35 research outputs found
Statistics of Merging Peaks of Random Gaussian Fluctuations: Skeleton Tree Formalism
In order to study the statistics of the objects with hierarchical merging, we
propose the skeleton tree formalism, which can analytically distinguish the
episodic merging and the continuous accretion in the mass growth processes. The
distinction was not clear in extended Press-Schechter (PS) formalism. The
skeleton tree formalism is a natural extension of the peak theory which is an
alternative formalism for the statistics of the bound objects. The fluctuation
field smoothing with Gaussian filter produces the landscape with adding the
extra-dimension of the filter resolution scale to the spatial coordinate of the
original fluctuation. In the landscape, some smoothing peaks are nesting into
the neighboring peaks at a type of critical points called sloping saddles
appears, which can be interpreted as merging events of the objects in the
context of the hierarchical structure formation. The topological properties of
the landscape can be abstracted in skeleton trees, which consist of line
process of the smoothing peaks and the point process of the sloping saddles.
According to this abstract topological picture, in this paper, we present the
concept and the basic results of the skeleton tree formalism to describe (1)
the distinction between the accretion and the merger in the hierarchical
structure formation from various initial random Gaussian fields; (2) the
instantaneous number density of the sloping saddles which gives the
instantaneous scale function of the objects with the destruction and
reformation in the mergers; (3) the rates of the destruction, the reformation,
and the relative accretion growth; (4) the self-consistency of the formalism
for the statistics of the mass growth processes of the objects; (5) the mean
growth history of the objects at the fixed mass.Comment: 16 pages, 4 figures, submitted to MNRAS at 28th July, not yet
refereed until 4th Oc
Evolutionary SED diagnostics of starburst galaxies: signature of bimodality
We construct an evolutionary spectral energy distribution (SED) model of a
starburst region, from the ultraviolet to submillimetre wavelengths. This model
allows us to derive the star formation rate, optical depth by dust and apparent
effective radius of starburst regions at various wavelengths; as a result, the
intrinsic surface brightness of starburst regions can be derived. Using this
SED model, we analyse 16 UV-selected starburst galaxies and 10 ultraluminous
infrared galaxies. The derived star formation rates and optical depths are
compared with emission line measurements and found to be consistent. The
derived apparent effective radii are also consistent with observations. From
the SED analysis, we find a bimodal property of the star formation rate with
the optical depth and the compactness of stellar distributions. While mild
starbursts have a limiting intrinsic surface brightness L(bol) x r_e^{-2} ~
10^{12} Lsun kpc^{-2}, intense starbursts tend to be more heavily obscured and
concentrated within a characteristic scale of r_e ~ 0.3 kpc. We suggest that
the mild starbursts can be triggered by a self-gravitating disc instability in
which feedback is effective in the shallow gravitational potential. On the
other hand, the intense starbursts can be induced via an external dynamical
perturbation like galaxy merging, in which feedback is less effective due to
the deep gravitational potential attained by the large gas concentration within
the central starburst region.Comment: 22 pages, 15 figures, accepted for publication in MNRA
J- and Ks-band Galaxy Counts and Color Distributions in the AKARI North Ecliptic Pole Field
We present the J- and Ks-band galaxy counts and galaxy colors covering 750
square arcminutes in the deep AKARI North Ecliptic Pole (NEP) field, using the
FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer
(FLAMINGOS) on the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
limiting magnitudes with a signal-to-noise ratio of three in the deepest
regions are 21.85 and 20.15 in the J- and Ks-bands respectively in the Vega
magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are
broadly in good agreement with those of other results in the literature,
however we find some indication of a change in the galaxy number count slope at
J~19.5 and over the magnitude range 18.0 < Ks < 19.5. We interpret this feature
as a change in the dominant population at these magnitudes because we also find
an associated change in the B - Ks color distribution at these magnitudes where
the number of blue samples in the magnitude range 18.5 < Ks < 19.5 is
significantly larger than that of Ks < 17.5
Star Formation and AGN activity in Galaxies classified using the 1.6 {\mu}m Bump and PAH features at
We have studied the star-formation and AGN activity of massive galaxies in
the redshift range , which are detected in a deep survey field using
the AKARI InfraRed (IR) astronomical satellite and {\em Subaru} telescope
toward the North Ecliptic Pole (NEP). The AKARI/IRC Mid-InfraRed (MIR)
multiband photometry is used to trace their star-forming activities with the
Polycyclic-Aromatic Hydrocarbon (PAH) emissions, which is also used to
distinguish star-forming populations from AGN dominated ones and to estimate
the Star Formation Rate (SFR) derived from their total emitting IR (TIR)
luminosities. In combination with analyses of their stellar components, we have
studied the MIR SED features of star-forming and AGN-harboring galaxies.Comment: 45 pages and 63 figures, will be published in PASJ Vol.64 No.
An Optical Source Catalog of the North Ecliptic Pole Region
We present a five (u*,g',r',i',z') band optical photometry catalog of the
sources in the North Ecliptic Pole (NEP) region based on deep observations made
with MegaCam at CFHT. The source catalog covers about 2 square degree area
centered at the NEP and reaches depths of about 26 mag for u*, g', r' bands,
about 25 mag for i' band, and about 24 mag for z' band (4 sigma detection over
an 1 arcsec aperture). The total number of cataloged sources brighter than r'=
23 mag is about 56,000 including both point sources and extended sources. From
the investigation of photometric properties using the color-magnitude diagrams
and color-color diagrams, we have found that the colors of extended sources are
mostly (u*-r') 0.5. This can be used to separate the
extended sources from the point sources reliably, even for the faint source
domain where typical morphological classification schemes hardly work
efficiently. We have derived an empirical color-redshift relation of the red
sequence galaxies using the Sloan Digital Sky Survey data. By applying this
relation to our photometry catalog and searching for any spatial overdensities,
we have found two galaxy clusters and one nearby galaxy group.Comment: 34 pages, 15 figures, 2 tables. Accepted for publication in ApJS. The
pdf file with high resolution figures can be downloaded from
http://astro.snu.ac.kr/~nhwang/index.files/nep.htm
The mid-infrared view of red sequence galaxies in Abell 2218 with <i>AKARI</i>
We present the AKARI Infrared Camera (IRC) imaging observation of early-type galaxies (ETGs) in A2218 at z ~ 0.175. Mid-infrared (MIR) emission from ETGs traces circumstellar dust emission from asymptotic giant branch (AGB) stars or/and residual star formation. Including the unique imaging capability at 11 and 15 μm, our AKARI data provide an effective way to investigate MIR properties of ETGs in the cluster environment. Among our flux-limited sample of 22 red sequence ETGs with precise dynamical and line strength measurements (less than 18 mag at 3 μm), we find that at least 41% have MIR-excess emission. The N3 – S11 versus N3 (3 and 11 μm) color-magnitude relation shows the expected blue sequence, but the MIR-excess galaxies add a red wing to the relation especially at the fainter end. A spectral energy distribution analysis reveals that the dust emission from AGB stars is the most likely cause of the MIR excess, with a low level of star formation being the next possible explanation. The MIR-excess galaxies show a wide spread of N3 – S11 colors, implying a significant spread (2-11 Gyr) in the estimated mean ages of stellar populations. We study the environmental dependence of MIR-excess ETGs over an area out to a half virial radius (~1 Mpc). We find that the MIR-excess ETGs are preferentially located in the outer region. From this evidence, we suggest that the fainter, MIR-excess ETGs have just joined the red sequence, possibly due to the infall and subsequent morphological/spectral transformation induced by the cluster environment
The Subaru-XMM-Newton Deep Survey (SXDS) VIII.: Multi-wavelength Identification, Optical/NIR Spectroscopic Properties, and Photometric Redshifts of X-ray Sources
We report the multi-wavelength identification of the X-ray sources found in
the Subaru-XMM-Newton Deep Survey (SXDS) using deep imaging data covering the
wavelength range between the far-UV to the mid-IR. We select a primary
counterpart of each X-ray source by applying the likelihood ratio method to
R-band, 3.6micron, near-UV, and 24micron source catalogs as well as matching
catalogs of AGN candidates selected in 1.4GHz radio and i'-band variability
surveys. Once candidates of Galactic stars, ultra-luminous X-ray sources in a
nearby galaxy, and clusters of galaxies are removed there are 896 AGN
candidates in the sample. We conduct spectroscopic observations of the primary
counterparts with multi-object spectrographs in the optical and NIR; 65\% of
the X-ray AGN candidates are spectroscopically-identified. For the remaining
X-ray AGN candidates, we evaluate their photometric redshift with photometric
data in 15 bands. Utilising the multi-wavelength photometric data of the large
sample of X-ray selected AGNs, we evaluate the stellar masses, M*, of the host
galaxies of the narrow-line AGNs. The distribution of the stellar mass is
remarkably constant from z=0.1 to 4.0. The relation between M* and 2--10 keV
luminosity can be explained with strong cosmological evolution of the
relationship between the black hole mass and M*. We also evaluate the scatter
of the UV-MIR spectral energy distribution (SED) of the X-ray AGNs as a
function of X-ray luminosity and absorption to the nucleus. The scatter is
compared with galaxies which have redshift and stellar mass distribution
matched with the X-ray AGN. The UV-NIR SEDs of obscured X-ray AGNs are similar
to those of the galaxies in the matched sample. In the NIR-MIR range, the
median SEDs of X-ray AGNs are redder, but the scatter of the SEDs of the X-ray
AGN broadly overlaps that of the galaxies in the matched sample.Comment: Accepted for publication in PASJ Subaru special issue. 42 pages, 22
figures. Entire contents of Tables 3, 8, 9, 10, and 11, and ASCII format
tables are available from
http://www.astr.tohoku.ac.jp/~akiyama/SXDS/index.htm
Torus Constraints in ANEPD-CXO245: A Compton-thick AGN with Double-peaked Narrow Lines
We report on the torus constraints of the Compton-thick active galactic nucleus (AGN) with double-peaked optical narrow-line region emission lines, ANEPD-CXO245, at z = 0.449 in the AKARI NEP Deep Field. The unique infrared data on this field, including those from the nine-band photometry over 2–24 μm with the AKARI Infrared Camera, and the X-ray spectrum from Chandra allow us to constrain torus parameters such as the torus optical depth, X-ray absorbing column, torus angular width (σ), and viewing angle (i). We analyze the X-ray spectrum as well as the UV–optical–infrared spectral energy distribution (UOI-SED) with clumpy torus models in X-ray (XCLUMPY) and infrared (CLUMPY), respectively. From our current data, the constraints on σ–i from both X-rays and UOI show that the line of sight crosses the torus as expected for a type 2 AGN. We obtain a small X-ray scattering fraction (NH from the X-ray spectrum, we find that the gas-to-dust ratio is <4 times larger than the Galactic value
Number Density Evolution of Ks -band Selected High Redshift Galaxy Populations in the AKARI North Ecliptic Pole Field
We present the number counts of Ks-band selected high redshift galaxy
populations such as extremely red objects (EROs), B, z & K -band selected
galaxies (BzKs) and distant red galaxies (DRGs) in the AKARI NEP field. The
final catalogue contains 308 EROs (Ks<19.0 ; 54 percent are dusty star-forming
EROs and the rest are passive old EROs), 137 star-forming BzKs and 38 passive
old BzKs (Ks<19.0) and 64 DRGs (Ks<18.6). We also produce individual component
source counts for both the dusty star-forming and passive populations. We
compare the observed number counts of the high redshift passively evolving
galaxy population with a backward pure luminosity evolution (PLE) model
allowing different degrees of number density evolution. We find that the PLE
model without density evolution fails to explain the observed counts at faint
magnitudes, while the model incorporating negative density evolution is
consistent with the observed counts of the passively evolving population. We
also compare our observed counts of dusty star-forming EROs with a
phenomenological evolutionary model postulating that the near-infrared EROs can
be explained by the source densities of the far-infrared - submillimetre
populations. Our model predicts that the dusty ERO source counts can be
explained assuming a 25 percent contribution of submillimetre star-forming
galaxies with the majority of brighter Ks -band detected dusty EROs having
luminous (rather than HR10 type ultra-luminous) submillimetre counterparts. We
propose that the fainter Ks>19.5 population is dominated by the sub-millijansky
submillimetre population. We also predict a turnover in in dusty ERO counts
around 19<Ks<20.Comment: (37 pages, 14 figures accepted for publication in The Astrophysical
Journal