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 Physics , 2000, Abstract: We present a high-resolution VLA study of the total power and polarized radio continuum emission at 8.46 and 4.86 GHz of the irregular galaxy NGC 4449, known for its weak rotation and non-systematic gas motions. We found strong galaxy-scale regular magnetic fields, which is surprising because of a lack of ordered rotation required for the dynamo action. The strength of the regular field reaches 8 $\mu$G and that of the total field 14 $\mu$G, comparable to that of the total magnetic field strength in radio-bright spirals. The magnetic vectors in NGC 4449 form radial fans'' in the central region and fragments of a spiral pattern in the galaxy's outskirts. These structures are associated with large regions of systematic Faraday rotation, implying genuine galaxy-scale magnetic fields rather than random ones compressed and stretched by gas flows. The observed pattern of polarization B-vectors is similar to dynamo-type fields in normal spirals. Nonstandard, fast dynamo concepts are required to explain the observed field strengths, though it is unknown what kind of magnetic field geometry can be produced in slowly and chaotically rotating objects. The so far neglected role of magnetic fields for the dynamics and star formation in dwarf irregulars also needs to be revised.
 Physics , 2002, DOI: 10.1086/344304 Abstract: A detailed kinematic analysis of ionized gas in the nearby irregular galaxy NGC 4449 is presented. Observations are conducted in the spectral lines of Halpha and [SII]. Our scanning Fabry--Perot interferometric observations are presented from both a global as well as a local perspective. We have analysed the global velocity field, the spatially extended diffuse gaseous component (DIG), the HII region populations, and, furthermore, have determined the rotation curve based on the heliocentric radial velocities of the global Halpha spatial distribution. Our results for NGC 4449 show that the optical velocity field has a decreasing value in radial velocity along the optical bar from NE to SW. The DIG component that permeates the entire galaxy was analysed (up to a limiting surface brightness of ~ 3.165x10^-5 ergs cm$^-2 s^-1 steradian^-1). We find that the diffuse gas component presents peculiar kinematical features such as abrupt velocity gradients and highly supersonic velocity dispersions (sigma~4 times the values of the nearest HII regions) but that its kinematical and dynamical influence is important on both global and local scales. The optical rotation curve of this nearby irregular shows that the NE sector rotates like a solid body (V_rot~40 km s^-1 at R=2 kpc). For the SW side, our results are not conclusive; the behavior of the gas at those locations is chaotic. We conclude that the origin of such complex kinematics and dynamics is undoubtedly related to the aftermath of an interaction experienced by this galaxy in the past (abridged).  Physics , 2011, DOI: 10.1088/0004-6256/142/4/129 Abstract: We present a study of the star cluster population in the starburst irregular galaxy NGC 4449 based on B, V, I, and Ha images taken with the Advanced Camera for Surveys on the Hubble Space Telescope. We derive the cluster properties such as size, ellipticity, and total magnitudes. Cluster ages and masses are derived fitting the observed spectral energy distributions with different population synthesis models. Our analysis is strongly affected by the age-metallicity degeneracy; however, if we assume a metallicity of ~1/4 solar, as derived from spectroscopy of HII regions, we find that the clusters have ages distributed quite continuously over a Hubble time, and they have masses from ~10^3 M_sun up to ~2 x 10^6 M_sun, assuming a Salpeters' IMF down to 0.1 M_sun. Young clusters are preferentially located in regions of young star formation, while old clusters are distributed over the whole NGC 4449 field of view, like the old stars (although we notice that some old clusters follow linear structures, possibly a reflection of past satellite accretion). The high SF activity in NGC 4449 is confirmed by its specific frequency of young massive clusters, higher than the average value found in nearby spirals and in the LMC (but lower than in other starburst dwarfs such as NGC 1705 and NGC 1569), and by the flat slope of the cluster luminosity function (dN(L_V)\propto L_V^{-1.5} dL for clusters younger than 1 Gyr). We use the upper envelope of the cluster log(mass) versus log(age) distribution to quantify cluster disruption, and do not find evidence for the high (90%) long-term infant mortality found by some studies. For the red clusters, we find correlations between size, ellipticity, luminosity and mass: brighter and more massive clusters tend to be more compact, and brighter clusters tend to be also more elliptical.  Physics , 2003, DOI: 10.1051/0004-6361:20031009 Abstract: We present observations of the dwarf irregular galaxy NGC 4449 at 850$\mu$m and 450$\mu$m obtained with SCUBA at the JCMT. The distribution of the cold dust agrees well with that of the CO and H$\alpha\$ emission. To explain the integrated mm- through far-infrared continuum spectrum three dust components are required, with temperatures of 16 K, 39 K and 168 K, respectively. The dust mass is dominated by the cold dust component; we derive a total dust mass of \~3.8 x10^6 Msun, and with the local gas-to-dust ratio of ~130 a total gas mass of M(HI+H_2}~4.9 x 10^8 Msun. Comparison with the HI mass leads to a total molecular gas mass of ~3.4 x 10^8 Msun. We derive a conversion factor of the CO line intensity to molecular hydrogen column density XCO = N(H_2)/I(CO) which is at least 11 times larger than the Galactic value. These values are in accord with the lower metallicity of NGC 4449.