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Register a new userA kinematic study of the irregular dwarf galaxy NGC 4861 using HI and Halpha observations
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Context. Outflows powered by the injection of kinetic energy from massive stars can strongly affect the chemical evolution of galaxies, in particular of dwarf galaxies, as their lower gravitational potentials enhance the chance of a galactic wind. Aims. We therefore performed a detailed kinematic analysis of the neutral and ionised gas components in the nearby star-forming irregular dwarf galaxy NGC 4861. Similar to a recently published study of NGC 2366, we want to make predictions about the fate of the gas and to discuss some general issues about this galaxy. Methods. Fabry-Perot interferometric data centred on the Halpha line were obtained with the 1.93m telescope at the Observatoire de Haute-Provence. They were complemented by HI synthesis data from the VLA. We performed a Gaussian decomposition of both the Halpha and the HI emission lines in order to search for multiple components indicating outflowing gas. The expansion velocities of the detected outflows were compared to the escape velocity of NGC 4861, which was modelled with a pseudo-isothermal halo. Results. Both in Halpha and HI the galaxy shows several outflows, three directly connected to the disc and probably forming the edges of a supergiant shell, and one at kpc-distance from the disc. We measured velocity offsets of 20 to 30 km/s, which are low in comparison to the escape velocity of the galaxy and therefore minimise the chance of a galactic wind.
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Abridged. Context. The metal content of dwarf galaxies and the metal enrichment of the intergalactic medium both suggest that mass loss from galaxies is a significant factor for the chemical evolution history of galaxies, in particular of dwarf galaxies. However, no clear evidence of a blow-away in local dwarf galaxies has been found so far. Aims. We therefore performed a detailed kinematic analysis of the neutral and ionised gas in the nearby star-forming irregular dwarf galaxy NGC 2366 in order to make predictions about the fate of the gas and to get a more complete picture of this galaxy. Methods. A deep Halpha image and Fabry-Perot interferometric data of NGC 2366 were obtained. They were complemented by HI synthesis data from the THINGS survey. We searched for line-splitting both in Halpha and HI by performing a Gaussian decomposition. To get an idea whether the expansion velocities are high enough for a gas blow-away, we used the pseudo-isothermal halo model, which gives us realistic values for the escape velocities of NGC 2366. The good data quality also allowed us to discuss some peculiarities of the morphology and the dynamics in NGC 2366. Results. A large red-shifted outflow north west of the giant extragalactic HII region with an expansion velocity of up to 50 km/s is found in Halpha, but not in HI. Additionally, a blue-shifted component north of the giant extragalactic HII region was detected both in Halpha and HI with an expansion velocity of up to 30 km/s. A comparison with the escape velocities of NGC 2366 reveals that the gas does not have enough kinetic energy to leave the gravitational potential.
We present positions, kinematics, and the planetary nebula luminosity function (PNLF) for 35 planetary nebulae (PNe) in the nearest starburst galaxy IC10 extending out to 3kpc from the galaxys centre. We take advantage of the deep imaging and spectroscopic capabilities provided by the spectrograph FOCAS on the 8.2m Subaru telescope. The PN velocities were measured through the slitless-spectroscopy technique, which allows us to explore the kinematics of IC10 with high precision. Using these velocities, we conclude that there is a kinematic connection between the HI envelope located around IC10 and the galaxys PN population. By assuming that the PNe in the central regions and in the outskirts have similar ages, our results put strong observational constraints on the past tidal interactions in the Local Group. This is so because by dating the PN central stars, we, therefore, infer the epoch of a major episode of star formation likely linked to the first encounter of the HI extended envelope with the galaxy. Our deep [OIII] images also allow us to use the PNLF to estimate a distance modulus of 24.1+/-0.25, which is in agreement with recent results in the literature based on other techniques.
Abridged. The feedback between massive stars and the interstellar medium is one of the most important processes in the evolution of dwarf galaxies. This interaction results in numerous neutral and ionised gas structures that have been found both in the disc and in the halo of these galaxies. However, their origin and fate are still poorly understood. We here present new HI and optical data of two nearby irregular dwarf galaxies: IC 4662 and NGC 5408. The HI line data were obtained with the ATCA and are part of the Local Volume HI Survey. They are complemented by optical images and spectroscopic data obtained with the ESO NTT and the ESO 3.6m telescope. Our main aim is to study the kinematics of the neutral and ionised gas components in order to search for outflowing gas structures and to make predictions about their fate. We find the HI gas envelopes of both galaxies to extend well beyond the optical discs. The optical disc is embedded into the central HI maximum in both galaxies. However, higher resolution HI maps show that the HI intensity peaks are typically offset from the prominent HII regions. While NGC 5408 shows a fairly regular HI velocity field, which allows us to derive a rotation curve, IC 4662 reveals a rather twisted HI velocity field, possibly caused by a recent merger event. We detect outflows with velocities between 20 and 60 km/s in our Halpha spectra of both galaxies, sometimes with HI counterparts of similar velocity. We suggest the existence of expanding superbubbles, especially in NGC 5408. This is also supported by the detection of FWHMs as high as 70 km/s in Halpha. In case of NGC 5408, we compare our results with the escape velocity of the galaxy, which shows that the measured expansion velocities are in all cases too low to allow the gas to escape from the gravitational potential of NGC 5408. This result is consistent with studies of other dwarf galaxies.
We present a photometric estimation of the distance and reddening values to the dwarf irregular galaxy NGC 1156, which is one of the best targets to study the isolated dwarf galaxies in the nearby universe. We have used the imaging data sets of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) High Resolution Channel (HRC) of the central region of NGC 1156 (26 X 29) available in the HST archive for this study. From the (U-B, B-V) color-color diagram, we first estimate the total (foreground + internal) reddening toward NGC 1156 of E(B-V) =0.35 +/- 0.05 mag, whereas only the foreground reddening was previously known to be E(B-V)=0.16 mag (Burstein & Heiles) or 0.24 mag (Schlegel, Finkbeiner, & Davis). Based on the brightest stars method, selecting the three brightest blue supergiant (BSG) stars with mean B magnitude of <B(3B)> = 21.94 mag and the three brightest red supergiant (RSG) stars with mean V magnitude of <V(3R)> = 22.76 mag, we derive the distance modulus to NGC 1156 to be (m-M)_{0,BSG} = 29.55 mag and (m-M)_{0,RSG} = 29.16 mag. By using weights of 1 and 1.5 for the distance moduli from using the BSGs and the RSGs, respectively, we finally obtain the weighted mean distance modulus to NGC 1156 (m-M)_0 = 29.39 +/- 0.20 mag (d = 7.6 +/- 0.7 Mpc), which is in very good agreement with the previous estimates. Combining the photometry data of this study with those of Karachentsev et al. gives smaller distance to NGC 1156, which is discussed together with the limits of the data.
We study the resolved radio-continuum spectral energy distribution of the dwarf irregular galaxy, NGC 1569, on a beam-by-beam basis to isolate and study its spatially resolved radio emission characteristics. Utilizing high quality NRAO Karl G. Jansky Very Large Array (VLA) observations that densely sample the 1--34,GHz frequency range, we adopt a Bayesian fitting procedure, where we use H$alpha$ emission that has not been corrected for extinction as a prior, to produce maps of how the separated thermal emission, non-thermal emission and non-thermal spectral index vary across NGC,1569s main disk. We find a higher thermal fraction at 1,GHz than is found in spiral galaxies ($26^{+2}_{-3}%$) and find an average non-thermal spectral index $alpha = -0.53pm0.02$, suggesting that a young population of cosmic ray electrons is responsible for the observed non--thermal emission. By comparing our recovered map of the thermal radio emission with literature H$alpha$ maps, we estimate the total reddening along the line of sight to NGC,1569 to be $E(B-V) = 0.49 pm 0.05$, which is in good agreement with other literature measurements. Spatial variations in the reddening indicate that a significant portion of the total reddening is due to internal extinction within NGC,1569.
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