1,107 research outputs found
On the global structure of distant galactic disks
Radial and vertical profiles are determined for a sample of 34 edge-on disk
galaxies in the HDFs, selected for their apparent diameter larger than 1.3
arcsec and their unperturbed morphology. The thickness and flatness of their
galactic disks are determined and discussed with regard to evolution with
redshift. We find that sub-L* spiral galaxies with z \sim 1 have a relative
thickness or flatness (characterized by h_z/h the scaleheight to scalelength
ratio) globally similar to those in the local Universe. A slight trend is
however apparent, with the h_z/h flatness ratio larger by a factor of \sim 1.5
in distant galaxies if compared to local samples. In absolute value, the disks
are smaller than in present-day galaxies. About half of the z \sim 1 spiral
disks show a non-exponential surface brightness distribution.Comment: 13 pages, 8 figures, accepted in A and
AGN feedback works both ways
Simulations of galaxy growth need to invoke strong negative feedback from
active galactic nuclei (AGN) to suppress the formation of stars and thus
prevent the over-production of very massive systems. While some observations
provide evidence for such negative feedback, other studies find either no
feedback, or even positive feedback, with increased star formation associated
with higher AGN luminosities. Here we report an analysis of several hundred AGN
and their host galaxies in the Chandra Deep Field South using X-ray and radio
data for sample selection. Combined with archival far infrared data as a
reliable tracer of star formation activity in the AGN host galaxies, we find
that AGN with pronounced radio jets exhibit a much higher star formation rate
than the purely X-ray selected ones, even at the same X-ray luminosities. This
difference implies that positive AGN feedback plays an important role, too, and
therefore has to be accounted for in all future simulation work. We interpret
this to indicate that the enhanced star formation rate of radio selected AGN
arises because of jet-induced star formation, as is hinted by the different jet
powers among our AGN samples, while the suppressed star formation rate of X-ray
selected AGN is caused by heating and photo-dissociation of molecular gas by
the hot AGN accretion disc.Comment: 21 pages, 9 figures, 3 tables, accepted for publication by Ap
Body mass index and age affect Three-Factor Eating Questionnaire scores in male subjects
This cross-sectional analysis evaluated the effect of age and body mass index (BMI) on Three-Factor Eating Questionnaire scores in males. Subjects (n = 60) were recruited according to BMI status. Each completed the 51-item Three-Factor Eating Questionnaire. The group was split at the median age to produce a "younger" and "older" group for statistical analysis. A 2-way between-groups analysis of variance revealed a significant main effect of BMI on disinhibition (P = .003) and hunger (P = .041) with higher levels found in overweight males compared to healthy-weight counterparts. A significant main effect of age on hunger (P = .046) demonstrated older males were less susceptible to hunger than younger males. These insights provide a better understanding of eating behavior across the male life cycle and may assist health professionals to better guide men in weight management in the light of rising overweight/obesity. (c) 2009 Elsevier Inc. All rights reserved
On the Dynamical and Physical State of the `Diffuse Ionized Medium' in Nearby Spiral Galaxies
We have analyzed deep narrow-band H images and high-resolution
long-slit spectra for a sample of the nearest and brightest late-type galaxies
to study the morphology, physical state, and kinematics of the `Diffuse Ionized
Medium' (`DIM'). We find that the DIM covers most of the star-forming disk, and
is morphologically related to the presence of the giant HII regions. In
addition, the DIM and the giant HII regions differ systematically in their
physical and dynamical state. The DIM is characterized by enhanced emission in
the low-ionization forbidden lines ([OI], [NII], and [SII]), and even the
high-ionization [OIII]5007 line is moderately strong in the DIM. We
verify the inference made by Lehnert & Heckman that the DIM contributes
significantly to the global emission-line ratios measured in late-type
galaxies. We also find that the DIM is more disturbed kinematically than the
gas in the giant HII regions. The intrinsic FWHMs of the H and
[NII]6584 lines range from 30 to 100 km s in the DIM compared
to 20-50 km s in HII regions. The high-ionization gas in the DIM is even
more kinematically disturbed than the low-ionization gas: the
[OIII]5007 lines have intrinsic FWHMs of 70-150 km s. The
differing kinematics implies that `the DIM' is not a single monolithic phase of
the ISM. Instead, it may consist of a `quiescent DIM' with a low
ionization-state and small scale-height (few hundred pc) and a `disturbed DIM'
with a high ionization state and moderate scale-height (0.5 to 1 kpc). We argue
that the quiescent DIM is most likely photoionized by radiation leaking out of
giant HII regions, while the disturbed DIM is most likely heated by the
mechanical energy supplied by supernovae and stellar winds.Comment: 37 pages(including 7 tables) and 12 figures. To appear in the Dec 10,
1997 issue of The Astrophysical Journa
Constraining the extra heating of the Diffuse Ionized Gas in the Milky Way
The detailed observations of the diffuse ionized gas through the emission
lines H, [NII], and [SII] in the Perseus Arm of our Galaxy by the
Wisconsin H Mapper (WHAM)--survey challenge photoionization models.
They have to explain the observed rise in the line ratios [NII]/H and
[SII]/H. The models described here consider for the first time the
detailed observational geometry toward the Perseus Arm. The models address the
vertical variation of the line ratios up to height of 2 kpc above the midplane.
The rising trends of the line ratios are matched. The increase in the line
ratios is reflected in a rise of the temperature of the gas layer. This is due
to the progressive hardening of the radiation going through the gas. However an
extra heating above photoionization is needed to explain the absolute values.
Two different extra heating rates are investigated which are proportional to
and . The models show that a combination of both are best to explain
the data, where the extra heating independent of density is dominant for z
0.8 kpc.Comment: accepted for publication in Ap
Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-P\'erot observations
The properties of the gas in halos of galaxies constrain global models of the
interstellar medium. Kinematical information is of particular interest since it
is a clue to the origin of the gas. Here we report observations of the
kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to
determine the rotation curve of the halo gas. We have obtained a Fabry-P\'erot
data cube in Halpha to measure the kinematics of the halo gas with angular
resolution much higher than obtained from HI 21 cm observations. The data cube
was obtained with the TAURUS II spectrograph at the WHT on La Palma. The
velocity information of the diffuse ionized gas extracted from the data cube is
compared to model distributions to constrain the distribution of the gas and in
particular the halo rotation curve. The best fit model has a central
attenuation tau_H-alpha=6, a dust scale length of 8.1 kpc, an ionized gas scale
length of 5.0 kpc. Above the plane the rotation curve lags with a vertical
gradient of -18.8 km/s/kpc. We find that the scale length of the H-alpha must
be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation
curve above the plane rises less steeply than in the plane. This is all in
agreement with the velocities measured in the HI.Comment: A&A, in press. 13 pages, 19 figure
The Effect of Light Scattering by Dust in Galactic Halos on Emission Line Ratios
We present results from Monte Carlo simulations describing the radiation
transfer of line emission, produced both by HII regions in the disk
and in the diffuse ionized gas (DIG), through the dust layer of the galaxy
NGC891. This allows us to calculate the amount of light originating in the HII
regions of the disk and scattered by dust at high , and compare it with the
emission produced by recombinations in the DIG. The cuts of photometric and
polarimetric maps along the -axis show that scattered light from HII regions
is still 10\% of that of the DIG at ~pc, whereas the the degree of
linear polarization is small (\%). The importance of these results for the
determination of intrinsic emission line ratios is emphasized, and the
significance and possible implications of dust at high are discussed.Comment: 12 pages, LaTeX (aasms4.sty), 2 figures; ApJ Letters, accepted, June
5t
GaBoDS: The Garching-Bonn Deep Survey - III. Lyman-Break Galaxies in the Chandra Deep Field South
We present first results of our search for high-redshift galaxies in deep CCD
mosaic images. As a pilot study for a larger survey, very deep images of the
Chandra Deep Field South (CDFS), taken withWFI@MPG/ESO2.2m, are used to select
large samples of 1070 U-band and 565 B-band dropouts with the Lyman-break
method. The data of these Lyman-break galaxies are made public as an electronic
table. These objects are good candidates for galaxies at z~3 and z~4 which is
supported by their photometric redshifts. The distributions of apparent
magnitudes and the clustering properties of the two populations are analysed,
and they show good agreement to earlier studies. We see no evolution in the
comoving clustering scale length from z~3 to z~4. The techniques presented here
will be applied to a much larger sample of U-dropouts from the whole survey in
near future.Comment: 11 pages, 11 figures, replaced with version accepted by A&A. Minor
changes and tabular appendix with LBG catalogues. Version with full
resolution figures available at
http://www.astro.uni-bonn.de/~hendrik/2544.pd
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