We introduce xCOLD GASS, a legacy survey providing a census of molecular gas in the local universe. Building on the original COLD GASS survey, we present here the full sample of 532 galaxies with CO (1-0) measurements from the IRAM 30m telescope. The sample is mass-selected in the redshift interval 0.01<z<0.05 from the Sloan Digital Sky Survey (SDSS) and therefore representative of the local galaxy population with M_*_>10^9^M_{sun}_. The CO (1-0) flux measurements are complemented by observations of the CO (2-1) line with both the IRAM 30 m and APEX telescopes, HI observations from Arecibo, and photometry from SDSS, WISE, and GALEX. Combining the IRAM and APEX data, we find that the ratio of CO (2-1) to CO (1-0) luminosity for integrated measurements is r_21_=0.79+/- 0.03, with no systematic variations across the sample. The CO (1-0) luminosity function is constructed and best fit with a Schechter function with parameters L_CO_^* ^=(7.77+/-2.11)x10^9^K.(km/s).pc^2^, {phi}^*^=(9.84+/-5.41)x10^-4^Mpc^-3^, and {alpha}=-1.19+/-0.05. With the sample now complete down to stellar masses of 10^9^M_{sun}_, we are able to extend our study of gas scaling relations and confirm that both molecular gas fractions (f_H2_) and depletion timescale (t_dep_(H2)) vary with specific star formation rate (or offset from the star formation main sequence) much more strongly than they depend on stellar mass. Comparing the xCOLD GASS results with outputs from hydrodynamic and semianalytic models, we highlight the constraining power of cold gas scaling relations on models of galaxy formation.
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters and trace the evolution of X-ray scaling relations. In this paper we present the first data release from the XMM Cluster Survey (XCS-DR1). This consists of 503 optically confirmed, serendipitously detected, X-ray clusters. Of these clusters, 256 are new to the literature and 357 are new X-ray discoveries. We present 463 clusters with a redshift estimate (0.06<z<1.46), including 261 clusters with spectroscopic redshifts. The remainder have photometric redshifts. In addition, we have measured X-ray temperatures (TX) for 401 clusters (0.4<TX<14.7keV).
Recent observational progress has enabled the detection of galaxy clusters and groups out to very high redshifts and for the first time allows detailed studies of galaxy population properties in these densest environments in what was formerly known as the "redshift desert" at z>1.5. We aim to investigate various galaxy population properties of the massive X-ray luminous galaxy cluster XDCP J0044.0-2033 at z=1.58, which constitutes the most extreme currently known matter-density peak at this redshift. We analyzed deep VLT/HAWK-I near-infrared data with an image quality of 0.5" and limiting Vega magnitudes (50% completeness) of 24.2 in J- and 22.8 in the Ks band, complemented by similarly deep Subaru imaging in i and V, Spitzer observations at 4.5um, and new spectroscopic observations with VLT/FORS 2.
We present the X-ray point-source catalog produced from the Chandra Advanced CCD Imaging Spectrometer (ACIS-I) observations of the combined ~3.2deg^2^ DEEP2 (XDEEP2) survey fields, which consist of four ~0.7-1.1deg^2^ fields. The combined total exposures across all four XDEEP2 fields range from ~10ks to 1.1Ms. We detect X-ray point sources in both the individual ACIS-I observations and the overlapping regions in the merged (stacked) images. We find a total of 2976 unique X-ray sources within the survey area with an expected false-source contamination of ~30 sources (<~1%). Additionally, we present a Bayesian-style method for associating the X-ray sources with optical photometric counterparts in the DEEP2 catalog (complete to R_AB_<25.2) and find that 2126 (~71.4%+/-2.8%) of the 2976 X-ray sources presented here have a secure optical counterpart with a <~6% contamination fraction. We provide the DEEP2 optical source properties (e.g., magnitude, redshift) as part of the X-ray-optical counterpart catalog.
Photometric redshifts, which have become the cornerstone of several of the largest astronomical surveys like PanStarrs, DES, J-PAS and LSST, require precise measurements of galaxy photometry in different bands using a consistent physical aperture. This is not trivial, due to the variation in the shape and width of the point spread function (PSF) introduced by wavelength differences, instrument positions and atmospheric conditions. Current methods to correct for this effect rely on a detailed knowledge of PSF characteristics as a function of the survey coordinates, which can be difficult due to the relative paucity of stars tracking the PSF behaviour. Here we show that it is possible to measure accurate, consistent multicolour photometry without knowing the shape of the PSF. The Chebyshev-Fourier functions (CHEFs) can fit the observed profile of each object and produce high signal-to-noise integrated flux measurements unaffected by the PSF. These total fluxes, which encompass all the galaxy populations, are much more useful for galaxy evolution studies than aperture photometry. We compare the total magnitudes and colours obtained using our software to traditional photometry with SExtractor, using real data from the COSMOS survey and the Hubble Ultra-Deep Field (HUDF). We also apply the CHEF technique to the recently published eXtreme Deep Field (XDF) and compare the results to those from ColorPro on the HUDF. We produce a photometric catalogue with 35732 sources (10823 with signal-to-noise ratio >=5), reaching a photometric redshift precision of 2 per cent due to the extraordinary depth and wavelength coverage of the eXtreme Deep Field images.
We present here Stark widths and shifts for 20 Xe II multiplets which are of interest for laboratory plasma research as well as for the analysis of Hg-Mn stars spectra. For calculations the modified semiempirical approach was used. The obtained results are compared with the available experimental data.
The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. Combining the RASS Bright and Faint Source Catalogs (Cat. <IX/10>, 1RXS and <IX/29>) yields an average of about three X-ray sources per square degree. However, while X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. We use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g>15[mag]). Instead, we use SDSS photometry, correlations with the Two Micron All Sky Survey and other catalogs, and spectroscopy from the Apache Point Observatory 3.5m telescope to identify these stellar X-ray counterparts. Our sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. We identify 17 new X-ray-emitting DA (hydrogen) WDs, of which three are newly identified WDs. We report on follow-up observations of three candidate cool X-ray-emitting WDs (one DA and two DB (helium) WDs); we have not confirmed X-ray emission from these WDs.
Photospheric abundances are presented for 27 elements from carbon to europium in 181 F and G dwarfs from a differential local thermodynamic equilibrium (LTE) analysis of high-resolution and high signal-to-noise ratio spectra. Stellar effective temperatures (T_eff_) were adopted from an infrared flux method calibration of Stroemgren photometry. Stellar surface gravities (g) were calculated from Hipparcos parallaxes and stellar evolutionary tracks. Adopted T_eff_ and g values are in good agreement with spectroscopic estimates. Stellar ages were determined from evolutionary tracks. Stellar space motions (U, V, W) and a Galactic potential were used to estimate Galactic orbital parameters. These show that the vast majority of the stars belong to the Galactic thin disc.
The main goal of this work is to explore which elements carry the most information about the birth origin of stars and, as such, which are best suited for chemical tagging. We explored different techniques to minimize the effect of outlier value lines in the abundances by using Ni abundances derived for 1111 FGK-type stars. We evaluate how the limited number of spectral lines can affect the final chemical abundance. Then we make an efficient even footing comparison of the [X/Fe] scatter between the elements that have a different number of observable spectral lines in the studied spectra. When several spectral lines are available, we find that the most efficient way of calculating the average abundance of elements is to use a weighted mean (WM), whereby we consider the distance from the median abundance as a weight. This method can be used effectively without removing suspected outlier lines. When the same number of lines are used to determine chemical abundances, we show that the [X/Fe] star-to-star scatter for iron group and alpha-capture elements is almost the same. The largest scatter among the studied elements, was observed for Al and the smallest for Cr and Ni. We recommend caution when comparing [X/Fe] scatters among elements where a different number of spectral lines are available. A meaningful comparison is necessary to identify elements that show the largest intrinsic scatter, which can then be used limit of [X/H] are very abrupt.
The {chi}^1^ Fornacis cluster (Alessi 13) is one of a few open clusters of its age and distance in the Solar neighbourhood that ought to benefit from more attention as it can serve as a cornerstone for numerous future studies related to star and planet formation. Aims: We take advantage of the early installment of the third data release of the Gaia space mission in combination with archival data and our own observations, to expand the census of cluster members and revisit some properties of the cluster. Methods: We applied a probabilistic method to infer membership probabilities over a field of more than 1000deg^2^ to select the most likely cluster members and derive the distances, spatial velocities, and physical properties of the stars in this sample. Results: We identify 164 high-probability cluster members (including 61 new members) covering the magnitude range from 5.1 to 19.6mag in the G-band. Our sample of cluster members is complete down to 0.04M_{sun}_. We derive the distance of 108.4+/-0.3pc from Bayesian inference and confirm that the cluster is comoving with the Tucana-Horologium, Columba, and Carina young stellar associations. We investigate the kinematics of the cluster from a subsample of stars with measured radial velocities and we do not detect any significant expansion or rotation effects in the cluster. Our results suggest that the cluster is somewhat younger (about 30Myr) than previously thought. Based on spectroscopic observations, we argue that the cluster is mass-segregated and that the distribution of spectral types shows little variation compared to other young stellar groups. Conclusions: In this study, we deliver the most complete census of cluster members that can be done with Gaia data alone and we use this new sample to provide an updated picture on the 6D structure of the cluster.
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