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Register a new userSub-structure of the outer Galactic Halo from the 2 Micron All Sky Survey
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A pole-count analysis of the infrared 2MASS survey is presented, in order to identify faint stream-like structures within the halo of the Milky Way. Selecting stars with colours consistent with M-giant stars, we find a strong over-density of sources on a stream with pole (l=95,b=13), which corresponds to the pole of the orbit of the Sagittarius dwarf galaxy. This great-circle feature of width ~12 degrees, contains 5% of the late M-giants in the Halo. No other stream-like structures are detected in M-giants in the 2MASS Second Incremental Data Release (2IDR), and in particular, we find no evidence for a stellar component to the Magellanic Stream. This suggests that the present accretion rate of low-mass satellites with a luminous component is very low, and the formation of the luminous component of the Halo must have been essentially complete before the accretion of the Sagittarius dwarf galaxy, more than 3Gyr ago. We also search for great-circle streams using almost all high-latitude (|b|>30) sources in the 2IDR dataset. No narrow great-circle streams of width 0.5-2 degrees were found, though we were only sensitive to relatively nearby (<17kpc) remnants of massive (10^6 Msun) globular clusters. If the Galactic potential is close to being spherical, as some recent observations suggest, the lack of observed great-circle streams is consistent with the presence of dark matter substructures in the Halo. Although alternative explanations cannot be ruled out from our analysis of the 2IDR dataset, future experiments with better statistics have the potential to reveal the heating effect of dark matter substructure on stellar streams.
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We estimate the acceleration on the Local Group (LG) from the Two Micron All Sky Redshift Survey (2MRS). The sample used includes about 23,200 galaxies with extinction corrected magnitudes brighter than K_s=11.25 and it allows us to calculate the flux weighted dipole. The near-infrared flux weighted dipoles are very robust because they closely approximate a mass weighted dipole, bypassing the effects of redshift distortions and require no preferred reference frame. This is combined with the redshift information to determine the change in dipole with distance. The misalignment angle between the LG and the CMB dipole drops to 12 degrees at around 50 Mpc/h, but then increases at larger distances, reaching 21 degrees at around 130 Mpc/h. Exclusion of the galaxies Maffei 1, Maffei 2, Dwingeloo 1, IC342 and M87 brings the resultant flux dipole to 14 degrees away from the CMB velocity dipole In both cases, the dipole seemingly converges by 60 Mpc/h. Assuming convergence, the comparison of the 2MRS flux dipole and the CMB dipole provides a value for the combination of the mass density and luminosity bias parameters Omega_m^0.6/b_L=0.40+/-0.09.
We present the culmination of our near-infrared survey of the optically spectroscopically identified white dwarf stars from the McCook & Sion catalog, conducted using photometric data from the Two Micron All Sky Survey final All Sky Data Release. The color-selection technique, which identifies candidate binaries containing a white dwarf and a low mass stellar (or sub-stellar) companion via their distinctive locus in the near-infrared color-color diagram, is demonstrated to be simple to apply and to yield candidates with a high rate of subsequent confirmation. We recover 105 confirmed binaries, and identify 28 firm candidates (20 of which are new to this work) and 21 tentative candidates (17 of which are new to this work) from the 2MASS data. Only a small number of candidates from our survey have likely companion spectral types later than M5, none of which is an obvious L type (i.e., potential brown dwarf) companion. Only one previously known WD + brown dwarf binary is detected. This result is discussed in the context of the 2MASS detection limits, as well as other recent observational surveys that suggest a very low rate of formation (or survival) for binary stars with extreme mass ratios.
We introduce the properties of the Two Micron All-Sky Survey (2MASS) survey for IAU Symposium 204. 2MASS is a near-infrared survey of the entire sky characterized by high reliability and completeness. Catalogs and images for 47% of the sky are now available online. This data release has been used by Wright (2000) and Cambresy et al. (2000) to subtract the stellar foreground at 1.25 and 2.2 microns from COBE DIRBE data, revealing the cosmological near-infrared background.
The sub-millimetre wavelength regime is perhaps the most poorly explored over large areas of the sky, despite the considerable effort that has been expended in making deep maps over small regions. As a consequence the properties of the sub-millimetre sky as a whole, and of rare bright objects in particular, remains largely unknown. Here we describe a forthcoming survey (the SCUBA-2 ``All-Sky Survey, or SASSy) designed to address this issue by making a large-area map of approximately one-fifth of the sky visible from the JCMT (4800 square degrees) down to a 1 sigma noise level of 30 mJy/beam. This map forms the pilot for a much larger survey, which will potentially map the remaining sky visible from the JCMT, with the region also visible to ALMA as a priority. SASSy has been awarded 500 hours for the 4800 square degree pilot phase and will commence after the commissioning of SCUBA-2, expected in early 2008.
We have detected over 400 HI clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans 18 degrees in longitude, 40 degrees in latitude and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6 K, a median velocity width of 12.8 km/s, and angular sizes <1 degree. The motion of these clouds is dominated by Galactic rotation with a random cloud-to-cloud velocity dispersion of 18 km/s. A sample of clouds likely to be near tangent points was analyzed in detail. These clouds have radii on the order of 30 pc and a median HI mass of 630 Msun. The population has a vertical scale height of 400 pc and is concentrated in Galactocentric radius, peaking at R=3.8 kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.
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