8 research outputs found
Modeling the Gas Flow in the Bar of NGC 1365
We present new observations of the strongly-barred galaxy NGC 1365, including
new photometric images and Fabry-Perot spectroscopy, as well as a detailed
re-analysis of the neutral hydrogen observations from the VLA archive. We find
the galaxy to be at once remarkably bi-symmetric in its I-band light
distribution and strongly asymmetric in the distribution of dust and in the
kinematics of the gas in the bar region. The velocity field mapped in the
H-alpha line reveals bright HII regions with velocities that differ by 60 to 80
km/s from that of the surrounding gas, which may be due to remnants of
infalling material. We have attempted hydrodynamic simulations of the bar flow
to estimate the separate disk and halo masses, using two different dark matter
halo models and covering a wide range of mass-to-light ratios (Upsilon) and bar
pattern speeds (Omega_p). None of our models provides a compelling fit to the
data, but they seem most nearly consistent with a fast bar, corotation at sim
1.2r_B, and Upsilon_I simeq 2.0 +- 1.0, implying a massive, but not fully
maximal, disk. The fitted dark halos are unusually concentrated, a requirement
driven by the declining outer rotation curve.Comment: 43 pages, 15 figures, accepted to appear in Ap
A Search for Very Extended Ionized Gas in Nearby Starburst and Active Galaxies
We report the results from a pilot study of 10 nearby starburst and active
galaxies conducted with the Taurus Tunable Filter (TTF) on the Anglo-Australian
and William Herschel Telescopes. The main purpose of this imaging survey is to
search for warm emission-line gas on the outskirts (galactocentric distances R
> 10 kpc) of galaxies to provide direct constraints on the size and geometry of
the ``zone of influence'' of these galaxies on their environment. Gaseous
complexes or filaments larger than ~ 20 kpc are discovered or confirmed in six
of the galaxies in the sample (NGC 1068, NGC 1482, NGC 4388, NGC 6240, NGC
7213, and MR 2251-178). Slightly smaller structures are seen for the first time
in the ionization cones and galactic winds of NGC 1365, NGC 1705, Circinus
galaxy, and ESO484-G036. The TTF data are combined with new optical long-slit
spectra as well as published and archived radio and X-ray maps to constrain the
origin and source of ionization of these filaments. A broad range of phenomena
is observed, including large-scale ionization cones and galactic winds, tidal
interaction, and ram-pressure stripping by an intracluster medium. The source
of ionization in this gas ranges from shock ionization to photoionization by
the central AGN or in-situ hot young stars. The sample is too small to draw
statistically meaningful conclusions about the extent and properties of the
warm ionized medium on large scale and its relevance to galaxy formation and
evolution. The next generation of tunable filters on large telescopes promises
to improve the sensitivity to faint emission-line fluxes at least tenfold and
allow systematic surveys of a large sample of emission-line galaxies.Comment: 17 pages + 20 gif figures (high-resolution color version of these gif
figures will be available with the electronic version of the published
paper). Accepted for publication in the Astronomical Journal, November 2003
issu
Radial distribution of dust, stars, gas, and star-formation rate in DustPedia face-on galaxies
Aims. The purpose of this work is the characterization of the radial distribution of dust, stars, gas, and star-formation rate (SFR) in a sub-sample of 18 face-on spiral galaxies extracted from the DustPedia sample.
Methods. This study is performed by exploiting the multi-wavelength DustPedia database, from ultraviolet (UV) to sub-millimeter bands, in addition to molecular (12CO) and atomic (Hi) gas maps and metallicity abundance information available in the literature. We fitted the surface-brightness profiles of the tracers of dust and stars, the mass surface-density profiles of dust, stars, molecular gas, and total gas, and the SFR surface-density profiles with an exponential curve and derived their scale-lengths. We also developed a method to solve for the CO-to-H2 conversion factor (αCO) per galaxy by using dust- and gas-mass profiles.
Results. Although each galaxy has its own peculiar behavior, we identified a common trend of the exponential scale-lengths versus wavelength. On average, the scale-lengths normalized to the B-band 25 mag/arcsec2 radius decrease from UV to 70 ÎŒm, from 0.4 to 0.2, and then increase back up to ~0.3 at 500 microns. The main result is that, on average, the dust-mass surface-density scale-length is about 1.8 times the stellar one derived from IRAC data and the 3.6 ÎŒm surface brightness, and close to that in the UV. We found a mild dependence of the scale-lengths on the Hubble stage T: the scale-lengths of the Herschel bands and the 3.6 ÎŒm scale-length tend to increase from earlier to later types, the scale-length at 70 ÎŒm tends to be smaller than that at longer sub-mm wavelength with ratios between longer sub-mm wavelengths and 70 ÎŒm that decrease with increasing T. The scale-length ratio of SFR and stars shows a weak increasing trend towards later types. Our αCO determinations are in the range (0.3â9) Mâ pc-2 (K km s-1)-1, almost invariant by using a fixed dust-to-gas ratio mass (DGR) or a DGR depending on metallicity gradient