295 research outputs found
HERschel Observations of Edge-on Spirals (HEROES). II: Tilted-ring modelling of the atomic gas disks
Context. Edge-on galaxies can offer important insights in galaxy evolution as
they are the only systems where the distribution of the different components
can be studied both radially and vertically. The HEROES project was designed to
investigate the interplay between the gas, dust, stars and dark matter (DM) in
a sample of 7 massive edge-on spiral galaxies.
Aims. In this second HEROES paper we present an analysis of the atomic gas
content of 6 out of 7 galaxies in our sample. The remaining galaxy was recently
analysed according to the same strategy. The primary aim of this work is to
constrain the surface density distribution, the rotation curve and the geometry
of the gas disks in a homogeneous way. In addition we identify peculiar
features and signs of recent interactions.
Methods. We construct detailed tilted-ring models of the atomic gas disks
based on new GMRT 21-cm observations of NGC 973 and UGC 4277 and re-reduced
archival HI data of NGC 5907, NGC 5529, IC 2531 and NGC 4217. Potential
degeneracies between different models are resolved by requiring a good
agreement with the data in various representations of the data cubes.
Results. From our modelling we find that all but one galaxy are warped along
the major axis. In addition, we identify warps along the line of sight in three
galaxies. A flaring gas layer is required to reproduce the data only for one
galaxy, but (moderate) flares cannot be ruled for the other galaxies either. A
coplanar ring-like structure is detected outside the main disk of NGC 4217,
which we suggest could be the remnant of a recent minor merger event. We also
find evidence for a radial inflow of 15 +- 5 km/s in the disk of NGC 5529,
which might be related to the ongoing interaction with two nearby companions.
(Abridged)Comment: 39 pages, 38 figures, Accepted for publication in Astronomy &
Astrophysic
H-ATLAS/GAMA and HeViCS – dusty early-type galaxies in different environments
The Herschel Space Observatory has had a tremendous impact on the study of extragalactic dust. Specifically, early-type galaxies (ETG) have been the focus of several studies. In this paper, we combine results from two Herschel studies – a Virgo cluster study Herschel Virgo Cluster Survey (HeViCS) and a broader, low-redshift Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS)/Galaxy and Mass Assembly (GAMA) study – and contrast the dust and associated properties for similar mass galaxies. This comparison is motivated by differences in results exhibited between multiple Herschel studies of ETG. A comparison between consistent modified blackbody derived dust mass is carried out, revealing strong differences between the two samples in both dust mass and dust-to-stellar mass ratio. In particular, the HeViCS sample lacks massive ETG with as high a specific dust content as found in H-ATLAS. This is most likely connected with the difference in environment for the two samples. We calculate nearest neighbour environment densities in a consistent way, showing that H-ATLAS ETG occupy sparser regions of the local Universe, whereas HeViCS ETG occupy dense regions. This is also true for ETG that are not Herschel-detected but are in the Virgo and GAMA parent samples. Spectral energy distributions are fit to the panchromatic data. From these, we find that in H-ATLAS the specific star formation rate anticorrelates with stellar mass and reaches values as high as in our Galaxy. On the other hand HeViCS ETG appear to have little star formation. Based on the trends found here, H-ATLAS ETG are thought to have more extended star formation histories and a younger stellar population than HeViCS ETG
The selective effect of environment on the atomic and molecular gas-to-dust ratio of nearby galaxies in the Herschel Reference Survey
We combine dust, atomic (HI) and molecular (H) hydrogen mass
measurements for 176 galaxies in the Herschel Reference Survey to investigate
the effect of environment on the gas-to-dust mass ()
ratio of nearby galaxies. We find that, at fixed stellar mass, the average
ratio varies by no more than a factor of 2
when moving from field to cluster galaxies, with Virgo galaxies being slightly
more dust rich (per unit of gas) than isolated systems. Remarkably, once the
molecular and atomic hydrogen phases are investigated separately, we find that
\hi-deficient galaxies have at the same time lower
ratio but higher ratio than \hi-normal systems. In
other words, they are poorer in atomic but richer in molecular hydrogen if
normalized to their dust content. By comparing our findings with the
predictions of theoretical models, we show that the opposite behavior observed
in the and ratios is
fully consistent with outside-in stripping of the interstellar medium (ISM),
and is simply a consequence of the different distribution of dust, \hi\ and
H across the disk. Our results demonstrate that the small environmental
variations in the total ratio, as well as in the
gas-phase metallicity, do not automatically imply that environmental mechanisms
are not able to affect the dust and metal content of the ISM in galaxies.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA
Consumer Behavior Towards Lemongrass (Cymbopogon citratus) Tea in Benguet Province, Northern Philippines
Sensory evaluation was done with 256 respondents who were willing to participate in the study and chosen through quota sampling based on age and sex. The respondents evaluated pure lemongrass tea and lemongrass with pandan (Pandanus amaryllifolius) using the research questionnaire given to them. Analysis of variance, factor analysis, and cluster analysis were used to assess a degree of association between different study components.Results show that herbal teas were the most favored drinks among the respondents who strongly believe that these help in digestion and relieve stress. The sensory attributes driving acceptability of lemongrass teas were linked to light and clear green colors, citral aroma, and distinct taste. The high acceptability of lemongrass tea mixed with pandan, a locally appreciated herb, shows future possibilities in the product expansion lines
Insights into gas heating and cooling in the disc of NGC 891 from Herschel far-infrared spectroscopy
We present Herschel PACS and SPIRE spectroscopy of the most important
far-infrared cooling lines in the nearby edge-on spiral galaxy, NGC 891: [CII]
158 m, [NII] 122, 205 m, [OI] 63, 145 m, and [OIII] 88 m.
We find that the photoelectric heating efficiency of the gas, traced via the
([CII]+[OII]63)/ ratio, varies from a mean of
3.510 in the centre up to 810 at increasing
radial and vertical distances in the disc. A decrease in
([CII]+[OII]63)/ but constant
([CII]+[OI]63)/ with increasing FIR colour suggests that
polycyclic aromatic hydrocarbons (PAHs) may become important for gas heating in
the central regions. We compare the observed flux of the FIR cooling lines and
total IR emission with the predicted flux from a PDR model to determine the gas
density, surface temperature and the strength of the incident far-ultraviolet
(FUV) radiation field, . Resolving details on physical scales of ~0.6
kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC
891's disc have hydrogen densities of 1 < log (/cm) < 3.5
experiencing an incident FUV radiation field with strengths of 1.7 < log
< 3. Although these values we derive for most of the disc are consistent with
the gas properties found in PDRs in the spiral arms and inter-arm regions of
M51, observed radial trends in and are shown to be sensitive to
varying optical thickness in the lines, demonstrating the importance of
accurately accounting for optical depth effects when interpreting observations
of high inclination systems. With an empirical relationship between the MIPS 24
m and [NII] 205 m emission, we estimate an enhancement of the FUV
radiation field strength in the far north-eastern side of the disc.Comment: Accepted for publication in A&A. 25 pages, including 17 figures and 3
tables, abstract abridged for arXi
The identification of dust heating mechanisms in nearby galaxies using Herschel 160/250 and 250/350 micron surface brightness ratios
We examined variations in the 160/250 and 250/350 micron surface brightness
ratios within 24 nearby (<30 Mpc) face-on spiral galaxies observed with the
Herschel Space Observatory to identify the heating mechanisms for dust emitting
at these wavelengths. The analysis consisted of both qualitative and
quantitative comparisons of the 160/250 and 250/350 micron ratios to H alpha
and 24 micron surface brightnesses, which trace the light from star forming
regions, and 3.6 micron emission, which traces the light from the older stellar
populations of the galaxies. We find broad variations in the heating mechanisms
for the dust. In one subset of galaxies, we found evidence that emission at
<=160 microns (and in rare cases potentially at <=350 microns) originates from
dust heated by star forming regions. In another subset, we found that the
emission at >=250 microns (and sometimes at >=160 microns) originates from dust
heated by the older stellar population. In the rest of the sample, either the
results are indeterminate or both of these stellar populations may contribute
equally to the global dust heating. The observed variations in dust heating
mechanisms does not necessarily match what has been predicted by dust emission
and radiative transfer models, which could lead to overestimated dust
temperatures, underestimated dust masses, false detections of variability in
dust emissivity, and inaccurate star formation rate measurements.Comment: Accepted for publication in MNRA
A resolved analysis of cold dust and gas in the nearby edge-on spiral NGC 891
We investigate the connection between dust and gas in the nearby edge-on
spiral galaxy NGC 891. High resolution Herschel PACS and SPIRE 70, 100, 160,
250, 350, and 500 m images are combined with JCMT SCUBA 850 m
observations to trace the far-infrared/submillimetre spectral energy
distribution (SED). Maps of the HI 21 cm line and CO(J=3-2) emission trace the
atomic and molecular hydrogen gas, respectively. We fit one-component modified
blackbody models to the integrated SED, finding a global dust mass of
8.510 M and an average temperature of 232 K. We
also fit the pixel-by-pixel SEDs to produce maps of the dust mass and
temperature. The dust mass distribution correlates with the total stellar
population as traced by the 3.6 m emission. The derived dust temperature,
which ranges from approximately 17 to 24 K, is found to correlate with the 24
m emission. Allowing the dust emissivity index to vary, we find an average
value of = 1.90.3. We confirm an inverse relation between the dust
emissivity spectral index and dust temperature, but do not observe any
variation of this relationship with vertical height from the mid-plane of the
disk. A comparison of the dust properties with the gaseous components of the
ISM reveals strong spatial correlations between the surface mass densities of
dust and the molecular hydrogen and total gas surface densities. Observed
asymmetries in the dust temperature, and the H-to-dust and total
gas-to-dust ratios hint that an enhancement in the star formation rate may be
the result of larger quantities of molecular gas available to fuel star
formation in the NE compared to the SW. Whilst the asymmetry likely arises from
dust obscuration due to the geometry of the line-of-sight projection of the
spiral arms, we cannot exclude an enhancement in the star formation rate in the
NE side of the disk.Comment: Accepted for publication in A&A. 21 pages, including 13 figures and 4
table
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