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Xu Kong
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Xu Kong

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Astrophysics of Galaxies (31)
Cosmology and Nongalactic Astrophysics (22)
Astrophysics (4)
Solar and Stellar Astrophysics (4)
Instrumentation and Methods for Astrophysics (1)

Publications Authored By Xu Kong

The spectra of 413 star-forming (or HII) regions in M33 (NGC 598) were observed by using the multifiber spectrograph of Hectospec at the 6.5-m Multiple Mirror Telescope (MMT). By using this homogeneous spectra sample, we measured the intensities of emission lines and some physical parameters, such as electron temperatures, electron densities, and metallicities. Read More

We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for $z\sim$ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg$^2$ COSMOS field. We have identified 27 Lyman Alpha Emitter (LAE) candidates at $z=$ 6. Read More

We present a sample of 48 metal-poor galaxies at $ z < 0.14$ selected from 92,510 galaxies in the LAMOST survey. These galaxies are identified for their detection of the auroral emission line \oiii$\lambda$4363 above $3\sigma$ level, which allows a direct measurement of the electron temperature and the oxygen abundance. Read More

Observationally, a massive disk galaxy can harbor a bulge component that is comparably inactive as a quiescent galaxy (QG). It has been speculated that the quenched component contained in star-forming galaxies (SFGs) is the reason why the star formation main sequence (MS) has a shallow slope at high masses. In this paper, we present a toy model to quantify the quenched mass portion of SFGs ($f_{\rm Q}$) at fixed stellar mass ($M_{\ast}$) and to reconcile the MS slopes both in the low and the high mass regimes. Read More

Template-based extrapolations from only one photometric band can be a cost-effective method to estimate the total infrared (IR) luminosities ($L_{\mathrm{IR}}$) of galaxies. By utilizing multi-wavelength data that covers across 0.35--500\,$\mathrm{\mu m}$ in GOODS-North and GOODS-South fields, we investigate the accuracy of this monochromatic extrapolated $L_{\mathrm{IR}}$ based on three IR spectral energy distribution (SED) templates (\citealt[CE01]{Chary2001}; \citealt[DH02]{Dale2002}; \citealt[W08]{Wuyts2008a}) out to $z\sim 3. Read More

The average star formation rate (SFR) in galaxies has been declining since redshift of 2. A fraction of galaxies quench and become quiescent. We constrain two key properties of the quenching process: the quenching time scale and the quenching rate among galaxies. Read More

Affiliations: 1USTC, China, 2Shandong University, China, 3USTC, China, 4Dali University, China

We present a measurement of the spatial clustering of massive compact galaxies at $1.2\le z \le 3$ in CANDELS/3D-HST fields. We obtain the correlation length for compact quiescent galaxies (cQGs) at $z\sim1. Read More

Using a sample of ~6,000 local face-on star-forming galaxies (SFGs), we examine the correlations between the NUV-r colors both inside and outside the half-light radius, stellar mass M* and S\'{e}rsic index n in order to understand how the quenching of star formation is linked to galaxy structure. For these less dust-attenuated galaxies, NUV-r is found to be linearly correlated with Dn4000, supporting that NUV-r is a good photometric indicator of stellar age (or specific star formation rate). We find that: (1) At M*<10^{10. Read More

We present oxygen abundance measurements for 74 blue compact dwarf (BCD) galaxies in the redshift range in [0.2, 0.5] using the strong-line method. Read More

We investigate the structural properties of the underlying hosts of 34 blue compact dwarf (BCD) galaxies with deep near-infrared (NIR) photometry. The BCD sample is selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey in the Great observatories origins Deep Survey North and South fields. We extract the surface brightness profile (SBP) in the optical F 435W and NIR F 160W bands. Read More

A small fraction($<10\%$) of SDSS main sample galaxies(MGs) have not been targeted with spectroscopy due to the the fiber collision effect. These galaxies have been compiled into the input catalog of the LAMOST extra-galactic survey and named as the complementary galaxy sample. In this paper, we introduce the project and the status of the spectroscopies of the complementary galaxies in the first two years of the LAMOST spectral survey(till Sep. Read More

Using the Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) near-infrared high-resolution imaging from the 3D-HST survey, we analyze the morphology and structure of 502 ultraluminous infrared galaxies (ULIRGs; $L_{\rm IR}>10^{12}L_{\odot}$) at $1-1. Read More

In this paper, we apply a new statistical analysis technique, Mean Field approach to Bayesian Independent Component Analysis (MF-ICA), on galaxy spectral analysis. This algorithm can compress the stellar spectral library into a few Independent Components (ICs), and galaxy spectrum can be reconstructed by these ICs. Comparing to other algorithms which decompose a galaxy spectrum into a combination of several simple stellar populations, MF-ICA approach offers a large improvement in the efficiency. Read More

We present a study on physical properties for a large distant red galaxy (DRG) sample, using the $K$-selected multi-band photometry catalog of the COSMOS/UltraVISTA field and the CANDELS NIR data. Our sample includes 4485 DRGs with $(J-K)_\mathrm{AB}>1.16$ and $K_\mathrm{AB}<$23. Read More

It is unclear whether bulge growth is responsible for the flattening of the star formation main sequence (MS) at the high mass end. To investigate the role of bulges in shaping the MS, we compare the NUV$-r$ color between the central ($rRead More

We complement the PARSEC data base of stellar evolutionary tracks with new models of massive stars, from the pre-main sequence phase to the central carbon ignition. We consider a broad range of metallicities, 0.0001$\leq Z \leq$0. Read More

In this Letter, we investigate how galaxy mass assembly mode depends on stellar mass $M_{\ast}$, using a large sample of $\sim$10, 000 low redshift galaxies. Our galaxy sample is selected to have SDSS $R_{90}>5\arcsec.0$, which allows the measures of both the integrated and the central NUV$-r$ color indices. Read More

Utilizing a BzK-selected technique, we obtain 14550 star-forming galaxies (sBzKs) and 1763 passive galaxies (pBzKs) at z~2 from the K-selected (K<22.5) catalog in the COSMOS/UltraVISTA field. The differential number counts of sBzKs and pBzKs are consistent with the results from the literature. Read More

We present a study on the physical properties of compact star-forming galaxies (cSFGs) with $M_{*}\geq10^{10}M_{\odot}$ and $2\leq z\leq3$ in the COSMOS and GOODS-S fields. We find that massive cSFGs have a comoving number density of $(1.0\pm0. Read More

Using high-resolution HST/Wide Field Camera 3 F125W imaging from the CANDELS-COSMOS field, we report the the structural and morphological properties of Extremely Red Objects (EROs) at $z\sim1$. Based on the UVJ color criteria, we separate EROs into two types: old passive galaxies (OGs) and dusty star-forming galaxies (DGs). For a given stellar mass, we find that the mean size of OGs (DGs) is smaller by a factor of $\sim2$ (1. Read More

Many stellar models present difficulties in reproducing basic observational relations of very low mass stars (VLMS), including the mass--radius relation and the optical colour--magnitudes of cool dwarfs. Here, we improve PARSEC models on these points. We implement the T--tau relations from PHOENIX BT-Settl model atmospheres as the outer boundary conditions in the PARSEC code, finding that this change alone reduces the discrepancy in the mass--radius relation from 8 to 5 per cent. Read More

Affiliations: 1Shanghai Astronomical Observatory, 2USTC, 3Shanghai Astronomical Observatory, 4CSIRO Astronomy & Space Science, ATNF, 5USTC

In this Letter, we analyse the radial UV-optical color distributions in a sample of low redshift green valley (GV) galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation distribute in these galaxies. We find that the dust-corrected $u-r$ colors of early-type galaxies (ETGs) are flat out to $R_{90}$, while the colors turn blue monotonously when $r>0.5R_{50}$ for late-type galaxies (LTGs). Read More

Variations in the attenuation law have a significant impact on observed spectral energy distributions for galaxies. As one important observational property for galaxies at ultraviolet and infrared wavelength bands, the correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color index (or ultraviolet spectral slope), i.e. Read More

Since asymptotic giant branch (AGB) stars are bright and extended infrared objects, most Galactic AGB stars saturate the Wide-field Infrared Survey Explorer (WISE) detectors and therefore the WISE magnitudes that are restored by applying point-spread-function fitting need to be verified. Statistical properties of circumstellar envelopes around AGB stars are discussed on the basis of a WISE AGB catalog verified in this way. We cross-matched an AGB star sample with the WISE All-Sky Source Catalog and the Two Mircon All Sky Survey catalog. Read More

We analyze morphologies of the host galaxies of 35 X-ray selected active galactic nucleus (AGNs) at $z\sim2$ in the Cosmic Evolution Survey (COSMOS) field using Hubble Space Telescope/WFC3 imaging taken from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We build a control sample of 350 galaxies in total, by selecting ten non-active galaxies drawn from the same field with the similar stellar mass and redshift for each AGN host. By performing two dimensional fitting with GALFIT on the surface brightness profile, we find that the distribution of S$\`e$rsic index (n) of AGN hosts does not show a statistical difference from that of the control sample. Read More

Starting from a sample of 24 \micron\ sources in the Extended Groth Strip, we use 3.6 to 8 \micron\ color criteria to select ultraluminous infrared galaxies (ULIRGs) at $z\sim2$. Spectroscopy from 20-38 \micron\ of 14 objects verifies their nature and gives their redshifts. Read More

We present a research of morphologies, spectra and environments of $\approx$ 2350 "green valley" galaxies at $0.2Read More

In this letter, we use a two-color (J-L) vs. (V-J) selection criteria to search massive, quiescent galaxy candidates at 2.5Read More

Multi-band photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of a nearby Scd type galaxy M 101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-$A_\mathrm{FUV}$ relation, found to depend on a second parameter of birth rate b (ratio of present and past-averaged star formation rate), to constrain the dust attenuation. Read More

In a systematic search over 11 cluster fields from Cluster Lensing And Supernova survey with Hubble (CLASH) we identify ten passively evolving massive galaxies at redshift z~2.We derive the stellar properties of these galaxies using HST WFC3/ACS multiband data, together with Spitzer IRAC observations. We also deduce the optical rest-frame effective radius of these high redshift objects. Read More

Authors: Caty Pilachowski1, Carles Badenes2, Stephen Bailey3, Aaron Barth4, Rachel Beaton5, Eric Bell6, Rebecca Bernstein7, Fuyan Bian8, Michael Blanton9, Robert Blum10, Adam Bolton11, Howard Bond12, Mark Brodwin13, James Bullock14, Jeff Carlin15, Ranga-Ram Chary16, David Cinabro17, Michael Cooper18, Jorge L. C. Cota19, Marc Davis20, Kyle Dawson21, Arjun Dey22, Megan Donahue23, Jeremy Drake24, Erica Ellingson25, Lorenzo Faccioli26, Xiaohui Fan27, Harry Ferguson28, Eric Gawiser29, Marla Geha30, Mauro Giavalisco31, Anthony Gonzalez32, Kim Griest33, Bruce Grossan34, Raja Guhathakurta35, Paul Harding36, Sara R. Heap37, Shirley Ho38, Steve Howell39, Buell Jannuzi40, Jason Kalirai41, Brian Keeney42, Lisa Kewley43, Xu Kong44, Michael Lampton45, Wei-Peng Lin46, Axel de la Macorra47, Lucas Macri48, Steve Majewski49, Paul Martini50, Phil Massey51, Virginia McSwain52, Adam A. Miller53, Dante Minniti54, Maryam Modjaz55, Heather Morrison56, John Moustakas57, Adam Myers58, Joan Najita59, Jeffrey Newman60, Dara Norman61, Knut Olsen62, Michael Pierce63, Alexandra Pope64, Moire Prescott65, Naveen Reddy66, Kevin Reil67, Armin Rest68, Katherine Rhode69, Connie Rockosi70, Greg Rudnick71, Abhijit Saha72, John Salzer73, David Sanders74, David Schlegel75, Branimir Sesar76, Joseph Shields77, Jeffrey Silverman78, Josh Simon79, Adam Stanford80, Daniel Stern81, Lisa Storrie-Lombardi82, Nicholas Suntzeff83, Jason Surace84, Alex Szalay85, Melville Ulmer86, Ben Weiner87, Beth Willman88, Rogier Windhorst89, Michael Wood-Vasey90
Affiliations: 1Indiana U, 2U of Pittsburgh, 3LBNL, 4UC Irvine, 5U of Virginia, 6U of Michigan, 7UC Santa Cruz, 8U of Arizona, 9NYU, 10NOAO, 11U Utah, 12STScI, 13U of Missouri, 14UC Irvine, 15RPI, 16Caltech/IPAC, 17Wayne State, 18UC Irvine, 19ININ, Mexico, 20UC Berkeley, 21U of Utah, 22NOAO, 23MSU, 24CfA, 25U Colorado, 26Kavli/Peking, 27U of Arizona, 28STScI, 29Rutgers, 30Yale U, 31U Mass, 32U Florida, 33UC San Diego, 34LBNL, 35UC Santa Cruz, 36CWRU, 37NASA/GSFC, 38Carnegie-Mellon, 39NASA/Ames, 40Steward Observatory, 41STScI, 42U Colorado, 43U. Hawaii, 44USTC, 45LBNL, 46SAO, 47UNAM/IAC, 48Texas A&M, 49U Virginia, 50OSU, 51Lowell Obs, 52Lehigh U, 53UC Berkeley, 54P U Catolica, 55NYU, 56CWRU, 57Siena College, 58U of Wyoming, 59NOAO, 60U Pittsburgh, 61NOAO, 62NOAO, 63U Wyoming, 64U Mass, 65UC Santa Barbara, 66UC Riverside, 67SLAC, 68STScI, 69Indiana U, 70UC Santa Cruz, 71Kansas U, 72NOAO, 73Indiana U, 74U Hawaii, 75LBNL, 76Caltech, 77Ohio U, 78IPMU, 79OCIW, 80UC Davis, 81JPL, 82Caltech/IPAC, 83Texas A&M, 84Caltech/IPAC, 85JHU, 86Northwestern, 87U Arizona, 88Haverford, 89ASU, 90U Pittsburgh

This document summarizes the results of a community-based discussion of the potential science impact of the Mayall+BigBOSS highly multiplexed multi-object spectroscopic capability. The KPNO Mayall 4m telescope equipped with the DOE- and internationally-funded BigBOSS spectrograph offers one of the most cost-efficient ways of accomplishing many of the pressing scientific goals identified for this decade by the "New Worlds, New Horizons" report. The BigBOSS Key Project will place unprecedented constraints on cosmological parameters related to the expansion history of the universe. Read More

The correlation between infrared-to-ultraviolet luminosity ratio and ultraviolet color, i.e. the IRX-UV relation, was regarded as a prevalent recipe for correcting extragalactic dust attenuation. Read More

We analyze the role of bars in the build-up of central mass concentrations in massive, disk galaxies. Our parent sample consists of 3757 face-on disk galaxies with redshifts between 0.01 and 0. Read More

Using a simple two-color selection based on $g$-, $z$-, and $K$-band photometry, we pick out 1609 star-forming galaxies (sgzKs) and 422 passively evolving galaxies (pgzKs) at z\sim2$ from a $K$-band-selected sample ($K_{\rm AB} < 22.0$) in an area of $\sim 0.44$ deg$^{2}$ of the All-wavelength Extended Groth Strip International Survey. Read More

We present a study on Spectral Energy Distributions, Morphologies, and star formation for an IRAC-selected extremely red object sample in the GOODS Chandra Deep Field-South. This work was enabled by new HST/WFC3 near-IR imaging from the CANDELS survey as well as the deepest available X-ray data from Chandra 4 Ms observations. This sample consists of 133 objects with the 3. Read More

With the goal of investigating the degree to which theMIR luminosity in theWidefield Infrared Survey Explorer (WISE) traces the SFR, we analyze 3.4, 4.6, 12 and 22 {\mu}m data in a sample of {\guillemotright} 140,000 star-forming galaxies or star-forming regions covering a wide range in metallicity 7. Read More

In this paper we present a photometric and spectroscopic study of the nearby galaxy cluster Abell 0671 (A671) with 15 intermediate-band filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system and the Sloan Digital Sky Survey (SDSS) data. The photometric redshift technique is applied to the galaxy sample for further membership determination. After the color-magnitude relation is taken into account, 97 galaxies brighter than h_batc=19. Read More

We report the discovery of eight new quasars in one extragalactic field (five degree centered at RA=$08^h58^m08.2^s$, Dec=$01^o32'29.7''$) with the LAMOST commissioning observations on December 18, 2009. Read More

The redshift range from 2.2 to 3, is known as the 'redshift desert' of quasars because quasars with redshift in this range have similar optical colors as normal stars and are thus difficult to be found in optical sky surveys. A quasar candidate, SDSS J085543. Read More

With the imagery from GALEX, HST, 2MASS, and Spitzer, and at the resolution of MIPS 24 micron(~6"), we study the variations of the broadband spectral energy distributions (SEDs) of star-forming regions within the nearest prototypal major merger -- the Antennae galaxies. By including MIPS 24 micron dust emission into stellar population analysis, we reliably, albeit roughly, constrain the star formation histories of these 24 micron selected star-forming regions across the merging disks of the Antennae. Our population analysis is consistent with the star formation scenario that, most regions across the whole system are at a modest level of star formation with the exception of some localized intense starburst sites in the well-known overlap regions and the western-loop regions of northern galaxy NGC 4038. Read More

Using a simple color selection based on B-, z- and K-band photometry, BzK= (z-K)_AB-(B-z)_AB>-0.2, we picked out 52 star-forming galaxies at 1.4Read More

Many brightest cluster galaxies (BCGs) at the centers of X-ray selected clusters exhibit clear evidence for recent star formation. However, studies of BCGs in optically-selected clusters show that star formation is not enhanced when compared to control samples of non-BCGs of similar stellar mass. Here we analyze a sample of 113 BCGs in low redshift (z<0. Read More

Affiliations: 1Key Laboratory for Research in Galaxies and Cosmology, USTC, China, 2Center for Astrophysics, USTC, China, 3NAOJ, Japan, 4Center for Astrophysics, USTC, China

We present a study of the classification of z ~1 extremely red objects (EROs), using a combination of HST/ACS, Spitzer/IRAC, and ground-based images of the COSMOS field. Our sample includes about 5300 EROs with i-Ks>2.45 (AB, equivalently I-Ks=4 in Vega) and Ks<=21. Read More

In this paper we present a quantitative study of the classification of Extremely Red Objects (EROs). The analysis is based on the multi-band spatial- and ground-based observations (HST/ACS-$BViz$, HST/NICMOS-$JH$, VLT-$JHK$) in the Hubble Ultra Deep Field (UDF). Over a total sky area of 5. Read More

We have analysed, for the first time, the clustering properties of Wolf-Rayet (W-R) galaxies, using a large sample of 846 W-R galaxies selected from the Data Release 4 (DR4) of the SDSS. We compute the cross-correlation function between W-R galaxies and a reference sample of galaxies drawn from the DR4. We compare the function to the results for control samples of non-W-R star-forming galaxies that are matched closely in redshift, luminosity, concentration, 4000-\AA break strength and specific star formation rate (SSFR). Read More

We use a large sample of 174 Wolf-Rayet (WR) galaxies drawn from the Sloan Digital Sky Survey to study whether and how the slope of the stellar initial mass function depends on metallicity. We calculate for each object its oxygen abundance according to which we divide our sample into four metallicity subsamples. For each subsample, we then measure three quantities: the equivalent width of \hb emission line, the equivalent width of WR bump around 4650\AA, and the WR bump-to-\hb intensity ratio, and compare to the predictions of the same quantities by evolutionary synthesis models of Schaerer & Vacca. Read More

The E/SO sequence of a cluster defines a boundary redward of which a reliable weak lensing signal can be obtained from background galaxies, uncontaminated by cluster members. For bluer colors, both background and cluster members are present, reducing the distortion signal by the proportion of unlensed cluster members. In deep Subaru and HST/ACS images of A1689 the tangential distortion of galaxies with bluer colors falls rapidly toward the cluster center relative to the lensing signal of the red background. Read More


Subaru observations of A1689 (z=0.183) are used to derive an accurate, model-independent mass profile for the entire cluster, r<2 Mpc/h, by combining magnification bias and distortion measurements. The projected mass profile steepens quickly with increasing radius, falling away to zero at r~1. Read More