We present 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan ...Digital Sky Survey (SDSS). We use morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data- quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in our final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. We present new spectral classifications and H alpha measurements for an additional 79 stars. The catalog is dominated by main-sequence stars; we estimate the fraction of giants in ChESS is image10%. We identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. We derive distances from image10 to 2000 pc for the stars in our catalog using photometric parallax relations appropriate for dwarfs on the main sequence and calculate their X-ray and bolometric luminosities. These stars lie in a unique space in the L sub(X)-distance plane, filling the gap between the nearby stars identified as counterparts to sources in the ROSAT All Sky Survey and the more distant stars detected in deep Chandra and XMM-Newton surveys. For 36 newly identified X-ray- emitting M stars we calculate L sub(H alpha )/L sub(bol). The quantities L sub(H alpha )/L sub(bol) and L sub(X)/L sub(bol) are linearly related below image, while L sub(H alpha )/L sub(bol) appears to turn over at larger L sub(X)/L sub(bol) values. Stars with reliable SDSS photometry have an image0.1 mag blue excess in image, likely due to increased chromospheric continuum emission. Photometric metallicity estimates suggest that the sample is evenly split between the young and old disk populations of the Galaxy; the lowest activity sources belong to the old disk population, a clear signature of the decay of magnetic activity with age. Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk.
We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray ...and optical cluster detection methods. In 130 archival Chandra pointings covering 13 deg super(2), we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about 610 super(-14) ergs cm super(-2) s super(-1), with a median cluster core radius of 21". For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO 4 m MOSAIC g', r', and i' imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z 6 0.7. From the overlapping 6.1 deg super(2) X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5-2 keV) is L sub(X) = super((2.65 c 0.19)) x 10 super(43) ergs s super(-1). The clusters in our sample that are only detected in our optical data are poorer on average (64 s) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions.
We present the analysis of the color-magnitude relation (CMR) for a sample of 57 X-ray-detected Abell clusters within the redshift interval 0.02 less than or equal to z less than or equal to 0.18. We ...use the B - R versus R color-magnitude plane to establish that the CMR is present in all our low-redshift clusters and can be parameterized by a single straight line. We find that the CMRs for this large cluster sample of different richness and cluster types are consistent with having universal properties. The k-corrected colors of the individual CMRs in the sample at a fixed absolute magnitude have a small intrinsic dispersion of similar to 0.05 mag. The slope of the CMR is consistent with being the same for all clusters, with the variations entirely accountable by filter band shifting effects. We determine the mean of the dispersion of the 57 CMRs to be 0.074 mag, with a small rms scatter of 0.026 mag. However, a modest amount of the dispersion arises from photometric measurement errors and possible background cluster superpositions, and the derived mean dispersion is an upper limit. Models that explain the CMR in terms of metallicity and passive evolution can naturally reproduce the observed behavior of the CMR in this paper. The observed properties of the CMR are consistent with models in which the last episode of strong star formation in cluster early-type galaxies occurred significantly more than similar to 3 Gyr ago and the core set of early-type galaxies in clusters were formed more than 7 Gyr ago. The universality of the CMR provides us with an important tool for cluster detection and redshift estimation. A very accurate photometric cluster redshift estimator can be devised based on the apparent color shift of the CMR due to redshift. This calibrator has the additional advantage of being very efficient since only two bands are needed. An empirically calibrated redshift estimator based on the B - R color of the CMR for clusters with z < 0.20 produces an accuracy of Delta z similar to 0.010. Background clusters, typically at z similar to 0.25 and previously unknown, are found in this survey in the color-magnitude diagrams as secondary CMRs to the red of the target cluster CMRs. We also find clear cases of apparent X-ray substructure that are due to these cluster superpositions. This suggests that X-ray observations of clusters are also subject to a significant amount of projection contaminations.
We use a statistical sample of -500 rich clusters taken from 72 deg super(2) of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of similar to 30,000 red-sequence galaxies in clusters ...over the redshift range 0.35 < z < 0.95. We construct red-sequence luminosity functions (RSLFs) for a well-defined, homogeneously selected, richness-limited sample. The RSLF at higher redshifts shows a deficit of faint red galaxies (to M sub(v) greater than or equal to -19.7) with their numbers increasing toward the present epoch. This is consistent with the "downsizing" picture in which star formation ended at earlier times for the most massive (luminous) galaxies and more recently for less massive (fainter) galaxies. We observe a richness dependence to the downsizing effect in the sense that, at a given redshift, the drop-off of faint red galaxies is greater for poorer (less massive) clusters, suggesting that star formation ended earlier for galaxies in more massive clusters. The decrease in faint red-sequence galaxies is accompanied by an increase in faint blue galaxies, implying that the process responsible for this evolution of faint galaxies is the termination of star formation, possibly with little or no need for merging. At the bright end, we also see an increase in the number of blue galaxies with increasing redshift, suggesting that termination of star formation in higher mass galaxies may also be an important formation mechanism for higher mass ellipticals. By comparing with a low-redshift Abell cluster sample, we find that the downsizing trend seen within RCS-1 has continued to the local universe.
We present first results of an examination of the optical properties of the galaxy populations in Sunyaev-Zel'dovich Effect (SZE) selected galaxy clusters. Using clusters selected by the South Pole ...Telescope survey and deep multiband optical data from the Blanco Cosmology Survey, we measure the radial profile, the luminosity function (LF), the blue fraction, and the halo occupation number (HON) of the galaxy populations of these four clusters with redshifts ranging from 0.3 to 1. Our goal is to understand whether there are differences among the galaxy populations of these SZE-selected clusters and previously studied clusters selected in the optical and the X-ray. The radial distributions of galaxies in the four systems are consistent with Navarro-Frenk-White profiles with a galaxy concentration of 3 to 6. We show that the characteristic luminosities in griz bands are consistent with passively evolving populations emerging from a single burst at redshift z = 3. The faint-end power-law slope of the LF is found to be on average Delta *a --1.2 in griz. HONs (to m* + 2) for these systems appear to be consistent with those based on X-ray-selected clusters. The blue fraction estimated to 0.36 L*, for the three lower redshift systems, suggests an increase with redshift, although with the current sample the uncertainties are still large. Overall, this pilot study of the first four clusters provides no evidence that the galaxy populations in these systems differ significantly from those in previously studied cluster populations selected in the X-ray or the optical.
We have investigated 136 Chandra extragalactic sources, including 93 galaxies with narrow emission lines (NELGs)and 43 with only absorption lines (ALGs). Based on fx/fo, L sub(X), X-ray spectral ...hardness, and optical emission-line diagnostics, we have conservatively classified 36 normal galaxies and 71 AGNs. Their redshift ranges from 0.01 to 1.2, with normal galaxies in the range z = 0.01-0.3. Our normal galaxies appear to share characteristics with local galaxies, as expected from the X-ray binary populations and the hot interstellar matter (ISM). In conjunction with normal galaxies found in other surveys, we found no statistically significant evolution in L sub(X)/L sub(B), within the limited z range ( 0.1). The best-fit slope of our log(N)-log(S) relationship is -1.5 for both S (0.5-2 keV) and B (0.5-8 keV) energy bands, which is considerably steeper than that of the AGN-dominated cosmic background sources, but slightly flatter than the previous estimate, indicating that normal galaxies will not exceed the AGN population until f sub(X)(0.5-2.0 keV) 62 x 10 super(-18) ergs s super(-1) cm super(-2) (a factor of 65 lower than the previous estimate). A group of NELGs appear to be heavily obscured in X-rays. After correcting for intrinsic absorption, their X-ray luminosities could be L sub(X) > 10 super(44) ergs s super(-1), making them type 2 quasar candidates. While most X-ray-luminous ALGs do not appear to be significantly absorbed, we found two heavily obscured objects that could be as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A galaxy candidates. The X-ray spectra of both galaxies are soft, and one of them has a nearby close companion galaxy, supporting the merger/interaction scenario rather than the dusty starburst hypothesis.
We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS) imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive galaxy cluster at a redshift of z = ...0.3838. The lens (BCS J2352--5452) was discovered while examining i- and z-band images being acquired in 2006 October during a BCS observing run. Follow-up spectroscopic observations with the Gemini Multi-Object Spectrograph instrument on the Gemini-South 8 m telescope confirmed the lensing nature of this system. Using weak-plus-strong lensing, velocity dispersion, cluster richness N 200, and fitting to a Navarro-Frenk-White (NFW) cluster mass density profile, we have made three independent estimates of the mass M 200 which are all very consistent with each other. The combination of the results from the three methods gives M 200 = (5.1 ? 1.3) X 1014 M , which is fully consistent with the individual measurements. The final NFW concentration c 200 from the combined fit is c 200 = 5.4+1.4 -- 1.1. We have compared our measurements of M 200 and c 200 with predictions for (1) clusters from Delta *LCDM simulations, (2) lensing-selected clusters from simulations, and (3) a real sample of cluster lenses. We find that we are most compatible with the predictions for Delta *LCDM simulations for lensing clusters, and we see no evidence based on this one system for an increased concentration compared to Delta *LCDM. Finally, using the flux measured from the O II3727 line we have determined the star formation rate of the source galaxy and find it to be rather modest given the assumed lens magnification.
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