431 research outputs found
Molecular gas and star formation in M81
We present IRAM 30m observations of the central 1.6 kpc of the spiral M81
galaxy. The molecular gas appears weak and with an unusual excitation physics.
We discuss a possible link between low CO emission and weak FUV surface
brightness.Comment: 2 pages, 2 figures, to appear in "Pathways through an eclectic
Universe", J. H. Knapen, T. J. Mahoney, and A. Vazdekis (Eds.), ASP Conf.
Ser., 200
Hidden interaction in SBO galaxies
Galaxies, like plants, show a large variety of grafts: an individual of some type connects physically with a neighborhood of same or different type. The effects of these interactions between galaxies have a broad range of morphologies depending, among other quantities, on the distance of the closest approach between systems and the relative size of the two galaxies. A sketch of the possible situations is shown in tabular form. This botanical classification is just indicative, because the effects of interactions can be notable also at relatively large separations, when additional conditions are met, as for example low density of the interacting systems or the presence of intra-cluster gas. In spite of the large variety of encounters and effects, in the literature the same terms are often used to refer to different types of interactions. Analysis indicates that only few of the situations show evident signs of interaction. They appear to be most relevant when the size of the two galaxies is comparable. Bridges and tails, like the well known case of NGC 4038/39, the Antennae, are only observed for a very low percentage of all galaxies (approx. 0.38 percent, Arp and Madore 1977). In most cases of gravitational bond between two galaxies, the effects of interactions are not relevant or evident. For instance, the detection of stellar shells (Malin and Carter 1983), which have been attributed to the accretion of gas stripped from another galaxy or to the capture and disruption of a small stellar system (Quinn 1984), requires particular observing and reduction techniques. Besides these difficulties of detection, time plays an important role in erasing, within a massive galaxy, the effects of interactions with smaller objects. This can happen on a timescale shorter than the Hubble time, so the number of systems now showing signs of interaction suggests lower limits to the true frequency of interactions in the life-time of a stellar system
Study of ISM tracers in galaxies
We collected data for two samples of normal and interacting galaxies for a
total of 2953 galaxies having fluxes in one or more of the following wavebands:
FIR, 21 cm line, CO(1-0) lines and soft X-ray. The large set of data obtained
allowed us to revisit some of the already known relations between the different
tracers of the interstellar medium (ISM), such as the link between the FIR flux
and the CO line emission, the relation between X-ray emission and the blue or
FIR luminosity. The relation lacking from observations for early-type galaxies
has been discussed and explained in detail in the frame of a suitable
theoretical model, obtained by coupling chemo-dynamical N-body simulations with
a dusty spectrophotometric code of population synthesis.Comment: 2 pages, o appear in the Proceedings of the Conf. "From Stars to
Galaxies: Building the Pieces to Build Up the Universe", Vallenari et al.
eds., ASP Conf. Serie
Catching Spiral - S0 transition in groups. Insights from SPH simulations with chemo-photometric implementation
We are investigating the co-evolution of galaxies within groups combining
multi-wavelength photometric and 2D kinematical observations. Here we focus on
S0s showing star formation in ring/arm-like structures. We use smooth particle
hydrodynamical simulations (SPH) with chemo-photometric implementation which
provide dynamical and morphological information together with the spectral
energy distribution (SED) at each evolutionary stage. As test cases, we
simulate the evolution of two such S0s: NGC 1533 and NGC 3626. The merging of
two halos with mass ratio 2:1, initially just composed of dark matter (DM) and
gas, well match their observed SEDs, their surface brightness profiles and
their overall kinematics. The residual star formation today "rejuvenating" the
ring/arm like structures in these S0s is then a mere consequence of a major
merger, i.e. this is a phase during the merger episode. The peculiar
kinematical features, e.g. gas-stars counter rotation in NGC 3626, depends on
the halos initial impact parameters. Furthermore, our simulations allow to
follow, in a fully consistent way, the transition of these S0s through the
green valley in the NUV-r vs. Mr colour magnitude diagram, which they cross in
about 3-5 Gyr, before reaching their current position in the red sequence. We
conclude that a viable mechanism driving the evolution of S0s in groups is of
gravitational origin.Comment: 30 pages, 6 figures; accepted for publication in Advances in Space
Research, Special Issue: Ultraviolet Astrophysic
Are truncated stellar disks linked to the molecular gas density?
We know that the slope of the radial, stellar light distribution in galaxies
is well described by an exponential decline and this distribution is often
truncated at a break radius (). We don't have a clear understanding for
the origin of these outer truncations and several hypotheses have been proposed
to explain them. We want to test the various theories with direct observations
of the cold molecular gas for a few truncated galaxies in comparison with the
non-truncated ones. The answer to the existence of a possible link between
truncated stellar disks and the molecular gas density cannot be obtained from
CO maps in the literature, because so far there are no galaxies with a clear
truncation observed in CO at high resolution.Comment: 3 pages, 6 figures, to appear in Astrophysics and Space Science
(Apss), special issue of "Science with ALMA: a new era for Astrophysics"
conference, ed. Dr. Bachille
Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of H emission
line of a sample of 111 spiral galaxies with recognizable and well defined
spiral morphology and with a well determined environmental status, ranging from
isolation to non-disruptive interaction with satellites or companions. The form
and properties of the rotation curves are considered as a function of the
isolation degree, morphological type and luminosity. The line ratios are used
to estimate the metallicity of all the detected HII regions, thus producing a
composite metallicity profile for different types of spirals. We have found
that isolated galaxies tend to be of later types and lower luminosity than the
interacting galaxies. The outer parts of the rotation curves of isolated
galaxies tend to be flatter than in interacting galaxies, but they show similar
relations between global parameters. The scatter of the Tully-Fisher relation
defined by isolated galaxies is significantly lower than that of interacting
galaxies. The [NII]/H ratios, used as metallicity indicator, show a
clear trend between Z and morphological type, t, with earlier spirals showing
larger ratios; this trend is tighter when instead of t the gradient of the
inner rotation curve, G, is used; no trend is found with the interaction
status. The Z-gradient of the disks depends on the type, being almost flat for
early spirals, and increasing for later types. The [NII]/H ratios
measured for disk HII regions of interacting galaxies are higher than for
normal/isolated objects, even if all the galaxy families present similar
distributions of H Equivalent Width.Comment: accepted for publication in A&A (tables for HII region parameters
incomplete, contact [email protected] for the whole set of tables
Unifying Conflicting Models of Trust and Distrust for Enhanced Understanding and Predictive Power in Organizational Relationships: Proposing the Unified Trust-Distrust Model
This paper proposes the Unified Trust-Distrust Model (UTDM) to reconcile the differences in the literature on the complex relationship between trust and distrust. Extant research on trust and distrust follows two main approaches that are built on contradictory assumptions: trust has been conceptualized as a different construct than distrust by some researchers, while others consider trust and distrust to represent opposite ends of a single continuum. UTDM expands upon both of these approaches while resolving their contradictions; thus, UTDM provides a novel view of the trust-distrust relationship that has the potential for more explanatory power than previous models. Further, UTDM introduces ambivalence to the trust-distrust literature as a possible consequence of contradictory trust and distrust attitudes, and as an antecedent of trusting intentions. Ambivalence was shown in previous research to attenuate the relationship between trusting beliefs and trusting intentions. UTDM further expands the trust-distrust literature by expanding the nomological network of distrust by proposing two new antecedents of distrust: suspicion and situational abnormality. The measurement of this model is then discussed along with future research possibilities that naturally result from this model
HARKing and P-Hacking: A Call for More Transparent Reporting of Studies in the Information Systems Field
While researchers are expected to look for significant results to confirm their hypotheses, some engage in intentional or unintentional HARKing (Hypothesizing After Results are Known) and p-hacking (repeated tinkering with data and retesting). If these practices are widespread, one possible result is field-wide exaggerated (inflated) results reported in Information Systems (IS) publications. In this paper, we summarize the literature in HARKing and p-hacking across different disciplines. We offer an illustrative example of how an IS study could involve HARKing and p-hacking in various stages of the project to generate a more “publishable” result. We also report on a survey targeted at IS researchers to explore their experiences and awareness of this issue. Finally, we provide recommendations and suggestions based on the review of practices in other fields and advocate for more transparency in reporting research projects, so that study results can be interpreted properly, and reproducibility and replicability can be increased
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