644 research outputs found
Universal dark halo scaling relation for the dwarf spheroidal satellites
Motivated by a recently found interesting property of the dark halo surface
density within a radius, , giving the maximum circular velocity,
, we investigate it for dark halos of the Milky Way's and
Andromeda's dwarf satellites based on cosmological simulations. We select and
analyze the simulated subhalos associated with Milky Way-sized dark halos and
find that the values of their surface densities, , are in
good agreement with those for the observed dwarf spheroidal satellites even
without employing any fitting procedures. This implies that this surface
density would not be largely affected by any baryonic feedbacks and thus
universal. Moreover, all subhalos on the small scales of dwarf satellites are
expected to obey the relation ,
irrespective of differences in their orbital evolutions, host halo properties,
and observed redshifts. Therefore, we find that the universal scaling relation
for dark halos on dwarf galaxy mass scales surely exists and provides us
important clues to understanding fundamental properties of dark halos. We also
investigate orbital and dynamical evolutions of subhalos to understand the
origin of this universal dark halo relation and find that most of subhalos
evolve generally along the sequence, even
though these subhalos have undergone different histories of mass assembly and
tidal stripping. This sequence, therefore, should be the key feature to
understand the nature of the universality of .Comment: 12 pages, 5 figures and 3 tables, submitted to Ap
Cosmic Star Formation Activity at z=2.2 Probed by H-alpha Emission Line Galaxies
We present a pilot narrow-band survey of H-alpha emitters at z=2.2 in the
Great Observatories Origins Deep Survey North (GOODS-N) field with MOIRCS
instrument on the Subaru telescope. The survey reached a 3 sigma limiting
magnitude of 23.6 (NB209) which corresponds to a 3 sigma limiting line flux of
2.5 x 10^-17 erg s^-1 cm^-2 over a 56 arcmnin^2 contiguous area (excluding a
shallower area). From this survey, we have identified 11 H-alpha emitters and
one AGN at z=2.2 on the basis of narrow-band excesses and photometric
redshifts. We obtained spectra for seven new objects among them, including one
AGN, and an emission line above 3 sigma is detected from all of them. We have
estimated star formation rates (SFR) and stellar masses (M_star) for individual
galaxies. The average SFR and M_star is 27.8M_solar yr^-1 and 4.0 x
10^10M_solar, respectivly. Their specific star formation rates are inversely
correlated with their stellar masses. Fitting to a Schechter function yields
the H-alpha luminosity function with log L = 42.82, log phi = -2.78 and alpha =
-1.37. The average star formation rate density in the survey volume is
estimated to be 0.31M_solar yr^-1Mpc^-3 according to the Kennicutt relation
between H-alpha luminosity and star formation rate. We compare our H-alpha
emitters at z=2.2 in GOODS-N with narrow-band line emitters in other field and
clusters to see their time evolution and environmental dependence. We find that
the star formation activity is reduced rapidly from z=2.5 to z=0.8 in the
cluster environment, while it is only moderately changed in the field
environment. This result suggests that the timescale of galaxy formation is
different among different environments, and the star forming activities in high
density regions eventually overtake those in lower density regions as a
consequence of "galaxy formation bias" at high redshifts.Comment: Accepted for publication in PASJ Subaru Special Issue, 11 pages, 10
figure
"Direct" Gas-phase Metallicities, Stellar Properties, and Local Environments of Emission-line Galaxies at Redshift below 0.90
Using deep narrow-band (NB) imaging and optical spectroscopy from the Keck
telescope and MMT, we identify a sample of 20 emission-line galaxies (ELGs) at
z=0.065-0.90 where the weak auroral emission line, [OIII]4363, is detected at
>3\sigma. These detections allow us to determine the gas-phase metallicity
using the "direct'' method. With electron temperature measurements and dust
attenuation corrections from Balmer decrements, we find that 4 of these
low-mass galaxies are extremely metal-poor with 12+log(O/H) <= 7.65 or
one-tenth solar. Our most metal-deficient galaxy has 12+log(O/H) =
7.24^{+0.45}_{-0.30} (95% confidence), similar to some of the lowest
metallicity galaxies identified in the local universe. We find that our
galaxies are all undergoing significant star formation with average specific
star formation rate (SFR) of (100 Myr)^{-1}, and that they have high central
SFR surface densities (average of 0.5 Msun/yr/kpc^2. In addition, more than
two-thirds of our galaxies have between one and four nearby companions within a
projected radius of 100 kpc, which we find is an excess among star-forming
galaxies at z=0.4-0.85. We also find that the gas-phase metallicities for a
given stellar mass and SFR lie systematically below the local M-Z-(SFR)
relation by \approx0.2 dex (2\sigma\ significance). These results are partly
due to selection effects, since galaxies with strong star formation and low
metallicity are more likely to yield [OIII]4363 detections. Finally, the
observed higher ionization parameter and electron density suggest that they are
lower redshift analogs to typical z>1 galaxies.Comment: Accepted for publication in the Astrophysical Journal (15 November
2013). 31 pages in emulateapj format with 16 figures and 7 tables. Revised to
address referee's comments, which include discussion on selection effects,
similarities to green pea galaxies, and nebular continuum contribution.
Modifications were made for some electron temperature and metallicity
measurement
Low-Frequency Vibrational Spectra of Chlorophylls a and b in Solution: Effects ofAxial Coordination
The far-infrared spectra (500--100 cm-I) of chlorophyll a were
observed in three solvent systems (benzene-pyridine, benzene-tetrahydrofuran, and benzene-acetone). The observed spectra could
be classified into three types corresponding to the aggregate state,
the five-coordinate monomeric state, and the six-coordinate state.
The far-infrared spectra of I5N_and 26lV[g-substitutedspecies and
the polarized resonance Raman spectra of chlorophyll a and pheophytin a in the region of 500~100 cm-I were studied. These experimental results indicate that bands characteristic of the three
states are due to modes to which deformations of the macrocycle
make major contributions and vibrations around the Mg atom
make some contributions, and that no band observed in the far-
-infrared and Raman spectra is attributable to a vibrational mode
associated predominantly with the Mg atom and the coordinating
atoms. The spectral behavior of chlorophyll b in the benzene-pyridine
system was similar to that of chlorophyll a
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