Dong-Woo Kim - Academia.edu (original) (raw)
articles by Dong-Woo Kim
The Astrophysical Journal, 2018
We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e., a system... more We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e., a system expected to be old and relaxed long after the giant elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas morphology is disturbed and asymmetrical, with a cold front following a possible bow shock. We discuss possible origins of the disturbed hot halo, including sloshing by a nearby object, merger, ram pressure by external hotter gas, and nuclear outburst. We consider that the first two mechanisms are likely explanations for the disturbed hot halo, with a slight preference for a minor merger with a low impact parameter because of the match with simulations and previous optical observations. In this case, NGC 1132 may be a rare example of unusual late mergers seen in recent simulations. Regardless of the origin of the disturbed hot halo, the paradigm of the fossil system needs to be reconsidered.
Papers by Dong-Woo Kim
The Astrophysical Journal, 2002
Monthly Notices of the Royal Astronomical Society
Using the data products of the Chandra Galaxy Atlas (Kim et al. 2019a), we have investigated the ... more Using the data products of the Chandra Galaxy Atlas (Kim et al. 2019a), we have investigated the radial profiles of the hot gas temperature in 60 early type galaxies. Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at RMAX = 35 ± 25 kpc (or ∼0.04 RVIR) and declines both inward and outward. The temperature dips (or breaks) at RMIN (or RBREAK) = 3–5 kpc (or ∼0.006 RVIR). The mean slope between RMIN (RBREAK) and RMAX is 0.3 ± 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72 per cent (possibly up to 82 per cent) of our ETG sample. The remaining ETGs (18 per cent) with irregular or monotonically declining profiles do not fit the universal profile and require another expl...
Monthly Notices of the Royal Astronomical Society
Using globular cluster kinematics and photometry data, we calibrate the scaling relation between ... more Using globular cluster kinematics and photometry data, we calibrate the scaling relation between the total galaxy mass (M TOT , including dark matter) and total globular cluster system mass (M GCS) in a sample of 30 early-type galaxies (ETGs), confirming a nearly linear relationship between the two physical parameters. Using samples of 83 and 57 ETGs, we investigate this scaling relation in conjunction with the previously known relations between M TOT and the interstellar medium (ISM) X-ray luminosity and temperature, respectively. We confirm that M GCS can be effectively used as a proxy of M TOT. We further find that the L X,GAS-M TOT relation is far tighter in the subsample of core ETGs when compared to cusp ETGs. In core ETGs (old, passively evolving stellar systems) M TOT is significantly larger than the total stellar mass M STAR and the correlation with the hot gas properties is driven by their dark matter mass M DM. Cusp ETGs typically have lower L X,GAS than core ETGs. In cusp ETGs, for a given M DM , higher L X,GAS is associated with higher M STAR , suggesting stellar feedback as an important secondary factor for heating the ISM. Using the M GCS-M TOT scaling relations we compare 272 ETGs with previous estimates of the stellar-to-halo-mass relation of galaxies. Our model-independent estimate of M TOT results in a good agreement around halo masses of 10 12 M , but suggests higher star formation efficiency than usually assumed both at the lowand at the high-halo-mass ends.
Using the deepest available textitChandra\textit{Chandra}textitChandra observations of NGC 4649 we find strong evidences ... more Using the deepest available textitChandra\textit{Chandra}textitChandra observations of NGC 4649 we find strong evidences of cavities, ripples and ring like structures in the hot interstellar medium (ISM) that appear to be morphologically related with the central radio emission. These structures show no significant temperature variations in correspondence with higher pressure regions ($0.5\mbox{kpc}<r<3\mbox{kpc}$). On the same spatial scale, a discrepancy between the mass profiles obtained from stellar dynamic and textitChandra\textit{Chandra}textitChandra data represents the telltale evidence of a significant non-thermal pressure component in this hot gas, which is related to the radio jet and lobes. On larger scale we find agreement between the mass profile obtained form textitChandra\textit{Chandra}textitChandra data and planetary nebulae and globular cluster dynamics. The nucleus of NGC 4649 appears to be extremely radiatively inefficient, with highly sub-Bondi accretion flow. Consistently with this finding, the jet power evaluated from the ob...
The Astrophysical Journal, 2006
We have investigated 136 Chandra extragalactic sources without broad optical emission lines, incl... more We have investigated 136 Chandra extragalactic sources without broad optical emission lines, including 93 galaxies with narrow emission lines (NELG) and 43 with only absorption lines (ALG). Based on f X /f O , L X , X-ray spectral hardness and optical emission line diagnostics, we have conservatively classified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. Their redshift ranges from 0.01 to 1.2, with normal galaxies in the range z=0.01-0.3. Our sample galaxies appear to share characteristics with local galaxies in terms of X-ray luminosities and spectral properties, as expected from the Xray 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 X /L B , within the limited z range (≲ 0.1). We have built a log(N)-log(S) relationship of normal galaxies in the flux range, f X (0.5-8 keV) = 10-15-10-13 erg s-1 cm-2 , after correcting for completeness based on a series of simulations. The best-fit slope 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 normal galaxies will not exceed the AGN population until f X (0.5-2.0 keV) ~ 2 x 10-18 erg s-1 cm-2 (a factor of ~5 lower than the previous estimate). We have also built an X-ray luminosity function of normal galaxies in the luminosity range of L X = 5 x 10 39-10 42 erg s-1 , which is consistent with other survey results. A group of NELGs (most of them with f X /f O >0.1) appear to be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correcting for intrinsic absorption, their X-ray luminosities could be L X > 10 44 erg s-1 , making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG-X-ray bright, optically normal galaxy candidates) do not appear to be significantly absorbed, we found two heavily obscured objects, which could be as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A galaxy candidates with strong Balmer absorption lines, but no [OII] line. 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 investigate how to achieve the best possible ACIS spatial resolution by binning in ACIS sub-pi... more We investigate how to achieve the best possible ACIS spatial resolution by binning in ACIS sub-pixel and applying an event repositioning algorithm after removing pixel-randomization from the pipeline data. We quantitatively assess the improvement in spatial resolution by (1) measuring point source sizes and (2) detecting faint point sources. The size of a bright (but no pile-up), on-axis point source
A complete and unbiased sample of AGN types is required in order to understand the phenomenon of ... more A complete and unbiased sample of AGN types is required in order to understand the phenomenon of accretion on to supermassive blackholes, (an evolutionary phase that is believed to take place in all massive galaxies), their formation and evolution, and the shape of the Cosmic X- ray background. X-ray surveys provide the best means by which to select AGN, regardless
We present an X-ray and optical analysis of a flux limited (f2.0-8.0 keV > 10-14 erg s-1 cm-2)... more We present an X-ray and optical analysis of a flux limited (f2.0-8.0 keV > 10-14 erg s-1 cm-2) sample of 126 AGN detected in 16 Chandra fields. This work represents a small though significant subset of the Chandra Multiwavelength Project (ChaMP). We have chosen this limiting flux to have a reasonable degree of completeness (50%) in our optical spectroscopic identifications. The optical counterparts of these AGN are characterized as either broad emission line AGN (BLAGN; 59%), narrow emission line galaxies (NELG; 20%) or absorption line galaxies (ALG; 12%) without any evidence of an AGN signature. Based on their X-ray luminosity and spectral properties, we show that NELG and ALG are primarily the hosts of obscured AGN with an intrinsic absorbing column in the range of 1021.5< NH<1023.3 cm-2. While most of the BLAGN are unobscured, there are a few with substantial absorption. X-ray surveys such as the ChaMP nicely complement optical surveys such as the SDSS to completely dete...
The Astrophysical Journal, 2006
Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg 2 in the Lockman Ho... more Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg 2 in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities k10 24 cm À2 and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg À2 detected in the infrared in the Chandra/ SWIRE field, of which 4040% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only 4033% of all Compton-thick AGNs are detected in the X-rays at our depth [F(0:3 8 keV) > 10 À15 ergs cm À2 s À1 ]. We report the discovery of two sources in our sample of Comptonthick AGNs, SWIRE J104409.95+585224.8 (z ¼ 2:54) and SWIRE J104406.30+583954.1 (z ¼ 2:43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.
The Astrophysical Journal, 2010
We have compared the combined X-ray luminosity function (XLF) of LMXBs detected in Chandra observ... more We have compared the combined X-ray luminosity function (XLF) of LMXBs detected in Chandra observations of young, post-merger elliptical galaxies, with that of typical old elliptical galaxies. We find that the XLF of the 'young' sample does not present the prominent high luminosity break at L X > 5 x 10 38 erg s-1 found in the old elliptical galaxy XLF. The 'young' and 'old' XLFs differ with a 3σ statistical significance (with a probability less than 0.2% that they derive from the same underlying parent distribution). Young elliptical galaxies host a larger fraction of luminous LMXBs (L X > 5 x 10 38 erg s-1) than old elliptical galaxies and the XLF of the young galaxy sample is intermediate between that of typical old elliptical galaxies and that of star forming galaxies. This observational evidence may be related to the last major/minor mergers and the associated star formation.
The Astrophysical Journal, 2006
We present a systematic study of the low mass X-ray binary (LMXB) populations of 6 elliptical gal... more We present a systematic study of the low mass X-ray binary (LMXB) populations of 6 elliptical galaxies, aimed at investigating the detected LMXB − globular cluster (GC) connection. We utilize Chandra archival data to identify 665 X-ray point sources and HST archival data supplemented by ground observations to identify 6173 GCs. Applying rigorous X-ray and optical photometry and conservative matching criteria, we associate 209 LMXBs with red GC (RGC) and 76 LMXBs with blue GCs (BGC), while we find no optical GC counterpart for 258 LMXBs. This is the largest GC−LMXB sample studied so far. We confirm previous reports suggesting that the fraction of GCs associated with LMXBs is ∼ 3 times larger in RGCs than in BGCs, indicating that metallicity is a primary factor in the GC−LMXB formation. While as already known, the brighter (and bigger) GCs have a higher probability to host LMXBs, we find that this optical luminosity (or mass) dependency is stronger in RGCs than in BGCs. We also find that GCs located near the galaxy center have a higher probability to harbor LMXBs compared to those in the outskirts. The radial distributions of GC−LMXBs (for both RGC and BGC) are steeper than those of the whole optical GC sample, but consistent with those of the optical halo light, suggesting that there must be another parameter (in addition to metallicity) governing LMXB formation in GCs. This second parameter must depend on the galacto-centric distance. One possibility is a galacto-centric distance dependent encounter rate. We find no statistically significant difference in the X-ray properties (shape of X-ray luminosity function, L X /L V distribution, X-ray spectra) among RGC−LMXBs, BGC−LMXBs and field−LMXBs. The similarity of the X-ray spectra of BGC−LMXBs and RGC−LMXBs is inconsistent with the irradiationinduced stellar wind model prediction of more absorbed X-ray spectra in
The Astrophysical Journal, 1999
... RADIO-QUIET RED QUASARS DONG-WOO KIM1 Chungnam National University, Taejon, 305-764, South Ko... more ... RADIO-QUIET RED QUASARS DONG-WOO KIM1 Chungnam National University, Taejon, 305-764, South Korea AND MARTIN ELVIS Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Received 1998 May 11 ; accepted 1998 December 8 ...
The Astrophysical Journal, 2003
The Astrophysical Journal, 2002
We have identified a population of 'blank field sources' (or 'blanks') among the ROSAT bright uni... more We have identified a population of 'blank field sources' (or 'blanks') among the ROSAT bright unidentified Xray sources with faint optical counterparts. The extreme X-ray over optical flux ratio of blanks is not compatible with the main classes of X-ray emitters except for extreme BL Lacertae objects. From the analysis of ROSAT archival data we found no indication of variability and evidence for only three sources, out of 16, needing absorption in excess of the Galactic value. We also found evidence for an extended nature for only one of the 5 blanks with a serendipitous HRI detection; this source (1WGA J1226.9+3332) was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the presence of a red (O− E ≥ 2) counterpart in the X-ray error circle for 6 blanks. The identification process brought to the discovery of another high z cluster of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in nearby galaxies and two apparently normal type 1 AGNs. These AGNs, together with 4 more AGN-like objects seem to form a well defined group: they present unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible explanations for the discrepancy between the X-ray and optical data, among which: a suppressed big blue bump emission, an extreme dust to gas (∼ 40 − 60 the Galactic ratio), a high redshift (z ≥ 3.5) QSO nature, an atypical dust grain size distribution and a dusty warm absorber. These AGN-like blanks seem to be the bright (and easier to study) analogs of the sources which are found in deep Chandra observations. Three more blanks have a still unknown nature.
The Astrophysical Journal, 2008
We present new observational results of NGC 7619, an elliptical galaxy with a prominent X-ray tai... more We present new observational results of NGC 7619, an elliptical galaxy with a prominent X-ray tail and a dominant member of the Pegasus group. With Chandra and XMM-Newton observations, we confirm the presence of a long X-ray tail in the southwest direction; moreover, we identify for the first time a sharp discontinuity of the X-ray surface brightness in the opposite (northeast) side of the galaxy. The density, temperature, and pressure jump at the northeast discontinuity suggest a Mach number 1,correspondingtoagalaxyvelocityof1, corresponding to a galaxy velocity of 1,correspondingtoagalaxyvelocityof500 km s À1 , relative to the surrounding hot gas. Spectral analysis of these data shows that the iron abundance of the hot gaseous medium is much higher (1Y2 solar) near the center of NGC 7619 and in the tail extending from the core than in the surrounding regions (1/2 solar), indicating that the gas in the tail is originated from the galaxy. The possible origin of the head-tail structure is either ongoing ram pressure stripping or sloshing. The morphology of the structure is more in line with a ram pressure stripping phenomenon, while the position of NGC 7619 at the center of the Pegasus I group, and its dominance, would prefer sloshing.
The Astrophysical Journal, 2010
We employ the Chandra Multiwavelength Project (ChaMP) and the Sloan Digital Sky Survey (SDSS) to ... more We employ the Chandra Multiwavelength Project (ChaMP) and the Sloan Digital Sky Survey (SDSS) to study the fraction of X-ray-active galaxies in the field to z = 0.7. We utilize spectroscopic redshifts from SDSS and ChaMP, as well as photometric redshifts from several SDSS catalogs, to compile a parent sample of more than 100,000 SDSS galaxies and nearly 1,600 Chandra X-ray detections. Detailed ChaMP volume completeness maps allow us to investigate the local fraction of active galactic nuclei (AGN), defined as those objects having broad-band X-ray luminosities L X (0.5-8 keV) ≥ 10 42 erg s −1 , as a function of absolute optical magnitude, X-ray luminosity, redshift, mass, and host color/morphological type. In five independent samples complete in redshift and i-band absolute magnitude, we determine the field AGN fraction to be between 0.16 ± 0.06% (for z ≤ 0.125 and −18 > M i > −20) and 3.80 ± 0.92% (for z ≤ 0.7 and M i < −23). We find excellent agreement between our ChaMP/SDSS field AGN fraction and the Chandra cluster AGN fraction, for samples restricted to similar redshift and absolute magnitude ranges: 1.19 ± 0.11% of ChaMP/SDSS field galaxies with 0.05 < z < 0.31 and absolute R-band magnitude more luminous than M R < −20 are AGN. Our results are also broadly consistent with measures of the field AGN fraction in narrow, deep fields, though differences in the optical selection criteria, redshift coverage, and possible cosmic variance between fields introduce larger uncertainties in these comparisons.
The Astrophysical Journal, 2004
We present the results of the X-ray XMM-Newton observations of NGC 507, a dominant elliptical gal... more We present the results of the X-ray XMM-Newton observations of NGC 507, a dominant elliptical galaxy in a small group of galaxies, and report 'super-solar' metal abundances of both Fe and α-elements in the hot ISM of this galaxy. These results are robust, in that we considered all possible systematic effects in our analysis. We find Z Fe = 2-3 times solar inside the D 25 ellipse of NGC 507. This is the highest Z Fe reported so far for the hot halo of an elliptical galaxy; this high Iron abundance is fully consistent with the predictions of stellar evolution models, which include the yield of both type II and Ia supernovae. Our analysis shows that abundance measurements are critically dependent on the selection of the proper emission model. The spatially resolved, high quality XMM spectra provide enough statistics to formally require at least three emission components in each of 4 circum-nuclear concentric shells (within r < 5 arcmin or 100 kpc): two soft thermal components indicating a range of temperatures in the hot ISM, plus a harder component, consistent with the integrated output of low mass X-ray binaries (LMXBs) in NGC 507. The two-component (thermal + LMXB) model customarily used in past studies yields a much lower Z Fe , consistent with previous reports of sub-solar metal abundances. This model, however, gives a significantly worse fit to the data (F-test probability < 0.0001). The abundance of α-elements (most accurately determined by Si) is also found to be super-solar. The α-elements to Fe abundance ratio is close to the solar ratio, suggesting that ~70% of the Iron mass in the hot ISM was originated from SNe Type Ia. The α-element to Fe abundance ratio remains constant out to at least 100 kpc, indicating that SNe Type II and Ia ejecta are well mixed in a scale much larger than the extent of the stellar body.
The Astronomical Journal, 2006
We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part ... more We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SNe Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U À B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional $40% intrinsic scatter compared to the B band.
The Astrophysical Journal, 2018
We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e., a system... more We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e., a system expected to be old and relaxed long after the giant elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas morphology is disturbed and asymmetrical, with a cold front following a possible bow shock. We discuss possible origins of the disturbed hot halo, including sloshing by a nearby object, merger, ram pressure by external hotter gas, and nuclear outburst. We consider that the first two mechanisms are likely explanations for the disturbed hot halo, with a slight preference for a minor merger with a low impact parameter because of the match with simulations and previous optical observations. In this case, NGC 1132 may be a rare example of unusual late mergers seen in recent simulations. Regardless of the origin of the disturbed hot halo, the paradigm of the fossil system needs to be reconsidered.
The Astrophysical Journal, 2002
Monthly Notices of the Royal Astronomical Society
Using the data products of the Chandra Galaxy Atlas (Kim et al. 2019a), we have investigated the ... more Using the data products of the Chandra Galaxy Atlas (Kim et al. 2019a), we have investigated the radial profiles of the hot gas temperature in 60 early type galaxies. Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at RMAX = 35 ± 25 kpc (or ∼0.04 RVIR) and declines both inward and outward. The temperature dips (or breaks) at RMIN (or RBREAK) = 3–5 kpc (or ∼0.006 RVIR). The mean slope between RMIN (RBREAK) and RMAX is 0.3 ± 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72 per cent (possibly up to 82 per cent) of our ETG sample. The remaining ETGs (18 per cent) with irregular or monotonically declining profiles do not fit the universal profile and require another expl...
Monthly Notices of the Royal Astronomical Society
Using globular cluster kinematics and photometry data, we calibrate the scaling relation between ... more Using globular cluster kinematics and photometry data, we calibrate the scaling relation between the total galaxy mass (M TOT , including dark matter) and total globular cluster system mass (M GCS) in a sample of 30 early-type galaxies (ETGs), confirming a nearly linear relationship between the two physical parameters. Using samples of 83 and 57 ETGs, we investigate this scaling relation in conjunction with the previously known relations between M TOT and the interstellar medium (ISM) X-ray luminosity and temperature, respectively. We confirm that M GCS can be effectively used as a proxy of M TOT. We further find that the L X,GAS-M TOT relation is far tighter in the subsample of core ETGs when compared to cusp ETGs. In core ETGs (old, passively evolving stellar systems) M TOT is significantly larger than the total stellar mass M STAR and the correlation with the hot gas properties is driven by their dark matter mass M DM. Cusp ETGs typically have lower L X,GAS than core ETGs. In cusp ETGs, for a given M DM , higher L X,GAS is associated with higher M STAR , suggesting stellar feedback as an important secondary factor for heating the ISM. Using the M GCS-M TOT scaling relations we compare 272 ETGs with previous estimates of the stellar-to-halo-mass relation of galaxies. Our model-independent estimate of M TOT results in a good agreement around halo masses of 10 12 M , but suggests higher star formation efficiency than usually assumed both at the lowand at the high-halo-mass ends.
Using the deepest available textitChandra\textit{Chandra}textitChandra observations of NGC 4649 we find strong evidences ... more Using the deepest available textitChandra\textit{Chandra}textitChandra observations of NGC 4649 we find strong evidences of cavities, ripples and ring like structures in the hot interstellar medium (ISM) that appear to be morphologically related with the central radio emission. These structures show no significant temperature variations in correspondence with higher pressure regions ($0.5\mbox{kpc}<r<3\mbox{kpc}$). On the same spatial scale, a discrepancy between the mass profiles obtained from stellar dynamic and textitChandra\textit{Chandra}textitChandra data represents the telltale evidence of a significant non-thermal pressure component in this hot gas, which is related to the radio jet and lobes. On larger scale we find agreement between the mass profile obtained form textitChandra\textit{Chandra}textitChandra data and planetary nebulae and globular cluster dynamics. The nucleus of NGC 4649 appears to be extremely radiatively inefficient, with highly sub-Bondi accretion flow. Consistently with this finding, the jet power evaluated from the ob...
The Astrophysical Journal, 2006
We have investigated 136 Chandra extragalactic sources without broad optical emission lines, incl... more We have investigated 136 Chandra extragalactic sources without broad optical emission lines, including 93 galaxies with narrow emission lines (NELG) and 43 with only absorption lines (ALG). Based on f X /f O , L X , X-ray spectral hardness and optical emission line diagnostics, we have conservatively classified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. Their redshift ranges from 0.01 to 1.2, with normal galaxies in the range z=0.01-0.3. Our sample galaxies appear to share characteristics with local galaxies in terms of X-ray luminosities and spectral properties, as expected from the Xray 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 X /L B , within the limited z range (≲ 0.1). We have built a log(N)-log(S) relationship of normal galaxies in the flux range, f X (0.5-8 keV) = 10-15-10-13 erg s-1 cm-2 , after correcting for completeness based on a series of simulations. The best-fit slope 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 normal galaxies will not exceed the AGN population until f X (0.5-2.0 keV) ~ 2 x 10-18 erg s-1 cm-2 (a factor of ~5 lower than the previous estimate). We have also built an X-ray luminosity function of normal galaxies in the luminosity range of L X = 5 x 10 39-10 42 erg s-1 , which is consistent with other survey results. A group of NELGs (most of them with f X /f O >0.1) appear to be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correcting for intrinsic absorption, their X-ray luminosities could be L X > 10 44 erg s-1 , making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG-X-ray bright, optically normal galaxy candidates) do not appear to be significantly absorbed, we found two heavily obscured objects, which could be as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A galaxy candidates with strong Balmer absorption lines, but no [OII] line. 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 investigate how to achieve the best possible ACIS spatial resolution by binning in ACIS sub-pi... more We investigate how to achieve the best possible ACIS spatial resolution by binning in ACIS sub-pixel and applying an event repositioning algorithm after removing pixel-randomization from the pipeline data. We quantitatively assess the improvement in spatial resolution by (1) measuring point source sizes and (2) detecting faint point sources. The size of a bright (but no pile-up), on-axis point source
A complete and unbiased sample of AGN types is required in order to understand the phenomenon of ... more A complete and unbiased sample of AGN types is required in order to understand the phenomenon of accretion on to supermassive blackholes, (an evolutionary phase that is believed to take place in all massive galaxies), their formation and evolution, and the shape of the Cosmic X- ray background. X-ray surveys provide the best means by which to select AGN, regardless
We present an X-ray and optical analysis of a flux limited (f2.0-8.0 keV > 10-14 erg s-1 cm-2)... more We present an X-ray and optical analysis of a flux limited (f2.0-8.0 keV > 10-14 erg s-1 cm-2) sample of 126 AGN detected in 16 Chandra fields. This work represents a small though significant subset of the Chandra Multiwavelength Project (ChaMP). We have chosen this limiting flux to have a reasonable degree of completeness (50%) in our optical spectroscopic identifications. The optical counterparts of these AGN are characterized as either broad emission line AGN (BLAGN; 59%), narrow emission line galaxies (NELG; 20%) or absorption line galaxies (ALG; 12%) without any evidence of an AGN signature. Based on their X-ray luminosity and spectral properties, we show that NELG and ALG are primarily the hosts of obscured AGN with an intrinsic absorbing column in the range of 1021.5< NH<1023.3 cm-2. While most of the BLAGN are unobscured, there are a few with substantial absorption. X-ray surveys such as the ChaMP nicely complement optical surveys such as the SDSS to completely dete...
The Astrophysical Journal, 2006
Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg 2 in the Lockman Ho... more Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg 2 in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities k10 24 cm À2 and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg À2 detected in the infrared in the Chandra/ SWIRE field, of which 4040% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only 4033% of all Compton-thick AGNs are detected in the X-rays at our depth [F(0:3 8 keV) > 10 À15 ergs cm À2 s À1 ]. We report the discovery of two sources in our sample of Comptonthick AGNs, SWIRE J104409.95+585224.8 (z ¼ 2:54) and SWIRE J104406.30+583954.1 (z ¼ 2:43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.
The Astrophysical Journal, 2010
We have compared the combined X-ray luminosity function (XLF) of LMXBs detected in Chandra observ... more We have compared the combined X-ray luminosity function (XLF) of LMXBs detected in Chandra observations of young, post-merger elliptical galaxies, with that of typical old elliptical galaxies. We find that the XLF of the 'young' sample does not present the prominent high luminosity break at L X > 5 x 10 38 erg s-1 found in the old elliptical galaxy XLF. The 'young' and 'old' XLFs differ with a 3σ statistical significance (with a probability less than 0.2% that they derive from the same underlying parent distribution). Young elliptical galaxies host a larger fraction of luminous LMXBs (L X > 5 x 10 38 erg s-1) than old elliptical galaxies and the XLF of the young galaxy sample is intermediate between that of typical old elliptical galaxies and that of star forming galaxies. This observational evidence may be related to the last major/minor mergers and the associated star formation.
The Astrophysical Journal, 2006
We present a systematic study of the low mass X-ray binary (LMXB) populations of 6 elliptical gal... more We present a systematic study of the low mass X-ray binary (LMXB) populations of 6 elliptical galaxies, aimed at investigating the detected LMXB − globular cluster (GC) connection. We utilize Chandra archival data to identify 665 X-ray point sources and HST archival data supplemented by ground observations to identify 6173 GCs. Applying rigorous X-ray and optical photometry and conservative matching criteria, we associate 209 LMXBs with red GC (RGC) and 76 LMXBs with blue GCs (BGC), while we find no optical GC counterpart for 258 LMXBs. This is the largest GC−LMXB sample studied so far. We confirm previous reports suggesting that the fraction of GCs associated with LMXBs is ∼ 3 times larger in RGCs than in BGCs, indicating that metallicity is a primary factor in the GC−LMXB formation. While as already known, the brighter (and bigger) GCs have a higher probability to host LMXBs, we find that this optical luminosity (or mass) dependency is stronger in RGCs than in BGCs. We also find that GCs located near the galaxy center have a higher probability to harbor LMXBs compared to those in the outskirts. The radial distributions of GC−LMXBs (for both RGC and BGC) are steeper than those of the whole optical GC sample, but consistent with those of the optical halo light, suggesting that there must be another parameter (in addition to metallicity) governing LMXB formation in GCs. This second parameter must depend on the galacto-centric distance. One possibility is a galacto-centric distance dependent encounter rate. We find no statistically significant difference in the X-ray properties (shape of X-ray luminosity function, L X /L V distribution, X-ray spectra) among RGC−LMXBs, BGC−LMXBs and field−LMXBs. The similarity of the X-ray spectra of BGC−LMXBs and RGC−LMXBs is inconsistent with the irradiationinduced stellar wind model prediction of more absorbed X-ray spectra in
The Astrophysical Journal, 1999
... RADIO-QUIET RED QUASARS DONG-WOO KIM1 Chungnam National University, Taejon, 305-764, South Ko... more ... RADIO-QUIET RED QUASARS DONG-WOO KIM1 Chungnam National University, Taejon, 305-764, South Korea AND MARTIN ELVIS Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Received 1998 May 11 ; accepted 1998 December 8 ...
The Astrophysical Journal, 2003
The Astrophysical Journal, 2002
We have identified a population of 'blank field sources' (or 'blanks') among the ROSAT bright uni... more We have identified a population of 'blank field sources' (or 'blanks') among the ROSAT bright unidentified Xray sources with faint optical counterparts. The extreme X-ray over optical flux ratio of blanks is not compatible with the main classes of X-ray emitters except for extreme BL Lacertae objects. From the analysis of ROSAT archival data we found no indication of variability and evidence for only three sources, out of 16, needing absorption in excess of the Galactic value. We also found evidence for an extended nature for only one of the 5 blanks with a serendipitous HRI detection; this source (1WGA J1226.9+3332) was confirmed as a z=0.89 cluster of galaxies. Palomar images reveal the presence of a red (O− E ≥ 2) counterpart in the X-ray error circle for 6 blanks. The identification process brought to the discovery of another high z cluster of galaxies, one (possibly extreme) BL Lac, two ultraluminous X-ray sources in nearby galaxies and two apparently normal type 1 AGNs. These AGNs, together with 4 more AGN-like objects seem to form a well defined group: they present unabsorbed X-ray spectra but red Palomar counterparts. We discuss the possible explanations for the discrepancy between the X-ray and optical data, among which: a suppressed big blue bump emission, an extreme dust to gas (∼ 40 − 60 the Galactic ratio), a high redshift (z ≥ 3.5) QSO nature, an atypical dust grain size distribution and a dusty warm absorber. These AGN-like blanks seem to be the bright (and easier to study) analogs of the sources which are found in deep Chandra observations. Three more blanks have a still unknown nature.
The Astrophysical Journal, 2008
We present new observational results of NGC 7619, an elliptical galaxy with a prominent X-ray tai... more We present new observational results of NGC 7619, an elliptical galaxy with a prominent X-ray tail and a dominant member of the Pegasus group. With Chandra and XMM-Newton observations, we confirm the presence of a long X-ray tail in the southwest direction; moreover, we identify for the first time a sharp discontinuity of the X-ray surface brightness in the opposite (northeast) side of the galaxy. The density, temperature, and pressure jump at the northeast discontinuity suggest a Mach number 1,correspondingtoagalaxyvelocityof1, corresponding to a galaxy velocity of 1,correspondingtoagalaxyvelocityof500 km s À1 , relative to the surrounding hot gas. Spectral analysis of these data shows that the iron abundance of the hot gaseous medium is much higher (1Y2 solar) near the center of NGC 7619 and in the tail extending from the core than in the surrounding regions (1/2 solar), indicating that the gas in the tail is originated from the galaxy. The possible origin of the head-tail structure is either ongoing ram pressure stripping or sloshing. The morphology of the structure is more in line with a ram pressure stripping phenomenon, while the position of NGC 7619 at the center of the Pegasus I group, and its dominance, would prefer sloshing.
The Astrophysical Journal, 2010
We employ the Chandra Multiwavelength Project (ChaMP) and the Sloan Digital Sky Survey (SDSS) to ... more We employ the Chandra Multiwavelength Project (ChaMP) and the Sloan Digital Sky Survey (SDSS) to study the fraction of X-ray-active galaxies in the field to z = 0.7. We utilize spectroscopic redshifts from SDSS and ChaMP, as well as photometric redshifts from several SDSS catalogs, to compile a parent sample of more than 100,000 SDSS galaxies and nearly 1,600 Chandra X-ray detections. Detailed ChaMP volume completeness maps allow us to investigate the local fraction of active galactic nuclei (AGN), defined as those objects having broad-band X-ray luminosities L X (0.5-8 keV) ≥ 10 42 erg s −1 , as a function of absolute optical magnitude, X-ray luminosity, redshift, mass, and host color/morphological type. In five independent samples complete in redshift and i-band absolute magnitude, we determine the field AGN fraction to be between 0.16 ± 0.06% (for z ≤ 0.125 and −18 > M i > −20) and 3.80 ± 0.92% (for z ≤ 0.7 and M i < −23). We find excellent agreement between our ChaMP/SDSS field AGN fraction and the Chandra cluster AGN fraction, for samples restricted to similar redshift and absolute magnitude ranges: 1.19 ± 0.11% of ChaMP/SDSS field galaxies with 0.05 < z < 0.31 and absolute R-band magnitude more luminous than M R < −20 are AGN. Our results are also broadly consistent with measures of the field AGN fraction in narrow, deep fields, though differences in the optical selection criteria, redshift coverage, and possible cosmic variance between fields introduce larger uncertainties in these comparisons.
The Astrophysical Journal, 2004
We present the results of the X-ray XMM-Newton observations of NGC 507, a dominant elliptical gal... more We present the results of the X-ray XMM-Newton observations of NGC 507, a dominant elliptical galaxy in a small group of galaxies, and report 'super-solar' metal abundances of both Fe and α-elements in the hot ISM of this galaxy. These results are robust, in that we considered all possible systematic effects in our analysis. We find Z Fe = 2-3 times solar inside the D 25 ellipse of NGC 507. This is the highest Z Fe reported so far for the hot halo of an elliptical galaxy; this high Iron abundance is fully consistent with the predictions of stellar evolution models, which include the yield of both type II and Ia supernovae. Our analysis shows that abundance measurements are critically dependent on the selection of the proper emission model. The spatially resolved, high quality XMM spectra provide enough statistics to formally require at least three emission components in each of 4 circum-nuclear concentric shells (within r < 5 arcmin or 100 kpc): two soft thermal components indicating a range of temperatures in the hot ISM, plus a harder component, consistent with the integrated output of low mass X-ray binaries (LMXBs) in NGC 507. The two-component (thermal + LMXB) model customarily used in past studies yields a much lower Z Fe , consistent with previous reports of sub-solar metal abundances. This model, however, gives a significantly worse fit to the data (F-test probability < 0.0001). The abundance of α-elements (most accurately determined by Si) is also found to be super-solar. The α-elements to Fe abundance ratio is close to the solar ratio, suggesting that ~70% of the Iron mass in the hot ISM was originated from SNe Type Ia. The α-element to Fe abundance ratio remains constant out to at least 100 kpc, indicating that SNe Type II and Ia ejecta are well mixed in a scale much larger than the extent of the stellar body.
The Astronomical Journal, 2006
We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part ... more We present UBVRI photometry of 44 Type Ia supernovae (SNe Ia) observed from 1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The data set comprises 2190 observations and is the largest homogeneously observed and reduced sample of SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SNe Ia observed at high redshift. The decline rate of SN Ia U-band light curves correlates well with the decline rate in other bands, as does the U À B color at maximum light. However, the U-band peak magnitudes show an increased dispersion relative to other bands even after accounting for extinction and decline rate, amounting to an additional $40% intrinsic scatter compared to the B band.
The Chandra Multiwavelength Project (ChaMP) is measuring the luminosity function of X-ray selecte... more The Chandra Multiwavelength Project (ChaMP) is measuring the luminosity function of X-ray selected AGN out to z 5. to determine the history of supermassive black hole accretion. While we have evidence of a decline in the space density of AGN at z> 3, we must increase our completeness at faint optical magnitudes (21.5< i' 4 quasar candidates per Chandra field using optical color criteria, but with no stellar contamination (≲ 5%) thanks to fxfopt. These 3 nights of Gemini time with GMOS-N are ALREADY AWARDED through the Chandra/NOAO Joint time process. We will acquire Gemini/GMOS spectra of 49 faint Chandra X-ray counterparts with ip 4 X-ray AGN candidates.