Day 530

Thursday.

1310.4170
Perseus I:  A distant satellite dwarf galaxy of Andromeda
Martin et al

Discovery of a new dwarf galaxy Perseus I/Andromeda XXXIII, found in stacked imaging data of PanSTARRS-1 3pi survey.  27.9 deg away from M31, 785pm65 kpc from the Sun, 374pm10 kpc from its host.  Typical for reasonably bright dwarf galaxy (M_V=-10.3pm0.7) with exponential half-light radius of 1.7"pm0.4 or 400pm100 pc, and a moderate ellipticity (epsilon = 0.43).  Late discovery due to low surface brightness, and to the previous lack of deep, high quality photometric data in this region.  If confirmed to be a companion of M31, this could place interesting constraints on the bulk motion of the satellite system of M31.

1310.4177
DIrect measurement of dust attenuation in z~1.5 star-forming galaxies from 3D-HST: implications for dust geometry and star formation rates
Price, Kriek, Brammer, Conroy, ... Franx, ... Rix, ... van Dokkum, ... et al

Nature of dust in distant galaxies not well understood; few direct dust measurements have been possible, until recently.  Investigate dust in distant star-forming galaxies using NIR grism spectra for the 3D-HST survey, combined with archival multi-wavelength photometry; allows a direct comparison between dust towards SF regions (using Balmer decrements) and the integrated dust properties (comparing SEDs with stellar population and dust models) for a statistically significant sample of distant galaxies.  Select a sample of 163 galaxies between 1.36<z<1.5 with Ha SNR >=5 and measure Balmer decrements from stacked spectra---first in bins of integrated stellar dust attenuation: find there is extra dust extinction towards SF regions, though slightly lower than found for low-z SB galaxies.  Next, stack spectra in bins of  log(sSFR), log(SFR), and log(M*).  Find that on average A_{V,HII} increases with SFR and mass, but decreases with increasing sSFR.  The amount of extra extinction also decreases with increasing sSFR and decreasing stellar mass.  Results are consistent with the two-phase dust model -- in which galaxies contain both a diffuse and stellar birth cloud dust component -- as the extra extinction will increase once older stars outside the SF regions become more dominant.  Finally, using Balmer decrements, derive dust-corrected Hz SFRs and find evidence that SED fitting produces incorrect SFRs if very rapidly declining SFHs are included in the explored parameter space.

1310.4178
Which galaxies dominate the neutral gas content of the Universe?
Lagos, Baugh, .. Lacey, .. et al

Use GALFORM in LCDM to check relation between SFR, H2 and HI contents of galaxies.  Predicted global SFR density, and how much of this is contributed by galaxies with different stellar masses and IR luminosities are in agreement with observations.  At z<1, ~70% of the predicted H2 in the universe is locked up in galaxies with SFRs in the range 1-10 Msun/yr.  Model galaxies with moderately large SFRs, >10 Msun/yr, make a contribution that increases with redshift, reaching ~50% at z~2.  Current high-z galaxy surveys are limited to detect CO in galaxies with SFR>~30 Msun/yr, which in the model make up, at most, ~20% of the H2 in the universe.  This contrasts with the predicted cosmic HI density, which is always dominated by galaxies with low SFRs, <1 Msun/yr.  In terms of stellar mass, the predicted H2 density is always dominated by massive galaxies, M*>1e10 Msun, in contrast with the HI density, which is dominated by low mass galaxies, M*<1e9 Msun.  In the context of upcoming neutral gas surveys, suggest that the faint nature of the galaxies dominating the HI content of the universe will hamper the optical and IR counterpart identification, while for H2, expect follow up observations of molecular emission lines of already existing optical and IR galaxy catalogues to be able to uncover the H2 density of the universe.

1310.4184
Measuring cosmic bulk flows with Type Ia supernovae from the nearby supernova factory
Feindt, .. Aldering, .. Bailey, .. Fakhouri, .. Kim, Nugent, ...et al

Shows a bulk flow consistent with the direction of the CMB dipole up to z~0.06, thereby doubling the volume over which conventional distance measures have sensitivity to a bulk flow.  See no significant turnover behind the center of Shapley Supercluster.  A simple attractor model in the proximity of the Shapley Supercluster is only marginally consistent with the data, suggesting the need for another, more distant, source.  In 0.06<z<0.1, constrain the bulk flow velocity to <240 km/s (68% CL) for the direction of the CMB dipole, in contradiction to recent claims of the existence of a large amplitude dark flow.  Bulk flow velocity was determined from SN data binned in z shells by including a coherent motion (dipole) in a cosmological fit; a method of spatially smoothing the Hubble residuals was used to verify the results of the dipole fit.  To constrain the location and mass of a potential mass concentration responsible for the peculiar motion, fit a Hubble law modified by adding an additional mass concentration.