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Register a new userWillman 1 - a probable dwarf galaxy with an irregular kinematic distribution
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We investigate the kinematic properties and stellar population of the Galactic satellite Willman 1 (Wil 1) by combining Keck/DEIMOS spectroscopy with KPNO mosaic camera imaging. Wil 1 is an ultra-low luminosity Milky Way companion. This object lies in a region of size-luminosity space (M_V ~ -2 mag, d ~ 38 kpc, r_half ~ 20 pc) also occupied by the Galactic satellites Bootes II and Segue 1 and 2, but no other known old stellar system. We use kinematic and color-magnitude criteria to identify 45 stars as possible members of Wil 1. With a systemic velocity of v_helio = -12.8 +/- 1.0 km/s, Wil 1 stars have velocities similar to those of foreground Milky Way stars. Informed by Monte-Carlo simulations, we identify 5 of the 45 candidate member stars as likely foreground contaminants. We confirm a significant spread in the abundances of the likely Wil 1 red giant branch members ([Fe/H] = -1.73 +/- 0.12 and -2.65 +/- 0.12, [Ca/Fe] = -0.4 +/- 0.18 and +0.13 +/- 0.28). This spread supports the scenario that Wil 1 is an ultra-low luminosity dwarf galaxy rather than a star cluster. Wil 1s innermost stars move with radial velocities offset by 8 km/s from its outer stars and have a velocity dispersion consistent with 0 km/s, suggesting that Wil 1 may not be in dynamical equilibrium. The combination of the foreground contamination and unusual kinematic distribution make it difficult to robustly determine the dark matter mass of Wil 1. As a result, X-ray or gamma-ray observations of Wil 1 that attempt to constrain models of particle dark matter using an equilibrium mass model are strongly affected by the systematics in the observations presented here. We conclude that, despite the unusual features in the Wil 1 kinematic distribution, evidence indicates that this object is, or at least once was, a dwarf galaxy.
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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.
We investigate the spatial extent and structure of the Pegasus dwarf irregular galaxy using deep, wide-field, multicolour CCD photometry from the Sloan Digital Sky Survey (SDSS) and new deep HI observations. We study an area of ~0.6 square degrees centred on the Pegasus dwarf that was imaged by SDSS. Using effective filtering in colour-magnitude space we reduce the contamination by foreground Galactic field stars and increase significantly the contrast in the outer regions of the Pegasus dwarf. Our extended surface photometry, reaches down to a surface brightness magnitude mu_r~32 mag/sq.arcsec. It reveals a stellar body with a diameter of ~8 kpc that follows a Sersic surface brightness distribution law, which is composed of a significantly older stellar population than that observed in the ~2 kpc main body. The galaxy is at least five times more extended than listed in NED. The faint extensions of the galaxy are not equally distributed around its circumference; the north-west end is more jagged than the south-east end. We also identified a number of stellar concentrations, possibly stellar associations, arranged in a ring around the main luminous body. New HI observations were collected at the Arecibo Observatory as part of the ALFALFA survey. They reveal an HI distribution somewhat elongated in RA and about 0.3 deg. wide, with the region of highest column density coincident with the luminous galaxy. The HI rotation curve shows a solid-body rotation behaviour, with opposite ends differing by 15 km/s. There is a stream to lower velocities about 5 arcmin from the centre of the galaxy. We were able to measure ugriz colours in a number of apertures using the SDSS data and compared these with predictions of evolutionary synthesis models. (abridged)
We present the results of the analysis of three XMM-Newton observations of the Willman 1 dwarf spheroidal galaxy (Wil 1). X-ray sources are classified on the basis of spectral analysis, hardness ratios, X-ray-to-optical flux ratio, X-ray variability, plus cross-correlation with available catalogues in optical and infrared wavelengths. We catalogued 97 sources in the field of Wil 1. Our classification shows the presence of a $beta$-type symbiotic star in Wil 1. We classified one M dwarf foreground star in the field of Wil 1. Moreover, fifty-four sources are classified as background AGNs and galaxies. Our study shows that the luminosity of the X-ray sources of Wil 1 does not exceed $sim$10$^{34}$ erg s$^{-1}$ in the energy range of 0.2--12.0 keV, which is similar to observed luminosities of sources in nearby dwarf spheroidal galaxies.
The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Zsun, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mic with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mic, [OI] 63 mic, [OI] 145 mic, [OIII] 88 mic, [NIII] 57 mic and [NII] 122 and 205 mic have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J=4-3 to J=13-12), [NII] 205 mic and [CI] lines at 370 and 609 mic. This paper describes the sample selection and global properties of the galaxies, the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.
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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