1309.0809
A direct dynamical measurement of the Milky Way's disk surface density profile, disk scale length, and dark matter profile at 4 kpc < R < 9 kpc
Bovy, Rix
Present and apply rigorous dynamical modeling; infer unprecedented constraints on the stellar and DM mass distribution within the MW, based on large sets of phase-space data on individual stars. Model the dynamics of 16k G-type dwarfs from SEGUE, which sample 5 < R/kpc < 12 and 0.3 < |Z|/kpc < 3. Independently fit a parameterized MW potential and 3-integral, action-based distribution function (DF) to the phase-space data of 43 separate abundance-selected sub-populations (MAPs), accounting for the complex selection effects affecting the data. Robustly measure the total surface density within 1.1 kpc of the mid-plane to about 5% over the range 4.5 < R/kpc < 9. Using metal-poor MAPs with small radial scale lengths as dynamical tracers probes 4.5 < R/kpc < 7, while MAPs with longer radial scale lengths sample 7 < R/kpc < 9. Measure the mass-weighted Galactic disk scale length to be R_d = 2.15 pm 0.14 kpc, in agreement with the photometrically inferred spatial distribution of stellar mass. Measure dynamically the mass of the Galactic stellar disk to unprecedented accuracy: M*= (2.6pm0.3) e10 Msun and a total local surface density of Sigma_R0(Z=1.1 kpc) = 68pm4 Msun/pc2 of which 38pm4 Msun/pc^2 is contributed by stars and stellar remnants. By combining our surface density measurements with data on the terminal velocity curve, we find that the MW's disk is maximal in the sense that V_{c,disk}/V_{c,total}=0.83pm0.04 at R=2.2R_d. Also constrain the radial profile of the dark halo at such small Galactocentric radii, finding that rho_DM(r)~1/r^alpha with alpha<1.53 at 95% CL. Results show that action-based distribution-function modeling of coplex stellar data sets is now a feasible approach that will be fruitful for interpreting Gaia data.
1309.1036
The Lockman Hole project: gas and galaxy properties from a stacking experiment
Geréb, et al
Perform an HI stacking analysis to study the relation between HI content and optical/radio/IR properties of galaxies located in the Lockman Hole [area of the sky in which minimal amounts of neutral H gas are observed. Serves as a relatively clear window on distant objects. Located near the pointer stars of the Big Dipper and is about 15 sq deg in size. CDFS region is similar] area. In the z range covered by the observations (up to z=0.09), use the SDSS to separate galaxies with different optical characteristics, and exploit the deep L-band radio continuum image (with noise 11 u Jy/beam) to identify galaxies with radio continuum emission. IR properties are extracted from the Spitzer catalog. Detect HI in blue galaxies, but HI is also detected in the group of red galaxies - albeit with smaller amounts than for the blue sample. Identify a group of optically inactive galaxies with early-type morphology that does not reveal any HI and ionized gas. These inactive galaxies likely represent the genuine red and dead galaxies depleted of all [neutral? does plasma count?] gas. Unlike inactive galaxies, HI is detected in red LINER-like objects. Galaxies with radio continuum counterparts mostly belong to the sub-mJy population, whose objects are thought to be a mixture of SF galaxies and low-power AGNs. After using several AGN diagnostics, conclude that the radio emission in the majority of the sub-mJy radio sources stems from SF. LINERs appear to separate into 2 groups based on IR properties and HI content. LINERs with a 24 um detection show relatively large amounts of HI and are also often detected in radio continuum as a result of ongoing SF. The LINER galaxies which are not detected at 24 um are more like the optically inactive galaxies by being depleted of HI gas and having no sign of star formation. Radio LINERs in the latter group are the best candidates for hosting low-luminosity radio AGN.
A direct dynamical measurement of the Milky Way's disk surface density profile, disk scale length, and dark matter profile at 4 kpc < R < 9 kpc
Bovy, Rix
Present and apply rigorous dynamical modeling; infer unprecedented constraints on the stellar and DM mass distribution within the MW, based on large sets of phase-space data on individual stars. Model the dynamics of 16k G-type dwarfs from SEGUE, which sample 5 < R/kpc < 12 and 0.3 < |Z|/kpc < 3. Independently fit a parameterized MW potential and 3-integral, action-based distribution function (DF) to the phase-space data of 43 separate abundance-selected sub-populations (MAPs), accounting for the complex selection effects affecting the data. Robustly measure the total surface density within 1.1 kpc of the mid-plane to about 5% over the range 4.5 < R/kpc < 9. Using metal-poor MAPs with small radial scale lengths as dynamical tracers probes 4.5 < R/kpc < 7, while MAPs with longer radial scale lengths sample 7 < R/kpc < 9. Measure the mass-weighted Galactic disk scale length to be R_d = 2.15 pm 0.14 kpc, in agreement with the photometrically inferred spatial distribution of stellar mass. Measure dynamically the mass of the Galactic stellar disk to unprecedented accuracy: M*= (2.6pm0.3) e10 Msun and a total local surface density of Sigma_R0(Z=1.1 kpc) = 68pm4 Msun/pc2 of which 38pm4 Msun/pc^2 is contributed by stars and stellar remnants. By combining our surface density measurements with data on the terminal velocity curve, we find that the MW's disk is maximal in the sense that V_{c,disk}/V_{c,total}=0.83pm0.04 at R=2.2R_d. Also constrain the radial profile of the dark halo at such small Galactocentric radii, finding that rho_DM(r)~1/r^alpha with alpha<1.53 at 95% CL. Results show that action-based distribution-function modeling of coplex stellar data sets is now a feasible approach that will be fruitful for interpreting Gaia data.
1309.1036
The Lockman Hole project: gas and galaxy properties from a stacking experiment
Geréb, et al
Perform an HI stacking analysis to study the relation between HI content and optical/radio/IR properties of galaxies located in the Lockman Hole [area of the sky in which minimal amounts of neutral H gas are observed. Serves as a relatively clear window on distant objects. Located near the pointer stars of the Big Dipper and is about 15 sq deg in size. CDFS region is similar] area. In the z range covered by the observations (up to z=0.09), use the SDSS to separate galaxies with different optical characteristics, and exploit the deep L-band radio continuum image (with noise 11 u Jy/beam) to identify galaxies with radio continuum emission. IR properties are extracted from the Spitzer catalog. Detect HI in blue galaxies, but HI is also detected in the group of red galaxies - albeit with smaller amounts than for the blue sample. Identify a group of optically inactive galaxies with early-type morphology that does not reveal any HI and ionized gas. These inactive galaxies likely represent the genuine red and dead galaxies depleted of all [neutral? does plasma count?] gas. Unlike inactive galaxies, HI is detected in red LINER-like objects. Galaxies with radio continuum counterparts mostly belong to the sub-mJy population, whose objects are thought to be a mixture of SF galaxies and low-power AGNs. After using several AGN diagnostics, conclude that the radio emission in the majority of the sub-mJy radio sources stems from SF. LINERs appear to separate into 2 groups based on IR properties and HI content. LINERs with a 24 um detection show relatively large amounts of HI and are also often detected in radio continuum as a result of ongoing SF. The LINER galaxies which are not detected at 24 um are more like the optically inactive galaxies by being depleted of HI gas and having no sign of star formation. Radio LINERs in the latter group are the best candidates for hosting low-luminosity radio AGN.
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