absorption systems associated with cluster galaxies at z=0.3-0.9. We have cross-correlated quasars from the third data release of the SDSS (Cat. VII/243) with high-redshift cluster/group candidates from the Red-Sequence Cluster Survey (Cat. J/ApJS/157/1). We have found 442 quasar-cluster pairs for which the MgII{lambda}2796, 2803 doublet might be detected at a transverse (physical) distance d<2h^-1^_71_Mpc from the cluster centers. To investigate the incidence dN/dz and equivalent width distribution n(W) of MgII systems at cluster redshifts, two statistical samples were drawn out of these pairs: one made of high-resolution spectroscopic quasar observations (46 pairs), and one made of quasars used in MgII searches found in the literature (375 pairs).
- ID:
- ivo://CDS.VizieR/J/MNRAS/413/3059
- Title:
- 4098 galaxy clusters in SDSS Stripe 82
- Short Name:
- J/MNRAS/413/3059
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of 4098 photometrically selected galaxy clusters with a median redshift <z>=0.32 in the 270deg^2^ "Stripe 82" region of the Sloan Digital Sky Survey (SDSS), covering the celestial equator in the Southern Galactic Cap (-50{deg}<RA<59{deg}, |DE|<=1.25). Owing to the multi-epoch SDSS coverage of this region, the ugriz photometry is ~2mag deeper than single scans within the main SDSS footprint. We exploit this to detect clusters of galaxies using an algorithm that searches for statistically significant overdensities of galaxies in a Voronoi tessellation of the projected sky.
- ID:
- ivo://CDS.VizieR/J/A+A/551/A8
- Title:
- Galaxy clusters in XMM field within CFHT-LS D4
- Short Name:
- J/A+A/551/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The XMM-Newton Distant Cluster Project (XDCP) aims at the identification of a well defined sample of X-ray selected clusters of galaxies at redshifts z>0.8. As part of this project, we analyse the deep XMM-Newton exposure covering one of the CFHTLS deep fields to quantify the cluster content. We validate the optical follow-up strategy as well as the X-ray selection function. We search for extended X-ray sources in archival XMM-Newton EPIC observations. Multi-band optical imaging is performed to select high redshift cluster candidates among the extended X-ray sources. Here we present a catalogue of the extended sources in one the deepest LBQS ~250ks XMM-Newton fields targeting LBQS J2212-1759 covering ~0.2 square degrees. The cluster identification is based, among others, on deep imaging with the ESO VLT and from the CFHT legacy survey. The confirmation of cluster candidates is done by VLT/FORS2 multi-object spectroscopy. Photometric redshifts from the CFHTLS D4 are utilized to confirm the effectiveness of the X-ray cluster selection method. The survey sensitivity is computed with extensive Monte-Carlo simulations. At a flux limit of S(0.5-2.0keV)~2.5e-15erg/s/cm2 we achieve a completeness level higher than 50% in an area of ~0.13 square degrees. We detect six galaxy clusters above this limit with optical counterparts, of which 5 are new spectroscopic discoveries. Two newly discovered X-ray luminous galaxy clusters are at z>1.0, another two at z=0.41 and one at z=0.34. For the most distant X-ray selected cluster in this field at z=1.45 we find additional (active) member galaxies from both X-ray and spectroscopic data. Additionally, we find evidence of large scale structures at moderate redshifts of z=0.41 and z=0.34. The quest for distant clusters in archival XMM-Newton data has led to the detection of six clusters in a single field, making XMM-Newton an outstanding tool for cluster surveys. Three of these clusters are at z>1, which emphasises the valuable contribution of small, yet deep surveys to cosmology. Beta-models are appropriate descriptions for the cluster surface brightness to perform cluster detection simulations in order to compute the X-ray selection function. The constructed log N-log S tends to favour a scenario where no evolution in the cluster X-ray luminosity function (XLF) takes place.
- ID:
- ivo://CDS.VizieR/J/ApJS/193/28
- Title:
- Galaxy survey around 20 UV-bright quasars
- Short Name:
- J/ApJS/193/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We publish the survey for galaxies in 20 fields containing ultraviolet bright quasars (with z_em_~0.1-0.5) that can be used to study the association between galaxies and absorption systems from the low-z intergalactic medium (IGM). The survey is magnitude limited (R~19.5mag) and highly complete out to 10' from the quasar in each field. It was designed to detect dwarf galaxies (L~0.1L*) at an impact parameter {rho}~1Mpc (z=0.1) from a quasar. The complete sample (all 20 fields) includes R-band photometry for 84718 sources and confirmed redshifts for 2800 sources. This includes 1198 galaxies with 0.005<z<(z_em_-0.01) at a median redshift of 0.18, which may associated with IGM absorption lines. All of the imaging was acquired with cameras on the Swope 40" telescope and the spectra were obtained via slit mask observations using the WFCCD spectrograph on the Dupont 100" telescope at Las Campanas Observatory.
