arXiv subjects

Minsun Kim

Publications and source records attributed to Minsun Kim.

24 records · Page 2Linked to original sources

arXiv2009

The SWIRE/Chandra Survey: The X-ray Sources

We report a moderate-depth (70 ksec), contiguous 0.7 sq.deg, Chandra survey, in the Lockman Hole Field of the Spitzer/SWIRE Legacy Survey coincident with a completed, ultra-deep VLA survey with deep optical and near-infrared imaging in-hand. The primary motivation is to distinguish starburst galaxies and AGN, including the significant, highly obscured (log N_H >23) subset. Chandra has detected 775 X-ray sources to a limiting broad band (0.3-8 keV) flux ~4E-16 erg/cm^2/s. We present the X-ray catalog, fluxes, hardness ratios and multi-wavelength fluxes. The log N vs. log S agrees with those of previous surveys covering similar flux ranges. The Chandra and Spitzer flux limits are well matched: 771 (99%) of the X-ray sources have IR or optical counterparts, and 333 have MIPS 24 um detections. There are 4 optical-only X-ray sources and 4 with no visible optical/IR counterpart. The very deep (~2.7 uJy rms) VLA data yields 251 (> 4 sigma) radio counterparts, 44% of the X-ray sources in the field. We confirm that the tendency for lower X-ray flux sources to be harder is primarily due to absorption. As expected, there is no correlation between observed IR and X-ray flux. Optically bright, Type 1 and red AGN lie in distinct regions of the IR vs X-ray flux plots, demonstrating the wide range of SEDs in this sample and providing the potential for classification/source selection. The classical definition of radio-loudness, R_L, is not effective at selecting strong radio sources for red and relatively optically faint AGN. Using the 24 um to radio flux ratio (q_24) results in the usual ~10% radio-loud AGN (13 of 147).

astro-ph.HE↗

arXiv2009

Reddening and Distance of the Local Group Starburst Galaxy IC 10

We estimate the reddening and distance of the nearest starburst galaxy IC 10 using deep near infrared $JHK_{S}$ photometry obtained with the Multi-Object InfraRed Camera and Spectrograph (MOIRCS) on the Subaru telescope. We estimate the foreground reddening toward IC 10 using $UBV$ photometry of IC 10 from the Local Group Survey, obtaining $E(B-V)=0.52\pm 0.04$ mag. We derive the total reddening including the internal reddening, $E(B-V)=0.98\pm 0.06$ mag, using $UBV$ photometry of early-type stars in IC 10 and comparing $JHK_{S}$ photometry of red giant branch stars in IC 10 and the SMC. Using the 2MASS point source catalog of 20 Galactic globular clusters, we derive a relation between the metallicity [Fe/H]$_{CG97}$ and the slope of the red giant branch in the $K_{S}- (J-K_{S})$ color-magnitude diagram. The mean metallicity of the red giant branch stars in IC 10 is estimated to be [Fe/H]$_{CG97}=-1.08\pm0.28$. The magnitude of the tip of the red giant branch (TRGB) of IC 10 in the $K_{S}$ band is measured to be $K_{S,TRGB}=18.28\pm0.01$. Based on the TRGB method, we estimate the distance modulus of IC 10 to be $(m-M)_{0}=24.27\pm0.03{\rm (random)}\pm0.18{\rm (systematic)}$, corresponding to the distance of $d=715\pm10\pm60$ kpc. This confirms that IC 10 is a member of the Local Group.

astro-ph.CO↗

arXiv2006

Chandra Multiwavelength Project X-ray Point Source Number Counts and the Cosmic X-ray Background

We present the Chandra Multiwavelength Project (ChaMP) X-ray point source number counts and the cosmic X-ray background (CXRB) flux densities in multiple energy bands. From the ChaMP X-ray point source catalog, ~5,500 sources are selected covering 9.6 deg^2 in sky area. To quantitatively characterize the sensitivity and completeness of the ChaMP sample, we perform extensive simulations. We also include the ChaMP+CDFs (Chandra Deep Fields) number counts to cover large flux ranges from 2x10^{-17} to 2.4x10^{-12} (0.5-2 keV) and from 2x10^{-16} to 7.1x10^{-12} (2-8 keV) erg/cm^2/sec. The ChaMP and the ChaMP+CDFs differential number counts are well fitted with a broken power law. The best fit faint and bright power indices are 1.49^{+0.02}_{-0.02} and 2.36^{+0.05}_{-0.05} (0.5-2 keV), and 1.58^{+0.01}_{-0.01} and 2.59^{+0.06}_{-0.05} (2-8 keV), respectively. We detect breaks in the differential number counts and they appear at different fluxes in different energy bands. Assuming a single power law model for a source spectrum, we find that the same population(s) of soft X-ray sources causes the break in the differential number counts for all energy bands. We measure the resolved CXRB flux densities from the ChaMP and the ChaMP+CDFs number counts with and without bright target sources. Adding the known unresolved CXRB to the ChaMP+CDF resolved CXRB, we also estimate total CXRB flux densities. The fractions of the resolved CXRB without target sources are 78^{+1}_{-1}% and 81^{+2}_{-2}% in the 0.5-2 keV and 2-8 keV bands, respectively, somewhat lower, though generally consistent with earlier numbers since their large errors. These fractions increase by ~1% when target sources are included.

astro-ph↗

arXiv2006

Chandra Multiwavelength Project X-ray Point Source Catalog

We present the Chandra Multiwavelength Project (ChaMP) X-ray point source catalog with ~6,800 X-ray sources detected in 149 Chandra observations covering \~10 deg^2. The full ChaMP catalog sample is seven times larger than the initial published ChaMP catalog. The exposure time of the fields in our sample ranges from 0.9 to 124 ksec, corresponding to a deepest X-ray flux limit of f_{0.5-8.0} = 9 x 10^{-16} erg/cm2/sec. The ChaMP X-ray data have been uniformly reduced and analyzed with ChaMP-specific pipelines, and then carefully validated by visual inspection. The ChaMP catalog includes X-ray photometric data in 8 different energy bands as well as X-ray spectral hardness ratios and colors. To best utilize the ChaMP catalog, we also present the source reliability, detection probability and positional uncertainty. To quantitatively assess those parameters, we performed extensive simulations. In particular, we present a set of empirical equations: the flux limit as a function of effective exposure time, and the positional uncertainty as a function of source counts and off axis angle. The false source detection rate is ~1% of all detected ChaMP sources, while the detection probability is better than ~95% for sources with counts >30 and off axis angle <5 arcmin. The typical positional offset between ChaMP X-ray source and their SDSS optical counterparts is 0.7+-0.4 arcsec, derived from ~900 matched sources.

astro-ph↗

arXiv2001

Determination of the Distance to M33 Based on the Tip of the Red Giant Branch and the Red Clump

We have determined the distance to M33 using the tip of the red giant branch (TRGB) and the red clump (RC), from the VI photometry of stars in ten regions of M33 based on HST/WFPC2 images. The regions used in this study are located at R=2.6 - 17.8 arcmin from the center of M33. The distance modulus to M33 obtained in this study, for an adopted foreground reddening of E(B-V)=0.04, is (m-M)_{0,TRGB}=24.81+/-0.04(random)+0.15/-0.11(systematic) from the TRGB, and (m-M)_{0,RC}=24.80+/-0.04(random)+/-0.05(systematic) from the RC, showing an excellent agreement between the two (corresponding to a distance of 916+/-17(random) kpc and 912+/-17(random) kpc, respectively). These results are \~0.3 mag larger than the Cepheid distances based on the same HST/WFPC2 data and ground-based data. This difference is considered partially due to the uncertainty in the estimates of the total reddening for Cepheids in M33.

astro-ph↗

arXiv2001

Determination of the Distance to M33 Based on Single Epoch I-band HST Observations of Cepheids

We have determined the distance to M33 using single epoch I-band observations of Cepheids based on HST/WFPC2 images of five fields in M33. Combining the HST I-band photometry and the periods determined from the ground-based observations (DIRECT) for 21 Cepheids with log P>0.8 in the sample of 32 Cepheids, we derive a distance modulus of (m-M)_0=24.52+/-0.14(random)+/-0.13(systematic) for an adopted total reddening of M33, E(B-V)=0.20+/-0.04 (E(V-I)=0.27+/-0.05) given by Freedmand et al.(2001), the reddening to the LMC, E(B-V)=0.10, and the distance to the LMC, (m-M)_0=18.50. If the total reddening to M33 of E(B-V)=0.10+/-0.09 given by Freedman, Wilson, and Madore(1991) is used, the Cepheid distance modulus based on the I-band photometry will be increased by 0.20. Metallicity effect on the Cepheid distance to M33 is estimated to be small, delta(m-M)_Z=0.01 to 0.06, which leads to (m-M)_0=24.53 to 24.58 after this metallicity effect correction. Using the Wesenheit W_I, an extinction-free parameter, we derive a similar value, (m-M)_0=24.52+/-0.15(random)+/-0.11(systematic). These results are in reasonable agreement with those based on the ground-based multi-epoch BVRI observations of brighter Cepheids in M33, and are ~0.3 smaller than those based on the tip of the red giant branch and the red clump. It is needed to estimate better the reddening to Cepheids in M33.

astro-ph↗