9,015 research outputs found
Studying the evolution of galaxies in compact groups over the past 3 Gyr - II. The importance of environment in the suppression of star formation
We present an in depth study on the evolution of galaxy properties in compact
groups over the past 3 Gyr. We are using the largest multi-wavelength sample
to-date, comprised 1770 groups (containing 7417 galaxies), in the redshift
range of 0.01<z<0.23. To derive the physical properties of the galaxies we rely
on ultraviolet (UV)-to-infrared spectral energy distribution modeling, using
CIGALE. Our results suggest that during the 3 Gyr period covered by our sample,
the star formation activity of galaxies in our groups has been substantially
reduced (3-10 times). Moreover, their star formation histories as well as their
UV-optical and mid-infrared colors are significantly different from those of
field and cluster galaxies, indicating that compact group galaxies spend more
time transitioning through the green valley. The morphological transformation
from late-type spirals into early-type galaxies occurs in the mid-infrared
transition zone rather than in the UV-optical green valley. We find evidence of
shocks in the emission line ratios and gas velocity dispersions of the
late-type galaxies located below the star forming main sequence. Our results
suggest that in addition to gas stripping, turbulence and shocks might play an
important role in suppressing the star formation in compact group galaxies.Comment: (Accepted for publication in MNRAS, date of submission November 18,
2015
Mathematical modeling: effects on problem solving performance and math anxiety of students
This study determined the effects of the integration of mathematical modeling on the problem solving performance and math anxiety level of Grade 9 students. Two groups of students were exposed to different strategies: the control group was taught using guided practice while the experimental group was taught using the integration of mathematical modelling. Pretests and Posttests were given to measure the performance of both groups in terms of their problem solving skills and their math anxiety level. T-test of independent and dependent were used to determine whether there exists significant difference between the performance of the two groups in terms of their pretest and posttest scores. Questionnaire and Interview Method were implemented were used to elicit students' reactions on the integration of mathematical modeling in the classroom.Findings showed that there is a significant difference between the pretest and posttest mean scores of both groups in terms of their problem solving performance test and their mathematics anxiety test. However, when their posttest mean scores were compared, the experimental group made a large improvement in terms of their problem solving performance and a reduction in terms of their mathematics anxiety level, thus, the integration of mathematical modeling was effective in improving the problem solving performance and reducing the math anxiety level of students
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
ALMA [NII] 205 micron Imaging Spectroscopy of the Interacting Galaxy System BRI 1202-0725 at Redshift 4.7
We present the results from Atacama Large Millimeter/submillimeter Array
(ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII])
and the underlying continuum of BRI 1202-0725, an interacting galaxy system at
4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two
Lyman- emitters (LAEs), all within 25 kpc of the QSO. We detect
the QSO and SMG in both [NII] and continuum. At the (or 6.6 kpc)
resolution, both QSO and SMG are resolved in [NII], with the de-convolved major
axes of 9 and 14 kpc, respectively. In contrast, their continuum
emissions are much more compact and unresolved even at an enhanced resolution
of . The ratio of the [NII] flux to the existing CO (76) flux is
used to constrain the dust temperature () for a more accurate
determination of the FIR luminosity . Our best estimated equals K for both galaxies (assuming an emissivity index
). The resulting ratios are
statistically consistent with that of local luminous infrared galaxies,
confirming that traces the star formation (SF) rate (SFR) in
these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of
5.1 yr ( 30%) assuming Chabrier
initial mass function, takes place within a diameter (at half maximum) of 1.3
(1.5) kpc, and shall consume the existing 5 of
molecular gas in 10 years.Comment: 4 pages, 1 table, 4 figures; accepted for publication in the ApJ
Letter
Spatially resolved kinematics in the central 1 kpc of a compact star-forming galaxy at z=2.3 from ALMA CO observations
We present high spatial resolution (FWHM0.14'') observations of the
CO() line in GDS-14876, a compact star-forming galaxy at with
total stellar mass of . The spatially resolved
velocity map of the inner ~kpc reveals a continous velocity
gradient consistent with the kinematics of a rotating disk with km s and . The
gas-to-stellar ratios estimated from CO() and the dust continuum emission
span a broad range, and
, but are nonetheless consistent given the
uncertainties in the conversion factors. The dynamical modeling yields a
dynamical mass of which is
lower, but still consistent with the baryonic mass, (M=
M + M/M), if the smallest
CO-based gas fraction is assumed. Despite a low, overall gas fraction, the
small physical extent of the dense, star-forming gas probed by CO(),
smaller than the stellar size, implies a strong concentration
that increases the gas fraction up to
in the central 1 kpc. Such a gas-rich center, coupled with a high
star-formation rate, SFR 500 M yr, suggests that
GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong
nuclear starburst. Assuming its gas reservoir is depleted without
replenishment, GDS-14876 will quickly ( Myr) become a
compact quiescent galaxy that could retain some fraction of the observed
rotational support.Comment: Accepted for Publication in ApJL. Kinematic maps are shown in Figures
2 and
Structure-property relationships in metal-organic frameworks for hydrogen storage
Experimental hydrogen isotherms on several metal-organic frameworks (IRMOF-1, IRMOF-3, IRMOF-9, ZIF-7, ZIF-8, ZIF-9, ZIF-11, ZIF-12, ZIF-CoNIm, MIL-101 (Cr), NH2-MIL-101 (Cr), NH2-MIL-101 (Al), UiO-66, UiO-67 and HKUST-1) synthesized in-house and measured at 77 K and pressures up to 18 MPa are presented, along with N2 adsorption characterization. The experimental isotherms together with literature high pressure hydrogen data were analysed in order to search for relationships between structural properties of the materials and their hydrogen uptakes. The total hydrogen capacity of the materials was calculated from the excess adsorption assuming a constant density for the adsorbed hydrogen. The surface area, pore volumes and pore sizes of the materials were related to their maximum hydrogen excess and total hydrogen capacities. Results also show that ZIF-7 and ZIF-9 (SOD topology) have unusual hydrogen isotherm shapes at relatively low pressures, which is indicative of “breathing”, a phase transition in which the pore space increases due to adsorption. This work presents novel and more useful correlations using the modelled total hydrogen capacities of several MOFs. These total hydrogen capacities are more practically relevant for energy storage applications than the measured excess hydrogen capacities. Thus, these structural correlations will be advantageous for the prediction of the properties a MOF will need in order to meet the US Department of Energy targets for the mass and volume of on-board storage systems. Such design tools will allow hydrogen to be used as an energy vector for sustainable mobile applications such as transport, or for providing supplementary power to the grid in times of high demand
ALMA Observations of Warm Molecular Gas and Cold Dust in NGC 34
We present ALMA Cycle-0 observations of the CO (6-5) line emission
(rest-frame frequency = 691.473 GHz) and of the 435 dust continuum
emission in the nuclear region of NGC 34, a local luminous infrared galaxy
(LIRG) at a distance of 84 Mpc (1" = 407 pc) which contains a Seyfert 2 active
galactic nucleus (AGN) and a nuclear starburst. The CO emission is well
resolved by the ALMA beam (), with an integrated flux of
. Both the morphology
and kinematics of the CO (6-5) emission are rather regular, consistent with a
compact rotating disk with a size of 200 pc. A significant emission feature is
detected on the red-shifted wing of the line profile at the frequency of the
line, with an integrated flux of . However, it cannot be ruled out
that the feature is due to an outflow of warm dense gas with a mean velocity of
. The continuum is resolved into an elongated
configuration, and the observed flux corresponds to a dust mass of . An unresolved central core () contributes of the continuum flux and of
the CO (6-5) flux, consistent with insignificant contributions of the AGN to
both emissions. Both the CO (6-5) and continuum spatial distributions suggest a
very high gas column density () in the nuclear
region at .Comment: 10 pages, 13 figures, accepted for publication in Astrophysical
Journa
Extended [CII] Emission in Local Luminous Infrared Galaxies
We present Herschel/PACS observations of extended [CII]157.7{\mu}m line
emission detected on ~ 1 - 10 kpc scales in 60 local luminous infrared galaxies
(LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS). We find that
most of the extra-nuclear emission show [CII]/FIR ratios >~ 4 x 10^-3, larger
than the mean ratio seen in the nuclei, and similar to those found in the
extended disks of normal star-forming galaxies and the diffuse inter-stellar
medium (ISM) of our Galaxy. The [CII] "deficits" found in the most luminous
local LIRGs are therefore restricted to their nuclei. There is a trend for
LIRGs with warmer nuclei to show larger differences between their nuclear and
extra-nuclear [CII]/FIR ratios. We find an anti-correlation between [CII]/FIR
and the luminosity surface density, {\Sigma}_IR, for the extended emission in
the spatially-resolved galaxies. However, there is an offset between this trend
and that found for the LIRG nuclei. We use this offset to derive a beam
filling-factor for the star-forming regions within the LIRG disks of ~ 6 %
relative to their nuclei. We confront the observed trend to photo-dissociation
region (PDR) models and find that the slope of the correlation is much
shallower than the model predictions. Finally, we compare the correlation found
between [CII]/FIR and {\Sigma}_IR with measurements of high-redshift
starbursting IR-luminous galaxies.Comment: Accepted for publication in ApJ Letters. 5 pages, 2 figure
A Herschel/PACS Far Infrared Line Emission Survey of Local Luminous Infrared Galaxies
We present an analysis of [OI]63, [OIII]88, [NII]122 and [CII]158
far-infrared (FIR) fine-structure line observations obtained with
Herschel/PACS, for ~240 local luminous infrared galaxies (LIRGs) in the Great
Observatories All-sky LIRG Survey (GOALS). We find pronounced declines
-deficits- of line-to-FIR-continuum emission for [NII]122, [OI]63 and [CII]158
as a function of FIR color and infrared luminosity surface density,
. The median electron density of the ionized gas in LIRGs,
based on the [NII]122/[NII]205 ratio, is = 41 cm. We find
that the dispersion in the [CII]158 deficit of LIRGs is attributed to a varying
fractional contribution of photo-dissociation-regions (PDRs) to the observed
[CII]158 emission, f([CII]PDR) = [CII]PDR/[CII], which increases from ~60% to
~95% in the warmest LIRGs. The [OI]63/[CII]158PDR ratio is tightly correlated
with the PDR gas kinetic temperature in sources where [OI]63 is not
optically-thick or self-absorbed. For each galaxy, we derive the average PDR
hydrogen density, , and intensity of the interstellar radiation
field, in units of G, and find G/ ratios ~0.1-50 cm,
with ULIRGs populating the upper end of the distribution. There is a relation
between G/ and , showing a critical break at
~ 5 x 10 Lsun/kpc. Below , G/ remains constant, ~0.32 cm, and variations
in are driven by the number density of star-forming regions
within a galaxy, with no change in their PDR properties. Above , G/ increases rapidly with ,
signaling a departure from the typical PDR conditions found in normal
star-forming galaxies towards more intense/harder radiation fields and compact
geometries typical of starbursting sources.Comment: 23 pages, 12 figures. Submitted to ApJ, including 2nd round of
referee comments. Data tables can be found at: http://goals.ipac.caltech.edu/
and will also appear on the electronic version of the journa
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