We use available multifilter Hubble Space Telescope (HST) WFPC2 imaging of five (M81, M83, NGC 6946, M101, and M51, in order of distance) low- inclination, nearby spiral galaxies to study ancient ...star cluster populations. Combining rigorous selection criteria to reject contaminants (individual stars, background galaxies, and blends) with optical photometry including the U bandpass, we unambiguously detect ancient globular cluster (GC) systems in each galaxy. We present luminosities, colors, and size (effective radius) measurements for our candidate GCs. These are used to estimate specific frequencies, to assess whether intrinsic color distributions are consistent with the presence of both metal-poor and metal-rich GCs, and to compare relative sizes of ancient clusters between different galaxy systems. M81 globulars have intrinsic color distributions that are very similar to those in the Milky Way and M31, with approx40% of sample clusters having colors expected for a metal-rich population. The GC system in M51 meanwhile, appears almost exclusively blue and metal-poor. This lack of metal-rich GCs associated with the M51 bulge indicates that the bulge formation history of this Sbc galaxy may have differed significantly from that of our own. Ancient clusters in M101 and possibly in NGC 6946, two of the three later type spirals in our sample, appear to have luminosity distributions that continue to rise to our detection limit (M sub( )approx-6.0), well beyond the expected turnover (M sub(V) approx-7.4) in the luminosity function. This is reminiscent of the situation in M33, a Local Group galaxy of similar Hubble type. The faint ancient cluster candidates in M101 and NGC 6946 have properties (colors and r sub(eff)) similar to their more luminous counterparts, and we suggest that these are either intermediate-age (3-9 Gyr) disk clusters or the low-mass end of the original GC population. Potentially, these lower mass clusters were not destroyed because of different dynamical conditions relative to those present in earlier type galaxies. If the faint, excess GC candidates are excluded, we find that the specific frequency (S sub(N)) of ancient clusters formed in later type spirals is roughly constant, with S sub(N) = 0.5 plus or minus 0.2. If we consider only the blue, metal-poor clusters in the early-type spiral M81, this galaxy is also consistent with having formed a "universal" specific frequency of halo GC population, with a value of S sub(N) approx 0.6. By combining the results of this study with literature values for other systems, we find that the total GC specific frequencies in spirals appear to correlate best with Hubble type and bulge/total ratio, rather than with galaxy luminosity or galaxy mass.
We present the discovery of new star clusters in the central plane region ( and ) of the Milky Way. In order to overcome the extinction problem and the spatial limit of previous surveys, we use the ...Wide-field Infrared Survey Explorer (WISE) data to find clusters. We also use other infrared survey data in the archive for additional analysis. We find 923 new clusters, of which 202 clusters are embedded clusters. These clusters are concentrated toward the Galactic plane and show a symmetric distribution with respect to the Galactic latitude. The embedded clusters show a stronger concentration to the Galactic plane than the nonembedded clusters. The new clusters are found more in the first Galactic quadrant, while previously known clusters are found more in the fourth Galactic quadrant. The spatial distribution of the combined sample of known clusters and new clusters is approximately symmetric with respect to the Galactic longitude. We estimate reddenings, distances, and relative ages of the 15 class A clusters using theoretical isochrones. Ten of them are relatively old (age >800 Myr) and five are young (age 4 Myr).
We present a kinematic analysis of the globular cluster (GC) system in the giant elliptical galaxy (gE) NGC 4636 in the Virgo cluster. Using the photometric and spectroscopic database of 238 GCs (108 ...blue GCs and 130 red GCs) at the galactocentric radius 0.'39 < R < 15.'43, we have investigated the kinematics of the GC system. The NGC 4636 GC system shows weak overall rotation, which is dominated by the red GCs. However, both the blue GCs and red GCs show some rotation in the inner region at R < 4.'3 (=2.9R{sub eff} = 18.5 kpc). The velocity dispersion for all the GCs is derived to be sigma{sub p} = 225{sup +12}{sub -9} km s{sup -1}. The velocity dispersion for the blue GCs (sigma{sub p} = 251{sup +18}{sub -12} km s{sup -1}) is slightly larger than that for the red GCs (sigma{sub p} = 205{sup +11}{sub -13} km s{sup -1}). The velocity dispersions for the blue GCs about the mean velocity and about the best-fit rotation curve have a significant variation depending on the galactocentric radius. Comparison of observed stellar and GC velocity dispersion profiles (VDPs) with the VDPs calculated from the stellar mass profile shows that the mass-to-light ratio should increase as the galactocentric distance increases, indicating the existence of an extended dark matter halo. From the comparison of the observed GC VDPs and the VDPs calculated for the X-ray mass profiles in the literature, we find that the orbit of the GC system is tangential, and that the orbit of the red GCs is slightly more tangential than that of the blue GCs. We compare the GC kinematics of NGC 4636 with those of other six gEs, finding that the kinematic properties of the GCs are diverse among gEs. We find several correlations between the kinematics of the GCs and the global parameters of their host galaxies. We discuss the implication of the results for the formation models of the GC system in gEs, and suggest a mixture scenario for the origin of the GCs in gEs.
We present the Chandra Multiwavelength Project (ChaMP) X-ray point source number counts and cosmic X-ray background (CXRB) flux densities in multiple energy bands. From the ChaMP X-ray point source ...catalog, similar to 5500 sources are selected, covering 9.6 deg super(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 2 x 10 super(-17) to 2.4 x 10 super(-12) (0.5-2 keV) and from 2 x 10 super(-16) to 7.1 x 10 super(-12) (2-8 keV) ergs cm super(-2) s super(-1). 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 plus or minus 0.02 and 2.36 plus or minus 0.05 (0.5-2 keV), and 1.58 plus or minus 0.01 and 2.59 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(0) super(6) sub(5) (2-8 keV), respectively. We detect breaks in the differential number counts that 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. By 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% plus or minus 1% and 81% plus or minus 2% in the 0.5-2 and 2-8 keV bands, respectively, somewhat lower than but generally consistent with earlier numbers because of their large errors. These fractions increase by plus or minus 1% when target sources are included.
We present a photometric study of the GCs in the giant elliptical galaxy M60 in the Virgo Cluster, based on deep, relatively wide field Washington image CCD images. The CMD reveals a significant ...population of GCs in M60 and a large number of young luminous clusters in NGC 4647, a small companion spiral northwest of M60. The color distribution of the GCs in M60 is clearly bimodal, with a blue peak at image and a red peak at image. We derive two new transformation relations between the image color and Fe/H using the data for the GCs in our Galaxy and M49. Using these relations, we derive the metallicity distribution of the GCs in M60, which is also bimodal: a dominant metal-poor component with center at image, and a weaker metal-rich component with center at image. The radial number density profile of the GCs is more extended than that of the stellar halo, and the radial number density profile of the blue GCs is more extended than that of the red GCs. The number density maps of the GCs show that the spatial distribution of the blue GCs is roughly circular, while that of the red GCs is elongated similarly to that of the stellar halo. We estimate the total number of the GCs in M60 to be image and the specific frequency to be image. The mean color of the bright blue GCs gets redder as they get brighter in both the inner and outer region of M60. This blue tilt is seen also in the outer region of M49, the brightest Virgo galaxy. Implications of these results are discussed.
ABSTRACT M105 is a standard elliptical galaxy, located in the Leo I Group. We present photometry of the resolved stars in its inner region at R 4′ 4Reff, obtained from F606W and F814W images in the ...Hubble Space Telescope archive. We combine this with photometry of the outer region at R 12′ 12Reff from archival imaging data. Color-magnitude diagrams of the resolved stars in the inner region show a prominent red giant branch (RGB) with a large color range, while those for the outer region show better a narrow blue RGB. The metallicity distribution function (MDF) of the RGB stars shows the existence of two distinct subpopulations: a dominant metal-rich population (with a peak at M/H 0.0) and a much weaker metal-poor population (with a peak at M/H −1.1). The radial number density profiles of the metal-rich and metal-poor RGB stars are fit well by a Sérsic law with n = 2.75 0.10 and n = 6.89 0.94, and by a single power law ( ∝ R−3.8 and ∝ R−2.6), respectively. The MDFs of the inner and outer regions can be described well by accretion gas models of chemical evolution with two components. These provide strong evidence that there are two distinct stellar halos in this galaxy, blue metal-poor and red metal-rich halos, consistent with the results based on globular cluster systems in bright early-type galaxies (ETGs). We discuss the implications of these results with regard to the formation of massive ETGs in the dual halo mode formation scenario.
We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. We derive Fe/H ...values of 59 GCs based on the Brodie & Huchra method, and Z/H, age, and alpha /Fe values of 33 GCs from the comparison of the Lick line indices with single stellar population models. We also derive the metallicities, ages, and alpha /Fe values for the GCs in other nearby gEs (M87, M49, M60, NGC 5128, NGC 1399, and NGC 1407) from the line index data in the literature using the same methods as used for NGC 4636 GCs. The metallicity distribution of GCs in the combined sample of seven gEs including NGC 4636 is found to be bimodal, supported by the KMM test with a significance level of >99.9%. We discuss these results in the context of GC formation in gEs.
Dynamical analysis of compact groups provides important tests of models of compact group formation and evolution. By compiling 2066 redshifts from FLWO/FAST, from the literature, and from SDSS DR12 ...in the fields of compact groups in McConnachie et al. (2009), we construct the largest sample of compact groups with complete spectroscopic redshifts in the redshift range 0.01 < z < 0.22. This large redshift sample shows that the interloper fraction in the McConnachie et al. (2009) compact group candidates is 42%. A secure sample of 332 compact groups includes 192 groups with four or more member galaxies and 140 groups with three members. The fraction of early-type galaxies in these compact groups is 62%, higher than for the original Hickson compact groups. The velocity dispersions of early- and late-type galaxies in compact groups change little with groupcentric radius; the radii sampled are less than 100 h−1 kpc, smaller than the radii typically sampled by members of massive clusters of galaxies. The physical properties of our sample compact groups include size, number density, velocity dispersion, and local environment; these properties slightly differ from those derived for the original Hickson compact groups and for the DPOSS II compact groups. Differences result from subtle differences in the way the group candidates were originally selected. The abundance of the compact groups changes little with redshift over the range covered by this sample. The approximate constancy of the abundance for this sample is a potential constraint on the evolution of compact groups on a few Gigayear timescale. KCI Citation Count: 15
We present a study of the optical spectral properties of 115 ultraluminous infrared galaxies (ULIRGs) in the southern sky. Using the optical spectra obtained at the Cerro Tololo Inter-American ...Observatory (CTIO) 4 -m telescope and provided by the Two-degree Field (2dF) Galaxy Redshift Survey and the Six-degree Field (6dF) Galaxy Survey, we measure emission linewidths and fluxes for spectral classification. We determine the spectral types of ULIRGs with Hα measurement using the standard diagnostic diagrams. For ULIRGs without Hα measurement, we determine their spectral types using the plane of flux ratio between O iiiλ5007 and Hβ versus O iii linewidth based on our new empirical criterion. This criterion is efficient to distinguish active galactic nuclei (AGNs) from non-AGN galaxies with completeness and reliability of about 90 per cent. The sample of 115 ULIRGs is found to consist of eight broad-line AGNs, 49 narrow-line AGNs and 58 non-AGNs. The AGN fraction is on average 50 per cent and increases with infrared luminosity and Infrared Astronomical Satellite (IRAS) 25-60 μm colour, consistent with previous studies. The IRAS 25-60 μm colour distributions are significantly different between AGN and non-AGN ULIRGs, while their IRAS 60-100 μm colour distributions are similar.
ABSTRACT We performed a monitoring observation of a Jupiter-family comet, 17P/Holmes, during its 2014 perihelion passage to investigate its secular change in activity. The comet has drawn the ...attention of astronomers since its historic outburst in 2007, and this occasion was its first perihelion passage since then. We analyzed the obtained data using an aperture photometry package and derived the parameter, a proxy for the dust-production rate. We found that showed asymmetric properties with respect to the perihelion passage: it increased moderately from 100 cm at the heliocentric distance of rh = 2.6-3.1 AU to a maximal value of 185 cm at rh = 2.2 AU (near the perihelion) during the inbound orbit, while dropping rapidly to 35 cm at rh = 3.2 AU during the outbound orbit. We applied a model for characterizing dust-production rates as a function of rh and found that the fractional active area of the cometary nucleus had dropped from 20%-40% in 2008-2011 (around the aphelion) to 0.1%-0.3% in 2014-2015 (around the perihelion). This result suggests that a dust mantle would have developed rapidly in only one orbital revolution around the Sun. Although a minor eruption was observed on UT 2015 January 26 at rh = 3.0 AU, the areas excavated by the 2007 outburst would be covered with a layer of dust ( 10 cm depth) which would be enough to insulate the subsurface ice and to keep the nucleus in a state of low activity.
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